Another Electric & Hybrid Vehicle Tech Expo North America has concluded and it is evident that this show has grown by leaps and bounds. In just the few years since Parker Hannifin has started exhibiting, the interest and demand in EVs and PHEVs has seemingly exploded, and the 2019 show proved to have the most suppliers and attendees the show has ever seen.

From nearly every continent across the globe, there are innovations fast developing new and exciting technologies that will make the future of driving cleaner, safer, and more reliable. The Electric & Hybrid Vehicle Tech Expo North America is a must-attend event for OEMs, tier suppliers, and designers looking for the latest in the development and application of technology for electric vehicles. With over 8,500 attendees, 650 suppliers, and 150 speakers in 2019, Electric & Hybrid Vehicle Tech Expo North America is fast becoming the largest EV technology show in North America. 

This year, Parker Hannifin Engineered Materials Group (EMG) featured many new and innovative products -- from heat dissipating thermal interface materials, to electromagnetic interference (EMI) shielding products such as plastics, gaskets and coatings, sealing for complex groove designs, and closure force reduction, the Engineered Materials Group from Parker Hannifin is your single source provider for sealing, shielding and thermal management components in electric vehicles.

So what was new this year from Parker Hannifin EMG?

Parker's sealing solutions for batteries are available in large formats. Our versatile materials address your specific needs such as low compression set, temperature resistance, fire resistance, media resistance, and low closure force. Additionally, our seals can be customized in a wide range of geometries.

Parker has developed a new hollow "keyhole" seal design for easier installation, providing significantly lower compression load forces while maintaining seal reliability. Other key advantages of the keyhole profile design include improved rollover stability performance, larger application gap tolerances and lower reduction which provides lower application costs that would normally result from fasteners and thinner covers. 

Parker sealing solutions are available in various product designs, from O-Rings, press-in-place seals, extruded and spliced seals to custom designs. 

Parker Chomerics provides effective heat dissipation technologies in the form of thermal interface materials that are either robotically liquid dispensed or a die cut thermally conductive gap pad. Liquid dispensed thermally conductive materials such as THERM-A-GAP® GELS offer the reliability of traditional thermal interface materials, but with the ability to be robotically dispensed for fast, effective high volume productions.

And with a wide variety of performance and polymer options available, THERM-A-GAP GELS are ideal for most battery heat dissipation applications. 

THERM-A-GAP thermal gap filler pads dissipate heat generated from the battery pack and add additional support, vibration dampening or dialectic strength. They are also available in a variety of performance options from 1 W/m-K up to 6.5 W/m-K thermal conductivity. 
 

Beyond effective thermal management, another technology challenge Parker Chomerics helps to solve is the need to shield against EMI. The cables that travel between the battery and engine, as well as the battery and charger, see high current produced at low frequency. This produces a large magnetic field that can negatively affect other electronics within the vehicle. High shielding attenuation is also required to protect the battery and its circuits from any incoming EMI. Shielding is also required in the increased technology and communication required to ensure the proper advanced driver-assistance systems (ADAS) 

Replacement of metal housings with PREMIER electrically conductive plastic can contribute to reducing vehicle weight and cutting manufacturing costs. Here, an electrically conductive plastic alternative can be exchanged for the battery electronic control unit’s (ECU) conventional die-cast aluminum housing. Metal to plastic conversions not only eliminate 35% of the housing weight, but also provide cost reductions of up to 65% by eliminating secondary operations such as assembly and machining.

As electric and hybrid vehicles grow in popularity, Parker offers the engineering and materials expertise to help EV manufacturers produce the vehicles that consumers want at the scale needed.

With thousands of sealing, shielding, and thermal management solutions available, and over 50 locations around the globe, Parker is ready today to engineer solutions for your most critical EV applications.

Discover more from sealing, shielding and thermal interface materials for EVs from Parker EMG on our solutions webpage here. 

This blog post was contributed by Jarrod Cohen, marketing communications manager, Chomerics Division. 

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You just spent 6 months testing, stretching, aging and exposing your new seal design to 12 different chemicals. Finally, you are done, so what does a good technical drawing for a seal include? For most companies, the drawing is simple. For an O-ring, we draw a generic circle and show an ID and width with some sort of material call out. But now fast forward 20 years, someone consults the drawing, how do they know the criteria you used to select the seal specified?

Just last week I asked my customer who was having seal failure issues on their engine sensor, “Was the original seal specified to be compatible with biodiesel?” The engineer consulted their drawing, but besides the generic circle it lacked any background on what material compatibility was considered when the seal material was selected. The ASTM description on the drawing did not include a reference to or indicate compatibility with biodiesel.

Over time, the operating parameters of a system or product can change so it is important to know what parameters were used for the original seal selection. The goal of the drawing is to assure that the engineers and procurement team understand what performance is required from the seal and why the specific elastomer was chosen.

So how do you make your drawing more valuable to your company?

1. Define and list on your drawing all the operating conditions you anticipate the seal will see such as temperature, pressure and any other application specific operating conditions.

2. Prepare a list of fluids as well as the concentrations of each fluid that your seal will be exposed to and again add these on your drawing. In addition, make sure you consider fluids that could come into contact with the seal indirectly, through failure of other systems that are part of the product or even by cleaning the product.

3. List on the drawing the selected compound and manufacturer. Define clearly what testing the compound was put through or what testing is required for approval.

4. If you select a compound that was resistant to compression set, high temperatures or low temperatures as well as explosive decompression, this should be clearly stated on the drawing.

5. List clearly the industry standards the seal is required to meet, such as UL, FDA or NSF.

Time and time again, I see seal quality and performance failures when a new supplier is selected and the real requirements for the seal were either forgotten or not clearly defined. Clearly defining these parameters and making them transparent will allow your purchasing and technical team to understand, select and evaluate the correct compound that meets your products sealing requirements.

Once you select a compound for your specific application, it is important to test and validate that the compound chosen is compatible with the fluids you are using. Parker can typically supply small compound samples for soak testing in the fluids your seal is exposed to. If you choose to list an alternate compound on your drawing, that compound must also be tested and validated for compatibility.

Parker offers design assistance for all of our sealing products so before you even design the seal, define the space or groove the seal fits into. Call us, the earlier in the design process the better. Parker will assist you with selecting the proper seal, defining the elastomer requirements, and designing the mating groove; we can provide a cost-effective solution whether it is off the shelf or a custom manufactured solution

Remember when developing drawings standards, assure yourself that if someone consults a drawing that is 2 years old, 5 years old or even 20 years old, they will know what the original seal design intent was.

Fred Fisher, technical sales engineer, Parker Hannifin Engineered Materials Group

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I had a brief career in construction. We used an old hydraulic manlift for elevated projects, and it had a problem – we would start the day eye-level with our work, and after an hour would realize we were balancing on our toes to reach the same level. Cylinder drift was to blame. The lift cylinder was slowly retracting while the machine was off. In a manlift, it’s an annoyance requiring you to raise yourself every half hour, but the drift is dangerous if lifts are used to support heavy loads with the possibility that people or equipment may be under them. This is one reason why when doing automotive repairs and working underneath a car, you should always use solid jack stands or blocks instead of the hydraulic jack.

A guy on my crew told me the lift slowly sank because the piston seals needed to be replaced. I wasn’t a seal engineer at the time, so it sounded reasonable. Now I know drift is more complicated, and it’s critical to understand if you’re responsible for cylinder design. Hydraulic cylinders have two main components: the piston, which is acted upon by pressurized fluid to create force and motion, and the rod, which transfers force and motion to the machinery (in my case, the lift platform) (Fig. 1). Located elsewhere are valves that open and close, controlling fluid flow into the cylinder.

Figure 1. Typical hydraulic cylinder

Let’s remove the piston completely. We now have just a rod in a bore, which is known as a ram-style cylinder (Fig. 2). Assume we have perfect, leak-free valves and rod seals. If we shut both valves, zero oil can enter or leave the cylinder.

Figure 2. Piston removed -- ram style cylinder

Since moving the rod changes the fluid volume inside the cylinder (the rod takes up space), fluid MUST flow into or out of the cylinder for it to move.

Since this can’t happen while our perfect valves are closed, the rod can’t move. This is called hydraulic lock.

As you can see with hydraulic lock, bad piston seals wouldn’t cause drift in our manlift. Volume loss or escape from the cylinder is what caused us to slowly droop back to the floor. In my situation, either the valves were leaking, slowly reducing the volume of oil in the cylinder, or leaky rod seals (easier to spot) were allowing the fluid to escape the system.

There are a few caveats to this scenario. We assume oil is incompressible, which is not entirely true. Because the oil does squish and stretch a little, the rod will move a small amount with large load changes (read up on ‘bulk modulus of hydraulic oil’). This is not drift, since the oil quickly reaches equilibrium and the rod will not continue to move.

Single-acting cylinders (Fig. 3) are an exception, because oil leaking across the piston is leaving the system. This is similar to when the rod seals leak in double-acting cylinders – drift occurs. Double-ended cylinders (Fig. 4) are also an exception because the fluid volume in the cylinder does not change as the rods move.  Both of these systems require low leak piston seals to prevent drift.

Figure 3.  Single-acting piston
 

Figure 4.  Double-ended cylinder

Leakage across the piston doesn’t cause drift but can cause a number of other complications. Rod retraction relies entirely on the piston seal blocking pressure from crossing the piston; I’ve already described how simply pumping fluid into one side of a cylinder without a piston seal will only cause the rod to extend. Using fluid pressure to retract the rod is not possible without a piston seal.

When extending the rod or holding a load (valves open, no hydraulic lock applied), leakage across the piston seal slowly allows pressure to equalize on both sides of the cylinder. Once this happens, effective piston diameter drops to only the diameter of the rod (Fig. 5). Pushing or supporting the same load now requires higher fluid pressure. This can raise pressures higher than the system was designed to see, cracking pressure relief valves.
 

Figure 5.  Reduction in effective piston diameter

In summary, a leaky piston seal won’t cause drift, but it’s bad for efficiency and could damage the system.

In systems that are quickly cycling, a slow piston leak may go unnoticed as a tiny efficiency loss – the pressure reverses before a significant amount of fluid can leak past the seal to cause problems. On the other hand, cylinders that move slowly or must hold a position for extended periods benefit from no-leak piston seals.

At Parker, we see a wide variety of applications, and we manufacturer piston seals in many styles and materials to cover all of them. Softer durometer materials like those used for our PSP and T-seals are better for tight sealing. Harder durometer materials like our BP and PTFE cap seals are more extrusion resistant and wear longer in fast-stroking applications.

We also offer hybrid designs like our CQ profile. The CQ design utilizes glass-filled PTFE for low friction and long-wearing but also features a rubber insert to reduce leakage.

Cylinder drift is a concern in many hydraulic applications. It’s commonly mistaken as piston seal failure but is usually a combination of factors involving the valves. Understanding cylinder mechanics is vital to identifying the root causes of failure and for designing systems that are resistant to drifting.

Recommendations on application design and material selection are based on available technical data. They are offered as suggestions only. Each user should make his own tests to determine the suitability for his own particular use. Parker offers no express or implied warranties concerning the form, fit, or function of a product in any application. 

 
This article was contributed by Nathan Wells, application engineer, Engineered Polymer Systems Division.  

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Sealing Fundamentals | Face Seal

Closure force requirements are an important consideration for sealing applications, and the Applications Engineering team is often asked for guidance as to how to minimize or predict the amount of force it will take to close a properly-designed face seal groove.  

There are several factors to consider when trying to determine compressive load.  The most important of those considerations are:
 

• What is the hardness of the rubber (durometer)?
• How much will the O-Ring be compressed?
• What is the cross-sectional thickness of the O-Ring?
• How wide is the groove?
• What impact does material family play?

It is correct to assume that as the hardness of the rubber increases so too does the compressive load.  Parker’s O-Ring and Engineered Seals Division offers materials that cover a range of 40-95 durometers (Shore A scale).

Below is an example of compressive load for a 0.139” CS O-ring made from NBR (Buna-N) materials at different measures of hardness (60, 70, and 90):
 

Figure 1: Measure of compressive force requirements of a 0.139”CS, NBR material at different hardness levels.

Another intuitive thought is that as cross-section diameter increases, so does the compressive load requirement.  

Below is a plot of compressive load requirements per linear inch for the standard cross sections (0.070”, 0.103”, 0.139”, 0.210”, and 0.275”), and it follows that logic.
 

Figure 2: Compressive load requirements at different cross-sectional thicknesses on a 70 durometer NBR material.

Groove width impacts compressive load because of how it changes the amount of gland-fill in a given application.  If a groove is narrow, the O-ring is likely to make sidewall contact once compressed.  When sidewall contact occurs, it results in higher compressive load requirements because of how the part is being constricted in the groove.  If there is an application that has high gland fill, adding a draft angle can significantly reduce the compressive load requirements, as shown in Figure 3.  Figures 4, 5, and 6 show the impact of groove width and draft angle on gland fill.
 

Figure 3: Compressive force for 0.070" CS 70 Durometer NBR at 99.8% nominal gland fill when fully compressed.  The graph shows the impact of draft angle on compressive load for grooves that have very high gland fill.

Figure 4: This image shows an O-Ring being compressed with no sidewall contact.

Figure 5: This image shows an O-Ring being compressed the same amount as in Figure 4, but with a narrower groove.  The result is very high gland fill.

Figure 6: This is the same amount of compression as in Figure 5, but with a 3-degree draft angle added. The result is lower gland fill and lower stress on the O-Ring. 

A common myth in the sealing industry is that there is a correlation between material family and compressive load requirements, but as seen in the graphic below, that is not the necessarily the case.  The only truly accurate statement is that silicone materials have lower compressive load requirements than that of other materials.  Otherwise, many material families have significant overlap in the amount of compressive load they generate for the same amounts of squeeze.

Below is a plot of compressive load requirements per linear inch for various 70 durometer materials.

Figure 7:  Compressive load requirements by material family with hardness held at 70 durometer.

In summary, here are some ways to mitigate high compressive loads without sacrificing the amount of squeeze applied to the seal:
•    Use a softer (lower durometer) material.
•    Use a thinner cross-sectional diameter.
•    If gland fill is very high, widen the groove.  If that is not possible, consider adding a draft angle.
•    If appropriate for the application, switch to a silicone seal material.
•    If the application is conducive, consider using a hollow cross section from our extruded product line.
 

This article was contributed by William Pomeroy, applications engineer, Parker O-Ring & Engineered Seals Division. 

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It's no surprise that electronic enclosures and housings in aerospace and defense applications are built to meet the most stringent of military standards. These include but are not limited to environmental stresses, EMI shielding, and maintenance requirements. Additionally, the advanced technological requirements of the devices requiring these enclosures mean that these devices must be more rugged and more powerful, as well as smaller, lighter, and easier to replace.

This poses challenges for designers, leading them not only to suppliers who can meet these requirements but partners who can assist in the design and supply chain management of these complex units.

For environmentally-sealed and EMI-shielded electronics devices, there is no better full-system solution than an overmolded or vulcanized cover. 

So, what is overmolding/vulcanizing/mold-in-place gasket anyway?

1. Integration and permanent adhesion - Overmolded gaskets are integrated directly into an enclosure and permanently bonded onto to the housing. This adds a significant level of durability and means that the gasket will not experience wear as quickly as traditional gasketing in field operation.
    
2. Simplification of assembly - Because the gasket is already directly bonded onto the housing, there is no additional assembly needed. This means no more having to place a gasket in a groove or requiring an attachment method such as rivets or pressure sensitive adhesive.
    
3. Ease of maintenance and repair - Especially true in shipboard avionics, overmolded gaskets provide the benefit of minimizing maintenance procedure. There is no risk of forgetting to reinstall gaskets during disassembly and reassembly.
    
4. Tighter tolerance controls - Molding uses a precise process and tolerance-controlled tools meaning the gasket can meet tolerance controls of just a few thousandths of an inch.
    
5. Smaller form factors and custom geometries - With the tight tolerance controls of overmolded covers comes the ability to mold smaller form factors that will optimize sealing of covers and enclosures. The custom geometries mean that design factors such as closure force and sealing path are perfectly accounted for.
    
6. Consolidated supply chain - With the gasket provided directly on the cover, there is no need to work with multiple suppliers, each completing a small part of the assembly. Overmolded covers can be directly supplied in a ready-to-use form.
   

With more than 40 years of experience in overmolding, the Process Engineering team at Parker Chomerics can assist with full system enclosure design that takes into consideration such factors as ideal surface finish and groove dimensions to meet customer-driven requirements. We will work with customers to determine whether overmolding is the best solution and feasible based on all necessary specifications.

As devices become more complex, so do the associated supply chains. An electronic enclosure can quickly pick up more than 5 or 6 individual suppliers, each needing to meet various requirements of military standards. In addition to the difficulties of sourcing the best suppliers, a complicated web of interdependent timelines starts to appear. This is where Chomerics can provide significant support and logistical relief. Parker has an extensive network of first-class suppliers and can also work with customer-approved suppliers to manage a project from start to finish. Services offered can include: overmolding, machining, painting, dip brazing, embedded fasteners, part marking, etching, and custom packaging.

Overmolded covers provide countless benefits for customers looking for the best solution to durable and reliable EMI shielded, environmentally sealed housings while minimizing a complicated system of suppliers.

This blog post was contributed by Ben Nudelman, market development engineer, Chomerics Division.

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In our July Semiconductor entry, we noted that lowering the cost of ownership is a multi-faceted goal. We discussed how one of the areas for potential improvement is mechanical design and how the Parker EZ-Lok seal is a major solution to mechanical seal failure. In this entry, we’ll investigate a notably different type of cost-reduction opportunity – material selection – and see how Parker’s innovative HiFluor compounds can reduce seal costs to as little as half.

When it comes to the seal industry, the semiconductor market is well known as one where the most premium, chemical-resistant compounds are a necessity. Microelectronic manufacturing processes involve chemistries that push the limits of what elastomeric compounds can withstand in terms of both chemical aggressiveness and variety. The perfluorinated materials (FFKM) capable of withstanding these environments require intricate manufacturing processes regulated by closely-guarded trade secrets and the significant investment of resources.

These factors drive the price of FFKM compounds to the point of being as much as 50 times the cost of any other variety. Cutting just a slice out of this cost can result in significant savings – a chance to take out a quarter or even half the pie would be advantageous indeed. Fabricators should be continually on the lookout for more cost-effective compounds that show equal performance in their pertinent operations.

This is why Parker’s HiFluor compounds offer an opportunity for cost savings that shouldn’t go unnoticed.A unique hybrid of performance between FFKM and the simpler technology of fluorocarbon (FKM) elastomers, HiFluor offers the most superb chemical compatibility in the many semiconductor environments where the high temperature ratings of FFKM aren’t necessary – and at a fraction of the cost.

Not only can HiFluor be used where even FKM is lacking, but its performance in applications with aggressive plasma exposure is spectacular as well. This can be observed by its overall resistance to plasma-induced material degradation. However, Parker has also developed multiple formulations that display extremely low particle generation when most materials would be expected to suffer severe physical and chemical etch.

Need assistance deciphering exactly where this kind of cost-savings can be implemented? Parker O-Ring & Engineering Seals Division has all the resources needed to help their customers identify opportunities to utilize HiFluor seals.

For instance, one major semiconductor fab had several factors (other than their seals) dictating the frequency of their preventative maintenance (PM) intervals. The fab wanted to replace their seals at these intervals as a precautionary measure to limit the chance of them becoming another PM-increasing factor. However, this caused these premium FFKM seals to be a source of inflated cost. Parker engineers assisted with a process evaluation that resulted in over half the seals being replaced with cost-effective HiFluor O-rings, while the tool regions with more intense plasma exposure were reserved for the elite performance of Parker’s FF302.

Another major fab in the microelectronics industry switched from FKM to FFKM seals in their oxide etch process. The tool owner achieved the desired performance improvement, but soon began searching for less expensive options. Based on guidance from Parker engineers, he recognized the plasma resistance and low particulate generation of Parker’s HiFluor compound, HF355. After implementing this change, he retained the performance improvement, but at a fraction of the cost.

Semiconductor tool owners understand that their aggressive processes require the most robust, expensive FFKM seal materials. The price tag on these seals is greater than those from any other compound family. Fortunately, HiFluor is a proven sealing solution that can bridge the gap and provide the same kind of high performance at a much lower cost. To find out if HiFluor is right for your application, visit us at Parker.com/oes and chat with and engineer. 

This article was contributed by Nathaniel Reis, applications engineer, Parker O-Ring & Engineered Seals Division. 

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Electrically conductive plastics continue to provide reliable EMI shielding in a wide variety of applications. Specifically, thermoplastics can overtake bulky metal enclosures due to their superior weight, EMI shielding capabilities, and simpler manufacturing process. However, before purchasing any thermoplastic, it is important to consider performance capabilities.

Electrically conductive thermoplastics are typically sold as a pellet blend of two or more components, made up from a variety of base polymers and stainless steel pellets. In small applications and sizes, these blends can generally be effective but are always bound to have consistency issues. In transportation and handling the stainless-steel pellets will settle to the bottom, resulting in an inconsistently shielded final product. This problem becomes more evident when molders run large quantities of parts and when they store the mix in large containers.
 

Selecting a one pellet plastic material, like Parker Chomerics PREMIER PBT 250-FR, eliminates this problem, since there is no mixing of pellets. Instead of having stainless steel pellets as a separate component, stainless steel fibers are pultruded into the plastic pellets to provide shielding. Single pellet thermoplastics can be sold in large quantities, unlike pellet mixes.

Understanding the plastic’s UL 94 rating will help determine how it will perform under fire hazard conditions. In order to receive the UL 94 5VA certification, the plastic must stop burning after 60 seconds on a vertical plaque, with no drips or holes, according to the UL website. This rating, is the highest level of flammability resistance for any thermoplastic. The next rating down, UL 94 V-0, means the plastic can stop burning within 10 seconds on a vertical specimen and the drips are non-flammable. Most thermal plastics that are electrically conductive fall under the UL 94 V-0 rating and require an extra coating to be EMI shielded. But Parker Chomerics PREMIER PBT 250-FR earns a 5VA rating at 2.5 mm thickness without the need of a coating to achieve electrical conductivity.

In addition, plastics can also be more cost effective than metal enclosures. Although metals are typically more cost effective initially, the secondary machining requirements of

many metal components can add significant cost and lead time. For example, many die cast parts require machining operations to drill and tap threads while most thermoplastics can be molded with pre-formed holes and use thread forming screws. Also, plastics are significantly lighter than metal enclosures, helping to better achieve light-weighting goals.

Parker Chomerics PREMIER PBT 250-FR, a single pellet UL 94 5VA electrically conductive thermoplastic, is known for its excellent performance where petrochemical exposure is common. Typical applications include retail fuel dispenser pumps, housings, dispensers and face plates, electronic payment terminal housings, security access points, and more.

This blog contributed by Page Ludl, marketing co-op, Chomerics Division.

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Seals made of the fluoropolymer PTFE are used where many other sealing materials (such as rubber elastomers, polyurethanes, fabric-reinforced elastomer seals, etc.) reach their limits in terms of requirements such as temperature range, chemical, friction and wear resistance. That is why PTFE is the most frequently used fluoropolymer in challenging sealing applications. Parker Prädifa produces seals made from pure PTFE and numerous modified compounds with diameters of up to 4.5 meters using economical machining techniques.

Polymer materials like PTFE, PEEK, TPU and selected elastomers are suitable for machining such as turning or milling. This makes it possible to economically manufacture both larger and smaller volumes because no additional tooling costs for molds are incurred.
 

Parker Prädifa has been producing complex machined polymer seals with diameters of up to 3 meters for decades. In the light of a growing demand for increasingly large seals Parker Prädifa has continually developed the manufacturing technology of machining further and is now able to offer diameters of up to 4.5 meters at the highest level of quality. The production of even larger diameters is currently in the pipeline.

The production of large seals for challenging applications is not simply a matter of scaling up know-how of traditional seal design and machining. The reason is that XXL sizes not only pose particular handling challenges in the manufacturing process, but do so even earlier, in the design and testing stages.

The evaluation of the performance of large-scale seals under various load and temperature conditions requires sophisticated simulation models. Particularly critical factors to be considered in the design of large seals include thermal shrinkage and expansion. In addition, even relatively low pressures may result in extreme forces acting on the seals, leading to considerable deformations or even seal failure.

As damage caused by seal failure and leakage may be particularly severe in the case of large seals, reliable sealing functionality must be comprehensively validated prior to their utilization in the respective application. Parker Prädifa uses virtual prototyping for validation. Due to the advanced method of virtualization utilizing sophisticated FEA models costly tests with real-world parts can be avoided and development cycles significantly reduced.

Parker Prädifa ensures top quality of XXL sealing solutions using quality assurance technologies developed in-house. Picture: X-ray inpection of large-diameter seals.
 

Case Studies

• Renewable Energy – Sealing Solutions for Bearings in Wind Turbines
• Oil and Gas – Environmental Seals in FPSO Swivel Stacks
• Medical Device Technology – Seals for Magnetic Resonance Imaging (MRI) Systems
   

More information:

• Website: XXL Size Seals and Molded Parts
• Download Whitepaper: Large-Diameter Seals and Moldings - Material and Special Manufacturing Aspects
• Download Brochure: XXL- Size Seals and Molded Parts - Powerful Solutions for Large-Scale Applications

Article contributed by
Karel Kenis, business development manager PTFE
Engineered Materials Group Europe, Prädifa Technology Division

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Combination electromagnetic interference (EMI) shielding and weather gaskets, more commonly known as EMI shielded combo strip gaskets, are an excellent choice for a variety of applications that require a resilient, highly conductive sealing solution of knitted wire mesh with the integration of an elastomer for weather sealing. Typical applications include electronics cabinet doors, telecommunication trailers, wing panel gaskets for the protection against lightning strikes, and EMP specified requirements and sealing of shipboard and EMI.

There are five major features to consider for EMI shielded combo strip gaskets: the elastomers available, the metals available, the various mesh knit densities available, the various profile geometries available and the option of an overmolded gasket.

Elastomers are available in a silicone sponge or solid, or neoprene in sponge form to meet customer needs such as closure force, fluid resistance and NASA outgassing requirements. Elastomers allows for an increase in gasket life and reduces the overall ownership cost.  Three specific design parameters are the most important variables to take into consideration when evaluating elastomer choices. These criteria are fluid exposure, temperature requirements and necessary compression characteristics of the material. Generally, solid elastomers are used in conjuncture with cast or machined surfaces due to their larger force requirements for deflection. Sponge offerings have less force requirements for deflection and are therefore typically used in conjuncture with sheet metal enclosures.

A broad range of metal alloys are offered to meet the requirements of electrical and galvanic corrosion. This also makes it possible for customers to meet budgetary needs by using Monel (Ni/Cu alloy), Ferrex (SnCuFe), aluminum, or stainless steel.

Various mesh knit layers are available to meet with the required electrical performance. Military applications will require multiple layers to ensure maximum protection while in less extreme applications, less layers are needed. These variations reduce gasket replacement schedules and improve their durability, allowing them to be handled during in-field installation. Most critical of these criteria include galvanic compatibility, electrical
performance, overall gasket durability and temperature range requirements. 

There are round, square, or rectangle profile geometries available that allow for design leniency for application in specific performances.  Which geometry you'd choose depends on the criteria necessary to the application, including, but not limited to, gasket deflection percentage, necessary compression characteristics of the material, application load available for gasket deflection and planned gasket affixation method.

These combo strip gaskets are available in both bonded or overmolded version for tiered performance options. If needed, overmolded gasket can be used but only for wing panel applications.

This blog post contributed by Paige Ludl, marketing co-op, Chomerics Division.

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I have had many discussions with customers as to the value of using an ASTM elastomer compound description on their prints to define a specific application or elastomer requirement versus listing an approved Parker compound number.

Specifying a compound using the ASTM callout is a good start - it clearly defines what you want, it sets a minimum bench mark and it is easy for competitive vendors to understand what you are asking for. The ASTM standards also set specific test parameters which make it easier to do an "apples to apples" comparison between two compounds. However, over time here is what my customers have learned:

1) The ASTM standards are very general; so when my customer defined a specific FKM they needed using an ASTM callout, they received a compliant material that just barely met the ASTM specifications but did not meet their actual operating requirements. The supplier provided my customer with their lowest cost material. The quality of the material was poor and inconsistent, but it met the ASTM criteria they requested. This customer saw a 15% increase in assemblies requiring rework plus the number of warranty claims rose due to seal failures. The twenty cents per seal my customer saved for their $48.00 application was offset by the cost of increased product failures which also resulted in unhappy customers.

2) The ASTM standard does not specifically list what actual chemicals the seal has to be compatible with as well as the operating conditions. ASTM tests compatibility based on Standardized Testing Fluids which are Oils, Fuels and Service Liquids. ASTM uses standard oils which are defined by IRM 901 and 903. Again, the ASTM standards are excellent for comparing compounds, but most people do not have their seals operating in the ASTM reference oils and many sealing applications are exposed to multiple fluids.

3) Most of the engineers or purchasing people who reviewed or utilized an older drawing had no idea why the original engineer chose the compound or why they used the ASTM callout  specified. I typically find that most companies do not know exactly what the ASTM standard  is calling out.

So what is the best way to define and specify an elastomer? Most companies go through a technical process to specify, test and confirm that an elastomer is the correct choice for their application. All of the elastomers that were tested and approved for the application should be clearly listed on the drawing. In addition, the drawing should clearly state that  the approved materials listed were tested to confirm their suitability for the application. All substitutes or new elastomers must be tested and approved by engineering prior to use.

If you have questions regarding the suitability of an elastomer for your application,consult and work with your Parker Applications Engineer. We offer a plethora of compounds to suit your application needs. Ask our applications engineers and chemists for guidance; their vast seal design experience spans multiple industries and applications to solve your sealing challenges. 

  Fred Fisher, technical sales engineer, Parker Hannifin Engineered Materials Group

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We've all done it at least once: looked at a report, read the numbers on it, and come up with exactly the wrong conclusion. Pass/fail limits and results are printed right there, but for some reason, our brain just misinterprets the two. It's a passing value, but for some reason, we think it shows a failure instead. Imagine a police officer writing a speeding ticket for driving 53 MPH on a road with a 55 MPH speed limit.

It's not a problem with the test itself, it's a problem of interpretation. That means the old carpenter's adage, "measure once, cut twice; measure twice, cut once" doesn't address the issue. The same issue of misunderstanding the values on a test report occurs in the rubber seal industry about once a month. Passing results are misinterpreted to be failing results, and good values are thought to be bad ones. Here are four of the most common test report misunderstandings I've run into. 

Most low-temperature testing involves negative numbers and that creates some confusion when coupled with “greater than / less than” test limits. For example, it is common to see pass / fail limits for TR-10, the glass transition (Tg), and sometimes impact brittleness expressed in the form of “-30°C max.” I’ve talked to people who claim that a result of -32°C failed against a limit of “-30°C max” because everyone knows that 32 is a bigger number than 30. Just to be clear, -32°C passes, -28°C fails. This is a 2nd-grade math problem, but sometimes we adults forget how to do the simple things if we don’t do them often enough. If this gets confusing, the easy way to interpret temperature limits is to mentally replace “max” with “no warmer than” and “min” with “no colder than.”

Compression set is always expressed with a maximum limit, for example, 20% max. Therefore, all values up to and including 20% are passing values. I’ve heard people claim that a result of 20% fails against a limit of 20% maximum because it’s not below the maximum. I won’t disagree that “barely passes” isn’t a good situation to be in, but “barely passes” is still a passing value. Compression set is a measure of what percent of the original squeeze has been permanently lost. A value of 100% means the material has gone completely flat. A value of 0% means the material returned all the way to its original dimension. With the compression set, small numbers are good, big numbers are bad.

Commonly used in the passenger car and commercial truck industries, Compressive Stress Relaxation (CSR) is a measure of how much spring force the rubber has left after aging or being exposed to a fluid. The limits are always expressed as “10% min retained load force”, as one example of a common limit. CSR moves in the opposite direction as compression set, and perhaps this is why a result of 15% is frequently and incorrectly thought of as failing a “10% min” limit. For CSR, the more retained seal force, the better.

Most limits for tensile strength and elongation change after heat aging and fluid immersion are one-sided limits, meaning they only have one limit, not two. For example, a heat aging requirement may have limits of “-30%” or “-30% max” for the tensile strength change. What happens if the result is +2%? In other words, what if the result has the opposite sign from the limit? This is a passing result. There is no implied “to 0” limit attached to these one-sided limits. There is also no implied “mirror image” limit with the opposite sign. By this, I mean that a “-30% max” limit does not automatically include a matching “+30% max” limit. A result of +100% is still a passing value compared to a one-sided limit of -30% max. If a specification does not explicitly call out a two-sided requirement with both a high limit and a low limit, then it only has one limit.

This is something that happens frequently, but it doesn't make it any less embarrassing. In an ideal world, someone is there to patiently explain the data and the limits and show how the report actually shows passing data, not failing data, and does so in a way that doesn't make you feel worse about it. If I have been that person for you in the past, a thank you cake would be appreciated. You and I know who you are, but we can keep that to ourselves. Cookies are good too.

For more information on the proper way to read a test report, watch our video below. For further questions, please contact Applications Engineering Team at oesmailbox@parker.com or visit us at the Parker O-Ring & Engineered Seals Division. 

This article contributed by Dan Ewing, senior chemical engineer, Parker Hannifin O-Ring & Engineered Seals Division.

Answers to Your In-Service Rubber Properties Questions

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Most thermal pads, also known as thermally conductive gap filler pads, thermal gap pads, or thermal gap filler pads, have many different layer materials or carrier substrate options to choose from. It can be confusing which layer is supposed to stay on the product and which layer gets peeled off and removed before application. In fact, it’s one of our customer’s most asked about questions and can cause a lot of confusion on the manufacturing floor.

So, which layer should you peel off and which should stay on the thermal gap pad? Read on to find out.

Parker Chomerics, like many thermal gap pad vendors, offers several different gap pad layer options that must be peeled away before the gap pad is installed into the application. 

Think of a thermal gap pad as a sandwich of layers -- there is always a blue poly backing that keeps the gap pad together, but there are five additional carrier substrate options which provide the following benefits:

The woven fiberglass carrier option provides reinforcement and a clean break / low tack interface surface, allowing for re-use of the thermal pad if necessary or for prototyping.

As you can see from the diagram, you peel off the liner to expose the woven glass carrier which does not get removed from the thermal gap pad.

Example: THERM-A-GAP HCS10G.

The aluminum foil with PSA carrier’s primary function is to allow a pressure sensitive adhesive on the thermal gap pad to affix the thermal pad in place.

As you can see from the diagram, you peel off the liner to expose the aluminum foil carrier which does not get removed from the thermal gap pad.

Example: THERM-A-GAP A579.

The polyethylenenapthalate (PEN) film carrier permits the thermal gap pad to see a shearing motion and offers a clear, cost-effective dielectric film with fair thermal performance.

As you can see from the image at right, there is no clear film to peel off that exposes the PEN film carrier, which does not get removed from the gap pad.

Example: THERM-A-GAP 579PN.

The thermally enhanced polyimide carrier permits the thermal gap pad to see a shearing motion and offers an excellent dielectric film with enhanced thermal performance. 

As you can see from the image at right, there is no clear film to peel off, the polyimide carrier does not get removed from the gap pad.

Example: THERM-A-GAP 579KT.

The no carrier or “un-reinforced” option allows the thermal gap pad to have high tack surfaces on both sides, allowing for the pad to be highly conformable, but it does make cutting and handling of the product more difficult.

Once the liner is peeled back, there is no additional carrier on the thermal gap pad, the pad is now exposed.

Example: THERM-A-GAP 579.

Lastly, the base carrier liner, shown in blue, is persistent on the bottom of all thermal gap pad options, and must be peeled and removed prior to installation of the thermal gap pad.

This blue carrier is necessary, as it keeps the gap pad intact and more easily to handle prior to installation. We recommend keeping this blue poly carrier layer on just until the gap pad is placed for the final time.

This blog was contributed by Jarrod Cohen, marketing communications manager, Parker Chomerics Division.

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Are you uncertain of what to look for when comparing material data reports for various elastomers?  Ever wonder about the impact a seal’s durometer has in the application? Have you asked, ‘What is compression set and why is it important?’ These are the types of questions and concepts covered in the O-Ring Elastomers chapter of Parker’s O-Ring eHandbook. 

Since its debut in 1957, the Parker O-Ring Handbook has become a fixture on the reference shelves of engineers and seal specifiers worldwide. According to Steven Weinzierl, Ph.D., Parker's Global e-Business Customer Support Manager, "Parker's O-Ring Handbook is one of the world's most complete reference books for everything and anything related to the technology and application of O-Rings. It is downloaded thousands of times a month from www.parker.com, making it one of Parker's most downloaded knowledge assets." By creating an interactive, digital version of this resource, Parker is expanding it's customer base and utilizing various forms of multi-media to provide visual explanations and demonstrations that further enhance an industry staple.

Seal manufacturers compile material data sheets of physical properties, compression set, and a myriad of other combinations of testing; all intended to demonstrate the seal material’s capability. But what are these characteristics, and how does one relate the results to an application? 

The Physical and Chemical Characteristics chapter explains the lab testing behind each data point on a test report. Video snips of laboratory equipment testing O-rings illustrate how data is generated. Animations create a visual explanation of testing such as TR-10. Brief summaries of each characteristic explains how data can be applied to an O-ring in service. Photographs and vibrant charts help to put context around the data, in order to bring to light how each bit of information should be interpreted.

Perusing the Physical and Chemical Characteristic chapter will allow you to evaluate rubber test reports with a greater understanding than ever before.

Further subsections of the Material Selection Guide feature a compound family overview including a description of compound advantages, typical temperature maximum/minimum, and compatible fluids. A list of incompatible fluids is also detailed, allowing the user to receive a concise summary of the most common, and even the more obscure elastomer types.

Check out the Parker O-Ring eHandbook sections highlighted above or download the full version of the Parker O-Ring Handbook for further information and useful tips on how to select an O-ring.

This article was contributed by:

Dorothy Kern
Applications Engineer Lead
O-Ring & Engineered Seals Division

Samantha J. Sexton
Marketing Communications Manager
O-Ring & Engineered Seals Division

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Why is Shore A Hardness Important?

Material selection for military applications requires careful consideration, as there are strict requirements to ensure maximum durability, security and of course performance. In munitions, or missiles and missile launch systems, materials that provide electromagnetic interference (EMI) shielding and environmental sealing are critical for the functionality and field life of the application.

Let's look at three areas of a munitions application -- specifically nose cones, cable shielding, and connectors, as each of these areas exemplify why EMI and environmental shielding are a necessity.

Nose cones are what goes over the top of missiles, planes and other airborne technologies to assist with aerodynamics and to protect the electronic components inside. In missiles, all the electronics are stored within the nose cone and the fuel is held inside the canister. If these two parts are not properly shielded from each other, contamination can become a catastrophic event.

Therefore, shielding the nose cone from EMI and other outside environmental dangers and shielding the components of the missile from each other is of utmost importance.

Another threat to missile electronic malfunction is external tampering from malicious forces. Unintended or intentional EMI can result in misfires, false trajectory, and other problems. Often, anti-jammers are installed to help prevent this problem in combination with EMI shielding materials.

Cable shielding is a woven fabric that goes over cables to prevent electromagnetic cross-talk between the cables and the components. Typically, a metal mesh is wrapped around the cables that will prevent any EMI from interacting with the cables or emitting from the cables.

Different amounts of layers can be added to increase EMI shielding effectiveness, however adding more layers will also add more weight. Cable shielding that is lighter, typically non-metal based, is ideal for applications where weight is of concern like in munitions.

Connectors are where wires are plugged into to keep electric circuits intact. In munitions, connectors can be a failure point because environmental agents can more easily enter which is why they require more attention to be shielded properly.

The complexity of military electronics has increased significantly on air, sea and land-based applications. The environments in which systems are required to operate are often extreme. Design engineers need to consider wide variations in ambient temperature, shock and vibration, and electromagnetic interference (EMI).

With a wide choice of shielding materials and a range of advanced shielded optical windows, Parker Chomerics helps ensure the protection of complex electronics from damage and compromised reliability caused by EMI.

Sensitive electronic components can be kept within their operating temperature range limits by using heat management materials that include highly conformable, thermally efficient gap fillers and gels.

Parker Chomerics offers the products, technical know-how, close customer support and supply chain capabilities to meet these challenges and deliver superior, reliable and cost-effective solutions.

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Form-in-place EMI gaskets, also known as FIP EMI gaskets, is a robotically dispensed electromagnetic interference (EMI) shielding solution that is ideal for modern densely populated electronics packaging.

The most important distinction of form-in-place EMI gaskets is that they were developed for applications where inter-compartmental isolation is required to separate signal processing and/or signal generating functions.

Simply put, form-in-place gaskets are meant to reduce “noise” between cavities on a printed circuit board (PCB) or in an electronics enclosure. 

In addition, form-in-place gaskets provide excellent electrical contact to mating conductive surfaces, including printed circuit board traces for cavity-to-cavity isolation. Parker Chomerics form-in-place gasket materials are known as CHOFORM. 

1. Small form factor - form-in-place gaskets can be dispensed in smaller bead sizes than most traditional EMI shielding gasket solutions, 0.018” tall by 0.022” wide. 
    
2. Excellent adhesion - 4-12 N/cm adhesion on prepared surfaces such as machined metals, cast housings, and electrically conductive plastics.
    
3. High shielding effectiveness - Parker Chomerics CHOFORM materials can provide more than 100 dB shielding effectiveness in the 200 MHz to 12 GHz frequency range.
    
4. Quick programming - Because form-in-place EMI gaskets are robotically dispensed, a standard CAD file can be used to program the dispensing system and quickly map out the dispensing pattern.
    
5. Complex geometries - The positional tolerance of the gasket can be held to within 0.001” and is able to follow very complex geometries including sharp turns, corners, and serpentine patterns. Other gaskets such as die cut sheets or o-rings manufacture and/or fabricate into such shapes and patterns. 
    
6. “T” joints - Traditional extruded gaskets are difficult to mate at intersections or “T” joints. The robot dispensing systems produce reliable junctions between bead paths to provide continuous EMI/EMC shielding and environmental sealing.
    
7. Integrated solutions - CHOFORM technology combined with a Parker Chomerics supplied metal or conductive plastic housing provides an integrated solution ready for the customers’ highest level of assembly. This approach requires no additional assembly or process steps for the installation of gaskets and/or board-level auxiliary components. 

1. Large form factor enclosure sealing that can accommodate a groove. For larger areas such as machined covers that can accommodate a gasket groove, other EMI shielding solutions are better suited. In most applications, conductive elastomers such as the CHO-SEAL product line by Parker Chomerics will provide better shielding and sealing. Form in place gaskets can be dispensed in bead sizes only as large as about 0.062” tall x 0.075” wide.
    
2. Enclosures requiring submersion or durable weather sealing. Because of the small form factor, FIP gaskets will not meet stringent environmental sealing requirements such as IP 67 or higher. While silicone-based, the material is better at preventing dust and environmental moisture from entering an enclosure. FIP gaskets can be paired with additional sealing gaskets for enhanced weatherproofing. 
    

This blog post was contributed by Ben Nudelman, market development engineer, Chomerics Division.

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More often than not, an O-ring makes for a great sealing element. They seal over a wide range of pressure, temperature and tolerance. Normally they require very little room, are readily available, and easily sourced. However, there are specific applications that may be better suited for an alternate type of seal, such as a double chamfer radial seal. 

1. When the O-ring fails by spiraling in a reciprocating application or during installation, the double chamfer seal is a good alternative. The wide, flat base of the double chamfer makes it resistant to rolling, and therefore, a solution for O-ring spiral failure. The FEA below demonstrates the O-ring rolling in a gland. 

2. High pressure or large clearance gap applications can result in an extruded O-ring. A common solution is to add a back-up ring as a support to the O-ring. The back-up ring is a great solution, however this can add complexity in several ways. One, it adds another item to the bill of materials. Second, the back-up can be difficult to install, resulting in damage. Finally if the back-up is forgotten or incorrectly assembled during installation, the O-ring will leak. A high pressure high temperature double chamfer radial seal replaces the O-ring and back-up combination with a single sealing solution. In addition, known issues with scarf cut back-up rings are the chance of the angled edge damaging the O-ring. By eliminating the scarfed back-up, we are eliminating a possible failure mode. 

3. A third advantage has to do with available groove space on the hardware. Standard O-rings require a specific groove depth and width, which can be difficult in tight locations or with limited hardware space. Since double chamfer radial seals are easily customized, they can be designed for a more shallow groove, and seal just as well as an O-ring. Double chamfer radial seals are easily customized in both size and material for most any application. For example, since the product is extruded rather than molded, the custom sizes will likely not need a costly mold and instead, use existing extrusion tooling configured for the desired size. And since the double chamfer radial seal is extruded rather than molded, there is no parting line on the finished product. This can be an advantage for gaseous or vacuum applications when even the smallest change in sealing surface finish will create a leak path.

We've all done it at least once: looked at a report, read the numbers on it, and come up with exactly the wrong conclusion. Pass/fail limits and results are printed right there, but for some reason, our brain just misinterprets the two. It's a passing value, but for some reason, we think it shows a failure instead. Imagine a police officer writing a speeding ticket for driving 53 MPH on a road with a 55 MPH speed limit.

It's not a problem with the test itself, it's a problem of interpretation. That means the old carpenter's adage, "measure once, cut twice; measure twice, cut once" doesn't address the issue. The same issue of misunderstanding the values on a test report occurs in the rubber seal industry about once a month. Passing results are misinterpreted to be failing results, and good values are thought to be bad ones. Here are four of the most common test report misunderstandings I've run into. 

Most low-temperature testing involves negative numbers and that creates some confusion when coupled with “greater than / less than” test limits. For example, it is common to see pass / fail limits for TR-10, the glass transition (Tg), and sometimes impact brittleness expressed in the form of “-30°C max.” I’ve talked to people who claim that a result of -32°C failed against a limit of “-30°C max” because everyone knows that 32 is a bigger number than 30. Just to be clear, -32°C passes, -28°C fails. This is a 2nd-grade math problem, but sometimes we adults forget how to do the simple things if we don’t do them often enough. If this gets confusing, the easy way to interpret temperature limits is to mentally replace “max” with “no warmer than” and “min” with “no colder than.”

Compression set is always expressed with a maximum limit, for example, 20% max. Therefore, all values up to and including 20% are passing values. I’ve heard people claim that a result of 20% fails against a limit of 20% maximum because it’s not below the maximum. I won’t disagree that “barely passes” isn’t a good situation to be in, but “barely passes” is still a passing value. The compression set is a measure of what percent of the original squeeze has been permanently lost. A value of 100% means the material has gone completely flat. A value of 0% means the material returned all the way to its original dimension. With the compression set, small numbers are good, big numbers are bad.

Commonly used in the passenger car and commercial truck industries, Compressive Stress Relaxation (CSR) is a measure of how much spring force the rubber has left after aging or being exposed to a fluid. The limits are always expressed as “10% min retained load force”, as one example of a common limit. CSR moves in the opposite direction as a compression set, and perhaps this is why a result of 15% is frequently and incorrectly thought of as failing a “10% min” limit. For CSR, the more retained seal force, the better.

Most limits for tensile strength and elongation change after heat aging and fluid immersion are one-sided limits, meaning they only have one limit, not two. For example, a heat aging requirement may have limits of “-30%” or “-30% max” for the tensile strength change. What happens if the result is +2%? In other words, what if the result has the opposite sign from the limit? This is a passing result. There is no implied “to 0” limit attached to these one-sided limits. There is also no implied “mirror image” limit with the opposite sign. By this, I mean that a “-30% max” limit does not automatically include a matching “+30% max” limit. A result of +100% is still a passing value compared to a one-sided limit of -30% max. If a specification does not explicitly call out a two-sided requirement with both a high limit and a low limit, then it only has one limit.

This is something that happens frequently, but it doesn't make it any less embarrassing. In an ideal world, someone is there to patiently explain the data and the limits and show how the report actually shows passing data, not failing data, and does so in a way that doesn't make you feel worse about it. If I have been that person for you in the past, a thank you cake would be appreciated. You and I know who you are, but we can keep that to ourselves. Cookies are good too.

For more information on the proper way to read a test report, watch our video below. For further questions, please contact Applications Engineering Team at oesmailbox@parker.com or visit us at the Parker O-Ring & Engineered Seals Division. 

This article contributed by Dan Ewing, senior chemical engineer, Parker Hannifin O-Ring & Engineered Seals Division.

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Composite materials have been replacing metal structures throughout the aircraft industry primarily to save weight, improve fuel economy and reduce costs.  But the lack of electrical conductivity in these materials is a disadvantage when compared to the conventional metal airframes of the past. The conventional, metal airframe allowed designers to take advantage of the natural Faraday cage it formed to protect equipment against interference. There were many opportunities to ground items of equipment reliably by connecting directly to a convenient surface ground.

Today, a typical airframe consists of around 50% composites. Major structures include the fuselage and wing fairing, as well as large sections of the wings, fin and horizontal stabilizers. 

Inside the aircraft there are numerous electrical systems capable of generating EMI which can potentially disturb the operation of critical systems. These include fluorescent lights, light switches, dimming circuits, AC-powered window heaters, motors and generators, data and power cables, and transmitters such as radio and radar. 

External storms are also a major source of potentially disruptive electrical interference and can cause physical damage to the aircraft through lightning strike impact.  

Replacing metal structures with composites means compromising the EMI shielding and lightning strike protection of the aircraft, as the composites themselves are not electrically conductive. To overcome this issue, woven or non-woven copper-aluminium mesh, or an expanded foil, can be embedded in composite structures to restore lost shielding and grounding properties. The embedded metal provides an optimal combination of electrical conductivity, weight, and corrosion resistance. Solid metal strips can be used in the radome area to handle very high concentrations of lightning energy. 

Embedded conductors, however, do not solve all the technical challenges that come with the increasing use of composites. It is very difficult to ensure reliable electrical continuity between individual composite panels after the airframe is assembled and still promote conduction of lightning energy. 

Electrical components are typically bonded or grounded directly to the airframe. These connections to the mesh can often fail to meet the very low impedance requirements because of environmental stresses such as vibration and temperature variation. The exposed mesh in the locations where grounded or bonded modules are made (fig 1, at left), can be vulnerable to environmental exposure (temperature, humidity, oxidation) that increases electrical impedance.

To overcome this challenge, a lightweight coating such as Parker Chomerics CHO-SHIELD technology can be applied to optimize conductivity in this area. CHO-SHIELD® 4994 is a highly conductive, silver-filled polyurethane coating designed for aerospace applications and has superior EMI shielding properties. The coating provides excellent adhesion and wear resistance and is resilient to most operation and environmental fluids. The coating is compatible with many primers and top coat systems.

In areas where high corrosion protection is needed, a copper-based urethane coasting such as Parker Chomerics CHO-SHIELD® 2002 can be used. When used on a composite, CHO-SHIELD 2002 provides the conductivity necessary to achieve excellent shielding effectiveness while maintaining its electrical and mechanical stability in hostile environments. CHO-SHIELD 2002 is designed to be used with Chomerics CHO-SHIELD® 1091 primer to ensure correct adhesion. 

The aircraft antennas will also need to be shielded and grounded against lightning strike. This can be achieved by using an expanded woven MetalasticTM EXP-URE gasket material. Electrically conductive grease can be applied at ground connections, to support reliable electrical connectivity under temperature and vibration. Attention must be paid to viscosity and surface-wetting properties when formulating greases for aerospace applications. Parker Chomerics CHO-LUBE® 4220 has a resistivity better than 100mΩ-cm and is an example of an aerospace-grade grease. It is formulated to support electrical interconnections, improve metal to metal contact and provide long-term oxidation protection for exposed mesh or electrical terminals.

Conductive sealants such as Parker Chomerics CHO-BOND® 2165 or CHO-BOND® 1019 can be applied at locations requiring electrical continuity and environmental protection. Typical airframe areas treated are screw holes, fasteners, antenna connection points and exposed conductors on external areas. Where conductive gaskets are used to promote electrical continuity between composite components, a conductive sealant can be applied to provide improvement in continuity. These areas are generally around the wheel wells, engine mounts, wings and the tail section, where high vibration occurs (figure 2, above). 

In addition to these methods which will improve EMI performance throughout the airframe, a lightweight conductive heat shrinkable tube such as Parker Chomerics CHO-SHRINK® 1061 can be used to shield the aircraft’s cabling against the effects of EMI and can provide a weight saving of up to 60% compared to traditional methods.

This blog post contributed by Mel French, marketing communications manager, Chomerics Division Europe

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Automated form-in-place (FIP) dispensing of EMI shielding gaskets can be ideal for complicated patterns on electronics housings because automation allows for control over the size and shape of the bead. In addition to form-in-place EMI gaskets, thermally conductive gels can also be automatically dispensed, and often span oddly shaped gaps and conform to complex geometries. 

The ability of dispensed thermally conductive gels to conform effectively makes them convenient solutions for reducing temperature and increasing the efficiency of electronics applications. Some automated systems can dispense both form-in-place EMI gaskets and thermally conductive gel on the same machine, allowing them to be dispensed simultaneously in the same program to easily integrate both materials into one housing. 
 

1. Be sure to use the correct tip diameter for the target bead dimensions and the particle size of the form-in-place material being dispensed. As a rule of thumb, the inner diameter of the tip should be six times the largest particle size of the material. A shorter tip with a larger tip diameter maximizes material flow and produces less back pressure.
   
   Tapered tips also produce less back pressure than straight walled stainless-steel tips, however they are more flexible which can cause variations in dispense paths. 
    
2. The height of the form-in-place bead should be 85% of the width, and the desired compression is 20 – 30%. We recommend staying below 40% compression. If there are limits on the width of a bead but a taller bead is necessary, a double bead can be used to increase the ratio of height to width. Allow for higher tolerances in start and stop zones compared to straight runs and minimize the number of starts and stops in a bead profile.
    
3. To maximize thermal gel performance, choose a dispense pattern that will contact the entire target area on both the heat sink and component surfaces without air in between. Thermally conductive gel can be dispensed as a dot, a serpentine, a spiral, an X, or in various other shapes. The more simple the profile, the less likely that air will be introduced into the bead. A shot-size calibration process can help ensure dispense rates are consistent for a repeatable dispense volume.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
    
4. Choose the proper valve type for your material and application. The viscosity of the material, the amount of material to be dispensed, and the abrasive nature of the material are the most important variables to consider when choosing a valve. Pneumatic valves with time-pressure dispensing systems are popular in the industry, where an air pulse pushes a piston that allows material to flow out of a disposable dispensing needle.
   
   Auger valves displace precise amounts of material from cavities in a dispensing chamber with an auger screw, however filled materials are often too abrasive to achieve successful dispensing since the screw grinds down the particles. Positive-displacement valves are a good option for abrasive materials, where a motor-driven piston forces material out of a disposable barrel, because the system is not affected by external factors such as temperature and humidity.
   
   Spool valves have very tight shot size control and a long life span when constructed with tungsten carbide, making them ideal for repeatable, consistent shots.
   
   
5. Keep in mind z-height obstructions with both form-in-place and thermally conductive gel materials. Tall walls next to the dispense path require a longer dispense tip, and the length of the dispense tip has an impact on the dispense speed. The slower the dispense speed, the longer the cycle time.

This blog post was contributed by Erika Dudek, FIP dispensing co-op, Chomerics Division.
 

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Most pharmaceutical manufacturers produce drugs in large vats of living cell cultures. For the production of these drugs, it is extremely important to ensure that these cell cultures are not exposed to any cytotoxic contaminants that may leach out of the seals. It is also imperative that cytotoxic contaminants not be present in the finished drug, especially for infants, and for patients who are pregnant or nursing.

Before an O-ring is approved for the pharmaceutical industry, it needs to be tested for cytotoxicity (cell toxicity). This is usually tested in the United States per USP <87>, and internationally per ISO 10993-5. These two tests are very similar in methodology and criteria. Both cytotoxicity tests use L-929 mouse fibroblast cells, which are an industry-standard cell used for cytotoxicity testing. Cultures of these cells are produced in glass flasks prior to testing. Extracts are prepared using 3 test articles: the O-ring material, a negative control article (HDPE), and a positive control article (PVC for USP <87>, and powder-free latex gloves for ISO 10993-5). These extracts are then added to the cell cultures. Cells are incubated with the extracts and then examined after 48 hours. The grading scale is from 0 to 4, with 0 meaning cells are completely unaffected, and 4 meaning all cells are destroyed. For the test to be valid, the HDPE extract must have a grade of 0, and the PVC extract must have a grade of 3 or 4. The O-ring material meets the requirements if the biological response is less than or equal to grade 2. Materials that pass the requirements of USP <87> or ISO 10993-5 are generally considered non-toxic to cells.

Parker offers several O-ring compounds that have been tested for cytotoxicity. 

If you have any questions or would like to learn more about O-ring Cytotoxicity testing, please feel free to contact Parker applications engineering or check out our interactive O-Ring eHandbook. You can also visit the Parker O-Ring & Engineered Seals Division website for more information.

To learn more about Parker's solutions for medical and life sciences applications, stop by booth #1701 at Medical Device and Manufacturing West in Anaheim, February 11-13.

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