Sealing and Shielding

Perhaps you know Parker’s newest EPDM material is EM163-80. Featuring breakthrough low temperature functionality, resistance to all commercially available phosphate ester fluids, and the ability to be made into custom shapes, extrusions, and spliced geometries, EM163 represents the best-in-class material for applications needing to seal phosphate-ester-based fluids. The latest news is that EM163 meets the full qualification requirements of both NAS1613 Revision 6 (code A) and the legacy Revision 2 (no code). We’ve been inundated with questions about the specification differences between Revision 6 and 2, enough that it makes sense to devote a blog topic explaining the fluids, conditions, and dynamic cycling requirements which are required to qualify EM163-80 to each specification.  

The easiest part of this comparison is evaluating the areas of Revision 6 which are very much a copy and paste from Revision 2. Compression set conditions, aged and unaged, plus temperature retraction requirements, aged and unaged, are identical. Lastly, both specifications require a test to verify the elastomers will not corrode or adhere to five different metal substrate materials. That is pretty much where the similarities end.  Now for the contrasts.

Specimen Size

The first subtle difference is the specimen size. Both specs require testing to measure the change in physical properties and volume following a heated immersion in phosphate ester fluids. For the most part, No Code qualification requires testing to be completed on test slabs or O-rings, while the newer revision, Code A, requires testing on test slabs AND O-rings. Not a big difference, but still, a difference.

The fluid conditions are very similar in both specs, but not identical. There are only two temperatures for the short term 70 hour exposure: 160°F and 250°F. Another similarity is that the longer soaks are at 225°F for 334 and 670 hours. The more difficult A Code also requires 1000 and 1440 hours at 225°F. We begin to see the requirements for the later revision are more reflective of the industry conditions, right?

Fluids

Next, we look at the fluids, which truly are a key difference between the two documents. Revision 2 fluid is exclusively for AS1241 Type IV, CL 2 while revision 6 states the elastomers must meet “all commercially available AS1241 Type IV, Class 1 and 2, and Type V”. Table 1 outlines the AS1241 fluids in context of both NAS 1613 revisions.

 Table 1: AS1241 fluids

Basically, to pass Revision 6, the material must demonstrate compatibility for all six commercially available fluids, while Revision 2 only has one fluid which is must be verified for compatibility. Again, we see Revision 6 is much more comprehensive than Revision 2.

Endurance Testing

Last, we look at the functional testing of the materials, referred to as dynamic or endurance testing. Both specifications require endurance testing on a pair of seals, which have been aged for a week at 225°F. The appropriate fluids are outlined in the table above.

Revision 2 has a gland design per Mil-G-5514. There is a 4” stroke length and the rod must travel 30 full cycles each minute. The rod is chromium plated with a surface finish between 16-32 microinches. PTFE anti-extrusion back up rings are necessary for the 3000 psi high pressure cycling. A temperature of 160°F is maintained for 70,000 strokes and then increased to 225°F for an additional 90,000 strokes.

Revision 6 has a much more demanding endurance test with fives phases and slightly different hardware. The rod must be a smooth 8 to 16 microinches Ra with a cross-hatched finish by lapping, and the cycle is 30 complete strokes per minute but only 3” rather than 4”, which means the speed can be more conservative. A pair of conditioned seals are placed in AS4716 grooves, adjacent to a PTFE back up ring. Similarities to Rev 2 are that there is a pressure of 3000 psi for the dynamic cycling at both 160°F and 225°F, however before and after each high temperature cycle there is a low temperature, -65°F soak. The first soak is static for 24 hours, followed by the 160°F high pressure cycling. The second low temperature soak requires 10 dynamic cycles at ambient pressure followed by 10 cycles at 3000 psi. The final low temperature soak requires one hour static sealing at 3000 psi followed by an 18 hour warm down period. 

If you read carefully through the tests, you begin to see the Revision 6 seals must go through a more rigorous test with harsh low temperature, low pressure conditions. However, Revision 2 is not without its own challenges. The required hardware configuration; ie, low squeeze and more rough surface finish, is far from optimum and not what we recommend in actual service conditions. Added to the difficulty is the longer stroke length and faster speed. The fact that EM163-80 has passed both specifications proves it is the next generation EPDM seal material ready for flight.

For more information on this or other topics, visit Parker O-Ring & Engineered Seals Division online and chat with our experienced applications engineers or email us at oesmailbox@parker.com.  

This article was contributed by Dorothy Kern, applications engineering manager, Parker O-Ring & Engineered Seals Division.

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Electric vehicle battery covers pose unique sealing challenges in the automotive industry. The significant size of the sealing perimeter, the materials and size of the seal mating hardware, and the aggressive performance requirements (physical and chemical) all play a crucial role in the design of this critical seal. For fully electrified vehicles, battery seals run the full circumference of the vehicle. This large seal is imperative to the performance, life and functionality of the battery which can result in costly repairs and is the most expensive item to replace on an electric vehicle.

With these exacting obstacles in mind, many manufacturers are looking for options on how to seal this critical joint. Two common methods are extruded and spliced homogeneous rubber gaskets and dispensed form in place gaskets (FIP). Deciding which is best requires some evaluation of the pros and cons of each strategy.

Extruded gaskets have many benefits. Parker’s vehicle electrification experts can design and engineer a custom extruded cross section, providing the exact force needed to maintain a seal and keep closure force low with our innovative hollow profiles. Parker’s O-Ring & Engineered Seals Division offers extruded designs in a wide variety of materials to ensure that long term durability, sealing tests, and flammability requirements can be achieved. The extruded gasket sealing strategy often employs a cast or machined groove on the battery cover. If the design requirements do not permit a groove to be included, Parker has a variety of pressure sensitive adhesives (PSAs) that can hold the gasket in place.

Other benefits include:

• Custom design for your application
• Offered in a wide range of materials and temperature ranges
• Improved long-term material performance
• Application equipment not required
• Fully cured material for installation ease
• Instant seal upon compression
• Seals large gaps
• Flexible, accommodating some application movement
• Decrease downtime with improved serviceability over form in place gaskets

The one challenge with extruded seals is installation. As electric vehicle annual volumes continue to increase, it is important to be able to install the gaskets easily and quickly. For this reason, Parker has a variety of tools and methodologies to simplify and speed up installation.

Dispensable form in place gaskets are often used when design for manufacturing specs require a high level of automation. Parker has a range of non-conductive ParPhorm form-in-place (FIP) gasket technologies available.

When evaluating which technology to utilize, customers should recognize that FIP gaskets will require an investment in automation equipment to apply correctly at high volumes. This would include robotics and ample floor space. Additionally, the nature of FIPGs require higher cleanliness on the mating surfaces to ensure that the gasket adheres to the flange adequately. In application, some FIPGs have higher compression set characteristics that lead to less long-term durability of the flange that if not accounted for could lead to failure. Another factor when considering FIPG materials, is the in-line cure time that can be prohibitive depending on your production process. Finally, many battery manufacturers require that the gasket be easily serviceable so that mechanics can open and close the cover as needed over the life of the vehicle. FIPGs adhere to the cover in such a way that makes removing the gasket more difficult than an extruded or molded seal and could complicate the serviceability of the joint.

Sealing the electric vehicle battery perimeter is critical. Parker’s engineering experts are here to guide you through the decision-making process, customizing a sealing strategy that works best for your requirements. Whether you choose extruded, form-in-place or some other alternative, contact our engineering team today to help. Visit us online and chat directly with an engineer today.

This blog was written by Miles Turrell, electric vehicle applications engineer, Engineered Materials Group

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Dissolvable and degradable materials are used in oil and gas operations to create high pressures in hydraulically fractured wells, while also minimizing well intervention keeping wells flowing and preventing blockages. These materials are designed to withstand the high pressures and temperatures that are experienced during an application, and then gradually break down into tiny particles that do not need to be recovered. Because these materials naturally dissolve or degrade, operators are not required to run a wire line down the hole to drill them out — saving considerable time and reducing costs.

These innovative materials are gaining popularity in the oil and gas industry. As competition increases in the global energy market, producers seek technologies that will reduce costs and improve well efficiencies. It has been estimated that over the next two to three years, greater than 30 percent of well servicing and stimulation consumables will be dissolvable products (currently less than 10 percent).

Dissolvable metals and degradable elastomers replace the traditional composite products used in completion operations and can be customized to the application, including diameter, composition, strength, and rate of dissolution for common wellbore fluids. More operators are using aluminum-based materials because they are stronger than magnesium alloys, allowing much smaller overlaps (1.8 percent) in ball and seat applications. Thermoplastic elastomers have consistent high tensile strength and elongations for ambient and elevated temperatures, which provides customers with consistent performance over a wide range of temperatures. Parker’s degradable elastomers can be custom designed providing specific engineered shapes meeting the customer’s needs.

Advantages of dissolvables and degradables include:

• Reduced operating costs. Less well intervention is required (no need to drill out), which also reduces the risk of damage to the casing.
• Faster path to production of the well. Dissolvable materials can be formulated to allow for production to begin in as little as 48 hours after deployment, with no need to wait for a coil line crew.
• High product performance to improve the overall completion performance of the well. Degradable materials can be used for pressures exceeding 10Ksi and temperatures exceeding 200°F, providing ideal frac conditions.
• Highly engineered products that can be processed via multiple methods to produce desired shape. Parker provides multiple processing capabilities to produce products that can meet the specific needs of individual wells.
• Opportunity for dual material use for product performance. A wide range of material offerings allows for combined use—for example, elastomer and thermoplastic can be bonded to the aluminum or used in combination.

Dissolvable metals and degradable thermoplastics and elastomers must perform in harsh, corrosive down-hole environments in oil and gas wells. Parker’s dissolvable and degradable products are made with metal, thermoplastics, and thermosets (elastomers), providing operators with a wider range of material options. For example, Parker offers frac balls in delayed-reaction coatings such as Teflon, nickel, and epoxy. Our 94-Series provides a smooth C2-inhibitive coating with no cracks, rough spots, or nodules, which reduces corrosion and extends life cycle.

Because of our comprehensive range of material offerings, Parker can be an operator’s single provider of dissolvable products, allowing customers to reduce their vendor base. Parker also provides customers with inventory management options, further streamlining operations. Proprietary rate of dissolution (ROD) calculators are derived from broad-spectrum dissolution testing on our dissolvable metal products and are a handy tool for optimizing frac design and product selection for specific well conditions.  

Parker engineers work with oil and gas design teams around the world to customize dissolvable and degradable materials for specific applications. Our proprietary materials are compounded in-house; this also allows us to provide quick-turn delivery production orders and sample requests in a matter of days, including optical inspection to ensure tight tolerances, custom labeling, laser marking, and packaging services.

Parker’s dedicated oil and gas sealing experts, dedicated development labs, and processing equipment are at the forefront of emerging applications for dissolvable/degradable technologies in the energy field. For more information, or to discuss your project needs with a Parker engineer, visit us at OTC, booth #3639. Not attending? Visit our webpage to learn more about our high-performance sealing materials for oil and gas applications. 

Now, watch this video to find out more.

This article was contributed by Dana Severson, regional sales manager - oil & gas, Engineered Materials Group, Parker Hannifin.

Advanced Material Development for High-Pressure/High-Temperature Oil & Gas Extraction

Do Your Seals Meet the Demands of the Oil and Gas Industry?

Custom Designed Packing Elements for the Most Challenging Applications

My grandpa used to have a rusty, old air compressor in his shop. As a child, when my siblings and I would visit him, he’d use it to power air wrenches, grinders, and inflate flat soccer balls for us. I noticed it had a port labeled “ADD OIL DAILY” that was covered in the same thick layer of greasy dust as all the other unused junk in his shop. Knowing my grandpa, if asked about adding oil he probably would have said, “Oil is expensive. That’s how the companies get ya!”  The compressor’s seals leaked so badly, you could hear the hissing even over the loud motor. I was certain one day it would explode.

Pneumatic tools are common in factories, tool shops, and DIY garages around the world. Using compressed air for power is convenient, simple, and — when maintained properly — safe and efficient. However, air treatment costs can add up fast. Traditional rubber seals used in air tools require clean, low moisture, compressed air with the proper amount of lubrication added. Good Filter/Regulator/Lubricator systems (FRLs) cost as much as the tools themselves! So, what would happen if we didn’t have to provide pristine air?

Today we have the technology to create seals for tools which don’t require daily or even yearly upkeep. You’ll find these tools labeled “maintenance-free,” which sounds great to the guy responsible for maintenance. It sounds even better to the guy paying for maintenance … and to engineers designing tools who want to keep warranty costs down.

Early pressure seals were made out of leather. My grandpa’s compressor probably wasn’t that old, but even since his time, we’ve come a long way.

When I’m asked for seal recommendations in totally dry-running applications, my mind clicks to a material called PTFE (chemical name polytretrafluoroethylene). Most people know PTFE by the brand name Teflon®1 and are familiar with its use when applied to cookware as a high temperature, slippery, non-stick coating.

PTFE is a semi-hard plastic which feels slick to the touch thanks to its low friction properties. It’s considered self-lubricating because it leaves micro deposits on the sealing surface and reduces friction after just a few strokes. Because of this, it’s good for high-speed sealing and can operate completely dry.

By adding fillers to PTFE, seal manufacturers can tailor materials for greater suitability in meeting performance requirements for a wide range of conditions. String-like additives including fiberglass and carbon fiber increase pressure rating, wear resistance and seal life. Dry lubricant-type additives such as graphite or molybdenum disulfide (MoS2) further increase a seal’s ability to run without lubrication, and at higher speeds and pressures. In pneumatic medical, pharmaceutical, and food processing systems, clean grade mineral-based strengtheners may be used as additives.

PTFE seals for dry running equipment are available in several profile configurations:

• Uni-directional spring-loaded PFTE lip profiles which are good for both linear and slow rotary applications (See Parker's FlexiSeal® Profiles in Catalog EPS5340)
• Dual-acting, O-ring energized "cap" seals for easy installation in linear stroking applications (See Parker's offering in our linear sealing Catalog EPS5370)
• Wear bands which support moving components and prevent contact during shock loading can be made from PTFE for light- and medium-duty systems

For more difficult dry-running applications, tougher engineered plastics such as Nylon, polyester, UHMW-PE, and PEEK are used.

Where cost is the over-riding factor, internally-lubricated rubber elastomer materials are recommended in common, standard profiles:

• For slow speed, lower pressure, completely dry-running applications, a thin, light load lip geometry like Parker's 8400 Profile can accommodate cost, low friction, and low break-away force requirements
• Parker's Standard PolyPak® (SPP) Profile seal tightly at low pressure, and also work great as heavy-duty rod wipers

These common profiles are available in internally-lubricated XNBR (a tougher variant of NBR), which is my go-to rubber for low- and no-lube applications. 

An air compressor was one of the first power tools I bought. I knew little about seals back then and just needed something to top off the air pressure in my car tires and power a nail gun. I purchased one advertised as maintenance-free because I am, after all, my grandfather’s offspring. Oil costs money.

Even though dry systems don’t benefit from the protective aide afforded by lubrication, the same set of “good seal design principles” apply whether the system is fully hydraulic, lightly lubricated, or completely dry. Let’s take a look at a few seal design concepts and elaborate on how a lack of lubrication affects them.

The sliding movement of seals generates heat through friction. Rub your hands together and they get warm. Rub them faster or press together harder, and they get hot quicker. Excessive heat is the enemy of seals; they begin to soften and wear out faster. We counteract this by using tougher materials which can handle the temperature. Alternatively, we can design methods to cool the system.

Pneumatic systems are unique in that they either pull air from outside (compressors) or vent to atmosphere (tools and cylinders). Expanding gas has a small cooling effect on the latter.

Compressing gas generates heat, so compressors are a good example of a worst-case scenario. In addition, they operate at high speed and pressure. The housing of my compressor is covered with fins to help dissipate heat during long run cycles. Seal materials like PTFE, PEEK, and FKM (energizers) are often used because they can handle hot temperatures.

Our catalog recommends a maximum surface roughness of 12 µin Ra for linear and rotary applications. PTFE will benefit from a smoother surface, creating a tighter seal and reducing wear. Applications where leakage is critical, like in cryogenics or when sealing explosive gases, a highly polished finish of 4-6 µin Ra is best.

A minimum hardness of 25 Rc is recommended for linear and rotary applications. Softer materials can be used in light duty applications, but the surface may wear or become grooved over time, especially in rotary applications.

Some PTFE fillers are abrasive. While tough fillers like fiberglass and carbon fiber provide superior wear resistance, we recommend a minimum surface hardness of 60 Rc to prevent abrasion of the hardware. Mild fillers such as graphite, bronze, and aramid fiber are okay with the minimum requirement of 25 Rc.

Dirty air is a problem in all pneumatic systems. If the system is exposed to contaminated air, or to a dirty environment, abrasive particles can accelerate wear of both the hardware and the seals. Using wear resistant materials (like fiberglass-filled PTFE) along with a hardened sealing surface will prolong the life of the equipment.

Seal geometry also plays a role here. Sharp-lipped profiles like our FBD-V FlexiSeal and PolyPak (SPP & DPP) prevent junk from building up under the seal lip and wearing it away. Filling the spring cavities of FlexiSeals with silicone is an option to make the seals easier to clean when used in extremely dirty environments that require equipment washdown.

Air and non-reactive gases like nitrogen are compatible with all seal materials (so long as they’re used within the material’s temperature capability range). Caustic gases like pure oxygen, chlorine, and hydrogen sulfide (H2S) will degrade many seal materials. PTFE is highly resistant to most forms of chemical attack and is a good choice when compatibility is a concern.

PTFE has one weakness and that’s water. The material is extremely hydrophobic. The protective layer that naturally deposits itself on the hardware gets washed away in wet environments. As a result, seals wear quickly. Carbon fiber-filled PTFE and UHMW-PE plastic are recommended in potentially wet applications.

Having helped design dozens of compressors, the geeky engineer side of me is waiting for the compressor I have at home to break so I can look at the seals. It is entirely possible, however, it will keep working for me for tens of years without failing and just maybe, will someday inspire a blog post from my grandkids.

As technology improves, customers are looking for tools which last longer and cost less to operate. At Parker, we are constantly working and testing to provide tougher seal materials and new designs to aid you in making better products. Take a look at our catalogs and reach out to us if you have questions. Thanks for reading!

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.

1Teflon is a registered trademark of DuPont.

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

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Galvanic corrosion (also known as bimetallic corrosion or dissimilar metal corrosion) is the breakdown of metallic surfaces as a result of the difference in electrical potential of adjacent metals and the presence of an electrolyte.

Stated differently, when two dissimilar metals are in contact in a corrosive environment, one of the metals will begin to corrode. This process is the same one that occurs inside of a battery. The metal that will be corroded and the speed of this breakdown are dependent on the difference in metals and the environment.

For galvanic corrosion to occur, three conditions must be met:

1. Difference in electrical potentials of the two metals in contact with one another

All metals have an electrical potential assigned to them, based on their nobility. Metals such as platinum, silver, and monel have lower corrosion potentials whereas metals such as copper, aluminum, and tin have much higher potentials. Any two dissimilar metals will have a galvanic mismatch and therefore a change of corrosion.

1. Electrical path between the two metals

In situations of EMI shielding, the electrical path is inherently created by the conductivity of the gasket, coating, or sealant.

1. A fluid able to break down the metals

Examples of such fluids can include atmospheric humidity or salt fog environments. As this mist or moisture condenses and collects at the flange or gasket interface, it will create the electrolyte needed to start breaking down the metals.

For aluminum substrates that are going to be exposed to harsh environments such as military and industrial applications, chromate conversion coatings (also known as chem filming) are recommended. On top of this coating would be a conductive or non-conductive top coat. For steels and coppers, nickel or tin plating is often used.

Corrosion-resistant conductive coatings, such as CHO-SHIELD 2000 series conductive paints, are developed with stabilizers to create a very conductive and galvanically inactive surface for high-level EMI shielding in harsh environments.

Because EMI shielding gaskets are in direct contact with structural metal substrates, the corrosion potential must be considered. Historically, conductive fillers have needed to adapt to increasing requirements of galvanic corrosion resistance. Only within the last couple of decades have filler systems such as silver-plated aluminum replaced traditional silver-plated copper or nickel-plated graphite, to dramatically improve corrosion resistance in enclosures that experience moisture and salt fog.

Despite the excellent performance of silver-plated aluminum fillers, the development of a nickel-plated aluminum filler has set the gold standard for both EMI shielding levels as well as corrosion resistance. This filler system, utilizing inherently stable compounds, exhibits the best results on chem filmed aluminum flanges relative to any other filler system, with a 20-50% reduction even compared to silver-plated aluminum.

A properly designed interface requires a moisture-sealing gasket whose thickness, shape and compression-deflection characteristics allow it to fill all gaps caused by uneven flanges, surface irregularities, bowing between fasteners and tolerance buildups. If the gasket is designed and applied correctly, it will exclude moisture and inhibit corrosion on the flange faces and inside the package.

Follow the below steps to maximize corrosion resistance in enclosures:

1. Where other requirements are met, select nickel-aluminum filled elastomers for best overall sealing and corrosion protection.

2. Use silver-aluminum gaskets as the next best alternative to nickel-aluminum filled materials.

3. In aircraft applications, a “seal-to-seal” design can be used with the same gasket material applied to both flange surfaces.

4. Use a Co-extruded or Co-molded gasket – extruded or molded in parallel, these gaskets consist of a conductive and non-conductive elastomer in one piece. The non-conductive material is placed outboard to interface with the moisture, effectively minimizing a key condition causing galvanic corrosion.

5. Coat surfaces with a corrosion resistant plating.

6. Avoid designs that create areas for moisture to pool. Use drainage holes to allow liquids to flow away from the interface.

7. Avoid sharp edges or protrusions such as dovetail grooves that can damage gaskets.

8. Select the proper protective coating and use additional environmental sealants.
    

In order to conduct direct comparative shielding effectiveness testing of gasket panel sets before and after environmental exposure cycling in a standardized test set-up, Parker Chomerics established CHO-TP09. This test method is based on IEEE-STD-299 and takes into account environmental aging conditions such as salt fog, humidity, and extreme temperature cycling.

Proper enclosure design and the implementation of conductive filler systems engineered to minimize galvanic corrosion are key drivers in extending the life span of electronic enclosures and lowering long term maintenance/replacement costs.

Article contributed by Ben Nudelman, market development engineer, Parker Chomerics Division.

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EMI shielding gaskets such as conductive elastomer gaskets come in many different materials and almost a limitless number of shapes and sizes.

They are most commonly made of a base material of silicone or fluorosilicone with added conductive fillers such as silver, silver-plated aluminum, nickel-plated graphite, and others. Conductive elastomers represent one of the most versatile products in the category of EMI shielding gaskets.

From a manufacturing perspective, there are two key processes used to create these gaskets: splicing and molding. Check out the detailed list below for information about choosing the process that makes the most sense for you.

Conductive elastomer gaskets are often extruded in long strips, available in bulk or cut to specific lengths. To create custom sized O-rings, the extrusions are cut to the proper length and the ends are adhered (fused) together. Known as splicing, this process utilizes a proprietary adhesive to create an immensely strong bond.

• Bulk material relatively easy to extrude in long lengths, splicing is a process that can allow for quicker turnaround.
• Hundreds of standard extrusion profiles made to match almost any current design requirements.
• When O-ring sizes or design requirements change, splicing can accommodate these changes usually without significant lead time or cost.
• Requires very little or no tooling, meaning low upfront capital investment.
• Can be used with hollow cross-section profiles, creating parts that can accommodate low compression force enclosures.

• Limited in their complexity to singular “loops”.
• Will not retain their shapes like molded O-rings.
• Will not hold to tight tolerances that are common in molded parts.
• There is a limit to how small, in length, gaskets can be spliced.

Molding involves compressing uncured conductive elastomer material into a specially designed mold. The material takes the shape of the mold and retains this shape when cured.

• Allows for a great deal of complexity in parts which can include multiple joints and variability in cross sections across a single part.
• Hold tolerances to within a few thousandths of an inch.
• Will retain the shape in which they were molded.
• In high volumes, molded gaskets can cost less than spliced gaskets as the manual labor is minimized and the process is optimized.
• Can be made in very small o-rings and parts.

• Unless molded gaskets match industry standard gaskets that are commonly available, each new gasket will require a new mold.
• Not compatible with hollow gaskets – molded gaskets cannot have hollow cross sections like spliced extrusions.
• Very large diameters, in length, are not economical.

Between molding and splicing, there is virtually an endless number of profiles and shapes that can be developed. For more information on choosing and designing an EMI shielding gasket, check out the Conductive Elastomer Handbook below.

This blog post was contributed by Ben Nudelman, market development engineer, and Scott Casper, applications engineer, Chomerics Division.

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