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The Elastomerics Blog by Stockwell Elastomerics

Thursday, February 12, 2015

Remembering “Mr. S.” – Elbridge Stockwell Jr.

In 2003 I started working at Stockwell Rubber Company, 4th generation US manufacturer located in Northeast Philadelphia.  Part of my training was to sit with Elbridge Stockwell (3rd generation President) and pick his brain.  The reason was very apparent; Mr. S. as he was affectionately known throughout the company was a treasure chest of knowledge.  At a company where the pace is very fast, the time spent was a nice deviation… Mr. S. would patiently answer my questions and offer detailed explanations followed by pages of notes with even finer details.  When I worked with Mr. S. he was in his later years, I’m sure slower than he was in his younger years, but what was still clear and present was his passion for the industry, company and people.

Stockwell Rubber Company was a smaller organization in the 1970s and 1980s… I recently learned that Mr. S. mortgaged his home to purchase a larger facility to help grow the company.   It struck a cord with me; in business there is always risk, however very few people would be willing to put their skin in the game as Elbridge did… for this we thank you Mr. S, you literally set the foundation for us!

Signed Steve and the Stockwell Elastomerics family


posted by Steve Hughes at 1:07 PM comments

Wednesday, February 11, 2015

Part 2: Custom EMI Gaskets - Particle Filled, Conductive Rubber

Environmental EMI Gaskets
EMI - Environmental Gaskets
This is part 2 (ref part 1) of a two part blog series about EMI / RFI gaskets offered by Stockwell Elastomerics.  Most EMI gaskets manufactured by Stockwell serve several functions; the first is to shield EMI emissions, the second is to protect a device from being interfered with by external emission (often referred to as susceptibility).  Lastly, Stockwell EMI gaskets also perform the dual function of environmental sealing, protecting electronics from water damage from splashing, washing or rain.

How is silicone rubber conductive?
The short answer is - it’s not. Silicone rubber, the polymer of choice for most conductive rubber products, is not inherently conductive however the raw compound can be densely mixed with very fine conductive particles. Since they are so densely mixed, the powder-like particles create an electrical path through the rubber. The silicone rubber still maintains its elastomeric properties allowing it to be compressed. There is some trade off with tensile strength due to the fill, but this is typically not a concern since EMI gaskets are used in a compressed state.

How are particle filled EMI gaskets made?
Stockwell Elastomerics manufactures conductive filled EMI gaskets by either compression molding the gasket directly or by cutting parts from pre-manufactured sheets.

  • Molding EMI gaskets – best selected for volumes justifying a mold investment.  Very often the payback is quick if there is material saving over die cut parts.  Molding EMI gaskets allows for 3D features such as sealing beads that can reduce the clamp pressure needed to make a seal.  In general, conductive adhesive backings are not available (with some exceptions).
  • Waterjet cut or die cut EMI gaskets – cutting pre-formed sheets or rolls of material allows Stockwell to quickly manufacture custom EMI gaskets.  EMI gasket sheets are readily available with or without 3M conductive PSA backings.  Waterjet cut EMI gaskets are often preferred for optimizing yield and responsive manufacturing.
EMI Gasket Materials
Stockwell Elastomerics offers several EMI gasket materials, most often the delineation is between commercial applications and military applications. Some military applications require material to meet MIL-DTL-83528, this specification concisely defines the base polymer (silicone or fluorosilicone) and the specific conductive fill, silver coated aluminum is the most common.

Commercial and military applications not requiring MIL-DTL-83528 often use nickel coated graphite particles as the conductive fill. Nickel graphite is significantly lower cost than silver/aluminum with very good shielding properties.

Below are Stockwell Elastomerics materials commonly specified for EMI application.

Custom EMI Gasket Manufacturer
Stockwell Elastomerics is a U.S.A. EMI gasket manufacturer supplying custom EMI gaskets globally to OEMs. With a core competence in silicone and a responsive manufacturing model; Stockwell Elastomerics offers many material and processing options to meet most EMI gasketing requirements.

For more information regarding the above products or other EMI gaskets offered by Stockwell Elastomerics, please call 1-800-523-0123 or email service@stockwell.com.

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posted by Steve Hughes at 4:46 PM comments

Monday, January 12, 2015

Part 1: Custom EMI Gaskets – Combination EMI Gasket, Sponge & Wire Mesh

This is part 1 of a two part blog series about EMI / RFI gaskets offered by Stockwell Elastomerics and to help give a better understanding of options available to engineers tasked with EMI gasket design.

Most EMI gaskets manufactured by Stockwell Elastomerics serve several functions; the first is to shield EMI emissions, the second is to protect a device from being interfered with by external emission (often referred to as susceptibility).  Lastly, Stockwell EMI gaskets also serve as an environmental seal, protecting electronics from water damage from splashing, washing or rain.

What is an EMI Combination Gasket?
Combination EMI GasketsCombination EMI gaskets combine a traditional closed cell sponge gasket with a knitted wire mesh cord.  The gasket material most often specified is silicone sponge because of its long life, weather resistance, and functional temperature range.  The knitted wire mesh cord is most often made from Monel, a metal alloy that has very good corrosion resistance.  Additionally the wire mesh is bonded to the “dry” edge of the gasket, which means it’s protected from water and fluids, this greatly minimizes corrosion.

There are variations on these material options when specific properties are needed; as an example Stockwell Elastomerics offers fluorosilicone sponge that has better chemical/fuel resistance over un-fluorinated silicone.  Fluorosilicone is often specified for aerospace applications where fuel exposure is a concern.

Why use a Combination EMI gasket over a filled EMI gasket?
Combination EMI vs. filled EMI gasket is a common question – while they are both used to manage EMI their physical characteristics are very different.  Combination EMI gaskets are often thick (0.125” & 0.25”) as compared to a particle filled EMI gasket, they are also softer.  This thicker / softer combination allows for lower clamp force and wider tolerances between sealing faces.  This is advantageous for large EMI gaskets and enclosures made of sheet metal.  Combination EMI gaskets are often used for NEMA enclosures with added EMI attenuation.

Particle filled silicones and fluorosilicones are the most common “filled EMI” gasket materials.  These are very good for EMI attenuation and sealing water, capable of sealing to IP66 and IP67.  Filled materials tend to be harder and thinner; this requires a more rigorous bolt pattern and tighter tolerance sealing faces.

• Click for more about Combination EMI Gaskets
• Click for more about Filled EMI Gaskets

Stockwell EMI Gaskets
Stockwell Elastomerics manufactures both, combination and filled EMI / RFI gaskets, their Applications Engineers can assist in selecting which type is the best fit for your design.  Stockwell Elastomerics manufactures their EMI gaskets in the USA at their Philadelphia, PA location and ship globally to OEMs and contract manufacturers.

For more information regarding the above products or other EMI gaskets offered by Stockwell Elastomerics, please call 1-800-523-0123 or email service@stockwell.com.

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posted by Steve Hughes at 1:05 PM comments

Tuesday, December 02, 2014

St. Gobain NORSEAL® Silicone Sponge Sheet and NORSEAL® Silicone Sponge Tapes


Just announced, St. Gobain Performance Plastics – Foams and Tapes division, will be consolidating their product brands.  Stockwell Elastomerics has been a longtime partner of St. Gobain’s, maintaining inventory and fabricate components from their high performance materials; most notably the closed cell silicone sponge products and Strip-N-Stick™ silicone sponge tape, currently living under the brand name COHRlastic®.  COHRlastic silicone sponge products will become NORSEAL silicone sponge and Strip-N-Stick™ will become NORSEAL® silicone sponge tape.  While the legacy names will be phased out the part numbers will remain.



St. Gobain silicone sponge product numbers offered by Stockwell Elastomerics
- R-10480S – Soft Closed Cell Silicone Sponge, Low Compression Set
- R-10480M – Medium Closed Cell Silicone Sponge, Low Compression Set
- R-10470M – Medium Closed Cell Silicone Sponge, Specification Grade
- R-10470F – Firm Closed Cell Silicone Sponge, Specification Grade
- R-10460M – Medium Closed Cell Silicone Sponge, UL94 HBF
- R-10400M – Medium Closed Cell Silicone Sponge, UL94 V0
- R-10404 – Medium Closed Cell Silicone Sponge, Thermally Conductive
- R-10490 – Medium Closed Cell Fluorosilicone Sponge
- R-10450 – Medium Closed Cell Silicone Sponge, Reinforced

St. Gobain silicone sponge tape product numbers offered by Stockwell Elastomerics
- SNS-100S – Medium Closed Cell Silicone Sponge Tape, Silicone PSA
- SNS-200A – Medium Closed Cell Silicone Sponge Tape, Acrylic PSA
- SNS-300AR – Medium Closed Cell Silicone Sponge Tape, Reinforced

This transition in branding is still in progress so please check back for updates.  For more information about custom silicone gaskets and cushioning pads fabricated from St. Gobain COHRlastic materials… transitioning to NORSEAL silicone materials, please contact Stockwell Elastomerics at 1-800-523-123 or email service@stockwell.com.

NORSEAL® , COHRlastic® &  Strip-N-Stick™ are registered trademarks of St Gobain Performance Plastics

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posted by Steve Hughes at 8:25 AM comments

Tuesday, November 18, 2014

New EMI Shielding Gasket Materials Webpage

Stockwell Elastomerics has expanded the webpage and datasheets for EMI gasket materials.  With a core competence in silicone elastomers, Stockwell Elastomerics offers a variety of silicone based EMI materials to help attenuate electronic emissions and seal out environmental conditions.  Below are brief summaries about EMI / environmental gasket materials offered by Stockwell Elastomerics.


Nickel Graphite Filled Silicone or Fluorosilicone - are the most commonly specified products for their very good attenuation and relatively low cost.  Products such as SNE-553 and SNE-540 also offer environmental sealing; they are capable of meeting IP65, IP66, and IP67, when properly compressed.  Nickel plated graphite filled sheets are available in .010” - .125”, parts can also be compression molded by Stockwell Elastomerics.




Silver Aluminum Filled Silicone or Fluorosilicone – are most often specified when lower volume resistivity is needed or MIL-DTL-83528 specified materials are required.  Silver plated aluminum filled EMI shielding gaskets are typically manufactured in .010 - .062” sheets or compression molded.



Knitted Monel Wire Mesh / Closed Cell Spongealso called combination EMI gaskets, are most often specified for large EMI gaskets with low clamping force.  Silicone foam, silicone sponge and fluorosilicone sponge materials can be used in conjunction with knitted Monel mesh. These custom EMI gaskets are typically manufactured 0.125” or 0.25” thick.




Stockwell Elastomerics is a U.S. EMI gasket manufacturer offering several methods to deliver custom EMI components, including 3D molded EMI parts, die cut EMI gaskets and rapid waterjet cut EMI gaskets. Stockwell Elastomerics also offers 3M conductive peel and stick adhesive backings for flat cut EMI gaskets and select molded EMI gaskets.

For more information about custom EMI shielding gaskets manufactured by Stockwell Elastomerics, please call 1-800-523-0123 or email service@stockwell.com.

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posted by Steve Hughes at 2:31 PM comments

Wednesday, October 22, 2014

Insulation for Silicone Rubber Heaters and Flexible Heaters

silicone foam insulation
Silicone Rubber Heater Insulation Materials

Stockwell Elastomerics supplies silicone sheet materials and custom silicone parts to commercial and industrial markets.  While Stockwell Elastomerics does not supply uncured or semi-cured silicone sheets for the construction of flexible heater, silicone foam and silicone sponge sheets are sold as insulation backers to the flexible heater / silicone rubber heater markets.  These high temperature foam backings help improve heater efficiency by reducing heat loss. Heater foam insulation from Stockwell Elastomerics may be permanently bonded with silicone RTV or tacked in place with DP-1001 peel and stick backing.

Silicone Foam Sheet Insulation - has an operating temperature of 200°C (392°F) with intermittent exposures to 250°C (482°F).

     Open cell silicone foam (BF-1000) - very good insulation and has a UL 94V-0 flame rating.
     Thermal conductivity = 0.06 W/m-K.

     Closed cell silicone foam (HT-800) - good insulation, UL 94V-0 flame rating and water resistance.
     Thermal conductivity = 0.09 W/m-K.

Silicone Sponge Sheet Insulation – has an operating temperature of 260°C (500°F)
     High temperature closed cell silicone sponge offers higher temperature resistance, good
     insulation and is tougher than the foams.  Closed cell sponges are available with
     UL 94HB and UL 94V-0 flame ratings.
     Typical thermal conductivity = 0.11 W/m-K.

Silicone sheet insulation is available in a wide range of thickness and sizes.  Stockwell Elastomerics offers heater insulation materials in sheets or rolls 36” wide; custom cut insulation pads are also available. Additionally, Stockwell Elastomerics offers silicone sheet materials with or without adhesive backing. High temperature silicone adhesive or moderate temperature acrylic adhesive backings are available too.

For more information about silicone insulation sheets for silicone rubber heaters and flexible circuits, please contact Stockwell Elastomerics at service@stockwell.com or 1-800-523-0123.

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posted by Steve Hughes at 11:27 AM comments

Friday, October 03, 2014

Custom Foam Port Plugs for Environmental Test Chambers

Stockwell Elastomerics is custom gasket manufacturer with a core competence in silicone materials. Typically the gaskets and rubber components made by Stockwell Elastomerics are used to protect electronics from the environment. Conversely, Stockwell Elastomerics Port Plugs are used to keep the environment inside the enclosure.
Custom Port Plugs
Custom Silicone Foam Port Plugs

Environmental testing chamber plugs are used for testing high temperature, sub-freezing temperature and humidity. Port Plugs from Stockwell Elastomerics can be made to standard sizes for 2”, 3”, 4”, 6” round ports; as a rapid response supplier, Stockwell Elastomerics can quickly waterjet cut custom geometries with minimal additional cost.

Stockwell Elastomerics Port Plugs


The pictures illustrate the advantage of a concentric plug, having foam on either side of the cable allows the foam to conform more tightly. Large rectangular blocks and port plugs with custom cutouts are easily produced with minimal additional charge.






Lower cost single layer plugs - in a previous post it was mentioned that the black layered plugs cost less with a shorter lead time, recent events have shifted this. Now the single layer with the grey closed cell silicone foam top layer offers better cost savings.

Stockwell Elastomerics manufactures custom gaskets for a wide variety of industries needing to meet rugged environmental conditions, from high heat, freezing, high humidity. Many OEM customers who buy silicone gaskets also buy custom port plugs for their test chambers.

For more information about Stockwell Elastomerics Port Plugs, custom port plugs or custom silicone gaskets, please call 1-800-523-0123 or email service@stockwell.com.

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posted by Steve Hughes at 3:58 PM comments