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The Elastomerics Blog by Stockwell Elastomerics

Wednesday, May 04, 2016

Highly Conductive Silicone Rubber - Reinforced Nickel Graphite Filled

SNE-540-R and SNE-556-R are 40 and 65 durometer (Shore "A"), respectively, and have low volume resistivity that challenges silver coated aluminum filled silicones at a fraction of the cost.

SNE-540-R and SNE-556-R have conductive fabric reinforcement that enhances the conductivity and tensile strength but still allows for Z-axis compression for EMI and environmental sealing. Traditional, particle filled silicone rubber materials have lower strength due to the heavy loading of conductive filler. This lower strength is often problematic for gaskets with thin walls that are susceptible to breaking or over stretching. The fabric reinforcement in SNE-540-R and SNE-556-R addresses these issues.

Additionally, SNE-540-R and SNE-556-R fabric reinforced EMI silicones are manufactured in continuous rolls (12" and 15" wide) which enable large EMI gaskets to be made in one piece. Standard thicknesses for SNE-540-R and SNE-556-R are .020" and .032", custom thicknesses are also available.

See the Highly Conductive Reinforced Nickel Graphite Filled Silicone section of the EMI Sheilding Materials page for more details, and view the SNE-540-R data sheet (PDF) and SNE-556-R data sheet (PDF) for additional technical information.

Benefits of SNE-556-R Reinforced EMI Gasket Material
* High conductivity EMI gasket
* Continuous EMI Sheet Roll
* Cost benefit from nickel graphite filled silicone
* Dimensional stability of cut EMI shielding gaskets
* Environmental sealing EMI Gasket
* Available with 3M conductive adhesive backing

Example 1: an EMI enclosure with many bolts, the reinforcement prevents the gasket from stretching during installation ensuring holes in the EMI gasket align well with the fastener holes in the enclosure.

Example 2: an EMI gasket with narrow walls, the reinforcement allows the part to be handled and installed without breaking (see above image).

Contact Stockwell Elastomerics for more information about SNE-540-R and SNE-556-R fabric reinforced EMI silicones and other EMI gasket solutions.  

Phone: 1-800-523-0123

Click to view additional EMI Materials information.

posted by Steve Hughes at 4:02 PM comments

Tuesday, April 12, 2016

ASTM C 1166 Flame Propagation Test on HT-800 Silicone Foam

Silicone Foam Burn
Continually committed to testing and validating their materials, Rogers Corporation recently had HT-800 silicone foam tested by a third party for flame propagation per ASTM C 1166. ASTM C 1166 is a vertical burn test that evaluates the flame propagation and reports the melting/burning behavior. A common test requirement for rail applications, the Federal Railroad Administration has a limit of 4” of flame propagation on an 18” test specimen.

ASTM C 1166 Test Results:
As expected, BISCO HT-800 silicone foam passed the 15 minute burn with flying colors:

• Thin (approx. 2mm):  average propagation of 1.7”, no melting or dripping
• Thick (approx. 13mm): average propagation of 1.3”, no melting or dripping

As we’ve known, HT-800 and the BISCO HT-800 family of silicone foams; BF-1000, HT-870, HT-800, HT-820 and HT-840 perform very well in burn tests. These Rogers Bisco silicone foams are all UL 94V-0 flame rated. In addition, we did a “solder torch test” on HT-800 (we’ll post a video in a later blog), HT-800 did not catch fire, drip or melt even with the more aggressive flame.

Stockwell Elastomerics is a Preferred Converter for Rogers Corporations Bisco silicone products and Poron urethane foam products. Stockwell Elastomerics maintains inventory of the vast majority of both the HT-800 family and Poron family of products.

For more information about custom cut gaskets, silicone foam gaskets or gaskets and pads made from Poron, please call 1-800-523-0123 or email

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posted by Steve Hughes at 2:02 PM comments

Tuesday, March 08, 2016

IP67 Test, Moto 360 Sport, Consumer Reports

GPS watch, water resistant to 50m
A recent Consumer Reports tested the Moto 360 Sport smartwatch for water resistance with the IP67 water test simulating a submersion up to 1 meter deep for 30 minutes. Unfortunately the watch did not pass the test. From a pressure standpoint, this test is relatively benign (1.42 psi or 0.1 bar) and arguably represents the bare minimum sealing for a sport and GPS watch.  As a point of reference my Suunto GPS watch is rated to 50 meters and 5 bar.  So what what was the root cause of the Moto 360 Sport's failure?  To understand this we'd need to know what gasket material was used, the tolerance stack ups, the amount of gasket compression, the installation or dispensing method or if a gasket was even part of the design.  Below are some common root causes of gasket design and IP67 failure modes.

  • Gasket Stress Relaxation - this is when the gasket relaxes and stops pushing back, letting external pressures push past the gasket.  Usually a result of improper gasket material selection for the specific application.
  • Tolerance stack - if the variation in the sealing faces and gasket are not fully accounted for leaving minimal compression on the gasket
  • Dispensing seam or flash - dispensed gaskets share a starting and ending point, it's possible to have a small "bump" or "divot" that may not have been accounted for in a tolerance analysis or closure force. Similarly, a molded gasket with flash can make a minute gap and allow ingress.
  • Closure force vs. rigidity - often in an attempt to compress a gasket the housing flexes creating an ingress point
  • O-ring roll - seen more often where an o-rings is installed into an non-matching gland, the gasket is worked into the gland and can be rolled or twisted
  • Thermal cycling - the heating an cooling of the devices on/off mode creates internal pressures or vacuums that can "suck" in water.  
The above are just a few, general causes we see with IP6X failures.  The root cause of the Moto 360 Sport could be due to one of the above or one of many others.  As Consumer Reports mentions, the other Moto 360 smartwatches passed the IP67 test and were rated very highly.  Hopefully Motorola will get to the root cause and possibly raise the sealing bar on the sport category of the rugged smartwatch industry.

For more information on IP67 gaskets, NEMA gasket, UL 50E gaskets or other custom enclosure gaskets and submerged gaskets, please contact Stockwell Elastomerics at 1-800-523-123 or via email to

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posted by Steve Hughes at 1:23 PM comments

Friday, February 26, 2016

Street light, leaving the lens open

The picture shown is of an induction street light in New Jersey with its lens cover open.  One could argue that this helps the unit run cooler, especially when wind blown rain enters the housing... of course this is absurd, the lens cover should be closed and sealed to protect the light from the elements.  As with all lighting capital expenditures there is an anticipated ROI, this is especially true with solid state lighting like LEDs or induction. The long life and low maintenance cost associated with new lighting technology is considerable contributor to realizing the return on investment.

White PaperSpecifying Gaskets for Outdoor LED Lighting Fixtures

Being a gasket nerd, I pay attention to gasket materials used on a wide range of products and what type of sealing is being done.  Time and time again I see housings with low cost or improper materials used; often these will pass initial testing but given time in the field they become useless or offer minimal protection against the outdoor elements.  I commonly see massive compression sets, peeling gaskets and dry rotted gaskets... these enclosures are barely protected from ingress, almost as much as the light shown in the picture with its cover open.

There is hope.  Stockwell Elastomerics works with many reputable lighting companies, some are house hold names and others that are smaller specialty manufactures.  These companies are committed to investing time and effort to ensuring they're housing is sealed properly.  They understand the small added cost of a quality gasket material is minuscule when compared to field repair or damage to the reputation of their brand.  The companies Stockwell works with are manufacturing quality lighting fixtures that will live up to the IP64, IP65, standards IP66 over the life of their product.

Stockwell Elastomerics maintains inventory of UL 50 and UL 94 gasket materials that are well suited for outdoor lighting applications.  For more information on how Stockwell Elastomerics can help with your lighting gasket design, please contact or call 1-800-523-0123.

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posted by Steve Hughes at 1:49 PM comments

Tuesday, February 16, 2016

Custom Gasket Design Tips

Gaskets are arguably the least sexy part of a mechanical design, equally arguable is that they are one of the most critical parts with in a design…especially in wet and outdoor applications.  One customer told me they had a million dollar recall due to a bad gasket design, they came to Stockwell Elastomerics to help resolve the design issue.  In this particular case, the geometry was fine but the material selection was incorrect.  Stockwell was able to work with the customer to develop a proper gasket that met their long term requirements.

With gasket designs all factors need to be considered early, these include: cost, regulations, life expectancy, environmental condition, and manufactuability.  I was recently working with a customer who was at the beginning of their design,  he had come across a Machine Design article that I had worked on a few years back, the article is still viable and helps give some focus when starting a custom gasket design.  Below is a link to the Machine Design article.  Please feel free to contact Stockwell Elastomerics to discuss your custom gasket application.

Summary of considerations for gasket design:
  •           Define Function
  •           Identify regulatory requirements
  •           Understand environmental conditions
  •           Material Selection
  •           Consider manufacturability
Machine Design Article:
Other useful Tech tips:
Stockwell Elastomerics is a custom gasket manufacturer with staff Applications Engineers available to help with your gasket design.  With onsite die cutting, molding, waterjet cutting, tool-less knife cutting and a very comprehensive inventory, Stockwell is able to offer the right manufacturing method and material for your custom gasket.
For more information, please contact Stockwell by phone at 1-800-523-0123 or email

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posted by Steve Hughes at 9:06 AM comments

Tuesday, January 12, 2016

UL Flame Rated Adhesive for Gaskets and Pads

Stockwell Elastomerics has added 3M 9375W to its pressure sensitive adhesive line up. Custom gaskets are made from materials that meet specific performance requirements; fluorosilicone is used for chemical and fuel resistance, silicone is used for its wide temperature range and UV resistance, Poron foam is used for its excellent rebound. Much like the gasket material, the pressure sensitive adhesive backing is selected based on performance. 3M 9375W was designed to meet various flame ratings, including UL 94, FAR 25.853, NFPA 1971 and FMVSS 302. Stockwell Elastomerics can laminate 3M 9375W to UL 94V-0 flame rated silicone foam, FAR rated silicone foam, or UL rated Poron foam. In addition to flame retardant 3M 9375W, Stockwell Elastomerics offers UL 746C rated adhesive covering a variety of bonding substrates.

3M 9735W Flame Retardant Adhesive Properties:
• UL 94
• FMVSS 302
• FAR 25.853
• Ultimate Bond to Stainless Steel: 160 oz/in
• Ultimate Bond to ABS: 86 oz/in
• Ultimate Bond to Polycarbonate: 87 oz/in
• Link to datasheet

Other performance adhesives:
3M 9485, wide temperature and strong bond
256M, general purpose, cost effective
F9473PC, VHB grade, good chemical resistance and strength
8311, repositionable for gasket placement
9472LE, adhesive for low surface energy materials
DP-1001, high temperature peel and stick adhesive
3M 9713, Electrically conductive adhesive for EMI gaskets
Listing of more gasket adhesive options

For more information about UL rated adhesives or 3M 9375W flame retardant adhesive please call 1-800-523-0123 or email

Stockwell Elastomerics is a custom gasket manufacturer with a core competence in silicone rubber and other high performance gasket materials. Stockwell Elastomerics is a Roger Corp. Preferred Converter carrying the Bisco Silicone and Poron Urethane products, a St. Gobain Preferred Converter and 3M Select Converter.

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posted by Steve Hughes at 2:42 PM comments

Friday, November 27, 2015

ASTM D6576 and Closed Cell Silicone Sponge

Military Specification Mil-R-6130C established requirements for cellular rubber used for sponge gaskets and cushioning pads in defense equipment in the 1980’s and 1990’s. Both closed cell (Type 2) and open cell (Type 1) sponges were covered in this specification. Grades A and B were typically met by neoprenes and Grades B and C were met by silicones. There were three (3) firmness conditions: Soft, Medium and Firm. Soft condition called out 2 to 7 psi Compression Force Deflection (CFD), Medium called out over 7 to 14 psi CFD and Firm specified over 14 to 21 CFD. CFD is basically defined as the amount of force needed to deflect one square inch of sponge by 25% per ASTM D1056.

In the 1990’s a committee was convened to develop the ASTM D6576 Standard for Flexible Cellular Rubber materials. ASTM D6576 was derived from ASTM D1056, which lists six (6) categories of sponge firmness. The intermediate firmness ranges are narrow and difficult to control in full production batches of closed cell sponge. A subset of the products covered by this standard are closed cell silicone sponge products. Apparently one of the leading producers of closed cell silicone sponge was not represented on the ASTM committee, and these six compression force deflection, or firmness ranges were published with the standard on April 10, 2000.

Many of us in the industry did not anticipate the cancellation of Mil-R-6130C by the US Department of Defense on March 19, 2001. Mil-R-6130C was replaced by ASTM D6576. Why is ASTM D6576 an issue? As one example, Mil-R-6130C condition soft formerly required 2 to 7 psi CFD; now ASTM D6576 condition soft requires a tighter 2 to 5 psi CFD. Producing and certifying to these tighter firmness ranges has been difficult for the silicone sponge manufacturers. Therefore, they frequently request an exception to this specific property.

Comparative Firmness Conditions

ASTM D6576
Deflection Categories

Deflection Categories

Stockwell Elastomerics
Silicone Sponge

CFD Values
CFD Values
St Gobain
CFD Values
Super Soft
0 to 2 psi
2 to 7 psi
2 to 7 psi
2 to 5 psi
5 to 9 psi
7 to 14 psi
6 to 14 psi
9 to 13 psi
6 to 14 psi
13 to 17 psi
14 to 21 psi
R10490 Fluorosilicone
9 to 18 psi
17 to 25 psi
12 to 20 psi

Design Considerations:

  • If ASTM D6576 is a requirement on your new silicone sponge gasket designs – your engineering team should confirm whether the narrow compression force deflection range of the ASTM D6576 standard is necessary. We can provide certifications for ASTM D6576 for silicone sponge materials taking an exception to the narrow compression force deflection range.
  • If ASTM D6576 is called out on a requisition for an existing gasket drawing requiring closed cell silicone sponge for a Government Prime contractor, and vendor certifications and / or test reports are needed, expect a waiver on the compression force deflection range.
  • If the gasket drawing is a legacy design and Mil-R-6130C is requested, let us know. Even though the specification is officially expired, with adequate lead time a material batch can be tested and qualified to meet this specification with a certificate of conformance.
  • Closed cell silicone sponge is produced like baking a cake. Instead of dough; a thin preform of catalyzed silicone gum is heated and allowed to expand. Controlling the density, thickness and compression force deflection of the cured silicone sponge may require more leeway than ASTM D6576 allows.

For more information and assistance with ASTM D6576 and closed cell silicone sponge, please call 1-800-523-0123 or email

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posted by Bill Stockwell at 2:37 PM comments