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The Elastomerics Blog by Stockwell Elastomerics

Monday, August 08, 2016

Turnout Gear Foam Padding

Stockwell Elastomerics holds inventory of high temperature, flame retardant silicone foam used by turnout gear manufacturers for padding and cushioning. Turnout gear foam padding is sold in sheets or pre-cut shapes. Custom cutting silicone foam and closed cell silicone sponge can be done without investing in tooling; Stockwell Elastomerics offers tool-less flash cutter (CNC oscillating knife) and waterjet cutting requiring no tooling and fast cut pads.

HT-800 and HT-820 flame rated silicone foam are high temperature foams that resist burning, they are UL 94V-0 (vertical burn test) rated. HT-800 medium firmness silicone foam is highlighted in the video below. HT-800 exhibits surface cracking but does not burn through nor catch fire. There are silicone foam options in the HT-800 family.

FPC flame block material is a heavily filled flame blocking silicone rubber with a reinforced backing. FPC silicone fire block was specifically design to resist burn through. FPC flame block is often used for industrial applications to protect components during a fire. The reinforced layer allows stitching of FPC.

R-10400 closed cell silicone sponge is a slightly tougher and higher temperature silicone that has similar burn resistance as HT-800 and HT-820 foams. R-10400 flame rated silicone rubber is also available in sheets or custom cut parts.

Another benefit of silicone foam and silicone rubber materials is their ability to remain flexible at sub-zero temperatures - this means the turnout gear pads offer cushioning even in extreme cold weather.

For more information on turnout gear pad material and other flame retardant silicone foams, please contact Stockwell Elastomerics at 1-800-523-0123 or email More information about Stockwell Elastomerics' products and services can be found at

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posted by Steve Hughes at 1:44 PM comments

Friday, July 22, 2016

Thermal Gap Filler - Heat Transfer Video

The video below illustrates how thermal gap filler pads work. In this video TC-3008 is applied to the bottom of a beaker to minimize the air pockets and make better contact with the heat plate. Below are several points to take notice of in the video.


Variety of hardnesses and conductivity (0:06 sec) – from left to right, St. Gobian TC-2006 (violet), TC-3006 (green), TC-3008 and Bergquist Gap Pad Ultra Soft V0 (blue, white, mauve), more options available

Soft gap filler pads (0:09 sec) – gap filler are usually measured on the Shore00 scale since they are very soft, they are easily squeezed by finger

Permanent deformation (0:11 sec) – thermal gap filler pads have a dough or gum like composition, they generally do not rebound fully after being compressed

Toughness (0:012 sec) – since gap filler are heavy loaded with conductive particles they can tear easily if handled roughly. This is not typically an issue due to how these material are used.

Thermal pad was cut to size (0:19 sec) – parts can be cut into basic or complex geometries

Release liners (0:25 sec) – gap filler pads are supplied with lines since they are tacky

Fast install and no greasy mess (0:28 sec) – pre-cut, tacky gap fillers, install quickly without messy grease or paste

Tacky gap filler (0:34 sec) – generally there is no adhesive applied to gap filler but they are tacky enough to stick in place as shown being stuck to the bottom of the beaker

High temperature (0:44 sec) – thermal gap filler pads have a typical operating temperature of 200°C (392°F)

Heat transfer (0:47 sec) – the video illustrates the enhanced heat transfer to the beaker which brings the beaker with the thermal gap filler to a boiler faster. Note: this is not an intended use of these gap filler pads.

Why thermal gap filler from Stockwell Elastomerics (0:57 sec) - Less air entrapment, more surface contact, better heat transfer

For help selecting a Gap Pad, thermal gap filler, or thermal interface material (TIM), please contact Stockwell Elastomerics at 1-800-523-0123 or email

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posted by Steve Hughes at 4:31 PM comments

Monday, July 18, 2016

Preformed Silicone O-rings Are Better

This Stockwell Elastomerics video highlights the benefits of using a preformed o-ring. The video shows our operator installing a standard o-ring cord into a complex gland design, contrasted with a preformed silicone o-ring specifically made for the gland.

Time savings – the video shows the significant time savings gained by using a preformed gasket. When extrapolated over hundreds or thousands of gaskets, there can be quite a cost savings due to faster throughput. Other project cost considerations that factor in are manufacturing capacity and opportunity, contributing to a quick payoff on buying a custom o-ring mold.

pre-formed silicone o-ring
Risk Prevention - There is a much lower risk of twisting or pinching a preformed o-ring gasket. Forcing a standard o-ring cord into a complex gland lends itself to these installation errors; twisted o-rings and pinched o-rings are well known failure modes. The video shows how the pre-formed silicone o-ring drops right into the complex gland.

Silicone durometersSilicone rubber is excellent for environmental sealing and it is available in durometer values ranging from 10 – 70 Shore "A". The low durometers, 10 and 20 are better for larger cross-sections since they can be stretched very easily during installation. Soft silicone o-rings enhance sealing at a lower closure force. Soft silicone o-rings are often used for IP 67 submerged gaskets.

Custom silicone o-rings – Stockwell Elastomerics manufactures custom silicone o-rings. Custom o-rings are available in standard silicone durometers (10 – 70 Shore A), electrically conductive o-rings or EMI o-rings and fluorinated silicone o-rings. Stockwell Elastomerics does not inventory or provide off the shelf o-rings.

Stockwell Elastomerics O-ring Offerings

For more information on custom preformed silicone o-rings, EMI o-rings, or preformed fluorosilicone o-rings, please call 1-800-523-0123 or email

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posted by Steve Hughes at 10:09 AM comments

Thursday, July 14, 2016

What is expanded rubber, closed cell rubber?

Silicone, neoprene, EPDM and other polymers can be made in solid form (e.g. tires and tubing), but they can also be expanded with a blowing agent. A good analogy is bread - flat bread is unleavened (no yeast) which would represent solid rubber, adding yeast expands the dough adding pockets of air, this would represent expanded rubber.  Adjusting the amount of expansion effectively adjusts the material density and level of firmness. Expanded rubber is usually referred to as sponge rubber or foam rubber.

Sponge or Foam?
silicone foam
Expanded Silicone, Neoprene and Urethane (PORON)
There is some debate on which term to use and they are often interchanged. Stockwell Elastomerics refers to sponges as product being made from gum base and foams from liquid bases.  Example: Silicone sponge would be made from High Consistency Rubber (HCR) which somewhat resembles potters clay in raw form. Foams on the other hand are made from Part “A” and Part “B” liquids that are then cast; some foams are also made via mechanical frothing.  Note: there are differences between cast foams and expanded sponge.  Stockwell Elastomerics' Application engineers are available to help select a material suited for your project.

Why Use Expanded Rubber?
One of the main benefits of expanded rubber is its softness - a very soft solid rubber would be a 10 durometer on the Shore A scale, foams and sponges are usually even softer. These soft rubber materials can be used to seal anything from car doors to hand-held electronics. Expanded silicone and other expanded polymers have a wide compression range - this means more tolerance is allowed between sealing faces. Also, since there is less actual material due to the air cells it generally costs less per unit volume.

Example: Large NEMA enclosures may have significant flatness tolerances between the door and enclosure; a soft closed cell sponge gasket can be used to take up the variation without putting too much stress on the door (0.5" thick gasket compressed 50% = 0.25" gap filling).

Hardness of Expanded Rubber
Hardness of expanded rubber isn’t typically measured on a durometer scale the way solid rubber materials are, they are measured per ASTM D1056 which compresses a 1in² disc 25% and reports a value. This is referred to as Compression Force Deflection (@25%) or CFD.  Most expanded rubber manufacturers report the CFD to allow side by side comparison of materials. Note: CFD is not to be confused with compression set (a materials inability to rebound, view more info on C-set).

Closed Cell Rubber
Typically when the cell structure is mentioned, it is referring to a foam or sponge as opposed to a solid rubber.  Expanded rubber can be either open cell or closed cell, it will depend on the specific product.  Expanded sponge rubber tends to be closed cell but there are products that are then crushed to make them ultra-soft.  The crushing process pops the closed cells, making them open. As mentioned above, Stockwell Elastomerics' Applications Engineers are available to help navigate material options.

Common expanded rubber materials offered by Stockwell Elastomerics:

For more information about expanded rubber products, soft gasket materials or applications engineer assistance, please contact Stockwell Elastomerics at 1-800-523-0123 or email

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posted by Steve Hughes at 9:43 AM comments

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