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The Elastomerics Blog by Stockwell Elastomerics

Thursday, June 14, 2018

Gasket Materials Testing - Weather, Sun, Age

Dan Shanahan, Marc Ebiri and Alex
Santayana with Weather Testing Board

Philadelphia Roof Top - Sun, Weather and Age Testing of Gasket Materials

Gaskets are frequently used in outdoor enclosures and potentially exposed to sunlight. So we wanted to run an experiment with side-by-side testing of a variety of materials including: SBR (styrene-butadiene rubber), neoprene (polychloroprene), EPDM (ethylene propylene di-monomer), ECH (epichlorohydrin), PORON® microcellular urethane foam, silicone foam, silicone sponge, solid silicone and fluorosilicone. 37 samples of various gasket materials mounted and tagged on a board that was placed on the roof of our facility.

We will be checking these during the summer for the effects of sunlight aging, which may show up as surface cracking, shrinking or discoloration. We also retained control samples of each material for comparison.

Our summer intern, Marc Ebiri, will be helping with the evaluation of the samples on the weather aging board, along with gasket immersion testing and other projects.

We think silicone rubber will outperform the other categories. Look for a follow-up blog post here after the experiment is finished.

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Thursday, May 24, 2018

Designing a Battery Pad for Li-Ion Pouch Cells

Stockwell Elastomerics has a long history of fabricating battery pads from microcellular polyurethane such as PORON® and silicone foams such as BISCO®. The Elastomerics Blog first touched on battery compartment pads in 2011, but since then, advancements in lithium-ion (Li-ion) battery technology make the topic of battery pads worth revisiting. Today's light and powerful lithium batteries have changed the way we live, and are used in everything from handheld electronics to, electric vehicles (EV). Unfortunately, if not designed correctly, this useful source of power can become a dangerous source of destruction.

Examples of battery pad applications include:
Of the three primary lithium cell types (prismatic, pouch and cylindrical), the soft-bodied pouch style is becoming the most popular because of its highly efficient packaging. However, these customizable batteries have an important design consideration that should not be overlooked - the change in battery volume by 5-10% due to swelling. Restricted batteries without room to expand can become damaged and result in a potentially spectacular failure. Li-ion battery pads provide more than just compliance to swelling cells; they also provide mechanical support while protecting against shock, vibration, and thermal runaway. Using a Li pouch cell pad can even improve charging performance because a light force against a pouch battery helps improve contact of internal layers.

Providing a compressible foam cushion for the battery is at first glance a simple solution, but in actuality, it requires highly technical materials engineered for the challenge. Products such as PORON 4790-92 and BISCO BF-1000 are two materials that are popular and well-suited for this application.

Key properties of a material used to make battery pads include:
  • Consistent force over a wide compression range for the entire 8-10 year battery life. 
  • Resistance against long-term stress relaxation, especially when exposed to high levels of heat. 
  • Vibration and shock reducing characteristics to prevent damage. 
  • Extreme temperature resistance and thermal insulation to prevent run away. 
  • ROHS/REACH compliance as well as flame retardant characteristics. 
  • Compression set resistance to prevent permanent deformation.
Understanding which materials are best suited for battery assemblies is one of Stockwell Elastomerics' specialties because we work closely with vendors and customers to study test data and contrast products. If you have a battery pad application and are worried about short circuits, reach out to Stockwell Elastomerics' application team for a shortcut to the solution.

PORON® and BISCO® are a registered trademarks of Rogers Corporation.

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Friday, March 16, 2018

Low Dielectric Loss Elastomers For Radome Antenna Assemblies

When designing radomes (also called radar domes) or other types of signal transmitting antennas, engineers must pay close attention to the electrical properties of the materials used in and around those assemblies. The electrical characteristics of a material can be used to enhance an antenna design, whereas failure to account for these lesser-known factors can have catastrophic consequences.

Unique properties like the inorganic chemistry of silicone rubber make it an ideal candidate for use in critical antenna assemblies, and this is one of the reasons engineers specify silicone. Products like R10480S are soft, and conformable so they can seal out rain and salt water on a composite radar dome which can be flexible and wavy. Low-density foams such as MF1 are lightweight and long-lasting, so they make good spacers and insulators without contributing a risk of shedding or contamination. A silicone thermal gap pad like TC3008 can be used to help transfer heat away from a high powered amplifier or power supplier.

Some cutting-edge designs take advantage of these flexible materials to tune or bend signals, and this allows for more compact packaging - an advantage when aerodynamics, weight or space is important. In this type of application, the lesser known electrical properties of materials become more critical and must be understood.

Dielectric constant and loss tangent are two key material properties that are important as inputs during the simulation and design phase of an antenna assembly. Both of these properties describe how an electromagnetic wave transmits through a medium and are affected by thickness, density, cell structure, and pigments.

For many suppliers the dielectric and loss tangent of their materials is unknown, but Applications Engineers at Stockwell Elastomerics understand these factors and offer customers valuable insight and design support through the development and introduction of new products. Experienced with a variety signal transmitting applications, Stockwell Elastomerics' Applications Engineers contribute expertise that can be translated into high-quality parts for customers.

Contact Stockwell Elastomerics for further assistance with engineering design and components for radome antenna assemblies.

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Wednesday, February 07, 2018

Thermal Gap Filler Pads – Provided Kiss Cut on Release Liner

.200” thick TC2006 thermally conductive gap
filler pads, kiss cut against protective liner
ThermaCool® TC2006 and ThermaCool® TC3008 thermally conductive gap filler materials are inherently tacky. When thermal gap filler pads are cut from these silicone gel base materials using water jet cutting and die cutting processes, our experience indicates they need to stacked and separated to prevent the tacky edges from sticking together. However, this secondary procedure adds cost and additional handling.

Stockwell Elastomerics invested in a digital flash cutter to complement its water jet cutting and die cutting capabilities. The high speed knife blade can be programmed to kiss cut thermal gap filler pads from .020” to .250” thick against a protective release liner. However, the high speed digital knife cutting process reduces edge tackiness, allowing thermal pads to be provided on a sheet with a material saving common line cutting patch. TC2006 and TC3008 thermal gap filler pads can be provided with minimal edge waste, without the secondary stacking and edge separation process.

Thermal gap filler pads are available in .020” thick to .250” thick. These pads are provided with a protective release liner on both sides that is removed during assembly.

TC2006 Thermal Gap Filler (datasheet PDF) has a good balance between thermal conductivity (1.6 W/m-K) and less compressive force.

TC3008 Thermal Gap Filler (datasheet PDF) provides higher thermal conductivity (3.0 W/m-K) with slightly firmer compressive force.

Note: Ultra-soft ThermaCool® TC3006 (1.1 W/m-K) and Bergquist Gap Pad® V0 Ultra-Soft can be cut readily using the digital flash cutter. However, the digital cutting process does not eliminate the edge tack of these ultra-soft thermal materials.

Contact Stockwell Elastomerics for further assistance with thermal gap filler pads and thermal interface materials.

ThermaCool® is a registered trademark of Saint-Gobain.
Gap Pad® is a registered trademark of The Bergquist Company.

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Monday, December 18, 2017

Silicone Sponge Gaskets with Conductive Coating Solve ESD Grounding Issues in Test Chambers.

Closed cell silicone sponge rubber is non-conductive, having a volume resistivity of 1 x 1014, test technicians and electrical engineers would typically want to keep this away from static sensitive test procedures. However, the broad temperature capability of closed cell silicone sponge, from -80°F to 400°F make it the ideal gasket product for sealing out air and humidity in environmental test chambers and integrated circuit test and handling equipment.

Other ESD foam products do not have the excellent compression set properties of high performance silicone sponge products like R10480-S (less than 10%). Nor will other ESD foam products perform over the broad temperature range of closed cell silicone sponge.

Stockwell Elastomerics is offering test strips of .250” thick x .500” wide soft closed cell sponge for evaluation. Half of the length is plain (orange) and the other half has our electrically conductive ESD grounding which is cross-linked into the surface to withstand moderate wear, deflection and long term aging under compression. The difference can be seen with an ohmmeter or multimeter, as demonstrated in this video:

Contact Stockwell Elastomerics for further assistance with materials for ESD protection, and ESD protection products such as conductive grounding pads (Conpads™), ESD gaskets and pads.

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Monday, October 23, 2017

Stockwell Elastomerics Announces ESOP

Stockwell Elastomerics Molding Operations
First Shift Crew
October is employee stock ownership month. And Stockwell Elastomerics is pleased to announce its new ESOP (Employee Stock Ownership Plan).

I made this announcement in a series of employee meetings earlier this October. Until now, the business was 100% owned by the family; now the employees will be beneficiaries of the new Stockwell Elastomerics Perpetuity Employee Stock Ownership Trust.

Why use the word Perpetuity? Perpetuity and Sustainability are my goals for the business and stakeholders of the business, including employees, customers, vendors and the neighboring community. Stockwell Elastomerics is a 4th generation privately held manufacturing business, founded in 1919. Our roots are deep in Philadelphia, and many of our 80 employees, including management, professional engineering staff and production staff live in the city. We are proud to be a successful Urban Manufacturing business.

I hope that even more employees now take even more interest in the details of the business. Especially in a custom manufacturing business, it's the little things that add up to providing great customer support and consistently high quality. I hope this ESOP builds even more engagement now and many decades into the future.

- Bill Stockwell
Stockwell Elastomerics, Inc.

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Wednesday, September 13, 2017

Custom Gaskets for Autonomous Vehicles

Stockwell Elastomerics is helping the industry that is redefining vehicle travel for the 21st century by supporting autonomous vehicle development with precision custom gaskets. Manned and unmanned self-driving vehicles contain an elaborate system of cameras and sensors, combined with sophisticated operational software which relies on OTA updates. These vehicles operate in outdoor conditions exposed to rain, snow and UV light, so it is vital that these sensor systems are protected.
autonomous vehicle

High performance silicone elastomers from Stockwell Elastomerics are currently being used by the industry for environmental sealing, thermal management and EMI shielding.

Stockwell Elastomerics supplies materials that help designers meet IP water seal ratings as well as UL 94 flame ratings. Electrically conductive silicone products for EMI shielding such as SNE-540 and SNE-556 nickel graphite silicone are in stock. These EMI materials can become a vital component to ensure operational success with respect to data transfer.

Technical data about materials for EMI gaskets and silicone gaskets is available via these links:

For more information or request a prototype, please contact Stockwell Elastomerics at 1-215-335-3005 or email to make an inquiry.

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