Steel Rule Die for Custom Gasket Cutting

Often when people hear “custom” and think high cost; special setup charges, and tooling charges. In reality custom gaskets can be custom made for relatively low cost. If volumes warrant die cutting (often 500+ pcs) a steel rule tool can be made. A die for a six inch square window gasket with fastener holes at each corner can be made for less than $200. When amortized over a few thousand pieces, tooling cost quickly become pennies/per part.

Steel ruled dies are often made by accurately laser burning the part geometry into engineered, dimensionally stable plywood. Then a long steel blade (almost like a razor blade) is precisely bent and press fitted into the wood. Holes are made by pressing punch sets into the plywood. Tools in the 12” x 12” range can hold a tolerance of less that .012”.

Stockwell uses steel rule dies to cut Poron urethane foam, silicone foam, silicone sponge, and neoprene sponge. It is important to know that softer and thicker foam or sponges tend to have wider tolerances because the material compresses before it is cut through. Solid silicone gaskets, thermal gasket, emi gaskets can also be cut with steel rule dies.

Gaskets and pads can be made many ways. Stockwell takes into consideration gasket material type, gasket thickness and quantity to determine the production method that is most cost effective. Very tight tolerance gaskets or low volume gaskets can be waterjet cut with no tooling charge.

For more information about gaskets or gasket materials cut with steel rule dies, visit http://www.stockwell.com/ or call 215-335-3005.

Formex – Thin UL Rated Polypropylene Sheet

Formex GK polypropylene sheet has been engineered to meet electronic equipment requirements. Formex has a high dielectric strength making it a good electrical insulator, does not absorb moisture and is UL listed carrying a UL94 V0 or VTM-0 flame rating.

Over the last few years Stockwell has been laminating Formex to other UL94 rated materials such as HT-800 & BF-1000 silicone foams. Laminations are most often used as either a stiffening layer or as a protective top layer. An example of a stiffening layer would be a thin wall dust gaskets that is flimsy. Adding a thin layer of Fomex between the adhesive layer and rubber creates a stiffening effect which aids in assembly. An example of a protective layer would be a battery pads that will see wearing from installation and removal of the battery. In this case, a layer of Formex polypropylene is bonded to the top of the pad.

Stockwell carries thin grades of Formex, which are available for direct die cut parts, waterjet cutting (may have frayed edges) or as a lamination. Laminations to Poron foam or silicone foam are most common. Pressure Sensitive Adhesive (PSA) backing is also available. For more information regarding Formex polypropylene and other UL rated materials stocked and converted by Stockwell Elastomerics visit http://www.stockwell.com/ or call (215) 335-3005.

Rubber Temperature Range

Whether you are designing a pad or gasket it is important to know how the environment will affect your part. In most cases, pad and gasket are dynamic in their operation. As an example a door gasket on a NEMA enclosure will compress and rebound as the enclosure heats up and cools off due to thermal expansion. If the gasket loses its ability to rebound (i.e. takes a compression set) or even worse brakes down, the seal could be lost leading damage or system failure.

Excessive heat can be linked to many gasket failures in the form of compression set. I recently saw a sprinkler control enclosure that used a sponge cord (likely a chloroprene blend) that took a major compression set. This set made the gasket virtually useless. In a wind driven rain situation, there would be ingress of water. Luckily this box was mounted inside a garage. It is important to know that elevated temperatures can encourage compression set. ASTM has tests for sponges and foams at 2 different temperatures 158°F & 212°F.

Catastrophic failure of a gasket or pad can also be attributed to exceeding the operational temperature of the “rubber”. Below is a list of materials and their general operating temperature ranges. Note, refer to specific manufactures datasheet before selecting a material.

General Operating Temperatures for Common Materials*
Urethane: less than 250°F (121°C)

Natural Rubber: less than 250°F (121°C)

Chloroprene (Neoprene): less than 300°F (149°C)

Nitrile (Buna-N): less than 300°F (149°C)

EPDM: less than 400°F (204°C)

Fluorosilicone: 400 – 500°F (204 – 260°C)

Fluorocarbon: 400 – 500°F (204 – 260°C)

Silicone: 400 – 500°F (204 – 260°C)
*Temperatures are general, values will vary with grade. Refer to specific specifications for actual product temperature ratings.

For more information about gasket and pad materials such as solid silicone, silicone sponge, silicone foam, fluorosilicone sponge, Neoprene, EPDM, Nitrile, Poron urethane foams or other gasket materials, please contact Stockwell at (215) 335-3005 or visit our website at www.stockwell.com.