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.

Fast Gasket, Quick-Turn Gasket, Next Day Gasket, or Quick Gaskets!

It is not a rare occurrence at Stockwell to receive an urgent call requesting next day gaskets or pads. Many times there is field requirement or engineering build where time is critical. Stockwell inventories a wide range of materials and thicknesses. Stock materials include solid silicone, closed cell silicone sponges, UL rated silicone foams, Neoprene sponges, EMI gasket materials, and Thermal management materials just to name few. These stock materials in combination with 3 in-house water jet cutting, die cutting and molding presses with 12” x 12” sheets molds, allow for quick response to urgent request.

Helpful hints for fast gaskets to fix a problem or meet a deadline:
- Supply an electronic CAD file (2D .dxf or 3D .iges)
- Work with in-stock materials
- If an adhesive backing is required, inform us of the type of metal, plastic or painted surface to be bonded to
- Indicate smallest quantity required
- Provide ship-to information and carrier account number- Supply a credit card or purchase order (existing customers)

Providing an electronic CAD file helps expedite the Water Jet programming. With a wide cross section of materials in stock, Stockwell can usually find a material to meet gasketing requirements. Since it is often a race against the clock / shipping pickup, knowing the minimum quantity helps to manage processing. Often additional parts can ship within a few days.

Acrylic Adhesive Backed Silicone Gaskets

Is Silicone PSA required for silicone material?
We often see silicone based adhesive specified with silicone materials. Silicone adhesives are expensive as compared to acrylic adhesives, in some cases more than 5 times the cost of acrylics. Silicone PSA’s bond strength is not as good as acrylics and there are limited offerings. So why are silicone adhesives being specified? Silicone adhesives can be adhered to silicone material without surface preparation. Many fabricators do not have the technology to apply acrylics to silicone materials, however Stockwell has been doing it for years.

When should silicone adhesives be specified?
Silicone adhesives do have their niche, they are great for very low and high temperature extremes where acrylics and rubber based adhesive lose their efficacy.

Having a Pressure Sensitive Adhesive (PSA) backing on gaskets is not required to make a good seal but is often recommended to aid in assembly. The added cost of the adhesive is offset quickly with the time saved during assembly.

For more information about materials contact visit Stockwell Elastomerics at stockwell.com or call 215-335-3005.

Large Custom Gaskets

Every so often we receive inquiries for large custom gasket. In some case they are extreme such as the one shown below. In many cases they are for NEMA enclosures (commonly NEMA 4). A single piece gasket generally offers the best seal, however many gaskets exceed the width of the material. In this case a jointed corner may be an option.

Single Piece - a single piece gasket will offer consistent deflection force around the gasket. The con to a large single piece gasket is the center waste. If engineer are making multiple gaskets they can create an assembly level drawing that show several gaskets nested.

Joint and Bond – when a single piece is required but the gasket dimensions exceed the material dimensions, a jointed and bonded gasket may be an option. In most cases this is a die or water jet cut male/female dove tail that is then UV bonded. This type of gasket needs to be evaluated to see that the extra labor of bonding does not exceed the material savings. Also, for foams and sponges the corners will be firmer than the gasket material.

Joint (no bonding) – similar to the Jointed and Bonded gasket, a male/female dove tail is die or water jet cut. In this case the gasket is provided in 4 pieces and is mated during installation. In some cases a bond is never required. This is most dependant on the enclosure configuration and the level of sealing required.

Materials most commonly used for large custom gaskets are silicone foam and silicone sponge. Since the sealing area is relatively large (i.e. square inches) the soft nature of these materials allow for lower closure forces to get proper deflection for sealing.

For more information please feel free to contact us at service@stockwell.com or 215-335-3005.