November 2017

Custom Die Cut Gaskets

Practically every non-metallic gasket is cut from a sheet or roll of gasket material. Cutting methods include oscillating knife, laser, waterjet and steel punch dies although the most common process is steel rule die cutting. It’s cost-effective for medium quantity orders but needs special tools. Knowing a little about the process will help gasket buyers understand when this might be the one to use.

The “cookie cutter” process

A steel rule die is a steel strip bent to the profile of the part being cut. This is embedded into a plywood or phenolic board that holds it in shape. The exposed edge of the steel knife is sharpened so it can cut through the material. The board is then mounted into a press. Bringing the tool down into the gasket material cuts out the gasket.

To use the material efficiently gasket makers typically “nest” steel rule dies. This might mean cutting a small gasket from the center of a much larger one or combining a number of different gasket shapes in one tool.

For higher volume production a gasket maker might use a rotary die machine. Here the steel rule die is wrapped around a cylinder. Strip material is fed underneath and the die cuts out the gasket shapes as it rotates.

“Kiss cutting”

When cutting all the way through normal practice is to have a relatively soft sacrificial material underneath. This helps extend the life of the cutting edge. However, sometimes it’s better not to cut all the way through. This is “kiss cutting,” because the knife just “kisses” the backing material. It keeps the gaskets together in a single sheet while making them easy to separate when needed. This simplifies storage and is particularly useful when the gasket material has a pressure sensitive adhesive backing.

Dies for your gaskets

We’ve been cutting gaskets at Hennig for many years and have a lot of dies in inventory. If you want die cut gaskets it’s possible we already have the tools needed. Call or email to find out.

Yes, Cork is Still Used as a Gasket Material

Cork, the bark of the cork oak tree, has been used as a sealing material for centuries. The Romans “corked” wine bottles with it – something it still does today – and before modern elastomers were developed it was widely used as a gasket material. Cork gaskets are less common today, but they still have a role.

Properties of Natural Cork

Cork has a closed-cell structure that gives it excellent resilience. A layer can be compressed to around half its thickness and still recover when the load is removed. It’s also lightweight, flexible, and resists attack by water, many oils and even ozone. At around 275°F (135C) its upper temperature limit is lower than some elastomers, but that’s not its biggest weakness. Those are a vulnerability to mold, fungi and acid attack, and as an entirely natural material, its properties are somewhat unpredictable.

Composite Cork Gasket Material

Cork- rubber composites address these deficiencies. Typically these are 70% cork with a synthetic elastomer binder making up the balance. The elastomer imparts some of its own characteristics to the composite and is usually chosen to improve chemical compatibility and sealing performance. Processing also takes out much of the natural variability.

Composite cork gasket material is available that incorporates a number of different elastomers. EPDM, Neoprene, Nitrile and silicone are just a few. The material is produced as a sheet up to ¼” (6mm) thick and is easily die-cut. It readily takes a pressure sensitive adhesive coating, making it easy to apply in many gasketing and sealing applications.

The “Green” Dimension

Cork is cut from the cork oak tree once every nine years. The tree doesn’t die but instead grows a new layer of protective bark. This makes cork a renewable material, something that may be important in some applications and for some users.

There’s Still a Place for Cork Gaskets

Cork is waterproof and has great compressibility. Modern elastomers may offer better chemical resistance and a wider temperature range, but for sealing water and oil, don’t overlook this oldest of gasket materials.