January 2018

Why Steel Rule Die-Cut Gaskets are Disappearing

No one likes waiting for a gasket, especially when it’s for an urgent repair. No one wants to keep spare gaskets in inventory either. That’s why more gaskets are being water-jet cut. As tooling-free processes, they offer a faster turnaround than die cutting. Here’s more detail.

Steel Rule Die Lead Time and Storage

Each die is made to cut a unique non-metallic gasket. The sharpened blade is pressed into a slot cut in a backing board. Then ejection rubber is fitted around the blade to push out the cut gasket shape.

These take days or weeks to make so gasket manufacturers keep previously used tools in storage. At Hennig, we have thousands taking up space. If a customer wants a die cut gasket we check whether we have the tool needed. If we don’t, water-jet cutting is faster.

Tool Maintenance and Repair

Steel rule edges wear. That affects quality and accuracy, so they need sharpening and/or changing. Likewise, ejection rubber needs regular replacement.

In addition to faster order turnaround, these processes offer:

  • Better edge quality – no compression means straight and square edges.
  • Higher accuracy – water-jet machines can maintain tolerances as tight as +/- 0.0005” while die cutting struggles to beat +/- 0.010”. That’s because the machines are more precise and there’s no deflection or compression of the gasket material.
  • No tooling charges.

Die Cutting for Higher Volumes

Water-jet machines cut quickly, but not as fast as a tool in a press. (And rotary die cutting is even faster.)

Against that, the die cutting press takes time to set up. The breakeven point depends on gasket size, but water-jet and laser usually win for small quantity orders. Die cutting gets cheaper per piece for large quantities but don’t overlook tooling charges.

Speed Wins

With water-jet machines, gaskets can be cut to order. That enables a rapid turnaround that avoids holding spare gaskets in inventory. No wonder die cut gaskets are going away.

When to Use Felt Gasket Material

Most gasket materials are elastomeric or rubber-like in nature, but there’s another material that’s surprisingly effective in some sealing applications: wool. When compressed to a uniform density wool becomes felt. Felt has been used for sealing and gasketing for a long time and still has its uses.  Felt seals suppliers offer a variety of options

A “Non-Woven” Material

Most felt is produced by compressing wool into rolls of material. Wool fibers have a kind of “fish scale” surface that lets them hook together randomly. This creates a material that’s soft and compliant with a high level of resiliency. It can absorb and hold liquids even better than an open cell foam while resisting attack by oils and temperatures up to 200°F. An added benefit is that felt won’t unravel or fray like woven fabrics.

Industrial wool felt is specified by an SAE standard. This assigns grades from F-1 to F-55. Higher numbers indicate lower density, and these grades have less ability to absorb vibration and resist abrasion.

Felt is produced from other materials, most notably polyester fiber. Polyester felt will withstand temperatures up to 300°F but its properties and behavior are not addressed by the SAE standard.

Uses of Felt Gasket Material

  • Noise-deadening

Thanks to strong resilience, felt gasket material can absorb movement between surfaces that would otherwise cause rattles and squeaks. By preventing the transmission of vibration it’s also a good sound-deadening material.

  • Filtration

The random orientation of fibers in felt make it a very effective filtration medium. Filtration is further enhanced by soaking in oil. Wool fibers hold oil on their surface, which traps very small particles being drawn through.

This ability to retain oil also makes felt a good seal against moving surfaces such as shafts. The wool adapts to changes in gap while oil provides lubrication and simultaneously prevents fluid transmission.

Compliant but Durable

As a soft gasket material, felt is similar to an open cell neoprene, EPDM or silicone foam. Its upper-temperature limit is lower, but depending on grade, abrasion resistance can be higher. If you’re looking for a material that can lubricate as well as seal, ask about felt.