Silicone Gaskets

Silicone is an excellent material for gasket applications. It resists most chemicals, stays flexible over a wide temperature range, has good elongation and doesn’t take much of a compression set. If used where it could come into contact with foodstuffs or beverage products though, it must be food-grade.

This isn’t just a recommendation. If you’re making or handling food the Food and Drug Administration (FDA) mandates the use of materials from their approved list. Here’s what to know about food-grade silicone.

Silicone Basics

Silicone, (notice the letter ‘e’ that distinguishes it from silicon,) is produced by heating silica, (also known as silicon dioxide or SiO2,) with carbon. This produces polymer chains that can be processed into liquids and elastomeric solids and gels.

Solid silicone gasket material is sold in sheet form in thicknesses from 1/32” up ¼”. Important points for gasket applications are:

• Temperature range: -67⁰F to 450⁰F (-55⁰C to 230⁰C)
• Durometer: 30 to 80 Shore A
• Resists UV light and ozone
• Resists most chemicals, except for chlorine, methane and acetates

Why and When to Ask For “Food-Grade”

FDA regulation 21 CFR 177.2600 is a list of materials considered suitable for use with food. Silicone is on the list, but unless you specify food-grade silicone you’ll almost certainly get material that isn’t suitable for use around food products.

Silicone that isn’t food-grade contains additives, mostly colorings, that could contaminate product or make it taste off in some way. Food-grade silicone is white, and for this reason is sometimes called “white silicone”.

Food-grade silicone gaskets should be used in food processing and handling equipment. Storage vessels, kettles, mixers and even freezer doors are all good applications. Be sure to check what cleaning chemicals will be used, as those containing chlorine could damage the silicone.

Hennig Gasket for Food-Grade Material

People involved with food understand the importance of avoiding contamination. No one wants to make someone sick, which is why kitchens and food processors should always use food grade-materials. Stainless steel is ubiquitous for hardware, but when it comes to gaskets, food-grade silicone is often the way to go.

What a difference an “e” makes! Silicon is the material of electronics. It’s hard and brittle and makes lousy gaskets. Silicone on the other hand is soft and elastic, which makes it a good choice in many gasket applications. Here’s what makes this polysiloxane material so useful.

Basic Chemistry

Silicon and silicone are closely related. Silicon is a naturally-occurring element while silicone is a polymer that combines silicon atoms with those of oxygen and the H₃C hydrocarbon compound. The result is a soft, plastic-like material that springs back after being compressed.

More Silicone Properties

In addition to compressibility, other useful features of silicone include:

• Poor adhesion, so it doesn’t mark surfaces
• Low toxicity, making it useful for food and medical applications
• Resists degradation by ultraviolet light (sunlight)
• Low electrical conductivity
• Repels water
• Ozone resistant
• Retains its flexibility over a temperature range of -94 to +392°F

These properties make silicone gaskets a good choice in a range of food, medical and electrical applications. It won’t taint foods and it handles a wider temperature range than many other gasket materials.

Silicone Weaknesses

In some regards, silicone performs less well as a gasket material than the alternatives. Some others have higher strength and better compression set recovery for instance. It’s also attacked by hydrocarbons like most oils and fuels, and resistance to acids and alkalines is poor. In short, unless you need the special properties of silicone there may be better alternatives.

Silicone Forms

Silicone is available in both solid sheet and as a foamed or cellular material. Silicone foam may be either closed or open cell.

Silicone comes in many colors, (which may not be food grade, so check before ordering.) There are also many variants tailored for specific application needs. Some will go to lower temperatures than that given above, while others have been engineered for higher strength or even electrical conductivity.

If you’re considering using silicone gaskets we respectfully suggest speaking with one of our material specialists. There are many instances where silicone is an excellent choice, but sometimes other materials may perform better.

The silicone gasket around the door or access panel of an electrical enclosure has two jobs. Not only does it keep dust out, but it also keeps electrical noise in. Or it does if made from the right material.

The Noise Problem

Electrical noise, sometimes called electromagnetic interference (EMI) or radio frequency interference (RFI) is a problem in some environments. By interfering with wireless transmissions EMI makes phone calls difficult and disrupts wireless data transmission. It can also induce currents in other conductive materials. That can lead to spurious data signals, possibly giving rise to false alarms or affecting process control equipment.

Conversely, sometimes sensitive electrical equipment needs shielding from environmental EMI. Placing it in a metal enclosure keeps the EMI outside, avoiding problems of signal interference.

EMI Sources

EMI travels through air, spreading out from a source much like ripples on a pond. Circuit breakers, relays, transformers and switches can all produce EMI. This is one reason they’re often placed in an enclosure. Motors, power cables and welding equipment also produce EMI, but aren’t so easily shielded. However, sensitive electronics near these items may need to go in an enclosure.

Conductive Shielding

When waves of EMI meet a conductive material the energy spreads out over the surface rather than continuing on. Gaskets and flanges however provide an opportunity for leakage.

With most enclosures, closing the door leaves an uneven gap. That could allow dust inside, which is the main reason a gasket is fitted around the opening. Electrical enclosures are usually sealed with silicone gaskets, which offer good compression and stand up to elevated temperatures. However, silicone is not naturally electrically conductive. That results in a leak path where EMI can escape.

Ask for Electrically-Conductive Gasket Material

When replacing gaskets around an electrical enclosure, or specifying new, always consider the need for EMI shielding. Electrically-conductive gasket materials are available, but it’s important this issue is raised when speaking with the material supplier. In many cases conventional silicone gasket material will be sufficient, but if EMI could be a concern, let your vendor know.