Silicone Gaskets

What is Food Grade Silicone?

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’s Special About Food Grade Silicone Gasket Material?

Silicone makes excellent gaskets. It works over a wide temperature range, has a low compression set, high elongation, and is resistant to water, ozone, many acids, and UV light. If you’ve shopped for silicone gaskets or gasket material you probably noticed some formulations are specified as “food grade.” Here’s what that food-grade silicone gasket material means and why it might matter in your application.

Composition, Properties and Forms of Silicone Gasket Material

Silicone is an elastomeric polymer made from silica, (which is silicon dioxide, or sand), water and methanol. Silica is chemically inert and very stable, even at temperatures as high as 550 °F. It’s also an electrical insulator.

As a gasket material silicone has two weaknesses. First, it’s not oil-resistant and should not be used where it might be exposed to oil-based greases and lubricants. Second, it has poor wear and abrasion resistance so is best used as a static gasket rather than in applications where there’s sliding or dynamic contact.

Silicone gasket material is produced as a solid sheet in a range of thicknesses. It’s also available in foam and sponge form.

Food Grade and Non-Food Grade Silicone

Pure silicone is white. If it has no additives and is not ink-marked it will probably be suitable for use with foods. However, it’s important to check that it complies with 21CFR Part 177.2600 before using it in food or beverage-related applications. This is the FDA regulation that governs the purity of materials classed as food grade.

Some silicones are formulated with fillers, coloring, or both. This is to provide a particular appearance, improve wear behavior or reduce compression. However, some of these can leach out into the liquids or solids they come into contact with. If you need food-grade silicone gasket material with additives, check it meets FDA standards.

Ask Your Silicone Gasket Material Supplier

If you’re installing or replacing gaskets on food processing and preparation equipment they should be food grade, as defined by the FDA. Silicone is a good choice for food-grade gasket material.  Contact Hennig Gasket & Seals for various silicone gasket material options for your application.

Gasket Materials for Washdown Environment

Cleaning is important in many industries, but pharma and food and beverage have it down to a fine art. For those sectors frequent intensive washdowns are a way of life and equipment gaskets must be up to the task. Silicone gasket material and neoprene gasket material are, open-cell foams are not. Here’s some detail.

The Washdown Process

Water heated to 170°F is blasted at 1,500psi of pressure to remove every trace of dirt and contamination. For extra-thorough cleaning caustic chemicals might also be added, creating an even more challenging sealing environment.

NEMA and IP Ratings

Enclosures are rated for the “ingress protection” they provide. NEMA is the US system while elsewhere they like the “IP” categories. A NEMA 4 rating, broadly equivalent to IP66, means an enclosure is designed to resist jets of high-pressure water from a hose. In other words, washdown. A step up in protection is NEMA 4x or IP69k. NEMA 4x protects against aggressive chemicals while IP69k is a rating for steam jet cleaning.

Gasket Materials for Washdown Environments : EPDM, Silicone, Neoprene

First, note that equipment and enclosures should be designed in a way that prevents water jets from directly impinging on the gasket material. Even with that though, the gasket outer surface is still going to get soaked.

This is why open-cell foam is not appropriate. It’s going to let water soak through to the interior. Closed-cell foam is better and solid better still, (though not as soft or compressible.)

Second, the gasket material must resist attack by hot water, possibly incorporating caustic chemicals. Good candidates are EPDM, silicone, and neoprene. Some points to note about each of these are:

  • EPDM gasket material is also UV-resistant. That makes it a good choice outdoors and wherever UV light is used.
  • Silicone gasket material is flexible from –100 to 500°F.
  • Neoprene gasket material works over a range from -40 to 250°F. It also has good oil resistance but is attacked by ozone.

Ask the Experts

You should know the strengths and limitations of the gasket materials you’re considering. The specialists at Hennig Gasket have a lot of knowledge and experience. Call them or reach out by email.

UV Resistant Rubber Sheet

You’ve probably seen dried up and cracked nitrile and neoprene gaskets. Chances are, you’ve replaced a few too! In many cases the culprit is ozone. Here we’ll explain what ozone is, how it forms and what processes/activities expose gasket materials to ozone. Then we’ll suggest materials to use if you have an ozone problem which includes UV resistant rubber sheet.

An oxygen compound

Ozone is just oxygen atoms bound together in groups of three. Its chemical symbol is O3. In nature, ozone exists only in the stratosphere, a layer of the atmosphere five to thirty miles up. However, it can be produced artificially at ground level, and those are the processes that break down nitrile and neoprene gasket materials.

Oxygen atoms react readily with other elements. That’s why iron rusts and aluminum oxidizes. O3 is even more reactive than regular O2, so oxidizes materials even faster. When it contacts gasket materials like nitrile rubber (Buna-N,) natural rubber and neoprene it changes how their polymers are crosslinked. This hardens the material, which then cracks under load.

Ozone-producing processes

Ozone forms in the presence of ultraviolet (UV) light and electrical sparks. Both can break the bonds between oxygen and itself and other elements to free up individual atoms. These quickly recombine as O3.

UV light is widely used for purification and disinfection. Many city water systems use UV purification and UV disinfection is widespread in the medical sector. Ozone is a natural byproduct and itself is used for purification.

Electrical sparks are common around brushed electric motors, especially those using high voltages. High voltage switchgear is another source of ozone.

UV Resistant Rubber Sheet

When choosing a gasket material for an ozone-producing environment stay away from nitrile rubber and neoprene. Instead, consider silicone and EPDM materials. These are available with similar properties to nitrile and neoprene but are less susceptible to oxidation. Other good choices are PTFE and Viton/FKM.

Talk to the UV resistant rubber sheet materials specialists

If you think ozone could be an issue in a gasket application, talk to our specialists. They’ll help you select an EDPM, silicone or other ozone-resistant material suitable for your application.

Low Temperature Gasket Material

Many elastomeric gasket materials have a problem with low temperatures. Here we’ll look at some applications that pose challenges and suggest low-temperature gasket materials worth considering.

Low-Temperature Gasket Material Applications

Seals and gaskets are used in many low-temperature environments. One of the most common is food storage. Freezers and cold rooms are typically kept between -80 and 20°F, depending on the application. Pharmaceuticals and medical products are other industries with low-temperature storage requirements.

Industries that do product testing often employ climatic chambers. These need effective seals to minimize the expense of maintaining low temperatures, and it’s also important to consider the equipment inside. And as Chicagoland residents understand, midwest winters can challenge sealing materials used outdoors, especially if exposed to wind.

Glass transition and TR10

Polymers get their flexibility from chains of molecules moving against one another. As temperatures fall the chains are less able to move and eventually become fixed. Materials scientists call this point the glass transition temperature.

For people who need to choose and use gasket material a more useful indicator of low-temperature flexibility is the TR10 value. This was explained in, “What is TR-10 (temperature of retraction) for Gasket Material?

Good Low-Temperature Gasket Material Choices

Oil-resistant FKM only goes down to around 5°F. NBR is useable as low as -20°F and some specialized grades will go lower. However, these aren’t low enough for many freezer-type applications. Silicon is good for temperatures as low as -65°F and fluorosilicon will go to -80°F but both are expensive. That leaves cost-effective EPDM as an excellent low-temperature gasket material.

The TR10 value for EPDM is between -49 and 9°F, depending on grade. That makes EPDM seals a good choice for many commercial and industrial low-temperature storage facilities. Furthermore, EPDM is available in FDA-approved grades for food industry use.

The chief limitation of EPDM seals is poor resistance to mineral oils and hydrocarbon products. They are good with steam and hot water though, as well as caustic cleaners.

Consider price as well as performance

In low temperatures, many gasket materials become too stiff to seal effectively. Silicon offers good performance but less expensive EPDM comes close for many applications.

Silicone Gasket Material – The Ends and Outs

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.

Enclosure Sealing to Prevent EMI Leakage

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.

Properties of Neoprene Gasket Material

Neoprene, which is also known as “polychloroprene,” is a type of synthetic rubber produced by the polymerization of chloroprene. Neoprene gasket material has become very common due to the fact that it resists the likes of ozone, sunlight, oxidation and many petroleum derivatives. Additionally, neoprene is characterized as being weather-, combustion-, water- and chemical-resistant. As you can see, it’s popular because it is resistant to many types of damages. What’s more, it’s also resistant to damage from twisting and flexing.

Here’s a closer look at the properties of neoprene so you can judge whether or not it’s a good material for your application:

  • Stretch and cushioning properties: Neoprene is elastic and form-fitting, able to conform to various sizes and shapes. It’s also cushioning, able to absorb shock.
  • Various grades available: From cloth inserted neoprene, which is reinforced with nylon for additional stability, to flame retardant neoprene, which passes a variety of flammability specifications, there are several grades available to suit any application. Other popular grades include commercial, FDA approved, diaphragm and high tensile strength.
  • General gauge thicknesses vary in size from 3/32-inch up to 2 inches.
  • Hardness ratings vary from 40 to 80.
  • Plate finish.
  • Neoprene can withstand temperatures ranging from -20 degrees F to 180 degrees F.
  • Tensile strength ranges from 900 to 1,000 PSI.
  • Elongation ranges from 350% to 400%.
  • Finally, widths are 36 inches, 48 inches or 72 inches.
  • Pressure sensitive adhesive, or PSA, are available upon request.
  • We fabricate neoprene gaskets through proven manufacturing processes that include waterjet cutting, flash cutting and die cutting.

One other neat feature about neoprene is that it’s impermeable, meaning that it can work as a tight barrier to prevent the escaping of gases or liquids.

For more information on the neoprene material and neoprene gaskets, and to speak with someone about placing an order, contact us today.