Food Grade Gaskets

Why Use PTFE Seals in Food Industry Applications?

Commercial cooking kettles used for boiling and preparing foods usually have a food grade gasket around the lid. By creating a good seal this helps the vessel build and retain pressure. This raises the boiling point of water, shortening cooking time while also destroying pathogens. A defective gasket can result in food not reaching the required temperature, potentially creating a health hazard. Additionally, the gasket itself can provide places for bacteria to become established.

This gasket leads a hard life. Not only must it withstand the heat and pressure of cooking, but it’s also expected to go through multiple cleaning cycles. In addition, it’s essential that it not transfer anything or impart any taint to the food being cooked. Several materials are available for such gaskets, but in many situations the best sealing option is PTFE.

A Versatile Sealing Material

Polytetrafluoroethylene, or PTFE, better known by it’s DuPont tradename of Teflon, has a number of properties that make it an excellent choice for a food grade gasket. At the atomic level it consists of a long chain of carbon atoms, each one of which links to two fluorine atoms. This linkage is so strong that PTFE won’t bond to anything else, hence its non-stick properties.

PTFE doesn’t melt until 635°F and is usable at temperatures up to 260°F. At lower temperatures it remains flexible well below freezing, as low as -100°F or even lower, depending on formulation. It’s also a good electrical insulator. Of particular relevance for food industry gasket applications, it doesn’t absorb water and it’s biologically inert. It does however resist attack by almost all chemicals, including aggressive cleaning and disinfecting agents like chlorine dioxide.

PTFE Seal Alternatives

Other materials have properties that are close or superior to PTFE in some regards. Silicone for example is flexible at low temperature, has good compressibility and a higher upper temperature limit. However, silicone does not fare well with steam, which is found in many food preparation environments. It also lacks resistance to acids, alkalies and chlorinated solvents, so is limited in its potential as a food grade gasket.

FDA Approved Seal Material

Gaskets & Seals made entirely of PTFE are covered by 21 CFR 177.1550, meaning they have FDA approval for food industry use. (PTFE incorporating filler material may not meet FDA requirements.) At Hennig we can supply PTFE sealss in thicknesses ranging from 0.015″ to 0.50″. Call or email for further information.

PTFE Makes an Excellent Material for FDA Gaskets

Buying gaskets for dairy, brewery and food processing equipment is difficult. The choice is limited to FDA gaskets or FDA approved gasket material because it’s essential to avoid tainting or contaminating the product. Cleaning and sterilization routines are a way of life, so gasket material must stand up to high temperatures and caustic cleaning agents. And last, clamping forces are low in equipment like kettles, mixers and sanitary pipe fittings, so the material must be soft.

Polytetrafluoroethylene, (PTFE) sometimes referred to as Teflon®, meets all these requirements. That’s why it’s used for gasketing throughout the food industry. PTFE is listed by the FDA under 21 CFR 177.1550, although this approval really only covers virgin PTFE material. PTFE with markings, adhesive backing or filler can be used in food applications, providing the inks, adhesives and fillers also meet FDA standards. If purchasing gaskets like these for a food industry gasket application, have the material supplier confirm they qualify as FDA gaskets.

Some gasket materials will absorb traces of food preservatives, but PTFE is almost completely non-reactive. It doesn’t pick anything up and neither does it pass anything over so there’s no risk of food being contaminated with traces of elastomers or cleaning agents. The Shore D hardness of PTFE is around 50, so it’s soft and easily compressible. That’s important when pipes and vessels are secured with clamps rather than bolted flanges. PTFE also has the advantage of retaining its properties at temperatures as high as 400°F (204°C). That’s why it survives steam cleaning.

PTFE is not perfect though. It has a tendency to creep, which could lead to reduced clamping loads. This is because, unlike elastomeric gasket material, PTFE doesn’t cross-link, so bolted joints with PTFE gaskets may need occasional re-torquing.

In food processing it’s essential to use FDA gaskets. These will typically be PTFE, although some other materials are FDA approved too. If a gasket is going to contact food products it’s always best to discuss the application with the material supplier and make sure the correct material is chosen.

Selecting FDA Gasket Material for Food Industry Applications

An FDA investigation of a food contamination incident found a gasket at the root of the problem. Cleaning agents weren’t penetrating small cracks and E. Coli was able to gain a foothold. In their findings, the FDA suggested inspectors should:

  • Look at how frequently a food manufacturer inspects and replaces gaskets
  • Challenge the effectiveness of Clean-in-Place (CIP) procedures
  • Verify that gasket material is FDA approved for use

Responsible food manufacturers conduct rigorous cleaning and inspection regimens. Whenever any doubt exists as to the fitness of a gasket it gets replaced, but that presents those performing the refurbishment with the question of what material to use.

The FDA maintains listings of approved FDA gasket materials. PTFE and many elastomers such as NBR, SBR and EPDM are included, but two points are sometimes overlooked by those shopping for FDA gaskets. First, any markings, such as part numbers or other information used for traceability must also be FDA compliant. Second, any adhesives used to hold the gasket in place must also comply with FDA requirements.

Where should FDA gaskets be used?

Any surface coming into direct contact with food must be manufactured from materials known to be safe. (“Safe” in this context means either materials already listed by the FDA or those it considers “Generally Recognized As Safe” (GRAS).) This includes gaskets used in food preparation equipment such as kettles and mixing vessels, as well as those used in sanitary couplings; the kind of fittings used for moving dairy or brewery products.

How to select appropriate materials?

One approach would be to trawl through the various applicable FDA documents, noting which would work in your application. A less time-consuming approach is to ask your gasket vendor for advice. Describe your application in detail, particularly the temperatures and pressures involved and the cleaning regimens employed, and they’ll know which materials are suitable. You’ll receive FDA gaskets that work in your application and contamination risks will be reduced.

Food Grade Gasket Manufacturing

Food grade non-metallic gaskets are made from materials approved by the FDA for repeated and demanding contact with edible products. They must withstand high pressures, have a wide temperature tolerance and be extremely resistant oils, acids and chemicals without degrading or becoming susceptible to bacteria formation—for the obvious reason that food-grade gaskets and seals must not impact food quality or safety whatsoever. FDA-approved food-grade non-metallic gaskets are also used in pharmaceutical and cosmetics manufacturing for the same reason.

There are several materials that we can use to fulfill food grade non-metallic gasket orders:  

White Nitrile (Buna-N)—Commonly used in food processing because it remains durable and flexible when cycling between temperatures of -31°F to +230°F. It is highly resistant to petroleum, mineral and vegetable oils, acids and a wide range of aromatic hydrocarbons.

White Neoprene—Works well in food-processing and packaging environments, as well as pharmaceutical, commercial kitchens, cosmetics plants and grocery store applications with a temperature tolerance of -20°F to +180°F.

Red or White FDA Silicone—Have a temperature tolerance between -94°F to +392°F and are often used in everything from food processing to laboratory and surgical applications because of its low volatility and durability. Resists oils and acids well.

EPDM—Food-grade EPDM has a temperature tolerance of  -20°F to +230°F. It’s smooth, resists abrasion, is color-stable, non-marking and odor-free; for these reasons, it has earned the additional approval of the USDA for poultry and meat processing.

PTFE—As one of the most chemically-resistant plastics available, FDA-compliant PTFE is extremely common in food and beverage processing, cosmetics and pharmaceutical manufacturing. It also has an outstanding temperature tolerance of -328°F to +500°F.

Gylon®—This is a specific brand of PTFE with a 450°F to +500°F . It is extremely chemical and temperature resistant with reduced creep relaxation qualities.

While all of these materials (and a few others not listed here) are FDA-compliant, not all of them are suitable to all food, cosmetics or pharmaceutical production processes. Please contact Hennig Gasket and Seals, Inc. at 1-800-747-7661 and we can discuss which food-grade, non-metallic gasket material would be best for your needs.

How Hot is too Hot? Choosing the Right Gasket Material for a Non-Metallic Gasket

For non-metallic gasket applications, the operating temperature of the finished product is a major consideration. You need to know the temperature range (and other strengths and weaknesses) of potential materials so you can get the most durable custom gaskets and seals. Otherwise, they could prematurely harden, crack, deform and lose strength, elasticity and resilience, etc.

The following is a list of common non-metallic gasket materials, their properties and their most stable operating temperature ranges (in Fahrenheit). Understand that while there may be wiggle room on either end, it’s best to aim for somewhere in the middle of each particular material’s temperature range so that the gasket or seal performs optimally for the longest period of time before replacement is needed.

Nitrile: -30 to 250F (very resistant to oils, aromatic hydrocarbons, fuels and solvents).

Neoprene: -35 to 225F (resistant to weather, water, combustion and a long list of chemicals).

Polyurethane: -35 to 225F (resistant to oxygen, ozone, cracking, abrasion, cuts, grease and heavy loads; frequently used in machine mounts, electrical equipment wear pads and applications needing shock absorption).

Ethylene Propylene: -70 to 250F (resists severe weather conditions, acids, oxygen, alkalis, hot and cold water and ketones; not suitable for use with oils or fuels).

Fluorocarbon: -15 to 400F (its low friction and resistance to wear and tear make this a good material for gaskets that endure movement, a wide temperature variation and frequent reassembly).

Silicone: -65 to 450F (very resistant to hot, cold and oxygen, but poor resistance to oils and fuels; frequently used in food processing and medical applications).

Polytetrafluoroethylene: -238 to 574F (extremely wide temperature range, also stands up to harsh conditions of all sorts; frequently used in food processing, pharmaceutical, laboratory, semi-conductor, petrochemical and chemical and electrical applications).

Temperature range is, of course, just one aspect of a non-metallic gasket material that you will need to consider before project implementation; nevertheless, temperature tolerance is crucial. If you need custom gaskets and seals for your project, please call us at 1-800-747-7661 to discuss your needs with us.

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.