Graphite Gaskets

Is Graphite Metallic or Nonmetallic?

Graphite is something of a wonder material for gasket applications. Not much will attack it and it seals over a very wide temperature range. Graphite gasket material is sold mostly in sheet form and has a dark gray, silver-ish color that looks a lot like lead. This is one reason people sometimes assume it’s a metal. The other reason is that graphite conducts electricity, which is something associated with metals.

In this blog we’ll set the record straight.

What You Should Know About Graphite

Graphite is a form of carbon. Carbon atoms can arrange themselves in several ways, which determines its properties. In graphite the atoms are arranged in layers. These can slide over one another, which is what makes graphite slippery, but at the same time, the layers are surprisingly strong.

Carbon is found on the top right side of the periodic table, between boron and nitrogen. This tells us it’s not a metal, because those elements are grouped in the center of the table.

Useful Properties for Gaskets

Graphite is soft and conforms to match uneven surfaces, a key requirement for a gasket material. It also retains its properties over a temperature range from -400°F to 950°F in air (and higher in non-oxidizing atmospheres.)

Another requirement for gaskets is chemical compatibility, and here graphite excels. It resists almost everything except for a few highly oxidizing chemicals.

Graphite Reinforcement

One weakness of graphite is a tendency to creep under load. This is remedied by mounting it to a stainless steel carrier via little hooks or tangs stamped into the metal. Alternatively, it’s often bonded to stainless foil for increased creep resistance.

Not for Food and Beverage

Unfortunately, graphite is unsuitable for applications where it would come into contact with food or drink. This is because carbon particles can detach and enter into the media. PTFE is usually an acceptable alternative.

Graphite for Gasket Applications

Graphite, particularly when reinforced with stainless steel, makes an excellent gasket material for many applications. Hennig Gasket carries a wide range of types, widths and thicknesses. Contact us to learn more.

Flexible Graphite Gasket Material – When to Use

If you need an alternative to PTFE gasket material, how about graphite? Produced as sheet material, flexible graphite gasket material withstands high temperatures while deforming easily enough to take up imperfections in flange surfaces.

Chemistry and Production

Graphite is a form of carbon. It’s used in pencils because it’s easy to slide the layers apart and spread them on paper. To produce a useful gasket material the graphite is first expanded and then passed through a machine called a sheeter.

Expanding entails exposing small pieces of graphite to sulfuric or nucleic acid. These force the atomic layers apart, making the graphite expand dramatically and forming what look like tiny worms. These “worms” are then fed into a sheeter that compacts them into a sheet of flexible graphite material.

For added strength, the graphite can be laminated onto either a thin stainless steel foil or a stainless tang.

Properties of Flexible Graphite Gasket Material

The practical upper-temperature limit is around 750 °F (399 °C) although some grades will go to 900 °F (482 °C). You may see claims that graphite can withstand temperatures as high as 5,400 °F (2,982 °C) but this is in an oxygen-free atmosphere, which few gaskets ever experience.

A limitation of sheet form expanded graphite is low tensile strength. Laminating onto 316 stainless raises this from around 700 psi to a much more useful 5,000psi. In terms of gasket applications, this means pure graphite sheet has very low resistance to pressure: foil and tang forms of graphite sheet are far more useful.

The downside of combining graphite with stainless is that this slightly reduces both compressibility and recovery behavior.

Graphite has excellent resistance to water, steam, hydrocarbons, and many acids and alkalies. However, sulfuric or nucleic acids will cause rapid decomposition. Note that graphite is not suitable for food, medical or pharmaceutical applications because there’s a possibility of releasing carbon particles into the fluid.

Flexible Graphite Gaskets Cut to Size

Hennig Gasket & Seals carries flexible graphite gasket material in a range of thicknesses. Gaskets can be cut to sizes up to 48” in diameter. Contact us for more information.

Non-Stick Graphite Gaskets Reduce Downtime

Study our website and you’ll see gaskets can be made from a wide range of materials. One of the most versatile yet under-appreciated of these is graphite. Graphite gasket temperature range handles temperatures from -400°F to +875°F, provide excellent dimensional stability and resist chemical attack. On top of that, they have an additional advantage that’s not obvious: they don’t stick to flanges.

The Cost of Flange Cleaning

When replacing a gasket it’s essential to clean flanges thoroughly. Many gasket materials stick to these flanges and have to be scraped off. That’s a problem, for two reasons. First, there’s a risk of scratching the faces while scraping, and that can create leak paths. Second, doing the job properly, (and avoiding early replacement,) takes time.

As explored in “Focus on the Cost of Sealing,” (December 2015,) gasket replacement almost always means taking equipment, or even an entire plant, offline. Each application is different, but the cost of downtime usually dwarfs the price of even the most expensive gasket. The less time that’s needed to swap out the old gasket for the new one, the faster the plant gets back into production, so anything that reduces down time is worth considering.

Just Carbon

Graphite is one form of carbon. That’s the same element that forms diamonds. It’s strong, inert and resists temperature and pressure extremes, but what makes graphite special is its slipperiness. In graphite the carbon atoms are formed into layers that can slide over one another. That helps when closing up a gasketed joint because the material moves easily to fill uneven gaps and take up flange deformation or surface imperfections.

Graphite Gasket Materials

Here at Hennig Gasket we carry graphite material in a range of sheet thicknesses and widths as well as flexible homogenous graphite rolls. These can be cut to practically any desired shape and provide excellent sealing in many different applications. For especially challenging applications ask about the graphite-sided kammprofile gasket. Whichever graphite gasket you choose though, you can be sure of one thing; you won’t waste time scraping old material off the flanges!

Does Your Application Need a Graphite Seal or Gasket?

High temperatures challenge many gasket materials. Nitrile gaskets will go up to about 95oC, silicone gaskets to 200oC and PTFE to 260oC, but what if you need to go higher? One option is to go with a metal gasket. A better one is to ask about graphite. Graphite seals and gaskets retain their properties at temperatures as high as 450oC, and have some other very useful sealing characteristics.

Properties of graphite

Graphite is a form of carbon where the atoms are arranged in layers or sheets. That lets them slide over one another easily, which translates to a slippery feel when rubbed between finger and thumb. (It’s also what lets a “lead” pencil write – graphite actually rubs off onto the paper.)

This slipperiness or low coefficient of friction is useful in gasketing or sealing. As mating surfaces are brought together graphite allows some slip. That accommodates any rotation or sideways movement as the clamping load goes on without damaging the sealing material. Used as a dynamic or shaft seal the low friction properties of graphite minimize energy losses and heat build-up while maintaining an effective barrier.

Graphite is also a very soft material, (which might seem odd when you consider it’s a cousin of diamond,) but that lets it flow into surface irregularities, which is what provides the sealing function.

Like PTFE, graphite is quite inert. It resists attack from most corrosive chemicals, even at high temperatures, and likewise doesn’t contaminate them.

Graphite seals and gaskets

It’s possible to buy graphite for use as a gasket or seal. It’s also used as a coating for some metal gaskets, (Kammprofile gaskets are an example,) where it provides excellent sealing performance along with temperature and chemical resistance. If you’re looking for gasket material for a high temperature application, ask Hennig Gasket if graphite seals might be right for you.

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.