PTFE Gasket Sheet – Three Things to Know

Sep 25, 2022

PTFE is an extremely useful gasket material. So useful that it’s sometimes purchased in sheet form for cutting to shape as needed. Here we’ll talk about the strengths of PTFE gasket sheet and then we’ll discuss three things you should know.

Pros for PTFE Gasket Sheet

PTFE is chemically inert, which makes it a good material for sealing against almost everything except fluorines and nitric acid. It also has a very wide temperature range. Grades vary but it’s generally usable from -100 to 500 °F. Famously slippery, its low friction surface is advantageous in some applications.

Your gasket supplier can cut PTFE gaskets to shape (waterjet and die cutting both work well,) or you can buy sheet PTFE and cut gaskets yourself. Thin sheet is readily cut by knife and thicker sheet is easily milled.

Important Things to Know

Besides the strengths of this material, it’s important to be aware of:

  • Tendency to creep
  • Limitations for food applications
  • Sheet thickness tolerances

Creep

Creep is a progressive, non-reversible deformation that occurs under load. This reduces clamping force, which eventually causes leaks.

The solutions are to either use it only in low-load applications, which is often impractical, or use a filled grade. PTFE fillers include glass, carbon, graphite, bronze and other materials, sometimes in combination. These raise strength but at the expense of a less slippery surface and reduced chemical resistance.

Food Limitations of PTFE Sheet Material

Pure PTFE is so inert it can be used in applications where it comes into direct contact with food. This is not true for the filled grades. These are likely to discolor or taint foodstuffs so are not permitted in such applications.

Sheet Thickness Tolerances

Thickness is an important gasket characteristic. Thickness tolerance depends on how the PTFE sheet is produced. The options are molding or skiving. Skiving entails cutting a thin layer away from the surface of a cylinder of PTFE, and it produces a more consistent sheet. For precise PTFE sheet thickness, specify skived material.

PTFE Sheet From Hennig Gasket & Seals

We can supply molded and skived sheet 60” square. Thicknesses range from 1/32” to 4”. Contact us to learn more

PTFE Gaskets
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Hi-Temp Gasket Material Applications

Jul 01, 2022

Most gasket applications are satisfied by various forms of synthetic rubber. Neoprene, NBR and SBR for example all work well when temperatures are below 200 °F. Above this, things get more complicated. If you have an application for hi-temp gasket material, here’s what you should know.

How Hot is Too Hot?

Gasket material specifications sometimes give a range for the upper temperature limit. This is because there’s no single temperature at which a material stops working. Instead, it breaks down gradually.

Heat hardens rubber and rubber-like materials, but time at temperature is as important as the peak value the material sees. Pressure is another factor: in a high-pressure application it might be prudent to use a material with a higher upper temperature limit.

Most commonly-used gasket materials top out at around 200 – 225 °F. If you have an application where temperatures are consistently above 225 °F consider exploring options for high temperature gasket material.

Hi-Temp Gakset Material:  Elastomeric Materials

With a sustained temperature limit of 225 °F, EPDM is an elastomer that goes hotter than NBR, SBR and Neoprene. Most grades of silicone, fluorosilicone and fluorocarbon (Viton) gasket material will endure 500 °F, and 600 °F for short periods.

Hi-Temp Gasket Material:  Compressed Non-Asbestos and PTFE

Compressed non-asbestos materials are composed of fibers, (mostly aramid,) in an elastomer binder such as NBR or SBR. The fibers provide strength and pressure resistance and the binder holds them in place.

Compressed non-asbestos materials are made in many grades and formulations but most will withstand up to 750 °F. In contrast, the limit for PTFE is 600 °F.

Very High Temperature Gasket Materials

Choices are limited for temperatures above 750 °F but one of the most widely used materials is vermiculite (a clay-like mineral.) This is either applied to a solid gasket or incorporated into a spiral wound gasket for pipe joints. Its upper temperature limit is around 1,800 °F.

Advice on Gasket Materials for High Temperatures

High temperatures are bad for many gasket materials. As gasket material suppliers of a large inventory of materials, ask us for a material quote if you need to seal hot fluids or in a hot environment.

High Temperature Gaskets
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Fiber Gasket Material – It’s Broad Meaning

Jun 20, 2022

Although the word “fiber” is often used to describe sheet gasket material, fiber gasket material is a very broad category. In this blog post we’ll explore what types of material count as “fiber” and when and why you might want to use them.  Hennig Gasket & Seals is gasket material suppliers of all types. 

Two Main Categories of Fiber Material

“Fiber” can refer to vegetable fiber gasket material, or to sheets composed of fibers bound in an elastomeric matrix. Each provides varying levels of the temperature and chemical resistance, strength, and conformability needed in a good gasket, but there are differences between them. What’s more, within each category there are many variations of composition.

In addition, “fiber” can also mean ceramic fiber or cellulose-based gasket material. Those are quite specialized and won’t be covered here, but if you’re interested in them the specialists at Hennig Gasket  can help.

Vegetable Fiber Gasket Material

This material is made by a similar process to papermaking. Plant material is crushed and pulped to leave a mass of fibers. These are spread and dried as sheets.

Vegetable fiber gasket material, often referred to as “Detroiter” material, is very thin and has good dielectric properties. It’s resistant to water, air and most fuel oils, as well as gasoline and benzine. Adding cork to the mix results in a thicker, more compressible material.

Compressed Fiber Gasket Material

This is made by mixing aramid fibers in an elastomer like NBR or SBR, then rolling it into sheet form. Aramid is a contraction of aromatic polyamide, which is a high-strength synthetic polymer. (One of the tradenames it goes by is Kevlar.)

In gasket applications aramid supplies strength and temperature resistance while the elastomeric binder provides compressibility. Manufacturers tailor the material to specific gasket applications through elastomer selection and by varying the amount of aramid used.

Compressed fiber gasket material offers strength, good compressibility, and creep-resistance. Chemical resistance depends on the type of elastomer incorporated. As gasket material suppliers of a wide range of compressed fiber gasket material from well-known manufacturers like Garlock, Klinger, UTEX, Flexitallic and JM Clipper, we have the material to accmodate your application needs.

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What is Vellumoid and When Would You Use It?

Apr 28, 2022

The name may be unfamiliar but Vellumoid is one of the oldest gasket materials. Age hasn’t rendered it obsolete though and there are still applications where it may be a good choice. In this blog post we’ll explain what Vellumoid Gasket Material is and where you might want to use it.

A Mix of Paper, Glue and Sugar

Vellumoid is cellulose fiber impregnated with a protein glue and gylcerin. It was developed back in the 1890s. Apparently seeking to develop a waterproof paper, the inventor created something that looked and felt like vellum, (a high-quality form of parchment.) And from those humble origins, they named it “Vellumoid”.

Today the Vellumoid company, based in Worcester, MA, has grown an entire family of materials from this simple beginning. The original material is sold as “Branded Vellumoid” while variants are impregnated with other materials that perform well in gasket applications.

Properties and Performance of Vellumoid

The original Vellumoid is very water-resistant, which was the original goal, and also holds up well against antifreeze, water-based cutting fluids, gasoline and lubricating oils. It’s also mold-resistant, (by virtue of the glycerin,) so is often a good choice in damp locations.

Compressibility is excellent, which is one of the traits that make it interesting for gasket use. However, tensile strength is low and the upper-temperature limit is 250⁰ F (121⁰ C).

Other variants of Vellumiod incorporate materials that improve properties. Velbuna WG-5 for example is impregnated with nitrile and withstands up to 300⁰ F (149⁰ C) and Vellutherm 600 goes up to 350⁰ F (177⁰ C).

When to Use Vellumoid

Excellent compressibility makes it good for sealing uneven flange surfaces. That’s something you might encounter when rebuilding or restoring vintage machinery, and where Vellumoid might help add authenticity. Of course, it will work just as well in modern piping systems carrying hot or cold water or similar fluids.

If you think Vellumoid might be a good choice for your application, contact us. We sell vellumoid in sheet form and can cut it to the size and shape you need.

Vellumoid Gaskets
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SBR Gasket Material: Don’t Overthink It

Apr 07, 2022

You have a lot of options when you’re looking for gasket material, and some of them can get very expensive. While it may be tempting to select a highly engineered polymer with exceptional temperature and chemical resistance properties, ask whether that’s what you really need. In many cases, you may be better off using Styrene Butadiene Rubber, better known as SBR Gasket Material.

SBR Gasket Material:  An Alternative to Natural Rubber Gasket Material

SBR red rubber gasket material was developed during WWII. At the time most rubber came from Asia, and as more rubber was needed for tires, scientists were searching for an alternative. Styrene-Butadiene Rubber, derived from the Buna polymer developed in Germany in 1929, met that need.

Natural rubber has many things in its favor as a material for gaskets as well as tires. It’s soft and elastic, with good compression recovery. That lets it conform to uneven flange faces and expand to fill the gaps. However, it doesn’t fair well outdoors and its temperature range and chemical resistance are so-so at best. SBR improves on natural rubber with a wider temperature range and better weathering and chemical resistance properties. It’s also a very economical choice.

Don’t Over-Engineer the Application

SBR Gasket Material isn’t the highest performing gasket material available, but for many applications, it’s good enough. Use it when temperatures won’t go above 170° F or below -30° F and for sealing against air, water and steam. Use it when flange faces may be uneven, and use it in applications that need good impact strength and abrasion resistance.

Don’t use SBR gasket material to seal against hydraulic fluid, solvents or oils as this will make it swell excessively. Neither is it a good choice for outdoor applications with exposure to UV and/or ozone.

Many alternative gasket materials provide higher performance but at a higher price. Rather than considering what might happen in-service, focus on what’s known for sure. You may find that SBR is up to the task and will save you some money. For more information, discuss your application with the specialists at Hennig Gasket & Seals.

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Gum Rubber Sheet: Cushioning and More

Feb 07, 2022

Gum rubber sheet is natural rubber in an industrial form. It’s very flexible, has great elongation, high resilience, and resists abrasion and tearing. This makes it one of the best materials for cushioning against impacts and damping vibration. There are a lot of man-made, synthetic versions of rubber but for many applications, and especially for cushioning, it’s hard to beat the original, natural gum rubber sheet material.

Gum Rubber: An Elastomer That’s Grown

Gum or natural gum rubber is made from the sap of the rubber tree, Hevea brasiliensis. The tree is cut to release the sap, also known as latex. This is allowed to coagulate before being passed through rollers to produce sheets. From here additives go in and the rubber is vulcanized to increase cross-linking. The resulting material is chemically very similar to synthetic rubbers like SBR and nitrile.

Properties of Gum Rubber Sheet

As a natural product, there’s always some variation in how gum rubber behaves. In general, though, tensile strength is around 2,800 psi, elongation is a hard-to-beat 550%, and compression set is very low. Gum rubber is known for being extremely flexible, and it remains so down to around -40 °F. Its upper-temperature limit is a relatively low 140 °F, making this one of its limitations.

Gum rubber resists attack by most acids, alkalies, and organic salts, (such as citrates.) Its chemical weaknesses are oils, gasoline, and hydrocarbon solvents. It’s also susceptible to attack by UV light and ozone, which means it’s not a material for prolonged outdoor use.

Gum Rubber Sheet Applications

Flexibility and resilience make impact absorption one of the main uses of this material. That’s why it’s a good choice for cushioning pads and bumpers and why it’s also used for vibration absorption.

Gum rubber is used in seals of various types, such as around doors and for skirting around containers and hoppers because it’s very flexible. Conveyor belt scrapers are another use.

Ask Hennig Gasket & Seals for Gum Rubber Sheet available up to 48″ wide and a range of thicknesses.

 

Rubber Gaskets
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Four Applications for Felt Gaskets

Jan 11, 2022

Industrial felt is a nonwoven textile made from wool, polyester, or a combination of the two. If you think felt is just a crafting material, think again. Industrial felt is produced to rigorous specifications and felt gaskets are found in a wide range of applications.

Basics of Felt Gasket Material

Industrial felt is made by entangling wool and other fibers. It’s sold in roll form and in a range of thicknesses and densities. It can be supplied with a PSA to simplify installation.

SAE standards assign F numbers to felt, which makes it practical to specify the type needed. Those most often used for gaskets are F-3, F-51 and F-55 although other grades are available.

Felt resists tearing and abrasion and polishing rather than wearing metal surfaces it rubs against. It’s compressible with good elastic recovery, and when made from wool it’s considered a “green”/sustainable material. Perhaps the most interesting thing about felt though is its open structure. This lets it hold and filter fluids, which leads to a host of applications.

Four Felt Gasket Applications

The main uses are:

  • Sealing

Felt gaskets are used as bearing seals and as wipers in motion systems. The fibrous structure stops dust from reaching the bearing surface and can also retain oil or grease for lubrication.

  • Lubrication

Felt is comparable to foam in how it can hold oil but has the advantage of “wicking” behavior. This refers to how it can “suck up” oil, which makes it an effective way of lubricating shafts and guideways.

  • Filtration

Felt is an excellent material for removing particulates from liquids and gases. It works down to micron level and can be oil-impregnated for even higher performance.

  • Noise and vibration attenuation

Felt gaskets are used in architectural and automotive applications to reduce the transmission of noise and vibration. This results from individual fibers absorbing energy by rubbing together rather than transmitting it.

Discuss Your Application With Us

If sealing, lubrication and filtration are of interest, talk to us. Our specialists can review your application and recommend a felt to improve performance, reliability and life. Contact us today!

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Sponge Rubber for Sealing

Jan 10, 2022

Gaskets seal mating surfaces. They do this by deforming under pressure to take up surface imperfections. Softer gasket materials provide more deformation, and if you’re looking for a material that deforms a lot, sponge rubber may be what you need.

Basics of Sponges

A sponge material contains a large number of holes. This makes it lighter than a sold piece of the same material and gives it the ability to hold fluids in those holes, (better-called pores.).

The properties of a sponge derive from a combination of:

  • The material – neoprene, nitrile, EPDM, and silicone are the most common
  • Pore size and distribution – more pores reduce density and larger pores hold more fluid
  • Whether pores are open or closed

Open Vs. Closed Sponge Rubber Gasket Material

If pores are interconnected in a way that lets fluid move through, the material has an open cellular structure. Washing sponges have this characteristic to hold water and release it when compressed.

Sealing/gasketing applications generally need a closed structure. Here the pores are filled with nitrogen gas generated during manufacture and are not connected. Squeezing a closed cell sponge material compresses the nitrogen, which adds to the elastic behavior of the material.

The firmness of Sponge Rubber Sealing Material

Closed-cell materials are firmer than those with an open structure. Material manufacturers typically refer to sponge rubber as being soft, medium or firm. They may also reference density with a denser material being firmer.

Using Sponger Rubber for Sealing

Solid rubber materials spread sideways when compressed. This can be a problem in sealing applications where the material will be deformed a lot. An advantage of sponge over solid rubber is that it doesn’t spread out significantly.

Sponge rubber is used for vibration damping because the cellular structure provides a form of mechanical impedance. It also makes a good shock absorber and a thermal insulator. Common sealing applications are those where an air or watertight seal are needed but pressures are low. Hatches, doors and panels are examples.

For more information, or to discuss a specific application, speak with a specialist at Hennig Gasket.

Sponge Rubber
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Where Not to Use Nitrile Rubber Gaskets

Dec 09, 2021

Nitrile rubber, also known as NBR and Buna-N is a useful gasket material that many buyers refer to as nitrile. Useful though it is, Nitrile Rubber Gaskets are not a solution to every sealing challenge. Here’s some advice on when and when not to use it.

Properties of Nitrile Rubber

Nitrile or NBR is a synthetic rubber with good flexibility and resilience over a temperature range of -30 to +200 °F (-34 to +93 °C). It has good strength and abrasion resistance and a low compression set, all of which make it an effective gasket material. It’s also available as FDA-approved white nitrile for food industry applications.

A particular strength of nitrile is its ability to withstand attack by oils and fuels. Many gasket materials swell and break down when exposed to lubricants, hydraulic fluids or gasoline, but not nitrile. As a result, it’s used extensively with engines, generators, and fuel and hydraulic systems.

It does however have some weaknesses. It’s not for high-temperature applications, it doesn’t have good weather resistance and it will be attacked by polar solvents.

Polar Solvents and Nitrile Rubber Gaskets

Polar solvents are those where the molecules are composed of atoms with significantly different electrical charges. One example is oxygen and hydrogen. Others are acetone, ethanol, and acetic acid. In chemistry terms, these are considered to have a high permittivity or dielectric constant. You might notice that compounds with a high dielectric constant, like pure water, are also good electrical insulators.

Nitrile is susceptible to attack by polar solvents like those listed above. Interestingly though, while water is also polar, it’s a solvent to which nitrile has some resistance. However, for sealing against water, better gasket material choices would be neoprene or EPDM.

Consider Conditions Before Asking for Nitrile

Nitrile Rubber gasket material is a good choice for sealing against fuels, oils, and lubricants. It should not be used with chemicals like acetone, ethanol, and acetic acid. Neither should it be used outdoors or where temperatures exceed 200 °F. If the application involves water, check with a materials specialist at Hennig Gasket before ordering.

Nitrile Gaskets
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Slippery PTFE Washers

Oct 08, 2021

PTFE is an excellent material for a wide range of sealing applications, including PTFE washers. Being chemically inert, it resists attack by almost all acids and alkalis. It’s soft, so it deforms readily to fill uneven gaps between surfaces, and it remains flexible and useable over a wide temperature range, (in comparison to other gasket materials). It’s a good thermal and electrical insulator, but it has one other useful attribute: low friction.

Low-Torque Tightening

Low friction means other surfaces experience almost no resistance as they slide over PTFE, (also known by its Chemours tradename, Teflon.) That’s advantageous when closing up a joint where one surface slides against the seal or gasket as it means all the applied force goes into the joint.

A product that exploits this behavior is the PTFE washer. Consider this a special type of gasket that benefits from low friction. Slippery surfaces help ensure the fastener fitted over the washer seals without moving or tearing the washer surface.

Applications for PTFE Washers

  • Plumbing — use PTFE washers under bolts and when fastening fittings to delicate or easily marked surfaces
  • Electronics — insulating properties and high-temperature resistance make PTFE washers a good choice for distributing screw loads in electrical assemblies
  • Mechanical assemblies — PTFE washers let bolt heads tighten down without putting and stresses into the surface underneath
  • Food industry – PTFE is available in food grades and withstands aggressive cleaning regimens

PTFE Washers:  Shapes, Sizes, and Forms

PTFE comes in sheet form and both filled and pure PTFE grades. It’s readily die-cut, water jet cut, and flash cut.

While there’s an assumption that washers are circular, they don’t have to be. Hexagonal shapes will utilize the PTFE sheet better while squares and rectangles may be more useful in some applications. Tabs can help resist rotation during fastening, although the slipperiness of PTFE means this is rarely an issue.

We are happy to provide a quote for PTFE washers custom fabricated to your specs.

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