What is Vellumoid and When Would You Use It?

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.

SBR Gasket Material: Don’t Overthink It

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.

Gum Rubber Sheet: Cushioning and More

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.


Four Applications for Felt Gaskets

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!

Sponge Rubber for Sealing

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.

Where Not to Use Nitrile Rubber Gaskets

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.

Slippery PTFE Washers

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.

When to Use EPDM Rubber Gaskets

EPDM is a soft, silicone-like material suitable for a wide range of gasket applications. It’s often molded into seals and ‘O’ rings but it’s also produced in sheet form of various sizes and thicknesses. This is ideal for laser, waterjet and die-cutting custom gaskets. Like all gasket materials though, EPDM does have some limitations. Here’s some guidance on when and when not to use EPDM Rubber Gaskets.

EPDM Gasket Material Basics

EPDM is an acronym for Ethylene Propylene Diene Monomer. The short version of the chemistry explained in, “Understanding EPDM Gasket Material,” is that this forms long interlocked molecular chains. This gives it an elastic behavior somewhere between neoprene and silicone.

Strengths of EPDM Rubber Gaskets

EPDM has characteristics that make it good for a wide range of gasket applications. Chief among these are:

  • Withstands attack by a wide range of chemicals including acids, alkalis and ketones
  • Good resistance to steam and caustic cleaners
  • Good resistance to UV light
  • Remains flexible at temperatures as low as -40°F (-40C)
  • Upper temperature limit around 225°F (107°C)
  • Good ozone resistance
  • Good dielectric properties mean it’s a good choice for electrical sealing
  • Good abrasion resistance
  • Excellent elastic recovery.
  • Won’t impart a taint to liquids or solids it comes into contact with

Limitations of EPDM Rubber Gaskets

EPDM should not be used with oils and fuels as these cause swelling. The upper limit to strength is around 1100 PSI.

Good Applications for EPDM Rubber Gaskets

EPDM works where the application needs a gasket material more robust than neoprene and less expensive than silicone. The three main classes of application are:

  • Food and drink processing equipment (mixer seals is a common application) as it’s available in food grades and withstands aggressive cleaning regimens.
  • Sealing outdoors, where it withstands low temperatures and exposure to UV.
  • Electrical cabinets and enclosures, where ozone may be generated.

More Information

If you have a gasket application that needs a more robust material than neoprene, EPDM might be the answer. Contact the specialists at Hennig Gasket to learn more.

Viton Washers for Fuel and Hydraulic Systems

Gasoline, diesel and hydraulic oil are some of the hardest fluids to seal against. They make most gasket materials swell, which increases pressure on the joint and leads to gasket failure. Nitrile rubber is one of the rare exceptions but its upper temperature limit is around 200⁰F. If you’re concerned that nitrile won’t be up to the job it’s time to move to Viton washers.

Viton™, FKM and FPM

The first thing to know about Viton is that it’s a trademark, (originally held by DuPont and now their spinoff, Chemours.) The technical term for this type of elastomer is a fluoroelastomer. In lay terms, it’s a synthetic rubber composed mostly of carbon and fluorine. In Europe fluoroelastomers are designated as FPM while here in the US we use the ASTM abbreviation of FKM. Whichever term you use, they’re essentially the same thing.

Properties of Viton and Other Fluoroelastomers

Viton and other fluoroelastomers are more expensive than almost any other gasket material, but three characteristics make them the preferred solution for the toughest sealing challenges:

  1. Excellent resistance to oil-induced swelling
  2. Highly resistant to most chemicals
  3. High-temperature strength (Viton goes to 400⁰F (204⁰C) and higher)

In addition, Viton has good UV and ozone resistance. Other points to note are that, while sufficient for most applications, tensile strength and resilience or elasticity are not high. Also, Viton is incompatible with acetone and many organic acids.

Applications for Viton Washers

High cost means Viton is reserved for difficult applications. Sealing pipes and fittings in fuel and hydraulic oil systems is a good example. Viton washers are a cost-effective way of minimizing the risk of potentially hazardous leaks and costly downtime in these situations. Likewise, it’s often the smart choice in systems handling corrosive chemicals where leaks must be prevented at all costs.

Viton Washers and Gaskets From Hennig

Viton comes in sheet form and a number of grades. We can water jet, flash or die cut the size and shape you need. Our specialists can help you decide what’s right for your application. Call (312) 243-8270 or 1-800-747-7661 or contact us.

Neoprene: It’s For More Than Wetsuits

Surfers and divers are very familiar with neoprene. It’s been the material of choice for wetsuits for decades. It’s also a versatile gasket material, although used in a different form to wetsuit material. Here’s what you should know about neoprene gasketing.

Synthetic Rubber

Neoprene is a DuPont tradename for polymerized chloroprene, which is one of the synthetic rubbers developed in the 1920s and 1930s. Chloroprene is composed of carbon, hydrogen, and chlorine which produce a clear liquid. Polymerization forms the molecules into long chains that interlock to create a soft, flexible material.

Neoprene is made as a solid, (described as homogenous neoprene,) and closed-cell foam. It’s this latter version that’s used in wetsuits with the pockets providing thermal insulation. Foamed neoprene provides good cushioning and is used for gasketing as it forms a soft, waterproof seal. (Pressure-sensitive adhesive applied to one or both sides makes it easier to fix in place.)

Neoprene is also used as a binder with Aramid fibers. This results in a higher-strength neoprene gasket.

Neoprene Properties for Gaskets

Being soft, (40 – 70 Shore A durometer,) and flexible with good elastic recovery, homogenous neoprene conforms readily to mating surfaces. It has excellent water resistance, (hence the wetsuit usage,) and also withstands oils, ozone, and some acids. Food grades are available.

The practical temperature range for neoprene gasketing is -20 to 180°F. This makes it unsuitable for sealing steam or other hot fluids. A bigger limitation is a lack of strength. Depending on grade, maximum tensile strength is 900 – 1,000 psi, meaning neoprene is not suitable on its own for high-pressure applications. Bound with Aramid though, it offers much higher strength.

Ask Us About Neoprene Gasketing

Homogenous neoprene comes in sheet and roll form up to 72” wide and in a range of colors. Thicknesses range from 3/32” up to 2”. We can waterjet, flash, or die-cut neoprene to the size and shape you need. If you’re looking for inexpensive gasket material and don’t need high strength, neoprene may be the gasket material for your application. Call us to discuss.