Selecting Materials for Rubber Washers

Dec 15, 2024

Rubber washers are used for two types of application: sealing and vibration damping. Another use is load-spreading in fastening applications, but this usually requires metal, so isn’t covered here. What is covered are some principles to use when selecting washer material and an overview of the materials available. First though, what are washers and where are they used?

Rubber Washer Basics

A washer is a disc-shaped piece of thin material with a hole through the center. The hole typically takes a screw or bolt, the head of which is bigger than the hole and fits over the washer.

One category of applications is sealing, typically in faucets and valves. In use the washer creates a seal against a mounting face to close off the flow of fluid. The washer material needs abrasion resistance, because it slides against the face as the valve is closed, and good recovery so it springs back to its original dimension.

The other category is vibration damping. Circuit boards are a good example. A screw through a hole in the board mounts it to the chassis. A rubber washer between the screw head and the board provides security while reducing vibration from the chassis.

Material Selection Guidelines for Rubber Washers

When selecting rubber washer material, consider:

Temperature – the range the material will see
Environment – exposure to sunlight, ozone
Media – the fluid being sealed
Pressure – the loads being applied

Materials for Rubber Washers

“Rubber” is a generic term for elastomers that are flexible and compressible at room temperature. Materials that can be used, subject to the criteria listed above, are:

Red rubber/SBR – temperature range of -22 to 158°F, good abrasion resistance
Nitrile – temperature range of -40 to 225°F, resistant to most fats, oils, fuels and water
Neoprene – good water resistance
EPDM – resists most chemicals and oils
Silicone – exceptionally wide working temperature range
Viton® – resists oils and fuels, wide temperature range

Select for the Application

Washer material should be chosen with the same care as is used for gaskets. Hennig Gasket and Seals stocks a wide range of suitable materials and can cut custom sizes to order.

Applications, Rubber Gaskets

Comments are off for this post

What to Consider for a Valve Cover Gasket

Nov 14, 2024

Valve covers can be hard to seal. That’s because they’re often made from thin material that bends as the fasteners are tightened. The result is uneven compression of the gasket material, which often leads to leaks. If you’re looking for a valve cover gasket for industrial equipment or an engine application, here’s what to consider.

Standard Gasket Material Factors

As with every gasket application, the first points to determine are:

Temperature of the media being sealed
Environment – where the gasket will be placed in service
Media – does it have corrosive properties and what gasket materials is it incompatible with?
Pressure – the load the gasket will be subjected to determines the material strength needed

Establish these and you’re on your way to determining the best material for your valve cover gasket, but there is one other point to consider.

Dealing with Deflection

If the valve cover is likely to deform as it’s tightened down the gasket material needs enough compressibility to not leave any gaps. This leads to softer, (lower durometer, in the case of elastomeric materials), and thicker materials. Softness ensures sufficient deflection while thickness matters because of the percentage deformation needed. (1/16” deflection is a smaller percentage of gasket material ¼” thick than if the material is only 1/8” thick.)

Candidate Gasket Materials

The application will determine the material. If you’re sealing a valve cover on a diesel engine with high temperatures and oil, an aramid fiber gasket might be the right choice. (Frenzelit Novatec® fiber with graphite gaskets provide good chemical resistance and handle high temperatures.)

Elsewhere, perhaps in air compressors or covers over industrial valves, rubberized cork can be effective. In select cases NBR gasket material or EPDM gasket material may work well too.

Replace, Don’t Reuse

It can be tempting to reuse a valve cover gasket when the joint was only opened up for an inspection. Don’t do this.

Most gasket materials take a compression set. This means they don’t spring back to their original thickness. The amount may be too small to see, but reusing the gasket risks leaks.

Contact Hennig Gasket & Seals for custom sealing solutions.

Applications, EPDM Gaskets

Comments are off for this post

Food-Grade Silicone Gasket Material

Oct 01, 2024

A number of gasket materials meet the FDA’s criteria for being Generally Regarded as Safe (GRAS) but the most versatile is silicone gasket material. FDA-compliant silicone rubber is a good choice for sealing and other applications in the food and beverage, medical and pharmaceutical industries. Here’s what you should know.

The Risks of Indirect Contact

Material used for gaskets and seals shouldn’t end up in food or other substances consumed by humans, but it can come into contact with them, either accidentally or by design. Solids and liquids may for example touch the seals and gaskets used in mixers, kettles and storage vessels.

If this happens, especially at elevated temperatures, there’s a risk of some of the chemicals in the seals being picked up by the foodstuff. In the best case, this might impart a taint or color but, depending on the details of the material, it could transfer potentially harmful chemicals that end up being ingested.

To avoid this, always use FDA-compliant materials wherever contact with foodstuffs is possible.

FDA Regulations

Among other activities, the Food and Drug Administration (FDA) regulates the materials used in food, beverage and pharmaceutical manufacturing. For elastomers like those used in gaskets and seals, the relevant regulation is 21 CFR 177.2600. This identifies what can and cannot come into contact with anything consumed by humans.

Some materials are considered GRAS, meaning their use is permitted. FDA-compliant silicone rubber is one such material.

Food-Grade Silicone Gasket Material

Silicone is an excellent material for gaskets. It’s soft but doesn’t take a compression set, and springs back to its original size when unloaded. It has a working temperature range of -67 to 450°F, and it resists mild acids and oils.

Food-grade silicone is almost always white, because it’s the colored additives that can result in contamination. Some buyers will ask for “white silicone” but this doesn’t guarantee it meets FDA standards. To be safe, when buying food grade silicone, always specify compliance with 21 CFR 177.2600.

We carry FDA-compliant silicone rubber in 48″ wide rolls and thicknesses from 1/32 to 1/4″. Cutting services are available.

Silicone Gaskets

Comments are off for this post

Waterjet Cutting for Soft Gasket Materials

Sep 01, 2024

Soft gasket materials like sponge rubber are tricky to cut accurately because they tend to distort. We deal with this by offering waterjet cutting. It’s a fast and efficient process that’s ideal for cutting large, complex shapes from thinner material. Here’s why to ask for it.

What is Waterjet Cutting?

The process uses a thin jet of fast-moving water to slice through material. The machines look like laser cutters with a gantry that moves the cutting head over a sheet of material. A pump pressurizes the water to around 90,000 psi, forcing it through an orifice 0.015” diameter. This stream of water moves faster than sound, which lets it wear away material it flows against.

For faster cutting an abrasive material is fed into the stream. Abrasive waterjet cutting can cut metals as well as non-metals.

Advantages for Gasket Materials

Applies little force to the material being cut, which minimizes distortion
Accuracy of +/-0.007”
Kerf (the width of the material cut away) less than 0.050”
Tight nesting is possible to improve material utilization
Cut holes with diameters as small as 20% of the sheet thickness
Cut stacks of sheet material: Maximum cut thickness is around 6”, although this is material dependent

In comparison with laser cutting, two advantages are:

No heat affected zone on material edges
High cutting speeds on nonmetallic materials: Rubber sheet ¾” thick can be cut at up to 90’/minute.

Limitations

As the jet moves through the material it deflects rearwards from the direction of travel and can waver slightly from side to side. This results in striations along the sides of thicker material and requires lower speeds when moving into corners.

On thick material jet divergence creates a slight taper from top to bottom. This is handled by angling the waterjet away from the edge of the piece being cut, so putting all the taper in the offcut “lace”.

Gaskets Cut by Water

Hennig Gasket and Seals can waterjet gaskets up to 6’x8’ and 5’x13’. If you’re interested in waterjet-cut gasket material, contact us for a quote.

FAQs

Comments are off for this post

Fuel-Resistant Gasket Materials

Aug 01, 2024

Gasoline, diesel and kerosene are difficult fluids to seal. Pick the wrong material and you risk a flammable liquid leaking. In this blog we’ll discuss fuel-resistant gasket materials and why it’s important to choose from the short list of those available.

The Fuel Sealing Challenge

Hydrocarbons, the basis of most liquid fuels, cause many materials to swell. This happens because either fuel causes a chemical reaction in the material, it acts as a solvent and partially dissolves the material, or the material absorbs some of the fuel. With some fuel/material combinations all three are possible.

These changes increase the load on the joint and may make the gasket extrude out sideways. They’ll also make the material less elastic and therefore more likely to fail. What’s more, the changes aren’t reversible.

The Best Fuel-Resistant Gasket Material

The first choice for almost every fuel application should be nitrile rubber, sometimes called NBR or Buna-N. Nitrile is a synthetic rubber with a working temperature range of -30 to 200⁰F. Hardness is typically 60 – 80 shore and it resists compression set and abrasion.

Nitrile resists attack by a long list of chemicals, especially hydrocarbons like oils, greases and of course fuels. Other chemicals it withstands include ozone plus solvents like acetone and MEK.

Alternatives to Nitrile

Most fuel applications don’t need the gasket material to have a high upper temperature limit. If this is necessary the best alternative is probably FKM/Viton®. Viton remains flexible at up to 400⁰F and has similar fuel-resistance to nitrile rubber. The main reason for choosing nitrile over Viton, assuming the upper temperature is below nitrile’s limit, is cost. Viton is not cheap.

Another fuel-resistant gasket material to consider is PTFE. This lacks the compressibility and elastic recovery of nitrile or Viton but conforms readily to uneven surfaces and has a very wide working temperature range.

Nitrile Rubber From Hennig Gasket & Seals

We carry nitrile gasket material in a range of sheet thicknesses and can waterjet, flash or die-cut it to the precise geometry you need. Contact us for more information.

Nitrile Gaskets

Comments are off for this post

Rubber for Vibration Damping

Jul 01, 2024

Another use for rubber, besides sealing and impact absorption, is vibration damping. This is where its natural elasticity is used to absorb vibrations rather than letting them spread through a machine or structure.

Most elastomeric materials will dampen vibration to an extent, although the reduction is related to vibration frequency. Vibration dampening rubber however is rubber that’s been optimized for the purpose of reducing vibration transmission.

Why Dampen Vibration?

Vibration in a structure can loosen fasteners, accelerate fatigue and cracking, and transmit sound. Thrumming in air ducts is an example of this last effect where air movement makes panels vibrate.

Vibration is reduced by placing an absorbent material between joints. As vibrations pass from the rigid members into this softer material, they make it compress and recover. This absorbs energy that would otherwise be transmitted through the structure.

In the case of vibrating panels the solution is a little different. Here the goal is to stop the panel moving. This is done by adding mass, often in the form of a heavy elastomeric (rubberlike) material. This might be bonded to the surface or can be sprayed on like a paint.

Vibration Dampening Rubber

Natural rubber or gum rubber makes an excellent vibration-absorbing material. Firmness is measured by durometer with lower durometer material being softer and more vibration-absorbing.

Gum rubber is flexible from -40°F but its upper limit is only around 140°F. It tends to harden when exposed to UV, so is best restricted to indoor applications. Its resistance to acids, alkalies, and citrates is good but it is attacked by oils, gasoline, and hydrocarbon solvents.

Closed cell rubber has excellent vibration dampening characteristics with the cell walls acting like micro-springs. It does however lack strength and can be damaged if over-compressed.

Damping or Dampening? Hennig Doesn’t Mind

We have it on good authority that either word works. “Dampen” means to reduce, which is why some people prefer that to “damping” which is the act of dampening. Whichever you like to use is fine with us. Just remember to consult our specialists for your vibration dampening rubber needs.

Rubber Gaskets

Comments are off for this post

Introduction to Pump Packing Materials

Jun 01, 2024

Packing is a simple but cost-effective way to minimize leakage from around pump shafts. Over time though, it needs periodic adjustment to take up wear. Eventually, when the pump packing material no longer seals effectively, it must be replaced.

This blog provides an overview of packing and discusses the options for pump packing materials.

Sealing Around the Shaft

A fundamental challenge in pump design is to prevent the fluid being pumped from escaping along the impeller shaft. Mechanical seals are an option, but they add complexity and cost. As a result, most pumps rely on compression packing.

Packing involves surrounding the shaft with a braided, rope-like material. This is pushed into a region of the pump housing called the stuffing box. A cylindrical packing gland is passed over the shaft and used to compress, (or stuff), the packing material around the shaft. The gland, sometimes called the follower, is bolted into place to maintain compression on the packing. As the packing wears, these fasteners are tightened to maintain the seal.

Friction, Heat and Leakage

As the packing material presses against the shaft, rotation generates heat from friction. To prevent overheating, the packing gland is tightened to a level that allows a very small leak. Thus the fluid being pumped the both lubricates and cools the packing-shaft interface.

This creates two challenges: the packing material must withstand sliding contact with the shaft, and it must also have appropriate chemical compatibility.

Options for Pump Packing Materials

The principal material choices are fabric reinforced rubber and graphite. Homogeneous rubber with no reinforcement works in some applications while expanded PTFE with graphite fiber is used in others.

At Hennig Gasket & Seals we carry a wide range of Garlock pump packing materials. Their Chevron® line has solutions for most packing needs, while for abrasive liquids Garlock SLUDGE-PAK® is often the answer.

Packing material selection is driven by shaft speed in surface feet per minute, and fluid type and temperature. For advice on what will suit your application, please have this information to hand when you contact us.

Garlock Gaskets

Comments are off for this post

What is Compressibility of Gasket Material

May 01, 2024

Compressibility goes to heart of what gaskets do. Here we’ll explain what gasket compressibility is and why it’s such an important property of gasket materials.

Compress to Seal

Gaskets are used to seal mating services, particularly between flanges. They take up imperfections in the two surfaces that would otherwise let the fluid being sealed leak out, and accommodate any changes in the gap as might be caused by temperature changes or vibration.

Gasket material works by deforming against the harder flange to take up even microscopic deviations in the surface. Compressibility is a measure of how readily the material does this.

Recovery From Compression

Gasket compressibility goes hand-in-hand with recovery. This is the degree to which the material springs back to its original thickness after being compressed.

Recovery matters because every joint is somewhat dynamic. Whether it’s opened and closed repeatedly, like an access door or panel, or just subject to varying temperatures, loads and vibrations, the effective gap being sealed will keep changing size. To maintain a seal the gasket material must expand and compress with these changes.

Closely related, compression set is when a material doesn’t spring back to its original thickness as the clamping load is removed.

Compressibility Measurement and Specification

The ASTM F36 test provides a standardized way of measuring gasket compressibility. The data needs some interpretation because the test conditions almost certainly don’t replicate your application, but it lets you compare materials.

Compressibility is stated as a percentage of the original thickness. Recovery is given as a percentage of the compression.

Material Selection Considerations

In general, materials that compress readily under light loads lack strength. Open cell foam is a prime example. You wouldn’t use this to seal a pressurized gas or liquid as it would almost certainly fail.

EPDM, neoprene and cork are examples of materials with good compressibility. Higher strength materials tend to have lower compressibility.

Gasket material manufacturers publish ASTM F36 test data, but for advice on a specific application, consult a gasket specialist, like those at Hennig Gasket & Seals.

FAQs

Comments are off for this post

Synthetic Cork for Gaskets: Advantages & Properties

Apr 01, 2024

Cork is one of the oldest gasket materials, but it still has a role in sealing applications. It’s a flexible, closed-cell material that resists water and oil, and has excellent compressibility. However, as a natural material – cork is the bark of the cork oak tree – it can vary in quality. It’s also susceptible to various types of mold.

Synthetic cork is intended to have the same wide set of useful properties but without these limitations.

Composition Cork Vs. Cork Rubber

The natural cork used for gaskets is almost always composition cork. This is a conglomeration of cork particles held together with a binder. It’s produced in sheets up to ¼” thick and is usually die cut to produce gaskets.

The synthetic cork used for gaskets, also known as rubberized cork or cork rubber, improves upon composition cork by adding an elastomeric material. Rubberized cork is usually composed of 70% natural cork particles and 30% neoprene or NBR.

In addition to its role as a gasket material, natural cork has long been used as a stopper for wine bottles. In recent years supply shortages and problems resulting from natural variability have prompted development of synthetic cork. Made primarily from polyethylene, this works for sealing bottles, but isn’t going to make good gaskets.

Properties of Rubberized Cork

Neoprene resists oils and greases. Cork made with NBR resists these plus fuels and many solvents. The upper temperature limit for both is 250 °F.

Good applications are those that need a very compressible material. Flanges with uneven surfaces and those made from material that deforms under load are often best sealed with rubberized or synthetic cork gasket material.

Hennig, For All Your Gasket Material Needs

When replacing a gasket it’s usually best to stick with the material that came out. If that looks like a composition or synthetic cork, we can help. We carry rubberized gasket material in sheet and roll form, up to 48” wide and ¼” thick. Synthetic cork is readily die cut to the shape needed. Contact us for a quote.

Cork Gaskets

Comments are off for this post

Measure the Hardness of Rubber Gasket Material

Mar 01, 2024

When specifying gasket material, along with factors like strength, working temperature range and chemical resistance, it’s important to consider hardness. Hardness determines how well a material fits against uneven surfaces, with softer materials performing better.

The hardness of rubbers and other elastomeric materials is specified primarily in terms of durometer or Shore number. Here’s an introduction to this rubber hardness scale.

Measurement by Indentation

Hardness is generally measured by pressing a point into a sample of material. Measuring the size, depth, or both, of the resulting indentation indicates the hardness.

For materials softer than metals, hardness is measured with durometer. This uses a calibrated spring to push a conical foot into the material. The foot penetrates further into softer material with depth inversely proportional to hardness.

A procedure for durometer testing is given in ASTM D2250. This standard covers factors like test duration, material temperature, material thickness, and minimum distance of the indenter from an edge.

Rubber Hardness Scales

The readout from a durometer is a dimensionless number on a scale from 0 to 100. A 0 shows the indenter went through the material while a reading of 100 means it left no mark at all.

As the hardness of rubbers and other elastomers covers a wide range – think latex gloves to golf balls – hardness values are reported using one of three scales. Developed by Albert Shore in the 1920s, these scales are identified as 00, A and D.

Originally there were other scales, but these are the only ones used today, and only Shore A and D are relevant for gasket material. The scales overlap so for example, the hardness of a particular rubber could be either 75 Shore A or 50 Shore D.

Specifying Rubber Gasket Material Hardness

Softer rubbers and elastomeric materials are preferred for sealing applications, with Shore A the rubber hardness scale used most often. Common gasket materials like NBR, EPDM and silicone are produced in a wide range of hardnesses: most are available from 30 to 80 Shore A. If you need assistance with hardness specification, Hennig Gasket and Seals can help.

Rubber Gaskets

Comments are off for this post

1 2 3 … 14 Next »