What is Compressibility of Gasket Material

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.

How to Measure Bolt Circle Diameter

Two styles of gasket are used for pipe flanges: full face gaskets and ring gaskets. Full face gaskets need holes for the flange bolts to pass through. When you order this type of gasket the manufacturer needs to know the diameter of the bolt circle. Here we’ll explain what that is and how to measure it. First though, an explanation of the two gasket styles.

Gasket Styles

A full face gasket has roughly the same outside diameter as the flanges being joined. The inside diameter is of course equal to the bore of the pipe. Flange bolt holes in the gasket simplify assembly as the bolts hold the gasket in place and stop it intruding into the flow. The downside is that all the bolts must come out when installing a new gasket.

In contrast, a ring face gasket sits inside the bolts and can be replaced without completely disassembling the joint. They also have a smaller outside diameter, which saves material. They are used principally on raised face flanges where the sealing surfaces are inside the bolt hole diameter.

A full face gasket can be used with raised face flange. Likewise, ring gaskets can be used on flat face flanges, providing the impact of the reduced gasket width is considered.

Bolt Circle Diameter Measurement

The bolt circle is defined as a circle running through the centers of all the bolt holes. As these points are in space they can’t be measured directly. However, there is way.

The bolt holes will all be the same diameter and arranged in diametrically opposite pairs. Looking at the flange end-on, measure from the left edge of the leftmost hole to the left edge of the hole diametrically opposite. (Or measure from right edge to right edge.)

To eliminate any measurement error, repeat on a number of other hole pairs and average the result. This is the number you’ll give your gasket manufacturer, along with inner and outer diameters, number of bolt holes, and the bolt hole diameter. With this information they’ll cut the gasket to the size you need.

How to Install a Gasket

The costs of gasket failure are far greater than the price of the gasket itself. A leaking joint means wasted gas or liquid, and that can have safety and environmental implications. Unplanned downtime cuts into production, reducing output and perhaps needing expensive overtime working to make good the shortfall. Then there’s the actual time and effort involved in opening up the joint, cleaning the faces and installing a new gasket.

Bottom line: you only want to do the job once, so do it right. Here’s what and what not to do.

Don’t reuse an old gasket. It’s a false economy. The material has been compressed and creep has taken place. It won’t have the recovery of a new gasket so it won’t seal as well.

Do clean the mating faces thoroughly. Residual gasket material or adhesives will reduce the ability of the new gasket to make a good seal.

Don’t use a gasket that’s thicker than what the flanges need. Remember, the purpose of the gasket is just to take up surface imperfections and misalignment and to handle expansion and contraction. An unnecessarily thick gasket is more likely to fail.

Do choose a gasket that’s appropriate for the joint TEMP – that’s Temperature, Environment, Media and Pressure. Soft gaskets – those made from materials like neoprene, graphite, fiber or cork – should not be used in high-pressure applications. Ask your gasket material supplier if they can provide pressure-versus-temperature (PxT) charts for your preferred material.

Don’t overtighten a soft gasket joint. Once the gasket has been crushed the material loses its ability to recover as the joint opens up. That leads to leaks.

Do follow the correct bolt tightening procedure. See “How To Bolt Flanges” for details.

Don’t glue thin gaskets together to make one thick enough for the joint. It won’t behave like a gasket of the right thickness and will almost certainly fail prematurely.

Do it right

Replacing a gasket outside of scheduled maintenance periods is often awkward and expensive. Achieving a long life is a function of gasket selection and installation, and these dos and don’ts will help.

NEMA vs IP Rating

NEMA and IP ratings are two systems that define the levels of safety and environmental protection provided by an enclosure. The enclosures themselves are usually fabricated from steel or durable plastic, but they need an opening for assembly or access to the equipment inside. That opening is sealed with a gasket, which is key to how the enclosure is rated.

NEMA vs IP Rating:  Different standards, same goal

NEMA ratings define enclosure protection in terms of the environment. IP ratings, (the system used in Europe and elsewhere,) define ingress protection (hence “IP”) in terms of solid objects and liquids. These systems overlap and the most widely used ratings are as follows:

  • NEMA 2 (Indoor use, protects against vertical drops) – broadly equivalent to IP11
  • NEMA 3 (Outdoor use, protects against rain and snow) – comparable to IP54
  • NEMA 4 (Protection against hose-directed water) – IP50
  • NEMA 6 (Temporary immersion at limited depth) – IP67

Gasket Implications

The two factors to consider are the cutting method and material. A gasket cut from strip has joins, and that creates potential leak paths. A gasket cut by die, laser or waterjet has no such joins and so provides better protection.

The gasket material must be compressible to seal completely all around the opening. (Hinges and clamps sometimes create gaps that vary widely.) If the enclosure will be opened frequently the material should also resist taking a compression set. Cellular gasket materials are a popular choice, but a closed-cell structure is essential to prevent water penetration.

When selecting any gasket material, it’s important to consider the environment. Those used outdoors could suffer UV exposure and wide temperature swings. Gaskets used near high voltage electrical equipment need good ozone resistance. Flammability may also be a concern.

NEMA an IP Rated Gasket Material

Closed-cell silicone foam is often used for enclosure gaskets due to its low compression set and wide temperature range. EPDM can be a cost-effective alternative and has good UV resistance, but depending on the environment and protection needed there may be other options. To explore the range of gasket materials appropriate to your application, speak with a Hennig Gasket product specialist.

CIP Process and Affect on Seals and Gaskets

PTFE seals are widely used in the food and beverage industries. One reason is that they won’t contaminate foodstuffs. A second is that PTFE resists attack by acidic products like fruit juices. And third, they stand up well to the intensive cleaning and sterilization processes used in those industries.

Here’s a closer look at how those processes influence gasket selection.

Gasket Cleaning Protocols:  CIP

Food and beverage (F&B) manufacturers are acutely aware of the risks of product contamination. That’s why regular cleaning and sterilization is a way of life. Facilities producing liquid products often employ Clean-in-Place (CIP) protocols.

CIP is where cleaning fluids are pumped through the pipes, tanks, mixers, kettles and filling equipment. A combination of aggressive chemicals, turbulence, and rinsing remove contamination from surfaces that contact the food and could otherwise harbor pathogens.

The alternative, Clean-out-of Place (COP) entails stripping down plumbing systems to remove components like valves for cleaning. For many F&B companies, it’s slower and less effective than CIP.

Gasket Cleaning:  The CIP environment

CIP usually starts with a hot water pre-rinse. This is followed by running caustic soda through the system at 80°C (176°F). Caustic soda, chemical formula NaOH, (sodium hydroxide,) is highly corrosive. It kills and removes practically everything it comes into contact with. The caustic is then followed by thorough rinsing to get the surfaces food-ready.

Some plants and processes use acid in place of caustic soda. Nitric or peracetic acids are common choices. Steam and ozone are other alternatives sometimes used.

Gasket Cleaning Impact on Gasket Material Selection

Materials like NBR, EPDM, and neoprene have no problem handling CIP temperatures. Where they struggle is with resistance to acids, alkalies and often also water, steam, and ozone.

PTFE seals and gaskets function at temperatures up to 260°C (500°F). More importantly, they won’t react with any chemicals, whether acidic or alkaline. In addition, most grades of PTFE don’t impart any taint to product and are FDA-approved.

If you’d like to learn more about the advantages of PTFE seals in processes that need cleaning and sterilization, contact a material specialist at Hennig Gasket.

6 Tips for Preventing Gasket Blowout

Gaskets in flanged joints fail in two ways. Either they allow a very slow leak or they blow out. A blowout can be quite spectacular, but also dangerous and expensive. As it’s something to be avoided, here’s an explanation of what causes it and some ways of making sure it doesn’t happen.

Recognizing a Blowout

A blowout occurs when the gasket material fails catastrophically. This can happen when the gasket is resisting significant internal load. A steam system might be one example but it could be any application where the media being sealed against is under pressure. When this pressure exceeds the strength of the gasket the material is likely to fail fast, forming a hole that releases the media.

In a steam system, this results in a dangerously hot jet. In other situations, it could be acid or a flammable fluid that escapes.

Blowout Prevention

One factor is the tensile strength of the gasket material, but a flange system is more complex than that. The gasket is held in place by the clamping force. This creates friction between the flange surfaces and the gasket, and that resists movement.

Analysis of the forces in a flanged joint shows that clamping force is a bigger factor in blowout prevention than material tensile strength. (The full analysis is available on the Fluid Sealing website.) Thus anything that reduces clamping force can cause a blowout. Here are six tips to prevent that happening.

  1. Follow best practices when bolting flanged joints together. Use the recommended tightening pattern.
  2. Don’t overtighten. This makes the flanges rotate, compressing the gasket at its outer edge while there’s little or no contact on the inside. It can even crush the material, guaranteeing a failure.
  3. Minimize vibration through the joint.
  4. Choose gasket materials with low creep. (Silicone and nitrile rubber are particularly good.)
  5. Consider the effect of temperature. High temperatures will lengthen bolts, (which reduces clamping load,) and let gasket material creep. Conical spring washers may help.
  6. Use the thinnest gasket possible that handles unevenness in the flange faces.

Where to Buy Gasket Material

Gasketing is complicated. Every application has a unique combination of temperature, environment, media, and pressure to consider and there’s almost never a ‘one-material-suits-all’ solution. As a result, even a small HVAC, food processing or chemical application might need gasket materials ranging from nitrile rubber to EPDM, silicone, fiber and even PTFE.

Many companies will sell you some of these. The danger is that when they don’t carry a full range they’ll propose a material that’s not ideal for your application. Here’s some advice for deciding where to buy your gasket material.

Consider Material Range

Stocking nitrile rubber and neoprene foam does not constitute a full range. You should look for a vendor that carries all these types of gasket material:

  • Fiber
  • Felt
  • Cork and cork/rubber
  • Fiberglass
  • Compressed Non-Asbestos
  • Various types of rubber
  • Closed and open-cell foam
  • Graphite
  • PTFE
  • Specialized brand name materials like Viton and Santoprene

Look for Rapid Turnaround Capabilities …

It’s rare to have the luxury of buying gasket material just to put into storage. Usually, there’s an immediate need, and you can’t wait for delivery. Keeping a full range of gasket material in stock ties up money and space though, so some businesses don’t want to do it. Always look for a material supplier who maintains a comprehensive inventory.

… And Gasket Cutting Services

Material is one thing, but you still have to cut gaskets from it. A stockist with waterjet cutting capabilities can produce installation-ready gaskets in just a few hours, sometimes faster. That saves you time and results in a more accurate gasket with better edge quality.

Location is another factor to consider. Today’s rapid delivery services mean material can ship almost anywhere in the country in 24 to 48 hours, but there are still advantages to finding a local vendor. Closer is faster, and likely cheaper too.

Range and Speed

When searching for gasket material, similar isn’t good enough. It’s essential to buy the right material for each application and get it without a long wait. That’s why you should look for a supplier with a broad inventory and the ability to deliver quickly.

Cutting with Water: How the Waterjet Machine Works

Waterjet cutting produces small or large gaskets in just minutes. There’s no tooling, it’s fast and edge quality is extremely good. Waterjet eliminates the wait for tooling that goes with steel rule die cutting and it avoids the heat and fumes of laser cutting. That’s why we prefer it for many different gasket materials. Here’s how it works and why we’re such fans.

High Intensity

A jet of water from a garden hose can sting the skin. In a waterjet cutting machine that jet is far thinner and traveling at supersonic speeds. The water is powered by an intensifier pump that produces 60,000 psi or more. This forces the water through a 0.006” diameter hole in a piece of sapphire.

With such high pressure and velocity, the jet of water slices through material like a knife. For cutting harder materials, adding an abrasive powder to the water increases cutting speed.

Machine Operation

The cutting head is mounted on a gantry. This spans the machine bed, which is where the material being cut is placed. Here at Hennig Gasket we can handle sheets up to 8′ x 6′. The gantry provides one axis of motion and the sheet moves under the gantry for the second. By interpolating motion between the two it’s possible to cut incredibly intricate shapes.

Waterjet machines are programmed directly from CAD files and there’s no special tooling needed. The programming package helps maximize material utilization by nesting gaskets efficiently. This, plus a very small kerf (the cut width,) helps minimize waste.

Types of Gasket Material

Cutting speed and maximum material thickness depend on hardness. Speeds of up to 500”/minute are possible, but this drops as thickness increases. Sheet EPDM, neoprene, cork and silicone gasket material can be cut quickly and accurately, and maximum thickness can be up to 6”.

Fast Turnaround

Using a waterjet to cut gaskets from sheet material is fast and cost-effective. Perhaps the biggest benefit though is the speed with which we can satisfy an order. Curious how fast that is? Put us to the test.

What UL Ratings Mean for Gasket Materials

Industrial enclosures often have to meet NEMA and IP standards for ingress protection. These aren’t the only standards designers should consider though. There’s also UL50 and UL50E. Established by Underwriters Laboratories, these were developed to ensure that electrical enclosures would be safe. Safety depends at least in part on the gasket, so there are UL standards for gasket materials too.

The UL difference

Achieving NEMA or IP certification entails passing some stringent tests. However, these tests only verify dust and water resistance. They don’t explicitly test the gasket material. UL testing does.

Gasket material is tested because environment and use affect how long it lasts. Some gaskets are exposed to UV outdoors. Others, especially if near high voltage equipment, can be attacked by ozone. Some enclosure gaskets will endure periodic recompression when the door is repeatedly opened and closed. Other are in continuous compression, as might be the case around an electronics assembly.

These variables place different demands on the gasket material. Many gaskets might hold up to NEMA and IP testing but the material could degrade slowly and reduce the protection the enclosure provides.

Gasket Material Certification

To address the impact of use and environment on enclosure performance, UL developed tests for gasket material. These are defined in UL157, “Standard for Gaskets and Seals”. This covers both foam and solid elastomeric and composite gasket materials.

Materials passing UL157 can be considered as “UL Recognized Components”. Using components certified this way in an end product simplifies the process of getting UL approval. (Other UL standards may also be applicable.)

Buy UL-Rated Gasket Material

When designing equipment, using UL-rated materials will save time and money in testing. And later, when gaskets are being replaced, it might also be prudent to stick with UL157 materials. These range from neoprene and EPDM foams to silicon and even cork. (But note that adding a pressure sensitive adhesive nullifies any prior UL rating.)

Finding the right UL-rated gasket material for a specific application can be difficult. If unsure what to use, consult a material specialist at Hennig Gasket.

Gasket Material to Dampen or Attenuate Vibration

Yes, your next gasket should seal, but it could do more than that. A gasket is an excellent way of reducing the transmission of sound and vibration. That can extend equipment life and improve performance while creating a better environment for those nearby.

Gasket Material Properties for Vibration Dampening

The goal is to have the material acting like a spring: compressing and springing back in response to the excitation force. In other words, they need a combination of resilience and compressibility. Closed cell foams do this particularly well as the gas in each cell compresses and then expands.

Compressibility also depends on the nature of the material used. Softer elastomers like some grades of silicon or the urethane foam used in PORON® compress under relatively light loads. Others, like some nitrile rubbers, need more force to achieve a given level of compression.

For effective vibration dampening, compressibility, resilience and also thickness must be related to the excitation frequency and amplitude. Clamping force also plays a part as compression alters the material’s vibration response.

Vibration Dampening Gasket Materials

Silicone rubber and foam, nitrile sponge, and urethane foams can all attenuate vibration effectively. Less well known is that both felt and rubber-bonded cork material can also be used to cut or even eliminate the transmission of sound and vibration. Remember that the addition of a pressure sensitive adhesive (PSA) makes the material much easier to install or apply.

Situations benefiting from vibration dampening

Vibration-attenuating gasket materials are especially useful in HVAC systems where they can reduce noise significantly. Industrial machinery also benefits, with less vibration translating to higher quality output and longer equipment life.

Elastomeric gasket material is found in a growing number of electronics devices. Here it improves life by “ruggedizing” the equipment against knocks or drops. Recently a patented was granted for a vibration-attenuating camera mount that utilizes two gaskets for dampening. (US 9,654,692)

Next Steps

Gasket material selection is a complex field where every application is different. If vibration reduction is of interest ask for advice from a Hennig Gasket specialist today.