FAQs

Gasket Material to Dampen or Attenuate Vibration

Feb 05, 2018

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.

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The Importance of Testing Gasket Material

Jun 19, 2017

One cause of leaking joints is fluid-gasket incompatibility. Some materials swell and others become brittle. Elasticity and recovery decline faster than expected and fluid finds a way out. Temperature and pressure accelerate this material breakdown and hasten premature failure.  Testing gasket material for performance becomes a very important exercise.

Your Situation May Be Unique

The published information about which gasket materials to use and avoid with various fluids is always only a guide. The range of fluids to seal is virtually unlimited, and environmental factors vary. The only way to be completely sure any given gasket material will perform satisfactorily is to put it in the application.

Sample Testing

Gasket replacement is often costly, so while there’s no better test than to see how it performs in-service this isn’t a practical approach. The alternative is to expose samples of the gasket material or materials being considered to conditions like those in the application.

The simplest approach is to immerse pieces of the candidate materials in the fluid. Retain a control sample to allow quick comparisons to the initial material condition. Recover a test piece periodically to check for deterioration, or set up multiple samples for a range of test durations. Overall test duration should be as long as possible to replicate the in-service conditions.

If equipment is available, heat or cool the material to the temperature expected. Obviously, temperature cycling is hard to replicate, as are clamping loads. If the gasket material will be used outdoors, and particularly if it’s likely to see sunlight, place one or more samples outside.

Evaluation

Ideally, you would measure thickness to assess swelling, and look at compression under load and recovery. Often though, visual examination and feel are enough to gauge if the material is going to survive in the application.

Ask Hennig

Testing gasket material still doesn’t guarantee a long life, but it does reduce the probability of premature failure. Compared to the trouble of replacing a leaking gasket the effort is often worthwhile. Hennig Gasket is always happy to supply gasket material samples for evaluation. If you’d like to run your own tests, contact us today.

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Gasket Leak Detection and Repair (LDAR) Protocols

Jun 05, 2017

Leaking volatile organic compounds, (VOCs) can cause breathing difficulties for people living or working near the source. Some VOCs, known as volatile hazardous air pollutants (VHAPs,) may even cause cancer or birth defects.

According to the EPA, valves are the largest source of leaks. They account for some 60% of the 70,000 tons of VOCs that escape each year. Next up are flanged connections, responsible for around 30% of “fugitive” emissions. Valves generally leak around the stem or gland. For flanged connections gaskets play an important role leak prevention.

Create a Formal Program

No business wants to be associated with problems like these. That’s why a leak detection and repair (LDAR) program is so important. LDAR is required under 25 different Federal standards, but even if a business doesn’t come under one or more of these, a program still provides benefits.

Leaks are lost product, and that’s wasted money. Leaks tend to get worse over time too, so early detection can prevent a larger problem in the future. Relying on informal, ad hoc inspections is no way to monitor equipment condition. Instead, use a LDAR program to formalize the process.

LDAR Basics

The EPA publication, “Leak Detection and Repair: A Best Practices Guide” explains how to run an effective program. The five key steps of this are:

  • Identify components that need testing for leaks – valves and anything that uses a gasket to seal fluids.
  • Define “leak” in terms of a ppm level. (The EPA suggests using a tighter level than required by applicable standards.)
  • Implement a monitoring program – “Method 21” is a formal process documented in the EPA booklet referenced above.
  • Repair leaks. The EPA recognizes that not all leaks can be fixed immediately but expects prompt action. Either keep gaskets on-hand or find a reliable supplier who can make-to-order and has short lead times.
  • Keep records

Choose Quality

Replacing gaskets can be expensive, but neglecting them could cost more. Buy quality gaskets from an established supplier and install them with care. That way they’ll last longer and you’ll have fewer problems.  Hennig Gasket & Seals has been in the business of manufacturing custom cut gaskets and seals for over 100 years.  Contact us today.

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Gasket Material Compatibility Chart for Chemicals

May 22, 2017

Selecting the right material for a gasket is never easy. Temperature and pressure must be considered, and so too must the nature of the fluid being sealed. Some combinations of fluid and gasket material are just incompatible. Choose wrongly and the gasket will fail prematurely. When purchasing gasket material, mention the intended purpose. That way a material specialist can tell you if there’s a better alternative.  View our rubber sheet gasket material compatibility chart for chemicals.

Learning More About Material Compatibility

Some of the most frequently used gasket materials are neoprene, nitrile rubber, EPDM, silicone and Viton®. (Technically, this last one is a DuPont tradename for fluoroelastomer or FKM as it’s known in the ASTM standards.) Each has strengths and weaknesses in terms of chemical compatibility. “Rubber Gaskets & Seals” on our website provides a summary of what chemicals various gasket materials do and do not work with.

The other way to approach material selection is from the perspective of the chemical. Unfortunately that means identifying every possible chemical, which makes for a very long list. For some commonly used fluids the lists below highlight good and bad combinations. But don’t rely solely on these – always ask advice!

Good Material Compatibility Pairings for Chemicals

  • Acetone (a form of ketone): EPDM
  • Aldehydes (found in many food ingredients): SBR
  • Ammonia: Good choices are neoprene and EDPM gasket material
  • Animal fats: Nitrile, Viton®
  • Automatic transmission fluid: Nitrile rubber (NBR) and Viton®
  • Brake fluid: EPDM and styrene-butadiene rubber (SBR)
  • Ethylene glycol (antifreeze): nitrile rubber, Viton®, EPDM and neoprene work well
  • Fuels and oils: Nitrile rubber (NBR), Viton®
  • Ozone: EPDM, silicone, Viton®

Bad Gasket Material Pairings for Chemicals

  • Acetone (a form of ketone): Avoid contact with nitrile rubber, neoprene, silicone and Viton®
  • Aldehydes (found in many food ingredients): Nitrile
  • Ammonia: Poor with SBR and Viton®
  • Animal fats: SBR
  • Automatic transmission fluid: Avoid EPDM, SBR and Silicone
  • Brake fluid: Viton®
  • Fuels and oils: EPDM, SBR, Silicone
  • Ozone: Nitrile and SBR

Seek Advice for Material Compatibility with Chemicals

These lists give only a superficial overview of a complex subject. The only sure way of selecting the correct gasket material for any given chemical is to seek guidance from a material specialist. At Hennig Gasket, if we don’t know we’ll find out.  Contact us Today.

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How Flanges Influence Gasket Material Selection

May 23, 2016

If flange and enclosure door surfaces were perfectly smooth and perfectly aligned, gaskets wouldn’t be needed. In the real world though, uneven gaps are always present and must be sealed to prevent leaks or contamination. Sealing options range from inexpensive red rubber and buna N materials to advanced silicone rubber gaskets, and include materials as diverse as graphite, PTFE and paper.

When replacing gaskets it’s common to use the same material that’s just been removed. If joints never change, that approach is often adequate. But by considering the nature and design of the sealing surfaces or flanges, it may be possible to select a longer-lasting material.

Impact of flange material

Some flanges can’t take high clamping forces, especially as they age. Plastics tend to become brittle and some metals lose ductility as they age, particularly if put through repeated temperature cycles. This means a soft, easily compressed gasket material is needed.

Impact of flange geometry

Bolt patterns or the position of clamps and latches can distort the mating surfaces, leading to uneven gaps. For example, an enclosure door with a single central latch can leave large gaps at the corners when closed. Also, a flange that’s been assembled and dissembled repeatedly for many years will start to distort, creating uneven gaps.

Flange alignment can change over time. After years of service it’s possible that piping will have moved, with the result that flange faces are no longer parallel. Again, the result is an uneven gap. Another problem is surface imperfections resulting from careless gasket removal.

These problems demand thicker gasket material that provides more compression. But thicker material needs higher loads to compress down in the joint, and those loads can lead to more distortion in the flanges.

Things change

Flanges and mating surfaces change over time and products that performed well, perhaps red rubber or buna N gaskets, may no longer be up to the job. When replacing gaskets, consider the condition of the sealing surfaces or flanges. A different material may last longer in the joint.

 

FAQs, Flange Gaskets
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Interpreting ASTM F36 Compressibility Data

Apr 25, 2016

Gaskets seal gaps of varying size by compressing under load. Best practice is usually to keep that load as low as possible, which is why softer gasket materials are preferred. For products like silicone or PTFE gaskets durometer numbers give a good indication of material hardness, (following the ASTM D2240 standard,) but they don’t show how that material will perform in a joint. That means turning to the ASTM F36 test data.

Compressibility and Recovery

When selecting gasket material it’s important to understand its compression and recovery behavior. This is because joints tend to move, whether due to varying temperatures, (media and environmental,) or loads. A material that compresses easily but has no recovery may not do a good job of sealing a joint that experiences a lot of cycling.

ASTM F36 provides a standardized method of testing and measuring compressibility and recovery. The test has two parts. First, the material is put under a load of 5,000 psi for 60 seconds and the reduction in thickness measured. Then the load is taken off and the material given another 60 seconds to spring back before the thickness is measured again. Both compressibility and recovery are expressed as percentages.

Caveats

The conditions F36 testing is done under don’t necessarily reflect the actual usage conditions as temperatures, pressures and loads will almost certainly be different. Neither do they take time into account, which in reality is a significant factor when dealing with viscoelastic materials, (where properties change over time.) What the numbers do provide is a basis for comparing between different gasket materials.

Typical F36 Numbers

Compressibility and recovery values vary greatly between different materials. For example, expanded PTFE has a compressibility of around 68% but recovery of just 12%, while the same numbers for a neoprene gasket could be 7 to 17% compressibility and 50% recovery. This would suggest the neoprene material would perform better in an application where flange faces are in good condition but gasket loads cycle. Of course, other factors such as temperatures, media and pressures must also be considered.

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Why Thinner Gasket Material Usually Works Better

Feb 15, 2016

Gasket materials come in many thicknesses. To give one example, at Hennig Gasket neoprene gasket material is available from 3/32” all the way up to 2” thickness. Customers will sometimes ask what thickness they should buy, but a gasket material supplier really can’t help with that. It depends completely on the application. However, it’s generally agreed that a gasket should be as thin as possible, providing it still seals. There are four reasons. A thinner gasket:

1. Has greater blow-out resistance. Being thinner, the gasket present less area to the internal pressure, so is less prone to deformation and failure.

2. Has a lower leak rate. All gaskets will allow some quantity of fluid to pass through. This is just a natural function of their structure and the make-up of the fluid being constrained. (Anyone who’s ever tried piping helium knows how its small molecules let it escape from almost anywhere!) So the less gasket material that’s exposed to the fluid, the less will leak.

3. Retains fastener torque better. This stems from the creep relaxation characteristics of the gasket material. When there’s less thickness there’s less creep, (think of it happening on a percentage basis,) so more torque is retained.

4. Is less expensive. Material cost relates more to volume or weight than area, and thicker gaskets need more material. Secondly, thickness also influences cutting method and thicker materials could be more expensive to cut to shape. Neoprene gasket material 3/32” thick die cuts readily, but a thickness of 2” may call for a waterjet.

Note though that points 1 and 2 really only apply to situations where the gasket resists pressure, such as in pipelines. In no-pressure situations such as a gasket sealing around an electrical enclosure, the benefit is primarily Point 4 – cost.

All About the Gap

How thick a gasket should be depends entirely on the application. Remember that it’s purpose is to take up an uneven gap between two surfaces. The key is having enough thickness that the gasket compresses and fills the voids, but no more.

FAQs, Gasket Material, Neoprene Gaskets
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Choosing Gasket Material

Jan 18, 2016

When changing a gasket most technicians choose a new one made from the same material. If a paper, fiber or cork gasket came out of the joint, then the replacement is usually the same.

That’s not necessarily bad, assuming the gasket hadn’t failed prematurely, but it could also be a missed opportunity. Other gasket materials might hold up better in the application. That would allow more time between inspection and replacement, reducing downtime frequency and saving on maintenance hours.

Gasket materials are specified by multiple criteria, and the importance of each depends on what the application needs. One way of looking at these properties is to divide them into mechanical – their gap-filling ability – and material – how well they handle the media.

Mechanical properties

Whether looking for boiler seals or food grade gaskets, the primary considerations are thickness and hardness. Thickness is easy to understand, (always choose the thinnest that will do the job,) but hardness is less obvious. Gasket material hardness is reported in terms of Durometer, usually on the Shore A scale. (See “Measuring Gasket Material Hardness.”) When comparing two materials of the same thickness, the softer one is usually the better choice.

Other properties to look at are compressibility and creep relaxation. Compressibility measurement is defined by the ASTM F36 standard and describes the load needed to provide a given level of deformation. In general, higher compressibility implies lower loads are needed to secure a joint. Creep relaxation, addressed in ASTM F38, indicates how the gasket thins over time, which reduces bolt loading.

Material properties

Gasket material must be appropriate for the media. For example, nitrile gaskets are preferred for applications involving petroleum, mineral or vegetable oils but don’t perform well with ozones, ketones, esters and aldehydes.

The ability to handle expected temperatures is also important. This is especially critical where the environment causes severe temperature gradients through the joint. (Imagine piping liquid nitrogen in the desert southwest.) Nitrile gaskets may be appropriate for the media but an alternative, like silicone, might handle the temperatures better, (although has poor hydrocarbon resistance.)

FAQs, Nitrile Gaskets
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The Difference Between Soft, Semi-Metallic and Metallic Gaskets

Jan 04, 2016

Gasket selection is driven by the needs of the application. Temperature, environment, media and pressure dictate the gasket required. While there are many different types, to aid selection they are usually separated into three classes:

  • Soft
  • Semi-metallic
  • Metallic

Soft gaskets

These are made from materials that compress easily, such as elastomers like nitrile, (NBR,) EPDM and silicone, as well as graphite, PTFE and fibrous materials. Their corrosion resistance is good but they are limited in the temperatures they can handle. Nitrile gaskets for example only work from -60 to 250°F (-51 to 121°C) and EPDM is only slightly better with a range of -70°F to 350°F (-57°C to 177°C). Silicone gaskets will however go up to 500°F (260°C) and PTFE is effective from cryogenic temperatures up to 450°F (232°C).

Soft gaskets are also limited in their ability to handle high pressures. The best applications are those involving sealing variable gaps as might be found around the doors of an electrical enclosure.

Semi-metallic gaskets

Bridging the gap between metallic gaskets and soft gaskets, the semi-metallics combine features of each. The two main types are spiral-wound and metal-jacketed, although other forms exist. Spiral wound gaskets are made from a ribbon of soft material like PTFE or graphite layered with metal, usually in a ‘V’ form to provide compressibility. Jacketed gaskets consist of a metal cover over a filler material.

Semi-metallic gaskets can handle a wide range of temperatures and pressures up to 6,000 psi, (based on ANSI pressure class 2,500,) so are used in applications ranging from refineries and chemical processing plants to aerospace.

Metallic gaskets

As the name implies, this type of gasket is made from metal. That allows it to resist pressures as high as 10,000 psi but also means it has virtually no compression. Very high bolt loads are needed to create enough deformation for joint sealing.

Metallic gaskets are vulnerable to galvanic corrosion. To minimize problems the gasket metal should be close to the flange material on the electrochemical scale. Alternatively, the material should be chosen to make the gasket the sacrificial element.

FAQs, Nitrile Gaskets, Spiral Wound Gaskets
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Open or Closed-Cell Gasket Material

Dec 07, 2015

When it comes to gasket material hardness the general advice is that softer is better, providing it seals the joint. Elastomeric gaskets used for sealing enclosures are a good example. When the enclosure door is closed there’s often a large and uneven gap remaining, (especially in the case of light-duty plastic enclosures.) A soft gasket compresses easily where the gap is smaller while filling the larger gaps, providing a seal all the way around the opening.

Interconnected cells

Many softer gasket materials, such as silicone, urethane and neoprene, are available with a cellular structure that makes them very soft. These cells are easily seen in cross-section. What gasket material buyers may not appreciate though is that these cells may be open or closed. This matters because it gives the gasket material different performance characteristics.

In a closed cell material, each cell is completely sealed off from its neighbors. That makes it feel harder because when compressed the air inside has no place to go. In an open material the cells are interconnected, so under compression the air moves through and out of the material, making it feel softer.

Different characteristics

Closed cell materials take on a compression set more readily than do open materials. This is because, under load the air inside permeates slowly through the cell walls. When the load is removed, although the material tries to spring-back it can’t draw air in, leaving the gasket material permanently deformed. In contrast, an open cell material “breathes,” drawing air back in to each cell as the material rebounds.

The weakness of open cell gasket materials is a lack of water-resistance. Just as in a sponge, the interconnected cells let water move through the structure. Although a load may close up the openings and provide some resistance, open cell gasket materials are not recommended for situations where water exposure is possible.

Consider the application

An open cell structure makes for a softer gasket, and one less likely to take a compression set. However, a closed cell material provides better water resistance. Select your gasket material based on the application.

 

 

FAQs, Rubber Gaskets
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