Gaskets for Vacuum Chambers

May 21, 2018

Vacuum chambers are used in many industries. Their largest application area in the physical vapor and directed vapor deposition, (PVD and DVD,) process industries. Here they are used for applying both decorative finishes and hard protective coatings. Vacuum eliminates contaminants that would cause oxidation or reduce purity. The cutting tool, semiconductor and nuclear industries are all big users. They’re also used in scientific research even for growing engineered diamonds.

A Difficult Sealing Environment

The gaskets used for sealing these chambers are critical pieces of the equipment. They fit around access ports where they have to withstand high clamping forces as well as extremely low vacuum. That means they need strength and good compression set resistance. Another requirement is a wide temperature range and there’s also a fourth, more specialized challenge.

Outgassing

Emptying a vacuum chamber of air, (pumping it down,) takes time because molecules cling to the interior surfaces. These surfaces must be given time to give up these molecules in a process called “outgassing”.

Materials give up their attached air molecules at different rates, which makes outgassing behavior an important consideration when selecting gasket material for vacuum chambers. Slower outgassing means longer pump-down times, which in turn reduces chamber throughput.

Suitable Materials for Vacuum Chamber Gaskets

The most popular choice is Viton®. Technically a polymer from the fluorocarbon family, (Viton® is the DuPont trade name,) this has a wide temperature range, (-20 to +400°F) and good compression set resistance. Most importantly though, it provides shorter outgassing times than the alternatives.

These alternative materials are silicon, Butyl, Buna-N and EPDM. Silicon gasket material outgasses more slowly than Viton® but has a wider temperature range and good ozone resistance. In ultra-low vacuum applications, meaning pressures below 7.5×10-10 Torr, elastomeric gaskets are replaced by copper.

Finding the Right Material for Vacuum

Every vacuum chamber has access ports, and access ports need gaskets. An important consideration for the gasket material is outgassing behavior as this affects pump-down time. If outgassing is a concern in your gasket application, the specialists at Hennig Gasket will be happy to offer advice.

Applications
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What UL Ratings Mean for Gasket Materials

May 07, 2018

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.

FAQs
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Gasket Material for Natural Gas

Apr 16, 2018

Natural gas is widely used for heating and cooking and it’s the energy source for much of our electricity. Perhaps less well known, it’s also essential for fertilizers and plastics.

The systems that store and distribute natural gas need gaskets. Here we’ll discuss the materials most often used, but first, a short primer.

Hydrocarbon Origins and Uses

Like coal and oil, natural gas is formed from plant and animal remains. Decomposition produces methane, (CH4), and when trapped underground we call it natural gas. Natural gas is odorless, so a trace of mercaptan, (CH4S) is added to make it detectable.

Reacting natural gas with steam separates the hydrogen and a second reaction, this time with air, results in NH3, or ammonia. Chemists call this the Haber process and it’s the first step in producing fertilizers.

Like methane, plastics are also composed of carbon and hydrogen atoms. The difference is that the atoms are formed into long chains to create polyethylene, polypropylene and similar materials.

Storage and Distribution

When held above 200 bar (3,000 psi) natural gas is known as compressed natural gas (CNG). This makes it sufficiently dense for use as a vehicle fuel. When pipelines aren’t an option, for easier transportation cooling to below -184°F produces liquefied natural gas (LNG).

The Sealing Challenge

The biggest issues are permeability and flammability. Simply put, the very small methane molecules can find their way through some materials, and they burn readily. Fortunately, as it’s lighter than air, escaping natural gas tends to disperse quickly.

Sealing CNG and LNG presents additional challenges. Gasket materials must retain some flexibility at very low temperatures and should have the strength to resist extrusion through joint faces.

Materials for Natural Gas Gaskets

For most low pressure, ambient temperature applications nitrile and neoprene gasket materials are the first choice. In more challenging applications many engineers opt for more expensive Flexitallic spiral wound gaskets. PTFE and graphite are other options.

Every gasket application has some unique challenges. If you need material for natural gas gaskets, ask a product specialist at Hennig Gasket for advice.

Neoprene Gaskets, Nitrile Gaskets
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Neoprene Gasket Applications

Apr 02, 2018

Neoprene is a synthetic polymer that resembles rubber, but as a derivative of chloroprene, it is far more durable in extreme temperatures, when exposed to oils and several chemicals, and it endures harsh weather conditions. But not all Neoprene gaskets are created equal—there are several variations or “grades” of neoprene. Each grade of neoprene gasket has its ideal application depending on factors such as temperature and pressure tolerances, the environment where it will be used, etc:

  • Commercial Grade Neoprene—15-50% Neoprene mixed with other elastomers; this blend is fine for general commercial gasket applications, but not in situations where high oil resistance is necessary.
  • Medium Grade Neoprene—51%+ Neoprene content; also suitable for many general manufacturing applications where a lower tensile strength will suffice.
  • High Grade Neoprene—100% Neoprene is extremely resilient in the harshest, most demanding environments while maintaining its resiliency, abrasion resistance and tensile strength.
  • FDA Neoprene—A mixture of Neoprene and other FDA-improved materials; gaskets made from this grade are used in the food industry, but also in many government-approved and military applications where oil resistance is key.
  • PSA Ready Neoprene—Available upon request, this Neoprene has one side with a matte finish and is designed to be used with pressure sensitive adhesives.
  • Nylon Cloth Inserted Neoprene—This grade is reinforced with one or two layers of nylon; good for improved creep reduction and stability.
  • Diaphragm Neoprene—Polyester insertions improve performance under high pressure applications requiring high levels of oil and petroleum resistance.
  • Flame Resistant Neoprene—Especially useful in potentially flammable, electric and high-heat applications, it passes the following flammability specifications: UL-94-HF-1, UL-94-HFB, MIL-R-6130C, FMVSS-302.

These grades vary in durometer ratings between 40, 50, 60, 70 and 80, can withstand temperatures between -20F to +180°F and come in sheets with several widths and thicknesses that can be cut (waterjet, flash and die cut) to exact specifications from your blueprints, or even reverse engineered.

Please contact Hennig Gasket & Seals if you have any questions about the different grades of neoprene that might best fit your application: 1-800-747-7661. We can custom manufacture any neoprene gasket you need to the most accurate specs possible.

Neoprene Gaskets
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Gasket Material Selection

Mar 19, 2018

It’s said that what comes out of the joint is what goes back into the joint, but sometimes we’re asked if there’s a better material to use. That’s because the expense of replacing a gasket often far outweighs the cost of the part. When that’s the case a little extra spent on better gasket material might save a lot.

Unfortunately, there’s no easy answer to the material question. All we can say is, “It depends.” Here’s why, along with some guidance on selecting the best gasket material.

Four Key Criteria

It’s impossible to determine an appropriate material without knowing the temperature, environment, media and pressure the gasket will experience. It’s also important to determine the actual range of every parameter and every operating condition. Cleaning with caustic agents, for example, creates very different gasket challenges than handling a benign fluid like milk.

Temperature

This refers to the temperature of the media. Many elastomers harden when cold, making them less able to resist pressure and reducing their ability to flex as the joint changes size. Neoprene, for example, has a lower limit of -40°F while high-performance fluoroelastomer (FKM) only goes to -10°F.

Environment

Temperature is one factor, sunlight another. A gasket used outdoors in a midwestern winter could see low temperatures while one exposed to the desert sun will get extremely hot. In addition, UV light damages some common gasket materials. NBR, for example, has poor UV resistance while EPDM holds up much better.

Media

Some gasket materials suffer swelling when exposed to oils and other will oxidize rapidly. Brake fluid is incompatible with nitrile rubber and FKM while silicone and EPDM are a poor match for gasoline.

Pressure

The pressure inside a pipe or enclosure can force gasket material to extrude out sideways. Harder materials generally hold up better but require higher clamping forces. In extreme cases, it may be necessary to consider PTFE, spiral-wound or metal gaskets.

Seek Advice

Every gasket application is different and it’s never easy to say which is the best material to use. Start by determining the four criteria listed above, then consult a material specialist.

Gasket Material
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Oxygen Compatible Materials

Mar 05, 2018

Many industries use oxygen. It’s one of the most reactive elements, which makes it useful in processes from steelmaking to paper production as well as healthcare and waste treatment. This reactivity, (a willingness to form chemical bonds with other elements,) also creates sealing problems. Here’s an overview of the challenges posed by oxygen and a discussion of the best gasket materials to use.

The Air We Breathe

Oxygen is one of the most plentiful elements and makes up some 20% of the air we breathe. It’s also locked into the oceans as water. At temperatures above -297°F (183°C) it’s a gas. Oxygen has a strong affinity for electrons, which is what lets it bond readily with many other chemicals. Rust and oxidation are the common results, although fire and explosions are always possible.

Oxygen Production

Oxygen is produced by cryogenic distillation or pressure swing adsorption (PSA). As the name implies, the cryogenic process entails cooling air until it becomes liquid, allowing the oxygen to boil off. This produces a very high purity gas.

PSA involves pushing air through aluminosilicate minerals. These take up the nitrogen, leaving just oxygen, but at a lower purity than the cryogenic process.

Keeping Oxygen Systems Clean

Given that oxygen is highly reactive, it’s essential that any surface it touches is clean. Some industries have special requirements for oxygen-clean surfaces. The standards applicable to your industry will specify the type and degree of cleaning needed.

Materials for Gaskets in Contact with Oxygen

Liquid oxygen can only be sealed by materials capable of withstanding very low temperatures. PTFE gaskets are a good choice as is FFKM (perfluoroelastomers) gasket material.

Good gasket materials for gaseous oxygen include neoprene, EPDM, silicone, butyl and Viton® (a DuPont brand name for FKM.) Rubber materials such as SBR and natural rubber should be avoided because of their tendency to react with oxygen.

Ask an Expert

Always consider temperature, pressure and the environment along with the media being sealed. For this reason, it’s prudent to consult with a materials specialist before ordering gaskets or gasket material.

Gasket Material
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Best Gasket Material for Nitrogen

Feb 19, 2018

Many industries use nitrogen. Some users even generate their gas on-site. If your company is among them you ought to be familiar with the best gasket materials to use.

Industrial Uses of Nitrogen

Liquid nitrogen is used when very low temperatures are needed. This is often for preserving biological samples or other organic material although other uses include cooling for superconductors and to aid in machining.

Applications for gaseous nitrogen include fertilizer production, food preservation, and annealing stainless steel. It’s also used in the production of electronic components like transistors and diodes.

Nitrogen Production and Storage

Nitrogen is produced by separation from air. (The air around us is approximately 78% nitrogen.) There are two methods:

  • fractional distillation
  • pressure swing adsorption (PSA).

Distillation entails chilling air until it becomes liquid, then raising the temperature slowly to let the individual components boil. In contrast, PSA is done at ambient temperature and in simple terms consists of pushing air through a membrane that separates the various constituents.

Distillation produces higher purity gas but is energy-intensive. PSA scales more easily for local or on-site gas generation, and this is the process most often adopted by manufacturers who don’t want to depend on deliveries and storage.

Suitable Materials for Gaskets in Nitrogen Systems

Nitrile and natural rubber gasket materials are good choices for gaseous nitrogen, although EPDM is generally considered best. EPDM gasket material has good heat resistance and a working temperature range of around -60 to 320°F (-50 to 160C). Resistance to oxidation, UV, ozone, and abrasion are all good and it also withstands water, acids, and alkalies along with ketones and alcohols.

Handling liquid nitrogen demands a gasket material with excellent low-temperature performance. If an elastomer is needed Santoprene® may be a good choice. A trade name for a class of thermoplastic vulcanizate (TPV) materials, this behaves much like EDPM but some grades remain flexible at even lower temperatures.

Consult a Materials Expert

Every gasket application is different so it’s always prudent to learn more about the material before purchasing. Specialists at Hennig Gasket are ready to help.

EPDM Gaskets, Nitrile Gaskets
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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.

FAQs
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Why Steel Rule Die-Cut Gaskets are Disappearing

Jan 22, 2018

No one likes waiting for a gasket, especially when it’s for an urgent repair. No one wants to keep spare gaskets in inventory either. That’s why more gaskets are being water-jet cut. As tooling-free processes, they offer a faster turnaround than die cutting. Here’s more detail.

Steel Rule Die Lead Time and Storage

Each die is made to cut a unique non-metallic gasket. The sharpened blade is pressed into a slot cut in a backing board. Then ejection rubber is fitted around the blade to push out the cut gasket shape.

These take days or weeks to make so gasket manufacturers keep previously used tools in storage. At Hennig, we have thousands taking up space. If a customer wants a die cut gasket we check whether we have the tool needed. If we don’t, water-jet cutting is faster.

Tool Maintenance and Repair

Steel rule edges wear. That affects quality and accuracy, so they need sharpening and/or changing. Likewise, ejection rubber needs regular replacement.

In addition to faster order turnaround, these processes offer:

  • Better edge quality – no compression means straight and square edges.
  • Higher accuracy – water-jet machines can maintain tolerances as tight as +/- 0.0005” while die cutting struggles to beat +/- 0.010”. That’s because the machines are more precise and there’s no deflection or compression of the gasket material.
  • No tooling charges.

Die Cutting for Higher Volumes

Water-jet machines cut quickly, but not as fast as a tool in a press. (And rotary die cutting is even faster.)

Against that, the die cutting press takes time to set up. The breakeven point depends on gasket size, but water-jet and laser usually win for small quantity orders. Die cutting gets cheaper per piece for large quantities but don’t overlook tooling charges.

Speed Wins

With water-jet machines, gaskets can be cut to order. That enables a rapid turnaround that avoids holding spare gaskets in inventory. No wonder die cut gaskets are going away.

Flange Gaskets
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When to Use Felt Gasket Material

Jan 08, 2018

Most gasket materials are elastomeric or rubber-like in nature, but there’s another material that’s surprisingly effective in some sealing applications: wool. When compressed to a uniform density wool becomes felt. Felt has been used for sealing and gasketing for a long time and still has its uses.  Felt seals suppliers offer a variety of options.

A “Non-Woven” Material

Most felt is produced by compressing wool into rolls of material. Wool fibers have a kind of “fish scale” surface that lets them hook together randomly. This creates a material that’s soft and compliant with a high level of resiliency. It can absorb and hold liquids even better than an open cell foam while resisting attack by oils and temperatures up to 200°F. An added benefit is that felt won’t unravel or fray like woven fabrics.

Industrial wool felt is specified by an SAE standard. This assigns grades from F-1 to F-55. Higher numbers indicate lower density, and these grades have less ability to absorb vibration and resist abrasion.

Felt is produced from other materials, most notably polyester fiber. Polyester felt will withstand temperatures up to 300°F but its properties and behavior are not addressed by the SAE standard.

Uses of Felt Gasket Material

  • Noise-deadening

Thanks to strong resilience, felt gasket material can absorb movement between surfaces that would otherwise cause rattles and squeaks. By preventing the transmission of vibration it’s also a good sound-deadening material.

  • Filtration

The random orientation of fibers in felt make it a very effective filtration medium. Filtration is further enhanced by soaking in oil. Wool fibers hold oil on their surface, which traps very small particles being drawn through.

This ability to retain oil also makes felt a good seal against moving surfaces such as shafts. The wool adapts to changes in gap while oil provides lubrication and simultaneously prevents fluid transmission.

Compliant but Durable

As a soft gasket material, felt is similar to an open cell neoprene, EPDM or silicone foam. Its upper-temperature limit is lower, but depending on grade, abrasion resistance can be higher. If you’re looking for a material that can lubricate as well as seal, ask about felt.

felt
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