Applications

UV Resistant Rubber Sheet

Sep 02, 2019

You’ve probably seen dried up and cracked nitrile and neoprene gaskets. Chances are, you’ve replaced a few too! In many cases the culprit is ozone. Here we’ll explain what ozone is, how it forms and what processes/activities expose gasket materials to ozone. Then we’ll suggest materials to use if you have an ozone problem which includes UV resistant rubber sheet.

An oxygen compound

Ozone is just oxygen atoms bound together in groups of three. Its chemical symbol is O3. In nature, ozone exists only in the stratosphere, a layer of the atmosphere five to thirty miles up. However, it can be produced artificially at ground level, and those are the processes that break down nitrile and neoprene gasket materials.

Oxygen atoms react readily with other elements. That’s why iron rusts and aluminum oxidizes. O3 is even more reactive than regular O2, so oxidizes materials even faster. When it contacts gasket materials like nitrile rubber (Buna-N,) natural rubber and neoprene it changes how their polymers are crosslinked. This hardens the material, which then cracks under load.

Ozone-producing processes

Ozone forms in the presence of ultraviolet (UV) light and electrical sparks. Both can break the bonds between oxygen and itself and other elements to free up individual atoms. These quickly recombine as O3.

UV light is widely used for purification and disinfection. Many city water systems use UV purification and UV disinfection is widespread in the medical sector. Ozone is a natural byproduct and itself is used for purification.

Electrical sparks are common around brushed electric motors, especially those using high voltages. High voltage switchgear is another source of ozone.

UV Resistant Rubber Sheet

When choosing a gasket material for an ozone-producing environment stay away from nitrile rubber and neoprene. Instead, consider silicone and EPDM materials. These are available with similar properties to nitrile and neoprene but are less susceptible to oxidation. Other good choices are PTFE and Viton/FKM.

Talk to the UV resistant rubber sheet materials specialists

If you think ozone could be an issue in a gasket application, talk to our specialists. They’ll help you select an EDPM, silicone or other ozone-resistant material suitable for your application.

Applications, EPDM Gaskets, Silicone Gaskets
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Low Temperature Gasket Material

Jul 22, 2019

Many elastomeric gasket materials have a problem with low temperatures. Here we’ll look at some applications that pose challenges and suggest low-temperature gasket materials worth considering.

Low-Temperature Gasket Material Applications

Seals and gaskets are used in many low-temperature environments. One of the most common is food storage. Freezers and cold rooms are typically kept between -80 and 20°F, depending on the application. Pharmaceuticals and medical products are other industries with low-temperature storage requirements.

Industries that do product testing often employ climatic chambers. These need effective seals to minimize the expense of maintaining low temperatures, and it’s also important to consider the equipment inside. And as Chicagoland residents understand, midwest winters can challenge sealing materials used outdoors, especially if exposed to wind.

Glass transition and TR10

Polymers get their flexibility from chains of molecules moving against one another. As temperatures fall the chains are less able to move and eventually become fixed. Materials scientists call this point the glass transition temperature.

For people who need to choose and use gasket material a more useful indicator of low-temperature flexibility is the TR10 value. This was explained in, “What is TR-10 (temperature of retraction) for Gasket Material?”

Good Low-Temperature Gasket Material Choices

Oil-resistant FKM only goes down to around 5°F. NBR is useable as low as -20°F and some specialized grades will go lower. However, these aren’t low enough for many freezer-type applications. Silicon is good for temperatures as low as -65°F and fluorosilicon will go to -80°F but both are expensive. That leaves cost-effective EPDM as an excellent low-temperature gasket material.

The TR10 value for EPDM is between -49 and 9°F, depending on grade. That makes EPDM seals a good choice for many commercial and industrial low-temperature storage facilities. Furthermore, EPDM is available in FDA-approved grades for food industry use.

The chief limitation of EPDM seals is poor resistance to mineral oils and hydrocarbon products. They are good with steam and hot water though, as well as caustic cleaners.

Consider price as well as performance

In low temperatures, many gasket materials become too stiff to seal effectively. Silicon offers good performance but less expensive EPDM comes close for many applications.

Applications, EPDM Gaskets, Silicone Gaskets
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Sealing Helium: Best Gasket Materials to Use

Aug 20, 2018

Helium is used for cooling in electronics manufacturing. It’s used extensively for leak testing and it can be the inert gas in MIG and TIG welding. That means a lot of equipment needs gaskets to keep helium contained. Here’s some advice on what to use.

Helium Properties

Only hydrogen has a lower atomic number than helium. That means, even compared to other atoms, helium atoms are small and light. Unlike hydrogen though, helium, (symbol: He) is very unreactive. It won’t burn or oxidize and doesn’t form compounds, all of which make it safe and easy to handle.

This “friendly” nature and small atomic size make helium the preferred gas in leak testing. If a pressure or vacuum chamber has even the smallest crack or pore helium will find a way through. In fact, helium is so good at finding holes in materials that it’s quite difficult to contain: at the atomic scale many materials have pores that helium can pass through.

Low Permeability Materials Needed

A material that lets helium pass is considered permeable. (The same material may be impermeable to larger atoms.) Permeability is measured in terms of the volume of gas that can pass through a given area in a set time.

Most polymers have a helium permeability coefficient. This indicates how well the material blocks the passage of helium. These values are useful when choosing appropriate gasket material.

Gasket Materials for Helium

Helium is so unreactive it can be used with any gasket made from an elastomeric polymer. The issue to watch for is permeation. (A gasket that lets the gas escape isn’t working very well!)

The polymer with the lowest helium permeation coefficient is nitrile rubber, (a.k.a. NBR or Buna N.) EPDM has only slightly higher permeation, closely followed by FKM/Viton. The material to avoid is silicone as helium can pass through it quite quickly.

When selecting a gasket for helium it’s also important to consider temperature and pressure along with compression set resistance. In most room temperature applications nitrile rubber/NBR/Buna N works well, but if in doubt, consult a material expert at Hennig Gasket.

Applications
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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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