How to Install a Gasket

Oct 28, 2019

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.

FAQs
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White Nitrile Rubber

Oct 14, 2019

Gaskets made from white nitrile rubber won’t impart any taste to food. That’s one reason they’re used in food and beverage production but it’s not the material’s only useful property. Here’s a look.

Understanding White Nitrile Rubber

White nitrile rubber – chemical name Acrylonitrile Butadiene – carries the ASTM designation NBR and is sometimes referred to as white Buna-N. A blend of neoprene and SBR, white nitrile rubber is an abrasion-resistant elastomer. Shore hardness is around 60, putting it somewhere between tire tread and a pencil eraser, making it firm yet flexible.

White nitrile is usable over temperatures from around -40°F to 220°F (-40 to 105°C.) It resists attack by oils, fats, greases and hydraulic fluids although it is vulnerable to ozone, ketones, esters and aldehydes. (These were explained in a previous blog post, “Ketones and Gasket Materials”.)

Nitrile rubber is produced in a range of colors, but white nitrile is, as the name suggests, white. This gives it some useful applications.

Applications for White Nitrile Rubber Gaskets

As it doesn’t mark surfaces or impart a taint, white nitrile is available in grades approved by the FDA for food use. It’s also non-allergenic. Consequently, white nitrile gaskets are common in food and beverage production as well as pharmaceuticals.

White nitrile rubber is also used in applications where appearance matters. The smooth white finish is often desirable, especially in medical applications, and has a secondary benefit: it shows up leaks that would be unseen against dark materials.

In addition to sealing and gasketing applications, white nitrile is used for cushioning and protection. You may see it as liner in food processing equipment and also as bumper protection strips. A less obvious, though still common application, is for food grade rubber scrapers.

Talk to Hennig Gaskets & Seals

Gaskets for food and pharma use must comply with FDA requirements. White nitrile is often a good choice for such applications, although it has other uses too. As an attractive, non-marking material it works well in situations where appearance matters. Learn more by talking to our specialists.

Food Grade Gaskets, Nitrile Gaskets
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Spiral Wound Gasket Manufacturers

Sep 30, 2019

Spiral Wound Gasket Manufacturers and Suppliers are your best resource for understanding the selection process.  When choosing a gasket material recovery and compression set should be important considerations. That’s because joints flex and move under changing temperature and pressure. If the gasket material can’t adapt to a varying distance between flanges the joint is certain to leak.

Rather than rely on the inherent material properties, spiral-wound gaskets seal by acting like a spring, expanding and contracting to fill the space available. Spiral-wound gaskets aren’t the solution to every gasketing problem, but for flanged joints, and especially those in petrochemical industries, they can be an excellent solution.

Spiral-wound gasket construction

Spiral-wound gaskets are made from a flat metal strip coiled into a shape rather like a clock spring. Interleaved with the steel is a good sealing material like PTFE or graphite. The metal is given a bend as these are coiled so that in profile it has a ‘U’ or ‘V’ form.

This profile gives the gasket its excellent recovery. Imagine the flange faces pressing against the legs of the ‘V’: closing the gap compresses this shape while opening it lets the ‘V’ spread further apart. In this way, the gasket stays in contact with each flange and maintains a good seal.

Most spiral-wound gaskets have a solid metal outer ring. This prevents over-tightening which would damage the gasket. Some also have an inner ring to protect against chemical attack or high pressure.

When to use a spiral-wound gasket

Spiral-wound gaskets excel in flange applications that see big swings in temperature and pressure. (The kind of environment that makes bolts lengthen and clamping pressure drop.) In addition, when the non-metallic element is PTFE or graphite these gaskets provide excellent resistance to chemical attack. This is why spiral-wound gaskets are the gasket of choice in refinery and related petrochemical applications.

Spiral Wound Gasket Manufacturers and Suppliers

It takes specialized equipment to manufacture spiral-wound gaskets. The leading producers are Flexitallic and Garlock. At Hennig we stock gaskets from both, and if you need something non-standard we can get that for you too. If you have an application you think needs a spiral-wound gasket, call or email and we’ll be happy to help.

Spiral Wound Gaskets
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NEMA vs IP Rating

Sep 16, 2019

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.

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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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SBR Rubber Sheet – When (and when not) to Use

Aug 19, 2019

It’s hardly surprising the SBR Rubber Sheet (red rubber) is one of the most widely used gasket materials. Firm and smooth, it conforms readily to mating surfaces. Good tensile strength and abrasion resistance ensure durability, providing it’s not used in the wrong places. Here’s what you should know about using red rubber gasket material.

SBR Rubber Sheet:  A Proven Elastomer

Red rubber is produced by blending Styrene Butadiene Rubber (SBR) with natural rubber. SBR was one of the first synthetic rubber materials, produced by polymerizing styrene and butadiene in a roughly 3:1 ratio. Invented early in 20th Century, production increased rapidly during WWII as supply chain challenges limited availability of natural rubber. SBR’s strengths include resistance to cracking, abrasion resistance and low cost. Unlike natural rubber, it hardens with age.

When natural rubber is added to SBR the result is a red-colored elastomer with the best characteristics of each. Several grades are available with varying properties. Hardness is in the range 75 – 80D on the Shore A scale. (For more information, refer to “Understanding Gasket Material Hardness”.) The main limitations of red rubber are a temperature range limited to -20 to 160°F and swelling when exposed to hydrocarbons.

Applications to Avoid with SBR Rubber Sheet

Red rubber is not suitable for use with oils and fuels like gasoline and diesel. It also offers poor resistance to chemicals, solvents and hydraulic oils. In addition, it is degraded by ozone, so electrical, (especially high voltage,) applications are best avoided.

Good Applications for SBR Rubber Sheet

Red rubber gaskets perform well when sealing against air and water, both hot and cold. Saturated steam is also usually sealed effectively by red rubber.

SBR Rubber Sheet:  Often the Right Choice

Many sealing and gasketing applications don’t need high-temperature capability or high levels of chemical resistance. When that’s the case red rubber is often a better choice than newer and more exotic materials. Produced in a range of sheet thicknesses, it lends itself to die as well as water jet cutting and can be a very cost-effective choice. For more information call or email the specialists at Hennig Gasket.

SBR Gaskets
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Polyurethane Foam Gasket Not a Seal

Aug 05, 2019

Polyurethane, sometimes referred to just as ‘urethane’ is one of the most widely used materials for seals and gaskets. It’s inexpensive and has characteristics that make it very useful. Just be careful not to use urethane gasketing foam when you need a polyurethane seal!  A polyurethane foam gasket is different from a polyurethan seal.

Polyurethane properties

Polyurethane is formed by reacting isocyanate with polyol. Isocyanate is a simple compound of nitrogen oxygen and carbon while polyols are formed from oxygen, hydrogen and carbon. Put them together and you get materials that make excellent seals and gaskets.

Polyurethane seals work well from around -65°F up to 210°F. Below this minimum they become brittle while at higher temperatures they melt. Polyurethane is tough with good impact resistance and load bearing capacity. It’s also resistant to attack by petroleum and hydraulic oils.

Polyurethane is produced in a range of hardnesses, although the bulk of the material used for seals is around 95 Shore A. It’s tough, stronger than natural rubber, and abrasion resistant.

Polyurethane becomes a lot softer when foamed. This entails adding a foaming agent to the isocyanate/polyol reaction to create a gas. As the liquid solidifies this leaves bubbles dispersed throughout the material, which gives it a springy resilience.

Applications for polyurethane foam

Cushioning is probably the biggest application. Polyurethane foam is used in furniture, shoes and anywhere else that compliance and recovery are sought after. Gasketing is another common use. Here it’s compressibility cushions against impacts and takes up manufacturing tolerances.

One time not to use polyurethane foam is when sealing is needed. Most polyurethane foams have an open cell structure, so fluids can pass through.

Polyurethane seal applications

With it’s excellent abrasion resistance, polyurethane is often used in situations where there’s relative movement. Seals around rods in hydraulic cylinders is one example, where the oil resistance also helps ensure long life. Pipe seals are another common application, as are wipers and shaft seals.

Buy the right polyurethane!

Polyurethane, or just plain urethane, is a good choice for many seal and gasket applications. Just remember that in it’s foamed state it may not provide much of a seal!

Polyurethane 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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CIP Process and Affect on Seals and Gaskets

Jul 08, 2019

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.

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PTFE Seals – When Elastomers Aren’t Up to the Task

Jun 24, 2019

Elastomers are often the first choice for sealing and gasketing, but they’re not always the best. Silicone, neoprene, EPDM and Buna-N all have limitations that disqualify them from some applications. When that’s the case it may be time to consider PTFE seals.

Limitations of Elastomers

Elastomers are challenged by temperature extremes, aggressive chemicals and UV light. Some swell when in contact with oils, others outgas or give up molecules to the fluid being sealed against.

Food processing is a difficult environment. While it’s important to avoid product taint the materials must also endure aggressive cleaning regimens. Medical and pharmaceutical equipment presents similar challenges.

Many elastomeric materials harden in UV light, making them unsuitable for outdoor environments. Others will outgas, making them a bad choice for vacuum applications.

How PTFE Seals Score

PTFE is composed of carbon atoms bonded to fluorine. That makes it almost totally inert and a good choice for food, pharma and medical applications.

Less flexible than an elastomer, PTFE can nevertheless seal down to around -460°F. It’s also functional at temperatures as high as 570°F.

PTFE is unaffected by UV light, making it useful for outdoor applications or those involving UV sterilization. It has excellent electrical insulating properties and won’t swell when exposed to steam or oils. Another benefit from using PTFE seals in dynamic applications is a very low coefficient of friction.

PTFE Seals Limitations

Under load, especially at elevated temperatures, PTFE will creep. Joints should be designed to minimize the clamping forces applied directly to the material.

A second limitation is low strength. Some elastomers offer higher tensile strength combined with less elongation at breakage.

To address these issues PTFE formulators incorporate a range of fillers. Ranging from glass and carbon fiber to bronze and molybdenum disulfide, these can increase strength and hardness and reduce friction.

Seek specialist advice

When your sealing application challenges elastomeric materials it may be time to consider PTFE. However, with a large number of PTFE formulations available it’s difficult to know which is ideal. In such cases consult a materials specialist like those at Hennig Gasket.

PTFE Gaskets
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