The Role of Fiber Gaskets

Mar 27, 2017

While there are many new elastomeric sealing materials, it’s often prudent to follow the mantra, “What comes out of the joint goes back into the joint.” Especially in older processing and heating equipment that is often a fiber gasket. Many different materials can be used to provide the fibers, so the properties and applications of these gaskets vary enormously.

Back to Asbestos Gaskets

In 1899 an Austrian called Richard Klinger discovered a way of making effective soft gaskets by compressing asbestos fibers into sheet form. These sealed under low loads and resisted steam, oil, water and high temperatures and pressures. That made them ideal for use in boilers, heat exchangers and heating and hot water systems as well as oil refining and other process industries.

By the 1980’s the health hazards of asbestos were well-known and gasket manufacturers were substituting other materials with similar properties. Sticking with fibrous material in a binder meant they could use the existing manufacturing processes, one reason why fiber gaskets remain commonplace today.

Modern Fiber Gaskets

The main types of fiber gasket material are:

  • Cellulose
  • Cellulose with rubber
  • Cellulose with insulating fiber
  • Cellulose with synthetic fiber
  • Cellulose with vulcanized fiber
  • Vegetable fiber (Detroiter)

These are all available in a range of sheet thicknesses and die-cut readily. They are considered “soft” gaskets, meaning they are suitable for applications with relatively low clamping forces, such as Class 150 and 300 flanges.

Fiber Gasket Properties

Gasket properties are determined by both fiber and binder material. For example:

  • Vegetable fiber (Detroiter) gaskets – upper temperature limit of around 250°F (121°C), good resistance to oil, gasoline, water and steam. Generally inexpensive.
  • Cellulose fiber with rubber – upper temperature limit around 350°F (177°C), good resistance to oil, gasoline, water and steam.
  • Aramid fiber in NBR binder – upper limit on temperature can be up to 825°F (440°C), suitable for a wide range of industrial applications.

Fiber Gasket Identification

If you’ve removed a fiber gasket and aren’t sure what type it is, bring it in. Our materials experts should be able to help.

Fiber Gaskets
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Brewery Gaskets? We’ll Drink to That!

Mar 13, 2017

Most gaskets are used to seal fluids or for environmental protection. Every so often though we are asked for a gasket for a less common application. One interesting example is the silicone or EPDM gaskets used around manways in brewery tanks.

Equipment Cleaning

Brewing depends on fermentation, a natural process involving lots of enzymes and chemistry. If the equipment is less than perfectly clean bacteria may contaminate what will become beer.

To avoid this, breweries clean and sterilize rigorously. Every mash tun and fermentation tank, plus the pipework in between, is treated with steam, caustic cleaning solutions, or both. Larger tanks often need someone to go inside to do the cleaning, which is why they’re usually constructed with a “manway”.

Manway Gaskets

A “manway” is an entrance point big enough for a man to enter through. Usually circular or oval, if located at the bottom of the tank, they need to withstand the pressure and temperature of the liquid inside. Some are just cover plates bolted to a flange, but in brewery equipment, it’s far more common to have a hinged door that clamps shut.

Regardless of design, every manway needs a gasket to stop it leaking. Those used in breweries must tolerate cleaning chemicals and steam as well as process heat. To avoid the need for high clamping forces, they should be soft, and ideally will resist taking a compression set. They also have to be food-grade to avoid imparting any kind of taint or contamination.

Suitable Gasket Materials

For manways in brewery tanks food-grade silicone and EPDM gaskets are the most common choice. Both are elastomers, so while they are elastic and deform under even quite light loads, they do not compress. Silicone gaskets have the higher temperature limit, typically 400°F (204°C), and are resistant to fungal attack, but have poor tolerance to steam.

EPDM gaskets have a lower upper-temperature limit, (250°F – 121°C) but are resistant to steam, ozone, acids, and alkalis. For this reason, these are the type of gasket used in many brewery tank manways.

Manway Gaskets
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Hennig Gasket & Seals – Part of Chicago

Feb 27, 2017

Hennig Gasket has been in business close to a century, and there’s still a Hennig at the helm. The business was started by Otto Hennig in 1920 before passing to James Hennig. He ran it for forty years until his retirement in 1987, and now it’s run by third and fourth generations of the family.

A lot has changed in that time. When Otto Hennig started the business the automobile was in its ascendancy, electricity was spreading across the country, and demand for gaskets for heating systems and manufacturing operations was growing. Of course, Chicago endured a few challenges in that period, but who knows, maybe cork or fiber gaskets made by Hennig found their way in to some of the bootlegger’s stills!

Some things haven’t changed though. We still make traditional cork and fiber gaskets, die cutting them from sheet, or if we don’t have the tooling, using an oscillating knife or even just hand cutting. If you’re maintaining or restoring aging equipment that used gaskets like these we can supply replicas of the originals. Alternatively, you may prefer upgrading to one of the many modern gasket materials that manufacturers have developed.

One example of material changes is the rise and fall of asbestos gaskets. Once essential in high temperature applications like boilers, (and perhaps stills,) these have been replaced by a range of non-asbestos gasket materials like Garlock BLUE GARD®. (This incorporates aramid fibers in a nitrile, neoprene or SBR binder.)

Neoprene and SBR gasket materials have themselves been around a long time, (just like Hennig Gasket & Seals!) but today there many newer alternatives. Elastomers like EPDM and FKM are proving valuable in many applications, especially for sealing against corrosive and high temperature fluids.

The best way of learning about gasket material properties is by speaking with an expert. At Hennig we’ve accumulated a wealth of knowledge and experience. And if you’re in the Lower West Side neighborhood of Chicago, call in. Just look for the brick mill-style building at 2350 West Cullerton.

Gaskets & Seals
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Understanding Gasket Tolerances

Feb 13, 2017

Like everything manufactured, gaskets have tolerances on their key features. These are dictated by a combination of material characteristics and manufacturing process. It’s important to understand these tolerances if your new gasket is going to fit.

Key Features

Unless a gasket goes in a channel the outer dimensions aren’t usually critical. What does matter though are the bolt hole positions, bolt hole diameter, and the inner shape, (because the gasket should not intrude into the flow.)

Gasket Material Thickness

Tolerances are dependant on the type of material and industry standards.  RMA commercial gauge sheet rubber tolerance chart shows typical tolerances. 

Manufacturing Process Tolerances

Here at Hennig, gasket material is cut in four ways: die cutting, oscillating knife (flash cutting,) water jet and by hand. Die cutting, used for quantity orders, is probably the least accurate yet also the most repeatable. The oscillating knife and water jet machines provide excellent accuracy, and as they cut one gasket at time repeatability is about the same. Hand cutting is the least accurate.

Here’s some more detail on each process:

  • Die cutting. Accuracy, defined as conformance to design, is set by the precision to which the steel rule is set into the mounting block. A laser-cut block can usually hold +/- 0.015” (+/-0.381mm) although this tolerance increases with the size of the tool. Larger tools are less precise. Softer, thicker material deforms more during cutting and a convex edge profile may result. Die-cut gaskets are very consistent, with the first piece identical to the last, (until the blade starts to wear.)
  • Water jet cutting. Accuracy is set by the precision of the gantry and table motion. In general, this is around +/-0.007”.
  • Oscillating knife. Machine repeatability is claimed as 0.010mm but in practice +/-0.003” (+/-0.076mm) is more typical. Softer and thicker materials can show greater variation.

Consider Tolerances When Ordering

Critical gasket dimensions influence the choice of cutting methods. In such cases, it’s important to let us know about these at the quotation stage.

Flange Gaskets
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The Role of Gaskets in Minimizing Fugitive Emissions

Jan 30, 2017

Fugitive emissions are a serious matter for chemical plants and petrochemical facilities. First, the EPA is focused on reducing unplanned releases of VOC’s into the atmosphere, and second, it’s a cost-saving opportunity. Studies blame valves for the bulk of these emissions, but flanged joints and their associated gaskets play a part too.

Hunting Fugitives

Defined as “… unanticipated or spurious emissions from any part of the process plant,” in 2014 the Fluid Sealing Association estimated fugitive emissions amounted to some 300,000 tons annually. Furthermore, it’s thought a high proportion are hydrocarbon gasses like methane believed to be environmentally harmful.

Plants handling such chemicals are expected to implement Leak Detection And Repair (LDAR) protocols, preferably on a monthly basis. “Sniffing” technology is the method most commonly employed, although IR camera technology is increasingly available.

Prevention First

Should a LDAR survey reveal a leak the next step is usually to shutdown the affected equipment for valve repair or gasket replacement. Unplanned shutdowns are disruptive and expensive, making it essential to avoid such events. While leak-free performance can never be guaranteed, buying different types of quality gasket materials and following good sealing disciplines will reduce the likelihood of problems.

Three Principles to Follow

  • Select material appropriate to the media, pressure and temperature. Nitrile gasket material for instance is generally compatible with hydrocarbons like gasoline but should not be taken above 250°F. A neoprene gasket will perform better against ammonia, alcohols and mild acids while high temperature applications may need a fluorocarbon or PTFE gasket. In particularly arduous conditions a spiral wound gasket might be needed.
  • Analyze the joint to determine material thickness and hardness needed. The general rule for gasket materials is “as thin and soft as possible.” The goal is always to ensure the gasket compresses sufficiently to seal the gap when the joint is bolted up. High bolt loads risk deforming the flange, potentially causing leaks.
  • Follow good gasket replacement disciplines. Clean flanges thoroughly and verify mating surfaces are undamaged. Tighten bolts following the recommended sequence to avoid uneven compression and the risk of gasket extrusion.
Gasket Material
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Gasket Swell Isn’t Always Bad

Jan 16, 2017

If gasket material isn’t chosen to suit the fluid being sealed, problems are almost inevitable. One reason is that some fluids will make the gasket grow thicker. This is an effect called swell. It increases bolt loads and can lead to material extruding out of the joint. Almost every gasket material has a fluid that will make it swell to some degree.

Bad Combinations

To give one example, an Acrylonitrile Butadiene Rubber (NBR) gasket swells significantly when exposed to acetone or methyl ethyl ketone yet shows almost no growth in the presence of vegetable or mineral oils. Hydrocarbons and petroleum products are a particular problem because they will cause swelling in several widely used gasket materials. EPDM, Styrene Butadiene Rubber (SBR) and Neoprene gaskets are prime examples and should not be used to seal these fluids.

Information on susceptibility to oil swelling is given in the ASTM D2000 classifications for elastomeric materials. This was addressed in “Buna-N (Nitrile) Gaskets and Oil” and “ASTM and Gaskets.”  Rubber gasket material sheet properties are essential to know.

Some Exceptions Apply

There are times when a gasket installer might use swell to his advantage. This would be when it’s difficult to get the required level of compression. To give two examples:

  • Thinner flanges not meeting ASME/ANSI standards may distort as bolts are torqued, resulting in a variable gap.
  • Bolts may lack the thickness or strength to take the necessary loads.

Faced with these problems, choosing a gasket material prone to swelling can be the solution. When exposed to fluid in the pipe the inner region of the gasket will swell, increasing the loading achieved.

Buy the Right Gasket Material!

Harnessing the swell effect doesn’t just mean deliberating selecting the wrong material. This would swell unpredictably, possibly with catastrophic results. However, some gasket material manufacturers produce so-called “controlled swell” material. Often employing Styrene Butadiene Rubber (SBR) binders, these provide predictable growth. (“Controlled swell” material is available for fluids other than hydrocarbons, even water!)

Ask About the Material

If you have a hard-to-seal joint “controlled swell” gasket material might be worth considering. Discuss what’s available with the material specialists at Hennig Gasket & Seals.

Rubber Gaskets
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Custom Gasket Cutting

Jan 02, 2017

One of the challenges with replacing gaskets is that you don’t always know what kind of replacement is needed until you get the joint apart. If you’re lucky it takes a standard gasket that you can collect or have shipped out. If you’re unlucky though you’ll need a fabricator who provides custom gasket cutting — FAST.

The Cost of Downtime

When a gasket starts failing prompt replacement is essential: product is being lost, yields are falling, and profits suffering. Worse still, you might be risking both ground contamination and fugitive emissions from pipeline leaks, which could lead to legal action and fines.

Unfortunately, gaskets can’t be replaced without taking joints apart. That means shutting down production so that pipes are cool and empty. Once the new gasket is in place, start-up may take several hours. Lost production means lost sales, and that money may never be recovered.

Gaskets and Inventory Costs

Few maintenance departments have the luxury of keeping in stock every gasket that might ever be needed. Even if there was enough space and Accounting would tolerate the costs, the material ages and eventually becomes unusable.

Just-in-Time Delivery

Many maintenance operations have adopted a different approach. Instead of carrying a large gasket inventory, they’ve aligned themselves with custom gasket suppliers capable of rapid delivery.

Configuring a business to cut and deliver custom gaskets in just hours takes a significant commitment of time and money. A large inventory of gasket material is essential, as are flexible cutting processes that don’t demand long lead-time tooling.

With an extensive range of material on-hand, plus computer-controlled cutting machines, Hennig is positioned to provide the fastest possible turnaround. To save time, new gaskets are often reverse-engineered from the one that’s been removed, and it’s not uncommon to work from photocopies of gaskets and even hand-drawn sketches.

Gaskets Aren’t Expensive, Downtime Is

When you need a gasket in a hurry, think of Hennig. A massive inventory of gasket material, combined with flexible cutting/manufacturing processes means we can produce a custom gasket in just hours. That means less downtime, which goes straight to your bottom line. Contact us today for fast and accurate custom cut parts.

 

Gaskets & Seals
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Enclosure Sealing to Prevent EMI Leakage

Dec 19, 2016

The silicone gasket around the door or access panel of an electrical enclosure has two jobs. Not only does it keep dust out, but it also keeps electrical noise in. Or it does if made from the right material.

The Noise Problem

Electrical noise, sometimes called electromagnetic interference (EMI) or radio frequency interference (RFI) is a problem in some environments. By interfering with wireless transmissions EMI makes phone calls difficult and disrupts wireless data transmission. It can also induce currents in other conductive materials. That can lead to spurious data signals, possibly giving rise to false alarms or affecting process control equipment.

Conversely, sometimes sensitive electrical equipment needs shielding from environmental EMI. Placing it in a metal enclosure keeps the EMI outside, avoiding problems of signal interference.

EMI Sources

EMI travels through air, spreading out from a source much like ripples on a pond. Circuit breakers, relays, transformers and switches can all produce EMI. This is one reason they’re often placed in an enclosure. Motors, power cables and welding equipment also produce EMI, but aren’t so easily shielded. However, sensitive electronics near these items may need to go in an enclosure.

Conductive Shielding

When waves of EMI meet a conductive material the energy spreads out over the surface rather than continuing on. Gaskets and flanges however provide an opportunity for leakage.

With most enclosures, closing the door leaves an uneven gap. That could allow dust inside, which is the main reason a gasket is fitted around the opening. Electrical enclosures are usually sealed with silicone gaskets, which offer good compression and stand up to elevated temperatures. However, silicone is not naturally electrically conductive. That results in a leak path where EMI can escape.

Ask for Electrically-Conductive Gasket Material

When replacing gaskets around an electrical enclosure, or specifying new, always consider the need for EMI shielding. Electrically-conductive gasket materials are available, but it’s important this issue is raised when speaking with the material supplier. In many cases conventional silicone gasket material will be sufficient, but if EMI could be a concern, let your vendor know.

Silicone Gaskets
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Fiber or Rubber Gasket Material

Dec 05, 2016

One of the most important properties in a gasket material is compressibility, and this leads many gasket buyers to think they need rubber. In many cases though there is an alternative: fiber gasket material. “Fiber gaskets” is a broad heading as there are many different types. Here we’ll explain what “fiber” means, how it differs from rubber and other rubber-like elastomeric materials, and when you might want to use it.

What is a Fiber Gasket?

Fiber gasket material is made through a process similar to papermaking. Strands of fiber are spread out and impregnated with a resin material. This dries to form sheets that are easily cut to shape.

Many different type fibers are used to produce gaskets with differing strength, compressibility and temperature ratings. These range from vegetable fiber and cellulose to more exotic materials like aramid, (a strong, heat resistant synthetic fiber.)

When additional compressibility is needed cork or a rubber binder (often NBR) is added. Alternatively, cellulose fiber material can be vulcanized to make a paper-like material that’s both hard and lightweight. When this has electrical insulating properties it’s known as “fish paper.”

Possibly the oldest type of gasket still in use is the vegetable fiber or “Detroiter” gasket. This is made from vegetable fibers impregnated with a glue-glycerine compound. It remains a popular choice in some applications.

Fiber Gasket Properties and Applications

Fiber material makes gaskets with high tensile strength, (so they’ll resist internal pressure,) and an upper temperature limit of 250 – 350°F. They have excellent resistance to chemicals, particularly oils, so are used in many industrial situations, especially chemical and petroleum product manufacturing.

The Contrast with Rubber

While true rubber is a natural product, the rubber used in gaskets is almost always a synthetic version. Synthetic rubbers function over a wider temperature range and are less vulnerable to damage by UV light. Commonly used materials are nitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), neoprene and EPDM. Available in a range of thicknesses and grades of hardness, these have generally good compressibility but are vulnerable to the effects of petroleum oils.

Hennig Gasket & Seals manufactures custom gasket from a large variety of fiber gasket material.  Contact us today for a fast quote.

Flange Gaskets
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How Does Foam Seal?

Nov 21, 2016

Foam gaskets for HVAC systems and enclosure panels and doors are cut from elastomeric materials with a cellular structure that looks like sponge. Although compressible, sponges tend to absorb water, so we’re sometimes asked how foam can make a good sealing material.

Open or Closed?

Foam is made by trapping bubbles in the material as it solidifies. These form during the chemical reaction that creates the elastomeric material. Foam manufacturers control the size of these bubbles by managing the reaction process and using chemical additives.

An important property to consider in foam gasket material is whether the cellular structure is open or closed. When the structure is closed bubbles are closed off from one another and there’s no way for air or any other fluid, to move between them. In contrast, in an open structure most of the cell walls are missing, which lets fluid travel through readily.

Sponges are generally open because their purpose is to absorb water. Foam with a closed structure doesn’t have this ability, and that makes it fluid-resistant.

Open cell foam can be used as gasket material provided complete impermeability isn’t needed. Compressing it to less than 50% of its free thickness leaves very little space for liquid to pass through. This allows it to be used where light water exposure is possible.

Other Pluses and Minuses

A cellular structure makes elastomeric gasket materials less dense, which is beneficial when weight is a concern. They also tend to be soft and compress easily, although closed cell material is firmer because the air inside the cells has nowhere to go. While compressed, the air slowly permeates through the cell walls, and recovery is slower when the load is taken off.

Identification

Flexible cellular materials are covered by ASTM D1056. This standard uses a three character code to describe foam materials. The first character is either a “1”, meaning an open structure, or a “2”, meaning closed. When ordering a foam gasket material it’s important to be clear which is needed. If in doubt, speak with a Hennig Gasket material specialist.

Foam
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