Why Use PTFE Seals in Food Industry Applications?

Sep 12, 2016

Commercial cooking kettles used for boiling and preparing foods usually have a food grade gasket around the lid. By creating a good seal this helps the vessel build and retain pressure. This raises the boiling point of water, shortening cooking time while also destroying pathogens. A defective gasket can result in food not reaching the required temperature, potentially creating a health hazard. Additionally, the gasket itself can provide places for bacteria to become established.

This gasket leads a hard life. Not only must it withstand the heat and pressure of cooking, but it’s also expected to go through multiple cleaning cycles. In addition, it’s essential that it not transfer anything or impart any taint to the food being cooked. Several materials are available for such gaskets, but in many situations the best sealing option is PTFE.

A Versatile Sealing Material

Polytetrafluoroethylene, or PTFE, better known by it’s DuPont tradename of Teflon, has a number of properties that make it an excellent choice for a food grade gasket. At the atomic level it consists of a long chain of carbon atoms, each one of which links to two fluorine atoms. This linkage is so strong that PTFE won’t bond to anything else, hence its non-stick properties.

PTFE doesn’t melt until 635°F and is usable at temperatures up to 260°F. At lower temperatures it remains flexible well below freezing, as low as -100°F or even lower, depending on formulation. It’s also a good electrical insulator. Of particular relevance for food industry gasket applications, it doesn’t absorb water and it’s biologically inert. It does however resist attack by almost all chemicals, including aggressive cleaning and disinfecting agents like chlorine dioxide.

PTFE Seal Alternatives

Other materials have properties that are close or superior to PTFE in some regards. Silicone for example is flexible at low temperature, has good compressibility and a higher upper temperature limit. However, silicone does not fare well with steam, which is found in many food preparation environments. It also lacks resistance to acids, alkalies and chlorinated solvents, so is limited in its potential as a food grade gasket.

FDA Approved Seal Material

Gaskets & Seals made entirely of PTFE are covered by 21 CFR 177.1550, meaning they have FDA approval for food industry use. (PTFE incorporating filler material may not meet FDA requirements.) At Hennig we can supply PTFE sealss in thicknesses ranging from 0.015″ to 0.50″. Call or email for further information.

Food Grade Gaskets, PTFE Gaskets
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The Popularity of Garlock Gaskets

Aug 29, 2016

Everyone has favorites – favorite teams, favorite food, and some of our customers have a favorite gasket material manufacturer. At Hennig Gasket we want to give customers the gasketing solution that meets their needs, which is why we stock material from all the leading manufacturers.

“Leading” is key. We’re not going to sell you a material or product that will disappoint, so we’re particular who we deal with. The materials we stock and distribute come from established manufacturers with long track records and deep understanding of sealing and gasketing. One of those manufacturers, and certainly one of the best known, (customers ask for it by name,) is Garlock.  Hennig Gasket is a stocking distributor of all Garlock Gasket Material.

About Garlock

Part of EnPro Industries, who specialize in engineered industrial products, Garlock is in the business of sealing fluids and protecting pipelines. They manufacture around the world, including in the US, and their products are used in industries ranging from food and pharmaceuticals to petrochemicals.

Technology-Driven

Garlock prides itself on the quality of application engineering (AE) support provided, and backs that up with extensive testing and product development capabilities. They continually invest in their production facilities and use R&D to ensure a steady flow of new product innovations.

Non-Asbestos Sheet Gasket Material

We carry two lines of Garlock compressed gasket material: Blue-gard and the Garlock 9000 series. The Blue-gard sheet materials consist of aramid heat-resistant synthetic fibers, fillers, and an elastomeric binder. This can be SBR, NBR, EPDM or neoprene. The 9000 series materials are similar but replace the aramid with carbon fibers. The 9800, 9850 and 9900 all handle continuous maximum temperature of 650°F.

Why Garlock?

When replacing a gasket it’s usually a safe strategy to make the new gasket the same as the old. As Garlock gasket material is among the most widely used, it makes sense to stay with that, unless it wasn’t performing.

Global reach means Garlock gasket material is available around the world. That’s useful for multinational manufacturers wanting to standardize on their gaskets: they just have to ask for Garlock.

Garlock are undisputed experts in sealing technology and have AE facilities second-to-none. When a joint proves particularly difficult to seal they have experts who can usually find a solution.

You don’t stay in business a long time without being dependable, (and at Hennig we’ve 90 years experience to back that up!) Garlock has been around a long time too, and we believe that speaks to their reliability and customer focus.

If You Want Garlock Gasket Material …

… we’ve got it. We know Garlock is a favorite of many of our customers, and they make a quality product. That’s why we’re happy to offer Garlock gaskets and gasket materials.

Garlock Gaskets
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Eight Tips for Maximizing the Life of Boiler Seals

Aug 15, 2016

Taking a boiler out of service is both expensive and disruptive. It can leave a building without heat, hot water, or steam for days, meaning lost production and unhappy customers or tenants. That’s why it pays to schedule boiler maintenance some time out, preferably for shutdowns or holiday periods. Many facilities make this an annual event, so the manhole and handhole boiler gaskets as well as the seals used in pipe flanges need to last at least that long.

  1. Don’t assume any rubbery material will do the job. It won’t. Buy good quality boiler seals from a reputable supplier. (Look for those made from EPDM as they hold up well to steam.)
  2. Clean the surfaces to be sealed thoroughly. The new seal should contact only the metal surfaces, not scale, corrosion, or scraps of old seal. Take care to avoid scratching the metal surfaces though as that will create a leak path.
  3. Avoid using any adhesives, sealants or anti-seize compounds on the seal or flanges. These can lower friction and allow the seal to move as the joint is tightened.
  4. Center the seal in the flange. This ensures clamping loads are distributed evenly across the surface. Not doing so creates areas of high and low load that reduce gasket life and let leaks form.
  5. Minimize the surface area of the seal exposed to atmosphere. Hot air leads to oxidation of the seal material, quickly reducing it’s life. If necessary, add shields to protect against hot air.
  6. Don’t overtighten the joint. This accelerates the process of the material taking a compression set and will lead to premature failure.
  7. Excessive heat and pressure shorten seal life. Temperatures and pressure above 380°F and 180 Bar should be avoided.
  8. Never reuse old gaskets. The material will have taken a compression set.

It’s worth investing time and money in buying quality boiler seals and fitting them carefully. When the job’s done properly the seals should function as intended for at least twelve months. That reduces the chance of premature failure, which would almost certainly require an unplanned, and expensive, shutdown.

Boiler Gaskets
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What to Look for in Boiler Gasket Material

Jul 18, 2016

Gaskets are part of every boiler and steam or hot water system. They’re used around the many handholes and manholes provided for access and inspection, to prevent leaks in exhaust ducting, and wherever pipes are joined. If a boiler gasket fails the consequences are usually serious. Hot water, steam, or exhaust gas leaks are dangerous and reduced efficiency increases operating costs. That’s why safety experts recommend boiler gaskets be inspected regularly and replaced every year.

Boiler Basics

Every boiler consists of a burner or heating element and some form of heat exchanger. Water, often chemically treated to prevent corrosion, enters the heat exchanger and is heated to a target temperature. In a steam-producing boiler temperatures and pressures can exceed 380°F and 180PSI.

Exhaust gases go up a flue and steam or hot water enter the piping system. In steam systems the vapor condenses as it cools and the condensate returns to the boiler to be reused. Condensing boilers tend to produce a corrosive condensate, (actually carbonic acid,) in the exhaust stack.

Boiler Maintenance

Shutting down a boiler is expensive and disruptive, so it’s always better done as part of scheduled maintenance rather than in response to a leak. Most boilers benefit from an annual inspection and clean. Removing accumulated soot and scale improves efficiency and components should be checked for correct operation. As that involves opening handholes and manholes, it’s also a good opportunity to replace gaskets, even if they show no sign of leaks. (And never reuse a gasket as that could lead to an unplanned shutdown!)

Boiler Gasket Materials

On the fire side of the boiler gasketing is usually done with fiberglass rope or tape. This can handle temperatures of more than 1,000°F. Another option is graphite foil, often formed into a spiral wound gasket for sealing flanges.

On the water side the primary consideration is tolerance to steam. Secondary requirements are good tensile strength, (to resist the internal pressures,) and resistance to corrosive acids and water treatment chemicals. Heat and oxygen tend to oxidize many elastomeric gasket materials, and this should also be considered when selecting boiler gaskets.

All-in-all, the water side environment usually leads to EPDM gaskets. They have a wide temperature range, good compressibility, and the excellent steam resistance that’s needed.

Boiler Gasket Selection

Downtime is expensive, so it’s important to ensure the new gaskets will provide at least 12 months of trouble-free service. Boiler gaskets should be selected based first on performance and secondly, on ease of installation and replacement. A well-made gasket will fit comfortably, providing good coverage of the mating surfaces. Contact a Hennig specialist today to ask what’s recommended for your boiler.

Boiler Gaskets
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Understanding EPDM Gasket Material

Jul 04, 2016

When buying elastomeric material to seal a joint many people go straight for neoprene gaskets. Neoprene works well in many applications, but there are cases where other materials will perform better. One such material that should be considered for outdoor use, or situations where abrasive wear is possible, is EPDM.

EPDM is rubber-like in appearance and properties, so good compressibility and recovery is a hallmark of EPDM gasket material. Like all gasket materials though, it has strengths and weaknesses. This overview should help prospective buyers decide whether to consider EPDM gaskets.

Chemistry and properties

EPDM is an acronym for ethylene-propylene diene monomer. Ethylene and propylene are hydrocarbons and gases at room temperature, yet combine to make solid polymers like polyethylene and polypropylene. By adjusting the proportions and controlling the polymerization process it’s possible to create long molecular chains with more rubbery properties. That’s EPDM.

Sometimes referred to just as EPM, EPDM is a very stable material that resists heat, oxidation, and the aging effects of ultraviolet light. Unlike many other elastomers it’s flexible at low temperatures, and depending on how it’s formulated, works over a range of -60°F to 300°F.

EPDM has good mechanical properties too. Tensile strength is in the range of 7 to 21 Mpa, which is higher than other elastomers like silicone (5 – 10 MPa), nitrile (12 – 15 MPa) and neoprene (5 – 8 MPa). It’s also resistant to abrasive wear, which can’t be said for silicone.

In terms of chemical resistance, EPDM holds up well to acids and alkalies and is a good choice when dealing with both brake fluids and ketones. It also has good resistance to steam. Where it fares less well is against hydrocarbon oils and petroleum products as these produce swelling.

EPDM gasket applications

Relatively immune to sunlight, water and low temperatures, EPDM is often a smart choice for gaskets that will be outside. Good compression set resistance means it recovers well in applications where a joint may open up from time to time, and high electrical resistance means EPDM gaskets may be appropriate for some electrical installations.

A silicone competitor

In the gasket world silicone is known as a high performance material with a wide temperature range and good flexibility. In many applications though, an EPDM gasket could be a more cost-effective choice. Its temperature range is almost as wide and it’s a stronger, more durable material.

Consult the materials specialists

EPDM is available in a wide range of formulations with properties that vary considerably. To get a better understanding of EPDM gasket material options for your application a discussion with the specialists at Hennig Gasket & Seals Inc. is recommended.  Contact us today.

EPDM Gaskets
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Non-Stick Graphite Gaskets Reduce Downtime

Jun 20, 2016

Study our website and you’ll see gaskets can be made from a wide range of materials. One of the most versatile yet under-appreciated of these is graphite. Graphite gasket temperature range handles temperatures from -400°F to +875°F, provide excellent dimensional stability and resist chemical attack. On top of that, they have an additional advantage that’s not obvious: they don’t stick to flanges.

The Cost of Flange Cleaning

When replacing a gasket it’s essential to clean flanges thoroughly. Many gasket materials stick to these flanges and have to be scraped off. That’s a problem, for two reasons. First, there’s a risk of scratching the faces while scraping, and that can create leak paths. Second, doing the job properly, (and avoiding early replacement,) takes time.

As explored in “Focus on the Cost of Sealing,” (December 2015,) gasket replacement almost always means taking equipment, or even an entire plant, offline. Each application is different, but the cost of downtime usually dwarfs the price of even the most expensive gasket. The less time that’s needed to swap out the old gasket for the new one, the faster the plant gets back into production, so anything that reduces down time is worth considering.

Just Carbon

Graphite is one form of carbon. That’s the same element that forms diamonds. It’s strong, inert and resists temperature and pressure extremes, but what makes graphite special is its slipperiness. In graphite the carbon atoms are formed into layers that can slide over one another. That helps when closing up a gasketed joint because the material moves easily to fill uneven gaps and take up flange deformation or surface imperfections.

Graphite Gasket Materials

Here at Hennig Gasket we carry graphite material in a range of sheet thicknesses and widths as well as flexible homogenous graphite rolls. These can be cut to practically any desired shape and provide excellent sealing in many different applications. For especially challenging applications ask about the graphite-sided kammprofile gasket. Whichever graphite gasket you choose though, you can be sure of one thing; you won’t waste time scraping old material off the flanges!

Graphite Gaskets
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Buna-N (Nitrile) Gaskets and Oil

Jun 06, 2016

When working with a gearbox, a pump, or part of a fuel system, it’s essential to select a gasket material with resistance to hydrocarbons. Mineral and vegetable oils, along with diesel, gasoline and similar fuels, attack many materials, causing them to swell or break down. The notable exception is nitrile rubber. Nitrile rubber gaskets, often referred to as Buna-N or NBR gaskets, offer excellent resistance to oil.

Nitrile Rubber Chemistry

Nitrile rubber is made from a blend of acrylonitrile (chemical formula C3H3N) and butadiene (C4H6.) Each component is mixed with water as an emulsion before being combined in a polymerization reaction. This makes the carbon (C) and hydrogen (H) atoms form into long chains that tangle round another to form a rubbery compound.

Increasing the proportion of acrylonitrile makes the rubber stronger and reduces its gas permeability. The trade-off is that it results in a rubber that’s stiffer at low temperatures.

Rubber and Swelling

Most rubber absorbs oil and swells up in size. This is a problem in gaskets used in gearboxes and engines because it can lead to leaks. However, acrylonitrile reduces this tendency. So the greater the proportion of acrylonitrile used in the nitrile rubber formulation the less it will swell.

Swelling is covered in the ASTM D2000 specification. Most nitrile gasket materials are classed as ‘BF,’ ‘BG’ or ‘BK.’ The ‘B’ indicates an upper temperature limit of 100°C and the second letter shows how much the rubber will swell. ‘F’ is swell of 60% by volume, (under specified conditions,) while ‘G’ is 40% and ‘K’ 10%.

When and When Not to use Nitrile Gaskets

Good applications are those where peak temperatures are moderate and there’s exposure to oils. However, nitrile rubber does not hold up well to ozone and oxygen, so should not be used in places where these are present. Water purification equipment is one such location.

The Application Dictates the Gasket Material

If there’s any question about the properties of various gasket materials, consult the specialists at Hennig Gasket. They can explain the material choices available for your application.

Buna N, Nitrile Gaskets
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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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ASTM Testing for Creep Relaxation

May 09, 2016

Open an electrical enclosure and you may see that the neoprene gasket material has taken on the imprint of the door or cover. In technical terms, it’s taken a compression set. In many gasket applications compression set can lead to sealing problems, due to a phenomenon known as creep relaxation.

Introduction to creep

Apply a load to an elastic material and it compresses. This happens because unlike in a metal, the atoms are linked in a way that lets them move. In gasket materials this is good because it lets the gasket deform to take up the irregularities between the two surfaces being sealed. However, there is a downside to this compressibility.

Rubber and rubber-like materials, as used in neoprene gaskets for example, have the ability to spring back. Release the load and the material returns to its original shape, more or less. Some materials do this better than others. The issue is that the material takes on a permanent deformation, or worse still, continues to deform. This behavior is called “creep” or more accurately, “viscoelastic creep.” It’s related to both the strength of the material and the time and temperature to which it’s subjected.

When creep is a problem

In a bolted joint the compressed gasket creates the torque in the securing bolts. But as the gasket material creeps and the gasket thins, the bolts are able to relax. That reduces the torque and the joint begins to loosen.

Polyurethane, silicone and nitrile gaskets tend to have lower creep than some other materials, as quantified by testing to ASTM 38.

ASTM testing

The principle is to measure the thickness of a sample of gasket material, subject it to load, temperature and time, then release the load. The recovered thickness is measured and the difference used to calculate a percentage reduction.

Taking creep relaxation numbers into account when choosing gasket material.

As with testing to ASTM 36, the absolute test values are less important than the ability to make comparisons between gasket materials. It’s a parameter of particular importance when lasting bolt tightness is essential.

Neoprene 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.

FAQs
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