When it comes to food, Freudenberg wants to be sure that its sealing materials are free of harmful substances.
In the food processing industry, in order to guarantee food safety, both the food and the hardware that come into contact with it must meet particularly stringent criteria. These guidelines also apply to sealing materials.
In China, specific standards were created in 2016 with the two standards GB 4806 and GB 9685, which deviate from the existing relevant American and European regulations for food-grade materials. To meet the stringent Chinese regulations, FST has now successfully tested two proven VMQ materials: 70 VMQ 117055 and 60 VMQ 117117 for their conformity with Chinese guidelines.
The Chinese standard GB 9685 specifies which ingredients may contain materials that come into contact with food in a so-called positive list. A large number of seal-relevant ingredients that conform to 21 CFR 177.2600 of FDA (U.S. Food & Drug Administration) and European EU (Reg.) 1935/2004 are not listed here. This applies to elastomers. For a global food release, new material compositions must therefore be developed or proven materials tested for their conformity with the specifications.
Global food approvals require extensive testing
The basic requirements for gasket materials as well as sensory tests and migration tests are defined in standard GB 4806. Two of Freudenberg’s newly developed EPDM materials have successfully passed the tests: 75 EPDM 386 and 85 EPDM 387.
After extensive testing, FST’s two new VMQ materials now meet the requirements of the Chinese standards. As an example: the silicones in the migration measurement in mg/dm2 had a result of <1, and are far below the specified limit of ≤10.
In addition to the EPDM materials which are characterized by media resistance, good processing behavior and a long service life, FST’s new silicones, 70 VMQ 117055 and 60 VMQ 117117 provide grease-resistant material selection for use in contact with food in the Chinese market.
Gallagher Fluid Seals is a preferred distributor of Freudenberg sealing. For information about Fruedenberg, or if you have needs for a custom solution, contact our engineering department.
The search for the ideal Polytetrafluoroethylene (PTFE) gasket has been elusive. Competing applications and workplace variables have led to the creation of myriad solutions, yet none that has proven fully adaptable and appropriate for universal adoption.
Garlock Sealing Technologies considered this to be a critical yet entirely solvable shortcoming. And it is against this backdrop that in 2016, they set out to compile a comprehensive list of attributes for the ideal PTFE gasket — a wish list, as it were — in order to build a better gasket.
Working with a third-party survey development company, Garlock developed an exhaustive questionnaire that probed every aspect and functionality of PTFE gaskets, testing and adjusting the questions until they had a workable, finalized version.
Using this final questionnaire, Garlock conducted extensive interviews at 15 major chemical processor companies, speaking with 20 engineers responsible for process operations, projects, maintenance and reliability. The goal was simple: to discover the ideal characteristics and their relative importance that engineers sought in a PTFE gasket.
After several months of data collection, Garlock analyzed the feedback and noted the most popular responses:
28% of respondents said that they struggled with how different gaskets required different compressive loads and how to ensure that those gaskets had been installed properly
21% expressed frustration with the creep properties of PTFE gaskets
21% desired a gasket that seals with less compressive load
14% expressed frustration at the installation inconsistencies of their fitters
14% expressed frustration with leaking, especially after a successful installation and start-up
From those answers, Garlock drew the following conclusions, representing the most desirable and essential PTFE gasket characteristics:
Seal: Seals easily
Installation and assembly: Forgiving of poor installation or assembly practices
Forgiving: Forgiving of poor flange conditions
Retention: Maintains a seal after installation
Flexible: Can be used in a broad range of services to avoid user confusion and reduce inventory
Introducing: GYLON EPIX
Garlock used this feedback in developing a next generation PTFE gasket — GYLON EPIX. Featuring a hexagonal surface profile, GYLON EPIX offers superior compressibility and sealing for use in chemical processing environments. Its enhanced surface profile performs as well or better than existing 1/16″ or 1/8″ gaskets, allowing end-users and distributors to consolidate inventory, lower the risk of using incorrect gasket thicknesses and reduce stocking costs.
GYLON EPIX checks off the most desirable gasket attributes:
Installation and assembly: Even distribution of the bolt load over the contacted area of the gasket during the assembly process
Retention: Retention of the bolt load administered at assembly
Seal: Efficient translation of bolt load to sealing performance
Forgiving: The ability to perform in imperfect flanges and installation conditions
GYLON EPIX with its raised, hexagonal profile allows it to perform the job of both traditional 1/16” and 1/8” gaskets. It accomplishes this by combining the bolt retention of the former with the forgiveness for bad flange conditions of the latter, a truly innovative feature for PTFE sheet gasketing. Continue reading The Ideal PTFE Gasket for Tough Applications – GYLON EPIX→
Tensile Strength | Ultimate Elongation | Modulus of Elasticity
Rubber Compound Data sheets usually display a number of physical properties as recorded from standard test methods. Among the most common are three measured on the Tensometer:
Tensile Strength (at break)
Modulus of Elasticity
The Tensometer stretches a specimen, or dumbbell, cut from a sheet of rubber, until it breaks. During the test, the force required and length of the gauged section are measured continuously. These measurements are used to calculate the various results, which considers the actual dimensions of the test specimen.
While Tensile Strength and Ultimate Elongation are pretty well understood by most, Modulus is not as well understood. Unlike the other two, the Modulus values are not usually reported at break, but rather at various elongation percentages as recorded during the test. Modulus is reported in pounds per square inch (psi) or Megapascals (MPa) at a given elongation percentage as below:
Modulus @ 100% Elongation: 610 psi 4.2 MPa
You might ask, “What does knowing the Modulus do for me?” While Modulus and Durometer are somewhat related, there can be a pretty large variance in modulus values between two compounds of the same durometer. In an application that requires a rubber seal to be stretched into place, a low modulus compound might be considered to make assembly easier. On the other hand, a firmer compound would be preferable in an application where stretchiness is not desirable. In this case, a high modulus compound would be superior. Higher modulus is also a good indicator of a compound’s ability to resist extrusion in high pressure sealing applications.
This article is not intended to explain at length, the technical aspects of tensometer testing and resultant properties. To see an actual test performed on an 80 Durometer EPDM, look below:
Chemical plants are one of the biggest industrial users of corrugated metal hose assemblies. Processes performed in the plants involve some of the most demanding environments:
Temperatures ranging from extreme heat to cryogenics
Mixing and transfer of hazardous compounds
Equipment configurations that result in less-than-ideal piping situations
Metal hose can handle all of these factors and has some other inherent benefits over other hose types when it comes to the kind of applications seen in chemical plants. Let’s dig into some of the main areas of consideration and concern when dealing with chemical hoses.
Metal Hose Handling Considerations
Mishandling of hoses is one of the main contributors to premature failure. Because chemical plants have so many different inputs and outputs, hoses are often used to facilitate the transfer of chemicals from trucks, trains, or barges to the plant and even within the plant from one unit to another. Chemical blending manifolds are a great example of this, where a single hose assembly may be used for various connections at different times depending on what operations the plant is performing.
The need to easily connect and disconnect these hoses quickly and often makes cam and groove couplings a popular choice for chemical plants. When moving hoses from one outlet to another, it’s tempting for users to abuse the “arms” on the fitting and over-bend the hose or torque it into position. Always try and keep the hose as straight as possible, and avoid twisting it. Additionally, hoses are made to flex, but extremely tight bends (especially near the end fitting) can damage the hose and cause it to fail prematurely. Operators should keep this in mind to prevent deformation of the hose when making connections.
Metal Hose Attributes
There are several intrinsic features of metal hose assemblies that make them well-suited for chemical plant service. Chiefly among them is that they are not susceptible to permeation. This is a huge benefit for both operator safety, and plant safety. The metal core is puncture-resistant, and in the event of a leak, the hose will typically develop a small crack or pin-hole and does not burst apart.
Metal hoses also have a more compact end fitting configuration. Because end fittings are welded onto the end of the hose instead of a barbed or crimped mechanical attachment, they don’t take up as much of the hose’s flexible length. This results in more working live length compared to non-metallic assemblies, which further facilitates handling and easier installation by the operators. It also means that metal hose is easily customized without the need for adapters. Stainless steel fabrication techniques provide the ability to use a wide array of fitting configurations, and can be tailored to prevent media entrapment, resist end-pull, or to accommodate high system pressures.
Finally, one of the handling benefits of metal hose is its light weight. Calling metal hose lightweight might sound contradictory, but pound for pound, metal hoses generally offer higher working pressures than rubber or composite chemical transfer hoses. This gives metal hose a wide range of potential applications, and also translates into easier handling and installation by operators. Continue reading Considerations for Using Metal Hose in Chemical Plants→
Polymer wear rings were developed to offer an alternative to dissimilar metal wear rings.
One of the advantages to using a polymer material such as nylon or filled-Teflon instead of a metallic bearing . Whereas when you use bronze or metallic bushings, these materials are prone to point loading on the edges of the bearing.
This property of polymer bearings combined with solid lubricants can yield a product that is much less likely to damage moving components.
5 Advantages to Polymer Wear Rings
Polymer style bearings can be held to very close tolerances in the radial dimension to provide support without excessively opening the extrusion (E) gap by a large amount. Polymer bearings such as filled Teflon can support a compressive load up to 1000 PSI. Nylons up to 36,000 PSI and polyester fiber with resin, up to 50,000 PSI.
Hydraulic cylinders that are found in excavators often use higher compression materials because they experience extreme side and shock loads. However, most applications do very well with filled Teflon materials.
Bearings come solid or split. If designed properly, split bearings provide equivalent support, while improving installation options with no compromise in performance. Solid bearings, or bushings, are convenient when installing on the outboard side of a rod groove. Split bearings are essential when installing in a piston groove designed to function internally in a system.
Nylon or composite bearings are typically cut to allow for installation due to their stiffness. However, a Teflon bushing can be made into a ring, or cut from a roll of sliced strip.
The only time a bushing needs to be cut from a ring is if installation does not allow the strip to be deformed for a clean install. Strip installation allows for variability in length, lower manufacturing costs, and the product can generally be acquired off the shelf.
Materials for Polymer Bearing Configurations
When selecting materials, we must consider the maximum load, the speed of the system, and whether there is any lubrication in the system.
The load (or pressure over area) that the bearing will see is the first consideration. This dictates which materials will be the best fit.
It’s important to use a material that has a minimum compressive strength rating so that it will not fail under the highest loading condition. The industry standard is to employ a safety factor so that the bearing is specified to be used well beyond its design limit.
Teflon should be your first consideration due to cost and ease of installation. Nylon or composites will provide much higher load rating, but the cost and installation need to be considered.
Teflon and composites provide service without lubrication, and the composites provide excellent service in aqueous solutions. Bushings are typically used in medium to slow reciprocating service. Rotary creates challenges that may or may not work depending on the design of the bushing.
There are many series of injection molded nylon bushings. However, nylon in low-lubrication or high-loading may create high-friction, and can be noisy. Nylon, as a low-cost bushing, can be used in some high load situations.
A final consideration before going into large scale production is the cost of taking a bearing design into high production. Some bearing materials are expensive and can only be processed by machining, which limits the cost reduction scenarios at high volumes.
Materials such as filled-PTFE or thermoplastics that can be molded offer cost competitive solutions for high-production applications. Eclipse provides bearings in everything from low-quantity applications, such as bridges and dams, to mid-quantity applications in aerospace.
Gallagher Fluid Seals is a preferred distributor of Eclipse Engineering. Call us at 1-800-822-4063 for more information on Eclipse seals.
Article written by Cliff at Eclipse Engineering, Inc. For the original article, visit their website.
Vesconite, a market leader in grease-free polymer bushings and wear materials, has developed a food-grade, high-temperature, abrasion-resistant bearing poloymer.
The polymer is known as Hitemp 150 FG (food grade), and its name signifies that it can be used in applications that run at temperatures up to 150ºC and in which food contact is incidental or likely.
The previous version of Hitemp 150 did not explicitly use food grade ingredients, but, as a result from calls from the food industry to produce a similar hard-wearing product for use in food applications, alternative ingredients were sought for food safety.
“We have produced this Hitemp 150 FG product in which a food-approved ingredients have been used,” comments technical sales representative Eddie Swanepoel.
“It is cream with a streaky marble look as opposed to the previous rust-coloured Hitemp 150 polymer,” he notes.
The next step is to have the polymer approved as compliant with Standard 51 of the US’s National Sanitation Foundation (NSF), the standard that deals with polymer materials and components used in food equipment, including products that come into contact with food and beverages.
Vesconite Bearings is confident that the newest version of the Hitemp 150 FG polymer will be judged to be food grade since all the raw materials ingredients are certified as food grade.
Stay tuned for this excellent addition to the product catalog from Vesconite.
Strong oxidizers can damage metal, causing pitting or rust and treating possible safety concerns.
In chemistry, strong oxidizers are substances (like chromic acid) that can cause other substances (like seals and gaskets) to lose electrons. So, an oxidizer is a chemical species that undergoes a reaction that removes one or more electrons from another atom.
This causes a change in mass. Metals will turn into their respective heavier oxides, and the carbon in graphite will oxidize into carbon dioxide—which, although molecularly heavier, is a gas at room temperature.
This happens in pumps, valves, pipelines or any other equipment that have seals and gaskets carrying a strong oxidizer. It will cause pitting or rust and, depending on your choice of seal material, may require shorter service intervals. Ultimately, you may have to look for a more suitable material that can handle strong oxidizers.
More importantly, an oxidizing agent can cause or contribute to the combustion of another material.
The U.S. Department of Transportation defines oxidizing agents specifically. DOT’s Division 5.1(a)1 means that a material may enhance combustion or quickly raise pressure causing a rapid chemical reaction. A fire may start or, even worse, create or facilitate an explosion.
There have been instances of fires or explosions in mining, chemical process and even fertilizer factories where strong oxidizers were used.
A West Texas fertilizer company storage and distribution facility caught fire on April 17, 2013. As firefighters attempted to extinguish the blaze, the plant exploded with the force of 10 tons of TNT, killing 15 people and injuring 200. It destroyed 60 nearby homes and left a 93-foot-wide crater where the plant once stood.
All said, it is important to choose the right sealing material for strong oxidizers. There are multiple products on the market for the chemical processing, oil and gas, mining and aerospace industries.
A fluoropolymer, such as polytetrafluoroethylene (PTFE), can handle most strong oxidizers, as long as the temperature is below 260 C (500 F). This is also true with a modified PTFE because they are chemically inert and stable.
Strong oxidizers will weaken most other material to various degrees. Much of a material’s capability to withstand a strong oxidizer depends on the used concentration, the service temperature and the service pressure. Therefore, consult with the sealing material manufacturer to ensure compatibility.
How Graphite Handles Strong Oxidizing Environments
Graphite starts as natural mineral flake and is mined in various parts of the world. The flakes form a layered structure of completely crystalline graphite, which is essentially elemental carbon. In this form, it is used for products like powdered lubricant and lead in pencils. It has excellent lubricity in this form.
Expanded graphite is produced with the use of strong oxidizing agents such as sulfuric and nitric acids. The acids weaken the bonds between the graphite layers, the flakes are then rinsed, dried and exposed to high heat.
The heat causes the layers to separate and expand dramatically to form expanded worm-like macro structures. The structures can then be recompressed into flexible graphite forms.
Flexible graphite is a soft material that is resistant to many strong chemicals and high heat. It has a low coefficient of friction and is proven to be advantageous over braided carbon or graphite fiber packings mainly as it is a better conductor of heat—a plus on moving shafts.
Flexible graphite is also naturally lubricious, conformable and resilient. It has good corrosion resistance and is compressible, allowing it to conform to most mating surfaces or valve cavities.
The chemical compatibility of flexible graphite can be enhanced with a blocking agent like PTFE. However, flexible graphite’s temperature limit will be restricted by PTFE’s limit of 260 C (500 F). If high temperature is an issue, this configuration will not work.
Flexible graphite, in combination with PTFE, is an extremely effective material in sealing fugitive emissions or volatile organic compounds (VOCs). VOCs have been targeted by several government agencies as a source of air pollution. Although, flexible graphite alone has a long way to go in stopping all fugitive emissions, it is a trusted sealing material for valves, flanges and stems in the chemical process, power generation, and oil and gas industries.
Flexible Graphite Pitfalls
Flexible graphite may be susceptible to chemical attack in the presence of strong oxidizing fluids, including air at extremely high temperatures. These include liquids such as 20 percent concentration of nitric acid or a 98 percent concentration sulfuric acid, the same chemicals that are used to break down mined graphite into expanded graphite flake.
Some flexible graphite compositions include oxidation inhibitors or are physically structured to extend temperature capability when exposed to these extra strong oxidizers.
The class of organic chemicals that should not be used are those that are highly oxidizing like nitrates, persulfates, perbenzoates and peroxides. Unacceptable compatibility for inorganic chemicals includes molten sodium, potassium hydroxide and chlorine dioxide.
However, many of the chemicals depend on the concentration, and some engineering groups can create an inhibitor that is right for a specific oxidizer. For instance, a 704 stainless steel cladding provides the user with protection against strong oxidizers while still providing the benefits of flexible graphite.
When in doubt, do a test loop using a pump to pressurize the strong oxidizer exposing it to flexible graphite. The pressure, temperature and concentration of the oxidizer must be exact as used in service, as to provide some idea of how the material will react to a given chemical.
It is easier to list the chemicals that are not compatible with flexible graphite (about 50) than those that are (more than 600 tested). A list of incompatible materials are listed below:
The RoTechBooster ensures abundant, reliable, and consistent seal gas flow, through fluctuating operating conditions; thus, clean and dry gas is supplied to the gas seal in every situation.
Features of the RoTechBooster
Electric driven centrifugal design
Delivers seal gas flow as defined by API
24,000 hours of operation before required maintenance
Various models available, depending on requirements
Advantages of the RoTechBooster
Simple to set-up, easy to operate
High reliability and availability
Unlimited continuous operation
Avoid seal failures
Low maintenance costs
Eliminates the concern of unreliable external seal gas source
RoTechBooster Case Study: Clean Gas Despite Fluctuating Operating Conditions
The “Dock Sud“ combined power cycle plant in Buenos Aires, Argentina, is designed to adjust the power generation to the fluctuating electrical demand throughout all seasons. Managing the high demand during the summer months is particularly challenging, and the requirements for system component reliability are correspondingly high.
The power plant uses diesel engines and gas turbines to drive the generators. The diesel-driven generators run on a regular basis. The gas turbines are operated in start/stop mode so that they can respond quickly to high energy requirements or cope with peak loads.
As a low-pressure gas supply for the plant was only available to use for the gas turbines, a MAN Diesel & Turbo four-stage geared compressor with dry gas seals provided the means to increase gas pressure to the appropriate level for them. There is one geared compressor for each of the two gas turbines on site. Another geared compressor is used as back-up. Due to the nature of the operation, the turbines stop and start frequently placing the geared compressors in a pressurized stand-by mode when electrical demand drops. Continue reading RoTechBooster Supplies Compressor Seals in the Power Plant→
FLOOD-GARD Offers Bearing Protection in Challenging Flooded Environments
Garlock has launched FLOOD-GARD Bearing Isolators for flooded applications. The patent-pending seal design provides bearing protection even in the most challenging flooded environments, extending the life of rotating equipment such as gearboxes, pumps, and motors.
“FLOOD-GARD™ allows Garlock to unlock value for our customers by taking industry leading bearing isolator technology, and advancing it even further, into a seal that excels in flooded conditions,” says Kevin Allison, Product Manager, KLOZURE®.
The latest addition to Garlock’s family of KLOZURE® Bearing Isolators, FLOOD-GARD™ is a revolutionary seal that combines improved safety and overall process efficiency with cost savings through extended equipment and bearing life. FLOOD-GARD’s Cam-Lock design provides excellent bore retention while allowing easy installation by hand, without the need for an arbor press. Other benefits include the ability to accommodate up to .015” of radial shaft misalignment and patented PTFE unitized construction that eliminates metal-to-metal contact, all while achieving an IP66 rating in most configurations — flanged, small cross section, step shaft and vertical.
Patented seal design provides bearing protection even in the most challenging flooded environments, extending the life of rotating equipment
Rugged, unitized construction for ease of installation
IP66 in most common design configurations
Available in standard and small cross section configurations
Substantially reduced installation time – NO ARBOR PRESS NEEDED
No metal-to-metal contact between stator and rotor
Handles up to .015″ of misalignment
FLOOD-GARD™ allows Garlock to unlock value for our customers by taking industry leading bearing isolator technology, and advancing it even further, into a seal that excels in flooded conditions.
Original content can be found on Parker’s Websiteand was written by Dorothy Kern, applications engineering manager, Parker O-Ring & Engineered Seals Division.
For some applications, a critical component of selecting a seal material is a phenomenon known as “outgassing”. However, even within the elastomer community, outgassing is not something that is commonly considered. Which begs the questions: what is outgassing and why is it important?
Outgassing is usually most relevant in vacuum applications, where the vacuum causes the elastomer to release constituent material. The constituent material could include water vapor, plasticizers, oils, byproducts of the cure reaction, or other additives used in the seal material. Outgassing becomes a problem if a thin film of those chemicals condenses and is deposited on nearby surfaces. Such a film poses major challenges in highly sensitive applications, such as optics or electronics, where cleanliness is of utmost importance. A seal material with low outgassing is essential because it shows the seal material does not emit volatile constituents under vacuum conditions.
Weight loss of compounds in vacuum
Outgassing is most often characterized by weight loss of the seal material. The ASTM test method E595 is one way to quantify outgassing by measuring Total Mass Loss (TML %), Collected Volatile Condensable Materials (CVCM %) and a reported value for Water Vapor Regain (WVR %). Measurements are taken following a 24 hour exposure to vacuum of 5×10-5 torr at a temperature of 257°F.
Taken together, these three parameters tell a complete story. The TML is reported as the percent of the specimen’s initial weight that is lost during the test; under standard criteria, the result must be less than 1.00% mass loss. Obviously, minimizing TML is a good thing, but it is not the only important factor. Collected volatile condensable material (CVCM) is the amount of outgassed matter from a specimen that condenses onto a collector during the maintained time and temperature. CVCM is of particular concern because any material that readily condenses in the test is likely to condense on and contaminate nearby surfaces during use. To pass the standard CVCM requirement, the amount collected relative to the initial mass of the specimen must be less than 0.10%. The final measurement, WVR, is the mass of the water vapor absorbed by the specimen after a 24-hour stabilization at 23°C in a 50% relative humidity atmosphere. There is seldom a pass/fail limit for WVR; instead this result is merely reported. In many applications, the small amount of water vapor lost by a seal may not be of concern, particularly if the application already includes a means of controlling moisture. Further, any WVR is presumed to be equal to the portion of original TML that was water vapor. The difference between TML and WVR is therefore presumed to be volatile organic material that has evaporated out of the material (only some of which condenses in the CVCM test), so minimizing the difference between TML and WVR is also of considerable importance.
To illustrate, we can look at the most recent outgassing data completed on a few popular low temperature fluorocarbon materials. Table 1 contains the results from a 3rd party laboratory to measure the outgassing properties of VM125-75 and VX065-75. Both had undetectable amounts of CVCM and very small differences between TML and WVR. VX065-75 in particular displayed remarkably little outgassing as well as a low WVR.
There are a few additional resources detailing seal materials that are known for having low weight loss. The O-Ring Handbook ORD 5700, Table 3-19 (page 65 of the pdf), has a few legacy materials with weight loss percent after a two-week exposure to 1 x 10-6 torr vacuum level, at room temperature. Additionally, non-Parker resources such as the NASA website contain an interesting summary of a much broader range of materials.