Tech Talk Blog

Our team has seen a spike in interest in slipper seals.

Slipper seals, made from filled PTFE, are designed to act as a low friction interface between a static elastomer expander and the dynamic mating surfaces. i.e shaft or bore. With filled PTFE like our Ultraflon, slipper seals offer exceptional wear life, extrusion resistance, low friction and elimination of stick slip. Slipper seals can be used in both hydraulic and pneumatic applications, lubricated or dry and across a broad temperature range. Since these seals depend on the elastomer for their energizing function, the temperatures will depend on the operating capabilities of that elastomer.

PTFE slipper seals are made in a variety of geometries and cross sections to accommodate the design envelope. There are piston seals, rod seals, wiper seals and a variety of supporting components to make up a complete cylinder design. Tri Star has seal engineers on staff to assist in the design of your slipper seal requirements.

You know the drill – if you have a question, Ask The Experts!

Previous blog addressed importance of crystallinity control on PTFE as it relates to porosity, changes in physical strength and dielectric values. More Tri Star testing has shown better detail on the effects of processing and crystallinity. Specific gravity is the primary gage of crystalline or amorphous stages of polymers. In the case of PTFE the range is generally between 2.1 and 2.3 for unfilled resin. Testing showed that at 2.1 SpG the crystallinity of the molded product was approximately 38%. At 2.13 it was 47%, 2.15- 53%, 2.17 – 60%, 2.2 – 70%. Remember, the higher the crystallinity the lower the flex life, higher compressive stress, lower recovery, more permeability and lower wear life.

Another part of the equation has to do with microvoids as it relates to crystallinity. Microvoids are generally a result of poor attention to preforming conditions and to a lesser extent the sintering process. Microvoids, or porosity, have a direct bearing on crystallinity. As an example, a low microvoid material at 2.13 SpG would be 47% crystalline. However, if processing problems occur and void content grows you could see a substantial increase in crystallinity.  At a 1% microvoid level the 2.13 sample at 47% crystallinity would increase to 53%. Doesn’t sound like much but could have a great influence on the properties and wear of the material. Additionally, at 1% void content the dielectric strength of the PTFE would drop from it’s normal 500 v/mil to 320 v/mil. This is significant when considering PTFE as a dielectric insulator. For more information on the importance of quality in PTFE, contact Tri Star via this blog site or our website @www.tstar.com.

There is a lot of talk these days about biodegradable plastics, renewable resources, carbon footprints and the like. It’s interesting that as companies look at the feasibility of biodegradable plastics they also look at how it affects the other aspects of the ecology. If it takes more energy and produces more negative effects on nature we have to be able to justify the efforts. Today’s bioplastics technology is catagorized several ways. There are pure bio polymers that are based on polylactides (fermented bacteria), cellulose ( naturally occuring wood product), lignin (a macromolecular by-product of paper), biopolymer blends (combination of bio sources) and finally polymer blends which utilize biomaterials and petroleum products.

Bioplastic products are further classified by either compostable or true biodegradable. Compostable bioplastics degrade by at least 90% within 6 months by natural environmental conditions; i.e. temperature, humidity and pH. This degradation occurs through typical composting breakdowns and the result is by-products such as water, carbon dioxide, methane and humus.  Some biodegradable polymers will break down through naturally occuring micro-organisms such as bacteria or fungi. Today, most of the bioplastics that fall into this category are packaging films and consumables but that is changing. More and more bioplastics are being developed with higher engineering potential. Materials that can withstand loads, can be extruded into shapes and molded or machined into finished parts for things as diverse as musical instruments to display panels in store fronts. It is also available in stock shapes such as rod, sheet, tube and custom profiles. Tri Star Plastics is working closely with bio-partners to develop more and more options in this interesting new world of bio-plastics. For more information on this technology, contact our Technical Department at www.tstar.com or send us a return blog! More interesting things on the way!

Recent headlines tell us that everything from our kitchen cutting boards, Tupperware and soda fountain delivery tubing are infected with everything from fecal matter to salmonella. There are solutions available thanks to new polymer technology using antimicrobial additives and surface treatments. Many polymers are now available with silver ions which help to effectively inhibit the potential growth of bacteria, yeast and fungi on the polymer surface. By using unique zeolite carriers with silver ions, a counter force to the sodium ions present in moisture  interrupt respiration, reproduction and metabolism of destructive microbes. TriStar offers several polymer solutions now in molding and extrusion resins to dramatically reduce the potential of microbial growth in your products. Browse through our Video Learning Center for even more information.

The growth of plastics in medical devices is growing exponentially around the world.  Plastics are regulated like any other materials that may come in contact with human tissue or fluids and that usually falls under testing procedures issued under USP or ISO10993. There are three time scales for biocompatible devices. “Limited” would be less than 24 hour exposure, “Prolonged” is 24 hours to 30 days and “Permanent” is 30 days and longer. Device’s are categorized as Surface Devices which would be items such as electrodes for monitoring, contact lenses, catheters, endotracheal tubes, sigmoidoscopes and similar devices. Second would be Externally Communicating Devices such as  laprascopes, blood administration devices, pacemakers, oxygenators and the like. Finally are Implant Devices such as orthopedic pins or plates, heart valves, grafts, stents and similar devices.

Testing of these devices includes mechanical, thermal, chemical tests as well as systemic injection, intracutaneous and implantation. All of these must be done before a plastic component can be approved. Typical materials for biocompatible applications include medical grades of PVC and Polyethylene, PEEK, Polycarbonate, Ultem PEI, Polysulfone, Polypropylene and Polyurethane. For more specific information on Biocompatible materials as well as special plasma preparation treatments of all of these materials, contact TriStar Plastics at www.tstar.com and visit our Video Learning Center and our Materials Database.

Torlon PAI from Solvay is one of the outstanding polymers for high temperature applications. Torlon is available in various forms and with different enhancements to meet diverse applications such as bearings, dielectric insulators and structural components. Torlon’s physical properties maintain very high values even at the maximum operating temperatures.

You can learn more in our Video Learning Center, too!

Tivar HOT is a unique UHMW grade that has a dramatically higher continuous operating temperature (275F) than standard UHMW. Tivar HOT still has excellent wear and abrasion resistance, doesn’t absorb moisture, has excellent chemical resistance and meets FDA, USDA and 3A guidelines. We have found this product to be excellent for higher temperature zones in food processing and packaging equipment but it has also proven to be a great material in down-hole oil drilling applications!

Pretty diverse material. If you need excellent abrasion resistance, low friction, self lube bearing material with all of the other attributes mentioned, consider Tivar HOT from TriStar! And while you are looking around the site – stop by the Video Learning Center for some more information!

Fluoroloy H, aka Rulon  H, is an interesting combination of ceramics and PTFE. This unique dielectric material is used inside connectors for high power applications. The Fluoroloy H material has a slightly better dielectric constant compared to standard Teflon but has a higher rate of thermal conductivity.  This allows the heat being generated at the center conductor to transfer to the outer conductor more efficiently, which in turn increases the power level efficiencies of the connector. The thermal conductivity of Fluoroloy H is 1.21 W/m C and virgin Teflon PTFE is 0.24 W/m C. Fluoroloy H is easy to machine, similar to virgin or glass filled PTFE. Available in rod, sheet and tape.

For improved dielectric properties as well as heat sink properties, Fluoroloy H from TriStar Plastics is a  unique design option.

If you are interested, learn some more about Fluoropolymers or if you have a question that’s driving you crazy – Ask The Experts!

PCTFE has long been the go to material for valve seats, seals and gaskets used in cryogenic applications. But one thing that makes PCTFE unique is that it can be processed to meet a broad molecular state, i.e. crystalline or amorphous. PCTFE is a melt fluoropolymer and when molded in either sheet, rod or tube form it can be set at a specific crystalline state through a unique quenching process. This process is not as easily manipulated with extruded PCTFE rod so if you are looking for controlled molecular values you need to consider molded product.

As an example of some of the differences in physical properties between the amorphous PCTFE and crystalline PCTFE, consider these values:

Property                                            Amorphous                               Semi Crystalline                              Crystalline

% Crystallinity                                       40%                                                    55%                                               65%

Ultimate Tensile (psi)                      25,000                                           17,200                                              15,600

Elongation at Break (%)                        4                                                       2                                                         1.5

Tensile Modulus of Elast. (psi)   1,110,000                                           NA                                                 760,000

Compressive Strength   (psi)         34,000                                           37,500                                             38,000

Flexural Strength (psi)                    58,000                                            43,000                                              37,000

Flex Mod. Of Elast. (psi)               1,800,000                                     1,700,000                                    1,650,000

Crystalline/amorphous values are monitored by specific gravity and performance in cryogenic service utilizing amorphous grades of PCTFE has been well documented in terms of service life, sealability and property retention.

Ask The Experts at TriStar for more information on how PCTFE can be “custom tailored” to your application through molecular manipulation!

Polymer gears are common place in many industries and applications. The advantages of a polymer gear include noise reduction, self lubricating features, dramatic weight reduction and cost savings. From paper mill gears to drive gears in copiers, polymer gears have been successfully used for years. But, everything you know about metal gear design gets thrown out the door with polymers. There are many different factors that have to be considered when designing gears out of plastics including thermal expansion and contraction, physical strength, moisture absorption and possible chemical exposure.

Typical polymers for gears are cast nylons, injection molded nylons, polyester and acetal. Various fillers help to strengthen the base polymers such as glass and carbon fiber, aramid fibers and other additives are used to improve lubricity. More recently high end polymers like PEEK and Torlon have been used to make high temperature gears or gears where exceptional strength is required. No matter what the material, designing polymer gears will require some extra thought and a change from the norm. Tooth profiles and overall height may need to be changed to accomodate bending forces. Contact conditions at the root of the tooth may need modifications from the norm. Flex strength of the polymer will definitely come into play so input and output torque requirements will need to be reviewed closely.

While there are a lot of advantages to polymer gears you can’t overlook the basic differences of steel gears and polymer gears. Material choice and adherence to design changes required to address the physical, thermal and wear requirements of the gear must all be looked at closely. Tri Star has several thermoplastic and thermoset materials used frequently for gears and our engineering department can help you in this process. Have more questions? Ask The Experts – they are bound to know something. Or check out our Video Learning Center for a deeper look.