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!

The Dixon M-Liners from Saint Gobain have become very difficult to obtain since they come from overseas. Tri Star is now offering a size for size equivalent product in it’s Tri Steel product line called Tri Steel PE. This product is a rolled steel backed polymer lined bearing. The polymer liner is a special PEEK/PTFE combination that has a thicker dimension  than normal steel backed bearings. This allows for post machining of the ID to tighter tolerances without removing the primary bearing source. Learn more from Tri Star’s website www.tstar.com and review the information on Tri Steel Bearings or watch our Tri Steel video on the Video Learning Center.

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.

If you have been machining metal for a while the change to plastics can be a little daunting. There are some tricks to the trade and some basic things you need to know about thermal expansion, speeds and feeds and the use of coolant.  The biggest thing to remember is that most plastics, especially those that are thermoplastic, will melt when they get hot enough. Thermosets won’t melt but can be brittle to machine so they are a totally different problem. Since heat is the culprit you must machine each plastic with the knowledge that it will grow, sometimes very rapidly, and then shrink again after machining. Some materials have to be machined once, normalize at room temperature, and then go back for final cuts. Sharp tooling, properly designed tools, speeds and feeds are all critical so there will be a learning curve. TriStar offers a “Machining Plastics” seminar and design manual through their website. For even more tips, Ask The Experts – that’s what they are there for! It’s not rocket science but there are tricks to the trade!

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.

Ultracomp Composite Bearings are designed for extreme loads where impact and vibration may occur. Because of it’s very high impact strength it can take extreme loads as well as shock loads. Ultracomp requires no lubrication which eliminates maintenance, is much kinder to the environment and reduces overall costs of ownership.  Ultracomp absorbs virtually no moisture, takes static loads up to 55,000 psi and handles dirty, gritty environments. Ultracomp is also an excellent underwater bearing for applications as diverse as bowthrusters, rudder bearings, roller bearings, dockside equipment exposed to salt air and water. Also an excellent bearing material for construction, material handling and ag equipment.

Visit our Video Learning Center to learn more about all we have to offer.

UHMW Polyethylene is an interesting material in the polymer world.  It’s one of the lowest cost plastics on the market yet it offers some properties that few other polymers do. UHMW is best known for it’s abrasive wear resistance and impact strength but even within this small polymer family there are variations. UHMW stands for ultra high molecular weight and under this description UHMW is produced with a molecular weight range of 3.5 to 6 million. The molecular weight has a fairly dramatic impact on several key properties. For instance, a 4 million molecular weight grade has an abrasion resistance of 100 when measured using a sand slurry test. A 6 million molecular weight is 75 which is a further 25% improvement! Compare this with steel which has a resistance of 160 and you can see why UHMW is the material of choice for abrasive wear environments.

There are several other variations on UHMW including cross linked, glass and moly enhanced and even a high temperature grade.

Check out our Materials Resources Guide to see the entire selection.

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!