Tech Talk Blog

All of us in the fluoropolymer business are suffering what could be called a perfect storm of bad news! First, the raw material situation. One of the key ingredients in the processing of fluoropolymers is a mineral called fluorspar. This is a material that is critical in the production of not only fluoropolymers but pharmaceuticals, hydrofluoric acid, refrigerants and any other product that requires a fluorine based stock. China controls most of the worlds resources on this mineral and it became part of a war of words and ultimately manipulation in the world market. Countries, including the USA, are now scrambling to reopen old or open new mining resources of this critical mineral. So this shortage, as well as a worldwide surge in demand for fluoropolymers and a reduction in processors of the PTFE resin, all leads  to this very difficult situation. The bad news is there is no end in sight. The EU has declared fluorspar to be on it’s worldwide shortage list until 2030. So we all  will have to deal with this out of control pricing escalation for years to come. Best if you call Tri Star and place blanket orders for your requirements for the future!!

Did you realize there are probably over 300 types of Rulon? Rulon is a self-lubricating material that can almost be considered “generic” in some ways.  It is a PTFE material with various fillers; it is the type and amount of filler that makes each variation of Rulon unique.

When choosing Rulon, we ask:

1) What is the application function – bearing? Seal? Gasket? Some materials can be used for all applications.

2)  What is the temperature? -400 to +550 is the general range Rulon can accept. For design purposes, we need to know how much press fit and close in to account for in the gradient.

3)  What is the environment? Some types are made for FDA or USDA environments or for resisting abrasion. Most PTFE materials don’t do well in water, but a few do.

4)  What is the speed? All types of Rulon can take 400/500 feet per minute without lubrication; but we need the load to be a bit more accurate. Rotating? Oscillating? Linear?

5)  What are the loads on that bearing? Most can handle 1000 psi, but others can withstand higher levels.

6)  What type of hardware (consider temperature)? Only a few types of Rulon can work with stainless steel.

7)  What is the surface finish? 8-16 rms on the shaft is recommended, but for holding purposes, we would suggest 32 rms.

We can help you choose the right Rulon for your application.

For removing excess adhesive during the bonding process we do NOT recommend using any solvents. Some of the solvent can migrate under the Rulon and destroy the bond on the edges – may cause a lifting up of the material when under load in the application. We recommend instead waiting until the adhesive dries and then scraping off the excess, or in some cases we use a belt sander if enough space is available to use it effectively. Alternatively, if we do not want to generate that kind of dust, and to keep the finished parts clean, we will mask off any areas where the excess adhesive can be a problem, and then just peel the masking material off after the glue has dried.

For removing old Rulon, or other similar PTFE material, so that new material and adhesive can be applied, heat the part up to approximately 250 degrees F. That breaks the adhesive bond and you then can peel off the Rulon that is remaining. Then you can scrape off the remaining old adhesive or sandblast it. Sandblasting leaves a good surface for rebonding new material to. If there is very little Rulon left, and the flatness of the metal is critical, then we suggest milling off the old material. Again, the swirls from the milling operation provide an excellent surface to bond new material to.

Molecular weight and crystallinity are two factors in PTFE that determine many of it’s performance qualities. Both of these properties are highly dependant on the sintering operation of the PTFE production. If the material is cooked (sintered) too long or at too high a temperature it can degrade the polymer. Molecular weight is a measure of the polymer chain length and it affects flex life, tensile strength and elongation. As molecular weight increases so do these properties and paying attention to gel temperatures and dwell times during sintering is extra critical.

Crystallinity of PTFE can vary considerably depending on processing. This value can be seen in small variations in the specific gravity although in practice most PTFE materials fall in the 50-60 percent crystalline percentage. Increasing crystallinity decreases flex life, increases compressive stress and decreases recovery values, permeability and wear life. Other properties of PTFE, such as thermal, chemical, electrical and friction, are not generally affected by crystallinity changes.

So, sintering and other processing steps do a make a difference in deterimining the quality of PTFE. If you need to maximize the performance of your PTFE parts, including Rulon, Fluorosint, Ultraflon or even generic products, be sure you contact Tri Star Plastics first.  We can help you select the right material and the right process.

Question: I am using Rulon J on a very small diameter shaft with a light load and medium speed condition. For some reason I am getting more stiction and friction than I expected. Any suggestions?

Answer: One of the issues with Rulon and any PTFE based bearing material is that there is an optimal load range to get the performance you desire. If the bearing is too lightly  loaded you will experience an increase in friction. That is a phenomenom common to PTFE. The thing to remember is the higher the load, the lower the friction. Reducing the surface contact area by either shortening the bearing or machining small reliefs on the ID of the bearing will increase surface loading. That will in turn reduce the friction. It may take some experimenting to get the result you want but it really does work!

Rulon XL is a new alloyed polymer with excellent wear compared to even other Rulon materials. Rulon XL is compatible with soft mating surfaces such as stainless steel and aluminum, has a very low coefficient of friction and good chemical resistance with the exception being alkalis. The polymer also exhibits excellent resistance to deformation making it a good choice for bearings or seals. Rulon XL has a PV rating of 10,000 with a P of 1200 psi and a V or 400 sfpm. It is the best Rulon choice for vacuum service and also works well in steam or other wetted environments. Available in rod, sheet, tube or skived tape. Contact Tri Star at www.tstar.com for more information.

Rulon bearing materials, and other filled PTFE materials like Fluorosint and Ultraflon, have a unique reaction where coefficient of friction is concerned. Unlike most materials which theorize that higher loads and speeds mean higher friction, filled PTFE products are just the opposite. WIth these materials, the higher the load – the lower the friction. Same goes for speed as a general rule. Design your PTFE bearings with the thought in mind that surface contact area can be reduced dramatically to optimize friction properties. Remember, more is not necessarily better when it comes to PTFE based bearing materials.

Still have questions? Don’t hesitate! Ask The Experts!

Rulon 142 is an excellent material for high load, high speed linear guideway liners for machine tools. Commonly used as an inexpensive insurance policy to possible lube failures on machines, Rulon 142 is bonded to the dynamic component on the X-Y-Z tables of some of the world’s leading machinery builders. Rulon 142 is also an excellent material for rebuilding machine tools where the efficiency and tolerances have been lost over time. Easy to install using CE211 or CE211FC adhesives available from stock. Rulon 142 is commonly used as an cost effective alternate to Turcite B and is fabricated using the same techniques. For more information on Rulon 142, visit www.tstar.com and check out our Shooting Star Archives for a number of articles on Rulon and more!

Rulon J is a polymer reinforced PTFE material with extremely low friction and long wear life. Developed by Dixon Industries over 40  years ago, Rulon J is best used in light duty, high speed bearing applications. Operating temperatures of -400 to +550F are attainable with Rulon J as with all Rulon materials. Rulon J is commonly used in applications where absolute minimal stick slip can be tolerated, no lubrication can be used and speeds are running as high as 500 sfpm. Rulon J can be found in office machines, X-Y-Z guides on analytical instruments, fine movement aerospace components and similar types of equipment. For more information Rulon J visit www.tstar.com or simply Ask The Experts your direct question.

Rulon 641 is an FDA cleared bearing material that has excellent wear resistance in non-lubricated bearing applications. It is non-abrasive so works well against soft metals like stainless and aluminum. Rulon 641 is white in color so pleasing to the eye for food and pharmaceutical applications. Excellent material for linear, rotary or oscillating applications with very low coefficient of friction a K (wear) factor. There are two new FDA cleared materials compatible with the 641. Rulon 1439 is advised if the bearing is in a submerged or wetted environment. Both materials are inert to chemicals including all new sanitizing technologies in food and drug industries. For more information visit www.tstar.com and click on Rulon Bearings.