Tefloninės alyvos

 

PTFE oils

One friction modifier whose efficacy is the center of much attention is polytetrafluoroethylene (PTFE or TFE, for short, the generic name for DuPont Chemical's Teflon), of which there is a family of similar yet distinct formulations. PTFEs boast the lowest coefficient of friction of any known material. Back in 1980, DuPont told everybody that their studies showed PTFE offered "no significant benefits as an engine additive." This statement set off a storm of controversy that still has DuPont spokespeople walking on eggs. However, you will notice that none of the PTFE additive suppliers are allowed to use the word "Teflon" in their advertisements or product information.

For most people "Teflon" calls up the mental image of a no-stick frying pan. PTFE engine oil treatments work quite a bit differently than the PTFE in a cooking utensil, however. When coating a frying pan the metal is spotlessly cleaned in prepara tion for the application of PTFE. This situation is never going to happen spontaneously in a motor, no matter what you use as a pour-in cleaning agent.

As a motor oil additive, PTFE powder is held in suspension in a liquid carrier. Because most (if not all) PTFE resins are more or less tailored for their end use, and because few (if any) of the available powders have been tailored for use as an oil additive, PTFE oil additive marketers must select a PTFE that was compounded for some other purpose (such as frying pans, wire insulation, etc.).

Powders come in different particle sizes, with the smaller sizes typically costing a bit more than the larger sizes. For those who can not afford (or find a source for) the size they want, custom grinding houses can take a less expensive 400 to 500 micron powder, freeze it with liquid nitrogen, and grind it to whatever size is needed. Most of the PTFE oil additives use a particle anywhere from 20 microns down to the sub-micron size.

The very characteristic of PTFE that makes it so slippery also makes it tough to get it where the action is in the motor. For this reason, the carrier liquid is often an affinity agent that bonds the PTFE to the friction areas. These take the form of chemicals such as tricresyl phosphate (TCP) and triaryo phosphate (TAP). The use of the right affinity agent has the positive side effect of boosting lubrication performance whether or not there is any PTFE involved. Some of the affinity agents are so tenacious that it is jokingly said you could lubricate your engine with water if it had enough affinity agent in it. Because of this, some high-performance oils (such as Synthoil) are blended to include affinity agents from the start.

Listening to some of the claims made for PTFE you might get the impression that it is the solution to almost any problem you might have, real or imagined. So why aren't the Big Oil companies putting it in their products?

Most of the oil companies are reluctant to discuss what is or is not in their oil. Off the record, however, many oil company spokespeople express concern that as a solid, PTFE does not stay in suspension forever. If the oil sits for too long the PTFE will settle out; an unacceptable situation for the oil companies we talked to. And as difficult as it is to get the PTFE in suspension in ideal situations, once combustion by-products and oxidation begin to change the chemical composition of the oil, keeping the PTFE in suspension poses a whole new set of problems.

Most oil company engineers also cited additive package balance as a major consideration. Whether talking about pour point depressants or oxidation inhibitors, each felt that whatever the gain in friction reduction the price was too high in other areas of lubricant performance.

If a PTFE additive sounds good to you, the best bet is to contact the manufacturer for test data that can be correlated against other known good lubricants. The Sequence IIID, Sequence VD, and L-38 tests previously mentioned, for example, are industry-wide standards that readily allow comparison against traditional lubricants. The manufacturer that can back up its claims with test results is a lot more convincing than the one with beautiful sales brochures filled with unsubstantiated claims.