an open question for the techies to ponder:
thermal coating is a speacial coating/layer applied to the surface of a device intended to inhibit heat tranfser. the application on the M7 pulley raises a question.
Given the intimate metal to metal contact of the near press fit pulley to shaft heat is going to pass into the pulley. after the pulley/ blower shaft reaches steady state, the temps would be the same, unless heat is being removed from the pulley faster than it is getting into it. The question I see is: isn't the thermal barrier restricting heat removal from the rest of the pulley to the surrounding air, already a poor heat transfer medium?

by comparison, coating the inside and outside of a header does keep the exterior surface cooler, but that functions by preventing the hot exhaust gas from getting the header hot to begin with.

as an example coated piston tops can run cooler by not absorbing as much heat through the coating, but also getting rid of it through the un-restricted, uncoated bottom side to the engine oil.

 

Valid reasoning from what little I know John.
Is it's intention to isolate the belt from the heat of the pulley?

 

JLM,

It is not clear if you are concern that he heat built up on the pulley would be too high for the belt. You can argue both ways. One as you reason, and the other is that the coating reduces the heat transfer from the pulley to the belt.

If you are concern the reduced heat dissipation from the SC shaft to the pulley will increase the temperature of the shaft bearing then I agree it would tends to be worst off. However I would think the delta is minimal at best.

We need numbers.

 

What about placing the pulleys (one plain and the other coated) on a firmly fitting steel shaft; then uniformly heating the shaft to temperatures that might simulate those under "real life" conditions, and measuring the temperature of the pulley surface that would come into contact with the belt? While not an ideal test, do you think this or something similar might help us understand if the coated pulley truly helps protect the belt from the deleterious effects of high temperatures as might be seen with 19% pulleys?

Other questions: Since the supercharger pulley rotates at a very rapid rate, how long would it take the constant friction of the belt to wear down the coating? Of course, this assumes that one can easily measure the thickness of that layer of coating. Also, when items such as pulleys are ceramic coated, how thick (thin) is that surface layer? Thanks...

 

Hey, you could incorporate vanes on the pulley to remove heat...but the added aero friction would at some point generate more heat and so on and so forth.

 

Vendor X is claiming all the these advantages:
Reduced heat transfer from the SC shaft to the belt.
Reduced SC temp (I read by promoting heat dissipation thru the small ribs on the unique pulley design).
Reduced belt slippage (I read by better friction characteristic of the coating between the belt contact surface)
Reduced belt squirm thru CAD-optimized belt/pulley interface (not the topic of this discussion).

Well choice of the word "reduced".

Without the benefit of measurement my guess of most stainless pulleys dissipate heat quite well because of the high rotational speed. On the other hand stainless steel is a relative poor heat conductor compared to mild steel and especially aluminum so it tends to insulate the heat originates from the SC from transfering to the belt.

Also consider what is the heat gradient on the pulley of a given design. Is the heat generated by the belt/pulley friction at the circumference greater than the heat originates from the SC that transfer to the pulley thru the shaft?

For the relative long heat path thru the long steel (not the best heat conductor) shaft I think at the pulley's belt interface surface the heat originates from the SC is not significant comparing to the temperature that matter for the belt. Aluminum pulley may offer the best heat dissipation characteristic for the heat generated by the belt friction without getting fancy.

All these arguments seem to be splitting hair without measurements taken from carefully instrumented setup to determine which keep the belt at the lower temperature.

 

If the pulley is 100% coated, wouldn't the coating prevent the heat from being transferred into the pulley in the first place? If the pulley were only coated on the anterior side, then yes, I can see that heat could be transferred from the shaft to the pulley and then be trapped. However, I would think that if the pulley were coated, it would have been the total surface area...or, I would hope so at least...

 

Let's assume that the heat buildup of a supercharger pulley comes from the slight belt slippage at high speed/high boost conditions. The purpose of the barrier coating would be to keep the heat generated by the outer diameter of the pulley from 'sinking' into the shaft and causing trouble there, right? Now the belt, heated by it's slip on the blower pulley continues across and around the crank and accessory pulleys. The belt has a chance to shed some of the heat into these larger and more numerous pulleys it encounters for a much greater time. By the time the belt goes full circle back to the blower, it's temperature should be reduced measurably. Once it makes contact with the hot blower pulley, it's able to absorb some of the heat of friction more effectively and keep this pulley cooler before starting the process over.

Or, the heat generated by the blower running hard does not find it's way through the shaft, into the pulley and then to the belt interface creating a lesser amount of available friction due to the barrier coating blocking heat transfer. A bonus here as well.

Then again, it could all just sound real good in marketing.

 

thermal barriers only effect the rate of heat transfer; so a coating at the shaft contact will slow down heat transfer, but after a while...the temps will be the same. Unless heat is being removed from the pulley through some other mechanism, faster than is get put back in, the pulley will be at the same temp as the shaft, presumably the heat source.
It would make sense to minimize the transfer of heat into the pulley (coat the shaft contact, but that is so tight a connection, metal-to-metal, I doubt you can do much) and maximize heat removal (no coating where the belt can pick up heat and get rid of it, or where the air can contact the pulley and get rid of heat.)