RandyBMC has stated in no uncertain terms that:
http://www.webbmotorsports.com/forum...63&start=0

He has also confirmed that:

1) He doesn't know how hot the seal got during installation.
2) He doesn't know how hot the seal gets while in use.
3) He does know that the seal wasn't damaged during installation.
4) He does know that the seal was compromised during installation.

But, that common sense dictates the seal must be compromised by the heat of putting on the spindle. Fair enough. Let's see how common sense compares with science.

I decided to model the supercharger pulley spindle and the shaft, to see just how much heat is transferred in a worst case scenario.

Now, both the spindle and the supercharger shaft are made of steel. The spindle has a mass of 118 g (0.26 lb). The mass of the shaft is unknown, but modelling it as 350 mm long by 20 mm diameter, gives a mass of 863 g (1.90 lb). They have a contact area of about 25.4 mm (1&quot of the length of the shaft, for a surface area of about 1600 mm^2 (2.5 in^2). The spindle has a surface area exposed to air of about 3300 mm^2 (9.7 in^2). Let's say as a worst case scenario, that the spindle is completely heated to 560 Kelvin (550 F). Let's say the ambient temperature is a balmy 305 Kelvin (90F).

There are several types of heat transfer, but radiation and convection with the surrounding air can be modelled like this:

H = C*A*(Th-Ta)

where:

H = heat dissipated in Btu/h
C = combined coefficient of convection and radiation in Btu/(h*ft^2*degrees F)
A = surface area of the spindle
Th = surface temperature of the spindle
Ta = temperature of the surrounding air

More later, must eat.

 

OH no!, somebody is stealing my fun with numbers!!! .......

 

Andy, I'm eagerly awaiting your results!

 

the absolute worst case is no heat loss through the blower rotors, case, air, etc., and complete heat transfer from the hub at 560K and the shaft at 305K.

final K temp, assembled shaft and hub worst case,= ((118x560)+(863x305))/981

 

JLm bet him to the punch!!!

 

whats that roughly 145 degrees F, 62.51 degrees celcius, 335.67k?

 

my onus is the fastest and the lightest onus

 

I'm still cooking dinner, but figured I'd poke my head back in here. This plot shows how much the MP45 heats up air at 10 psi and 16,000 rpm (lower than boost and speeds seen by a 15% pulley at stock rev limit):



Looks like a little over 180 F on top of the 90 F ambient, for about 270 F. So, if the supercharger outlet sees 270 F during operation, and the seal sees 145 F during installation (at most), then how was the seal compromised during installation again?

 

and the point is?

 

Andy,

I think the calculation is partially correct. You also have to factor in the distance from the pulley to the bearing. While heat will be transfered it won't be consistent over the lenght of the shaft. The part of the shaft nearest the pulley will increase in temperature more than a part of the shaft at the extreme distance from the pulley.

Also, your calculation is relevant to the average heat transfer across the entire shaft. The entire mass of the shaft is not relevant, since the entire shaft is not absorbing the heat only the part of the shaft in contact with the pulley. Therefore I think density plays into the calculation. I remember seeing a calculation dealing with this, but I have to go and dig it out.

 

Okay, so the hub is heated to 550 F, then slid onto the shaft, which is 90F. They have a contact area of 2.5 in^2. Fourier's Law says the rate of heat transfer by conduction is:

q = K * A * (T2 - T1)/(X2-X1)

q is the rate of heat tranfer
K is the coefficient of thermal conductivity
T2 is the hotter temp
T1 is the cooler temp
X2-X1 is the distance travelled

The coefficient of thermal conductivity for steel is pretty crappy, about 40 (W/m*K). That's why you can hold onto one end of a steel rod while the other end is heated red hot. Aluminum is over 5 times as conductive.

_________________

SHOW ME THE NUMBERS! 1/4 Mile Database

 

[removed]

Changed my mind. I don't want to contribute to this thread.

 

The point is the seal is not comprimised, due to the heat fit method, other factors also play in as well heat from engine, blah, blah, I think this is enough evidence to show the seal is not comprimised, unless it is damaged in other ways, hitting the shaft on the end or something to cause failure(the old if it doesnt fit beat it until it does method

 

I personally think that all Randy's testing caught up with him, just one of the down sides of pulling thing on and off repeatedly, i think that he probably exerted a horzintal load on the bearing, maybe several minor loads, eventually leading to failure. Not that im claiming he does shotty work, im not, i think that the result of all his testing(which im thankful for)started to cause premature failure, kinda like a bolt thats taken in and out alot eventually the threads wear out.....

 

Andy,

Without getting into a pissing contest, here are some facts:

1. I have a failed seal on a supercharger that used the heat on hub.

2. The equations above do not take into consideration all of the factors - ie radiant heat transferance to an object less than 1/4" away - not along the shaft, but directly through ambient transferance.

3. I have done both scientific data collection and real world testing, and the real world always throws in a wrench! As long as the equation considers all points, it will be accurate. The trick is using the right equation with all variables accounted for.

You have a hub that is slid directly onto a shaft at 550F. I challenge you to put your finger within 1/4" of that hub after the first second it has been slid onto the shaft. That is a direct correlation.

If you would like to challenge my methods of testing, so be it. I am doing testing that I believe reflects accurately the entire picture. Dyno runs, track testing, temp collection, abuse tests, and *gasp* equations. I think you are a sharp guy, and I appreciate the data and questions you bring to the table. I do see a pattern of attack, and this is the post I am writing to address your questions.

I have seen the failure, and I changed products. I think that was the conservative way to go. I don't shove that down people's throats, and I am happy - considering I have done several installs using that pulley - that all of the other superchargers are fine. If anyone wants the original style heat-on hub pulley, I have 18 of them left that have been on my shelf for some time now.

Like I stated earlier, I am happy to discuss this matter on the phone with you or privately by any other means, but to drag on in a pissing match isn't going to get us anywhere. I have an opinion based on my personal experience, and if you disagree, great! I know from what I've seen.

Randy

_________________

Click the pic to enter the world of Webb Motorsports!




This still ain't no disco!

 

Im not 100% familiar with the story but from what i understand, the pulley didnt make it all the way on, heat was applied...<intermission> supercharger seal failed.

My question adn i guess there is only one guy to answer it: What if any sort of pushing and pulling was performed on the half on pulley while it was "half on". Maybe the seal was compromised due to axial loading that its not designed for? Im not familiar with the seal in question... just throwing out ideas :smile:

--
Cheese

 

Even if the supercharger shaft was only 1/10 as long as I estimated, and weighed 1/10 as much, the ideal theoretical equilibrium temp would only be a 265F increase over ambient. I suspect in reality, the seal is heated less during pulley installation than it is during operation at high rpm, high boost.

 

>>I personally think that all Randy's testing caught up with him, just one of the down sides of pulling thing on and off repeatedly, i think that he probably exerted a horzintal load on the bearing, maybe several minor loads, eventually leading to failure. Not that im claiming he does shotty work, im not, i think that the result of all his testing(which im thankful for)started to cause premature failure, kinda like a bolt thats taken in and out alot eventually the threads wear out.....

Actually, that would have nothing to do with a seal failure. The hub stays in place, while the pullies are interchanged, so the whole argument is really moot.

Randy

 

>>Even if the supercharger shaft was only 1/10 as long as I estimated, and weighed 1/10 as much, the ideal theoretical equilibrium temp would only be a 265F increase over ambient. I suspect in reality, the seal is heated less during pulley installation than it is during operation at high rpm, high boost.


Andy,

Your calculations that you are using are incorrect and only show a partial picture of what is going on. The length of the shaft and weight are irrelevant to the discussion. Heat is flowing up the spindle. The spindle could be ten miles long. The heat getting up the first 1/4" is all that we are worried about. The length and weight only matter if you are trying to measure the entire heat transferance and the average resting temperature of both masses. Also, heat will transfer along the surface at a different speed than through the entire rod. It is a vector. You also aren't measuring the heat transferance to air from the pulley or the heat from the shaft to the air as it becomes heated. The calculations required to perform this and give an accurate number, would require a ton of calculations and are far beyond the calculations provided by you. A much simpler method would be just to perform a test with a thermistor and measure the result.

Unfortunately it would take me a while to combine the right equations together, but you are looking at more of a 3-dimensional Fouriers law, with multiple coefficients, such as this:




For such a simple item it would be much easier to perform a silly test then to try and begin to calculate this, and this is only part of the equations needed.

 

>>
>>I decided to model the supercharger pulley spindle and the shaft, to see just how much heat is transferred in a worst case scenario.
>>
>>Now, both the spindle and the supercharger shaft are made of steel. The spindle has a mass of 118 g (0.26 lb). The mass of the shaft is unknown, but modelling it as 350 mm long by 20 mm diameter, gives a mass of 863 g (1.90 lb). They have a contact area of about 25.4 mm (1&quot of the length of the shaft, for a surface area of about 1600 mm^2 (2.5 in^2). The spindle has a surface area exposed to air of about 3300 mm^2 (9.7 in^2). Let's say as a worst case scenario, that the spindle is completely heated to 560 Kelvin (550 F). Let's say the ambient temperature is a balmy 305 Kelvin (90F).
>>
>>There are several types of heat transfer, but radiation and convection with the surrounding air can be modelled like this:
>>
>>H = C*A*(Th-Ta)
>>
>>where:
>>
>>H = heat dissipated in Btu/h
>>C = combined coefficient of convection and radiation in Btu/(h*ft^2*degrees F)
>>A = surface area of the spindle
>>Th = surface temperature of the spindle
>>Ta = temperature of the surrounding air

Heat Transfer of this type must be modeled after Conduction Heat Transfer, not radiation or convection. Conduction is the tranfer of heat from solid to solid via Kinetic Energy. Convection is the transfer of heat by liquids or gases by current. Radiation is the transfer of heat by electromagnetic rays. Since I don't think the pulley and shaft are liquid and there are no lasers in the supercharger, we need to stick with Heat Transfer by Conduction.

 

dgszweda1 wrote:
I don't think you and I are using the same terminology? Why is the length of the shaft irrelevant? If the shaft is shorter, there is a smaller mass to absorb the heat that is transferred. If the shaft is longer, there is a larger mass. True, the item in question is how hot the seal gets, but that will depend on what happens to the rest of the heat. As far as radiant and convection heat, remember that is being emitted from all surfaces of the spindle, and the surface area NOT facing the seal is much greater than that which faces the seal. So, that 550F spindle is rapidly cooling off by transferring its heat to the air, the shaft, and nearby objects like the seal and the aluminum case of the supercharger itself. To imply that the seal sees anywhere close to 550F is silly.

I agree that testing would be a much better way of figuring this out than calculations. That's one reason why I am disappointed that RandyBMC hasn't done any to back up his very matter-of-fact claim that the seal is compromised. As jlm has in his sig, the onus of proof is on he who asserts the positive. RandyBMC has positively stated that the proverbial sky is falling, as far as heated-hub pullies are concerned. Yet you and I are scratching our heads with calculations trying to make sense of it.

As I see it now, there is no proof whatsoever that the seal is damaged or compromised or molested in any way with the installation of a heated spindle. Even in a hypothetical situation where all of the heat dissipated from the spindle to the section of the shaft protruding from the seal and the blower case, there just isn't much heat to go around. And that's common sense. :smile:

 

It was just a proposed thought, i dont know what you did Randy, and it was no type of attack, as per your phone call i will be resoving that issue quickly....

The failure you had, could be of many reasons, the point i was making was just a thought, not one of anyone lack of mechanical skills or anything like that, it was ment as a comment no diffrent than me saying it was just a faulty seal, NO one actually knows the actual cause of failure, we all are just speculating, and if you notice i did say "I personally think", and "I am not claiming that he does shotty work".

As far as heat being the cause, we just don't know, how many friction fit pulleys have been installed, and how many failures, how many failures due to a 19%, 17%, 15%, how many stock failures, actually i would like to know these answers, anybody? As well we need to know how many are out there to, per group and total....

 

so kids, what did we learn today?

Well the question is not how hot the pulley got now? Andy, you are saying:

>>That's one reason why I am disappointed that RandyBMC hasn't done any to back up his very matter-of-fact claim that the seal is compromised. >>

From what i gathered from what Randy said, he claimed the seal was compromised, and it was. what you mean to question rather is HOW it was compromised. i think we already established that it was compromised (or damaged, however you want to word it... both are the same to me).

Andy, why don't you propose a hypothesis to why it leaked oil and burned out the charger if you feel it wasn't compromised. (or do you feel it wasn't compromised during install only?) Most great scientists and physicists, after seeing a problem and disagreeing with one hypothesis, come up with one of their own. I'm interested to hear what you think the problem was....

-ABT-
_________________
<<sig>>

 

That me and Andy finally agree on something!!

 

I'm working on getting a thermister to test the actual heat at the seal. I have a screwed up supercharger to play with, so it should be dead-on accurate testing. I just have to figure a way to get the old hub off so I can put a new one on again.

I will talk with the guys over at Adam Aircraft (where I am a contract test pilot) where I sometimes can get very nice test equipment.

Randy