20FHK02

Sorry Buell I did not take account for the steel sleeve. So the entire pulley was treated as one piece of aluminum for a quick comparison.

I'm making something more fun now

20FHK02

I really wanted to install the pulley (can't resist its attraction...) so I went ahead and did a more realistic analysis:

Material properties were taken at 200F (~90C operating temperature) for stainless steel hub and set screws and T6061-T6 aluminum alloy.

Refine the mesh of the model (see pics below) and move the location of the set screw to the center of the model (the previous model has 2 half screws on each end). This results in a full screw in the middle and minimize boundary effects. And, because of the refinement, I was able to make the screw more "cylindrical".

Do not include any belt loads, vibration loads, etc.. Only analyze the stresses due to bolt force. I looked up some reference, using an assembly lubricant Molykote of u = 0.08, the bolt will develope 43 lb/ft-lb of axial force. So, for torque = 220 ft-lb, the resulting force is 9460 lb.

The hub flange surface area is 2.4 in^2, which is about the area of the washers. So the resulting pressure on the flange is about 4000 psi (huge isn't it?!!).

20FHK02

Close up look at the set screw location

20FHK02

Again, highly localize stress concentration. The von Mises stress is 41 ksi in the aluminum! The yield strength for aluminum is only about 20 ksi!!

20FHK02

Then I "moved" the set screw location 0.04" farther, which is 0.05" from the hub surface, and re-ran the analysis. Guess what, the von Mises stress dramatically reduced to 27 ksi!!! And the overall max is on the steel hub now. Stainless steel has yield strength of about 30 ksi. But the max stress on the aluminum is still higher than 20 ksi.

Keep in mind that the results were due to bolt force only, and there are other types of loads on the real pulley. I really wish the screws could have been several hundredth inches more from the hub...

There is always a fine line between analysis and reality. So maybe I'll just put it on for a couple of weeks, then take it off to see if there is any cracks. If one pulley could last several months before fracture, I think a couple of weeks should be OK

DCX Engineer

The new outer ring is made of steel. It is pressed on, welded and rebalanced. 10 and 15% larger rings are available.

20FHK02

Okay guys: I know I'm going into too technical here... but since I've done the analysis so why not share with the few who are interested, right?! But if you don't know what I'm talking about below, just jump to the Conclusion section.

Background
After intensive (sort of...) measurements, I found that the gap between the set screw OD and the hub surface is more like 0.025", intead of 0.01" that I previously stated. And the torque-force conversion factor was too conservative because previous analysis showed that even the stress on the steel was relatively too high for safety concern (because MB will not design a component such close to the margin).

So I re-ran the analysis with the more realistic gap size, and a u = 0.09 (i.e., 38 lb per ft-lb of torque) and the new flange pressure is now 3500 psi. And the flange thickness is assumed to be 3/16".

Results and Discussion
New results show that, isolating the aluminum body from the hub, the von Mises stress on the aluminum is now 29 ksi (see Fig. 1 & 2).

Although this still exceeds the yield, when evaluating the component stresses - radial (Fig. 3), hoop (Fig. 4), and axial (Fig .5), a major portion was contributed by axial stress, which is not realistic because the hub is not welded onto the pulley body. Therefore, the actual axial stress should be much lower.

Radial and hoop stresses are the main contributors for cracking if they are tensile, but results show that they are all compressive.

In addition, I also did a linearized stress calculation through the width of the gap. Results show that the linearized max radial stress is 20 ksi, and 13 ksi for hoop (axial is invalid). These are more comfortable numbers!

Note that the torque-bolt force conversion used here is actually for nuclear reactor vessels using 2.5-inch diameter bolts, so I think, a BIG think, the actual force on the crank bolt should be lower. But due to uncertainties and the fact that other types of forces are not included, so this conservative force is okay to be used.

Conclusion
The results from this revised analysis make me more comfortable now, although I still wish that the gap could have been a bit larger.

I know a theory is junk if it does not reflect reality. So I've decided to install the pulley and see what will happen!!

20FHK02

Isometric view showing the von Mises stress distribution on the aluminum body in the vicinity of the set screw, excluding the steel hub and set screw.

20FHK02

Front view of the model showing the mesh grid and the von Mises stress distribution.

20FHK02

Front view showing the radial stress distribution.

20FHK02

Front view showing the hoop stress distribution.

20FHK02

Front view showing the axial stress distribution. Note that the axial stress is not a valid representation of the actual situation.

20FHK02

Thank you for your time and attention.

Notes:
1. A real stock pulley model will not be made because I'm lazy to take the measurement and create a whole new model. But since it is all steel and the hub geometry is identical to the ASP one, so Case 4 is applicable to the stock pulley for comparison.

2. For an alloy pulley with steel sleeve, the stress will be worse than Case 3 because of a thinner alloy hub thickness. And the thin edge of the steel sleeve will create high stresses on the contact surface of the alloy side.

speedfrk

How do they press it on over the old pulley? Do they machine the old belt surface off first?

Buellwinkle

Way over my head. What's the outcome of the alloy pulley with steel sleeve and would the thinner sleeve on the Kleemann pulley make much of a difference or should those people worry?

KOMPRESSORnSC

20FHK02,
No, thank you! I only understand about 1/2 of what you're talking about, but it's 100% more than I knew before. My ASP pulley is on it's way to me now, hopefully to be installed by next weekend.

20FHK02

If you really want to know, I can do a detailed analysis on this using contact elements so that the aluminum and steel are no longer treated as welded together. But I need the dimensions of the thing and the outcome of the analysis might get into some people's proprietary territory...

DCX Engineer

Yes.

Buellwinkle

Use Kleemann's dimension's of .07" for the steel sleeve, the rest is T6061 alluminum.

20FHK02

Not wanting to offend anyone nor be involved in any legal issues, I will email the results to you.

Buellwinkle

It's that bad, I understand.

20FHK02

I can't say it is bad as I still haven't done the analysis yet :o

20FHK02

I found interesting results after separating the 2 materials and take the pulley to 3000 rpm

Does anybody happens to know the guesstimate force from the belt tensioners?? (Like typically they are around xx lb, etc.)

Buellwinkle

It's a high number like 180-200 lbs.

C230 Sport Coup

As far as legalities 20FHK02 , why not just state foir the record this is purely for fun, and the numbers don't neccesarily represent accurate values, since you're basing your analysis on theoretical values....
I kinda gathered that anyway, we're just dealing with theory here.