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Any metal casting expert here ? The metal color I want to ask
Hi Gang,
I bought for fun & experiment, a complete set of all these from Germany, used. Supposedly from a very very low mileage car, which I believe because the parts look so good. RIGHT REAR
.
The color of the bearing is what I want to ask. Is this normal casting color ?
Bearing #20 in EPC is super smooth and tight, by hand.
The bearing is so nice smooth to spin and firm..........
Above is the color I am asking.
I am NOT an expert...but, spent a TON of time some years ago looking at how to "color" metals (mostly titanium or stainless steel) with heat. This was as opposed to anodizing them, and, with luck not damaging the structure of the material at hand (making it weaker). Things have moved forward in the past number of years with vapor deposits and other coatings as opposed to using heat to alter the color of hard metals. As you have read on the Dean website, color can alter the tensile and impact strength of an item (mostly we would play with forged items, not cast as your parts are). To that, a thought I just had is there is no way that our car parts are anything more than a "junk metal" alloy - it is not like they are Metal Matrix Composite or even a higher end alloy (in my world of Titanium it would be 3Al/2.5V or 6/4)....
Now, to your part...well to my non expert eyes that sure looks like heat created coloration. While I would say it could have been from heat treating, my cars do not and have not had that appearance. If I had to make a call, that was at some point a bad bearing that severely over heated.
For reference - this is a Titanium bolt that I colored with my torch. It was FAR cheaper to get a stock bolt and torch it than pay $40.00 for the same bolt from a company called "Better Bolts". https://betterbolts.com/collections/...itle-ascending
Last edited by OldManAndHisCar; May 28, 2025 at 07:57 AM.
That colored region is part of a bearing assy Item A where when we buy from MB, we get the whole thing.
Unless someone replaced the bearing only inside the Item A assy...using heat....it is possible
OR.... someone replaced the flange ( item b) only while hearing up Item A
I am most interested in the wheel carrier /knuckle actually, item C , #10
Looks like it could be the interference press fit on that part. Does the bearing feel smooth?
On many parts that require press fits in industry, you heat the bearing hole and freeze the bearing. It can help reduce galling for really tight press fits for ISO H7 hole fits or above. Piston pins, pressed in some connecting rod designs, use this method too.
If you’ve ever installed bearings in this method, it’s pretty fun to watch them just drop in the hole, or use very little force to insert them.
On bearings, this can prevent out of round conditions where some of the material in the hole gets deformed, causing the bearing race to distort. Could be they used that procedure to insert the outer bearing. The heat pattern looks too uniform for a tech using a torch to change bearings. Looks like it was done on a machine.
I have seen that part on some other MB’s look the same way (coloring from heat) . So it’s probably one of many manufacturers MB uses to manufacture these parts that used the pre-heat press fit processes. It may be an aftermarket part, but if it has such low mileage, that would be doubtful. Can you identify the bearing manufacturer?
In case you’re interested (subject is somewhat technical and dry) and want to read about press fits:
I am NOT an expert...but, spent a TON of time some years ago looking at how to "color" metals (mostly titanium or stainless steel) with heat. This was as opposed to anodizing them, and, with luck not damaging the structure of the material at hand (making it weaker). Things have moved forward in the past number of years with vapor deposits and other coatings as opposed to using heat to alter the color of hard metals. As you have read on the Dean website, color can alter the tensile and impact strength of an item (mostly we would play with forged items, not cast as your parts are). To that, a thought I just had is there is no way that our car parts are anything more than a "junk metal" alloy - it is not like they are Metal Matrix Composite or even a higher end alloy (in my world of Titanium it would be 3Al/2.5V or 6/4)....
Now, to your part...well to my non expert eyes that sure looks like heat created coloration. While I would say it could have been from heat treating, my cars do not and have not had that appearance. If I had to make a call, that was at some point a bad bearing that severely over heated.
For reference - this is a Titanium bolt that I colored with my torch. It was FAR cheaper to get a stock bolt and torch it than pay $40.00 for the same bolt from a company called "Better Bolts". https://betterbolts.com/collections/...itle-ascending
When you mention Metal Matrix Composite I asked myself if you were a mountain biker. Long time trek rider here.
I'm pretty sure that is induction heated so the bearing can slide into bearing carrier because of interference fit. Pretty common practice to make pressing the bearing faster and more gentle.
On the flipside you can also freeze the mating part so it shrinks. Which is what I did when I did all four wheel bearings on my car.
IF normal that sure s funky and lazy MB as the part should have been cleaned up before selling IMHO.
With these heat marks from assembly limits troubleshooting in future as you cannot tell if bearing housing ever overheats.
I have seen a lot of cast steel and/or iron parts machined for interference fit roller bearings.
We would use hot oil to heat cast housing and put bearings in deep freezer or homemade nitrogen "freezer".
We did not like to use flames we the uneven heating could cause issues when you tried to press in bearing.
Now we were doing this for much larger bearings for large offshore anchor winches.
for small bearings like these we would just use a press as the bearing manufacturer designed press fit is not all that much and they recommend just pressing in with hydraulic press.
So for me to see these heat marks reminds me "the best or nothing" is just a marketing phrase.....
Any hoot I like how you cleaned it up - I would paint it as well.... Corrosion sucks.
for small bearings like these we would just use a press as the bearing manufacturer designed press fit is not all that much and they recommend just pressing in with hydraulic press.
Um, no, they are designed to be installed in an environment where the thermal changes (size) allows the bearing to be put into the (hot) casting and the casting shrinks around it. This is VERY common. IF the bearing was able to press in, the gap would be too large (less than a hair) and need to be filled with a LocTite type of fixing compound (that is subject to thermal failure).
UH in my world yes.
I was design engineer making assembly prints with bearing manufacturer spec sheets next to me.
I know what what we did.
For what type of applications? Even in bicycles it is now not uncommon to use thermal change to install bearings into carbon framesets while minimizing damage to the interface. Then, they STILL creak like mad (as compared to threaded systems).
Haha I like a thread where we’re ALL a little right.
Yes, the part is technically “heat treated” thru induction. Heat treating is a BROAD term. Anything from hardening to annealing/stress relieving is considered “heat treated”. The induction process could generate enough heat for stress relieving or hardening, if desired, depending on metallurgical properties of the part. Also some parts have built in bearing races and the whole part is hardened to add durability to the bearing races. I don’t believe that’s the case for this particular hub.
Hard to tell visually if the part is cast or forged without more in depth analysis.
Modern castings are very uniform, but this is a fairly high stress area.
Below is a confirmed MB forged part, and the wheel hub in question side by side.
Things are not always what they seem
You get the idea…
Last edited by crconsulting; May 29, 2025 at 11:55 AM.
Heat/cold helps install but not always required as it depends on the press fit interference and bearing OD and type.
We would press bearings in large steel sheaves used in cranes - roller bearings.
but when sheaves were a plastic called Nylatron we would put the sheaves out in the SUN in morning and put bearings in freezer.
For boom foot bearings or bronze bushings, when under 5"-6" OD they could be pressed in or for bushings hammered in using a piloted tool to fit bearing.
Now on large traction winches (drill ship anhcor winches) and water fall hoists (2 drum construction hoists), they would get hot/cold treatment as they would be very large (well over 6" OD) and press fit is huge and too much force required to overcome.
Heat/cold helps install but not always required as it depends on the press fit interference and bearing OD and type.
We would press bearings in large steel sheaves used in cranes - roller bearings.
but when sheaves were a plastic called Nylatron we would put the sheaves out in the SUN in morning and put bearings in freezer.
For boom foot bearings or bronze bushings, when under 5"-6" OD they could be pressed in or for bushings hammered in using a piloted tool to fit bearing.
Now on large traction winches (drill ship anhcor winches) and water fall hoists (2 drum construction hoists), they would get hot/cold treatment as they would be very large (well over 6" OD) and press fit is huge and too much force required to overcome.
Good input,
Yeah for sure smaller diameter is typically super easy to press. I used that induction heater for large bearings on street car (train) wheels.
What’s interesting about that bearing, (though have replaced a few of those assemblies, I don’t currently have the actual part in hand, nor did I note)
I don’t see a shoulder for the bearing to seat. So it’s appears to be held in place by press fit alone or possibly tapered? It’s also a deep bearing press, lots of surface area.
@S-Prihadi do you see a shoulder for that bearing to seat?
But you are correct, it will depend on desired class of press fit. Only way to tell designed press fit is disassemble and measure.
Cheers!
Last edited by crconsulting; May 30, 2025 at 10:23 AM.
For me, very different application (and temps). For bikes they tried to do press fit bottom brackets. They were the "solution" (not sure what the problem was). Well, fast forward a few years and most higher end bikes are back to using threads and not press in. Heck, most bike shops even if they had the tools did not have the staff capable of properly pressing in and aligning bearings for the spindle. There were a few brands that specifically said to put the bearings in a freezer and warm the frame before trying to insert them.
That said, I have ceramic bearings in my bike(s). I mean, if I ever do get the RPM of my crankset to about 13,000 or so I will see the performance they were designed for :-)
That said, I have ceramic bearings in my bike(s). I mean, if I ever do get the RPM of my crankset to about 13,000 or so I will see the performance they were designed for :-)
Haha, the lengths people will go to to get that DH KOM 😀
Not to get too OT but,
Funny how some people (moi included) who drive fast cars & motos, or lost their license. Figure out quick that you can go as fast as you want on a Mtn. Bike and nobody will be around to care.
Last edited by crconsulting; May 30, 2025 at 03:26 PM.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
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