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# Maximum torque of aluminium thread

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## Maximum torque of aluminium thread

(OP)
Hello,
I am new on the forum. Unfortunately, I have never had a "Strength of Materials" lessons, that sorry if my question is silly.

I am trying to find a formula how to calculate maximum permissible torque or stripping torque of thread in aluminum (not a bolt).
My connection is steel bolt M7x1 and thread M7 and aluminum housing (Rm - Tensile strength = 240MPa, Rp0.2 0.2% proof strength = 140MPa)

I did not find a formula which include different types of materials e.g. aluminum.
A

### RE: Maximum torque of aluminium thread

(OP)
I tryed to calculate the torque, can you tell me where I made mistake?

Housing thread = M7
Lenght of aluminium thread = 9,3mm = 0,0093m
Rm - Tensile strength = 240MPa
Rp0.2 0.2% proof strength = 140MPa

Steel bolt = M7x1

Stress area:
S=2*pi*r*l = 2*3,14*0,0035*0,0093 = 0,0002044 m2

Stripping force:
F/S = Rm --> F = 240*10^6*0,0002044 = 49059,36 N

Stripping torque:
M = F*0,5*d = 49059,36*0,5*0,007 = 171,7 kN

The 171,7Nm is unreal result. Process measured stripping torque is 17-18Nm.

### RE: Maximum torque of aluminium thread

I wouldn't use Ftu, maybe Fty ... but then its a shear failure (I think) so ... ?

I would not use the full thickness, three threads is a typical assumption.

Why do you want the torque to strip rather than a torque to install (1/3 of the steel bolt torque) ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

### RE: Maximum torque of aluminium thread

Hi Green strand

The stress area's you are using are incorrect, that stress area that you have calculated is for the whole cross section of the bolt. the are you need is the shear stress area of the aluminium thread. In addition the threads fail in shear and so you cannot use the value of tensile strength without multiplying it with a factor usually taken around 0.7.
have a look at this site under the heading of screw thread area's. The M7 thread is a non standard size so you will need to calculate the appropriate area's.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Maximum torque of aluminium thread

I think you misread ... he has pi*d*t (not pi*r^2)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

### RE: Maximum torque of aluminium thread

Are you trying to determine installation torque, or required thread engagement/housing thickness, or ????

### RE: Maximum torque of aluminium thread

Machinerys' Handbook has an excellent treatment of screw threads in dissimilar materials, with most of the data needed to do the calculations. The female thread is sized to exceed the strength of the male threaded member, generally a bolt or stud. You generally want the bolt to break rather than the thread to strip.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

### RE: Maximum torque of aluminium thread

green stand

I can tell you that I use to fix aluminum tooling plate all the time for strip threads.
aluminum will gall, corrode, because of dissimilar metals, will seize and strip out.
to prevent spark plugs from seizing on aluminum heads I would use anti seize. but no guaranty.
every time it has to be disassemble there is a chance it will gall. it's better to use
either Heli coils, or inserts.

### RE: Maximum torque of aluminium thread

There are many standard fastener torque charts online.

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