Pressure created by clamping base and cover

  • Thread starter Thread starter anlouk
  • Start date Start date
  • Tags Tags
    Base Pressure
AI Thread Summary
The discussion revolves around calculating the pressure created by clamping an aluminum base and cover with a PCA in between, using a formula provided by an electrical engineer. The formula involves torque per screw, torque coefficient, screw size, desired pressure, surface area, and the number of screws. There is confusion regarding the correct units for surface area, with one participant suggesting it should be in square meters rather than square millimeters. Additionally, the torque coefficient for stainless steel is sought, as the participant only has the value for aluminum/steel, which may significantly impact the pressure calculation. The calculated pressure values appear extreme compared to the compressive material's specifications, prompting a request for further clarification and advice.
anlouk
Messages
1
Reaction score
0
Could anyone help with a problem I have been asked to solve at work. Unfortunately I haven’t done anything like this since college (over 12 years) and am a bit confused now.

We have an assemblied unit, consisting of an aluminium base and cover with a PCA clamped between. The unit is clamped using 27 screws (M2 SS Pan TORX SEMS) with a torque value of 0.35Nm. The electrical engineer wants to place some compressive material into a milled pocket in the base, which will allow for tolerance build up in an area of the PCA and therefore needs to know the pressure caused by clamping the unit together.

I was given the following formula by another of the electrical engineers:
T = (C x D x P x A) / n

T = torque per screw (Nm)
C = torque coefficient
D = nominal screw size (m)
P = desired pressure (force per unit area) (N/sq m)
A = surface area (sq mm) – is this unit correct should this not be sq m?
n = no of screws

Could anyone confirm if this is the correct formula?
Also I can only find the torque coefficient for aluminium/steel (0.45 dry) and not stainless steel, does anyone know what this value is?
Will this affect the answer greatly as I worked out the formula using the aluminium/steel value (0.45 dry).

Depending on the surface area unit (surface area of unit is 8604.8788mm²) I am getting the pressure to be either:

Using surface area in mm² = 1.220238Nm² = 1.220238 Pa
Using surface area in m² = 1220238Nm² = 1220.238 kPa

Both values seem to be a bit extreme and when comparing to the data sheet of the compressive material, the graphical range for the pressure in kPA is in units of 100 upto 700kPa.

I would appreciate any advice given. Thank You.
 
Physics news on Phys.org
Well, for torque, the result of the equation, you should have units of N-m. So, yes the value of A should be in m^2 not mm^2.

Thanks
Matt
 

Thread 'Average velocity as a weighted mean'

Hello everyone, Consider the problem in which a car is told to travel at 30 km/h for L kilometers and then at 60 km/h for another L kilometers. Next, you are asked to determine the average speed. My question is: although we know that the average speed in this case is the harmonic mean of the two speeds, is it also possible to state that the average speed over this 2L-kilometer stretch can be obtained as a weighted average of the two speeds? Best regards, DaTario
View full post »

Thread '1:1 versus 2:1 Mechanical Advantage debate'

The rope is tied into the person (the load of 200 pounds) and the rope goes up from the person to a fixed pulley and back down to his hands. He hauls the rope to suspend himself in the air. What is the mechanical advantage of the system? The person will indeed only have to lift half of his body weight (roughly 100 pounds) because he now lessened the load by that same amount. This APPEARS to be a 2:1 because he can hold himself with half the force, but my question is: is that mechanical...
View full post »

Thread 'Newton's first law?'

Some physics textbook writer told me that Newton's first law applies only on bodies that feel no interactions at all. He said that if a body is on rest or moves in constant velocity, there is no external force acting on it. But I have heard another form of the law that says the net force acting on a body must be zero. This means there is interactions involved after all. So which one is correct?
View full post »

Similar threads

Converting torque applied to a bolt into the linear force exerted by the bolt
Replies
8
Views
159K

Hot Threads

Recent Insights

Back
Top