Pressure created by clamping base and cover

In summary, the electrical engineer needs to know the pressure caused by clamping a unit together with 27 screws. They were given a formula to calculate the torque per screw, but are unsure about the correct torque coefficient for stainless steel. Using the surface area of the unit in mm² and m², the pressure was calculated to be either 1.220238 Pa or 1220.238 kPa, which seems extreme compared to the data sheet. Matt confirms that the value of A should be in m² instead of mm² for the equation to produce results in N-m.
  • #1
anlouk
2
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.
 
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  • #2
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
 

FAQ: Pressure created by clamping base and cover

1. What is the purpose of clamping the base and cover together?

The purpose of clamping the base and cover together is to create a tight seal that prevents any external pressure from entering the enclosed space. This allows for precise control and measurement of the pressure inside the enclosed area.

2. How is pressure created by clamping the base and cover?

The pressure is created by the force applied by the clamps, which compress the base and cover together. This compression creates a seal that prevents any air or gases from escaping or entering the enclosed space, resulting in an increase in pressure.

3. What are some common materials used for the base and cover in clamping systems?

Some common materials used for the base and cover in clamping systems include metals such as aluminum, stainless steel, and titanium, as well as plastics such as acrylic and polycarbonate. The choice of material depends on the specific application and required pressure levels.

4. Can the pressure created by clamping the base and cover be adjusted?

Yes, the pressure can be adjusted by changing the amount of force applied by the clamps. This can be done by adjusting the tension on the clamps or using different sizes or types of clamps. Additionally, the thickness and material of the base and cover can also affect the pressure generated.

5. Are there any safety precautions to consider when using a clamping system to create pressure?

Yes, there are a few safety precautions to consider. It is important to carefully follow the manufacturer's instructions for proper clamping techniques and to not exceed the recommended pressure levels. It is also crucial to regularly inspect and maintain the clamps and materials to ensure they are in good condition and can withstand the pressure. Additionally, personal protective equipment should be worn when handling high-pressure systems.

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