Help Determining the Minimum Thickness of a Vacuum Chamber Lid

In summary, the individual is seeking advice on building a large vacuum chamber for woodworking using a cast iron bathtub. They would like to use a clear acrylic lid but are unsure if it is possible and what thickness would be needed. Suggestions are made to use a circular steel tube for better vacuum treatment and to avoid resin condensation on the lid. It is also recommended to build two identical systems for efficient cycling. The force from atmospheric pressure on the bathtub is calculated to be equivalent to the weight of 12000kg and it is suggested to use a tube instead. A method for calculating maximum stress and center deflection for a rectangular plate under a uniform load is provided. Another option suggested is to use vacuum bagging or a thin membrane over the surface
  • #1
chrisritson
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Hello. I am attempting to build a large vacuum chamber for woodworking (used to infuse wood with resin/stabilizer). I would like to use a cast iron bathtub, similar to the one pictured as the vessel. I would ideally like to use a clear acrylic lid (with a rubber gasket) like the one on my little vacuum chamber I've been using. Can someone tell me if this is possible and if so how thick would I need it to be? would 1"-2" work? bathtub dimensions are 60"x30" THANKS!

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  • #2
Welcome to PF.

Resin will condense on the clear lid. Flat surfaces will collapse under a vacuum. For vacuum treatment it is better to use a circular steel tube that you can slide your timber into on a small trolley. The tube would be open at one end where the door can be curved and will be much smaller than the length of the bath. If you must use a bath you should use a second bath, inverted as the cover.

By allowing the tube to tilt slightly, and by providing a top outlet for the vacuum pump, with a low drain at the bottom rear, you can allow the treatment fluid to flow into the vacuum as required, and the excess to be removed later when the vacuum is removed.

Building two identical systems next to each other makes it possible to cycle the loading, treatment and unloading cycles with the same fluid being transferred from one side to the other.
 
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  • #3
The force from atmospheric pressure is roughly 65N for square inch (10N for square cm). 60*30*65N=117000N. That'll be equivalent with the weight of 12000kg, more or less, if I did the math correctly.

I too think you should go with a tube instead.
 
  • #4
I agree the absolutely best approach is to use a tube/pipe; fyi, by going to pg 505 of the below online copy of "Roark's Formulas for Stress and Strain you will find the method of calculating the max stress and center deflection for a rectangular plate, simply supported, under a uniform (pressure) load, where q = load per unit area ie psi.

http://homepages.uc.edu/~caldwelm/Courses/Roark.pdf
 
  • #5
I suggest doing a search on vacuum bagging. You might just accomplish this with a thin membrane over the surface of your wood. Over a bathtub like this, I doubt that you will find a piece of plastic thick enough at a reasonable price. You might also investigate using this - https://www.smooth-on.com/product-line/ez-brush/ I don't know whether this technique will work for you, but it might be worth investigating.
 
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1. What is the purpose of a vacuum chamber lid?

A vacuum chamber lid is used to seal a vacuum chamber and maintain a low pressure environment for conducting experiments, testing materials, or storing sensitive objects.

2. Why is it important to determine the minimum thickness of a vacuum chamber lid?

The minimum thickness of a vacuum chamber lid is crucial because it affects the structural integrity of the chamber and its ability to maintain a vacuum. A lid that is too thin may not be able to withstand the pressure difference between the inside and outside of the chamber, leading to leaks or collapse.

3. How is the minimum thickness of a vacuum chamber lid determined?

The minimum thickness of a vacuum chamber lid is determined by considering the pressure differential, material strength, and safety factor. Several calculations and simulations may be required to accurately determine the minimum thickness for a specific chamber and its intended use.

4. What factors can affect the minimum thickness of a vacuum chamber lid?

The minimum thickness of a vacuum chamber lid can be affected by factors such as the size and shape of the chamber, the type of material used, the level of vacuum desired, and any external forces or stresses that may be applied to the lid.

5. Are there any standards or guidelines for determining the minimum thickness of a vacuum chamber lid?

Yes, there are several standards and guidelines that can be used as references for determining the minimum thickness of a vacuum chamber lid. These include industry standards such as ASME Boiler and Pressure Vessel Code and ISO 16949, as well as guidelines from organizations like the American Vacuum Society and the European Vacuum Society.

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