50AE Posted February 14, 2023 Posted February 14, 2023 Hi folks, I need your help with potential advice for finding a solution.I need to purchase a bigger vacuum chamber for varnish transformer impregnation, as my production has increased. The cheapest vacuum chambers use acrylic as a lid. Unfortunately, acrylic is attacked by the varnish solvents. For such application it is recommended to use glass lids, however the later chambers are much more expensive, unavailable locally and I cannot afford such right now.Is it possible to somehow coat the internal side of the acrylic lid with some sort of transparent substance that might protect the acrylic? Silicone? Kapton? Mica? I can sacrifice transparency, however I need a slight leftover of it to check if foam doesn't level up a lot.Best regards! 1
Arthur Posted February 14, 2023 Posted February 14, 2023 Many plastics will be affected by solvents. Maybe a container made of metal with a sealing area with a rubber gasket closed with a glass lid or a lid with a glass window. Lots depends on the scale of the chamber and the size of the opening and the viewing window that you want. Can you find a glass bell jar and a flat metal plate with the vacuum connector? Could you look at a pressure cooker as the container, rebuild the seal to work with suction and then machine a viewing port for a small glass window. The troubles come if it's possible to crush the vessel when the vacuum is too great. With any DIY chamber i'd want lots of protection between me and said container.
Arthur Posted February 14, 2023 Posted February 14, 2023 Could you buy a second one of the vacuum chambers that you already have? With this you could leave one holding vacuum while you emptied and reloaded the other. Having two items means that one can break and still leave you working albeit slower.
50AE Posted February 15, 2023 Author Posted February 15, 2023 The current vacuum chamber is DIY and very small, there fits only one transformer. It is made using a cut air pressure bottle and a washing machine glass lid. Another point - the transformer need some hours to stay within the varnish for proper completion of the process, so reallistically I need to really on a larger batch.
Arthur Posted February 15, 2023 Posted February 15, 2023 The bigger the opening the more risk of the glass imploding under outside air pressure.
Richtee Posted February 15, 2023 Posted February 15, 2023 Guess I’m not familiar with this process but what about using standard canning jars and a vacuum port/valve. ost commercial sealers have a vac hose for evacuating containers. You could get a dozen going at once.
MadMat Posted February 27, 2023 Posted February 27, 2023 (edited) Are you using ordinary varnish or some special dielectric type of varnish? If it is ordinary varnish simple water based polyurethane would hold up well to that solvent once it is FULLY CURED and the transparency would be great. If it is some special type of dielectric varnish, could you let me know what type of solvent we are talking about. The type of solvent is very important in picking something that is resistant to its effects. I used to work in the materials and R&D labs at a company that made circuit sub-assemblies and have a bit of experience using vacuum chambers for impregnating porous phenolic conformal coatings on circuit boards with wax for moisture resistance. Additionally, I have experience with a number of urethane, acrylic, silicone and epoxy resins used for various conformal coatings on circuit boards. Edited February 27, 2023 by MadMat
MadMat Posted February 27, 2023 Posted February 27, 2023 (edited) After thinking about it, I imagine the solvent used in your varnish couldn't be too aggressive or else the vapors would, in time, destroy your vacuum pump. I'm thinking that three or four coats of water based polyurethane varnish would protect your acrylic lid. Simply make sure to give adequate drying time for the poly urethane to fully cure. I would allow at least 24-48 hours. Hmm.... for that matter, is the acrylic lid actually being attacked? Acrylic should be able to withstand a solvent such as mineral spirits Edited February 27, 2023 by MadMat
Arthur Posted March 1, 2023 Posted March 1, 2023 Can you laminate a sheet of glass onto a thicker sheet of plastic. That way the plastic takes the load due to air pressure and the glass takes the solvent and is undamaged.
justvisiting Posted March 1, 2023 Posted March 1, 2023 Arthur, I thought of that too, but I think the glass would crack outward from where the hole is, not to mention having to make the hole- unless the hole for removing the air isn't in the lid. In my vacuum chamber, the hole is in the acrylic lid. I think that by the time he tries to laminate the glass and drill it, he could have bought a glass lid. I was thinking of maybe using a clear pressure sensitive plastic on the acrylic, and replacing it as necessary?
Arthur Posted March 1, 2023 Posted March 1, 2023 Sorry but in all the vacuum work I've ever done the exhaust to pump connector has been in the metal of the base. Search ebay in your country for Glass Vacuum Desiccators. these should be suitable vacuum and solvents, you could use one pump, thick wall tube and several desiccators
Arthur Posted March 1, 2023 Posted March 1, 2023 How large are the transformers that you need to vacuum coat?
50AE Posted March 29, 2023 Author Posted March 29, 2023 Hi folks,Apologies for replying a bit late. I'm attaching a content of the solvents taken from the varnish MSDS. Arthur, they are 105x105x115mm transformers, but I need to fit a multiple of them for a good production efficiency.
Arthur Posted March 29, 2023 Posted March 29, 2023 Do you have machining skills with steel? Is it possible that you could convert a surplus propane container and make a system of shelves and seals to hold a vacuum? Could you use two vacuum chambers? This way you could load one (in the morning?) and one (at end of day) and unload each after their 24 hours? Like this production would be continuous.
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