rmwsn Posted June 27, 2015 Share Posted June 27, 2015 Hi, do any of you who do resin casting make use of a pressure vessel of some kind to prevent bubbles in the finished item? Seems to be that 50-60psi is recommened. Can an electric car tyre pump be used as a compressor? Cheers. Link to post Share on other sites More sharing options...
peter220950 Posted June 27, 2015 Share Posted June 27, 2015 Never found a need for it myself but as I understand it you would need a vacuum not pressure, that way the air is 'sucked out' of the resin in the attempt to fill the void. The main problem is the size of vessel needed, which is related to the size of item you are casting. I have done 0 gauge coach sides and the tram chassis but wouldn't think a vessel big enough to hold one is a practical proposition. Also with a setting time of around 1 minute it's going to be a bit of a rush to get the resin into the mould, the mould into the vessel, and then get it pressurised/depressurised. What are you casting? and what resin are you using? If I'm correct in my belief you would need to be connecting the inlet of the compressor to the chamber, not the outlet. I would think putting the casing into a pressure vessel would only compress the air in the castings, leaving a potential problem when you de-pressurised? Although not always perfect I have found that a low viscosity resin and a bit of poking into awkward corners before it sets is sufficient, but always willing to learn from others. Interested to know more about applying pressure, I think the likes of Sparmac and JLRT use resin injected into moulds under pressure, but their moulds were built to withstand pressure, I'm guessing you're using rubber moulds? Link to post Share on other sites More sharing options...
RMweb Gold ian Posted June 27, 2015 RMweb Gold Share Posted June 27, 2015 Peter is right, commercial casters use a vaccuum chamber for bubble free casting. A tyre compressor wouldn't empty the chamber quickly enough for any sort of reasonably sized mould because the resin starts to set quickly. Link to post Share on other sites More sharing options...
ajaxjones Posted June 28, 2015 Share Posted June 28, 2015 I thought the vacuum was used more for bubbling out the air in the silicon moulding material several times, then using a vibrating table to clear out the rest. In part to exclude bubbles from the surfaces, and also to ensure no sub surface bubbles. Then pressure casting with the resin to compress/collapse the bubbles. If you have an enclosed 2 part mould then using a vacuum is likely to bring bubbles to the surface where they cant escape as they might be inside the mould. Less of an issue if you have a mould that is one part and the back surface is not seen. http://www.smooth-on.com/faq_display.php?faq_id=81 So far touch wood based on the Silicone I've used and vibration i've not had surface bubbles on the mould and the resin used is pretty good, but also the moulds don't have many intricacies where pressure moulding would help as well I understand Link to post Share on other sites More sharing options...
jonhall Posted June 28, 2015 Share Posted June 28, 2015 I echo everything that Peter has said - I use a Vacuum chamber for de-gassing moulds, but rely on low viscosity to get the quick setting resin into all the nooks and crannies. Jon Link to post Share on other sites More sharing options...
Dazzler Fan Posted June 29, 2015 Share Posted June 29, 2015 + Why not swing it around your head in a sling, to get bubbles to the pour surface? Link to post Share on other sites More sharing options...
peter220950 Posted June 29, 2015 Share Posted June 29, 2015 + Why not swing it around your head in a sling, to get bubbles to the pour surface? It's hard to get out of the wallpaper and curtains. Link to post Share on other sites More sharing options...
rmwsn Posted July 1, 2015 Author Share Posted July 1, 2015 Thanks for the info - I didn't have much idea about the technique - The part I was thinking about was part of a plastic toy where, due to age, one of the parts (about 5cm x 5cm got broken into pieces). From reading this I might be better off paying someone to do the casting. It is not urgent so probably put it into the todo box. I would have made a casting from an unbroken version of the toy. Link to post Share on other sites More sharing options...
peter220950 Posted July 1, 2015 Share Posted July 1, 2015 Thanks for the info - I didn't have much idea about the technique - The part I was thinking about was part of a plastic toy where, due to age, one of the parts (about 5cm x 5cm got broken into pieces). From reading this I might be better off paying someone to do the casting. It is not urgent so probably put it into the todo box. I would have made a casting from an unbroken version of the toy. For a one off it can be quite expensive, given that RTV mould material is around £20 - £25 and two cans of resin are about the same, there are small starter kits that might get all you need http://www.sylmasta.com/acatalog/Casting_Kits-1.html but I've not used them so can't comment on suitability. It's another example of where being in a club sometimes helps, there's usually a mug who can be conned into doing it for you, do you have a photo of the piece?. As a final thought, given that resin in itself isn't particularly strong, can you repair the damaged piece with either epoxy or body repair filler and re-spray? Link to post Share on other sites More sharing options...
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