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Thread: Pressure pot

  1. #1
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    Default Pressure pot

    Yes, another pressure pot thread! I have posted this by request from another forumite (hope it is clear enough Amos)

    Have just completed setting up my SuperCheap Auto pressure pot for resin casting and blank stabilising.
    Having looked at most of the pressure pots set up for this, most in the US supplied mainly by Harbor Freight, I was somewhat daunted at first by the complexity of some of the setups.

    Granted some were dual purpose pots, set up for both pressure and vacuum.

    A recent thread on IAP¹ conformed more to what I considered a workable minimalist approach, eliminating most of the complexity of previously viewed set ups.

    1 First order of business is to strip everything off the lid of the pressure pot, then remove to paint intake tube from underneath the lid. A ot of people have reported great difficulty with this task, I was however fortunate that fairly frim pressure on a pipe wrench got it moving and I got it removed. If you can't get it removed, or dont' want to, just cut it with a 4" grinder and a cut off wheel.

    2 When you look on top of the lid there are 2 threaded entrance holes, one is 3/8" BSP (the bigger of the two) and the other apparently 1/4" BSP (more on this later). I wanted to use the bigger (3/8" BSP)for the air inlet. First order of business was to step this down to 1/4" BSP so it would take a 1/4" BSP fitting. I bought all my fittings form the local Bunnings Warehouse.

    3 I then fitted a 1/4" BSP cut off valve and as my air system in the shed uses Ryco fittings, a Ryco male plug.

    4 Here we see the inlet side completed

    5 Most of the designs I have seen keep the supplied regulator. I don't see the need as all we are doing is bringing the pressure pot to a certain PSI, so all we really need is a pressure gauge.
    The original T piece was going to be used for this with the gauge mounted on one end, the opposite end fitted to the smaller of the 2 threaded holes on the lid and a pressure relief valve fitted to the male thread coming out on the left. This didn't work as the thread opposite the pressure gauge (male 1/4" BSP is a very sloppy fit and the thread at right angles is the right fit for this hole and what's more it doesn't take a female 1/4" BSP fitting. Don't quite know what it is, but it was originally the thread that fitted that hole, so a change of plan here.

    6 Here we have the oroiganl right angle fitting that held the regulator fitted back to the T piece with the pressure gauge mounted directly to it. Also we have a 1/4" BSP cut off valve fitted to the other side of the T piece.
    I could have used the original safety pressure valve here, but didn't see any purpose in this. When you are putting the pot under pressure you have full control with the valve on the inlet, if you are worried about accidentally over pressurising the pot (max working pressure is 80 psi) you can set the regualtor on your compressor to 80 psi.
    The cut off valve fitted can also be used to lower the pressure in the pot if you go a bit higher than you wanted to, whilst the inlet hose is still connected.

    Releasing the pressure before opening the pot after the blanks are cured can be done with either valve.

    If you are worried about not using the safety valve, you can fit that instead, it can still be
    pulled to release pressure. There have been quite a few reports from people that this safety valve is the main culprit for the pot losing pressure over a period of time, so I eliminated it.

    I have used joint compound on all joints as well as teflon tape. So far no leaks.

    I am now ready to do my first casting and will report on that in due course.

    I have made up a 3 tier rack for inside the pot to hold my moulds, although I only have 2 at this stage.
    The rack is a fairly good fit inside the pot so it is easy to lower without too much lateral
    movement. All shelves are 170mm sqaure with about 6mm cut off the corners. I have fitted a diagonal piece to the bottom which locates it in the dished bottom and a handles for ease of handling. The top sheld diffuses the incoming and prevents it blowing on the uncured resin.

    ¹"http://www.penturners.org/forum/showthread.php?t=35233&highlight=rite+passage"

    21/09/2016 - Due to unforeseen circumstances the photos from this thread have become lost in cyberspace, I have attached a pdf file I prepared some time ago to make up for this loss.
    Attached Files Attached Files
    Last edited by Big Shed; 21st Sep 2016 at 02:54 PM.

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  3. #2
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    Default

    Looks good BS, just a word of caution on the air supply side, you may want to fit an elbow or baffle on the inside of the lid as the air blowing straight down onto your moulding trays may cause the resin to splatter about a bit.

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    Quote Originally Posted by DJ's Timber View Post
    Looks good BS, just a word of caution on the air supply side, you may want to fit an elbow or baffle on the inside of the lid as the air blowing straight down onto your moulding trays may cause the resin to splatter about a bit.
    DJ, I elected to omit that and made the rack do the air diffusion job. If I had fitted an elbow I would have lost 1 shelf. I'll see how it goes, can always make a 2 tier rack and fit an elbow.

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    I'm not a pen person....but this sounds like fun

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    Default Many thanks for that detailed description Fred

    Thanks Fred, deserves a greenie, I will sit down and try to digest this a bit at a time with my pot beside me! Amos
    Good, better, best, never let it rest;
    Til your good is better, and your
    better, best.

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    G'day Fred,a great report on the pressure pot. Thanks for posting and thanks to Amos for asking.
    Fred, you have some very good points there. I left all the gear on the top of my pot. have fitted a 1/4 " fitting to the air intake pipe to accept the air hose. Like you ,I found enough strength to unscrew the paint uptake pipe from the inside of the tank.I do lose a bit of pressure,so take your point and will remove the fittings and use teflon tape and then replace everything. Have also made a rack( not as smart as yours) to defuse the air flow.
    If you dispense with the safety valve, what type of fitting do you ask for to screw into the hole.

    Have purchased some 4PU polyurthane resin ,white not clear, from Arms Model It in Brisbane.

    Sorry Fred ,starting to wander and do not want to steel your post.

    terry

  8. #7
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    G'day Terry, I just replaced the safety valve with a 1/4" BSP ball valve as shown in photo 3.

    Glad you found my ramblings of some use.

    Fred

  9. #8
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    So B_S what sort of pressures do you expect to operate at? is the pressure just there to expel all the air from the resin blanks??

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    Good stuff Fred, I have been playing with mine as well. I have found that the pot even at 40 psi is not getting rid of all the air bubbles.

  11. #10
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    Quote Originally Posted by salty72 View Post
    So B_S what sort of pressures do you expect to operate at? is the pressure just there to expel all the air from the resin blanks??
    The reading I have been doing suggests 25-60 psi.

    Quote Originally Posted by Simomatra View Post
    Good stuff Fred, I have been playing with mine as well. I have found that the pot even at 40 psi is not getting rid of all the air bubbles.
    At your age too! I think the secret is trying to avoid bubbles in the first place, ie don't stir too vigourously, stir without introducing too much air. Then let it sit long enough for the bubbles to rise to the surface before pouring.

    Mind you all this from reading other people's suggestions, I have just done my first 4, mainly worthless wood type casting, so we will see.

    I am using PR (polyester resin), haven't used PU (polyurethane). A lot of people using Alumilte (polyurethane) are using vacuum, then pressure.

  12. #11
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    Default Top Post !!

    Top Post Big Shed !!! Thankyou.

    Any info on the casting trays ??
    David
    Eat right, exercise, die anyway

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    Quote Originally Posted by dhurrang View Post
    Top Post Big Shed !!! Thankyou.

    Any info on the casting trays ??
    The moulds, or molds as our seppo friends call them, came from an IAP member, Gadget. They were $US25 each and are made from silicone rubber.

    I did look at making my own, and probably will still make some other sizes, but this got me started quickly. Barnes, and other suppliers like them, sell the silicone rubber for mould making.

    I will be looking at making some 25x25mm moulds for "worthless wood casting".

    Modelmaker in the US makes a mould for this purpose as well, but it is quite pricey and with shipping it would be cheaper to make my own.

  14. #13
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    when I was in the RAAF we used to mix all our resines and then place in vacuume for 3-5 mins. vacuum was nothing huge about 8-10psi ( I realise absolute is 14.7psi -but they tell me that 10 is a long way off)

    this would get rid of all air, warming the 2 pack would also help it as it thined it out

  15. #14
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    Looks like the perfect set-up Fred. Thanks for sharing, great explanation and photos. This is something I need to get around to doing. I can see a lot of value in it.

  16. #15
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    The pot held pressure perfectly for 24hrs at 60psi, no loss of pressure.

    Opened it this morning and had 4 perfectly cured casts, they were very easy to remove from the mould. On visual examination I could find no air bubbles at all, but the proof of the pudding will be when I turn.

    The worthless wood casts were not very successful as they had floated to the surface, so must find a way to hold them in place.

    The blanks are quite hard but the surface has a sticky feel to it.

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