Casting PR/Virbrating How and Why

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GregMuller

GregMuller

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Sep 12, 2004
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Miller Place, NY, USA.
In reading through the posts a number of people useing PR use some form of vibration to help with the bubbles. My first question is does it really work and the second question is how and at what point in the process do you do it. I am useing PR from casting craft and useing the resin saver molds. I have had decent sucess but have had some failure due to brittle blanks and bubbles. I do warm my resin before mixing and pouring and I have no plans on investing in a pressure pot. Time is not an issue for me as I have plenty of time for curing. So where in the process do you vibrate, what do you use to do it and for how long? Thanks.
 
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Well you will get many answers...

There are a lot of folks that have those H.F. ultra sonic heated cleaners. I have one also but didn't use it long I didn't find it useful.

Now it depends on what you are casting also. And anything you do to the resin must be done before you add MEKP weather it be vibrating and or heating. Another thing you mention is your cast are brittle. This is usually caused by heat too much MEKP I do mine at 3-4 drops per once. There are circumstances that effect that such as ambient temp. and the volume of your mold. The lower the ambient temp the more MEKP. It takes about 1/2 hr for mine to start to gel I leave set over night. The more volume you have a larger mold will generate a lot more heat less MEKP. If you start adding stuff dies & pigments effect curing.

Now I will give you a brief overview how I do it. I am casting labels don't use vibration or pressure I got it down to almost 100% success rate (wasn't the case a few years ago) I made my own mold similar to R.S. in volume but different in design. The bubbles I mite get is an occasional leak from the end of the tube the air has to come from some where.
FranklinMolds1.jpg

So after gluing the label and sealing it with CA. Sealing dose 2 things keeps the label from wetting and just as important keep any air in the paper or seam from leaking out. Then they go into the mold (after the CA dried 24 hr) then the mold with blanks in go in the oven to preheat at 125-150. I pore the resin in an appropriate cup like Hefty Crystal Clear. Then the cup goes into a pot of HOT tap water about 120 that thins the resin. Now I mix in the MEKP 3-4 drops per once. Then pore into molds I baby sit for about a 1/2 hr to make sure the plugs have the tubes sealed no bublles stuck to the side (as long as you are casting a label bubbles shoud'nt be an issue if you have something pointy or sticking out that could grab air when poring that could cause problems and need pressure) Now they will cure over night 12 hr the blanks will still be tacky in the morning so I put them (still in molds) outside in the sun for about 2-4 hr that finishes the cure.

If you can pore and turn your blanks in the same day chances are they are going to be brittle. Slower is better less heat more MEKP = more heat = brittle chippy blanks

Good luck always willing to share.

.
 
Vibrating with ultasonics or other means as well as slight heating before adding catalyst helps remove any dissolved gasses in the resin. Very similar to a soda bottle. Shake it and the dissolved carbonation comes out of solution. Heating lowers the viscosity and allows more gas to dissipate. Dissolved gasses are one of the contributing factors to bubbles in casts. Pressure while curing doesn't shrink the bubbles, it keeps the gas in solution.
 
Both Bruces gave excellent advice and I agree with both of them. I once used both vacuum and pressure for casting snake skin blanks. I now use neither. I use an ultrasonic cleaner with a heater and a toaster oven. I suppose I should update my snake casting article in the library. Actually, I should trash it and do another.

I use silicone plugs (powdercoating supply)instead of the hard black rubber plugs for the ends of the tubes. I now have no air leakage from the ends of the tubes when the air expands from the heat of curing. The silicone plugs are softer and do better to seal.

Do a good turn daily!
Bruce763:biggrin: aka Don
 
I have an old rattley HF drill press. When I started casting a few years ago, I'd warm the resin, pour in the mold and put it on the DP table and hit the switch! Those little bubbles couldn't wait to get outa there!! Moving on to a pressure pot, I don't use the shake method anymore, but IMHO...it worked well.
 
I find this interesting: some (including me)move from a pressure pot to vibration while others move from vibration to a pressure pot. I hope to never use my pressure pot again. But, who knows? I may start using it again tomorrow.
Do a good turn daily!
Don



Jim Burr said:
I have an old rattley HF drill press. When I started casting a few years ago, I'd warm the resin, pour in the mold and put it on the DP table and hit the switch! Those little bubbles couldn't wait to get outa there!! Moving on to a pressure pot, I don't use the shake method anymore, but IMHO...it worked well.
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I'm doing a lot of WW casts Don and although I did try them without pressure, the adhesion just wasn't there. With pressure the results are great!
 
None of my ww'ing equipment shakes enough to be useful! Well, maybe I could mount an off-balance 11" chunk of oak to my lathe and let that vibrate it...
 
It's funny, I was at a friend of mine's dentist office and he was upgrading some of his equipment including a small table to vibrator he uses to get bubbles out of casting material. I asked him if I could grab it from him in exchange for a custom pen. Deal done and it works great for my purposes...
 
Pressure has its uses. I just no longer use if for snake skins and labels which, by the way, is all I cast. Different types of castings require different techniques.
Do a good turn daily!
Don

Jim Burr said:
I'm doing a lot of WW casts Don and although I did try them without pressure, the adhesion just wasn't there. With pressure the results are great!
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its_virgil said:
Pressure has its uses. I just no longer use if for snake skins and labels which, by the way, is all I cast. Different types of castings require different techniques.
Do a good turn daily!
Don

Jim Burr said:
I'm doing a lot of WW casts Don and although I did try them without pressure, the adhesion just wasn't there. With pressure the results are great!
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I agree with Don. I have far better results using a heated ultra sonic cleaner than with a pressure pot EXCEPT in couple of situations.

The majority of my casting is done with Polyester Resin. When I do use Alumalite, I find pressure is an absolute necessity. Additionally, sometimes when I cast 3D (such as watch parts or seashells embedded in resin over a painted pen tube), I find that pressure helps eliminate the occasional air bubble that always tends to attach itself on a piece of seashell cast in PR.

Additionally, as Don suggests, If I never have to use the pressure pot again, I too, will be fine with that. In my shop, at least, pressure can add a whole set of new variables to an already finicky casting situation.
 
Ultra sonic cleaner

To Don and Penman, and Bruce.
How do you use the cleaner? Do you mix and then pour and place in the cleaner with heat on and are you still heating the resin before you mix. Bruce when you seal with CA is it a quick and dirty thing or are you sealing and then polishing. I Have not had a problem with the labels bleeding only air bubbles from the ends. Also where do you get the plugs from.
 
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Everyone has their favorite way. I used the ultrasonic cleaner a few times but I thought it took too long plus as soon as you stir in the MEKP you usually introduce a bunch of new bubbles. I had the best results using one of Curtis' vacuum chambers. I stir the MEKP into the resin then sit the cup into the chamber for like 30 seconds. You gotta have plenty of extra room in the cup because a ton of air will start to bubble up. To reduce the amount of bubbling I found it best to stop when its getting too high and slowly equalize the pressure then put it under vacuum again. When I equalize the pressure the second time and the bubbles on top settle I end up with a cup of resin that looks crystal clear. I was able to do the whole process in 90 seconds. Plus it eliminated the problem I had with the ultrasonic cleaner which was the resin is already hot so the time you have to work with the resin is greatly reduced.
 
Greg,
I have discovered that the resin can get too hot. I have backed off on the heat especially with the arrival of summer in Texas. I only use hot water from the tap and do not turn on the heat function. In the winter I will run the heater for half the full cycle then turn it off. I usually run the cleaner for at least two full 480 sec cycles and a third if I need the time or have the time. The reason for the hot water is to thin the resin so the air can leave easier. So, just enough heat to thin the resin. It doesn;'t take much.

I pour raw uncatalyzed resin into a container and place it in the watrer in the cleaner. Set the timer and turn it on. Repeat two or three cycles. My cleaner only goes for 480 seconds then I reset it. Remove the container, dry off the outside, add the catalyst (3 drops) and stir gently for 30 seconds. Pour into the mold and "wrangle" bubbles as necessary. I use a dental pick and run it under the tube to dislodge any bubbles that may be on the bottom of the tube. I don't pour on top of the tube but between the tube and the side of the mold. The resin will flow under and up the other side and over the top. I use a toaster oven to cure the blanks. I leave them in the oven for about 2 hours then de-mold and set them in the sun to finish. Do not try to remove the blanks from the mold if the resin is not good and hard. I usually cast 3 or 4 pairs of blanks at a time. Skins are glued on during the week and cast on weekends. Last saturday I made 20 bolt action while I was doing other stuff around the house and shop.

You may want to ready my "bubble free casting" article in the library.

Do a good turn daily!
Don

GregMuller said:
To Don and Penman, and Bruce.
How do you use the cleaner? Do you mix and then pour and place in the cleaner with heat on and are you still heating the resin before you mix.
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At 27 inHg the styrene in polyester resin will boil out. Styrene is used to thin polyester resin. I would suggest to keep the vacuum under 27 inHg so youj may need to let it go a little longer. When I was using vacuum I kept it at 25 inHg. You seem to have your system down. Happy casting.
Do a good turn daily!
Don

Gilrock said:
I had the best results using one of Curtis' vacuum chambers.
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I have a question. A few people wrote that you don't use vibration after you add the MEKP. Why not? With PR you have at least 10 minutes before it starts to thicken. I'm not trying to argue, but just wanting to understand why you can't use vibration right after you add MEKP.
 
GregMuller said:
Don,
I understand using the hot water to thin the resin and help it flow better but what does the vibrating do for the resin.
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BSea said:
I have a question. A few people wrote that you don't use vibration after you add the MEKP. Why not? With PR you have at least 10 minutes before it starts to thicken. I'm not trying to argue, but just wanting to understand why you can't use vibration right after you add MEKP.
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Everyone is going to give a different answer.

I don't know the science, but there is a difference between Ultra Sonic and say a table top vibrater (like a ban saw table top) I think the Ultra Sonic works at a much higher resolution and a molecular level. From my experience I have put warm perfectly clear (no bubbles) resin in ultra sonic and you can watch the tiny bubbles form and rise for a wile.

Any way I stopped using any vibration at all. I just heat the resin with hot tap water to about 100-110. Then I add MEKP and mix any bubble that get in the resin after mixing comes up quick and is not a problem. Even if there was a few small bubbles in the resin they would rise in plenty time.

Now there are always exceptions. I am casting smooth labels so any bubbles would just slid up the side. Now if you had something with a texture like a skin or anything a bubble could get hung on well you need to think about that. Also as Don said no more than 3 or maybe 4 drops per once any more your resin will cure to fast generate too much heat and be brittle. Mine take about a 1/2 hr. before it starts to get too thick to work and 10-12 hrs before hard then out in the sun for 2-3 hrs to finish.

Now the one thing I did use vibration for would be shredded money. But that was after mixing in resin in the mold and then in the pressure pot at 50 psi.

Simple label casting I just warm the resin warm the mold w/blanks then mix, pore and baby sit for an 1/2 hr on bubble watch.

***One note you can spend days building and prepping a blank to cast that's the fun part. Then when it comes time to actually pore the resin that's the scary part it can all go wrong and down the crapper. My nerves are at there worst after the resin is pored till the resin is cured and the blanks are out of mold then I can breath.

Lots of fun...

.
 
FWIW, an old hair clipper has a rather good vibrator in it if you use a bit of ingenuity and hook it up to shake the mold (round tube or rectangular, as you choose).

Not ulatrasonic but it certainly does a nice job of debubbling stuff that doesn't set up too fast for the bubbles to vibrate out.

Interestingly, they also make a rather good tool demagnetizer, being mostly a very powerful AC electromagnet.

Of course, don't try this at home if you aren't familiar with electrical stuff and safety procedures.

A caveat, it has a tendency to homogenize mica and such in thinner slower setting resins if you're trying to achieve a variegated or swirled effect.
 
Greg,
Vibration, from what ever source, helps the dissolved gases in the resin form bubbles and float to the top. Much like shaking a soda causes the dissolved carbon dioxide form bubbles and leave the solution. As Bruce Robbins mentioned in an earlier post dissolved gasses are the main contributing factor to bubbles in castings. The warm thinned resin makes it easier for the bubbles to rise.
Do a good turn daily!
Don

GregMuller said:
Don,
I understand using the hot water to thin the resin and help it flow better but what does the vibrating do for the resin.
Click to expand...
 
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