casting polyester resin HELP NEEDED ...

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socdad

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I’ve been casting feathers, watch parts & labels for several years using polyester resin. I changed to vertical casting a couple of years age and have run into a problem. A few blanks (several) have come out badly cracked. Some of the time it is one blank out of a batch of a dz. or so, lately it has been the entire batch. I warm the resin to 72 deg or so / no humidity to speak of / use 3-4 drops of Mekp per oz. I spoke with the folks at US Composites & they keep telling me the room if too hot / cold … or I’m using too much mold release (I’m not using any)


Any suggestions will be greatly appreciated …
 
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socdad

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Not sure how thick, thick is ... I am using tubes that are 3/4 - 1 inch in diameter casting bolt action (2 in) - zen rollerball (3 1/2 in) long ...
 

elyk864

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Doesn't sound like it's overly thick, maybe to much activator part. Curing to fast and generating to much heat.
 

jttheclockman

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Are you using Silmar41?? Are you using pressure pot?? I use Silmar and a pressure pot and I use clear plastic tubes and also cast verticle and do not have any problems. How old is the resin and how old is the catalyst?? I warm the resin in a toaster oven for about 15 minutes at 250. I use 4 to 5 drops Have not had any problems. I cast in a basement shop all year round. The pressure pot is an important question and I will explain if you use one.
 

BKelley

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I do some casting with PR and some times great results and next time phooie! After quite a bit of research, study and experimenting I have come to the conclusion it depends on if it is an odd numbered day and the color of Sox I’m wearing. Having my shorts on backward and inside out might have helped a little. I think casting has a certain percentage of failures built in. Do your best and learn to live with some failures.
Lots of luck.

Ben
 

socdad

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Are you using Silmar41?? Are you using pressure pot?? I use Silmar and a pressure pot and I use clear plastic tubes and also cast verticle and do not have any problems. How old is the resin and how old is the catalyst?? I warm the resin in a toaster oven for about 15 minutes at 250. I use 4 to 5 drops Have not had any problems. I cast in a basement shop all year round. The pressure pot is an important question and I will explain if you use one.
I use the same resin & Yes, I use a pressure pot, at least most of the time. Last effort I skipped that step & the blanks came out looking like cracked ice . I warm the resin, but not that warm.
 

socdad

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I do some casting with PR and some times great results and next time phooie! After quite a bit of research, study and experimenting I have come to the conclusion it depends on if it is an odd numbered day and the color of Sox I’m wearing. Having my shorts on backward and inside out might have helped a little. I think casting has a certain percentage of failures built in. Do your best and learn to live with some failures.
Lots of luck.

Ben
I understand that there will be poor outcomes, but this particular gremlin started when I started vertical casting. Growing tired of screwing up sliver pheasant/ jungle **** blanks.
 

Kenny Durrant

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I've been casting several years and, in my opinion, the simplest method is horizontal. Now I'm not saying don't use vertical but the horizontal method cuts back on a few problems. I had the same logic as Ben and that got very old real fast. I started thinking that I was getting by with several minor things and when something new happened or one item got worse that's when the blanks failed. That's when I started getting picky and developed a routine that worked almost all of the time. The drawbacks with vertical molds and P.R. are this. P.R. shrinks and in a vertical mold I had trouble with it sticking to the mold and shrinking outward pulling away from the tube. The air bubbles have farther to travel to get to the top. When I switched to horizontal molds the silicone plus flexed when the resin shrinks and relieved the stress on the tube. Air only had 3/4" to 1" to reach the top. Since the top of the mold had more surface area that helped as well. I also found a good mold release that I liked and seemed to do the job well. NOW don't take this the wrong way. Some people use vertical molds and have no issues but I guarantee you they have a detailed system and routine they go through. My advice would be to decide what you want to use and adapt a system to make repetition consistent so when something does change it might not be enough trash the blanks. Good Luck.
 

jttheclockman

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I use the same resin & Yes, I use a pressure pot, at least most of the time. Last effort I skipped that step & the blanks came out looking like cracked ice . I warm the resin, but not that warm.
I am in the camp of always using pressure even with Epoxy resins. I did my learning from CaptG many years ago and have followed the procedure over the years and have had no failures. Kenny makes some good points and I too have done vertical casting as well and in fact have many molds that are unused.

Again I will lay out my procedure. I warm the resin in a toaster oven after it is preheated to 200 to 250. Hard to tell with those things but that is what it is set on. I heat for about 15 minutes. I have my blank set up in the plastic tube with the stoppers in and ready for pouring as soon as I mix the resin. I have done anywhere from one blank to about 12 at one time. Now when I go to a larger amount of blanks I have to increase the time in the heat box because of the extra resin and this is important because when all said and done no bubbles are in the resin at all because of how thin it gets. I then mix about 5 drops of catalyst per ounce and add a few extra. Not critical with Silmar. I mix for 4 minutes. 5 if alot of resin. I then pour the mixed resin in the tubes making sure to pour against the side of the tube. This ellliminates any bubbles developing. If there are any they rise to the top right away. I then place in pressure pot. Here is where I said it is important to not (NOT) add pressure real fast. You want to slowly build up pressure because for one you run the risk of adding water dropplets if you do not have a water filter on the pot. Water in resin is not good. I build to 50lbs and leave 24 hours. I usually have some resin left over and leave it in the cup and I can tell the next day if it has cured. My pot seals well and does not lose pressure.

Now with my method the plastic tube stays on the blank and is turned off when turned down. There is no need for release which can cause havoc with poly resins. Now cracks can come from the resin being too old or the catalyst. There is a shelf life and it is extended if kept in a cool dark place though. I have used 2 year old resin with no problems. Another reason for cracking is air escaping from under the object that is adhered to the pen tube. Things such as carbon fiber or other sleeves. Even labels will emit air from under. The objects being cast need to be cleaned from oils or other contaminates that will interact with the resin. I learned this with my casting of the different braided materials I use. That is why I have mentioned before why I adhere my braiding with the same resin and put a light coat on it before I cast them. This seals any byproducts. Other than that that is all I can say. I have included a photo or two.
 

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Bob in SF

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Hi Jeff - I favor:
White or clear 3/4-1" PVC pipe segments
Light spray of Stoner mold release
Douglas and Sturgess Clear Polyester Casting resin, well mixed with a wooden tongue blade - resin link:
Home made vertical mold stand.
PR resin warming only if the garage shop is colder than 65 degrees
Pressure pot at 50psi for 1-2 days - mine leaks a little, so it's a natural gradual pressure release - since the chemical reaction is exothermic, the resin likes the warm and cozy pot (do not disturb).
Tap out the cast rods with a wooden dowel.
Let them cure for a week for through-and-through material consistency.
Turn and enjoy.

Warm regards - have fun - Bob
 

socdad

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I understand that there will be poor outcomes, but this particular gremlin started when I started vertical casting. Growing tired of screwing up sliver pheasant/ jungle **** blanks.
I find the editor amusing ... jungle **** must be offend someone.
 

socdad

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Just a quick thanks to all that offered information, I've used several of suggestions that were offered & at least so far have had much better results ...
 
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