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Munkin

Pyrex cubs cracking

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I have been hand pouring soft plastics for over a decade and have never had a problem with the pyrex cups. In the past week two have shattered when trying to use them for injection molds. The temp gauge says 350 but they are just shattering when I set them down on the wooden bench as I always have. Not sure what is going on here but it is a pain to clean this up.

 

Allen

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Those look great Mark. How flexible are they? Is there any chance that the sides could squeeze in and push plastic over the top - that would be equally scary. 

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They get real soft. Someone here made a stand to keep them up. When I started I bought four of each size. One four cup broke. But just like stated here I lost two one cup ones in the same day. Tempered glass is funny like that. I keep mine warm in a high sided griddle so clean up was easy when it cooled. There are some made with a different type of glass that are available, the same glass as lab beakers. 

Arcuisine Borosilicate Glass Measuring Cup 8.45 oz. https://www.amazon.com/dp/B00L2IG1SY/ref=cm_sw_r_cp_tai_hR9WCb861N2RH here are the one cup ones. 

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10 hours ago, mark poulson said:

Me too.  I had problems with the Pyrex and tried the silicone.  I have been using them for several years now.  I still have the Pyrex in the closet but don't use them.  I have the 2 cup size.

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3 hours ago, Jig Man said:

Me too.  I had problems with the Pyrex and tried the silicone.  I have been using them for several years now.  I still have the Pyrex in the closet but don't use them.  I have the 2 cup size.

That's the size I have, too, but I only cook a cup at a time, so handling is easy.  When I tried to heat two cups, the soft sides made it a nightmare.

I am just a hobby pourer, so that works for me.  People who do production might have a different experience, since they need larger amounts.  

 

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I am just a hoppy person myself and heating plastic in 4oz cups to make what I need. Re-heating the plastic after each shoot and adding more plastic when needed. 

 

Allen

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I don't pour as much plastic as these guys, but I have had three cups shatter.  One was hot out of the microwave, and I set it on a cold steel drill press table in my shop on a winter day.  Obviously it was thermal shock. 

The other two shattered when I dropped them.  

One thing I read that seems to increase the likelihood of shatter is micro cracks not visible to the human eye.  I quit using any form of steel stirring stick years ago and went to aluminum stir sticks with one end threaded for a phenolic handle.  I suppose one might argue that aluminum oxide on the aluminum rod could still scratch the glass, but the underlying metal gives enough that it would take insane impact to introduce micro cracks.  

I have an L shaped bait making bench in my shop.  One side of the L is all plastics and cups not is use go against the back of the bench. The other L of the bench is all for lead casting.   Any breakable item or item subject to thermal shock requires some care and forethought, but that doesn't stop me from also wearing heat resistant glove while I am working at the bait bench.  

If pyrex (soda lime) glass makes you nervous don't use it.  Silicone won't crack or shatter, but it also has its potential safety issues.  No matter what you choose to use its your responsibility to make sure you take the appropriate precautions and take the necessary care to work with molten materials safely. 

Some years ago I talked with one of the silicone ware companies about making a ribbed silicone cup for greater strength and rigidity for this market, but ultimately they felt it was to much of a niche market and passed on it.  I have done some experiments with silicone myself.  Not hardware store caulk, but high durometer, baking temp rated, food grade, catalyst kicked commercial silicone formulations.  It "can" be made stiffer than the cups most of you are working with, or a microwave safe plastic frame work could be incorporated.  This industry tends to have a lot of guys who started making worms because they wanted to save money on a bag of worms.  That means even if developed I suspect 7 out of 10 guys would probably try to come up with a cheaper way to make it themselves.  If you want to go that way the big key is … yep … you guesses it …  elimination of bubbles.  LOL.  


 

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Another one cracked tonight when I pulled it out of the microwave. It was a mixture of half pre-heated plastic mixed in with 1/2 fresh plastic. Looks like it is time to try out that Lee Pot I bought 3 years ago.

 

Allen

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3 hours ago, Munkin said:

Another one cracked tonight when I pulled it out of the microwave. It was a mixture of half pre-heated plastic mixed in with 1/2 fresh plastic. Looks like it is time to try out that Lee Pot I bought 3 years ago.

 

Allen

The Lee Pots I've tried have been too hard to get the temps right consistently.  I know there are people who use them successfully, but I've never been able to get them to work for me.

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12 hours ago, mark poulson said:

The Lee Pots I've tried have been too hard to get the temps right consistently.  I know there are people who use them successfully, but I've never been able to get them to work for me.

Agreed.  It sure didn't work for me.  First one I got, I was so excited.  Ended up being nothing but trouble.  As mentioned, inconsistent heating, clogging, impossible to keep clean, just an overall nightmare.  Bummer because as you said, Mark, I know guys who swear by them. 

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I had two Lee plastics pots.  I wound up throwing them away.  I think I recall that Lee discontinued them.  Might lend to how much hope to put into that solution.  I'd bet an electric fondue pot would be better.   

Edited by CNC Molds N Stuff

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From a non-plastic pouring engineer, the problem is always heat stress. A localized change in temperature that causes the glass to expand at different rates which causes stress cracks. But, I am pretty sure that you already know this as this problem is far from new.

Even resting on a wood surface, a fairly good insulator, does not solve the problem, ref - Munkin's post. My suggestion would be to choose the best insulator possible. This will reduce the heat stress. A platter of plaster of Paris would be ideal for this purpose.

Another fact that is demonstrated from the above posts, is that the life of the cups seems to be fairly constant. One cup breaks and shortly after the second cup breaks. So, if the first cup breaks then it is time to renew.

If the cups break after say 6 years, then renew after 3 years, safer still, annually.

Examine for micro cracks. Yes, they are very difficult to see. But, if you use a torch light, you will have more of a chance to see the refraction and reflected faults.

Another idea is a 'ping' test. As cracks develop, I am sure (theory) that the sound of a metallic tap would change. Tap the new cups and remember the sound, or buy an extra for the occasional ping test comparison. My guess is that the sound would ring less or dull  due to the micro cracks inhibiting the vibrations.

I feel uncomfortable posting outside my experience, but it is all engineering at the end of the day.

Dave

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Dear Guys, as I have already written in other post about this topic, I'm using the Dexas collapsible silicone measuring cup from several years with satisfaction even if its plastic handle is certified only for 120 °C (250 °F). I'm not a frequent pourer and I have already repaired that plastic handle, so I will continue to use it till I will see it really stiff. Now it is not more possible to find such silicone measuring cup on the market, but there is something better: https://www.amazon.co.uk/Chefn-SleekStor-Collapsible-Measuring-Cherry/dp/B000RN71XY

Its nylon handle resists till 200°C (340°F) and there are other similar solutions, you have only to search for them.

Bye

 

Cami

Edited by Cami

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Hate to hear you’re having a rough go with the Pyrex. Before I started pouring I had read a few mishaps of this sort and it made me nervous. Don’t know if this will do a thing for me if (when) I have one give up the ghost but here is my valiant attempt at safety. I gather up a few neoprene can cozies each year and slip them over the 1cup I use. Takes a little persuasion but they fit snug. My thought is I’m heating up less mass with a 1 cup, I’m providing a slight amount of insulation for the plastic, I’ve got a buffer between the cup and the counter top, and should it crack or pop most of the shrapnel and hot plastic should stay contained so I can leave dodge. Just my two cents.   

E299D73C-0A18-432E-B07E-702631861229.jpeg

BDC1F06D-EBE5-4E43-8A24-28B141F586F3.jpeg

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I like that idea. I'll have to try it out as I go from 1 cup to a fry daddy. Just seems as if there is no in between anymore Haha.

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I've only broken 1 cup, and I dropped that one on a concrete floor.  I've always stirred with metal table knives so I'm not sure why I'm so lucky...  I do make it a point to only set hot cups of plastic on wood or a heated metal surface. 

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On ‎4‎/‎29‎/‎2019 at 6:47 PM, Fishermanbt said:

Hate to hear you’re having a rough go with the Pyrex. Before I started pouring I had read a few mishaps of this sort and it made me nervous. Don’t know if this will do a thing for me if (when) I have one give up the ghost but here is my valiant attempt at safety. I gather up a few neoprene can cozies each year and slip them over the 1cup I use. Takes a little persuasion but they fit snug. My thought is I’m heating up less mass with a 1 cup, I’m providing a slight amount of insulation for the plastic, I’ve got a buffer between the cup and the counter top, and should it crack or pop most of the shrapnel and hot plastic should stay contained so I can leave dodge. Just my two cents.   

E299D73C-0A18-432E-B07E-702631861229.jpeg

BDC1F06D-EBE5-4E43-8A24-28B141F586F3.jpeg

Thanks and it reminds me of the 9 line medivac with is slightly more important that the call for fire.

 

Allen

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