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Cecil McKenzie 11-15-2017 11:08 AM

Cracking weights
I have been making a paperweight design that I have done for a long time. Lately they have been cracking on me. The design involves picking up a small piece of R 61 white on the pipe , gather and roll in various frits, expand and collapse, then case and form into relatively round paperweight. i heat the bottoms of these weights and form a small indention to finish bottoms. These have been cracking usually with one crack that goes through the base center.

I have been using R61 for a long time without this problem. I used some polarized filters and can see there is stress in the weights. Yesterday I made a clear weight with the same motions. It shows no sign of stress. I made a second weight with a transparent color . It also showed no sign of stress.

Is there anything to be learned from the nature of the cracks in paperweights? If it cracks with mainly one crack that goes through the base could that mean it is an annealing problem rather than a fit problem. Can using certain colors affect how much annealing is necessary? I think I will try to bring these weights up a little more than annealing temperature and annealing them for a longer time to see if the stress comes out.

Anyone else having fit problems with R61.

Thanks for any input.

Pete VanderLaan 11-15-2017 12:00 PM

Since you have polarized filters, make a simple cup with some of the white chips. Look at that. Then make a cup with the white inside and clear outside, Cut it on a saw. That will tell you a bunch.
Normally, checking through the base where the punty mark is and that's often a sign of being under-annealed. You do say however that you are finishing the piece heating that very spot and you may in fact be introducing strain doing it.
As to the white being a mismatch, it's entirely possible since different batches are ..well, different. None of those whites are really close to a 96 but they have so much lead in them that they are rather tolerant.

If you make the witness weight in clear and do what you do to the base, does it show retardation of light at that point?
Also, you don't say the actual size nor do you say what the schedule on annealing is. That's rather important information.

Cecil McKenzie 11-16-2017 11:08 AM

Thanks for the reply. i use just a set point controller. i usually leave it at temp for 2 hours or so after I am done. My annealer has six inch fiber walls and cools slowly. It parallels a Love controller set to cool down in 9 hours. This has worked for me for a long time with little problem. i used Zimmerman 74 until it became unavailable and switched to R 61.

I will try the cup tests to see if that tells me anything. I will also try a different batch of R 61.

I measured the weights. They are 3 to 3.25 inches in diameter. They all show stress but I think all the ones that have broken are 3.25 in diameter .

Pete VanderLaan 11-16-2017 03:02 PM

Experience tells me that it takes three separate things going wrong at the same time to create an event. First we have the white glass as a thing that doesn't quite fit. Then we have quite a short cycle annealing for the program and you say the work is showing strain. Finally you are indenting the weight with heat and then putting it away. I do view a weight about 3.25 inches across to be needing a soak time of about 3-4- hours before starting a cycle down and I would be forcing it down. You want the show done in nine hours and that in my mind is a stretch. If I was working a larger weight, I would have a cycle running more than 24 hours. Perhaps that's just me but in annealing thick stuff , I always use overkill.

Most likely getting another white will stop the basic checking but the fact that it checks through the punty mark says there's more to it. What you also don't say is what the base clear is. It matters.

Peter Bowles 11-16-2017 03:51 PM

Also worth doing a slump test in your annealer just to be sure your set points are as you think they are.
Maybe also put an extra flash or two once you have made the weight before putting away. You can introduce a huge amount of stress to a sphere if the outside is too cold comparative to the core at the time you put it away.

Pete VanderLaan 11-16-2017 04:19 PM

Really well said. Thanks Peter.
That's the fourth part of the storm,,, tooling.

Two years back, I had a person not far from here who was railing away at Gaffer for their terrible White. John and I went over it and I went to the shop and took some simple readings on the controls. The annealer was in fact running at about 800F but John was getting blamed.

When I finish up a batch of weights, I set the control program to not even stop soaking for at least four hours and those need to be pretty small.

Jordan Kube 11-16-2017 04:39 PM

A little longer annealing cycle that took it through the strain point before crashing should help if it's not just straight up incompatible color.

Pete VanderLaan 11-16-2017 05:27 PM

I well remember Frank Wooley, the senior melt engineer at Corning prior to his retirement saying how frequently mismatch was in actuality bad annealing. Frank at one point said to me that if a piece went in the box too cold, it could take up to 30 times longer to anneal than if it was put away at the proper temperature.

Eben Horton 11-17-2017 08:49 AM

Give it 2 extr flashes and the time needed to allow the surface to cool between the flashes before you break it off. The cracking will stop.

Randy Kaltenbach 11-17-2017 09:50 AM

I agree with Eben.

I've made many ppws and they started to go south on me with a single crack when I got "too proficient". It was such a smooth process that I wasn't getting enough reheat into them. Just another minute with a couple of long flashes fixed it for me.

Cecil McKenzie 11-17-2017 10:17 AM

Thanks for input. For the record I am using SP 87w Erbium. I made one with only white without the transparent frits on first gather. After annealing it showed no sign of stress with the polarized filters. This weight was a little smaller but I tried to use same timing in cooling etc.

i am leaning to the idea that I am putting them away too cool and will work on that timing and heating. Busy making a different item today but will get back to this soon. Thanks again for responses.

Pete VanderLaan 11-17-2017 11:37 AM

And it's worthy of note to see how long and how much information takes to be coughed up to make an evaluation. As I said "Three things". It's still not done but being too efficient can certainly bite you in the Ass.

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