05-01-2008, 11:33 PM
Join Date: Apr 2008
100 Pound Moly Glass Furnace Tutorial
If you are reading this post, then chances are you are interested in building a Moly glass furnace. We are building a 100 pound Moly furnace for glass and our threads have gotten nice reviews here on Wet Canvas. Because of all the support and recommendations to make this info easy to find, we decided to add this tutorial thread here.
Hopefully, it will help you understand Moly elements and how to use them for a furnace of your own.
The below links point to the threads which talk about what we learned while building our Moly furnace.
We believe the natural progression is from a "wire melter" to a "Moly melter".
The main differences between the two are as follows -
1) the Moly furnace requires an SCR to turn on the power.
(instead of a relay or SSR for the wire melter)
2) the Moly elements require a lower voltage to run, i.e. 60 volts. Therefore a 4 to 1 transformer is required to convert the 240 VAC residential voltage to 60 VAC.
(the wire melter can accept the 240 VAC house voltage as is)
3) the Moly elements must be sized to the actual furnace, taking into consideration the pounds of glass you want to melt.
(the wire melter requires sizing the wire elements for the size of the furnace)
Here are some links to other Moly glass furnace threads on Wet Canvas. Each one talks about a different aspect of a Moly furnace -
Moly Glass Furnace - SCR & temp control
This thread explains what we learned about the SCR. The first key thing here are that the SCR must have current limit. The current limit acts to regulate the amps when the Moly is cold at start up. The second key thing is that the SCR must have soft-start (the soft-start allows the voltage to rise gradually during start-up. This is necessary because the SCR is feeding into the transformer.
The following thread discusses these aspects of the SCR for a Moly furnace in detail -
Moly Transformer Step Down Explained
As discussed above, a transformer is required for a Moly glass furnace to convert 240 VAC to 60 VAC. This is a 4 to 1 step down ratio, thus a 4 to 1 ratio transformer is needed. We discovered that this type of transformer is easy to find on eBay and is a 480 VAC to 120 VAC transformer. We use it to convert 240 VAC to 60 VAC, and this can be done no problem, but the transformer must be "de-rated" by dividing the KVA in half. As an example, for a 100 pound Moly glass furnace, we needed 11 KVA. Therefore we purchased a 25 KVA transformer with the 480 to 120 volt rating. Because we were using it with 240 to 60 VAC, we had to "de-rate" it to 12.5 KVA. The new 12.5 KVA rating handles the 11 KVA we are using it for.
The next thread discusses this in more detail -
Mosi2 element sizing/configuration
Moly element sizing is discussed in great detail by the Moly element manufacturers known as Kanthal and I Squared R.
This next thread discusses both of these Moly element suppliers and how to download their handbooks -
Moly Hybrid Furnace (Moly & Wire Coil or Gas)
There has been a discussion started by Mark Wilson about a potential hybrid Moly furnace. Mark has helped a lot of people on here, including us, with info he has given out about temperature controllers, annealers, etc.
This next thread discusses this idea and Mark has said he will have more on this in the future -
Got Moly?! (glass furnace elements arrived) Pictures & testing results / videos...
This next thread we started once our Moly elements arrived from Duralite. The thread discusses our test procedure to ensure that the SCR, transformer and Moly elements worked as expected. We also talk in detail about the actual elements and accessories we purchased (with part numbers). This thread will also show our finished Moly furnace and discuss our lessons-learned on the build-out -
We want to thank Mark Wilson for providing advice to us about using a 4 to 1 step down transformer. We also want to thank Rollin Karg for showing us how to do a Moly furnace top using Kast-O-Lite 30.
When we first set out to build a Moly furnace a few months ago, we were originally just going to do it and keep it to ourselves. But over the years we have gotten a lot of great advice from the info on Wet Canvas and also on the other forums. So then we decided after a while to do it out in the open, and to talk about here.
We guess if it helps somebody down the line, then it will have been worth it.
Jill & Jimmy