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Polishing Bowl
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Odds and Ends



Fig.1. Is a cross section drawing of the first gas fired crucible furnace I made. I built it to make aluminum and bronze castings for telescope mountings I was making. It was fired by town gas (coal gas) and I used my wife's vacuum cleaner for a blower. To get a sufficient flow of gas I used to weight the pressure regulator on the gas meter. It took an A 20 crucible which held 66lbs of bronze or 19 Ibs of Aluminum. A nice size for aluminum but a bit heavy for bronze. As mine is a one man operation I have to lift and pour the full crucible on my own. The lifting of the crucible out of the furnace is a one hand operation. A one-man shank is used for pouring. Aluminum is a breeze. I don't even put on boots. I worked in sandals and wore shorts. However bronze is different. Because of its weight one has to has to get a close hold of a full pot, and boots long trousers and gloves are required. As my bronze castings are very small one has hold of the pot for quite a while before it is empty. I have to sit down for a few minutes after pouring it. I used scrap metal and it had to broken up to fit in the pot.

This furnace is simple in design and works well. As mentioned above it operated on town gas. Later, after I had passed it on to someone else to make my castings it was converted to operate on LPG and a high pressure blower was used. Now, the first pot of bronze takes 30 minutes to melt but with the furnace heated up only 20 minutes. This is pushing it though and is very hard on the lining.

Care must be taken lighting it when LPG is used. The gas valve is on the bottle which is a few feet away from the furnace. After turning on the gas and striking a match, gas is everywhere . It is best to light a piece of paper, drop it into the furnace and close the top. Then turn on the gas. Do not stand too close to the furnace as a large lazy flame envelopes it. Then the blower is switched on. For a second it would seem the flame has been blown out. Then it goes off with a bang and it seems as if the furnace has jumped into the air, shook itself then landed back on its feet. It is away and roaring.

I passed all my foundry over to someone else and they made my castings. But later I was having difficulty with deliveries so decided to go back to making them myself.. My casting requirements were greater so I decided to make a reverberatory furnace and use aluminum ingots. The furnace runs continuously and aluminum ingots are fed into the flue. The furnace tilts to empty the metal into a pot for pouring. It was necessary to set this furnace up in a different position and I had to get the gas supply company to move the gas meter. They said they would set me up properly this time, no more weighting the regulator. They installed three meters to feed me more gas. But they were unaware of one of the laws of fluidics. The gas will not flow through them all at once. It decides to flow through one meter and no gas will pass through the other. As the design of the meter prevented it being weighted. I could not get enough gas.

I decided to use LPG. (liquid petroleum gas). I obtained a 100lb bottle and a pressure regulator. The gas was fed through a " copper pipe to the furnace. The drawings of this furnace were lost long ago and the furnace was scrapped a few years ago so I do not have detailed dimensions However Fig. 2 shows a cross section of it A high pressure centrifugal blower was used. Reference to the drawing stows how simple the burner is. I would light the furnace up at 12 o'clock and turn the gas and air down, direct the flame at the bottom of the well and draw the flame out to pass up the flue This is to preheat the furnace. By 1 pm the inside of the furnace was red hot. The air and gas were opened up, the burner directed at the throat and aluminum ingots were fed into the flue and we were away. The furnace tilted to pour the molten metal into a crucible for pouring. Feeding the ingots and pouring the metal kept me on the move for a few hours. Two gas bottles were used as the gas was drawn off so fast that the bottle would freeze, it was disconnected, wheeled outside under a running water tap and a new bottle connected up. During the afternoon the bottles were swapped over a few times. And this even during our hot season. When the casting session was finished the hinged cover was lifted back and the lining scraped clean. When cool this dross etc. was easily removed and patching of the lining done.