GAS BURNERS
The gas burner used to heat the metal pot is made up of three sections. The largest burner heats the main part of the pot. Another pipe leads up to heat the throat, and a small burner heats the mouthpiece. The pot and throat burners are held near the pot by a rod which passes through the pot jacket and under the pot burner. The mouthpiece burner is held in place by a support and a screw which extends into the pot jacket.
The gas enters the burners through the pot gas burner cocks. The gas cock that feeds the pot burner has a larger inlet hole than those of the throat or the mouthpiece burners, because more gas is required for the pot burner. The inlet holes must be kept open and free from soot and metal, but should never be drilled larger at any time. Should you find a burner tip that has been drilled, a new tip should be applied by driving out the old tip and inserting a new one.
As the gas leaves the gas cock it passes through the air mixer. The air mixer is open on the bottom side and allows a flow of air to mix with the gas. Unless the gas is mixed with the proper amount of air it will not make sufficient heat under the pot. Do not at any time allow the gas to burn in the mixer. Sometimes when lighting the gas or when the pressure is low the flame may light in the mixer. It should then be turned out and relighted, holding a flame near the burner. Should the gas be allowed to burn in the mixer the heat will be lost before it reaches the burner; and furthermore, the burner will soon become clogged with soot.
From the mixer, the gas passes upward into the pot burner. The pot burner consists of a circular shaped chamber which is covered with a flat plate. The top rim of the chamber is notched, which allows the gas to flow out around the top plate, forming a very hot flame. The flame from the burner should be of a bluish appearance. A dirty burner will cause a yellow flame. There is very little heat in a yellow flame, and when the burner shows a yellow flame, it usually indicates a dirty burner or a fire in the mixer. A very important part of the burner is the top plate. When this plate becomes warped or badly burned it should be replaced with a new one.
Two pipes lead out from the front end of the pot burner to carry a flame up under the crucible throat. These pipes are fed through the front gas cock. The gas passes through a separate chamber in the front side of the pot burner. It is very essential that these burners are working properly as they keep the metal hot in the throat of the crucible.
The mouthpiece burner consists of a small pipe into which holes have been drilled to allow the gas to escape. This burner extends underneath the mouth of the crucible the full length of the mouthpiece. There are two extra holes on the right-hand end to give a little more flow of gas at that point. The holes should never be reamed out larger, but should be kept clean and free from soot or metal. Metal sometimes gets through the holes and partly fills the pipe. This retards the free flow of gas and causes loss of heat to the mouthpiece.
Good slugs from a machine are to a great extent dependent on good, clean burners. Only experience on various machines will enable one to tell just how much flame to carry in each burner on a machine. The governor should regulate the pot and throat burners, when once adjusted. However, it is better for the operator to regulate the mouthpiece burner with the gas cock, according to the size of the slug being cast.