This invention relates to an electric heater for a foundry ladle and, more particularly, to apparatus for operating and controlling the same so as to protect the integrity of the electric heating means constituting the electric heater.
It is common practice in the foundry industry to preheat ladles prior to having the molten metal introduced therein. This preserves the ladle lining against possible fracture and also conserves the metal itself against premature solidification. The practice over the years has been to heat ladles by an open gas flame which not only has been wasteful of energy but dangerous to operating personnel. It was therefore desirable to provide an electrically powered heater for this purpose and one approach in the prior art is found in U.S. Pat. No. 4,090,054.
The mechanical arrangement and construction of the '054 patent produced certain disadvantages, notably in the failure of the insulation separating the electrical heaters from the transformer atop the lid which resulted in premature failure and breakdown of the apparatus. Also, the apparatus of the '054 patent was not particularly suited for use of silicon carbide electrical heaters which are preferred in the foundry industry because of their reliability and long life.
In particular, the silicon carbide electrical heaters although possessing the foregoing advantages, are characterized by the disadvantage of being extremely fragile. For example, an electric heater which has been in use for 1000 hours showed no signs of wear but when accidentially bumped against a rigid object, shattered into small pieces.
The fragility of the silicon carbide type of electric heater is not only affected by the handling thereof but also by the environment. For example, such electrical heaters are extremely sensitive to thermal shock--a quick cooling can cause the electrodes to shatter.
The instant invention utilizes the advantages of the silicon carbide type electric heater and, by providing a structural arrangement and operation of the associated mechanical and electrical control apparatus, avoids the disadvantages also outlined above. According to the invention, a frame provides a pedestal on which the ladle to be heated is placed. The frame also is equipped with a vertical post on which a carriage travels for lowering and raising the electric heaters under certain electrical and mechanical safeguards which avoid both mechanical and thermal shock. Other objects and advantages of the invention may be seen in the details of construction and operation as set down in the ensuing specification.