Compensating Heating Element Arrangement for a Vacuum Heat Treating Furnace
A heating element arrangement for a vacuum heat treating furnace is disclosed wherein the heating elements that make up the heating element arrays have different electrical resistances or watt densities at different locations in the heating element arrays. This arrangement allows for placement of heating elements having electrical resistance selected to provide more or less heat as needed in the furnace hot zone to provide better temperature uniformity in the workload. The electrical resistances and watt densities of the heating element arrays are varied by using a first heating element having a geometry in one segment of a heating element array and a second heating element having a different geometry from that of the first heating element in another section of the heating element array.
1 . A vacuum heat treating furnace for the heat treatment of metal parts comprising:
a pressure/vacuum vessel;
a hot zone positioned inside said pressure vessel;
a heating element array positioned inside said hot zone; and
a source of electric energy connected to said heating element array;
said heating element array comprising:
a first heating element located in a first region of the hot zone and having a geometry selected to provide a first watt density;
a second heating element located in a second region of the hot zone and having a geometry selected to provide a second watt density,
wherein the first watt density value is selected such that said first heating element provides a first quantity of heat and the second watt density value is selected such that said second heating element provides a second quantity of heat different from the first quantity when said first and second heating elements are energized by said electric energy source;
whereby the first quantity of heat is provided in the first region of the hot zone and the second quantity of heat is provided the second region of the hot zone.
2 . A vacuum heat treating furnace as set forth in claim 1 wherein the geometry of the first heating element is the cross section of the first heating element.
3 . A vacuum heat treating furnace as set forth in claim 2 wherein the geometry of the second heating element is the cross section of the second heating element.
4 . A vacuum heat treating furnace as set forth in claim 1 wherein the geometry of the first heating element is the surface area of the first heating element.
5 . A vacuum heat treating furnace as set forth in claim 2 wherein the geometry of the second heating element is the surface area of the second heating element.
6 . A method of making a vacuum heat treating furnace for the heat treatment of metal parts comprising the steps of:
providing a pressure/vacuum vessel;
installing a hot zone inside said pressure vessel;
forming a first heating element having a geometry selected to provide a first watt density;
forming a second heating element having a geometry selected to provide a second watt density;
connecting the first and second heating elements to form a heating element array;
installing the heating element array inside said hot zone such that the first heating element is located in a first region of the hot zone and the second heating element is located in a second region of the hot zone; and
connecting a source of electric energy to said heating element array;
wherein the first watt density is selected to provide a first quantity of heat and the second watt density is selected to provide a second quantity of heat different from the first quantity when said first and second heating elements are energized by said electric energy source;
whereby the first quantity of heat is provided in the first region of the hot zone and the second quantity of heat is provided the second region of the hot zone.
7 . A method of making a vacuum heat treating furnace as set forth in claim 6 wherein the step of forming the first heating element comprises the step of forming the first heating element to have a cross section that provides the first watt density.
8 . A method of making a vacuum heat treating furnace as set forth in claim 7 wherein the step of forming the second heating element comprises the step of forming the second heating element to have a cross section that provides the second watt density.
9 . A method of making a vacuum heat treating furnace as set forth in claim 6 wherein the step of forming the first heating element comprises the step of forming the first heating element to have a surface area that provides the first watt density.
10 . A method of making a vacuum heat treating furnace as set forth in claim 9 wherein the step of forming the second heating element comprises the step of forming the second heating element to have a surface area that provides the second watt density.