Patent Grant
9891000
Field of the Invention
This invention relates generally to vacuum heat treating furnaces and in particular to a heating element arrangement for a vacuum heat treating furnace.
Description of the Related Art
Prior to the present invention, a center heating element arrangement was used in a vacuum aluminum brazing furnace manufactured by Ipsen Inc., the assignee of the present application. A center heating element is a heating element bank that is positioned between two separate workloads inside a vacuum furnace. This arrangement allows for faster and more uniform heating of such loads because when the load is split into two sections, the center heating element radiates heat toward the inside-facing surfaces of the workloads while the peripheral heating elements radiate heat toward the outside-facing surfaces of the workloads. This has only been accomplished in the past by providing the center element bank with its own dedicated power terminals, variable reactance transformer power supply, and a thermocouple for effecting temperature control.
The known center heating element arrangement leaves something to be desired with respect to design and operational flexibility. The requirement for a separate power supply complicates the power supply requirements for the vacuum furnace and results in a more costly design. That design also requires more penetrations in the furnace wall. Also, the fixed-in-place nature of the known arrangement prevents the vacuum furnace from being used for larger-size workloads.
In view of the foregoing, it would be desirable to have a vacuum heat treating furnace that avoids the undesirable aspects of the known arrangement for a center heating element, while still providing the benefits of a center heating element. Moreover, it would also be desirable to have a vacuum heat treating furnace having a center heating element that does not have its own connections outside the vacuum furnace, no separate power transformer, and no separate control thermocouple. It is further desirable to provide a vacuum heat treating furnace having a center heating element that is readily removable so that work loads of different sizes can be heat treated in the furnace.
In accordance with the present invention there is provided a vacuum heat treating furnace for the heat treatment of metal parts that includes a pressure/vacuum vessel, a hot zone enclosure positioned inside the pressure vessel to define a hot zone within the heat treating furnace, a heating element array positioned inside said hot zone enclosure, and a source of electric power for energizing the heating element array. In the vacuum heat treating furnace of this invention, the heating element array includes a first heating element, a second heating element, and a third or center heating element. The first heating element is suspended on an inner wall of the hot zone enclosure in a first region of the hot zone. The first heating element has a first end and a second end and the first end is connected to the source of electric power. The second heating element is suspended on the inner wall of the hot zone enclosure in a second region of the hot zone opposite to the first region. The second heating element has a first end and a second end and the first end is connected to the source of electric power.
The center heating element is suspended from the inner wall of the hot zone enclosure along a vertical chord or diameter of the hot zone. The center heating element has first and second ends. First and second connection terminals are provided at the first end of the center heating element. The first connection terminal is connected to the second end of the first heating element and the second connection terminal is connected to the second end of the second heating element. In this manner, the center heating element is connected to the source of electric energy through said first and second heating elements. The heating element array further includes a support member having a first end attached to the hot zone enclosure and a second end connected to the second end of the center heating element for supporting the center heating element in the furnace hot zone.
In accordance with another aspect of the present invention, the heating element array is provided with a first removable/reusable fastener that attaches the first terminal connection to the second end of the first heating element and a second removable/reusable fastener that attaches the second terminal connection to the second end of the second heating element.
In accordance with a further aspect of the present invention the heating element array is provided with a third removable/reusable fastener that attaches a first end of the first sub-element to the second end of the first heating element and a fourth removable/reusable fastener that attaches the first end of a second sub-element to the second end of the second heating element.
In accordance with a still further aspect of the present invention, the vacuum heat treating furnace of this invention includes two or more heating element arrays as described above that are arranged in spaced coaxial relation along the length of the furnace hot zone.
In accordance with a further aspect of the present invention there is provided a method for configuring a vacuum heat treating furnace for holding different size workloads. The method is implemented with a vacuum heat treating furnace that has a pressure/vacuum vessel, a hot zone enclosure positioned inside said pressure vessel to define a hot zone within the heat treating furnace, a heating element array positioned inside said hot zone enclosure, and a source of electric energy. The heating element array includes a first heating element suspended on an inner wall of the hot zone enclosure in a first region of the hot zone. The first heating element has a first end and a second end and the first end is connected to the source of electric energy. The heating element array also includes a second heating element suspended on the inner wall of the hot zone enclosure in a second region of the hot zone opposite to the first region. The second heating element has a first end and a second end and the first end is connected to the source of electric energy. The heating element array further includes a center heating element suspended from the inner wall of the hot zone enclosure along a vertical chord of the hot zone. The center heating element has first and second connection terminals at a first end thereof and a second end. The first connection terminal is connected to the second end of the first heating element and the second connection terminal is connected to the second end of the second heating element. In this manner the center heating element is connected to the source of electric energy through the first and second heating elements. The heating element array further includes a hanger assembly having a first end attached to the hot zone enclosure and a second end connected to the second end of the center heating element. The method includes the steps of disconnecting the center heating element from the first and second heating elements, removing the center heating element from the vacuum heat treating furnace, and then connecting a jumper heating element between the second end of the first heating element and the second end of the second heating element, whereby an electrical conduction path is established between the first and second heating elements.
The foregoing summary as well as the following detailed description will be better understood by referring to the drawings wherein:
Referring now to the drawings and in particular to
Vacuum furnace 10 also has one or more heating element arrays or banks to provide radiant heat within the hot zone 16. As shown in
First lateral heating element 24 includes heating element segments 38a, 38b, 38c, and 38d. The heating element segments 38a and 38b are connected together at a first heating element support 39a. Heating element segments 38b and 38c are connected together at a second heating element support 39b and heating element segments 38c and 38d are connected together at a third heating element support 39c. The heating element supports 39a, 39b, and 39c extend from and are attached to the hot zone enclosure 14 at spaced intervals as shown. Second lateral heating element 26 includes heating element segments 40a, 40b, 40c, and 40d. The heating element segments 40a and 40b are connected together at a first heating element support 41a. Heating element segments 40b and 40c are connected together at a second heating element support 41b and heating element segments 40c and 40d are connected together at a third heating element support 41c. The heating element supports 41a, 41b, and 41c extend from and are attached to the hot zone enclosure 14 at spaced intervals as shown.
First lateral heating element 24 is connected at one end to a first terminal connector 32 that extends through the hot zone enclosure and through the wall of the pressure/vacuum vessel 12. Likewise, second lateral heating element 26 is connected at one end to a second terminal connector 34 that also extends through the hot zone enclosure and through the pressure/vacuum vessel wall. The other ends of the first and second terminal connectors 32, 34 are adapted to be connected to a source of electric power 36. Arrangements for such power sources and suitable connections therefor are known to persons skilled in the art and no special design is needed for the arrangement according to the present invention. However, it is an advantage of the present invention that fewer power sources are needed for the heating element arrangement according to this invention than would be needed for the known heating element arrangements that include a center heating element.
The center heating element 28 is formed of a first heating element segment 42a and a second heating element segment 42b. First heating element segment 42a has a connection terminal 45a at a first end thereof whereby the first heating element segment 42a is connected to the first lateral heating element 24. Second heating element segment 42b has a connection terminal 45b at a first end thereof whereby the second heating element segment 42b is connected to the second lateral heating element 26. The first and second heating element segments 42a and 42b are connected to each other at second ends thereof as described in more detail below. In this manner the center heating element 28 provides a continuous conductive path between the first and second lateral heating elements 24 and 26. With the foregoing arrangement, the center heating element 28 is connected to the electric power source 36 through the first and second heating elements 24, 26 and forms a complete electrical circuit therewith.
In the embodiment shown in
As shown in
Referring back to
Referring now to
In accordance with an aspect of this invention, the center heating element 28 is removably connected to the first and second lateral heating elements 24 and 26 so that the center heating element 28 can be removed when needed in order to permit a single large workload to be heat treated in the vacuum furnace 10. The use of removable/reusable fasteners to attach the heating element segments 42a and 42b to respective heating element segments 38d and 40d is preferred to facilitate the removal and reinstallation of the third heating element 28. This arrangement provides greater flexibility for the user of the vacuum furnace according to the invention with respect to the sizes of workloads that can be accommodated in one vacuum furnace.
In the embodiment shown in
The heating element segments 38a-38d, 40a-40d, 42a, and 42b are preferably formed of graphite as known to those skilled in the art. The heating element segments can be formed of a refractory metal such as molybdenum. When the center heating element 28 is formed of a refractory metal, it is preferred that insulating spacers will be fixedly positioned between the heating element segments 42a and 42b in order to prevent contact between the segments when the center heating element is energized. The lateral heating elements used in the embodiments described and shown herein can be realized by use of curved graphite heating elements as described in U.S. Pat. No. 5,965,050, the entirety of which is incorporated herein by reference.
Referring to
Referring now to
Hanger assembly 110 also includes first and second pins 115a and 115b for attaching the bar 111 to the bracket 112. The pins 115a and 115b extend through aligned holes in the bar 111 and bracket 112. The pins 115a and 115b are retained in position with pairs of retaining wires 116a and 116b, respectively. The retaining wires are typically inserted in diametric through-holes formed in the ends of the pins 115a and 115b that extend beyond the sides of bracket 112. The bar 111, bracket 112, rod 113, pins 115a and 115b, the retaining wires 114a, 114b, 116a, and 116b are preferably formed of a refractory metal such as molybdenum. In order to electrically insulate the bar 111 from bracket 112, ceramic sleeves 117a and 117b are positioned around the central portions of the pins 115a and 115b that extend through the holes in bar 111. In addition, ceramic collars 118a and 118b are positioned around pin 115a so as to prevent contact between bar 111 and the sidewalls of bracket 112. Additional ceramic collars 118c and 118d are positioned around pin 115b between bar 111 and the side walls of bracket 112.
The hanger assembly 110 further includes a disc 121 positioned on bar 111 and retained in position with a retaining wire 122 that extends through a small hole in bar 111. A small notch 123 is formed in bar 111 near the end thereof that is distal from the bracket 112. The disc 121 is positioned at a distance along bar 111 from the notch 123 so that the bar 111 can extend through the hot zone insulation a distance sufficient to allow it to engage with a catch on the hot zone enclosure by twisting the hanger assembly 110. When the hanger assembly 110 is thus installed, the disc 121 abuts the hot zone insulation. The twist-lock feature is described in U.S. Pat. No. 4,321,415, the entirety of which is incorporated herein by reference.
The foregoing text describes the features of a single heating element array in accordance with the present invention. However, as shown in
In accordance with the present invention it is contemplated that in the heating element arrays, the heating element segments that make up the respective heating element arrays can be formed to provide different electrical resistances or watt densities at different locations in the heating element arrays. This arrangement allows for placement of heating elements having an electrical resistance and/or watt density 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. For example, in one embodiment the heating element segments located in an upper region of the hot zone will have a geometry that provides a first watt density and the heating element segments in a lower region of the hot zone will have a different geometry to provide a second watt density having a different magnitude than the first watt density. It is also contemplated that, when more than one heating element array is present in the vacuum furnace of this invention, all of the heating element segments in one heating element array will have the same geometry and all of the heating element segments in another heating element array will have a different geometry. In this manner the radiant heat output from one heating element array will be different from the radiant heat output of another heating element array, whereby the heat applied to the workload will be different in different zones of the vacuum furnace. Thus, for example, the heating element segments in the heating element array nearest the door of the vacuum furnace will have a geometry that provides a watt density sufficient to provide greater heat output than that of an inboard heating element array(s) in the hot zone. This aspect of the invention is described in copending U.S. patent application Ser. No. 13/728,122, the entirety of which is incorporated herein by reference.
It is further contemplated that when multiple heating element arrays are present in a vacuum furnace according to this invention, the heat output of each heating element array can be adjusted or trimmed at the electric power source. This is conventionally realized by use of a variable reactance transformer associated with the electric power source and connected to each one of the heating element arrays in the manner known to those skilled in the art. This aspect of the invention is described in U.S. Patent Application Publication No. 2013/0175256, the entirety of which is incorporated herein by reference.
In view of the foregoing description of preferred embodiments of a vacuum furnace according to the present invention, some of the advantages of the inventive concepts will be apparent to those skilled in the art. For example, the vacuum heat treating furnace according to the present invention includes a center heating element that is operatively connected to an electric power source through two lateral heating elements so that the center heating element is energized without the need for a separate power connection to the center heating element. Also, the center heating element used in the vacuum furnace of this invention is removably connected to the lateral heating elements and to the hot zone enclosure so that the center heating element can be easily removed, thereby permitting the vacuum furnace to be reconfigured for a single large workload to be processed in the vacuum furnace.
The terms and expressions which have been employed are used as terms of description and not of limitation. There is no intention in the use of such terms and expressions of excluding any equivalents of the features or steps shown and described or portions thereof. It is recognized, therefore, that various modifications are possible within the scope and spirit of the invention. For example, the heating element arrangement including a removable center heating element according to the present invention could be adapted for use in a vertical vacuum furnace. Accordingly, the invention incorporates variations that fall within the scope of the invention as described.
This application claims the benefit of U.S. Provisional Patent Application No. 61/866,178, filed Aug. 15, 2013, the entirety of which is incorporated herein by reference.
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