CA1057052A - Free floating flight in a retort - Google Patents
Free floating flight in a retortInfo
- Publication number
- CA1057052A CA1057052A CA233,970A CA233970A CA1057052A CA 1057052 A CA1057052 A CA 1057052A CA 233970 A CA233970 A CA 233970A CA 1057052 A CA1057052 A CA 1057052A
- Authority
- CA
- Canada
- Prior art keywords
- retort
- flight
- guide means
- strips
- heating surface
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B7/00—Rotary-drum furnaces, i.e. horizontal or slightly inclined
- F27B7/14—Rotary-drum furnaces, i.e. horizontal or slightly inclined with means for agitating or moving the charge
- F27B7/18—Rotary-drum furnaces, i.e. horizontal or slightly inclined with means for agitating or moving the charge the means being movable within the drum
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Muffle Furnaces And Rotary Kilns (AREA)
- Screw Conveyors (AREA)
- Heat Treatments In General, Especially Conveying And Cooling (AREA)
- Heat Treatment Of Articles (AREA)
- Food Preservation Except Freezing, Refrigeration, And Drying (AREA)
Abstract
FREE FLOATING FLIGHT IN A RETORT
Abstract A pair of helical strips for holding a flight adjacent the interior surface of a cylindrical heating retort. The flight is movable between the helical strips relative to the interior surface of the retort to prevent the occurrence of thermal stress cracking in the retort and/or the flight adjacent their interface.
Abstract A pair of helical strips for holding a flight adjacent the interior surface of a cylindrical heating retort. The flight is movable between the helical strips relative to the interior surface of the retort to prevent the occurrence of thermal stress cracking in the retort and/or the flight adjacent their interface.
Description
Background of the Invention This invention relates to the field of heat treating furnaces and more particularly is directed to a rotary retort used for continuous processing of workpieces, requiring controlled heat treating to produce, for example, carburizing, cabonitriding, carbon restoration or hardening. The flight or spiral which is mounted on the interior surface of the cylindrical retort is designed to move the workpieces from one end of the cylindrical retort to the other end.
In the prior art the retorts used for the continuous pro-cessing of workpieces have generally been heavy walled rough cast retorts with cast-in spirals or have been fabricated retorts of wrought materials with the internal spiral welded directly to the cylindrical shell. In the processing of particular types of workpieces it is necessary to have a smooth clean interior portion of the retort for the conveying of the workpieces through the heat treating process to prevent possible damage to the workpieces.
When using a smooth retort, it is generally necessary to weld a flight or spiral to the interior surface of the outer shell of the retort in order to provi~e the smooth interior surface necessary for certain specialized workpieces. Ilowever, thermal stresses are developed in the flight and the shell of the retort whenever the flight and shell are at different temperatures.
lfl~7~
The degree of stress depends upon the magnitude of the temperature differences. There are several conditions where the temperature differential is of significant magnitude to cause stress conditions that result in possible failure and cracking of either or both the flight and the retort. One condition is the rapid heating from a shut down condition up to the operating temperature which results in the shell being much hotter than the flight. In another situation, there may be accelerated cooling, by turning off the natural gas and permitting the combustion of air to flow through the burners or by opening of vents in electric heated versions.
As a result, the shell becomes cooler than the flight. In another typical condition, the cold incoming work keeps the flights cooler than the outer shell which is most severe with the first of the incoming load after the retort has been stabilized at the operating temperature (with no work passing through).
Therefore, the presence of these and other typical con-ditions may cause the premature failure of the retort by cracking occurring adjacent the intersection of the flight and the shell.
Typically, the failure will appear as a spiral crack in the retort following the path of the flight while in the flight the cracking is radially due to the temperature difference from the inside to the outside diameter of the flight, wherein the outside diameter of the flight is welded to the shcll.
As a result, when utilizing a retort having a smooth interior surface with the flight welded directly to this interior surface, problems ultimately occur with the failurc in the flight due to these thermal stresses, requiring a costly maintenance operation of replacing the flight and/or the retort shell.
Summary of the Invention 3n The present invention comprises a pair of helical strips which are secured to the interior surface of the retort on opposite ' 1~570SZ
sides of the flight for holding the flight adjacent to the interior surface of the retort. The flight is not directly connected to the interior surface of the retort and, therfore, is free to move relative to the interior surface of the retor~. The pair of helical strips do not protrude as far from the interior surface of the retort as the flight. Since the flight is "free floating", no thermal stresses develop between the flight and the retort due to temperature differentials. Because the strips are essentially small, narrow bands, very little temperature difference can exist across them, and thus the bands and the retort are kept at essentially the same temperature.
10By eliminating the prescnce of this thermal stress condition between the flight and the shell, the retort shell can be constructed of less ductile and less expensive materials. Furthermore, the desirable smooth bore features of the retort as required by certain workpieces is retained, : so that none of the parts or workpieces will become caught in the retort and become mixed with subsequent parts of a different configuration.
: This invention allows for the easy placement of the flight within the retort, by first tack welding the pair of helical strips to opposite ;~ sides of the flight, and then connecting the two strips permanently to the interior surface of the retort shell by continuous welds. The tack welds between the flight and the strips are readily broken by the first thermally produced stresses on the parts, thus permitting the flight to move between the strips.
The present invention provides an apparatus for heat treating workpieces which comprises a heating surface, guide means located on the heating surface for directing workpieces along the heating surface, and means connected to and extending away from said heating surface adjacent said guide means, for maintaining the general location of the guide means on the heating surface while permitting the guide means to move relative to the heating surface so that any temperature differential between the heating surface and the guide means will not cause thermal stress cracks in the heating surface and the guide means adjacent their interface.
,4 ~ -3-: E~
lC~570SZ
The present invention also provides a method of placing a helical flight on the interior surface of a cylindrical heat treating retort, said method being characterized by the step of positioning said helical flight on said interior surface by a pair of spaced helical strips continuously secured on the interior surface of the retort in a manner to confine the flight while allowing the flight to move relative to said retort.
Brief Description of the Drawings : Figure 1 is a partial sectional view of a rotary retort heat ; treating furnace; and Figure 2 is a partial perspective view of the flight attached to the retort shell.
,, .
: ~ -3a-, .................................. .
, '- ':' . ' :
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1~5705Z
Detailed Description of the Invention Referring to Figure 1, the cylindrical retort 10 is shown mounted in a heat treating furnace 12 supported by the legs 14. For specific details of the construction and operation of the heat treating furnace reference is made to United States Patent 3,441,259. Located between the retort 10 and the housing 12 is a heating chamber 16 which heats the outer surface or shell 18 of the retort 10. Positioned on one end 19 of the retort 10 is a circular plate 20 having an entry port 22 for receiving workpieces.
, A series of discharge ribs 24 are located at the other end 23 of the retort 10 adjacent a discharge chute 26 for directing the exiting workpieces.
Positioned on the interior surface 28 of the retort 10 is a flight or spiral 30 which proceeds in a helical orientation from adjacent one end l9 of the retort to adjacent the other end 23. As shown more clearly in Figure 2, the flight or flange member 30 is held in position on the interior surface 28 of the retort 10 by a pair of helical guide strips or bands 32 and 34. The lower surface 46 of the guide strip 34 is secured to the interior surface 28 of the retort by a continuous weld 48 and the bottom surface 50 of the guide strip 32 is also secured to the interior 28 by a continuous weld 52.
With respect to the centerline of the retort, the outside edge 54 of the flight 30 is positioned closely adjacent the interior surface 28, but is not attached to that surface. There is no gap between the inside surface 56 of the strip 34 and the side 40 of the flight 30. Similarly, there is no gap between inside surface 58 of the strip 32 and the side 44 of the flight 30. This is to insure that no foreign matter or workpieces can become lodged between the strips 32 and 34 and the flight 30.
Turning to the operation of the heat treating retort, reference i` again is made to Figure 1 where workpieces are fed into the inlet port 22 and ` proceed from the one end 19 to the other end 23 of the retort 10 by the rotative motion of the retort and the spiral orientation of the flight 30.
As the workpieces exit the end 23 of the retort, they are guided by the dis-charge ribs 24 into the discharge chute 26. Because the heating area 16 is ~35705Z
adjacent the exterior surface 18 of the retort, the retort becomes hotter than the flight 30 when first initiating the operation of the retort. This causes a temperature differential between the flight 30 and the retort 10 resulting in possible thermal stress failure if the flight were connected to the retort interior surface 28. However, as shown in Figure 2, because the outside edge 54 of the flight 30 is not connected r attached directly to the interior surface 28 of the retort, no significant thermal stresses are developed as a result of temperature differentials between the flight 30 and the retort 10. The flight 30 is preferably a single continuous flight extend-ing from the one end 19 of the retort in a spiral direction to the other end 23 of the retort.
With respect to the preferred method of constructing the disclos-ed invention, the top portion 36 of strip 34 is tack welded at spaced locations 38 to one side 40 of the flight 30 while the top portion 42 of the strip 32 is similarly tack welded at spaced locations 43 to the other side 44 of flight 30. Then, the flight with the attached strips is placed within the retort adjacent the interior surface 28. The strips 32 and 34 are respec-tively welded securely to the interior surface 28 by the continuous welds 52 and 48 which follow the spiral path of the helical strips 32 and 34 throughout their placement within the retort.
As a result of some thermal stresses which ~evelop between the strips 32 and 34 and the flight 30, the spaced tack welds 38 and 43 are designed to break after the retort is in operation in order to allow the flight to be in a "free floating" orientation with respect to the retort and the strips 32 and 34. The spiral configuration of the flight causes it to support itself against the interior surface 28 of the retort. Furthermore, the flight is welded at each of its extreme ends 60 and 62 to the interior ; surface of the retort in order to anchor it within the retort.
In the prior art the retorts used for the continuous pro-cessing of workpieces have generally been heavy walled rough cast retorts with cast-in spirals or have been fabricated retorts of wrought materials with the internal spiral welded directly to the cylindrical shell. In the processing of particular types of workpieces it is necessary to have a smooth clean interior portion of the retort for the conveying of the workpieces through the heat treating process to prevent possible damage to the workpieces.
When using a smooth retort, it is generally necessary to weld a flight or spiral to the interior surface of the outer shell of the retort in order to provi~e the smooth interior surface necessary for certain specialized workpieces. Ilowever, thermal stresses are developed in the flight and the shell of the retort whenever the flight and shell are at different temperatures.
lfl~7~
The degree of stress depends upon the magnitude of the temperature differences. There are several conditions where the temperature differential is of significant magnitude to cause stress conditions that result in possible failure and cracking of either or both the flight and the retort. One condition is the rapid heating from a shut down condition up to the operating temperature which results in the shell being much hotter than the flight. In another situation, there may be accelerated cooling, by turning off the natural gas and permitting the combustion of air to flow through the burners or by opening of vents in electric heated versions.
As a result, the shell becomes cooler than the flight. In another typical condition, the cold incoming work keeps the flights cooler than the outer shell which is most severe with the first of the incoming load after the retort has been stabilized at the operating temperature (with no work passing through).
Therefore, the presence of these and other typical con-ditions may cause the premature failure of the retort by cracking occurring adjacent the intersection of the flight and the shell.
Typically, the failure will appear as a spiral crack in the retort following the path of the flight while in the flight the cracking is radially due to the temperature difference from the inside to the outside diameter of the flight, wherein the outside diameter of the flight is welded to the shcll.
As a result, when utilizing a retort having a smooth interior surface with the flight welded directly to this interior surface, problems ultimately occur with the failurc in the flight due to these thermal stresses, requiring a costly maintenance operation of replacing the flight and/or the retort shell.
Summary of the Invention 3n The present invention comprises a pair of helical strips which are secured to the interior surface of the retort on opposite ' 1~570SZ
sides of the flight for holding the flight adjacent to the interior surface of the retort. The flight is not directly connected to the interior surface of the retort and, therfore, is free to move relative to the interior surface of the retor~. The pair of helical strips do not protrude as far from the interior surface of the retort as the flight. Since the flight is "free floating", no thermal stresses develop between the flight and the retort due to temperature differentials. Because the strips are essentially small, narrow bands, very little temperature difference can exist across them, and thus the bands and the retort are kept at essentially the same temperature.
10By eliminating the prescnce of this thermal stress condition between the flight and the shell, the retort shell can be constructed of less ductile and less expensive materials. Furthermore, the desirable smooth bore features of the retort as required by certain workpieces is retained, : so that none of the parts or workpieces will become caught in the retort and become mixed with subsequent parts of a different configuration.
: This invention allows for the easy placement of the flight within the retort, by first tack welding the pair of helical strips to opposite ;~ sides of the flight, and then connecting the two strips permanently to the interior surface of the retort shell by continuous welds. The tack welds between the flight and the strips are readily broken by the first thermally produced stresses on the parts, thus permitting the flight to move between the strips.
The present invention provides an apparatus for heat treating workpieces which comprises a heating surface, guide means located on the heating surface for directing workpieces along the heating surface, and means connected to and extending away from said heating surface adjacent said guide means, for maintaining the general location of the guide means on the heating surface while permitting the guide means to move relative to the heating surface so that any temperature differential between the heating surface and the guide means will not cause thermal stress cracks in the heating surface and the guide means adjacent their interface.
,4 ~ -3-: E~
lC~570SZ
The present invention also provides a method of placing a helical flight on the interior surface of a cylindrical heat treating retort, said method being characterized by the step of positioning said helical flight on said interior surface by a pair of spaced helical strips continuously secured on the interior surface of the retort in a manner to confine the flight while allowing the flight to move relative to said retort.
Brief Description of the Drawings : Figure 1 is a partial sectional view of a rotary retort heat ; treating furnace; and Figure 2 is a partial perspective view of the flight attached to the retort shell.
,, .
: ~ -3a-, .................................. .
, '- ':' . ' :
"' . ' , . ' ~ - - , :
1~5705Z
Detailed Description of the Invention Referring to Figure 1, the cylindrical retort 10 is shown mounted in a heat treating furnace 12 supported by the legs 14. For specific details of the construction and operation of the heat treating furnace reference is made to United States Patent 3,441,259. Located between the retort 10 and the housing 12 is a heating chamber 16 which heats the outer surface or shell 18 of the retort 10. Positioned on one end 19 of the retort 10 is a circular plate 20 having an entry port 22 for receiving workpieces.
, A series of discharge ribs 24 are located at the other end 23 of the retort 10 adjacent a discharge chute 26 for directing the exiting workpieces.
Positioned on the interior surface 28 of the retort 10 is a flight or spiral 30 which proceeds in a helical orientation from adjacent one end l9 of the retort to adjacent the other end 23. As shown more clearly in Figure 2, the flight or flange member 30 is held in position on the interior surface 28 of the retort 10 by a pair of helical guide strips or bands 32 and 34. The lower surface 46 of the guide strip 34 is secured to the interior surface 28 of the retort by a continuous weld 48 and the bottom surface 50 of the guide strip 32 is also secured to the interior 28 by a continuous weld 52.
With respect to the centerline of the retort, the outside edge 54 of the flight 30 is positioned closely adjacent the interior surface 28, but is not attached to that surface. There is no gap between the inside surface 56 of the strip 34 and the side 40 of the flight 30. Similarly, there is no gap between inside surface 58 of the strip 32 and the side 44 of the flight 30. This is to insure that no foreign matter or workpieces can become lodged between the strips 32 and 34 and the flight 30.
Turning to the operation of the heat treating retort, reference i` again is made to Figure 1 where workpieces are fed into the inlet port 22 and ` proceed from the one end 19 to the other end 23 of the retort 10 by the rotative motion of the retort and the spiral orientation of the flight 30.
As the workpieces exit the end 23 of the retort, they are guided by the dis-charge ribs 24 into the discharge chute 26. Because the heating area 16 is ~35705Z
adjacent the exterior surface 18 of the retort, the retort becomes hotter than the flight 30 when first initiating the operation of the retort. This causes a temperature differential between the flight 30 and the retort 10 resulting in possible thermal stress failure if the flight were connected to the retort interior surface 28. However, as shown in Figure 2, because the outside edge 54 of the flight 30 is not connected r attached directly to the interior surface 28 of the retort, no significant thermal stresses are developed as a result of temperature differentials between the flight 30 and the retort 10. The flight 30 is preferably a single continuous flight extend-ing from the one end 19 of the retort in a spiral direction to the other end 23 of the retort.
With respect to the preferred method of constructing the disclos-ed invention, the top portion 36 of strip 34 is tack welded at spaced locations 38 to one side 40 of the flight 30 while the top portion 42 of the strip 32 is similarly tack welded at spaced locations 43 to the other side 44 of flight 30. Then, the flight with the attached strips is placed within the retort adjacent the interior surface 28. The strips 32 and 34 are respec-tively welded securely to the interior surface 28 by the continuous welds 52 and 48 which follow the spiral path of the helical strips 32 and 34 throughout their placement within the retort.
As a result of some thermal stresses which ~evelop between the strips 32 and 34 and the flight 30, the spaced tack welds 38 and 43 are designed to break after the retort is in operation in order to allow the flight to be in a "free floating" orientation with respect to the retort and the strips 32 and 34. The spiral configuration of the flight causes it to support itself against the interior surface 28 of the retort. Furthermore, the flight is welded at each of its extreme ends 60 and 62 to the interior ; surface of the retort in order to anchor it within the retort.
Claims (10)
IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An apparatus for heat treating workpieces which comprises a heating surface, guide means located on the heating surface for directing workpieces along the heating surface, and means connected to and extending away from said heating surface adjacent said guide means, for maintaining the general location of the guide means on the heating surface while permitting the guide means to move relative to the heating surface so that any temperature differential between the heating surface and the guide means will not cause thermal stress cracks in the heating surface and the guide means adjacent their interface.
2. An apparatus according to claim 1 wherein said heating surface is a cylindrical retort.
3. The apparatus of claim 2 further characterized in that said means for maintaining the general location of the guide means includes a pair of spaced, parallel strips secured to and extending inwardly from said heating surface to define a channel with said surface sized to receive and hold said guide means, said guide means extending further from said surface than said strips.
4. An apparatus according to claim 3 wherein said guide means comprises a helical flight adjacent said heating surface, said flight being free to move within said means for maintaining the general location of the guide means, said flight having at least sufficient length to support itself within said means for maintaining the general location of the guide means.
5. An apparatus according to claim 4 wherein said flight is a single continuous piece.
6. An apparatus according to claim 4 wherein said flight consists of a number of sequentially joined helical segments.
7. An apparatus according to claim 3, 4 or 6 further including means for heating the cylindrical retort.
8. A method of placing a helical flight on the interior surface of a cylindrical heat treating retort, said method being characterized by the step of positioning said helical flight on said interior surface by a pair of spaced helical strips continuously secured on the interior surface of the retort in a manner to confine the flight while allowing the flight to move relative to said retort.
9. The method according to claim 8 wherein the step of positioning said helical flight on the interior surface of said cylindrical heat treat-ing retort comprises:
(a) positioning said helical flight on the interior of one-half of a matched pair of half shells for said cylindrical retort and continuously securing the portion of said spaced helical strips within said half shell to said half shell; and (b) joining the other half of said matched pair of half shells for said retort to said one-half of said matched pair of half shells for said retort and continuously securing the portion of said pair of helical strips within said other half of said matched pair of half shells for said retort, to said other half of said matched pair of half shells for said retort.
(a) positioning said helical flight on the interior of one-half of a matched pair of half shells for said cylindrical retort and continuously securing the portion of said spaced helical strips within said half shell to said half shell; and (b) joining the other half of said matched pair of half shells for said retort to said one-half of said matched pair of half shells for said retort and continuously securing the portion of said pair of helical strips within said other half of said matched pair of half shells for said retort, to said other half of said matched pair of half shells for said retort.
10. The method of claims 8 or 9 characterized by said strips being temporarily secured to said flight before the flight and the strips are installed in the retort, the connections between the strips and the flight being such that they are easily broken during initial operation of the retort so that the flight is then free to move.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US503731A US3927959A (en) | 1974-09-06 | 1974-09-06 | Free floating flight in a retort and method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1057052A true CA1057052A (en) | 1979-06-26 |
Family
ID=24003283
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA233,970A Expired CA1057052A (en) | 1974-09-06 | 1975-08-22 | Free floating flight in a retort |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US3927959A (en) |
| JP (1) | JPS5150804A (en) |
| CA (1) | CA1057052A (en) |
| DE (1) | DE2538356A1 (en) |
| FR (1) | FR2283955A1 (en) |
| GB (1) | GB1525752A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4025297A (en) * | 1975-09-22 | 1977-05-24 | Sunbeam Equipment Corporation | Rotary retort furnace |
| US4259060A (en) * | 1979-10-15 | 1981-03-31 | Agf Inc. | Discharge end structure for rotary retorts |
| GB2198519B (en) * | 1986-12-04 | 1990-10-03 | John Hall | Improved solid fuel burner |
| DE102008019835A1 (en) | 2008-04-19 | 2009-10-29 | Lwb Refractories Gmbh | Rotary kiln with a refractory lining and delivery for such a rotary kiln |
| DE102012006032A1 (en) | 2012-03-27 | 2013-10-02 | Mbb Fertigungstechnik Gmbh | Process for producing a flat prepreg material blank |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1179952A (en) * | 1916-01-11 | 1916-04-18 | Mathieson Alkali Works | Rotary kiln. |
| US3351181A (en) * | 1965-12-23 | 1967-11-07 | Kenneth M Allen | Conveyors of granular material |
| US3441259A (en) * | 1967-09-01 | 1969-04-29 | Pacific Scientific Co | Heat treating furnace |
| US3556498A (en) * | 1969-01-08 | 1971-01-19 | Duraloy Co The | Heat treating retort with helix |
-
1974
- 1974-09-06 US US503731A patent/US3927959A/en not_active Expired - Lifetime
-
1975
- 1975-08-22 CA CA233,970A patent/CA1057052A/en not_active Expired
- 1975-08-28 DE DE19752538356 patent/DE2538356A1/en active Pending
- 1975-08-30 JP JP50105552A patent/JPS5150804A/en active Granted
- 1975-09-05 FR FR7527322A patent/FR2283955A1/en not_active Withdrawn
- 1975-09-05 GB GB36583/75A patent/GB1525752A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US3927959A (en) | 1975-12-23 |
| JPS5335847B2 (en) | 1978-09-29 |
| DE2538356A1 (en) | 1976-03-25 |
| GB1525752A (en) | 1978-09-20 |
| JPS5150804A (en) | 1976-05-04 |
| FR2283955A1 (en) | 1976-04-02 |
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