US2898099A - Rotating drum heat-treating furnace with internal fan - Google Patents

Description

Aug. 4, 1959 E. G. DE CORIOLIS ROTATING DRUM HEAT-TREATING FURNACE WITH INTERNAL FAN Filed Nov. 7, 1956 2 Sheets-Sheet 1 K wm INVENTOR.

S u w m R m m C.m e/ d EM Y B 1959 E. G. DE CORIOLIS 2,898,099

ROTATING DRUM HEAT-TREATING FURNACE WITH INTERNAL FAN Filed Nov. 7, 1956 2 Sheets-Sheet 2 E G cle Comous BYW/% @TTORNEY 2,898,099 Patented Aug. 4, 1959 ROTATING DRUM HEAT-TREATING FURNACE WITH INTERNAL FAN Ernest G. de Coriolis, Toledo, Ohio, assignor to Surface Combustion Corporation, Toledo, Ohio, a corporation of Ohio Application November 7, 1956, Serial No. 620,917 Claims. (01. 263-34) This invention relates to the heat-treatment of articles and more particularly'to the circulation of a gaseous atmosphere through small articles to be heat-treated that are located in a rotary conveyer.

The art of heat-treating, especially carburizing, small articles in a continuous atmosphere furnace has proven difiicult. A suitable conveyor for transporting the small parts through the furnace in large quantities while uniformly exposing them to the heat-treating atmosphere has been the principal obstacle in this art. This ob- 'stacle has been substantially overcome by the rotary drum conveyor of Patent 2,624,561, Heyn, assigned to applicants assignee. However, many small parts, particularly those of suchsize or shape that relatively small interstices are formed among them, are not uniformly exposed to the atmosphere with the result that some parts have greater case depths than others. It has been found that by oscillating the drum with a net forward rotation,

the parts receive more tumbling action and are more uniformly subjected to the atmosphere. Even this is insuificient in some cases,-for instance, where small rollers for roller bearings are carburized.

To obtain still greater uniformity in case depth, a novel rotary drum or retort has been developed which contains a fan and means for obtaining positive circulation of the gases therein. The gaseous atmosphere is more 1 fully circulated past and through the work with this invention to obtain the utmost possible exposure and uniformity in case depth.

For further consideration of what is novel and the invention refer to the following portion of the specification,

the depending claims, and the accompanying drawing.

In the drawing:

Figure l is a cross-sectional view on line 1-1 of Fig ure .2 of apparatus embodying the invention,

. Figure 2 is an end view of the apparatus on line 2--2 of Figure 1,

Figure 3 is a circuit diagram employed with the apparatus of Figures 1 and 2, and

Figure 4 is a view of alternate apparatus to that shown in Figure 1.

According to Figure 1, a furnace 11 comprises wall means forming a heating chamber 12 and a charge vestibule 13. Chamber 12 is heated by horizontal radiant tubes '14, placed above and below rotary drum or retort 15. The drum, of cast alloy, contains a helical wall 16 integral therewith which extends from the charge end to discharge opening 17. The wall forms a helical passage 18 through which the particles to be heat-treated are carried as the drum rotates. The articles are generally charged into the drum to a depth equal to /2 to the height of wall 16 depending on the size and shape of the articles and the quantity desired to be heat-treated.

. The charge end of drum 15 has a vertical wall 20,

which encloses this end except for a central opening through which a tube 21. extends. This is sealed to and supported by the charge end wall of the vestibule. A charging trough 22, which is preferably of the vibratory type, carries articles placed thereon into the drum. An asbestos or metal curtain 23 is located outside the vestibule chamber 13 to cover the opening between tube 21 and trough 22 so as to maintain a minimum leakage of the atmosphere gas. Also, a flange 24 seals the opening between wall and tube 21.

A centrifugal or. radial flow fan 25 is located at the discharge end of drum 15 and has a shaft 26 extending outside the furnace to a sheave 27 which is driven through a belt 28, sheave 30, and motor 31. The fan and shaft are supported by a first bearing 32 and a second bearing (not shown) located ina water cooled housing 33.

A tapered casing 34 connects bearing 32 to housing 33 to maintain proper alignment of the bearings.

A cylindrical refractory bung 35 is sized to closely fit within the opening formed by drum 15 at the discharge end. The bung is held by a metal cylinder 36 which is indirectly affixed to buckstay 37 through flange 38. A plate 39 is afiixed to this cylinder to support housing 33 and casing 34. i

A tube or duct 40 is placed within the drum in the cylindrical space defined by the inner edge of helical wall 16. The duct thus makes passage 18 an enclosed one from the charge end of the duct to the discharge end at hole 17. A smaller duct 41 extends from the duct 40 to the central portion of fan 25 which is rotated in a counterclockwise direction as viewed from the charge end of the furnace so as to impart a similar motion to the gases drawn from ducts 40 and 41. The gases whirling in a counterclockwise direction then more easils enter duct 18, traveling therethrough until reaching the charge end of duct 40. From here, they re-enter duct 40 and repeat the process. A portion of the gases leave the drum through port 17 and enter the chamber 12. However, additional atmosphere gas is emitted to the chamber 12 through inlet 42 so that the pressure of the gas in the chamber soon equals that in the drum and this leakage is reduced to a minimum. Additional gas is also supplied drum 15 through inlet 43 to make up leakage through hole 17, through the opening above chute 22, and through the small annular openings between the drum and the bung and between the drum and the furnace wall.

Particularly when the gas atmosphere in chamber 12 and drum 15 is to be closely controlled, a wall 53 is fabricated around the drum and its mechanism at the discharge end. The chamber is gas-tightly constructed and additional gas may be admitted to pressurize it and prevent outward leakage of the furnace atmosphere gas through the aforementioned annular openings.

The drum is rotated through a sprocket 44 attached to its periphery outside the discharge end of the furnace. The sprocket enmeshes a chain 45 powered by a sprocket 46 and motor 47. The drum is supported at its discharge end by discs 48 co-acting with ring 50. At the change end, the drum rests on rollers 51 whose shafts 52 extend outside the charge end where they are rotatably supported.

According to Figure 4, the gases may be circulated from the fan through drum 15 and back through the chamber to that portion of the retort adjacent the fan. In this case, a series of holes 71 are provided in wall 20 and another series of holes 72 are provided at the discharge end of the drum. The centrifugal or radial flow fan is preferably replaced by an axial flow fan 73. The ducts 40 and 41 are eliminated in this case also, although a solid plug may be substituted therefor, if desried, to assure better flow of the gas through passage 18. The drive apparatus has been deleted from this View as it is similar to that of Figure 1.

'As previously mentioned, the work is more evenly subjected to the atmosphere if the drum is oscillated with a net advance. The parts are effectively tumbled in this manner thus being subjected more uniformly to the atmosphere. To accomplish this oscillation, motor 47 is reversible, having a forward winding 54 and a reverse winding 55. Current is supplied to winding 54 througha line 56, and to Winding 55 through a line 57; line 58 is a common ground. Line 60 supplies current to line 56 or 57 as regulated by a timer 61. This is a commercially available device that has two adjustable timing periods, one for regulating the length of time the drum rotates in the forward direction and one for the rearward direction. The degree of rotation depends, of course, on the time the drum rotates and this time, depends mainly on the characteristics of the parts to be treated and the depth to which they are charged in the drum. For small parts that closely pack, a greater degree of oscillation is required than for larger parts that do not closely pack and thus have large interstices among them. The degree of forward rotation generally is between 60 and 160.

In a typical example, bearing rollers are to be carburized with surface carbon of 1.00% and with 0.40% carbon content to a depth of .050 inch. They are placed in the bottom of the drum to a depth of 6", the drum having 10 flights between the charge end and the discharge hole, thus requiring 10 revolutions to transport the rollers through the furnace. With a given carburizing atmosphere at 1700 F., 8 hours are required in the furnace for the rollers to attain the desired case and the drum must make a net advance of 1 A revolutions per hour. Further, assuming the'drum rotates at a speed of revolutions per hour and a forward rotation of 90 is necessary to effectively tumble the parts, then the degree of rearward rotation may be found by the following formula:

where:

T=Total time in furnace, minutes N =Total number of revolutions required X: Number of degrees of forward rotation Y=Number of degrees of reverse rotation S=Speed of drum, degrees per minute direction and 79.4 in a rearward direction with a net forward advance of 10.5 This provides proper time in the furnace and ample tumbling action.

The invention thus provides means for recirculating atmosphere gas within a furnace and by the work to obtain maximum exposure of the work to the atmosphere. By recirculating the atmosphere gas, maximum use of the gas is thereby attained. Also, by recirculating the gas within the chamber, the temperature of the gas is maintained at an elevated amount and no heat loss occurs such as would happen if the gas were recirculated through a duct outside said chamber. By both oscillating the drum and tumbling the work, exposure of the Work to the atmosphere gas is even more uniform.

The foregoing illustrates the best mode of carrying out the invention, the scope of which is limited only by the depending claims.

I claim:

1. An atmosphere furnace comprising: wall means defining a heating chamber having first and second aligned openings; a drum having a longitudinal axis containing a helical wall which forms an unobstructed helical channel,.said drum having an open end; a wall gas-tightly 4 aflixed to the other end of said drum and having a hole in the central portion thereof; means for rotatably supporting said drum in said chamber with said hole aligned with said first opening and with said open end extending through said second opening; means for substantially continuously rotating said drum about its axis whereby to cause said helical wall to. advance work, charged into the drum through the first opening, through said drum along said helical channel, a bung extending into said open end and afiixed to a support outside said chamber, said bung being in close relationship to said open end; a fan located in said drum adjacent said open end and whose plane of rotation is perpendicular to the axis of said drum; a shaft connected to said fan and extending outwardly through said bung; bearing means supported by said bung for rotatably supporting said shaft; and means for rotating said shaft.

2. An atmosphere furnace comprising: wall means defining a heating chamber having first and second aligned openings; a drum having a longitudinal axis containing a helical wall which forms an unobstructed helical channel, said drum having an open end; a wall gas-tightly affixed to the other end of said drum and having a hole in the central portion thereof; means for rotatably supporting said drum in said chamber with said hole aligned with said first opening and with said open end extending through said second opening; a bung extending into said open end and affixed to a support outside said chamber, said bung being in close relationship to said open end; a fan located in said drum adjacent said open end and whose plane of rotation is perpendicular to the axis of said drum; a shaft connected to said fan and rotatably supported by said bung; means for rotating said shaft; a discharge hole located in the periphery of said drum intermediate said fan and said other end; and means for substantially continuously rotating said drum about its axis whereby to cause work therein, charged into said drum through said hole, to advance through said drum along said helical channel to said discharge hole.

3. Carburizing apparatus comprising: wall means forming a heating chamber having first and second openings in opposite ends thereof, said first opening having a charging chute extending therethrough; an elongated drum rotatably supported in said chamber, one end of said drum having a centrally located opening adjacent said first opening and through which said chute extends, the other end being tapered to a smaller diameter and extending through said second opening in close fitting, rotatable relationship thereto; a fan in said drum adjacent said tapered end for recirculating gases in said drum; a shaft extending outwardly through said tapered end and being connected to said fan; means outside said drum for rotating said shaft; a stationary bung supported outside said drum and extending into said tapered end in close fitting relationship thereto, said bung rotatably supporting said shaft; a helical passage in said drum formed by a helical wall therein; and a cylindrical tube concentrically located in said drum, said tube having one end adjacent the central portion of said fan and the other end terminating a substantial distance toward said other end of said drum.

4. In a carburizing furnace having a substantially gastight chamber, a rotatable drum located in said chamber having an open end which extends outwardly through a Wall of said chamber, said drum containing a helical wall which forms an unobstructed helical channel, means for rotatably supporting said drum, and means including a reversible motor located outside said chamber for rotating said drum, a fan adapted to be located in said drum adjacent said end and whose plane of rotation is perpendicular to the axis of said drum; a shaft connecting said fan and extending outside said end; means for rotating said shaft; and control means for said motor for controlling the period of time in which the drum is rotated in opposite directions, the period in one direction being longer the opposite in said drum.

5. In a heat treating furnace having a chamber, a rotatable drum located in said chamber, one end of which extends outwardly fromthe chamber, said drum containing a helical wall which forms an unobstructed helical channel, means for rotatably supporting said drum in said chamber, and a reversible motor for rotating said drum, a fan adapted to be located in said drum adjacent said end and whose plane of rotation is perpendicular to the x axis of said drum; a shaft connecting said fan and extending outside said end; means forrotating said shaft; and :control meansfor reversing said motor at predetermined intervals.

6. In a carburizing furnace having a substantially gastight chamber, the combination of a rotatable drum located in said chamber having an open end which extends outwardly through a wall of said chamber, said drum containing a helical wall which forms an unobstructed helical channel, means for rotatably supporting said drum, means including a reversible motor for rotating said drum, and control means for controlling the period of time in which the drum is rotated in opposite directions, the period in one direction being longer than the opposite direction, a fan adapted to be located in said drum adjacent said open end and whose plane of rotation is perpendicular to the axis of said drum; a shaft connecting said fan and extending outside said end; means for supporting said shaft independently of said drum; and means outside said drum for rotating said shaft.

7. In a heat-treating furnace having a heating chamber and a rotatable drum located therein, said drum containing a helical wall in contact with the inner surface thereof and whose height is less than the radius of said drum, the improvement which comprises: a tube adapted to be axially located in said drum within the space defined by the'inner edge of the helical wall, and a fan within said drum and located at one end of said tube and aligned with said tube to recirculate gas through said tube and drum.

8. In a heat-treating furnace having a heating chamber and a rotatable drum located therein, said drum containing a helical wall in contact with the inner surface thereof and whose height is less than the radius of said drum, the improvement which comprises: a tube adapted to be axially located in said drum within the space defined by the inner edge of the helical wall, and a centrifugal fan whose central portion is adjacent one end of said tube whereby gas in said drum is circulated from said fan through the passage formed by said Wall and said tube and back through said tube to said fan.

9. In a heat-treating furnace having a heating chamber and a rotatable drum located therein, said drum containing a helical wall in contact with the inner surface thereof and whose height is less than the radius of said drum, the improvement which comprises: a tube adapted to be axially located in said drum within the space defined by the inner edge of the helical wall, said tube being substantially in contact with the inner edge throughout the length of said tube, whereby said tube substantially encloses a portion of the passage formed by the helical wall; and a fan within said drum and located at one end of said tube for creating a flow of gas through the enclosed passage.

10. In a heat-treating furnace having a heating chamber and a rotatable drum located therein, said drum containing a helical wall in contact with the inner surface thereof and whose height is less than the radius of said drum, said drum having an opening in one end through which work to be heat-treated is charged, the improvement which comprises: a tube adapted to be axially located in said drum within the space defined by the inner edge of the helical wall, said tube being substantially in contact with the inner edge throughout the length of said tube, whereby said tube substantially encloses a portion of the passage formed by theihelicalwall, a first'end of said tube terminating near the end of said drum'opposite the end containing the opening, and the other end of said tube terminating in said .drum toward the end containing the opening; and a fan Withinsaid drum located adjacent the first end of said tube for creating a flow of gasthrough the enclosed passage'from said fan toward the end of said drum containing the opening.

11. 'Apparatus for transporting work througha'heating chamber and uniformly subjecting said work to a gaseous atmosphere comprising: a substantially horizontal rotatable drum; means for admitting gas to said drum; 2.

' charge opening at one end of said drum for receiving work to be heat-treated; a discharge opening near the other end of said drum; a helical wall attached to the inner surface of said drum, said Wall forming a passage for carrying work from the charge opening to the discharge opening when the drum is rotated, the height of said wall being less than the radius of said drum whereby the inner edge of said wall defines a cylindrical space in the central portion of said drum; a cylindrical tube located in said space, one end of said tube terminating near the discharge end of said drum and the other end of said tube terminating in said space toward the charge end of said drum; and a centrifugal fan whose plane of rotation is substantially perpendicular to the axis of said drum and whose central portion is adjacent said one end of said tube whereby gas in said drum flows through said passage toward the charge end of said tube and returns through said tube when said fan is rotated.

12. Apparatus for transporting work through a heating chamber and uniformly subjecting said work to a [gaseous atmosphere comprising: a substantially horizontal rotatable drum; means for admitting gas to said drum; a charge opening at one end of said drum for receiving work to be heat-treated; a discharge opening near the other end of said drum; a helical wall attached to the inner surface of said drum, said wall forming a passage for carrying work from the charge opening to the discharge opening when the drum is rotated, the height of said wall being less than the radius of said drum whereby the inner edge of said wall defines a cylindrical space in the central portion of said drum; and a cylindrical tube located in said space, one end of said tube terminating near the discharge end of said drum and the other end of said tube terminating in said space toward the charge end of said drum.

13. A heat-treating furnace comprising: wall means defining a heating chamber having a charge opening; a drum located in said chamber and having one end adjacent said opening and containing a hole through which 'work is charged; means [for rotatably supporting said drum in said chamber; an axial flow fan in said drum; drive means located outside said chamber for rotating said fan independently of said drum; a first port in said one end communicating with said chamber; a second port in the other end adjacent said fan and communicating with said chamber, whereby gases are recirculated by said fan through said first port and back through said chamber to said second port. 7

14. Apparatus for transporting work through a heating chamber comprising: a substantially horizontal rotatable drum; a charge opening at one end of said drum for receiving work to be heat-treated; a discharge opening near the other end of said drum; a helical wall attached to the inner surface of said drum, said wall forming a passage for carrying the work from the charge opening to the discharge opening when the drum is rotated, the height of said wall being less than the radius of said drum whereby the inner edge of said wall defines a cylindrical space in the central portion of said drum; and a cylindrical tube located in said space, one end of said tube terminating near the discharge end of said drum and the other end of said tube terminating in the space toward the charge end of said drum.

15. An atmosphere furnace comprising: meansdefiningaheating chamber having first and second aligned openings and adi'scharge chute; a drumwhaving a longitudinal axis located in said chamber and aligned with said openings, one end of said drum defining a charge hole axially aligned 'with one of said openings for receiving Work to be charged into said drum; means for rotatably supporting said drum in said chamber; a fan axially centered within and adjacent the other end of said drum and supported through said other opening; drive means located outside said chamber for rotating said fan independently of said drum; a portion of said drum adjacent saidother end defining a discharge hole aligned with said discharge chute to diseharge' work thereinto as the drum rotates; and means for substantially continuously rotating said drum about its axis to advance work charged into the drum through said charge hole through the drum to the discharge hole.

References Cited in the file of this patent UNITED STATES PATENTS 1,358,313 Hero Nov. 9, 1920 1,824,747 DeCoriolis Sept. 22, 1931 2,624,561 Heyn Jan. 6, 1953 2,638,687 Vincent May 19, 1953 2,669,444 Beetz Feb. 16, 1954 Maslin May 23, 1954

Images