Device for supporting and guiding a flow for metallic workpieces, and method for thermochemical treatment

Abstract

The present invention relates to devices used during the thermomechanical treatment of workpieces. During thermochemical treatment, metallic workpieces are mounted on and/or shielded by a high-temperature-resistant device configured specifically for this purpose in order to reduce dimensional and shape changes or warping. The inventive devices provide support and flow guiding for metallic workpieces during thermochemical treatment, and include a plate or a ring having a first and a second face, in which the second face is equipped with three or more support elements and the support elements are bound to a support plane.

Claims

1. A device for support and flow guiding for metallic workpieces in thermochemical treatment comprising a plate or a ring having a first and second face, wherein the second face is equipped with three or more support elements and the support elements are bound a support plane.

2. The device as claimed in claim 1, wherein said device comprises N support elements with 10N200.

3. The device as claimed in claim 1, wherein the plate or the ring has a cross-sectional area Q, each support element has a support area, and the sum total of the support areas of all support elements is 10% to 50% of the cross-sectional area Q.

4. The device as claimed in claim 1, wherein the plate or the ring and the support elements are in one-piece form.

5. The device as claimed in claim 4, wherein the support elements are in the form of lands.

6. The device as claimed in claim 1, wherein the second face is equipped with receptacles for the support elements.

7. The device as claimed in claim 6, wherein the receptacles are in the form of grooves.

8. The device as claimed in claim 1, wherein the support elements are in the form of round bars.

9. The device as claimed in claim 1, wherein the plate or the ring is made from graphite or carbon fiber-reinforced carbon (CFRC).

10. The device as claimed in claim 1, wherein the support elements are made from graphite, carbon fiber-reinforced carbon (CFRC), oxide-ceramic fiber matrix composite (OCMC) or another ceramic material.

11. The device as claimed in claim 1, wherein a surface of the support elements is equipped with particles of a ceramic material and the particles have an equivalent diameter in the range from 5 to 1000 nm.

12. A method of thermochemical treatment of one, two or more metallic workpieces comprising disposing a device as claimed in claim 1 on a first and/or second side of each workpiece.

13. The method as claimed in claim 12, wherein the workpieces have a cross section having an envelope circle with diameter D.sub.k, the device comprises a plate or a ring, the plate or the ring has a cross section having an envelope circle with diameter D.sub.a, and 0.5.Math.D.sub.kD.sub.a1.2.Math.D.sub.k.

14. The method as claimed in claim 12, further comprising carburizing one, two or more workpieces together in a furnace chamber, wherein one workpiece in each case is disposed between an upper and lower wall of the heating chamber in a vertical direction.

15. The method as claimed in claim 12, further comprising carbonitriding one, two or more workpieces together in a furnace chamber, wherein one workpiece in each case is disposed between an upper and lower wall of the heating chamber in a vertical direction.

16. The method as claimed in claim 12, further comprising quenching one, two or more workpieces together in a quench chamber, wherein one workpiece in each case is disposed between an upper and lower wall of the quench chamber in a vertical direction.

Description

[0169] The invention is elucidated in detail hereinafter with reference to figures and examples. Parts that are identical, similar and/or have the same function are given the same reference numerals. The figures show:

[0170] FIGS. 1-3 schematic top views and section views of devices of the invention;

[0171] FIG. 4 a perspective view of a device of the invention;

[0172] FIG. 5 a gearwheel borne in accordance with the invention;

[0173] FIG. 6 a gearwheel with a first and second device;

[0174] FIGS. 7-8 support elements arranged in a hexagonal pattern;

[0175] FIG. 9 a device with cylindrical support elements;

[0176] FIGS. 10-11 section views of support elements borne in recesses.

[0177] FIG. 1 shows a schematic top view and a section view of a device 1 of the invention with a ring 2 having a first face 2A and a second face 2B. Circular support elements 3 are disposed on the second face 2B. Every two support elements 3 are separated from one another by a circular recess or groove 5. The first face 2A is bounded by a flat surface or outer surface. The support elements 3 are set up such that at least three points on the surface of each support element 3 are arranged at a perpendicular distance T from the outer surface of the first face 2A, and a perpendicular distance of each point on the surface of the support elements 3 from the outer surface of the first face 2A is not more than T. The support elements 3 bound a support plane 4.

[0178] The ring 2 in the device 1 shown in FIG. 1 essentially has the shape of a circular cylinder having an outer and inner diameter D.sub.a and D.sub.i respectively. The device 1 shown in FIG. 1 is in one-piece form and made from a material of high thermal stability, for example graphite or carbon fiber-reinforced carbon (CFRC).

[0179] Expediently, the device 1 is manufactured by material-removing processing, especially by means of turning or circular milling and optionally linear milling from plates or cylindrical disks of graphite or carbon fiber-reinforced carbon (CFRC).

[0180] FIG. 2 shows a schematic top view and a section view of a further device 1 of the invention with a plate 2. Apart from the plate 2, the device 1 shown in FIG. 2 is of the same design as that in FIG. 1.

[0181] FIG. 3 shows a further device 1 of the invention with a ring 2 and support elements 3 that are separated from one another by circular recesses 5 and radial recesses 6.

[0182] FIG. 4 shows a schematic perspective view of a device 1 with a circular ring 2 having an outer diameter D.sub.a, an inner diameter D.sub.i, and support elements 3 having support surfaces 3A, wherein the support elements 3 are separated from one another by circular and radial grooves 5 and 6 respectively.

[0183] FIG. 5 shows a perspective full view and section view of a gearwheel 10 with a gear ring 11 and a flange 12, borne on a device 1. The device 1 shown in FIG. 5 is of the same construction as that in FIG. 4. The outside diameter D.sub.a of the device 1 is smaller than an external diameter D.sub.2 of the flange 12. The external diameter of the flange 12 is less than/equal to an internal diameter of the gear ring 11. Only a face of the flange 12 is supported by support elements 3 of the device 1. By contrast, the support elements 3 are not in contact with the gear ring 11. Furthermore, FIG. 5 shows a carrier 20 in grid form, on which the device 1 with the gearwheel 10 is disposed. The carrier 20 is typically made from graphite or carbon fiber-reinforced carbon (CFRC).

[0184] A thickness or distance T between an outer surface of the first face facing the carrier 20 and a support plane of the device 1 facing the gearwheel 10 is greater than a distance AH between lower faces of the gear ring 11 and the flange 12. This ensures that the gearwheel 10 does not come into contact with the carrier 20.

[0185] FIG. 6 shows a perspective view of a gearwheel 10 with a first device 1 and a second device 1. For illustration purposesin the manner of an exploded diagramthe second device 1 is shown in an opened position relative to the gearwheel 10. For the thermochemical treatment, a lower side of the gearwheel 10 is borne on the first device 1, and the second device 1 is placed on an upper side of the gearwheel 10. This configuration, in which a gearwheel 10 is disposed between two devices 1 and 1, is also referred to in the present invention as sandwich arrangement. The devices (1, 1) shown in FIG. 6 are of the same design and each comprise a ring having a hexagonal outer contour and a multitude of hexagonally configured support elements 3, each of which has a support surface 3A. The support surfaces 3A of the device 1 and 1 respectively bound a support plane on which the gearwheel 10 lies (device 1), and a support plane that rests on the upper side of the gearwheel 10 (device 1).

[0186] FIG. 7 shows a schematic top view of support elements 3 in the form of equilateral hexagons, with support surfaces 3A of a device (1, 1) of the invention, of the kind shown in FIG. 6. The support elements 3 are arranged in a two-dimensionally periodic pattern with hexagonal symmetry. The arrangement of the support elements 3 in a two-dimensional periodic pattern enables two-dimensionally homogeneous support of workpieces and virtually uniform flow of process gas and cooling fluid over the workpieces in the course of quenching. The repeat units (or Voronoi zones) of the hexagonal periodic pattern are shown in FIG. 7 by dashed lines. Each of the hexagonal support surfaces 3A is rotated by 30 degrees relative to the repeat unit of the hexagonal periodic pattern. This configuration enables simple and inexpensive production of the device of the invention from solid plates by means of material-removing processing. More particularly, the device can be manufactured by means of milling from a solid plate of graphite or carbon fiber-reinforced carbon (CFRC) (see FIG. 8).

[0187] FIG. 8 shows a top view, analogous to FIG. 7, of support elements 3 in hexagonal form that are arranged in a two-dimensionally periodic pattern having hexagonal symmetry. The support elements 3 are separated from one another by recesses 30 or grooves 30. Each of the recesses 30 runs along a center axis 30A. Each of the center axes 30A belongs to one of three groups of equidistant parallel straight lines, with the straight lines of two different groups being rotated relative to one another by an angle of 120 or 240 degrees.

[0188] FIG. 9 shows schematic perspective views of a device 1 of the invention in a simple view and in the manner of an exploded diagram. The device 1 comprises a ring 2 with receptacles or mounts 7 for cylindrical support elements 3. The receptacles or mounts 7 are in the form of radially oriented grooves with trapezoidal cross section. In an alternative embodiment of the device 1, not shown in FIG. 9, a longitudinal axis of the receptacles or mounts 7 is rotated by an angle of up to 45 degrees in a plane parallel to the outer surface of the ring 2 with respect to the respective radial direction. Preferably, the cylindrical support elements 3 are made from a material of high thermal stability, such as graphite, carbon fiber-reinforced carbon (CFRC), oxide-ceramic fiber matrix composite (OCMC) or another ceramic material.

[0189] FIG. 10 shows a section view of a device of the invention with a ring 2 having a receptacle 7 for a cylindrical support element 3 with outside diameter D.sub.s. The receptacle 7 takes the form of a groove having a cross section in the form of an equilateral triangle. A base side of the equilateral triangle has a length c, and a vertex angle opposite the base side is in the range from 60 to 120 (60120). The receptacle 7 is configured in such a way that a support element 3 borne in the receptacle 7 projects beyond a face 2 of the ring 2. Accordingly, the length c satisfies the relation D.sub.s.Math.cos(/2)<c<D.sub.s.Math.cot(45/4)

[0190] FIG. 11 shows a section view of a further device of the invention with a ring 2 having a receptacle 7 for a cylindrical support element 3 with outside diameter Ds. The receptacle 7 takes the form of a groove having a cross section in the form of a symmetric trapezium. A long and short base side of the symmetric trapezium have a length a and b respectively. An angle enclosed by the trapezium limbs is in the range from 60 to 120 (60120). The receptacle 7 is configured such that a support element 3 borne in the receptacle 7 projects beyond a face 2 of the ring 2. Accordingly, the lengths a and b satisfy the relations

D.sub.a.Math.cos(/2)<a<D.sub.s.Math.cot(454)

and

0bD.sub.a.Math.cot(45+/4)

respectively.

[0191] The invention illustrated and elucidated in detail by working examples in the present description is not limited by the examples disclosed. The person skilled in the art is able to infer a multitude of additional variations from the description without leaving the scope of protection of the invention. Embodiments disclosed by way of example in the description represent merely examples that should in no way be regarded as a limitation of the scope of protection, possible uses or the configuration of the invention. Instead, the description and the figures put the person skilled in the art in a position to rework the examples. At the same time, the person skilled in the art, with knowledge of the concept of the invention disclosed, is able to undertake various changes with regard to function, configuration and arrangement of individual elements of the examples without leaving the scope of protection defined by the claims and their legal equivalents disclosed in the description.

EXAMPLE 1

[0192] 72 untreated transmission gears made of steel and having a configuration of the kind shown in FIG. 5, with a gear ring having tip circle diameter 378 mm, a flange and an inner hole were provided. On each of the transmission gears, according to DIN EN ISO 12181-1:2011-07 and DIN EN ISO 12181-2:2011-07, concentric runout (i.e. circular radial runout tolerance) at the tip circle diameter (or the outer tooth flanks) and planar runout (i.e. circular axial runout tolerance) at a face of the gear ring were measured. The measurements were performed on a Gleason 300 GMS P gearwheel inspection system.

[0193] After the measurement, the transmission gears were carburized in an ALD ModulTherm system at 950 C. under low pressure at about 15 mbar and then quenched by means of compressed nitrogen. The duration of the thermochemical treatment with the process steps of heating, carburizing, diffusion and quenching was 2 hours. 36 of the 72 transmission gears were borne on devices of the invention over the entire process duration. As shown in FIG. 5, the flange of each of the 36 transmission gears was supported by means of a graphite ring equipped with circular and radial support lands, with the entire gear ring projecting in a free-floating manner above the graphite ring in radial direction.

[0194] The other 36 transmission gears, in a conventional manner, were placed directly on a carrier in a lattice form, made of carbon fiber-reinforced carbon (CFRC).

[0195] After the thermochemical treatment, concentric runout and planar runout of each of the 72 transmission gears were measured again. The averages of the measurement results after the thermochemical treatment are shown in table 1.

TABLE-US-00001 TABLE 1 Average after thermochemical treatment Concentric Planar runout runout Without support (36 parts) 62 m 71 m With support (36 parts) 46 m 40 m

[0196] It is apparent from table 1 that, with the inventive support, the radial and axial warpage of the 36 transmission gears supported in accordance with the invention and the associated increase in concentric runout and planar runout as a result of the thermochemical treatment is respectively 26% and 44% lower compared to the 36 transmission gears placed directly on the support.

EXAMPLE 2

[0197] 214 untreated transmission gears made of steel and having a configuration of the kind shown in FIG. 5, with a gear ring having tip circle diameter 378 mm, a flange and an inner hole were provided. On each of the transmission gears, according to DIN EN ISO 12181-1:2011-07 and DIN EN ISO 12181-2:2011-07, concentric runout (i.e. circular radial runout tolerance) at the tip circle diameter (or the outer tooth flanks) and planar runout (i.e. circular axial runout tolerance) at a face of the gear ring were measured. The measurements were performed on a Gleason 300 GMS P gearwheel inspection system.

[0198] After the measurement, the transmission gears were divided into two production batches having 108 and 106 transmission gears and in each case carburized in an ALD ModulTherm system at 950 C. under low pressure at about 15 mbar and then quenched by means of compressed nitrogen. The duration of the thermochemical treatment with the process steps of heating, carburizing, diffusion and quenching was 2 hours.

[0199] Table 2 shows the division of the transmission gears between the first and second production batches, and the configuration or use of the device of the invention for support and/or shielding of the transmission gears.

TABLE-US-00002 TABLE 2 Device Production batch 1 Production batch 2 None 54 54 Below 10 10 Above 18 18 Above & below 25 25 (sandwich)

[0200] 108 transmission gears, in a conventional manner, were placed directly on a carrier in lattice form, made of carbon fiber-reinforced carbon (CFRC).

[0201] In the case of 20 transmission gears, as shown in FIG. 5, the flange was supported by a graphite ring having circular and radial support lands, with the entire gear ring projecting in a free-floating manner above the graphite ring in radial direction.

[0202] 36 transmission gears were placed directly on a carrier in grid form and a graphite ring was disposed on the top side of each transmission gear in such a way that the support lands of the graphite ring face downward, i.e. toward the transmission gear.

[0203] In the case of 50 transmission gears, two graphite rings were used in each case in a sandwich arrangement, with the bottom side of the flange of a transmission gear resting on a first graphite ring, and a second graphite ring being disposed on the top side of the flange.

[0204] After the thermochemical treatment, concentric runout and planar runout were measured again on each of the 214 transmission gears, and the respective starting value was subtracted from the measurement result obtained. The increase in concentric runout and planar runout caused by the thermochemical treatment is shown in table 3.

TABLE-US-00003 TABLE 3 Concentric Planar Device Increase runout runout None Average 42 m 55 m Maximum 194 m 125 m Below Average 43 m 30 m Maximum 75 m 51 m Above Average 27 m 46 m Maximum 91 m 108 m Above & below Average 32 m 28 m (sandwich) Maximum 80 m 85 m

LIST OF REFERENCE NUMERALS

[0205] 1, 1 . . . device for support or shielding

[0206] 2 plate or ring

[0207] 2 . . . face of the plate or ring 2

[0208] 2A . . . first face/outer surface of the device 1, 1

[0209] 2B . . . second face of the device 1, 1

[0210] 3 . . . support element

[0211] 3A . . . support surface of a support element 3

[0212] 4 . . . support plane

[0213] 5 . . . circular recess/groove

[0214] 6 . . . radial recess/groove

[0215] 7 . . . receptacle for support element 3

[0216] 10 . . . gearwheel

[0217] 11 . . . gear ring

[0218] 12 . . . flange

[0219] 20 . . . carrier

[0220] 30 . . . recess/groove

[0221] 30A . . . groove axis/cutting axis/milling axis

[0222] T . . . distance between first face 2A and support plane 4

[0223] D.sub.i . . . internal diameter of the ring 2

[0224] D.sub.a . . . diameter of the envelope circle of the plate or ring 2

[0225] D.sub.2 . . . outer diameter of the flange 12

[0226] H . . . difference in height between gear ring 11 and flange 12

[0227] D.sub.s . . . diameter of cylindrical support elements 3

[0228] c . . . base side of a triangular cross section of a receptacle 7

[0229] Y . . . vertex angle of a triangular cross section of a receptacle 7

[0230] a . . . long base side of a trapezoidal cross section of a receptacle 7

[0231] b . . . short base side of a trapezoidal cross section of a receptacle 7

[0232] . . . vertex angle of a trapezoidal cross section of a receptacle 7