FLUID GUIDE FOR QUENCHING METAL WORKPIECES

Abstract

In a thermal or thermochemical treatment, metal workpieces together with a metal guide are arranged on a batch carrier. The present invention relates to a device for flow guidance for metallic pieces during such thermal or thermochemical treatment and quenching, as well as methods using the same. The fluid guide particularly ensures a uniform cooling of an inner and/or outer lateral surface of the workpieces during the quenching process.

Claims

1. A fluid guide for the quenching of metallic workpieces during thermal or thermochemical treatment, comprising a first and a second fluid baffle that are manufactured independently of one another from a material selected from graphite, carbon fiber reinforced carbon (CFRC), oxide ceramic matrix composite (OCMC) or some other ceramic material; wherein the first and the second fluid baffle are configured to delimit a substantially rotationally symmetrical flow channel with a clear width of 5 mm.

2. The fluid guide as claimed in claim 1, wherein a clear width of the flow channel is 50 mm.

3. The fluid guide as claimed in claim 1, wherein the first and the second fluid baffle are connected to one another by one or more struts.

4. The fluid guide as claimed in claim 1, wherein the first and/or the second fluid baffle have, independently of one another, one or more leadthroughs.

5. The fluid guide as claimed in claim 1, wherein the first and/or the second fluid baffle are equipped, independently of one another, with 3 to 40 support elements.

6. The fluid guide as claimed in claim 1, wherein said fluid guide comprises an annular or cylindrical pedestal (4) comprised of graphite, carbon fiber reinforced carbon (CFRC), oxide ceramic matrix composite (OCMC), or other ceramic material, for the mounting of a workpiece.

7. The fluid guide as claimed in claim 1, wherein said fluid guide comprises a third fluid baffle.

8. The fluid guide as claimed in claim 7, wherein the second fluid baffle and the third fluid baffle are configured to delimit a substantially rotationally symmetrical flow channel with a clear width of 5 mm and 50 mm.

9. A method for thermal or thermochemical treatment and quenching of metallic workpieces, comprising the steps: arranging 1 to 80 workpieces, in each case together with a fluid guide as claimed in claim 1, on a batch carrier; thermally or thermochemically treating the workpieces; loading the batch carrier with the workpieces and the fluid guides into a quenching device; and applying a flow of a cooling fluid to the workpieces, the workpieces being cooled from a temperature of 700 to 1220 C. to a temperature of 50 to 300 C.; wherein a flow is applied with a substantially rotationally symmetrical flow profile to each workpiece.

10. The method as claimed in claim 9, wherein the quenching device comprises a flow drive for generating a fluidic main flow, and a first and a second fluid baffle of the fluid guide are arranged between the flow drive and each workpiece in relation to the fluidic main flow, and the first and the second fluid baffle delimit in each case a substantially rotationally symmetrical flow channel.

11. The method as claimed in claim 9, wherein the flow profile in a radial direction has a local flow density maximum.

12. The method as claimed in claim 11, wherein a radius R.sub.M of a local flow density maximum of the flow profile and an inner radius R, of the workpieces satisfy the condition 0.8.Math.R.sub.iR.sub.M1.2.Math.R.sub.i.

13. The method as claimed in claim 11 wherein a radius R.sub.M of a local flow density maximum of the flow profile and an outer radius Ra of the workpieces satisfy the condition 0.8.Math.R.sub.aR.sub.M1.2.Math.R.sub.a.

14. The method as claimed in claim 10, wherein a third fluid baffle of the fluid guide is arranged between the flow drive and each workpiece in relation to the fluidic main flow, and the second fluid baffle and the third fluid baffle delimit in each case a substantially rotationally symmetrical flow channel.

15. The method as claimed in claim 9, wherein one or more workpieces are arranged in each case on a ring-shaped or cylindrical pedestal.

Description

[0144] The invention will be discussed in more detail below on the basis of figures and examples. In the figures:

[0145] FIG. 1 shows a perspective sectional view of a fluid guide for a toothed ring with internal toothing;

[0146] FIGS. 2-3 show perspective sectional views of fluid guides for toothed rings or toothed gears with internal or external toothing;

[0147] FIG. 4 shows a batch carrier with four toothed rings, each with a fluid guide;

[0148] FIG. 5 shows a sectional view of a flow channel delimited by a fluid guide;

[0149] FIGS. 6 and 7 show CFD flow profiles of known fluid guides; and

[0150] FIGS. 8 and 9 show CFD flow profiles of a fluid guide according to the invention.

[0151] FIG. 1 shows a perspective sectional view of a workpiece or toothed ring 6 with an internal toothing, which is arranged together with a fluid guide 1 according to the invention on a lattice-like batch carrier 7. The fluid guide 1 comprises a first or inner fluid baffle 2A, a second or outer fluid baffle 3, and an annular pedestal 4, on which the toothed ring 6 is mounted. The first and the second fluid baffle (2A, 3) are configured and arranged relative to one another such that they delimit a substantially rotationally symmetrical flow channel with a clear width of 5 mm, and the internal toothing of the toothed ring 6 projects into the flow channel 5. In a further expedient embodiment of the invention, by contrast to the illustration of FIG. 1, the first fluid baffle is configured as a hollow dome. FIG. 1 furthermore shows three axes (1,0,0), (0,1,0) and (0,0,1) of a Cartesian coordinate system, and an axis of rotation 100 of the fluid guide 1, which axis of rotation is coaxial with respect to the axis (0,0,1). In accordance with normal convention, the axis (0,0,1) represents the vertical direction.

[0152] The illustration of FIG. 1 corresponds to the test arrangement shown in FIG. 4, in which four toothed rings, each together with a fluid guide comprising two fluid baffles and one support, are arranged on a lattice-like batch carrier.

[0153] FIG. 2 shows a perspective sectional view of a workpiece or toothed ring 6 with an external toothing, which is arranged together with a fluid guide 1 according to the invention on a lattice-like batch carrier 7. The fluid guide 1 comprises a first or inner fluid baffle 2B, a second or outer fluid baffle 3, and an annular pedestal 4, on which the toothed ring 6 is mounted. The first and the second fluid baffle (2A, 3) are configured and arranged relative to one another such that they delimit a substantially rotationally symmetrical flow channel 5 with a clear width of 5 mm, and the external toothing of the toothed ring 6 projects into the flow channel 5. In a further expedient embodiment of the invention, by contrast to the illustration of FIG. 2, the first fluid baffle is configured as a hollow dome. FIG. 2 furthermore shows three axes (1,0,0), (0,1,0) and (0,0,1) of a Cartesian coordinate system, and an axis of rotation 100 of the fluid guide 1, which axis of rotation is coaxial with respect to the axis (0,0,1).

[0154] In accordance with normal convention, the axis (0,0,1) represents the vertical direction.

[0155] FIG. 3 shows a further embodiment of the fluid guide 1 according to the invention with an annular first or inner fluid baffle 2C. The other reference designations in FIG. 3 have the same meaning as discussed above in conjunction with FIG. 2.

[0156] In an expedient embodiment that is not shown in FIGS. 1-3, the fluid guide according to the invention comprises a third fluid baffle. The third fluid baffle is configured such that, when arranged centrally relative to the second fluid baffle, said third fluid baffle delimits a second, outer, substantially rotationally symmetrical flow channel. Said outer flow channel causes a uniform and preferably accelerated flow of cooling fluid over an outer surface of the workpiece. Uniform heat transfer at the outer surface of the workpiece is thus achieved.

[0157] According to the invention, one or more workpieces 6, each together with a fluid guide 1, is or are arranged on the batch carrier 7, thermally or thermochemically treated, and subsequently quenched. The quenching is preferably performed with a cooling gas that is composed primarily of nitrogen (N.sub.2) or of helium (He). Argon (Ar), hydrogen (H.sub.2) and air may likewise be used as cooling gas. During the quenching, the cooling gas is accelerated by means of a flow drive configured as a high-pressure fan, and a flow is applied to the workpieces 6 and fluid guides 1 substantially vertically downward from above, or in the direction (0,0, 1). For this purpose, the flow drive may be arranged, relative to the charge carrier, above or below or in a correspondingly configured fluidic recirculation loop.

[0158] FIG. 5 shows a schematic view of a partial frontal section of a fluid guide of the type illustrated in FIG. 1, with first and second fluid baffles 2A and 3 and a workpiece 6. The frontal section plane is spanned by the coordinate axes or base vectors (0,1,0) and (0,0,1). The axis of rotation of the fluid guide and of the first and second fluid baffles 2A and 3 runs coaxially with respect to the axis (0,0,1). A flow channel 5 is delimited by surfaces or surface regions of the first and second fluid baffles 2A and 3, in which radial components of respective surface normal vectors {right arrow over (s)}.sub.A, {right arrow over (s)}.sub.B and {right arrow over (t)}.sub.A, {right arrow over (t)}.sub.B are positive and negative respectively. For comparison, a further surface normal vector {right arrow over (t)}.sub.C for the second fluid baffle 3 is shown, which has a positive radial component and the associated surface region of which, in the context of the invention, is not assigned to the flow channel 5 and is situated outside the flow channel 5. In the frontal sectional view of FIG. 5, the vector (0,0,1) represents the radial direction in each case, and, in order to provide a simplified view, is illustrated for each surface normal vector {right arrow over (s)}.sub.A, {right arrow over (s)}.sub.B and {right arrow over (t)}.sub.A, {right arrow over (t)}.sub.B, {right arrow over (t)}.sub.C. In the frontal section plane of FIG. 5, the flow channel 5 is defined by the following mathematical relationships:

[00003]${\stackrel{.fwdarw.}{s}}_i.Math.\left(\begin{array}{c}0\\ 1\\ 0\end{array}\right)0,i=A,B,.Math.;{\stackrel{.fwdarw.}{t}}_j.Math.\left(\begin{array}{c}0\\ 1\\ 0\end{array}\right)0,j=A,B,.Math.$

[0159] Accordingly, the flow channel 5 is delimited in the direction of the coordinate axis (0,0,1) by the two dashed lines 110 and 120, the spacing h or (0,0,h) of which indicates the height of the flow channel 5.

[0160] FIGS. 6 and 7 show a radial sectional view and a plan view of the flow velocity field during quenching with nitrogen using a fluid guide known from WO 2019/149676 A1. The flow velocity field of FIGS. 6 and 7 was calculated using computational fluid dynamics (CFD) software, with realistic boundary conditions being specified. Both FIG. 6 and FIG. 7 show highly pronounced inhomogeneities in the flow, which are evidently attributable to flow separation and a pronounced recirculation region. The flow inhomogeneities cause intense fluctuations in the heat transfer between the workpiece and quenching gas and, in conjunction with this, spatially non-uniform cooling with corresponding thermal distortion.

[0161] FIGS. 8 and 9 show a radial sectional view and a plan view of the flow velocity field during quenching with nitrogen using a fluid guide according to the invention. The specifications or boundary conditions for the calculation of the flow velocity field of FIGS. 8 and 9 are identical to those of FIGS. 6 and 7. It is readily apparent from FIGS. 8 and 9 that the flow field exhibits no flow separation at the inner and outer lateral surfaces of the workpiece, and in particular, the formation of a circulation region is suppressed. The flow guidance at the surface of the workpiece is greatly homogenized. Furthermore, the local flow velocity and thus the heat transfer are increased. Even steels of relatively poor alloy content can thus be successfully treated.

Comparative Example

[0162] Four toothed rings composed of steel and with an internal toothing (outer diameter 450 mm, inner diameter 350 mm, height 40 mm) were provided. On each of the toothed rings, the roundness, that is to say the circular radial run-out tolerance of the internal toothing, was measured in accordance with DIN EN ISO 12181-1:2011-07. The measurements were performed on a Gleason 300 GMS P toothed-gear inspection system.

[0163] After the measurement, the four toothed rings were arranged, each with a known fluid guide, adjacent to one another on a lattice-like batch carrier and, in a SyncroTherm system from the company ALD, carburized at 950 C. at a low pressure of approximately 15 mbar and subsequently quenched using compressed nitrogen. The duration of the thermochemical treatment, with the method steps of heating, carburizing, diffusion and quenching, was 2 hours. The cooling rate during the quenching corresponded to approximately 7.7 Kelvin per second(K/s). The fluid guide known from WO 2019/149676 A1 comprises a support and a cover which are each configured as cylindrical rings with an outer and an inner diameter of 450 mm and 370 mm respectively and a height of 50 mm. Aside from a dome-shaped inner flow baffle and a rounded contour of the cover, the known fluid guide is of similar design to the fluid guide according to the invention shown in FIG. 4.

[0164] After the thermochemical treatment, the roundness of the toothed rings was measured again, and the minimum, average and maximum distortion were calculated for each toothed ring on the basis of the ratio of the roundness values before and after the thermochemical treatment.

[0165] Here, the following values were obtained for the roundness distortion:

[0166] Minimum distortion: 6%

[0167] Average distortion: 100%

[0168] Maximum distortion: 200%

Example

[0169] Analogously to the comparative example above, six toothed rings of the same type were measured and were each, together with a fluid guide according to the invention, carburized, quenched and subsequently measured again. The first batch with four toothed rings and four fluid guides according to the invention is shown in FIG. 4.

[0170] The following values were obtained for the roundness distortion:

[0171] Minimum distortion: 10%

[0172] Average distortion: 44%

[0173] Maximum distortion: 89%

[0174] It is apparent from the examples that the roundness distortion can be considerably reduced with the aid of the fluid guide according to the invention.

LIST OF REFERENCE DESIGNATIONS

[0175] 1 Fluid guide

[0176] 2A First/inner fluid baffle (first embodiment)

[0177] 2B First/inner fluid baffle (second embodiment)

[0178] 2C First/inner fluid baffle (third embodiment)

[0179] 3 Second/outer fluid baffle

[0180] 4 Pedestal (support)

[0181] 5 Flow channel

[0182] 6 Workpiece

[0183] 7 Batch carrier

[0184] 100 Axis of rotation

[0185] 110 Lower boundary of the flow channel

[0186] 120 Upper boundary of the flow channel

[0187] {right arrow over (s)}.sub.A Surface normal vector of the first/inner fluid baffle

[0188] {right arrow over (s)}.sub.B Surface normal vector of the first/inner fluid baffle

[0189] {right arrow over (t)}.sub.A Surface normal vector of the second/outer fluid baffle

[0190] {right arrow over (t)}.sub.B Surface normal vector of the second/outer fluid baffle

[0191] {right arrow over (t)}.sub.C Surface normal vector of the second/outer fluid baffle

[0192] h Height of the flow channel