US20090000710A1

US20090000710A1 - Quenching process utilizing compressed air

Info

Publication number: US20090000710A1
Application number: US11/823,649
Authority: US
Inventors: Richard A. Ford; Robbie L. Greenway; Steven R. Thompson
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2007-06-28
Filing date: 2007-06-28
Publication date: 2009-01-01

Abstract

A method for quenching a metal workpiece having an internal passage with at least one open end, wherein the workpiece has a plurality of bore holes extending between the internal passage and the external surface, the method including the steps of pressurizing the internal passage with a pressurized fluid source to prevent quenchant from entering the internal passage and the plurality of bore holes; flowing quenchant across the external surface to cool and harden the workpiece.

Description

TECHNICAL FIELD

A method generally related to heat treatment processes, and more specifically to an improved method for the heat treatment of metal parts having internal passages, utilizing compressed air to prevent quenchant from entering the internal passages of the heat-treated part.

BACKGROUND

It is common practice, for example in the metallurgical art, to heat treat and then cool or quench a workpiece or part for one or more of a variety of reasons. This heat treatment and cooling process may be used to develop desired microstructure and mechanical properties in the metal part, with the typical desire to avoid physical defects such as cracking, distortion and residual stresses which impact such characteristics as machinability during manufacture, assembly, or repair, and fatigue life of the part.
Within the context of this disclosure, heat treatment should be understood to mean any technique for the treatment of a ferrous (iron) substrate material such as steel, or any other metal part which involves cooling at least part of the said substrate material, especially, tempering, nitriding, carburizing, surface coating, plasma spraying, oxycutting, laser cutting, HVOF (high-velocity oxyfuel) spraying, flame spraying, etc. These various heat-treatment techniques are known and widely used in the industrial field.
Often the heat-treated metal parts are elongated and have one or more internal passages such as a shaft, cylinder tube, or the like, for material or fluid flow. The internal passages may run the full length or width of the part or not, and, they may intersect or cross one another.
A variety of methods and apparatuses for cooling certain parts and workpieces have been reported. It should be appreciated that the cooling or quenching treatment utilized in the present disclosure can be any treatment that serves to increase the hardness of the treated metal of a work piece with an internal passage.
Quenching of a workpiece with internal passages renders several issues that can lead to poor workpiece quality, increased waste and enormous production costs. Because the quenchant is allowed to contact both the internal passages and the external surface, rapid cooling occurs. The internal passages allow quenchant to flow through and between these passages, which causes rapid cooling as the quenchant is in direct contact with the internal passages and external surface. The rapid cooling can cause a build up of stress cracks in the workpiece.
The internal passages (which may also include cross holes, boreholes or oil holes or other secondary external surface passages, of varying diameter) can also harden out during quenching. Further, on a workpiece with more than one internal passage where the passages intersect each other, the likelihood of the aforementioned issue is elevated. Yet further, where the internal passages on the workpiece intersect and meet at a 90-degree angle, stress concentrators have been found at the intersection of those internal passages where quenchant remains following the quenching process, leading to an ever-increased concentration of stress, and ultimately stress cracking.
In the case of a workpiece with internal passages intersecting, the area of highest stress would be at the point creating a sharp angle (i.e., 90 degrees). This area of high stress build up is where cracks may form during and following quenching. Normally, either a radius or a chamfer would be used on an external surface to prevent the creation of a stress concentrator. However, due to the internal location of the intersecting passages, it is not feasible to create a chamfer or a radius in order to decrease the build up of quenchant, and therefore metallurgical stress, that can be developed at the intersection.
In the present disclosure, stress build up caused by fast quenching and quenchant remaining in the internal passages and boreholes was prevented. This was achieved by advancing compressed gas through one end of the workpiece and out through the cross or bore holes. By keeping quenchant out of the internal passage and boreholes, it allowed the internal passages of the workpiece to cool at a much slower rate. The slower cooling rate keeps stress from building up generally, especially in this area of concern, and the cracks that were forming upon quenching are prevented.
In the past, in order to overcome this problem of stress build up and to better control the cooling rate of the internal passages in the workpieces, operators attempted to prevent quenchant from entering the passages and boreholes, by utilizing appropriately sized bolts manually placed in the boreholes. Additionally, steel wool has been used to plug or fill the holes and passages.
These previously known passage-plugging techniques present several problems, including steel wool fusing to the part and being difficult to remove, or actually preventing proper hardening of the external surface due to the density of the plug material or the contact of the manually placed bolt heads to the external surface.
Further, in a patent to White et al. (U.S. Pat. No. 6,216,710) a method of removing liquid from pores contained in a permeable metal part is disclosed. A cleaning fluid is injected into the interior chamber of the part, and then the interior chamber is pressurized using a compressed gas causing the cleaning fluid to permeate through the pores to the exterior surface. The White et al. patent also teaches removing residual quench oil from a powered metal product after it has been quenched. However, the prior art process does not affect the quench rate at all and is not even used in the traditional heat treatment related quenching process. Also, it is only applicable to porous material such as a powder metal product.
The present disclosure is directed to overcoming one or more of the problems set forth above.

SUMMARY

The present disclosure, in one form, provides a method for quenching a metal workpiece having an internal passage with at least one open end. The workpiece has a plurality of boreholes extending between the internal passage and an external surface. The method includes the steps of pressurizing the internal passage with a pressurized fluid source to prevent quenchant from entering the internal passage and the plurality of boreholes and flowing quenchant across the external surface to cool and harden the workpiece.
Other advantages and novel features of the present disclosure will become apparent from the following detailed description of the disclosure when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of an exemplary workpiece for use in the present disclosure.

FIG. 2 is an illustrative side view of an embodiment of the present disclosure.

FIG. 3 is an enlarged partial cross sectional view, partial schematic view of an embodiment of the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for the purpose of illustrating the preferred embodiments of the disclosure only, and not for the purpose of limiting the same, FIG. 1 illustrates a metal workpiece 10 having an internal passage 12 and a plurality of boreholes 14. The workpiece 10 has at least one open end 18. The boreholes 14 are secondary internal passages that may run perpendicular to the direction of the internal passage 12, thereby creating an intersection 16, where the internal passage 12 and the boreholes 14 meet. The intersection may be at a 90-degree angle, and the diameters of the internal passage 12 and the boreholes 14 may be different. The workpiece 10 may be of an elongated shape, and made from a ferrous material or the like. The workpiece 10 is heat treated prior to the quenching process. The heat treatment, as would be known by those skilled in the art, may be of any means including but not limited to carburizing or hardening, conducted by furnace heating, induction heating, casting or forging.
FIG. 2 is useful in explaining the construction and operation of the quenching station 30. A mechanical mechanism (not shown) such as a conveyor or pulley system, or the like, operates to move the workpiece 10 from a heat treatment area to the quenching station 30.
In accordance with one embodiment of the present disclosure, the workpiece 10 is lowered into or immediately above a quench trough 40. The workpiece 10 may be supported and contained at selected positions by a plurality of locators 42 within or on (as seen in FIG. 3) the quench trough 40. The locators 42 may also provide opposed restraint against transverse deflection (not shown). The quench trough 40 is sufficiently sized to collect the volume of quenching liquid or quenchant 60 needed to cool each workpiece 10 or batch of workpieces, as may be seen in a large production facility. While the aforementioned quenching process is discussed as completed via batch style processing, it will be appreciated that the method may be appropriately arranged for continuous processing.
A storage tank 50, independent of quench trough 40, and having a quenchant containing bottom 52 and sides 54 is arranged vertically above and immediately adjacent to or over the quench trough 40. The quenchant 60 is contained within storage tank 50. The storage tank 50 may have a pipe 64 and be optionally provided with a valve 66, extending from one of the sides 54 adjacent the bottom 52 thereof, immediately over the quench trough 40. Storage tank 50 may have an inlet opening 62 which may be connected, by means of a pipe 65 having a pump 68 integral therein, to an outlet 70 of the quench trough 40. The pump 68 is operable to draw quenchant 60 out of the trough 40. Optionally, the quenchant 60 may be cooled through a heat exchanger for example (not shown) after being used for quenching, as the quenchant 60 may absorb heat from the workpiece 10.
As seen in FIG. 2 and FIG. 3, with the workpiece 10 contained and supported within the quench trough 40, at least one adapter 22 may be connected to at least one open end 18 of the workpiece 10. At least one adapter 22 may then be coupled 24 into fluid communication with a pressurized fluid source 26 via conduit 24. The pressurized fluid source may optionally be any compressed gas suitable for cooling a metal workpiece 10.
The pressurized fluid source 26 may be pneumatically operated (not shown). As would be known, the source may include a compressor to advance the compressed gas to a pneumatic line, and a pneumatic valve for activation and deactivation. When activated, the source 26 advances the pressurized fluid 26 through the adapter 22, into the internal passage 12 of the workpiece 10. The pressurized fluid 26 exits through the plurality of bore holes 14.
After pressurized fluid is advancing through workpiece 10, valve 66 is opened allowing quenchant 60 to rapidly flow over the workpiece 10. It would be understood that the quenchant 60 may be directed upward into the quench trough 40 to immerse the workpiece (as shown in phantom lines), or optionally, quenching station 30 may be arranged as an immersion station, where the workpiece 10 is submersed (not shown) in the quench trough 40 for an appropriate time for cooling. The pressurized fluid source 26 operates to advance compressed gas through the internal passage 12 and out of the boreholes 14 at a pressure sufficient to prevent quenchant 60 from entering the inner cavities of the workpiece 10.
By advancing the compressed gas 26 through at least one end of the workpiece 10 and out through the boreholes 14 at the sufficient rate, the quenchant is kept out, allowing the internal passages 12 and 14 of the workpiece to cool at a much slower rate. The slower cooling rate keeps stress from building up generally, especially in the special areas of concern 16, thereby preventing stress cracks in the workpiece.
It will be appreciated by those skilled in the art that given the flow rate of the quenchant, and the dwell time, that is the time for which the workpieces are exposed to the quenchant 60, is a function of the size, shape and length of the workpiece 10.

INDUSTRIAL APPLICABILITY

The industrial applicability of the quenching method described herein will be readily appreciated from the foregoing discussion. A method is described wherein quenching results in a cooled and hardened workpiece 10 with an internal passage 12 and plurality of boreholes 14 free from quenchant 60. Therefore the internal passage 12 and boreholes 14 are not susceptible to stress concentrators (not shown) building up at the internal intersections 16. Furthermore, preventing quenchant from entering the passage and boreholes allows the workpiece 10 to cool at a slower rate. It should be understood that a slower cooling a workpiece 10 with an internal passage further decreases the opportunity for the build up of stress concentrators.
Examples of the present disclosure are applicable to any quenching system employing a workpiece with an internal passage where it is desired that the internal passages of the workpiece are kept free from quenchant. For example, many elongated workpieces, such as input shafts, have a plurality of boreholes that intersect the internal passages and form internal 90 degree angles, may benefit from application of the teachings herein. In such workpieces, application of the foregoing method can provide better quality components and machine parts, free from stress and cracks, etc.
It will be appreciated that the foregoing description provides examples of the disclosed method. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely, unless otherwise indicated.
Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.
Accordingly, this disclosure includes all modifications and equivalents of subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A method for quenching a metal workpiece having an internal passage with at least one open end, wherein said workpiece has a plurality of bore holes extending between said internal passage and an external surface, the method comprising the steps of:

pressurizing said internal passage with a pressurized fluid source to prevent quenchant from entering said internal passage and said plurality of bore holes; and

flowing quenchant across said external surface to cool and harden said workpiece.

2. The method, as set forth in claim 1, wherein said plurality of bore holes extending between said internal passage and said external surface intersect said internal passage at near or equal to 90-degree angles.

3. The method, as set forth in claim 1, further comprising the steps of:

connecting at least one adapter to said at least one open end of said workpiece;

coupling said at least one adapter into fluid communication with said pressurized fluid source; and

directing said pressurized fluid directly through said adapter into said internal passage of the workpiece, wherein said pressurized fluid exits through the said plurality of bore holes.

4. The method, as set forth in claim 1, wherein said pressurized fluid source is compressed air at a pressure greater than the flow pressure of said quenchant.

5. The method, as set forth in claim 1, wherein the flowing step is performed by pouring quenchant across said external surface of said workpiece

6. The method, as set forth in claim 1, wherein the flowing step is performed by submersing said workpiece in a quench bath.

7. The method, as set forth in claim 1, wherein the flowing step is performed by spraying quenchant across said external surface of said workpiece.

8. The method, as set forth in claim 1, wherein the quenchant is a water and polymer mix.