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 
       [0001]    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 
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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. 
         [0010]    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. 
         [0011]    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. 
         [0012]    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. 
         [0013]    The present disclosure is directed to overcoming one or more of the problems set forth above. 
       SUMMARY 
       [0014]    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. 
         [0015]    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 
         [0016]      FIG. 1  is an exploded view of an exemplary workpiece for use in the present disclosure. 
           [0017]      FIG. 2  is an illustrative side view of an embodiment of the present disclosure. 
           [0018]      FIG. 3  is an enlarged partial cross sectional view, partial schematic view of an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    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. 
         [0020]      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 . 
         [0021]    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. 
         [0022]    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 . 
         [0023]    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 . 
         [0024]    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 . 
         [0025]    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 . 
         [0026]    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. 
         [0027]    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 
       [0028]    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. 
         [0029]    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. 
         [0030]    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. 
         [0031]    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. 
         [0032]    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.