CONSTRAINED QUENCHING APPARATUS AND HEAT TREATMENT APPARATUS

Abstract: This invention provides a constrained hardening apparatus for hardening a rod type special member, which is liable to be bent during the hardening thereof, while preventing the same member from being deformed. In a set of metal mold in which the contact surfaces of adjacent mold members are in an engaged condition, the inner side of the metal rnold consists of a plurality of projecting portions and recessed portions which have free ends the shape of which is in agreement with that of a material to be hardened, and hardening liquid ejection ports are provided in these recessed portions. Since the material is not pressed while it is soft, i.e., when the cooling of the material is started, deformation, such as flattening does not occur on even a hollow material, such as a pipe.

Description: The present invention relates to a constrained quenching apparatus for hardening a workpiece, e.g. a round bar, without warping and to a heat treatment apparatus employing that apparatus. The present invention is directed towards quenching of an asymmetrical workpiece which has a notable tendency to warping and of a hollowed workpiece which is difficult to be dealt with conventional quenching apparatus. Many machinery components having a round bar shape are subjected to a hardening process. When the component is symmetrical about a center axis, it is usually rotated about the axis during quenching to prevent warping. If the workpiece is asymmetrical about its center axis, such as round bar component extending a flat side thereof, it tends to warp by inconsistency of a cooling rate. For preventing from warping by the quenching such axially asymmetrical component, a press quenching method which is one of the constrained quenching is commonly utilized. In the press quenching method, a part or the entire of a workpiece is securely held at a pressure in a set of dies of which inside wall is adapted to match and accommodate the shape of the workpiece, and cooled down by thermal dissipation throughout the dies or direct immersion into cooling liquid. In the case of thermal dissipation throughout the dies, the cooling of the workpiece is effected through the dies which are directly cooled by liquid. US-A-3 294 597 provides a method for quenching a metal member such as a long channel member for use as truck trailer side rails. The moveable sidewall of the female die is moved to clamp the hot channel member between the fixed and moveable sidewalls of the female die sections, and thereby cause hot straightening of the channel member. The expandable male dies are then moved toward the female die members and into the channel member throughout its length and expanded laterally into engagement with the side flanges of the channel member. The female dies press against the outer surface of the channel member while held from the inside by the male dies, firmly clamping the channel member. Recently, tubular shaped components tend to be adopted instead of the traditional solid bars in machinery primarily in automobiles for minimizing the overall weight of the products. However, in the conventional press quenching method, the tubular workpiece is easily collapsed because it has a hollow inside thereof and being softened by heat. The press quenching method allows the cooling speed to be hardly controlled in desired locations. The quenching strain on the workpiece is a combination of a thermal strain and a phase transformation strain which is varied depending on the phase transformation temperature. Consequently the quenching strain does not depend on a cooling rate only, but also on the chemical composition of the material. Nevertheless, if the cooling rate is locally controlled, the warping of the asymmetrical workpiece can be suppressed to a certain degree in the early stage of the warping. Moreover, if the cooling rate is changed locally, the resultant hardness of a target region of the workpiece will be adjusted in combination with the heating temperature to almost a desired value providing a favorable material characteristic. It is an object of the present invention to provide a constrained quenching apparatus capable of quenching a tubular workpiece without warping or collapse, to provide a quenching apparatus where the cooling rate can be controlled locally on the workpiece, and to provide a heat treatment apparatus for quenching and tempering a required part of machinery components efficiently. The constrained quenching apparatus according to the present invention comprises a set of two or more dies disposed on a pressing means. The dies have plural projections provided on the inner side thereof, said projections coinciding with the contour of a workpiece when the dies are closed to their die faces being in contact, and have plural recesses therein defined by the projections for communicating with one another and extending to the outside of the dies. One or more of the recesses in at least one of the dies is provided with one or more cooling liquid blow holes. Preferably, plural cooling liquid blow holes are allocated in the each die, and a flow controlling means is fitted into each of the cooling liquid blow holes for determining an amount of the cooling liquid flow. The dies can be constructed by cutting the place of recesses from blocks, inner walls of said blocks coinciding with the contour of the workpiece, or by mounting separate projections to inner walls of blocks, said inner walls being larger than the contour of the workpiece. The heat treatment apparatus according to the present invention comprises an induction heater arranged close with the foregoing constrained quenching apparatus so that the workpiece can travel in the same height. Fig. 1 is a cross sectional view of a set of dies in which a workpiece is accommodated, showing a principal part of a constrained quenching apparatus of the present invention; Fig. 2 is a partially crosssectional side view of the two, upper and lower, dies of Fig. 1 being opened; Fig. 3 is a slant view of an exemplary form of the workpiece to be treated by the apparatus of the present invention; Fig. 4 is a crosssectional view of another set of dies where a workpiece is accommodated, similar to Fig. 1, according to the present invention; and Fig. 5 is a side view of a heat treatment apparatus according to the present invention. The present invention will be described in more details referring to the accompanying drawings. Fig. 3 is a slant view of a workpiece 1, that has a rack 2 provided on an outside of a hollow tube thereof and is to be exerted constrained quench with the use of apparatus according to the present invention. Figs. 1 and 2 illustrate a die set which is a main part of the constrained quenching apparatus for quenching the rack 2 of the workpiece 1 shown in Fig. 3. More particularly, Fig. 1 is a cross sectional view showing the workpiece held between two, upper and lower, dies. Fig. 2 is a partially cross sectional side view of the apparatus explaining its opened state with the upper and lower dies separated and the workpiece removed out as not shown. It is intended in the apparatus of the present invention that when the two dies 3 and 4 are closed to touch each other at the die faces 7, they exert no pressure on the workpiece at the beginning of the quenching. More specifically, the dies have plural projections 5 arranged on the inside thereof to coincide with the contour of the workpiece, as shown in Fig. 1. As the dies are closed, said projections come to lightly touch or to be very slightly spaced from the surface of the workpiece. The dies also have recesses 6 therein, which are defined by the projections 5, where liquid blow holes 8 are open. Each of the upper and lower dies has a cavity 13 and 14 respectively therein which leads to the liquid blow holes 8. A detachable plug having a sized orifice therein (not shown) is screwed into each of the liquid blow holes 8 for delivering a predetermined amount of cooling liquid flow. As shown in Fig. 2, each of the dies 3 and 4 has a couple of wide openings 9 and 10 at both ends thereof so that the workpiece which is greater in length than the dies 3 and 4 can be held and quenched. As described previously, the inner sides of the dies are provided with the projections 5 and the recesses 6 accompanying the liquid blow holes 8. Flows of the cooling liquid from the liquid blow holes are introduced into the recesses and discharged to the outside from outlets 11 provided at lengthwise end between the dies and the workpiece. The lower die 4 has drain passages 12 provided in the bottom of the recesses thereof for discharging a bottom remainder of the cooling liquid. Extra outlets may also be provided along the circumference of the workpiece or at other locations for ease of discharging the liquid from the recesses. The cavity 13 and 14 of the each die are communicated with liquid supply conduits 15 and 16 respectively. As described above, the apparatus carries out constrained quench without the risk of deformation of a hollowed workpiece, because the workpiece is not compressed by the dies. Although the workpiece will be exerted stress when it is driven to warp by cooling down, the workpiece has already been increased in the hardness so as not to be depressed on the surface. As compared with the prior art where a considerable pressure to the workpiece is exerted at the beginning of the quenching, the apparatus of the present invention imparts no such a constraining pressure to the workpiece at the start of the quenching, but allows the constraining force only if the workpiece is driven to warp by the cooling down of it. The apparatus of the present invention can reduce the warping also by changing the cooling speed locally with the location and size of the liquid blow holes and the location of the projections. This eliminates the root cause of warping to some extent before the obstruction of warping by constraint, so it is favorable from the standpoint of reduction of residual stress. Furthermore, the workpiece may selectively be adjusted in the degree and depth of hardness by determining the cooling rate locally in combination with the heating conditions. Although it is accepted in this invention that at least one liquid blow hole is provided in each of the upper and lower die, allocation of the liquid blow holes will give a desirable change in the quenching rate. For example, the cooling is faster where a blast of the cooling liquid from the liquid blow hole is directly applied and rather moderate where a flow of the cooling liquid is dissipated through the recesses. For prevention of warping of the workpiece that is the aim of this invention, the projections must be arranged in appropriate locations, but they may also be used for changing the cooling rate because their direct contacts in large area with the workpiece can retard the cooling effect. The cooling speed may also be control led with the use of flow regulating means for determining the flow of the cooling liquid from each of the liquid blow holes. The means comprise flow control valves disposed at their respective liquid blow holes or as mentioned before, plugs having different sized orifices therein, the plugs being screwed into their respective holes. In the latter case, the plugs of required sized orifices can be identified through a trial quenching process. The dies for the apparatus of the present invention may be constructed by cutting the place of the recesses from blocks, inner wall of which coincide with the contour of a workpiece, or by mounting separate projections to the inner walls of blocks where the inner wall is larger than the contour of the workpiece. The method of producing the dies is not limited to the foregoing manner of whether forming the recesses or attaching the projections, as far as the recesses are communicated to one another for readily discharging the cooling liquid supplied from the liquid blow holes to the outside. The previous embodiment of the present invention has been described in conjunction with the two, upper and lower dies. But as far as one set of dies can be divided into plural, it does not matter the number of the dies. An exemplary arrangement of the three separated dies will now be explained. Fig. 4 is a cross sectional view, similar to Fig. 1, showing a set of dies with the workpiece shown in figure 3 held therein. This die set consists of the three dies 31, 32, and 33 which have projections 5 provided on the inner side thereof to match the contour of the workpiece by adjoining die faces 34, 35 and 36. The other structural arrangements in Fig. 4 are identical to those shown in Fig. 1. The advantage of the three-die set is such that the two upper dies 31 and 32 move obliquely upwards denoted by the arrows 37, 38 in Fig. 4 for ease of loading and unloading of the workpiece, as compared with the two-die set of Fig. 1. In the two-die set, where the two dies are separated in vertical movement, edge regions of their inside have to slide parallel to the outside of the workpiece causing the removal of the workpiece to be sometimes difficult. Such a trouble is eliminated in the three-die set shown in Fig. 4. The three-die set is more preferable than the two-die set for hardening at high efficiency a number of workpieces even if the workpieces have a relatively simple tubular shape, although its price is increased. It is understood that if the workpiece has an intricate shape, the die set must be designed in number of dies in one set and location of separation in a set of dies. The constrained quenching apparatus of the present invention comprises the dies, shown in Figs. 1, 2, and 4, accompanied with a pressing means. Fig. 5 illustrates the above composition and also the entire arrangement of the apparatus constituting a heat treatment apparatus of the present invention. As shown, the constrained quenching apparatus denoted by 20 has a set of the dies of Fig. 4 actuated by a hydraulic pressing mechanism. The hydraulic pressing mechanism comprises a pair of hydraulic cylinders 21 provided for lifting up and down the die 31 which is joined to piston rods 22 of the cylinders 21. More particularly, the cylinders 21 with the piston rods 22 are mounted at an angle for moving the die 31 upward in a slanting direction. Another pair of cylinders are also mounted opposite to the two cylinders 21 for lifting up and down slantwise the die 32 of Fig. 4, which are not shown as on the far side in Fig. 5. The pressing means is not limited to the hydraulic mechanism but any other means, e.g. a mechanical actuator powered by an electric motor, will be used with equal success. The especially high efficient heat treatment apparatus can be set up by disposing an induction heater 23 adjacent to the constrained quenching apparatus 20, as shown in Fig. 5. As for the heating device, rapidly heat-up type is favorable for work efficiency, so the induction heater for heating the whole circle of a bar-shaped workpiece is especially preferable for performance of the constrained quenching apparatus of the present invention. More preferably, the induction heater 23 is arranged close with the constrained quenching apparatus 20 so that the workpiece 1 can travel in the same height, as shown in Fig. 5. If the workpiece 1 is a round bar, this is attained by arranging the apparatus so that the workpiece can travel in its axial direction. Sets of rollers 24 and 25 in Fig. 5 are provided for feeding axially the workpiece. In case of hardening a part of the bar workpiece, the workpiece is heated for a desired length and then fed into the constrained quenching apparatus by the rollers. In case of tempering by the same induction heater, the workpiece can be returned to them easily. Moreover the feeding becomes more easy by adding extensions to one end or both ends of the workpiece. Particularly, when the entire of the workpiece is to be heated, it can smoothly be set to a position by manipulating the extension(s). Such extensions 27 and 28 are connected at junctions 29 and 30 respectively to the workpiece 1 as shown in Fig. 5. The extensions may be either a solid or tubular bar which is joined to the workpiece detachably such as by threaded screw. The result of an experimental operation of hardening with the apparatus of the present invention will now be explained. The experimental operation was carried out in which the workpiece 1 having a rack 2 on a portion length of a tubular body as shown in Fig. 3 was heat treated with the heat treatment apparatus of the present invention shown in Fig. 5. The hardening was applied to not only teeth of the rack 2 but also a corresponding circumference of the tubular body. Main sizes of the workpiece are 23 mm in the outer diameter and 19 mm in the inner diameter at the segmented-circle crosssection of the racked portion, and 300 mm in its length, where the actually racked length is 180 mm. In addition, the region of full-circle crosssection at the left in Fig. 3 has an outer diameter of 25 mm, an inner diameter of 21 mm and a length of 450 mm. The material of the workpiece is carbon steel for machine structural use equivalent to JIS S40C. The workpiece 1 was heated by the high-frequency induction heater 23 to about 860°C and quenched with water by the constrained quenching apparatus of the present invention. The workpiece 1 was connected the extensions 27 and 28 which are the same crosssection as the workpiece for ease of handling. After the processing, the deflection (a maximum deviation from the center axis) of the workpiece was as low as 0.02 to 0.05 mm for a length of 200 mm. Those measurements are small enough to be negligible. It was also found no partial dent on the surface and no deformation as flattening of the tubular body. For comparison, the conventional quenching process cooling uniformly by water without constraint resulted in 2.0 to 3.2 mm of deflection. As set forth above, the constrained quenching apparatus of the present invention exerts no pressure at the start of the quenching, but allows the constraining force only if the workpiece is driven to warp by the cooling down of it. Accordingly, a hollowed workpiece as a tube can be prevented from the quenching strain without the risk of deformation as flattening. The flow of a cooling liquid is arbitrarily controlled in amount and location of the workpiece, so that also prevents warping and moreover controls physical characteristics of the workpiece. The heat treatment apparatus of the present invention permits heating of the workpiece at a higher efficiency. The steps of heating, quenching and tempering can readily be carried out in a succession while the transfer of workpieces from one step to another being increased in speed.

Claims: A constrained quenching apparatus comprising a set of two or more dies disposed on a pressing means, said dies having plural projections provided on the inner side thereof; said projections coinciding with the contour of a workpiece when said dies are closed with their die faces being in contact, and having plural recesses therein defined by the projections for communicating with one another and extending to the outside of said dies; one or more of said recesses in at least one of said dies being provided with one or more cooling liquid blow holes. A constrained quenching apparatus according to claim 1, wherein plural cooling liquid blow holes are allocated in the each die and a flow controlling means is fitted into each of said cooling liquid blow holes for determining an amount of the cooling liquid flow. A constrained quenching apparatus according to claim 1, wherein the dies are constructed by cutting the place of the recesses from blocks, inner walls of said blocks coinciding with contour of the workpiece. A constrained quenching apparatus according to claim 1, wherein the dies are constructed by mounting separate projections to inner walls of blocks, said inner walls being larger than the contour of the workpiece. A heat treatment apparatus comprising an induction heater arranged close with the constrained quenching apparatus as defined in claims 1, 2, 3 or 4 so that the workpiece can travel in the same height.

Inventors: KATO JUNICHI, SETO YOSHIKI, YAO YUGO, KATO, JUNICHI, SETO, YOSHIKI, YAO, YUGO
Applicants: NETUREN CO LTD, NETUREN CO., LTD.
Application year: 1993
Main classification: C21D1
IPC codes: C21D9, C21D1