JPS63297524A - Quenching method for rack bar composed of rack part and pipe part - Google Patents

Abstract

PURPOSE:To make quenching strain smaller and to make mechanical straightening unnecessary by executing the quenching of the rack part and the pipe part respectively under the specific conditions at the time of quenching the rack bar cover its whole length and circumference while shifting the rack bar. CONSTITUTION:The work W composed of the rack part (r) and the pipe (p) is supported with center shafts S1, S2, and a heating coil C and a cooling jacket J' con nected with a connecting member U at the prescribed interval are shifted in the work W shaft direction to execute quenching. Then, the quenching for rack part (r) is execut ed with the teeth part (g) downward under non-rotating condition and opening part of a horseshoe type cooling jacket J is faced downward, and fluid coolant is injected in the radial direction against the circular arc of the rack part (r) and in a diagonal direction from the underside against the teeth part (g). Further, the quenching of the pipe (p) is executed under condition of lower output from heating power source than that to the rack part (r) and while rotating the work W. By this method, the quenched layer having a prescribed depth is formed in the teeth part (g) of the rack part (r) and also in the pie part (p), a quenched layer having the prescribed depth according to the thickness of the pipe can be formed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a shaft-like member, that is, a rack part, in which one half of the length in the longitudinal direction is a rack formed on a solid outer periphery, and the other half is a hollow pipe part. Almost the entire length of the rack bar consisting of the pipe section.
The present invention relates to a hardening method in which the entire circumference is moved and hardened by induction heating.

(Prior Art) Conventional rack bars have tooth profiles formed over a predetermined length along the outer circumference of a solid material, and the entire member has been tempered. As disclosed in Japanese Utility Model Application Publication No. 57-133557, etc., it was sufficient to impart wear resistance by subjecting only the tooth profile portions of the rack bar to a stationary hardening treatment.

However, in order to meet the demand for weight reduction, rack bars used in automobiles and the like these days use solid materials for the rack part, but hollow pipes are connected to the rack part by pressure welding or the like to connect to the shaft part. There is a transition to a new structure.

In this kind of rack bar consisting of a rack part and a pipe part,
Even if the rack part of the solid material is made of tempered material, the pipe part is not tempered, and the influence on the structure caused in the connection process remains in the vicinity of the connection part. Therefore, if this type of rack bar is hardened over its entire length and circumference, it will impart wear resistance to the tooth profile, eliminate the residual influence of the connection structure, and improve the strength of the pipe section. If achieved, the rack bar quenching method can be replaced with the conventional rack bar quenching method.
Hardening treatment was required for almost the entire length and circumference of the steel.

(Progress leading to the completion of the invention) Since this type of rack bar is a shaft member, the inventor believed that the conventional method for moving and hardening the shaft member by induction heating would be applicable. We tried quenching using this method. This will be explained according to FIGS. 2(a) and (b).

In FIG. 2(a), W is a rack bar (hereinafter referred to as the work) consisting of a rack part r and a pipe part p, and the work W has a center axis S with its axis substantially horizontal at the heating position.
1. It is axially supported by S2.

One of the center shafts S is rotatable by a rotary drive source (not shown), and the other is freely rotatable, so if the rotary drive source is driven, the center shaft 31. The workpiece W supported by S2 is rotatable. C is a heating coil having an inner diameter that can face the outer periphery of the pipe portion p with a predetermined gap therebetween, and J is a cooling jacket having an annular shape. The cooling jacket J' and the heating coil C are integrally connected by a connecting member U so as to maintain a predetermined distance therebetween.

Figure 2 shows the process of hardening the workpiece W using the above configuration (
This will be explained according to the operation diagram of b).

First, the heating coil C is placed in a position facing the left end of the rack part r as shown in FIG.
After setting □, at time t1, the heating coil C starts to be energized as shown by the line opening and 8, and the supply of cooling fluid to the cooling jacket J is started, and after a predetermined time, at time t2, the line As shown (relative movement in the axial direction between the workpiece W and the heating coil C starts. The workpiece W is sequentially heated to the right by the relatively moving heating coil C, and jets are emitted from the cooling jet J' following the heated part. The cooling fluid cooled is sequentially rapidly cooled. At the time t3 when the heating coil C reaches the right end of the pipe section p, the current supply to the heating coil C is stopped as indicated by the line opening.
The heating coil C further moves and follows the cooling jet I-
At the time t4 when J' reaches the position where the heated part on the right side is cooled, the relative movement is stopped as shown by line 2, and at the time t5 when the heated part has been sufficiently cooled, lines A and C are shown. The rotation of the workpiece W is stopped by stopping the supply of cooling fluid to the cooling jacket J' and stopping the drive of the rotational drive source. By the above operations, almost the entire length of the workpiece W is hardened over the entire circumference.

However, the above attempt failed. This is because, in the above method, the ridge portion of the tooth end face located on the front side of the axial rotation over the entire tooth profile of the rack portion r, that is, the portion within the range indicated by the circle in FIG. 3(a), has a depth of approximately 2 mm. It turned out that this resulted in burn-through (parts that were not hardened).

In addition, as shown in Fig. 3(b), when a strain measurement test was carried out on the rack part r with respect to the axis of the pipe part p with both ends of the pipe part p supported, the total length of the rack part r was 192 m.
m (however, the length of the tooth-shaped part is 155 mm), and the diameter of the pipe part p is 24 mmφ.

In the case of a workpiece W with a wall thickness of 4.2 mmt, point P2 is distorted from point P1 to the opposite circumferential side of the tooth profile, that is, in the circular arc circumferential direction, as shown by the arrow, and the amount of distortion is 1.4 to 1.4 mm in the as-quenched state. 2.4mm, 1.1m even after tempering
It was found that the strain correction effect due to tempering could not be expected.

Therefore, the inventor believes that the cause of burnout is that the workpiece W has a tooth profile different from that of a normal shaft member with a circular cross section, and the cooling fluid injected toward the tooth profile has a circumferential surface. The shaft member is in a state where it does not flow down quickly, in other words, the cooling fluid is not cut properly, and the cooling fluid stagnates in the tooth profile valley, and the stagnant cooling fluid overflows and scatters as the workpiece W rotates, causing heating. It was assumed that the result was that the heat applied to the ridge of the tooth end face located on the forward side in the direction of shaft rotation of the advancing tooth profile, suppressing the temperature increase in that part to below the quenching temperature. It was also assumed that the large amount of quenching distortion was due to the synergistic effect of the small amount of shrinkage that would be compensated by the hardening of the tooth profile portion and the large amount of shrinkage that would be compensated by sufficient quenching of the circular arc circumferential portion.

Based on the above assumption, the present inventor attempted quenching by reducing the flow rate of the cooling fluid to an extent that does not stagnate in the tooth profile valleys, but to the lowest level that maintains the cooling ability that allows quenching. Although this attempt did avoid burn-through, only an extremely shallow hardened layer was formed on the peaks, and the work W as a whole could not be finished to the desired strength, resulting in results that were deemed unsuitable for use. There wasn't.

(Object of the Invention) The present invention provides a rack bar having one half in the longitudinal direction formed with a rack portion formed on the outer periphery of a solid material, and the other half consisting of a hollow pipe portion.
This was done in order to overcome the problem that the conventional shaft member hardening method cannot be applied due to the problems mentioned above when the entire circumference of the rack part is moved and hardened by induction heating. It is possible to form a quenched rim that provides wear resistance of appropriate hardness up to a predetermined depth for the pipe section, and desired hardness and toughness for the pipe section depending on its wall thickness, and it is also possible to quench with extremely low distortion. It is an object of the present invention to provide a method for hardening a rack bar consisting of a rack part and a pipe part.

(Structure of the Invention) The gist of the present invention is as follows: (11) Guides approximately the entire length and entire circumference of a shaft-shaped member, where one half in the longitudinal direction is a rack portion formed with a rack on the outer periphery of a solid material, and the other half is a hollow pipe portion. In the case of moving hardening by heating, (2) the shaft-like material is rotatably supported with its axis substantially horizontal, and (3) a heating coil has an inner diameter that can face the outer periphery of the pipe section with a predetermined gap. (4) A horseshoe-shaped cooling jacket that can follow the heating coil and has an opening facing downward is moved relative to the shaft material from one end to the other; The heating conditions are set so that the heating conditions can be switched at the time of transition between the rack part and the pipe part due to relative movement. The rack part is heated to form a quenched hardened layer of a predetermined depth on the tooth profile, and the pipe part is heated to form a quenched hardened layer of a predetermined depth depending on the wall thickness. The present invention provides a method for hardening a rack bar consisting of a rack part and a pipe part.

(Function of the Invention) When hardening the rack part, the present invention heats the rack bar in a non-rotating state with the tooth profile facing downward and under predetermined heating conditions, and uses a horseshoe-shaped cooling jacket with an opening facing downward for cooling. Therefore, the cooling fluid is cut well and there is no overflow of the cooling fluid in the direction of the tooth profile during heating (all tooth profiles in the rack part are reliably heated to the predetermined hardening temperature to a predetermined depth and cooled with a sufficient flow rate). The pipe is rapidly cooled by a fluid to form a predetermined quenched hardened layer, the entire tooth profile of the rack part is uniformly quenched along with the arc side, so the amount of shrinkage of each part approaches each other, reducing quenching distortion. The rack bar is rotated when hardening the part.

In addition, since the heating conditions are different from those for the rack section depending on the wall thickness of the pipe section, it is possible to uniformly form a quenched hardened layer that provides toughness and desired strength around the entire length of the pipe section, and to improve the heating conditions between the rack section and the rack section. It has the effect of removing residual effects that occur in the transitional structure with the pipe section.

(Example) The present invention will be described in detail below with reference to FIGS. 1(a) and (b).

The workpiece W of the example has the same shape as the member used in the trial experiment.

The heating device used is one in which an ordinary shaft member as shown in Fig. 2(a) is supported horizontally by the center shafts St and S2, and the center shaft S is rotationally driven by a rotational drive source. It suffices if the shaft member is equipped with a mechanism that can rotate the shaft member.
Furthermore, the heating coil C used is a normal shaft member heating coil equipped with a single-turn or double-turn heating conductor part formed in an inner diameter that can face the outer periphery of the pipe part p of the rack bar W at a predetermined gap. be.

However, the cooling jacket connected by the connecting member U so as to follow the heating coil is a horseshoe-shaped cooling jacket shown as J in FIG. 1(a). The cooling jacket J is fixed to the connecting member U with the opening facing downward, and the ends of both hanging sides extend to a position slightly below the lower circumference of the workpiece W supported by the center shaft 31, 32, As shown in the figure, the cooling fluid is injected from cooling fluid injection holes provided in the U-shaped inner periphery.

It is formed so as to be able to resist impact from the radial direction with respect to the arcuate circumference of the rack part r with the tooth profile g facing downward, and from the diagonally downward direction with respect to the tooth profile g. The flow rate of the cooling fluid to be injected is set to a flow rate that has a cooling ability that can sufficiently harden and cool the heated part.

The case where a work W is hardened using the heating coil C and the cooling jacket J will be explained according to the operation diagram shown in FIG. 1(b).

For example, it is assumed that the workpiece W is carried into the heating position with the rack section r on the left. Then, the workpiece W is moved to the center axis S.
L, , 32, the present invention provides rack portion r.
with the tooth profile g facing downward. Next, the heating coil C, which had been retracted in the direction of the center axis S, is moved to the workpiece W.
Place it opposite to the left end of the rack part r.

As described above (after positioning), set the heating power source to a predetermined output that can perform heating that can form a quenched hardened layer of a predetermined depth on the tooth profile of the rack part At the same time as the power supply to C is started, the supply of cooling fluid to the cooling jacket J is started as shown by line C.

Furthermore, the width of the festival indicates the size of the output of the heating power source.

Next, at time t1 after a predetermined time, the workpiece W is moved as shown by line 2.
- Heating coil CrBY starts relative movement to the right at a predetermined speed. According to the relative movement, the rack part r is sequentially heated from the left end side to the right end side to a predetermined hardening temperature, and the cooling jacket J, which moves relatively following the heating coil C, rapidly cools the heated part. In this state, the cooling fluid injected from the cooling jacket J is applied to the rack part r with the arc circumference facing upward and the tooth profile downward, and the tooth profile g from the diagonal downward direction. The cooling fluid that has cooled the heated parts at the respective positions of the radiation surface immediately flows down from the opening located below the cooling jacket (J). Therefore, there is no risk of cooling fluid remaining in the valleys of the tooth profile. Furthermore, since the workpiece W is in a non-rotating state, there is no possibility that the cooling fluid after the injection surface of the heated part will bleed out or scatter in the direction of the tooth profile during heating.

At time t2 when the heating coil C moves from the rack part r to the pipe part p due to the relative movement, the rotational drive source is driven to start rotating the workpiece W as shown by line A, and the heating coil C is transferred to the rack part as shown in the festival. The power is switched to lower than when heating r, so that heating is performed to form a thin quenched layer corresponding to the thin wall thickness of the pipe section p.

In this state, the pipe part p is sequentially hardened, but at the time t3 when the heating coil C reaches the right end of the pipe part p, as shown in the festival, the power supply to the heating coil C is stopped, and the heating coil C is moved further. At the time t4 when the following cooling jet 1-J reaches the position where it cools the heated portion on the right end side, the relative movement is stopped as shown by line 2. At time t5 after a predetermined time s when the heated part in the example above has been sufficiently cooled, the rotary drive source is stopped as shown by line A to stop the rotation of the workpiece W, and the cooling jig J is stopped as shown by line C. Stop the supply of cooling fluid to.

Through the above operations, the entire circumference of the workpiece W is hardened over almost the entire length, but the rack part r and the pipe part p are subjected to different hardening treatments that are suitable for each, and the workpiece W is released from the shaft support by the center Sl, 32. The material is removed from the heating position, and the cutting process is completed.

When the strain 1jtlJ constant test shown in FIG. 3(b) was carried out on the work W subjected to the above process, the strain was 1.25 to 1.27 mm in the as-quenched state, and the strain was found to be 1.25 to 1.27 mm in the tempered state. A test result of a strain amount of 0.6 mm was obtained. This value indicates that mechanical correction is not necessary as a post-process.

In addition, as a result of the hardness measurement test, no burn-through was found on the ridgeline of the tooth profile end of the rack part r, and a hardened layer of a predetermined hardness was formed to a predetermined depth on all tooth profiles, and a hardened layer of a predetermined hardness was formed on the entire tooth profile. Although the wall thickness is 4.2mmt, the surface layer is 1.25m thick.
A hardened layer of m was formed, indicating that the pipe portion p was treated to have both strength and toughness.

(Other Examples) In the above example, the heating conditions for the rack part r and the pipe part p were changed by changing the output of the heating power supply. Good too.

Further, in the above embodiment, from the rack part r side to the pipe part p (
H! Although the explanation has been given using the case of relative displacement hardening from the pipe part P side to the rack part R side, there is no problem and the same effects and effects as in the example can be obtained. Of course. However, in this case, the rotating workpiece W must be stopped without inertia and the tooth profile must be directed downward when moving to the rack part r, which is complicated and undesirable.

Although the present invention is directed to a rack bar having a structure in which solid material and pipe material are connected, for example,
It can also be widely applied to the quenching treatment of shaft-like materials similar to rack bars, which have a pipe-like structure with holes drilled along the axis on the blade side of solid materials.

(Effects of the Invention) According to the present invention, a rack bar consisting of a rack part and a pipe part can be hardened to a desired hardness and wear-resistant by just -times of relative movement hardening. It is possible to impart desired hardness and toughness to the pipe portion according to its wall thickness, and a finish with slight quenching distortion can be obtained, eliminating the need for mechanical correction in subsequent processes.

Therefore, the present invention not only dramatically improves the method of relative movement hardening using induction heating, but also meets the demand for lightweight rack bars with a product with a high-quality finish, and is also significantly superior in productivity. Because
It is prized for its great effects.

[Brief explanation of the drawing]

FIG. 1(a) is a front view of the cooling jacket used in the method of the present invention, FIG. 1(b) is an operation diagram for explaining the method of the present invention, and FIGS. 2<a> and (b) are A front view and an operation diagram respectively showing the case where the subject material of the present invention is subjected to the conventional shaft material quenching method, and Figures 3 (a) and (b) show objects for which the conventional shaft material quenching method is unsuitable. FIG. 3 is a cross-sectional view and a front view of the material.

Claims (1)

[Claims] Almost the entire length of the shaft-shaped material, one half of which is a rack formed on the outer periphery of a solid material, and the other half of which is a hollow pipe.
In the case where the entire circumference is moved and hardened by induction heating, the shaft-like material is rotatably supported with its axis line substantially horizontal, and the heating coil has an inner diameter that can face the outer periphery of the pipe section with a predetermined gap, and A horseshoe-shaped cooling jacket that can follow the heating coil and has an opening facing downward is moved relative to the shaft material from one end to the other, and the quenching that accompanies the relative movement is performed while the rack part prevents the shaft material from rotating. In addition, the tooth profile is facing downward, and the pipe part is heated with the shaft member in a rotating state, and the heating conditions are set so that it can be switched during the transition between the rack part and the pipe part due to relative movement. Heating that can form a deep quenched hardened layer,
A method for quenching a rack bar consisting of a rack part and a pipe part, characterized in that each pipe part is heated to form a quenched hardened layer of a predetermined depth depending on the wall thickness.