JPS5993831A - White pig iron hardening method of sliding surface of cam - Google Patents

Abstract

PURPOSE:To decrease residual stress and to prevent the grinding crack of a sliding surface of a cam in a method for forming a white pig iron hardened layer on the sliding surface with a torch by heating the cam at a specified temp. and for a specified time after cooling then cooling slowly the cam. CONSTITUTION:A cam 4 is preheated to about 400 deg.C and after the sliding surface of the cam 4 is heated to melt with a torch 1, the molten surface is allowed to cool. A martensite layer beta is then formed in the lower part of the sliding surface of the cam 4, and the sliding surface of the cam is cracked by the residual stress generated in the layer beta. The cam 4 is thereupon heated for 0.5-4.0hr at 300-600 deg.C and thereafter it is slowly cooled. The layer beta is thereby converted to sorbite, by which the residual stress is lessened and the above-described grinding crack is retarded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for forming a hardened white pig layer by heating and melting a cam sliding surface with a torch.

The method of white pig iron hardening layer on the cam sliding surface, which has already been proposed, involves preheating the cam to about 400°C and then heating and melting the cam sliding surface using TIG's 1.-ch.

It was then air cooled.

By the way, according to the above method, a martensite layer is formed at the bottom of the cam sliding surface, and when the cam sliding surface is ground,
Residual stress generated in the martensite layer caused cracks.

The present invention solves the above-mentioned problems, and the cam sliding surface is
・After heating and melting the cam, the cam is heated to 300°C.
The gist of the present invention is a method for hardening white pig iron on a cam sliding surface, which is characterized by heating at ~600°C for 5 to 4 hours and then slowly cooling.

Therefore, by heating and melting the cam sliding surface with a torch and then cooling it, a white pig iron hardened layer is formed on the cam sliding surface, and at this time, a martensite layer is formed under the white pig iron hardened layer. However, by heating the cam at 00° C. to 600° C. for 0.5 to 4 hours and then keeping it cool, the martensite layer becomes sorbite.

Therefore, since residual stress is reduced, grinding cracks can be prevented and grinding efficiency can also be improved.

Two embodiments of the present invention will be specifically described below.

1 to 4, the torch 1 is moved horizontally (in the horizontal direction in FIG. 1) by a drive device driven by a motor 2 as shown in FIG. reciprocate in the direction perpendicular to . A cam 4 for an internal combustion engine is installed inside the base 5. The eccentric interior 6. has a different center of curvature from the foundation interior 5 and has a smaller diameter than the foundation interior 5.
It consists of connection parts 7 and 7' that smoothly connect the foundation interior 5 and the eccentric interior 6, and the connection parts 7 and 7° are the foundation interior 5 and the eccentric interior 6.
The parts A-B and E-F connected to are formed in a curved shape,
The portions B-C and D-Et connected to the eccentric interior 6 are formed substantially straight. As shown in Fig. 4, the torch 1 is
Tungsten electrode 8. It has a nozzle 7 and a nozzle 9 provided so as to cover all four sides of the tungsten electrode 8.

First, as a preliminary step, the thickness is 16mmσ)ノjノ,
4. Preheat to 40[]℃.

Next, as a first step, attach the backing plate 10 to the cam 4 as shown in FIG. 4, connect it as shown in FIG. 1 electrode 8
is opposed to point A of cam 4. At this time, the distance between the electrode 8 and the sliding surface of the cam 4 is 25 mm when the electrode 8 faces between the cams 40B and 40C, and the distance between the electrode 8 and the sliding surface of the cam 4 is 25 mm. It is set vertically. Also,
The electrode 8 and the cam 4 are connected to a power source (not shown).

Subsequently, as a second step, as shown in FIG. 4, 81/MIN of arcon gas is ejected from the horn nozzle 9, and the electrode 8 is set to a negative potential, and a current of 11 OA is supplied between the electrode 8 and the cam 4. Zuroto electrode 8 and cam 4
An arc is generated between the two and the sliding surface of the cam 4 is heated and melted into a circular shape with a diameter of about 4 mm.

At the same time, by driving the motor 2, the drive unit H
A) Move the torch 1 to the right side of Fig. 1.
-Move horizontally 100 mml MIN to C. At this time, l・-chi1 is simultaneously turned on by the oscillator to the first
Period 80 times/MIN in the direction perpendicular to the drawing surface, amplitude 6 mm
Be vibrated with. Therefore, the electrode 8 meanders while melting the sliding surface into a circular shape with a diameter of 4 mm, and moves the sliding surface 2 from A to C, and the sliding surface from A to C is moved. As shown in FIG. 4, the entire width of 13 mm is heated and melted.

Next, when the electrode 8 reaches the position facing the zero point, only the movement of the l-ch 1 by the drive device 3 is stopped as the sixth steno knob, and at the same time as this stop, the cam 4 is eccentrically moved as shown in FIG. The outer circumference is 100 with the center of curvature of the interior 6 as the central axis.
As in the second step, the electrode 8 of the torch 1 is rotated at a circumferential speed of 100 mm/min while forming a circular heating melting point with a diameter of about 47 nm relative to the sliding surface.
mm, /MIN, frequency of 80 vibrations/MIN, amplitude of 6 mm, and heat melts the sliding surface up to C-+D over its entire width of 13 mm.

When the electrode 8 reaches the position '' where nine points are opposed, the cam 4 is stopped horizontally between D and F of the connection part 7' as shown in Fig. 3 as a fourth step. be done. At the same time, the motor 2 operates the drive unit to move the torch 1 to the positions D-*F in FIG. 6 at a rate of 100 mm/min. Then, the electrode 8 vibrates at a frequency of 80 times/min and an amplitude of 6 times, as in the second step, while vibrating at a frequency of 100+nm.
Move to the right in Figure 6 at a speed of /MIN, and move cam 4 D-F.
The sliding surface between the parts is heated and melted over a width of approximately 16 mm at the center thereof.

Therefore, the sliding surface between A and F of the cam 4 is heated and melted.

Next, in the fifth step, the cam 4 is naturally cooled (cooled with zero air) to 100°C, and as a result, the sliding surface between A and F of the cam 4 is polished, as shown in Figure 4. A chill layer α having an arcuate cross section and a depth of about 2 mm at the deepest part and a martensite layer β are formed around the chill layer α.

Furthermore, in the case of a cam for an internal combustion engine, the cam does not perform any internal operation inside the cam base (because the F
-> There is no need to form a chill layer α on the sliding surface between A.

Next, in the sixth step, the cam 4 was heated to 400°C.
After heating for 1 hour, cool in the air. As a result, the martensite layer β becomes sorbite.

Therefore, the martensite layer β becomes sorbite and °C
・Because of this, residual stress is small, so grinding cracks are less likely to occur when the cam sliding surface is ground.

The cam 4 is reheated at 300' in the sixth step.
A period of 0.5 to 4 hours in the range of C to 600 C is sufficient. If the temperature is too low or the 1 hour is too short, the martensite layer will not be fully formed.

Residual stress is not removed sufficiently. Further, if the temperature is too high or the 2 hours are too long, tempering will not be carried out.

[Brief explanation of drawings]

Claims (1)

[Claims] The cam sliding surface is heated and melted with a torch and then cooled. A method for hardening white pig iron on a cam sliding surface, which is characterized by slow cooling after drying.