JP2000063937A - Heat treatment of cast product with die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the bending by alternately repeating contraint and non- constraint during quenching so as to restrain the formation with the contraint and to prevent the development of crack for allowing the shrinkage with the non-constraint from happening so as to produce a cast product having good shape without developing the crack. SOLUTION: During P0-P2, i.e., the cast product (a work) after separating from a die, is constrained to correct the shape. Whereat, the work has sufficiently high temp. and is soft, and the correction of the shape can be easily executed. During P2-P3, the work is forcibly cooled while alternately repeating the constraint and the non-constraint. This alternate repeat of the constraint and the non-constraint is called as an intermittent constraint, too. For example, in the case of using 2 sec for the constraining time and 0.5 sec for the non-constraining time and 10 sec for the necessary time during P2-P3, the constraint and the non-constraint are repeated at 4 times. Since the deformation is restrained with the constraint, the bending can be prevented, and since the shrinkage is allowed with the non-constraint, the development of crack can be prevented from happening. On and after P3, the work is made to be non-constraint.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method suitable for die castings, especially for camshafts.

[0002]

2. Description of the Related Art As a technique for manufacturing a work such as a camshaft by a die casting method, there is, for example, Japanese Patent Publication No. 5-45347, "Die casting method and die casting apparatus". In this casting method, after pouring, the surface layer of the casting that is in contact with the mold is rapidly cooled, and when the surface layer becomes a shell-like solidified layer, it is released from the mold.
Further, it is known that the camshaft is heated to a quenching temperature by a high-frequency heating method or the like and then quenched by immersing it in a coolant or spraying the coolant. From the viewpoint of energy saving, it is desirable to immediately forcibly cool the cast product manufactured by the technique of the above publication with a coolant.

[0003]

However, if the work is elongated like a camshaft, it is easily bent. Therefore, a method of quenching the work while restraining the work with an appropriate jig can be considered. However, since a long and slender work is greatly shrunk by rapid cooling, if it is restrained by a jig, this shrinkage is hindered and the work may be cracked. Therefore, an object of the present invention is to provide a technique capable of forcibly cooling a work while preventing it from cracking.

[0004]

In order to achieve the above object, the first aspect of the present invention is to inject a molten metal for iron-based parts into a mold,
In the heat treatment method of releasing the mold when the surface layer of the cast product in contact with the mold is in the temperature range where quenching is possible and when it becomes a shell-like solidified layer, and quenching by spraying a coolant or immersing in a coolant, After molding, restrain the cast product to correct the shape,
It is characterized in that forced cooling is performed while alternately repeating restraint and non-constraint from the time of spraying the coolant or immersion in the coolant.

First, since the quenching is carried out by utilizing the retained heat immediately after the mold release, the heating for the quenching can be omitted. Since the step of transporting to the quenching furnace is not necessary, the number of steps can be reduced. Since the shape of the cast product is corrected before the start of quenching, quenching can be performed on a workpiece having a good shape. During quenching, restraint and non-restraint are repeated alternately, restraining deformation to prevent bending, and non-restraint allowing shrinkage prevents cracks from occurring.

In the second aspect, the constraint and the non-constraint are repeated until the martensitic transformation start temperature is reached, and thereafter, the constraint is not restrained. The martensitic transformation start temperature is about 180 ° C., and the subsequent thermal deformation is minute, so there is no need to restrain it. Further, austenite transforms to martensite below the martensite transformation start temperature, and metallurgical expansion starts. Therefore, by making it unconstrained, this transformation expansion is not hindered.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings should be viewed in the direction of the reference numerals. FIG. 1 is an overall view of a cast product according to the present invention, and a die cast product will be described taking a camshaft as an example. The camshaft 1 as a die casting product has a plurality of journal portions 2
a to 2e and five cam portions 3a to 3d formed between adjacent journal portions, for example, the journal portions 2a and 2b, and the same between the journal portions 2b and 2c and between the journal portions 2c and 2d. However, it is a camshaft for three cylinders.

The material composition of the cast product is shown in the following table as an example. A comparative example is the Metal Handbook (edited by The Japan Institute of Metals, revised 5th edition,
The standard chemical composition described in p. 596).
In the table, Sn is removed and Bi is bismuth.

[0009]

[Table 1]

The spheroidal graphite cast iron is cast iron in which graphite is spheroidized by adding Mg (magnesium) to the cast iron, and in the embodiment, it contains 0.01 to 0.03% of Mg. Furthermore, compared with the comparative example, the Si (silicon) component was 1.
It is characterized in that it is 5 to 2.0 times. This is because by increasing the amount of Si, the hardness of the non-quenched portion becomes small and the machining by a drill or a lathe becomes easy.

FIG. 2 is a layout diagram of heat treatment equipment according to the present invention. The equipment 10 includes a die casting machine 11 and a cutting machine 12.
It consists of a hardening machine 20 with a straightening mechanism and a tempering furnace 14. In the mold casting machine 11, a step of injecting a molten metal for iron-based parts into the mold, and the surface layer of the cast product in contact with the mold can be hardened. And a step of releasing the mold when a shell-shaped solidified layer is formed in a wide temperature range. Hardening machine with straightening mechanism 20
The detailed structure will be described with reference to the next figure. It is equipment for performing the entire or partial quenching by spraying or immersing the casting on the cast product removed from the mold. After that, tempering is performed in the tempering furnace 14 to enhance the toughness and the like of the cast product.

FIG. 3 is a principle diagram of a hardening machine with a straightening mechanism according to the present invention. The hardening machine with a straightening mechanism 20 includes a frame 21 and a spray nozzle 22 for spraying a coolant.
・ ・ Indicates more than one. The same applies below. ) And spray nozzle 2
2. The headers 23 supporting the ... and these headers 23 ...
· Supporting pillar 24 and cart 25 supporting this supporting pillar 24
A water collecting pan 26 that collects the coolant after injection, a pump 28 that pressurizes the coolant and sends it to the column 24 via the flexible hose 27, and a compressor 2 that sends air to the column 24.
9 and a correction mechanism 30. That is, the column 24 is a member that also serves as a conduit for the coolant and the air.

The correction mechanism 30 has a cradle 3 which is erected on the frame 21 so as to receive the journal portion of the camshaft 1.
1 ..., constraining claws 32 ... Arranged above the receiving bases 31 ..., an elevating frame 33 that supports these constraining claws 32, and elevating the elevating frame 33. The hydraulic cylinder 34, the pedestal 31, ... and the restraining claw 3
2, and air hoses 36 and 37 for supplying air.

Numeral 17 is a stand, 18 is a loader, and 19 is an unloader. The camshaft 1 exiting the cutting machine is placed on the stand 1.
7, the camshaft 1 is transferred to the hardening machine 20 by the loader 18, and after the hardening, the spray nozzles 22 ... Remove the camshaft 1 from the machine 20.

FIG. 4 is an enlarged view of part 4 of FIG.
1, a coolant passage 41 is opened, a porous metal or porous ceramics called a porous block 42 is fitted into the outlet of the coolant passage 41, and the porous block 42 is brought into contact with the journal portion 2b of the camshaft 1. It is a thing. Since the porous block 42 is a porous body, a coolant (air or a mixture mist of air and water is preferable)
Is dispersed appropriately, and a mild flow of coolant is applied to the journal portion 2b. 43 ... Side masks, which are shielding plates that prevent the coolant from flowing out to the cam portions 3a, 3e side. Without the side masks 43, 43, the coolant hits the cam portions 3a, 3e and cools them, and the cam portions 3a, 3e may become lower than the quenchable temperature. This inconvenience side mask 4
Prevent with 3,43. The side mask 43 can be moved by a link 44.

Similarly, in the restraining claw 32, the coolant passage 41,
A porous block 42, side masks 43, 43, and links 44, 44 are provided.

FIG. 5 is a sectional view taken along line 5-5 of FIG. 4, and shows that the upper surface or the lower surface of the porous block 42 is a curved surface 45 and the curved surface 45 is closely contacted with the journal portion 2b. It should be noted that the coolant passage 41 has a plurality of distribution passages 41 as shown in the figure.
It was made to branch to a ... so as to face the porous plug 42 on average. This is because the coolant is appropriately dispersed by the branching of the coolant passage 41 and the dispersing action of the porous plug 42, and the journal portion 2b can be cooled more uniformly. However, when the coolant is a gas such as air, since the self-dispersing property is high, the porous plug 42 is omitted and
The coolant passage 41 may only be branched into the distribution passages 41a.

FIG. 6 is a sectional view taken along line 6-6 of FIG. 4, showing that the side mask 43 is provided with coolant discharge passages 46, 46.

If there is no coolant discharge passage 46, the coolant sprayed on the journal portion 2b through the porous block 42 of FIG. 5 seeks a place to go to the cam portion 3a of FIG. 6, and the temperature of the cam portion 3a is increased. The inconvenience of lowering occurs. Therefore, if the coolant is discharged upward or downward through the coolant discharge passages 46 ... Therefore,
It is more preferable to provide the coolant discharge passages 46 ...
However, the side mask 43 has the coolant discharge passages 46, 46.
Whether or not the cooling medium discharge passages 46, 46 are provided is free, because the blocking effect of the cooling agent is large regardless of the presence or absence of the cooling medium.

FIG. 7 is a layout view of the spray nozzles. In order to cool the cam portions 3a to 3e evenly, the number of spray nozzles is 9 per revolution.
With 4 spray nozzles 22 arranged at 0 ° pitch,
A state in which the coolant is sprayed on the cam portions 3a to 3e is shown. The spray nozzle 22 is an air atomizing type mist nozzle, which is a type that atomizes a liquid coolant such as water with air (mist), and the cooling rate can be changed by changing the ratio of the liquid and the air. Can be changed. Specifically, the cooling rate increases as the amount of liquid increases, and the cooling rate decreases as the amount of air increases.

The operation of the technique of the present invention centering on the hardening machine with a straightening mechanism having the above construction will be described below. FIG. 8 is a heat treatment flow chart of a die casting product according to the present invention. ST
XX indicates a step number. ST01: The mold is assembled. ST02: The molten metal of the material components corresponding to the examples described in the above table is poured into the mold. ST03: In the hot water, the surface layer in contact with the mold is first cooled by the mold, solidification starts at 1150 to 1200 ° C, and the inside remains as a non-solid layer, but the surface layer is a shell-shaped solidified layer. Becomes Since the thickness of the solidified layer increases (grows) with time, the solidified layer is grown to the extent that the solidified layer is not broken. Manage this time. ST04: After a predetermined time has passed, the mold is divided and the cast product is taken out. ST05: Rapidly remove runners, flashes, etc. ST06: Straightening and pre-cooling the cast product. This ST0
6 will be described in detail below.

9 (a) and 9 (b) are diagrams of the pre-cooling procedure of the present invention. First, as shown in FIG.
a, 2b are placed on the pedestals 31, 31, and the restraining claws 32, 32
The release distortion is corrected by strongly suppressing with. Then, the air is forced through the coolant passages 41 ...
Flow as shown by the arrow toward the journals 2a, 2b
To force cooling. There is no concern that air will leak to the side due to the blocking action of the side masks 43 ... At this time, injection from the spray nozzles 22 ... Is not performed. As shown in (b), the journal portion 2a is softly cooled by the air appropriately dispersed in the porous block 42. The same applies to the other journal units 2b to 2d (not shown).

FIG. 10 is a cooling curve diagram of the camshaft according to the present invention, in which the horizontal axis represents time, the vertical axis represents temperature, the solid line graph represents the surface temperature of the journal, and the broken line graph represents the surface temperature of the cam. A1 on the vertical axis is the transformation point, and the Si component is 3.3.
If it is 7 to 4.34%, the temperature will be 780 to 800 ° C. Also, Ms is the martensite starting point, which is about 180
℃. Precooling is started at point P0, and then forced cooling is performed with air. When the journal portion reaches point P1 below point A1, precooling is terminated. On the other hand, the temperature of the cam portion is slightly lowered at the point P2 due to natural cooling, but it is in a region sufficiently higher than A1.

Returning to FIG. 8, in ST07, straightening and hardening are performed. The correction here is to correct the mold release distortion and suppress the deformation caused by the rapid cooling. The quenching action will be specifically described with reference to the drawings.

FIG. 11 is a diagram of the straightening / quenching process according to the present invention, in which the camshaft 1 is provided with the receiving bases 31, 31 and the restraining claw 3.
2 and 32 are restrained and the valve 47 is closed to stop the supply of air to the pedestals 31 and 31 and the restraining claws 32 and 32. Instead, mist-like cooling is performed from the spray nozzle 22. The agent is sprayed onto the cam portions 3a to 3e to quench it. The temperature of the cam surface at the start of cooling is A1
(780-800 degreeC) or more. Spray nozzle 22
For example, compressed air of 2 to 4 kgf / cm2 and 4 to
180-400 at 5 kgf / cm2 (liter / hour)
Of water to obtain a cooling rate of 120 ° C./sec at the start of cooling.

FIG. 12 is a diagram of the restraint, intermittent restraint and non-restraint of the present invention. The horizontal axis represents time, the vertical axis represents temperature, and the curve represents the temperature of the cam portion. P2 on the curve is the forced cooling start point, P3
Is the intersection with the martensitic transformation start temperature (Ms point). In the present invention, the shape is corrected by restraining the cast product between P0 and P2, that is, after the mold is released. Here, the work is sufficiently hot and soft, and shape correction is easy.

Between P2 and P3, forced cooling is performed while alternately repeating restraint and non-restraint. Alternately repeating this restraint and non-restraint is also called intermittent restraint. For example, restraint is 2 seconds, non-restraint is 0.5 seconds, and restraint and non-restraint are repeated four times if the time required for P2 to P3 is 10 seconds. Bending can be prevented because restraint suppresses deformation, and cracking can be prevented in advance because shrinkage is allowed without restraint.

After P3, it is unconstrained. The martensitic transformation start temperature is about 180 ° C., and the subsequent thermal deformation is minute, so there is no need to restrain it. Further, austenite transforms to martensite below the martensite transformation start temperature, and metallurgical expansion starts. Therefore, by making it unconstrained, this transformation expansion is not hindered.
In this way, a good quality cast product without cracks can be obtained.

Returning to FIG. 10, the cam portion is A1 (780 to 780).
From P2 point above 800 ℃), it is cooled rapidly and Ms
After passing the point (about 180 ° C.), austenite changes to martensite from that point. With this, the cam begins to burn. On the other hand, since the journal portion starts to be cooled from P1 below A1, it does not burn. This is especially true if the point Ms is not passed. That is, one of the features of the present invention is that the journal portion which is not desired to be quenched is forcibly set to A1 point or less in the preliminary cooling step to prevent quenching. By this processing, even if the journal portion becomes below the Ms point, there is no risk of burning.

Returning to FIG. 8, the tempering process may be performed in ST08. Tempering is a heat treatment accompanying quenching,
It may be appropriately carried out in order to enhance the toughness.

FIG. 13 is a quenching hardness graph obtained in the present invention, in which the horizontal axis represents the injection time and the vertical axis represents HRC (Rockwell hardness-C scale). In the present invention, the target hardness is 52 and the above spray nozzle is used. It was confirmed that the target hardness could be obtained if the injection time was set to 15 seconds or more in the arrangement and specifications.

The mold castings that can be treated by the method of the present invention are automobile parts such as camshafts, rocker arms and knuckle arms, or equivalent iron-based parts. Moreover, it is free to change the arrangement position of the cutting machine 12 of FIG. 2 and move ST05 (cutting process) of FIG. 5 to another step.

[0033]

The present invention has the following effects due to the above configuration. According to the first aspect, the quenching is carried out by utilizing the retained heat immediately after the mold release, and the heating for the quenching can be omitted. Since the step of transporting to the quenching furnace is not necessary, the number of steps can be reduced. Further, since the shape of the cast product is corrected before the start of quenching, quenching can be performed on a work having a good shape.
Further, during quenching, restraint and non-restraint are repeated alternately, restraining deformation to prevent bending, and non-restraint allowing shrinkage prevents cracking. Therefore, according to the first aspect, it is possible to manufacture a cast product having a good shape and no cracks.

Claim 2 is characterized in that the restraint and the non-restraint are repeated until the martensite transformation start temperature is reached, and thereafter the restraint is not restrained. The martensite transformation start temperature is about 180 ° C. Since the subsequent thermal deformation is minute, it is not necessary to restrain it. Furthermore, austenite transforms to martensite below the martensite transformation start temperature, and metallurgical expansion begins. Therefore, by making it unconstrained, this transformation expansion is not hindered.

[Brief description of drawings]

FIG. 1 is an overall view of a cast product according to the present invention.

FIG. 2 is a layout diagram of heat treatment equipment according to the present invention.

FIG. 3 is a principle diagram of a hardening machine with a straightening mechanism according to the present invention.

4 is an enlarged view of part 4 of FIG.

5 is a sectional view taken along line 5-5 of FIG.

6 is a sectional view taken along line 6-6 of FIG.

[Fig. 7] Layout of spray nozzles

FIG. 8 is a heat treatment flow chart of a die casting product according to the present invention.

FIG. 9 is a diagram of a preliminary cooling procedure according to the present invention.

FIG. 10 is a cooling curve diagram of the camshaft according to the present invention.

FIG. 11 is a diagram of a straightening / quenching procedure of the present invention.

FIG. 12 is a diagram of the restraint, intermittent restraint, and non-restraint procedure of the present invention.

FIG. 13 is a quenching hardness graph obtained by the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mold casting product (cam shaft), 2a-2e ... Journal part, 3a-3e ... Cam part, 10 ... Equipment, 11 ... Mold casting machine, 20 ... Hardening machine with correction mechanism, 22 ... Spray nozzle, 30 ... Correction mechanism, 31 ... Cradle, 32 ... Restraining claw, 41 ... Coolant passage, 42 ... Porous block, 43
… Side mask.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomoki Takahashi             1-10, Shin-Sayama, Sayama City, Saitama Prefecture             Within Da Engineering Co., Ltd. F-term (reference) 4K042 AA17 BA10 BA13 CA05 CA08                       CA17 DA01 DA02 DD02 DE02                       DE07 DF01

Claims (2)

[Claims] 1. A molten metal for iron-based parts is poured into a mold,
In the heat treatment method in which the surface layer of the cast product in contact with the mold is released in a temperature range that allows quenching and becomes a shell-like solidified layer, and is rapidly cooled by spraying a coolant or immersing in the coolant, A mold casting product characterized by performing forced cooling while alternately alternating restraint and non-constraint from when the coolant is sprayed or immersed in the coolant after restraining the cast product after mold release to correct the shape. Heat treatment method. 2. The heat treatment method for a die casting according to claim 1, wherein the restraint and non-constraint are repeated until the martensitic transformation start temperature is reached, and thereafter, the restraint is not restrained.