JPH1030412A - Manufacture of valve guide for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remarkably reduce a processing cost by mechanically treating both ends aloneof a valve guide. SOLUTION: Hard material powders 6, 8 having high compressivity are charged in both ends of a cylindrically bottomed molding chamber 3 of a molding die 1 at the time of sintering. Material powder 7 having low compressivity is charged in a center portion. The material powders 6, 7, 8 are pressurized in an axial direction by punches 4, 5 to form a green compact 9. After sintering the green compact, inner peripheral surfaces of both ends are mechanically finished. An inexpensive material can be adopted to the center portion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a valve guide used in a valve train of an internal combustion engine.

[0002]

2. Description of the Related Art Since a valve guide guides a reciprocating sliding movement of an engine valve while holding a shaft portion of the engine valve, high wear resistance is required. Therefore, a hard material such as gray cast iron, alloy cast iron, or a wear-resistant sintered alloy is used as a material for the valve guide.

[0003]

Materials having high wear resistance as described above generally have poor machinability (machinability).
In particular, it takes time to machine the shaft hole of the valve guide, and the life of the cutting tool used for it is short,
This causes the processing cost to increase.

The present invention has been made in view of the above-mentioned problems, and focuses on the fact that abrasion resistance is required mainly at both ends of a valve guide, and performs machining on only that portion. It is another object of the present invention to provide a method of manufacturing a valve guide for an internal combustion engine, which can significantly reduce the processing cost.

[0005]

According to the present invention, the above-mentioned problem is solved as follows. (1) A hard raw material powder having high shrinkage during sintering, and a raw material powder having lower shrinkage than that at the center, at both ends of an annular bottomed forming chamber in a mold. The raw material powder is filled in three stages, and the raw material powder is pressed in the axial direction with a punch to form a green compact having substantially the same shape as the valve guide to be manufactured. Machine finish the inner peripheral surfaces at both ends.

(2) In the above item (1), the amount of the raw material powder at the center is larger than that at each end.

(3) The inner peripheral portions of both ends of an annular bottomed molding chamber in a mold are filled with hard raw material powder having high shrinkage during sintering, and the other portions are filled with both ends. By filling the raw material powder with lower shrinkage than the inner peripheral part of the part, and pressing the raw material powder in the axial direction with a punch, a green compact having almost the same shape as the valve guide to be manufactured is formed, After sintering the green compact, the inner peripheral surfaces at both ends are machine-finished.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral (1) denotes a compacting die having a circular mold hole (1a). In the mold hole (1a), a round bar-shaped core (2) concentric with the mold hole (1a), and an annular molding chamber (3) is formed between the outer peripheral surface and the inner peripheral surface of the mold hole (1a). As shown in FIG. The radial dimension of the molding chamber (3) is substantially equal to the thickness of the valve guide to be manufactured.

(4) is a cylindrical upper punch which can be fitted into the molding chamber (3) substantially without a gap. (5) is a lower punch having the same shape and the same size as the upper punch (4), which is guided by the core (2) and can slide up and down in the mold hole (1a).

In order to form a green compact using such a compression molding apparatus, first, as shown in FIG. 1, the lower punch (5) is lowered to a predetermined position, and the molding chamber (3) is formed. ), A raw material powder (6), (7), (8)
Are weighed in order from the bottom so as to have a ratio of approximately 1: 2: 1, and filled in three stages. Lower and upper raw material powder
(6) As (8), hard materials having high shrinkage during sintering, such as Fe-Cr-Mo-C system, Fe-Cu-Ni-Mo-C system or Fe-Cr-C system boride An alloy powder to which (FeB) is added is used. As the raw material powder (7) in the middle stage, an inexpensive Fe-based alloy powder, for example, a Fe-C-based or Fe-Cu-C-based powder is used.

Then, as shown in FIG. 2, the upper punch (4)
Down into the mold cavity (3) and lower punch
(5) is raised, and the raw material powders (6), (7) and (8) are reduced to 5 to 7 tf /
Simultaneously pressurize at a pressure of cm ² to form a green compact (9) having substantially the same shape as the valve guide to be manufactured.

Next, the green compact (9) is taken out of the mold (1) and is housed in a sintering furnace (10) as shown in FIG.
After preheating at about 500 ° C. to evaporate the mold lubricant contained in the green compact (9), a protective gas such as decomposed ammonia gas is introduced into the sintering furnace (10), and the Sinter by heating at a temperature of ° C. for a predetermined time.

Both ends (11a) and (11a) of the valve guide (11)
Since it is made of a highly shrinkable alloy powder, both ends (11a) (11a) slightly shrink in the radial direction after sintering, as shown in an enlarged view in FIG.

The inner peripheral surface of the valve guide (11) is finished with a reamer (12) or the like as shown in FIG. It should be noted that the outer peripheral surface is subjected to finishing as needed only on the portion that is pressed by the cylinder head.

During the operation of the engine, the load acting on the valve guide (11) is a radial pressing force mainly based on a bending load acting on the shaft portion of the engine valve. 11) Both ends (11a) (11
It has a great effect on a). Therefore, it is sufficient to provide high wear resistance only to both ends (11a) (11a).

Therefore, as described above, the valve guide
Both ends (11a) and (11a) of (11) are slightly reduced in diameter using a highly shrinkable hard material, and only the inner peripheral surface of that portion is finish-processed to have a specified size. Since it is sufficient to perform no machining at all or only a very small amount of machining, the machining time can be shortened, the life of the cutting tool such as the reamer (12) is extended, and the machining cost is reduced.

Further, since an inexpensive material can be used for the central portion of the valve guide (11), the cost of raw materials can be saved and the cost can be reduced.

The present invention is not limited to the above embodiment. In the above embodiment, both ends (1
1a) For the entirety of (11a), a hard material having high shrinkage is used, but as shown in FIG. 6, only the inner peripheral portion (11b) of both end portions (11a) and (11a) is, for example, thick. A hard material having a high shrinkage by about half the thickness may be used. Even in this case, after sintering, both ends (11a) and (11a) slightly shrink in the diameter-reducing direction, so that it is sufficient to process only both ends similarly to the above. In this way, the amount of expensive hard material used can be saved, and a cheaper valve guide (11) can be obtained.

[0019]

According to the present invention, both ends of the valve guide, which are most likely to be worn, are made of a highly shrinkable hard material.
Since the diameter is reduced after sintering and only the inner peripheral portion is machined, the machining time is shortened, the life of the cutting tool is extended, and the machining cost is greatly reduced. Also,
Since a low-priced material can be used in the central portion, an inexpensive valve guide can be obtained.

[Brief description of the drawings]

FIG. 1 is a central longitudinal sectional front view showing a state in which a core and raw material powder are inserted into a mold in carrying out the present invention.

FIG. 2 is a view similar to FIG. 1, showing a state where raw material powder is pressed by upper and lower punches.

FIG. 3 is a vertical sectional front view showing a state in which a green compact taken out of a mold is accommodated in a sintering furnace and sintered.

FIG. 4 is an enlarged vertical sectional front view of the valve guide after sintering.

FIG. 5 is an enlarged vertical sectional front view showing the machining step.

FIG. 6 is a front view in central section showing another embodiment of the present invention.

[Explanation of symbols]

 (1) Mold (1a) Mold hole (2) Core (3) Molding room (4) Upper punch (5) Lower punch (6) (7) (8) Raw material powder (9) Green compact (10) Baking Furnace (11) Valve guide (11a) Both ends (11b) Inner circumference (12) Reamer

Claims (3)

[Claims] 1. A hard raw material powder having high shrinkage during sintering is provided at both ends of an annular bottomed forming chamber in a mold, and a raw material powder having lower shrinkage is also provided at the center. , And pressing these raw material powders in the axial direction with a punch to form a green compact having substantially the same shape as the valve guide to be manufactured, and sintering the green compact. And a method of manufacturing a valve guide for an internal combustion engine, wherein inner peripheral surfaces at both ends thereof are machine-finished. 2. The method for manufacturing a valve guide for an internal combustion engine according to claim 1, wherein the amount of the raw material powder at the center is larger than that at each end. 3. An inner peripheral portion of both ends of an annular bottomed molding chamber of a mold is filled with hard raw material powder having high shrinkage during sintering, and the other portions are filled with both end portions. The raw material powder having a lower shrinkage than the inner peripheral portion is filled, and the raw material powder is pressed in the axial direction with a punch to form a green compact having substantially the same shape as the valve guide to be manufactured. A method for manufacturing a valve guide for an internal combustion engine, comprising sintering a green compact and then mechanically finishing inner peripheral surfaces of both end portions thereof.