JPH0220818B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing cracks in internal combustion engine cylinder heads.

In a cylinder head of an internal combustion engine, the wall thickness is thinner between the intake and exhaust valve seats or between the intake and exhaust valve seats and the fuel injection nozzle hole than in other parts. For this reason, cracks were sometimes generated due to thermal stress caused by combustion. To solve this problem, remove the part of the cylinder head where cracks are expected to occur.
It is known to have an intermediate layer formed by thermal spraying or welding of a heat-resistant material, and a coating layer formed by thermally spraying a ceramic heat insulating material on the surface of this intermediate layer. In this case, a machining process is required to remove the part where cracks are expected to occur, a thermal spraying process is required to form an intermediate layer and a coating layer made of different materials, and it is also necessary to carry out normal machining of the cylinder head, which requires a lot of work. There are defects in the processing process and equipment that result in high costs.

The present invention provides a crack prevention method that requires extremely few processing steps, improves the bondability between the heat-resistant metal and the cylinder head, and is manufactured at low cost.

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a cylinder head, 2 is an intake valve seat, 3 is an exhaust valve seat, and 4 is a fuel injection nozzle hole. This nozzle hole may not be formed in the cylinder head casting. 6 is a heat-resistant metal layer for crack prevention obtained by the method of the present invention.

The production of the heat-resistant metal layer 6 will be explained with reference to A and B in FIG. 2, FIG. 3, and FIG. 4.

When the cylinder head is cast, a recess 5 is formed between the intake and exhaust valve seats 2 and 3 or between the intake and exhaust valve seats 2 and 3 and the fuel injection nozzle hole 4, as shown in FIG. 2A. That is, the recess 5 is formed at the same time as the cylinder head 1 is cast. FIG. 2B shows that when building up the heat-resistant metal layer, around the recess 5 to prevent the molten heat-resistant metal from flowing out.
A border portion 7 is formed.

Next, it is taken out from the mold in a high temperature state (400℃~
As shown in FIGS. 3A and 3B, a molten metal such as nickel, iron, or both may be injected into the recess 5 of the cast cylinder head 1 at a temperature of 700° C., or a molten metal of an alloy of both may be injected into the recess 5, or The heat-resistant metal layer 6 is fused and formed by welding overlay 6a using a welding rod made of the same material.

Thereafter, the heat-resistant metal layer 6, including the built-up 6a, is cut or ground by ordinary machining after being cooled to release stress and strain.

The present invention has the following special effects compared to the conventional art.

The process of forming the heat-resistant metal layer 6 up to the normal machining of the cylinder head 1 is practically within the scope of a foundry, and includes the conventional process of removing the crack prevention part by machining, and The thermal spraying steps for layers and coating layers are omitted.

That is, the recess 5 in which the heat-resistant metal layer 6 is fused and buried is formed by casting the cylinder head 1, and when removed from the mold, only the scale of the recess 5 is removed, and the heat-resistant metal layer remains as it is. It can be obtained by simply injecting molten metal or welding.

Furthermore, the heat-resistant metal injected into the recess 5
Improved bondability with In other words, the recesses 5 remain as cast surfaces on the grain blocking surface, and are still in a high temperature state (400
Since molten heat-resistant metal is injected or built-up into the recess 5 of the cylinder block 1 immediately after casting, which is at a temperature of 700°C to 700°C, the recess 5 and the heat-resistant metal layer 6 are
and are fused together in a so-called cross-linked state on the grain blocking surface of the casting surface. Therefore, the buried heat-resistant metal layer 6 does not fall out of the recess 5 over time.

In addition, in normal machining of the cylinder head 1, processing is performed after the heat-resistant metal layer 6 is fused and buried and slowly cooled, so the cylinder head 1 is sufficiently subjected to thermal stress distortion. A high-precision finish can be obtained, and there are no problems such as distortion after finishing.

As described above, the present invention has the advantage of being a method for preventing cracks in cylinder heads, since the number of processing steps is substantially limited to that of a foundry, making it easy and inexpensive.

[Brief explanation of drawings]

The drawings are examples of the method of the present invention, and FIG. 1 is a plan view of the main part of a cylinder head, and FIGS. 2, 3, and 4 are illustrations of the method of the present invention.
-A cross-sectional view. DESCRIPTION OF SYMBOLS 1... Cylinder head, 2... Intake valve seat, 3... Exhaust valve seat, 4... Heat injection nozzle hole, 5... Recess, 6... Heat-resistant metal layer, 6a
...Inner filling, 7...Edging part around the recess.

Claims (1)

[Claims] 1. A recess is formed between the intake and exhaust valve seats of the cylinder head or between the intake and exhaust valve seat and the fuel injection nozzle hole during cylinder head casting, and the heat-resistant metal is molten in the recess of the cylinder head cast in a high temperature state after being removed from the mold. 1. A method for preventing cracks in a cylinder head of an internal combustion engine, the method comprising: applying injection overlay or weld overlay, slowly cooling the overlay, and after cooling, performing normal machining including the overlay part.