JPH044069B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is applicable to small engines, that is,
Removes residual stress without a special heat treatment process in the casting process of cylinder liners made of cast iron or its alloys, which are used in engines of 2000 c.c. Regarding the method.

(Prior art) Cylinder liners for small engines have a cylindrical shape.
page), the wall thickness is 3.5 mm to 10 mm (published by Maruzen Co., Ltd. on April 10, 1971, Casting Handbook, page 711), and the material is cast iron or It is formed by casting using the alloy (published by Maruzen Co., Ltd., April 10, 1970, Foundry Handbook, page 711).

The casting process for the cylinder liner is generally as follows. First, in a sand mold (published by Maruzen Co., Ltd., April 10, 1970, Foundry Handbook, page 714), the temperature is 1350 to 1700℃ (published by Sanseido Co., Ltd., March 1, 1970, Mechanical Engineering Essentials No. 590). After pouring the molten metal of the cast iron or its alloy mentioned above (page), a molding process is performed in which the molded product is left in a sand mold for an appropriate period of time considering the structure and hardness of the molded product, and then the molded cylinder liner is taken out from the sand mold and cooled. A cooling process is performed, followed by shot blasting, a cleaning inspection process to check for defective products, and then heating at approximately 550°C for 2 to 4 hours in an electric furnace or heavy oil furnace to remove residual stress. A heat treatment step is performed, followed by a cooling step and a cleaning step in which shot blasting is performed again to complete the processing step. During each of these steps, there is a cooling step before and after the heat treatment step, but both of these are necessary in relation to the heat resistance of the machine that performs shotblasting, and the first cooling step in particular is It is considered a wasteful process since a heat treatment process is performed afterwards, but the purpose of the cleaning and inspection process that follows is to check for defective products and send only standard products to the heat treatment process, so as long as the heat treatment process exists, It cannot be omitted.

(Problems to be Solved by the Invention) In the conventional casting process, there is a special heat treatment process to remove residual stress, so the cooling process and cleaning process, which would normally be done only once, are must be carried out twice, causing a time loss in the entire process, or the amount of heat required to cool and then heat again, resulting in an economic loss.Furthermore, the heat treatment process and the subsequent cooling process This method also has the disadvantage of causing a loss in the work process of moving the molded product to perform the process.

(Summary of the Invention) The object of the present invention is to provide a method for removing residual stress in the casting process of cylinder liners for small engines that eliminates these drawbacks. We focused on the idea that the treatment could be done by using the residual heat generated during pouring without having to do it as a process, and we developed it after numerous experiments. 13 minutes after bathing
By setting the time to 20 minutes, it is possible to remove residual stress to a level higher than that of the conventional method or more.

(Example) Hereinafter, an example will be described in which the present invention is applied to a casting process of a cylinder liner for an engine having a displacement of 2000 c.c., in which the leaving time in the sand mold is set to 20 minutes.

The shape, material, etc. of the cylinder liner for an engine with a displacement of 2000 c.c. are roughly standardized as mentioned above, and in this example, the shape, material, etc. are exactly the same as the conventional one. It was carried out in the following.

In other words, the shape is cylindrical and the wall thickness is 3.5mm.
~10mm (product wall thickness). The dimensions during processing (casting) are approximately 5 mm to 20 mm thick, including processing allowance, and the material is cast iron or its alloy.

Furthermore, as mentioned above, full-surface sand molds are quite common for this type of cylinder liner.
A sand mold is also used in this example. The temperature of the molten metal during casting is 1350°C to 1700°C.

In this example, the leaving time in the sand mold was 2 after pouring.
minutes, 5 minutes, and then every 5 minutes up to 35 minutes. After each time, the molded cylinder liner was taken out of the sand mold and the upper and lower limits of the residual stress were measured using X-rays. The graph shown is created by connecting each lower limit. Comparing these measured values with the residual stress values of the same cylinder liner for a small engine as in the example, in which the residual stress was removed by special heat treatment as in the past, it was found that the difference between the two after being left in the sand mold for about 18 minutes. It was confirmed that the upper limits of It was also confirmed that the upper limit of residual stress became almost constant after 20 minutes of being left in the sand mold. As can be seen from these results, leaving the sand in the mold for more than 20 minutes makes little difference in effectiveness, but it does lead to a loss of time in the process.
The leaving time in the sand mold of 20 minutes in this example is the best. If the leaving time in the sand mold is set to at least 18 minutes, the same residual stress removal effect as in the conventional example can be obtained. Note that there was no difference in hardness or structure from the finished product in this example.

In the present invention, the leaving time in the sand mold is appropriately set according to the displacement and material of the engine to which the cylinder liner is attached, and the leaving time in the mold is set to a length proportional to the size of the displacement. However, as is clear from the measurement results in the above-mentioned embodiments, a certain degree of range is allowed for this standing time.

The thickness of the material is set at a range of about 5 mm to 20 mm, but this width is not affected by any heat during casting.

(Effects of the Invention) As is clear from the above description, according to the present invention, it is possible to achieve a residual stress removal effect equivalent to or better than that without performing a special heat treatment process, while at the same time By omitting this, the casting process of cylinder liners for small engines can be simplified and work efficiency can be improved.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

[Brief explanation of drawings]

The figure is a graph showing the relationship between the time left in the sand mold and the residual stress in a preferred embodiment of the present invention, and a comparison with the residual stress in a conventional treatment example of the same product.

Claims (1)

[Claims] 1 The shape is cylindrical and the thickness of the material is 5 mm to 20 mm.
It is a cylinder liner for a small engine of about
In the molding process in which molten cast iron or its alloy is poured and molded, the time for leaving it in the sand mold is set to 13 to 20 minutes after pouring, and residual stress is removed by residual heat generated during this time. A method for removing residual stress in the casting process of cylinder liners for small engines, characterized by: