JPS5952019B2 - Small cylinder liner manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a small cylinder liner, and more particularly, to a method for manufacturing a small cylinder liner that allows a cylinder liner for a small engine made of pearlite to be obtained by as-casting.

Methods of manufacturing castings such as large cylinder liners using molds on the outside diameter are widely known.

This outer diameter mold is manufactured using expensive alloy steel in order to increase the life of the mold, and the wall thickness of the mold is increased in order to prevent danger, improve precision, and extend the life of the mold.

As a result, the mold temperature rises excessively during repeated cycles, and in order to cool this down, conditions such as water cooling are added, and a cycle of about 9,000 shots can be achieved.

However, in the case of small cylinder liners, rapid heat conduction occurs from the contact surface between the outer diameter mold and the molten metal to the thick mold, causing rapid cooling and chilling at the corners of the casting surface.
Post-processing becomes impossible.

In addition, the matrix structure of the as-cast, rapidly cooled casting is prone to dendrite formation, which becomes the base structure of the ferrite 1, and this ferrite formation disrupts the so-called compatibility and balance with the piston ring, promoting wear.

For this reason, manhole covers where chill is not a problem,
As-cast castings are used for water pipe joints and the like.

In addition, cylinder liners that have been chilled after being cast are further heat-treated to become pearlite.
This is disadvantageous in terms of heat treatment cost and man-hours.

For this reason, outer diameter molds are not used to cast thin, small cylinder liners that are more susceptible to rapid cooling, and casting is performed using sand mold core cores and outer diameter sand molds, or centrifugal casting is used. ing.

In this case, both the outer diameter sand mold and the sand mold core must be disintegrated each time, resulting in low productivity and increased total cost.

In addition, centrifugal casting is difficult to manufacture because thin castings tend to have uneven wall thickness, and when trying to manufacture small cylinder liners, it is difficult to obtain sufficient uniformity unless ultra-high rotation is used. There's a problem.

Unlike sand molds, etc., casting using an outer diameter mold has the characteristic that casting can be repeated many times continuously, but conventional outer diameter molds inevitably require rapid cooling, It is not possible to generate pearlite in free casting.

It was thought that making the wall thickness of the outer mold even thinner would not only affect the life of the mold, but also have a negative effect on dimensional accuracy. It had never been thought that it would be possible to obtain high-grade cast iron with a high quality cast iron that satisfies mold life and dimensional accuracy in the as-cast state.

Therefore, the present inventors researched a small cylinder liner casting method using an outer diameter mold, which had been thought to be impossible in the past, and explored the possible conditions and range of the use of an outer diameter mold by changing various conditions. As a result, it is possible to obtain a small cylinder liner that is equivalent to or better than all-sand casting only under certain conditions and within certain ranges, that is, it is made of pearlite in the as-cast state and has finer graphite than when using a sand mold. Ta.

In other words, to date, outer diameter molds have been used that have a wall thickness that is at least five times the product wall thickness in order to increase the mold life, the strength of the surface that comes into contact with the molten metal, and to withstand rough handling. Furthermore, it has become common technical knowledge to perform water cooling to avoid heat accumulation in order to extend the life of the mold, and we have never seen an example in which the conditions for the sand mold core core and outer mold wall thickness were considered. However, through experiments in which the outer diameter mold wall thickness for this sand mold core core was varied over a wide range, the inventors succeeded in determining the outer diameter mold wall thickness, which is completely different from conventional outer diameter molds. By setting the wall thickness to approximately the same as that of a small cylinder liner, that is, approximately 50 to 150% of the wall thickness of a small cylinder liner, and using it in combination with a sand mold core core, rapid cooling of the molten metal can be prevented, and the planned pearlite It was possible to obtain as-cast castings from the ground.

In other words, the object of the present invention is to generate pearlite in the as-cast state by using a sand mold core core and an outer diameter mold, and by making the wall thickness of the outer diameter mold approximately the same as the thickness of a small cylinder liner. To provide a method for manufacturing a small cylinder liner, which is characterized by:

Embodiments of the present invention will be described in detail below with reference to the drawings.

An outer diameter mold 12 made of a frame having a wall thickness equivalent to that of a cylinder liner 10 for a small engine is produced, and the temperature of this outer diameter mold 12 is preheated and maintained at 150 to 500°C.

Next, the sand mold core core 14 is set in the outer diameter mold 12 core,
A commonly used molten metal for a green mold is poured between the outer diameter mold 12 and the sand mold core core 14.

The molten metal poured into the mold releases solidification heat to the outer diameter mold 12 and the sand mold core core 14, and solidification begins.

However, the heat release of the molten metal in contact with the sand mold core core 14 is extremely slow due to the heat insulation properties of the sand mold core core, and for this reason, most of the heat of the molten metal is transferred to the outer mold with excellent heat conduction. The outer diameter mold 12, which had been preheated in accordance with the flow,
temperature rises rapidly.

This temperature rise prevents the molten metal from cooling rapidly, and when 5 to 10 seconds have elapsed after the end of the molten metal injection, the outer diameter mold 12 is opened and the solidified cylinder liner is taken out together with the sand mold core core.

The cycle of inserting a new sand mold core again, closing the outer diameter mold, and pouring the metal can be repeated.

The outer diameter mold temperature has risen to about 600° C. in this case.

Since rapid cooling of the molten metal is prevented, there is no risk of chill occurring due to rapid cooling, and even in the as-cast state, the pearlite base is almost 100% without the base becoming ferrite.
Occur.

According to the results of various experiments in which the wall thickness of the outer diameter mold 12 is made thinner, cooling becomes slower and a structure closer to that of green casting can be obtained. There is a technical limit in this respect because deformation is likely to occur and the mold life is shortened.

Therefore, 50% of the cylinder liner wall thickness for small engines
It is difficult to practically use an outer diameter mold having a wall thickness below.

Furthermore, backing up the thin outer diameter mold with a heat insulating material is useful for preventing rapid cooling, but heat accumulates in the outer diameter mold, making it unusable in a short period of time.

On the other hand, by increasing the wall thickness of the outer diameter mold, it is possible to increase the mold life and prevent thermal deformation of the outer diameter mold. Therefore, it is not practical for an outer diameter mold having a wall thickness of 150% or more of a small cylinder liner wall thickness.

In this case, the term "cylinder liner for small engines" refers to the cylinder liner for engines used in passenger cars, motorcycles, motorcycles, etc. equipped with 2000cc class gasoline engines or 3000cc class easel engines. For example, diameter 50
~150mm, height 50~250mm, wall thickness 5~8m
The upper and lower limits of the wall thickness of the product part were mainly from 2 to 15 mm.

The lower limit is mainly due to the problem of uniformity which makes the hot water flow inappropriate, and the upper limit is due to the formation of ferrite.

An example of an experiment conducted using the experimental apparatus shown in FIG. 2 regarding the change in the metallographic structure of a cylinder liner for a small engine due to a change in the wall thickness of the outer diameter mold will be explained with reference to the metallographic micrograph shown in the drawing.

Furthermore, here A: CO2 mold B: Cast product part.

Wall thickness: 6 m/m (t) C: Outer diameter mold D: Mold wall thickness: 3 m/m E: Mold wall thickness: 6 m/m F: Mold wall thickness: 9 m/m G: Mold wall thickness: 18 m/m Mold Temperature 250℃ Molten metal composition C=3.25%, 5i=2.3%Mn=0
．． 6% P=0.3% 3% picral etch.

Parts D, E, and F, which range from 50 to 150% of the cylinder liner wall thickness, are as-cast and made of pearlite, but the outer mold wall thickness is 300% of the cylinder liner wall thickness. The G section has a ferrite base and is unsuitable for use as a cylinder liner.

Figure 4A shows a comparison of the structures of cylinder liners for small engines manufactured using other conventional methods and cylinder liners for small engines manufactured using the method of the present invention.
Do this for B and C.

A: Cylinder liner obtained by conventionally used sand mold core core and outer diameter sand mold B: External mold and sand mold core core having a wall thickness five times that of cylinder liner for small engines. Cylinder liner C obtained by using: A cylinder liner obtained by using the thin outer diameter mold and sand mold core core according to the present invention.

The outer diameter mold used here was made of cast iron, which is extremely inexpensive, and could be used repeatedly for about 3000 cycles.

Examining each structure, the cylinder liner obtained using only the sand mold A is made of pearlite, but the grain size of the crystals is large.

It can also be seen that the distribution of graphite is poor, with graphite growing in thick flakes.

In other words, in order to improve wear resistance, it is desirable for pearlite and graphite to be finely and uniformly dispersed and precipitated in the ground, but in sand casting, cooling is too slow and pearlite and graphite grow too much. .

The structure of the cylinder liner made by using the thick outer diameter mold B is excellent in that the graphite shape is fine flakes and the distribution is uniform, but since it is made of ferrite material, it is too soft and has poor wear resistance. Therefore, it is not compatible with conventional piston rings.

The structure of the cylinder liner made using the thin-walled outer diameter mold according to the present invention shown in Fig. C has graphite precipitated finely and evenly, and is made only of pearlite with high wear resistance, and the shape of the graphite is also better than that using a sand mold. Since the precipitation is fine and average, two conditions that determine wear resistance are satisfied.

Note that what appears white and amoeboid in the 400x magnified photograph is the phosphorus eutectic structure and not ferrite.

As described above, the method for manufacturing cylinder liners for small engines according to the present invention is extremely remarkable in that it combines the advantages of using an all-sand mold and an external mold. The diameter mold can be made of extremely cheap and thin materials such as cast iron, and the composition of the molten metal used for pouring does not require a special composition, and the molten metal for green molds that is commonly used can be used as is. This has the remarkable effect of making it possible to obtain a cylinder liner for a small engine made of high-grade cast iron using a simple method such as the following.

In this application, sand mold core cores include core cores made of inorganic materials with high heat insulation properties, such as concrete molds. It is not recommended to perform backups.

This is because the method of the present invention relies on the balance between the thermal conductivity and heat capacity of the outer diameter mold, the thermal conductivity of the outer diameter mold surface, in other words, the heat insulation, and the heat capacity of the molten metal. This is because when backing up, heat accumulation occurs in the thin outer diameter mold, causing thermal deformation of the outer diameter mold and causing problems in terms of dimensional accuracy.

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 the drawing]

The drawings show an embodiment of the invention, and FIG. 1 is a cross-sectional view of the mold;
Figure 2 is a vertical cross-sectional view of the mold, and Figure 3 is a vertical cross-sectional view of the mold. E, F, G are the second drawings, E, F,
Structure photograph of part G of the casting product, Fig. 4A is a 100 times enlarged micrograph of the whole sand casting metal structure, a is a 400 times enlarged micrograph, and Fig. 4B is the conventional thick outer diameter die cast metal. FIG. 4C is a 100 times enlarged micrograph of the structure of a cast metal according to the method of the present invention, and FIG. 4C is a 400 times enlarged micrograph of the structure. 10...Cylinder liner, 12...Outer diameter mold, 14...Sand mold core core.

Claims (1)

[Scope of Claims] 1. Pearlite is generated in the as-cast state by using a sand mold core core and an outer diameter mold, and making the wall thickness of the outer diameter mold approximately the same as the thickness of a small cylinder liner. A method for manufacturing a small cylinder liner characterized by: 2. The method for manufacturing a small cylinder liner according to claim 1, wherein the small cylinder liner has a wall thickness of 2 to 15 mm. 3 The wall thickness of the outer diameter mold is 50~ than that of the small cylinder liner.
A method for manufacturing a small cylinder liner according to claim 1 or 2, wherein the cylinder liner is in a range of 150%. 4. The method for manufacturing a small cylinder liner according to claim 1, which uses a sand core core for the cylinder bore core.