JPS58209443A - Cast iron piston and its production - Google Patents

Abstract

PURPOSE:To obtain a cast iron piston having excellent heat resistance and strength by forming a flake graphite cast iron layer of a specific thickness on the wall surface in a piston head part constituting a combustion chamber. CONSTITUTION:A core 1 is formed by a cold box method using a urethane resin, and an annular mold coating 3 is formed in the prescribed place of the core 1 corresponding to the mouth end part 2a of the combustion chamber 2 of a piston 7 by using flake graphite contg. 10% S as a base mold coating material, and using a phenolic resin as a binder and methanol as a solvent. The core 1 is fitted to the lower part of a master mold 4 in such a way that the piston head part is located downward. Molten metal is then charged into the mold to form an annular flake graphite layer 5 having 0.5-3mm. thickness on the surface of the piston head part corresponding to the part 2a formed with the mold coating 3. The cast iron piston 7 wherein the remaining part, i.e. piston body 6 is constituted of spheroidal graphite cast iron having >=90% spheroidization rate is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cast iron piston having a piston body made of spheroidal graphite cast iron, and a method for manufacturing the same.
4! The object of the present invention is to provide a cast iron piston with excellent heat resistance and strength.

In recent years, spheroidal graphite cast iron has been used as a piston for large diesel engines in place of aluminum alloy as a thin-walled structure that takes advantage of its excellent mechanical properties. Compared to aluminum alloy, spheroidal graphite cast iron has Because it has high strength and high heat resistance, and has a small coefficient of thermal expansion,
By reducing the clearance between the piston and cylinder, the wave noise caused by piston slap can be reduced, and because the number of heat conductors is small, the heat flowing through the piston to the lubricating oil and cooling water can be reduced, and the temperature of the combustion chamber can be reduced. The problem is that the engine's heat increases and the engine heat y; It has various advantages such as being able to use IP+ conveniently. However, if a piston made of spheroidal graphite cast iron is used in an engine where the heat load is high in some areas, the pistons will generate cracks and the lifespan will not necessarily be shortened compared to pistons made of aluminum alloy. It turned out that there was a major drawback that could not be improved.

This is due to poor heat soaking of the cast iron material, which causes some parts to be overheated (for example, the combustion chamber mouth end of page injection +!, combustion chamber engine of #I flow engine, pre-combustion chamber engine, etc.). This is because cracks occur due to the excessive thermal stress t that occurs as a result of an increase in the temperature gradient of the piston head portion (blowing) that constitutes the combustion chamber, such as the portion where gas hits the piston.

This invention was made to improve the drawbacks of conventional pistons made of spheroidal graphite cast iron. There are those who practice Shomanden.

The piston body of the cast iron piston according to the present invention is made of precipitated spherical Kuro-Kanbyouyoriki (Takubo Kurozuri), and at least partially between the walls of the piston head constituting the combustion chamber. Thickness 0.6-3m, more preferably 0.5-2
A flaky graphite cast iron layer of M+11 is formed. The thickness of flaky graphite T18100 directly below the casting surface in this part must be at least 0.6 m from the sharp point to prevent thermal cracking, and if it becomes too thick, the strength of the entire piston will decrease, which is not preferable. On the wall surface of the piston head that makes up the combustion chamber, the mechanical stress that occurs when fuel burns is small, but the thermal stress is greater. Lifespan will be improved. The flaky graphite formed on the wall surface of the piston head that constitutes the combustion chamber has the potential to reduce the mechanical strength of the cast iron, but it is caused by combustion pressure. Since the stress around the combustion amount is always small, there is no problem in terms of strength even if this part is made of flaky graphite. In addition, thermal stress occurs all around the end of the mouth of the combustion chamber in the case of a straight piston, but since the flaky graphite described above absorbs the positive thermal stress l, the original pressure of the four cracks is (The sword that greets you)
Also, since the thermal stress has no directionality, the tips of all the graphite flakes become the starting point for flies.As a result, the tiny 7Z reefs generated at the tips of countless graphite flakes release the thermal stress. As a result, the crack propagation speed slows down.

The iron piston mentioned in this invention can be manufactured according to the various examples shown in Figs. 1 to 6.

? For example, as shown in Figure 1, a bath water containing predetermined chemical components is created, a core is created using a cold box method using urethane resin, and a piston (7
) The core (It) corresponding to the mouth (2a) of the combustion chamber (2) is filled with earthy graphite containing 810% as a violet indicator and phenol resin as a binder, and furthermore, methane, - A ring-shaped coating mold (X (1) is formed using the mold as a solvent.Then, this core (1) is inserted into the lower part of the main mold (4) so that it is below the piston head part S, and #
Part 8: On the surface of the piston head corresponding to the part (2a) where 3 holes are formed on the coating mold, a ring-shaped flake graphite layer (51) with a thickness of about 1 inch is formed. Part of the piston body (618 spheroidized 490% or more spherical graphite piece Yoriki 1 and concentrated acid 2nd iron leg piston (7)
Create.

As a method for forming a flaky graphite cast iron layer, in addition to S, glJ materials that inhibit spheroidization, such as Ei%Pb and Sb.

Examples include a method of mixing an element such as Sn into a mold coating agent. In addition, by such a method, a layer of flaky graphite cast iron can be formed under the surface of the piston head. However, among the spheroidization-inhibiting elements, Te and B have a tendency to become white. However, since it has the opposite effect in terms of thermal cracking, it is not desirable to use it for the above purpose.

The flaky graphite cast iron layer (5) can also be formed using an organic binder whose hardening agent is a mold material that generates sulfur-based gas. For example, as shown in FIG. As a result, the sulfonic acid is thermally decomposed and a chemical gas is generated, which reacts with the bath water. The ridges are also flaky to the deep part, starting from S - iron layer L5
J can be formed □. However, in this case, be careful not to allow the flaky graphite to precipitate other than in designated areas.
Using a coating agent such as Fe2 (J3), which has the effect of vitrifying the molten metal when it is injected and preventing the reaction of the sulfide-based gas from the core (1) with the molten metal, another Type 1
It is necessary to form B+.

In addition, in Example 1 described above, the coating mold (3) does not necessarily have to be in a continuous ring shape, but may be intermittently. At this point, the flaky graphite cast iron layer (5) also becomes intermittent. Another value type! :(In addition to graphite, the coating mold base material for i may include alumina, zirconia, chromium sand, etc. However, graphite acts as a charcoal material and has the effect of assisting the formation of flaky graphite. It's convenient.

Alternatively, in the T method shown in FIG. 6D, the first honey mold I3: may be omitted and the second M-shaped mold (4) may be used as shown in FIG. The precipitation of flaky graphite is promoted only by the embrittlement gas emitted from the lifting platform and the core illumination force S.

In this invention, the mold base material, the bath medium of the mold coating agent, the spheroidizing agent, the caking agent for trout mold, its hardening agent, etc. are conveniently used in combination to form the necessary layer of flaky graphite cast iron. The thickness can be changed to the desired thickness. Also, the formation of molten metal -7-
The component, A strain method is not limited as long as the spherical shape of the piston body (6) is sufficiently ensured.

Hereinafter, this invention will be explained in detail in Example 1.

Specific example Cast iron (3 rods No. 1 D) 250 kg, steel scrap 13. ,−
Ll sure, return m 110 kg, Fe-8i Q,
Ite for 95 kgf, chemical composition 05.5%, Sj 2
．． 5%, hen 0.3%, PO, L111%, SQ,
010% R near high-class V-air furnace (500Hz
X 3 Q Q kW, 5 Q Q kg)

As shown in the following diagrams, a core (11) is created using the cold box method using urethane ++l BH. Apply a ring-shaped coating mold (using 810% raw graphite with 7i#) and phenol mBFIf binder and methanol as the interrogating medium at the designated location of tl+.
3) was formed. This core fi+ was fitted into the lower part of the main M (4), and spheroidized with 81-mg of the melt #h so that the remaining sleeve g was Q, 03-chi, and Fe-Si
As shown in Figure 2, a ring-shaped reed-like graphite cast iron layer (5) with a thickness of about 0.55 m is formed at the mouth end (2a). a Iron biston (7) was formed.

The piston body (6), which is the remaining part of the piston, was made of spheroidal graphite cast iron with a spheroidization rate of 90 cm or more.

Figure 5 I shows a ml photo of the S-iron piston (combustion chamber opening 4 of the piston head of 7i) part (2a) that was served in this way, based on the Gengakken v!J current photo (activity rate 100). show.

In this diagram @5, the upper 1/4 part; + (gray part) is a part of the piston model (6) made of spheroidal graphite cast iron; 1. The remaining part (whitish part) swimming in the lower 1/6th fishing space (black F!!, part) is flaky graphite trout f,
/I +51 is shown.

For the piston (7) obtained in this way (high f
f1j wave power V heat t Koyoru Enki Roushu station 0 This test is 1 piston (7) combustion to (2) mouth 4 g (2a)
After heating at i 450 C1 for 7 seconds, 2 to 1ooc
This was carried out by repeating the heating/cooling cycle of air cooling for 0 seconds (mF). For comparison, a colleague also tested a piston lζ made entirely of spheroidal graphite cast iron. In FIG. 6 showing the test results, straight line mA is for the cast iron piston obtained in the above specific example, and curved line B is for the cast iron piston of the comparative example.

From the test results shown in FIG. 6, the piston according to the present invention, which has one layer of flaky graphite cast iron at a predetermined location, cracks more slowly than the pistons in the comparison series made of only spheroidal graphite cast iron, and causes less cracking (deterioration). In the case of the comparative example with only the spheroidal graphite rust area, the number of 4-tables is small, but they grow large and long, whereas in the case of the piston made by Fueiaki, which has flaky graphite-iron structure, there are many fine lines. Although the sword appears 4, his skill is very unyielding, and it goes without saying that his outside life will be greatly improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view showing the method of manufacturing a cast iron piston according to this 9F5 method, and Fig. 2 is a schematic cross-sectional view showing a method of manufacturing a cast iron piston according to this invention. The schematic IIMwr plan view of the mounting part, FIGS. 3 and 4 are from this invention I.
Fig. 5 is a cross-sectional view showing the different parts of the method of assembling a cast iron piston, and Fig. 5 shows the combustion process of the cast iron piston shown in Fig. 2 and the end section. (1f410U)I
Copying 4 and Figure 6 are the 'Aj' phrases for the cast iron piston shown in Figure 51 and the square iron piston for comparison. Leather sword U
It is a graph showing the relationship between the number of thermal cooling cycles and the total crack length in the thermal fatigue equation. A review of the f dimensions that are expended on the second evil side (here, III.
・・・－・・・・・・・・・Nakako, 3〕・・・・・・・・・
・・・・・・・・・Tray type T4+・−・−・・・・・・・・・・
−・・Main student (5)・・・・・・・・・・−・・・・piece (
) to the black Tsuiya compilation theory (ll(b)...
...The piston is defective. Agent Shiji Figure 1 Figure 2 Figure 3 Figure 4 a Figure 51'1

Claims (1)

[Claims] 1. The piston body made of spheroidal graphite cast iron and the wall surface of the piston head constituting the combustion chamber have a thickness of 0.
A cast iron piston comprising a 5 to 3 m layer of flaky graphite cast iron. 2. In the method of manufacturing an S-iron piston having a piston body made of spheroidal graphite cast iron, vl'J! inhibits the cooling of graphite. A layer of flaky graphite cast iron with a thickness of 0.3 = 3 rm is formed on the wall surface of the piston head part constituting the combustion chamber by applying a coating agent containing i to predetermined areas of the mold. A manufacturing method for Kiyou pistons with special care. 3. In the a-shield method of a leg iron piston having a piston body made of spheroidal graphite (fc force), a gas containing a substance formed by forming graphite rods is pressurized. ! By molding using a mold made of # type material, a flaky graphite cast iron layer of 0.6 to 6s11 is formed on the image plane of the piston head that controls the appearance of the piston.8% Method of manufacturing a cast iron piston to be imitated.