JPS6289563A - Production of heat insulating piston - Google Patents

Abstract

PURPOSE:To improve the heat resistance of a piston and to extend the life thereof by forming a piston injection hole part consisting of a ceramic sprayed layer contg. microcracks and underlying metal sprayed layer on a pattern surface and casting the piston with said part as a core. CONSTITUTION:Heat insulating ceramics is thermally sprayed to the pattern 3 copying the piston injection hole part 2 by using plastic or wax and immediately a refrigerant is sprayed to a coating layer 4a to generated the many microcracks on the coating layer 4a. An Ni or Co alloy is then thermally sprayed onto the ceramic coating layer 4a to form the underlying metal coating layer 6a and thereafter the melt of a piston base metal 10 is poured with the pattern 3 as the core to cast a heat insulating piston 1. The heat resistance of the piston is thereby improved and the life thereof is extended.

Description

[Detailed Description of the Invention] (Industrial Application Field) In the production of pistons for internal combustion engines, a heat-insulating piston is manufactured by casting a core made by thermally spraying ceramic or the like onto a model of the piston nozzle hole into a mold. Regarding the manufacturing method.

(Prior Art) Conventionally, piston nozzle holes that form the combustion chamber are exposed to high temperatures, so they are required to have heat resistance and corrosion resistance to cope with the high temperatures.

Therefore, there is a method of spraying ceramic on the piston nozzle hole, or casting a ceramic sintered body shaped like the combustion chamber (Cumm1nic/TACoM A
Advanced Adiabatic Engine
by R.

Kamos 8AE Technical Paper
5eries* 840428 or Unexamined Japanese Patent Publication No. 1983-
(See Publication No. 87275).

Referring to the disclosure content of the above-mentioned publication, in a gas turbine or other component made of a heat-resistant metal material, a ceramic material having minute cracks on a metal coating layer that is more resistant to high-temperature corrosion than the heat-resistant metal material provided on its surface. A covering layer is formed.

This ceramic coating layer is first formed in an atmosphere controlled to have an oxygen partial pressure of 10-3 Torr or less, at a temperature that is at least the recrystallization temperature of the ceramic and lower than the respective melting points of the base material and the alloy of the coating layer. Ceramic particles are coated by thermal spraying on the base material coated with the heat-resistant metal material heated as follows, and then the surface of the ceramic coating layer is sprayed with a coolant and then rapidly cooled to form a ceramic coating. This causes cracks in the layers.

Parts with a ceramic coating layer made by this formation process have a dense alloy coating layer with few pores, which protects the base material from high-temperature corrosion, and also has the low thermal conductivity and high resistance of ceramics. It is effective in reducing the temperature of parts in vehicles.

(Problems to be Solved by the Invention) However, when the coating layer of ceramic sprayed by the above manufacturing method is used for the nozzle hole of the piston, the piston base material (
For example, cracks or peeling may occur between the piston base material and base metal immediately after thermal spraying or during actual machine operation due to differences in thermal expansion coefficient between the An-8i alloy (An-8i alloy) and the coating layer, or insufficient surface roughness of the base metal due to shot plus (K). Even in the case where thermal stress is alleviated by generating holes and microcracks, the ceramic layer is formed on the underlying metal layer and then cooled with a refrigerant etc. to generate microcracks in the ceramic layer. As shown in the figure, there was a problem in that cracks 5a in the direction across the micro cracks were formed between the base metal layer and the ceramic, causing the ceramic layer to peel off.

Furthermore, since ceramic spraying in these cases is carried out inside the recessed piston nozzle hole 2 as shown in FIG. An oxide layer 11 is formed on the coating layer,
This causes a decrease in the adhesion of the thermally sprayed layer, and there is also the problem that it is difficult to form the coating layer to a uniform thickness K, and the shape of the piston nozzle hole cannot be precisely formed.

In order to solve these problems, the purpose of the present invention is to spray ceramic onto the surface of a model made of the wall surface of the piston nozzle hole, rapidly cool it to form microcracks in the ceramic coating layer, and then coat the base metal. Provides a method for manufacturing an insulated piston that uses thermal spraying to ensure adhesion between the ceramic and base metal layers, prevents cracking and peeling of the ceramic layer due to thermal expansion, and improves heat resistance. It's about doing.

(Means for Solving the Problems) In order to achieve the above object, the method for manufacturing a heat insulating piston of the present invention includes thermally spraying a heat insulating ceramic on the surface of a model formed by molding the wall surface of a piston nozzle hole forming a combustion chamber. After that, the model is rapidly cooled to generate microcracks in the heat-insulating ceramic coating layer, and a base metal such as Ni or Co-based alloy is sprayed onto the coating layer to form a core to be placed in the mold. It is characterized by the fact that the core is cast to form an insulated piston.

(Function) Thermal spraying of ceramics, etc. is not done directly on the recessed surface of the piston nozzle hole, but rather on the surface of a convex model formed by molding the piston nozzle hole, which simplifies the thermal spraying process. ,
To obtain stable adhesion strength without introducing oxides due to splashing of oxidized molten powder that occurs during thermal spraying in a recess, and to obtain an accurate piston nozzle hole shape after completion. I can do it.

Furthermore, since the base metal is thermally sprayed after forming microcracks in the ceramic coating layer, the base metal coating layer is not affected by cooling such as refrigerant that forms microcracks. Improves adhesion strength between coating layers.

Because of this, the nozzle hole of the piston has heat resistance,
This is a heat insulating piston with a ceramic coating layer with high dimensional accuracy.

(Example) Embodiments of the present invention will be described based on the drawings.

FIG. 1 is a flowchart for producing the heat insulating piston 1 shown in FIG.

First, a model 3 of the piston nozzle hole 2 that forms the combustion chamber is created using a material such as plastic or wax that can be melted and incinerated at a predetermined temperature or higher (see FIG. 3).

Next, we added ZrO2* AJ203+ Cr to this model 3.
A 2O3-based ceramic 4 with excellent heat insulation performance is plasma sprayed. FIG. 4 shows a state in which a ceramic coating layer 4a is formed on the model surface 3a by thermal spraying, and the thickness of this coating is preferably CL5m or more in consideration of the heat insulation effect.

Further, during the thermal spraying process, care is taken to ensure that the temperature does not reach such a high temperature that the model 3 collapses, and measures are taken such as waiting for the model 3 to cool before spraying again.

Immediately after the ceramic 4 is thermally sprayed, a coolant is sprayed onto the surface of the coating layer 4a to generate numerous microcracks 5 in the thickness direction of the coating layer 4a (see FIG. 5).

The refrigerant used here is air or Ar.

Inert gases such as He and N2 are used. Furthermore, the width and spacing of the microcracks 5 can be arbitrarily adjusted depending on the thickness of the coating layer 4a and the cooling conditions. Preferably, the width and spacing of the microcracks 5 should be sufficiently small; for example, the width of the cracks 5 is 1 to 50 μm.
, the interval is about [L1 to 10w]. As a means for generating the microcracks 5, in addition to cooling, a sifting surface may be generated by an impact effect using the Sita plast method.

Next, the material used as the base metal 6 for ceramic spraying is, for example, N1A)*NtCrAJ, NtCr
AjY.

N1CoCrAjY, CoCrAjY, FeCrA
jY, etc., and any one of these is sprayed from a thermal spray gun 7 onto the ceramic coating layer 4a.

The thickness of the coating layer 6a of the base metal 6 is approximately α1 to 5cm. In addition, the metal powder used has a surface roughness of 2 after thermal spraying.
The particle size is as large as possible (10
~100μ), and the flight speed of the sprayed particles is preferably not too fast, and is optimally about 50 to 500 m/s.

Based on the above, a core 8 that will become a combustion chamber is formed on the model 3 with two types of coating layers: a ceramic coating layer 4a having micro-cracks 5 and a base metal coating layer 6a made of NteCo alloy. It is placed on the bottom of the mold 9 in which the piston is to be cast.

A piston base material 1 is placed in a mold 9 in which a core 8 is placed in a predetermined position.
A heat insulating piston 1 having a piston nozzle hole 2 formed of a coating layer formed by thermal spraying is cast.

During this casting process, plastic, wax, etc. are deposited on the coating layer 4a.
If it remains on top, apply heat to that part, etc.
Discard the remainder of Model 5.

In addition, when casting the core 8t, the model 3 part of the core 8 is removed in advance.
It may also be used as a shape based only on 6a.

An actual engine test was conducted using the thus manufactured heat insulating piston 1. According to the measurement results of this example, 10
It can be used for over 00 hours without any damage.
Considering that conventional pistons are subject to slight damage even after 50 hours, the new piston has significantly improved heat resistance and lifespan.

The following points can be cited as reasons for the above effects.

■ Surface roughness Rz is 50~ at the time of thermal spraying the base metal.
Since it has a large diameter of 100μ, it has excellent mechanical engagement with the molten metal and can withstand the thermal stress that occurs.

■ When spraying the base metal, unlike when spraying into the recess, there is no brittle oxide between the piston base material and the base metal when the molten metal is cast.

■ The micro-cracks formed in the ceramic relieve the thermal stress on the coating layer, and there is no occurrence of lateral cracks that intersect with the micro-cracks that would cause the ceramic to separate between the underlying metal and the ceramic coating layer.

(Effects of the Invention) As explained above, the present invention is capable of spraying ceramics, etc. on a model of the wall surface of the piston nozzle hole, without injecting oxides that weaken the adhesion strength into the coating layer. If the combustion chamber is created with an accurate shape, it will be possible to obtain an accurate combustion chamber shape, improving heat resistance and service life.

Furthermore, since microcracks are formed in the ceramic coating layer, it is possible to alleviate thermal stress due to the difference in coefficient of expansion with the base metal, thereby further improving heat resistance and service life.

[Brief explanation of drawings]

Fig. 1 is a flowchart showing the manufacturing process of the heat insulating piston according to the present invention, Fig. 2 is a partially enlarged sectional view of the heat insulating piston of the present embodiment, and Figs. 3 to 7 show the manufacturing process of Fig. 1. Figure 8 is a diagram for explaining the cause of peeling of the ceramic layer in the conventional example. Figure 9 is a diagram for explaining the cause of peeling of the ceramic layer in the conventional example. FIG. 3 is a partially enlarged sectional view showing a state of adhesion. 1... Heat insulation piston 2... Piston nozzle hole part 3
...Model 4...Ceramic 4a...
・Ceramic coating layer 5...Minute cracks 6...Base metal 8...Central core 9...Mold fang 1 figure fang 2 figure 4G...7': 7mi・I Kuki skin 1 eyebrow 5・...Minute 77 Tsuku Fang 5 Diagram O 6 Diagram Fang 7 Diagram 8 Diagram

Claims (1)

[Claims] (1) After thermally spraying a heat insulating ceramic on the surface of a model made of the wall surface of a piston nozzle hole forming a combustion chamber, the model is rapidly cooled to generate microcracks in the coating layer of the heat insulating ceramic; Next, a base metal such as Ni or Co-based alloy is thermally sprayed onto the coating layer to form a core to be placed in a mold, and the core is cast to form a heat insulating piston.