JPS61168463A - Surface machining of ceramic part - Google Patents

Abstract

PURPOSE:To improve the mechanical strength on the surface of ceramic by grinding the surface of part through rough grinding wheel then heating under high temperature for short time to form oxide on the surface thereafter grinding the oxide and the skin section slightly through finish grinding wheel thus shortening the thermal processing time. CONSTITUTION:The back face of an impeller 1 is ground efficiently by about 200mum by means of a rough grinding wheel 3 the while rotating the impeller 1, the surface of the impeller 1 is heated through a heater 4 to form oxide on the surface thus to eliminate crack produced through rough grinding. Then the impeller 1 is cooled to grind the back face of the impeller 1 two times by about 5mum by means of a finish grinding wheel 5 thereafter the oxide and the skin section are removed slightly to finish into smooth face thus to improve the strength to finish into smooth face thus to improve the strength after finish work. Consequently, the machining efficiency is improved while the mechanical strength on the surface of the impeller 1 can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a surface processing method for ceramic parts, and particularly to a method for surface processing ceramic parts suitable for use in ceramic parts requiring high surface strength.

[Background of the invention]

When grinding the surface of a ceramic part, if the depth of cut is increased using a rough-finishing whetstone whose abrasive grain size is significantly larger than the crystal grain size of the ceramic, cracks will occur intermittently on the ceramic surface. Reduce strength.

On the other hand, the following literature describes that the mechanical strength of the ceramic surface is improved by subjecting rough-processed ceramic parts to heat treatment (oxidizing the ceramic surface at high temperature).

K, Jakus et al.3 + “Effects of P
reoxidation on the strength
h and Fatigue of Hot-Pres
sedSilicon N1tricle, ”5u
rfacss and interface
Ceramic and Ceramic-Met
al SyStem, J., Pa5kand
A. Evans eds, Plenum Publ.
ishing Carp (1981) pp, 689
~699° Therefore, in order to confirm the results of the above paper, the present inventors investigated silicon nitride (Si) No ) and silicon carbide (
An experiment was conducted on SiC). The experiment consisted of (1) S
The surfaces of the L, N, and SiC test pieces were roughly ground using a diamond grindstone with an abrasive grain size of approximately 400 μm, and
After generating a crack of about 0 μm and holding it in the atmosphere for 1 hour at each temperature, the strength (bending fracture) was measured at room temperature. (2) The heating temperature was kept constant (1200°C) and the holding time was varied. We measured the strength when changing to

Figure 2 is a diagram showing the results for experiment (1);
The figure is a diagram showing the results for experiment (2). still,
In Figure 2, for reference, Si with no cracks,
N and smooth materials are also shown.

As is clear from Figure 2, without heat treatment,
The strength of Sia N4 rough ground material and SiC rough ground material is S
i, N, is quite low compared to the smooth material, however.

When heat treated in the air, the strength of Si and N4 rough abrasive materials increases significantly at temperatures above 800°C, and
The strength of a smooth material is reached at ℃. In addition, the strength of SiC rough abrasive material increases significantly from 1000°C and reaches its maximum strength at 1350°C. This strength is improved by heating in the atmosphere, which combines Si, N, or SiC with 0.0% in the atmosphere. It is thought that this is because the metal reacts to form an oxide, and this oxide eliminates cracks on the material surface.

Further, as is clear from FIG. 3, when the holding time is short, the variation in strength is large, but when the holding time is about 1.5 hours or more, the variation is small and the intensity is saturated. The holding time at which this strength is saturated becomes shorter as the heating temperature is raised, and in particular, in the case of 5iaN, roughly ground material, it decreased to about 15 minutes at 1400°C.

However, if the heating temperature is increased to 1200°C or higher.

As shown in FIG. 2, the strength decreases below the maximum value because the surface layer becomes rougher due to oxidation.

Therefore, in the method of improving surface strength by heat treatment described above, in order to improve processing efficiency, shortening the heat treatment time, that is, increasing the heating temperature and shortening the holding time, will improve the mechanical strength of the ceramic surface. There is no hope for improvement.

[Purpose of the invention]

An object of the present invention is to provide a surface processing method for ceramic parts that can shorten the heat treatment time, improve processing efficiency, and improve the mechanical strength of the ceramic surface.

[Summary of the invention]

In order to achieve this object, the present invention first grinds the surface of a ceramic component using a rough grinding wheel with a large abrasive grain size, and then heats the ceramic surface at a high temperature for a short period of time to form an oxide on the ceramic surface. Formed.

Next, the oxide and some of the surface layer of the ceramic are ground using a finishing whetstone with a small abrasive grain size.

[Embodiments of the invention]

An embodiment of the present invention will be described above with reference to FIG. Figure 1 shows an explanatory diagram of the surface processing method according to the present invention, in which 1 is an impeller for a turbocharger rotor made of Si and N4 with a crystal grain size of 4 μm, and 2 is an impeller that rotates with the impeller 1 fixed. a chuck; 3 is a diamond roughing grindstone with an abrasive grain diameter of approximately 400 μm; 4 is an infrared lamp-type heating device disposed around the impeller 1 to heat the surface of the impeller 1;
5 is a diamond finishing whetstone with an abrasive grain diameter of approximately 20 μm.

Next, the case where an impeller is processed by the surface processing method according to the present invention will be explained.

First, the back surface of the impeller 1 is subjected to high efficiency grinding with a depth of cut of 200 μm using the rough grinding wheel 3 . After the rough grinding is completed, while the impeller 1 is being rotated, the surface of the impeller 1 is heated at 1400°C for 15 minutes using a heating device [4] to form an oxide on the surface of the impeller 1 and roughen it. Eliminates cracks caused by grinding. Next, after cooling the impeller 1, the back surface of the impeller 1 is ground twice with a cutting depth of 5 μm using a finishing grindstone 5 to remove the oxide and some of the ceramic surface layer and finish it into a smooth surface. In the impeller 1 processed as above, the strength of the back surface after rough grinding was approximately 300 MPa, whereas the strength after finishing was improved to 550 MPa.

Therefore, in this embodiment, since the heat treatment time can be shortened, processing efficiency can be improved, and the mechanical strength of the surface of the impeller 1 can be improved.

In addition, in the present invention, the same effects as described above can be achieved also for SiC parts.

〔Effect of the invention〕

According to the present invention, it is possible to improve the processing efficiency and the mechanical strength of the ceramic surface.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing the relationship between heating temperature and strength for ceramics,
FIG. 3 is a diagram similarly showing the relationship between heating retention time and strength. 1...Si, N, impeller, 3...Roughing grindstone,
4... Heating first

Claims (1)

[Claims] Rough grinding is a method of improving the surface strength of a ceramic component by processing the surface of the ceramic component, which involves grinding the surface of the ceramic component using a rough grinding wheel with an abrasive grain size larger than the crystal grain size of the ceramic. process, heating the rough-ground ceramic surface at a predetermined temperature for a predetermined time,
a heat treatment step to form an oxide on the ceramic surface;
A method for surface processing a ceramic component, comprising a final grinding step of grinding the oxide and some of the ceramic surface layer with a finishing grindstone having a smaller abrasive grain diameter than the rough processing grindstone.