JPS5881918A - Fused silica roll for heat treatment furnace - Google Patents

Abstract

PURPOSE:To prevent the build-up which is made of the adhering substance piled up on a roll surface from strip by keeping the surface roughness of the roll used for heat-treating metal strip successively at predetermined value. CONSTITUTION:As a main component, a roll contains silica which is sintered with surface roughness of 20-140mum Rz on the outer surface of the roll. When the surface roughness of the roll is suitable, strip is in contact with only the protrusion 1 of the roll surface. Though adhered substance 2 sticks on the roll is removed by the friction between said substance and the strip coming successively. But when the difference between the protrusion and the depression is small, the adhering substance is put into the depression and is built up. Thus, when the surface roughness of the roll is kept in said range, the build-up is reduced, thereby preventing the occurrence of the defects on the strip surface.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the surface texture of fused silica rolls used for continuous heat treating of metal strip.

As rolls for continuous heat treatment furnaces of silicon steel, stainless steel, galvanized iron plates, etc., rolls made of heat-resistant alloys,
Those whose surfaces have been subjected to thermal spraying treatment, asbestos rolls, Kirkene rolls, fused silica rolls, etc., are used. These methods have different conditions such as temperature and atmosphere depending on the material to be heat treated, the purpose, etc., and are used depending on these conditions, but it cannot be said that they are always fully satisfied.

A common requirement for hearth rolls is the absence of build-up. The strip to be heat-treated moves on the roll in a specific atmosphere at a high temperature of 500°C to 1200°C, contacting and rubbing against it, and during this process, deposits from the strip stick to and accumulate on the roll surface, causing so-called This results in build-up, which causes defects such as strip flow and scratches.

Rolls made of heat-resistant alloys tend to generate build azo more easily as the heat treatment temperature increases, and even rolls that have been surface-treated by thermal spraying cannot necessarily be said to have a sufficient effect. Due to its characteristics, asbestos roll has a limited heat resistance, and as the temperature rises, its lifespan rapidly decreases. Toriki-Zenroll can be used in a reducing atmosphere and build-up is relatively rare, but it suffers from significant wear and tear and has a short lifespan. Also, of course, it cannot be used in an oxidizing atmosphere.

Furthermore, compared to the other roll materials mentioned above, the fused silica roll has less build-up, has excellent heat resistance and abrasion resistance, and has a long life. Furthermore, since the coefficient of thermal expansion is extremely small at 0.04% at 1000° C., it has good spalling resistance and can sufficiently withstand temperature changes caused by rapid movement of rolls into and out of the furnace.

However, the degree of build-up is affected by the condition of the surface of the fused silica roll that comes into contact with the strip.

On the other hand, it is generally said that the smoother the roll surface condition and the smaller the surface roughness, the better, but the inventors' experiments have shown that having a certain level of surface roughness gives better results for build-up. It has been found that the present invention has the greatest difficulty in adhesion from the strip, and even if adhesion does occur, it is removed before the build-up occurs and the strip becomes defective. The present invention provides a fused silica roll for use in a heat treatment furnace that has an appropriate surface condition that does not cause .

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

A fused silica roll having an outer diameter of 120 cm and a length of 1500 m and a wall thickness of 25 cm was manufactured by a casting method. The particle size structure is 0.3-0.
1 tra 40%, 0.1~0.04 tram1
0%, 0.0w 450cm, - Membrane physical properties are apparent porosity 10.
5% bulk specific gravity 1.94, bending strength 150 kg/f, chemical components 810299.8%, At 20.0.02%
, Fe203 was 0.08%, and crystallinity was 0%. The sintered rolls were subjected to surface grinding and polishing to produce rolls with different surface roughness as shown in Table 1 below.

Table 1: Surface roughness greater than 2o o II) 4 Rz was determined from experience to be a clear cause of scratches and was excluded from the test.

The rolls of A-G were set around a metal shaft and used at 500° C. or higher in a heat treatment test furnace. 1 month after the start of the test, 3
It was taken out of the furnace in January and June, and the condition of the surface was investigated. The results are shown in Table 2 below.

Table 2 As is clear from Table 2 above, brownish deposits are seen in all cases, but the smoother the surfaces with less roughness (A, B), the more they adhere to the entire surface. The surface roughness is large and the rough surface (C-G) has less adhesion, with adhesion on the convex portions of the uneven surface and no adhesion on the concave portions, leaving a white background color.

Regarding the relationship between the roughness of the text and scratches, I tested it by changing the speed of the IJ knob and the rotation speed of the roll, and found that there was no problem at all below /410tysRz, but 2
It was found that 0019NRz may cause scratches in the early stages of use.

As described in the examples, it was found that there were differences in the way deposits adhered depending on the surface condition of the fused silica roll, and similar results were obtained in repeated tests.

In general, it is said that the surface condition of a roll is smoother with less roughness and closer to a mirror surface, as this will cause less build-up and will not cause problems such as curvature and scratches.

However, according to the test results of the inventors on fused silica rolls, the surface roughness is small (/(7Rz
(below) is C20I91Rz or higher, which has a larger surface roughness)
It was found that there was a lot of deposits and build-up was likely to occur. This means that the surface roughness is large (201
1) xR'z or more), as shown in Figure 1, the strip contacts only the head of the convex part 1 of the unevenness of the roll surface, and the deposit 2
However, no adhesion occurs in the recess 3. The adhesion has a low adhesion strength due to low compatibility with molten silica (wettability 1 reactivity), so once it accumulates to a certain extent, it easily falls off and is removed by friction with the subsequent strip and does not grow into a large deposit. .

On the other hand, if the surface roughness is small and becomes less than 10PRz,
As shown in FIG. 2, since the difference in unevenness is small and the groove 4 is shallow, the deposits 2 enter and stick to the bottom of the groove. Therefore, the adhesion will be connected to the entire surface including the grooves, and if this happens, it will not be easily removed by the frictional force with the subsequent strip. - Once the entire surface is covered with foot deposits, it gradually accumulates on top of it, eventually resulting in a build-up.

Furthermore, it is clear that increasing the surface roughness to an extremely large extent will cause scratches, and this naturally limits the surface roughness. Therefore, the surface roughness is 4-10~/(104)sRz (L=
J! ξ■) is the most appropriate surface state.

Regarding C, D, E, and F, no build-up occurred even after one year of continuous use, and they have been used smoothly without any wear or the like.

In addition, the roll material is At203°Z for fused silica stone.
rO2", 5i02. ZrO2, CaO, MgO, C
It goes without saying that materials to which r2O3 and other components are added have similar effects if their chemical and physical properties are similar to those of fused silica.

The present invention is based on the above-mentioned system, but the roll according to the present invention has five
It exhibits remarkable effects when used at high temperatures of 00℃ or higher, especially 800℃ or higher◎

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing how deposits adhere to a fused silica roll for a heat treatment furnace with a large surface roughness according to the present invention, and Fig. 2 shows how deposits adhere to a conventional roll for a heat treatment furnace with a small surface roughness. It is an explanatory view showing how to wear a kimono. 1...Convex portion, 2...Adherence, 3...Concave portion, 4...
・Groove. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 255

Claims (1)

[Claims] The main component is sintered and bonded fused silica. -The surface roughness of the outer surface of the wheel is 20~/? l Ohr, mez (L =
Fused silica roll for heat treatment furnace, characterized by being Z F m )◎