JPS63183702A - Cold rolling method by multi-stage rolling mill - Google Patents

Abstract

PURPOSE:To prevent slip between rolls and to permit high-draft rolling by roughening the surfaces of intermediate rolls of a multi-stage rolling mill to a rough surface by shot dulling. CONSTITUTION:Two kinds of steel sheets having 1.4mm thickness and 1.2mm thickness are cold rolled from a steel sheet having 2.3mm thickness by the 12-stage cluster rolling mill provided with work rolls 1 having 210mm diameter and the intermediate rolls 2 having 290mm diameter. The slip is substantially prevented at the surface roughness Ra=1.0mum of the rolls 2 when draft is 39.1% at this time. The rolls slip when the draft is 47.8% and, therefore, the slip is prevented when the average roughness is increased to Ra=1.5mum by shot dulling. The high-draft rolling by the shot dulling is thereby permitted and the steel sheets having high quality without having surface flaws are efficiently produced by cold rolling.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method for cold rolling a metal strip using a multi-high rolling mill, particularly in a multi-high rolling mill driven by intermediate rolls.
The present invention relates to a cold rolling method that prevents slip between rolls and enables strong reduction rolling.

(Prior Art) In the field of cold rolling of metal strips, strong reduction rolling is being aimed at, and as shown in FIGS. 1 and 2, intermediate rolls are used to make such strong reduction rolling possible. Multi-high rolling mills such as a 12-high cluster rolling mill and a 6-high rolling mill are known. In the figure, 1 indicates a work roll, 2 indicates an intermediate roll, and 3 indicates a backup roll. In such a rolling mill, high rolling is possible by reducing the diameter of the work roll. However, when the work roll is directly connected to a drive shaft and driven directly by a motor, the work roll 1 has a small diameter. Therefore, the required drive torque increases, and the strength of the drive shaft becomes a problem. Therefore, an intermediate roll with a diameter larger than the work roll is connected to the drive shaft,
The required driving torque is reduced by transmitting the torque required for rolling to the work roll via the intermediate roll.

However, as a conventional knowledge, in this intermediate roll driven rolling mill, the torque necessary for rolling is transmitted through frictional contact between the intermediate roll and the work roll.
Inter-roll ** Coefficient μ between intermediate roll and work roll
If R is smaller than the limit value, a problem arises in that slip occurs between the rolls and torque is not transmitted.

11! To prevent such slip between rolls from occurring!
The limit of the friction coefficient μR is expressed by the following equation (3).

μRPR>PH... (1) PH=2G/DW ------(2) From equations (1) and (2), PR> 2 G/PRD...(3) In the above equation, PR is the friction coefficient between the intermediate roll and work roll, PR is the linear pressure between the intermediate roll and work roll, pH is the horizontal force between the intermediate roll and work roll, G is the torque required for rolling, DW indicates the diameter of the work roll.

In other words, inter-roll slip occurs outside the range of equation (3).

As is clear from the above formula (3), the diameter D of the work roll
When w has a small diameter, the friction coefficient μR that prevents slip between rolls needs to have a larger value. Therefore, in a multi-high rolling mill, driving the intermediate rolls is advantageous not only in terms of driving torque but also in terms of inter-roll slip.

(Problems to be Solved by the Invention) However, even in multi-high rolling mills that drive intermediate rolls, which are advantageous in terms of inter-roll slip, slip between the rolls often occurs during heavy reduction rolling, causing problems. ing.

Therefore, an object of the present invention is to provide a rolling method that prevents the above-mentioned slip between rolls in a multi-high rolling mill driven by intermediate rolls.

(Measures for Solving Problems 82) According to the present invention, cold rolling is performed using an intermediate roll whose surface has been roughened by shot dulling in an intermediate roll-driven multi-high rolling mill. shall be.

(Function) By applying shot dulling to the surface of the intermediate roll to make it a rough surface, the coefficient of friction (PR) between the intermediate roll and the work roll as expressed by the above formula (3) becomes large, and as a result, the friction coefficient (PR) between the intermediate roll and the work roll increases. can prevent slip between rolls.

(Example) In the 12-high cluster rolling mill shown in FIG.
Using a 101 work roll and an intermediate roll with a diameter of 290 u, a large number of low carbon killed steel plates with a thickness of 2.3 mm and a width of 900 mm were rolled using a work roll of 1.41 mm thick and a thickness of 1, 2 n.
The specimens were cold-rolled to two thicknesses A and B at a rolling speed of 200 m and 11 m, respectively. The rolling reduction rate of A is 39.1%, B
The rolling reduction ratio was 47.8%.

During the above-mentioned cold rolling, intermediate rolls whose surfaces have been subjected to shot dal processing and grindstone polishing to various surface roughnesses are used to prevent slippage between the intermediate roll and the work roll during each cold rolling process. The incidence was determined. The results are shown in the graph of FIG.

As is clear from the graph in FIG. 2, in this example, when the rolling reduction rate is 39.1%, if the surface average roughness (Ra) of the intermediate roll is 1.0 μI or more, the slip between the rolls can be almost eliminated. Although it can be prevented, the rolling reduction rate is 47.8%.
In the case of heavy reduction rolling, the average surface roughness of the intermediate roll (
Ra ) was required to be 1.5 μI or more in order to prevent slip between rolls. Therefore, such surface roughness can be obtained by Schottdal processing.

Figure 3 shows a case where the surface of the intermediate roll 2 of the multi-high rolling mill shown in Figure 1 is roughened by shot dulling (marked with ○).
The roll surface average roughness (Ra >) is shown when polished with a grindstone (x mark).

When polished with a whetstone, the roll surface roughness can be changed by changing the whetstone, polishing lubricant, and polishing conditions, and when shot dulling, the roll surface roughness can be changed by changing the shot grid and/or shot conditions. However, as shown in Figure 3, it is generally necessary to maintain the roll surface average roughness (Ra) at a high value necessary to prevent slip between rolls by applying shot dull processing. Can be done. Furthermore, this tendency is particularly noticeable for special rolls that have poor abrasiveness.

(Effects of the Invention) According to the present invention, in a multi-high rolling mill that drives intermediate rolls, it is possible to prevent slip between the intermediate roll and the work roll during hard rolling. This makes it possible to efficiently cold-roll a steel plate with excellent quality and no surface flaws.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of the roll arrangement of a multi-high rolling mill having intermediate rolls used in carrying out the present invention, and Fig. 2 shows the average surface roughness of the intermediate roll surface and the slip occurrence rate between the rolls due to differences in rolling reduction ratio. Figure 3 shows the average surface roughness of the intermediate roll and the roll material when the surface of the intermediate roll of the 12-high cluster rolling mill shown in Figure 1a is shot dulled and polished with a grindstone. It is a graph showing the relationship between 1... Work roll 2... Intermediate roll 3...
・Backup roll 4...Rolled material

Claims (1)

[Claims] 1. A cold rolling method using a multi-high rolling mill, characterized in that rolling is performed using an intermediate roll whose surface has been roughened by shot dulling in a multi-high rolling mill driven by intermediate rolls.