JPS6150041B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for vertically asymmetric rolling of strips. Here, vertically asymmetric rolling refers to rolling in which rolling conditions are different for the upper and lower surfaces of the strip. Specifically, rolling with upper and lower rolls with different diameters (D _{1 ≠} D _{2 )} as shown in FIG. Alternatively, it refers to winding rolling (γ ₁ ≠ γ ₂ ) and rolling that combines these a to c. Recently, a method of vertically asymmetric cold rolling of a strip has been widely studied from the viewpoints of high reduction in one pass, reduction of rolling load, improvement of the cross-sectional shape of the plate, and downsizing of the rolling mill. However, this method significantly impairs the quality of the strip due to (a) differences in gloss and surface roughness between the top and bottom surfaces of the strip, (b) warping of the plate, and (c) generation of heat streaks. There was a problem. Therefore, this invention was made in order to solve the above-mentioned problems in vertically asymmetric rolling of strips, and provides a cold rolling method that allows strips with excellent cross-sectional and surface shapes to be obtained by vertically asymmetric rolling. This is what we are trying to provide. This invention will be explained in detail below. The inventors conducted research to solve the above-mentioned problems in vertical asymmetric rolling, and as a result of repeated experiments, they found that the occurrence of differences in gloss, surface roughness, warping, heat streaks, etc. is greatly affected by the lubrication state during rolling. I found out that this happens. In other words, when the same type of lubricant is supplied at the same flow rate to the upper and lower surfaces of the strip as in the past during vertical asymmetric rolling, the film thickness of the lubricant between the rolling roll and the strip differs between the upper and lower surfaces, which causes a difference in gloss. It was found that this is the main cause of the differences. Therefore, in the present invention, the upper and lower surfaces of the strip are lubricated under different lubrication conditions to form a lubricant film with approximately the same thickness on the upper and lower surfaces of the strip. By the way, the film thickness t _d of the lubricant is expressed by the following relational expression if the amount of lubricant supplied is sufficient so that most of the lubricant injected onto the plate at the roll inlet does not enter the roll bit. t _d ∝η (Uo + Ui) / αP ₁ ... (1) where, η: Viscosity of lubricant Uo: Roll circumferential speed Ui: Speed of material (strip) entering the rolling mill α: Engagement angle P ₁ : Roll Two-dimensional yield stress of the material at the entry point of the tool. Rolling is carried out on the upper and lower surfaces of the strip under the same conditions.
In other words, in vertical symmetrical rolling, the above η, Uo, Ui, α
Since P ₁ and P 1 have the same value, the film thickness t _d is approximately equal on the upper and lower surfaces. However, in vertical asymmetric rolling, for example, in the cases shown in Figure 1 a and c, α in the above formula (1) differs on the upper and lower surfaces of the strip,
In the case of (b), since Uo is different, the film thickness _{t d} is different on the upper and lower surfaces. In addition, the oil film thickness is also affected by the concentration of the lubricant, and there is a relationship of t _d ∝ (concentration of lubricant) ...(2), and when the amount of lubricant supplied is insufficient, t _d ∝ (concentration of lubricant) supply amount) ......(3) is the relationship. This invention focuses on the fact that the film thickness of the lubricant changes depending on the lubrication conditions, that is, the viscosity, concentration, and supply amount of the lubricant as described above, and changes the lubrication conditions according to the degree of asymmetry in rolling. The lubricant film thickness is made to be approximately equal on both the upper and lower surfaces. Note that when the lubricant supply is sufficient, the viscosity (oil type, etc.) is changed, and when the lubricant supply is insufficient, the concentration and/or
Or adjust the lubrication condition by changing the supply amount. Here, this invention will be explained in more detail. Embodiment 1 FIG. 2 is a block diagram of an apparatus for carrying out this invention.
A cold rolling mill 1 rolls a strip S using rolls 2 and 3 of different diameters. In this embodiment, since the upper surface of the strip rolled down by the small diameter roll 2 has a larger bite angle α than the lower surface, the lubricant film thickness t _d is smaller than the film thickness of the lower surface from equation (1). Therefore, a higher concentration of lubricant is provided on the top surface of the strip. In FIG. 2, an emulsion of rolling oil and water is sprayed onto the rolling rolls 2, 3 and the upper and lower surfaces of the strip by nozzles 5, 6, respectively, and after lubricating and cooling the rolling rolls 2, 3 and the strip S, It is collected in the collection tank 11. The collected emulsion is sent to a centrifuge 13 by a pump 12,
Here, it is separated into high concentration and low concentration emulsions. Then, the emulsified liquid is stored in a high concentration tank 14 and a low concentration tank 15, respectively, depending on the concentration. The high concentration emulsion is sent to the nozzle 5 by the pump 16 and supplied to the upper surface side of the strip, which has poor lubricity, and similarly the low concentration emulsion is sent to the nozzle 5 by the pump 17.
and is supplied to the bottom side of the strip through the nozzle 6. The concentration of the emulsified liquid having both high and low concentrations is adjusted by a concentration adjusting device 18 provided between both tanks 14 and 15. In this embodiment, the oil supply system is of a circulation type, and rolling oil of the same brand is supplied to the upper and lower surfaces of the strip at different concentrations so that the lubrication state is approximately the same. Example 2 In this example, a rolling oil whose emulsification is somewhat unstable is used, and is supplied to the rolling rolls and the strip surface in a circulating manner. As shown in FIG. 3, the recovered emulsion of rolling oil and water is allowed to stand still in a recovery tank 21. Here, the emulsion is divided into two types of emulsions with different concentrations as the rolling oil is partially separated, and the high concentration emulsion separated in the upper layer is transferred to the tank 22, and the lower concentration emulsion is flow into the tank 24, respectively. The emulsified liquids are agitated in the tanks 22 and 24 by agitators 23 and 25, respectively, and the emulsified liquid with a low concentration of rolling oil is supplied to the lower surface of the strip from the nozzle 6 via the pump 26. Further, the high concentration emulsion is mixed with the low concentration emulsion sent from the concentration adjustment device 28 in the mixing tank 27, stirred by the agitator 29, and then passed through the pump 30 and the nozzle 5 to the upper surface of the strip. Supplied. In this embodiment, as in the first embodiment, rolling oil of the same brand is supplied to the upper and lower surfaces of the strip at different concentrations in order to eliminate differences in the lubrication state due to differences in rolling conditions. Embodiment 3 In this embodiment, two types of rolling oil having different lubricating properties are separately supplied to the upper and lower surfaces of the strip depending on the degree of asymmetry of the rolling conditions. Here, the lubrication properties specifically refer to viscosity, viscosity index, boundary lubrication performance, etc. In Figure 4,
A low viscosity oil stored in a tank 31, such as mineral oil-based rolling oil, is supplied via a pump 32 and a nozzle 6 to the lower side of the strip, which has excellent lubrication. Conversely, high viscosity oil stored in a tank 33, such as tallow-based rolling oil or polyvalent fatty acid ester, is supplied to the upper surface of the strip via a pump 34 and a nozzle 5. The oil supply system of this embodiment is of a direct type, and coolant (water) from a tank 7 is sprayed onto the exit side of the rolling mill 1 by a pump 8 and a nozzle 9. Embodiment 4 In this embodiment, as shown in FIG. 5, a highly lubricating oil such as beef tallow or wax is applied in advance to the top surface of the strip, which is poorly lubricated, using a pre-coat device 41 before the rolling mill 1. At the lower entry side and upper exit side of the rolling mill 1, coolant from a tank 7 (pre-coated beef tallow, which has lower lubricity than wax) is sprayed onto the strip and rolls 2 and 3 by a pump 8 and a nozzle 9. be done. Next, an example of the effects of this invention will be shown. Table 1 shows comparative data of rolling results by various rolling methods. Different speeds and different diameters have a large effect of reducing the rolling load, but when rolling with different diameters and different concentrations, the appearance of the rolled plate is almost the same as that of normal rolling, and if the conditions are finely adjusted, the rolling force can be reduced to about 1/5. Cold rolling of plates can be done efficiently under load.

[Table] As explained in detail above, in this invention, when the lubrication conditions differ between the upper and lower surfaces of the strip due to differences in rolling conditions, the lubricant concentration, viscosity, etc. are adjusted so that the lubrication conditions are approximately equal on both the upper and lower surfaces of the strip. I try to roll it. Therefore,
Even with so-called vertically asymmetric rolling, strips can be cold rolled without producing defects such as differences in gloss, differences in surface roughness, warpage, heat streaks, etc. in the finished product. Furthermore, the present invention enables the practical application of vertically asymmetric rolling, which has many excellent advantages such as high pressure reduction, low rolling load, good plate cross-sectional shape, and compact rolling mill.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of vertical asymmetric rolling. Second
5 to 5 are block diagrams of an apparatus for carrying out the method of the present invention, respectively. 1... Cold strip rolling machine, 2, 3... Roll, 5, 6, 9... Nozzle, 7... Coolant tank, 11, 21... Emulsion liquid recovery tank,
8, 12, 16, 17, 26, 30, 32, 34
...Pump, 13...Centrifugal separator, 14,15,
22, 24, 27, 31, 33...Tank, 1
8, 28...Concentration adjustment device, 23, 25, 29...
...Agitator, 41...Precoat device.

Claims (1)

[Claims] 1. Different lubricating properties are provided on the upper and lower surfaces of the strip so that the film thickness of the lubricant between the rolling roll and the strip is approximately equal on the upper and lower surfaces of the strip. 1. A method for vertically asymmetrical cold rolling of a strip, characterized by supplying a lubricant having the following properties. 2. A patent claim in which the supply of the lubricant comprises using lubricants of the same composition, supplying a high-concentration lubricant to one strip side and supplying a low-concentration lubricant to the other strip side. The rolling method according to item 1. 3. The supply of the lubricant comprises supplying a lubricant with high lubricity to one strip surface and supplying a lubricant with low lubricity to the other strip surface. rolling method. 4. The rolling method according to claim 1, wherein the supply of the lubricant comprises applying a highly lubricating lubricant to one strip surface in advance on the entry side of the rolling mill.