JPH044045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cold rolling metal strip.

A method is known in which three or more work rolls are arranged in a row to form two or more rolling passes, and the material is passed through these rolling passes continuously to roll a strip (one-stand multi-pass rolling method). It is being During rolling, the strip is wrapped approximately half a circumference around the work roll. In this rolling method, one rolling stand can perform rolling for a plurality of rolling stands, so there is an advantage that the entire rolling equipment can be downsized and the equipment cost can be reduced.

Generally, lubricants are used in cold rolling to reduce the rolling load and improve the surface quality of the product strip. The one-stand multi-pass rolling has different lubrication problems than the one-stand, one-pass rolling.
That is, in one-stand multi-pass rolling, there is some slip between the work roll and the strip wound around it. Therefore, when conventional lubricating oils are used, this slip causes seizure defects in the strip. These seizure defects become noticeable when the rolling reduction per stand exceeds about 60%.

In addition, in single-stand multi-pass rolling, by appropriately selecting the circumferential speed of the work rolls and adjusting the tension acting on the strip, it is possible to roll without strip breakage and to lower the rolling load. From this point of view, it is desired to further reduce the rolling load and power.

This invention was made to solve the above-mentioned problems in conventional cold rolling, especially one-stand multi-pass rolling, and it is possible to roll strips with low rolling load and power without causing seizure defects on the strips. The purpose of this invention is to provide a cold rolling method capable of rolling.

In this invention, in one-stand multi-pass rolling, a phosphate or oxalate solution is supplied to the strip surface immediately before rolling, and a phosphate film or oxalate solution with a basis weight of 0.01 to 10 g/m ² is applied to the strip surface during rolling. Forms an acid salt film. More preferably, when the phosphate or oxalate solution is supplied, it is used together with water, a water-soluble lubricant or rolling oil to roll the strip.

The phosphate film or oxalate film remains uniformly on the strip surface even after rolling, and is effective in preventing seizure during rolling and reducing rolling load and power. From this, the rolling method of the present invention can be put into practical use industrially by significantly reducing the number of rolling passes, reducing the number of stands in a tandem rolling mill, and further improving the mechanical properties of the final product by increasing the strain rate. The economical effect on strip manufacturing is significant.

This invention will be explained in detail below.

In this invention, as described above, a phosphate film or an oxalate film is formed on the surface of the strip during rolling. The phosphate film may be any of an iron-based phosphate film, a zinc-based phosphate film, a manganese-based phosphate film, and a phosphate film containing calcium, cobalt, nickel, etc. in zinc. Similarly, the oxalate film may be any of an iron-based oxalate film, a zinc-based oxalate film, a manganese-based oxalate film, and an oxalate film containing calcium, cobalt, nickel, etc. in zinc.

Oxalate film has the following features compared to phosphate film. In other words, the oxalate film remaining on the surface of the steel sheet after rolling has a radiant heat absorption efficiency of 50% compared to conventional cold-rolled steel sheets at the initial stage of heating with combustion gas in the continuous annealing step, which is the next step after rolling.
% or more, and furthermore, the steel plate temperature is
When the temperature rises to around 500℃, the oxalate film rapidly decomposes into FeO, CO ₂ and CO. Therefore, when cold rolling is performed with an oxalate film formed, if the rolling oil used is one that easily evaporates during annealing, the degreasing process can be avoided.
If continuous annealing is performed, an annealed steel plate without carbon stains and with less adhering iron powder can be obtained.

The basis weight of the phosphate or phosphate film is preferably 0.01 g/m ² or more in order to follow the increase in surface area of the steel sheet caused by high pressure rolling of 50% or more.
If it exceeds 10 g/m ² , it is an economic loss and, at the same time, the chemical conversion treatment takes too much time as a pre-process to cold rolling, which tends to cause unreasonable processes. Also,
Occasionally, parts of the rolling rolls may build up. Therefore, it was found that 0.01 to 10 g/m ² is preferable.

In the present invention, instead of applying a chemical conversion treatment to the steel strip to form a phosphate film or an oxalate film in advance, the phosphate film or oxalate film is formed on the steel strip in a rolling line. urge

This not only simplifies the process by eliminating the need for a chemical conversion treatment process prior to the rolling process, but also requires plastic processing when applying an aqueous solution of phosphate or oxalate to the roll bite. Since an aqueous solution of phosphate or oxalate is applied to the new, highly active surface of the steel that appears during the process, it is possible to form a strong film, and even in the later passes of the multi-stage pass, it is possible to prevent seizure defects. It has the advantage of effectively suppressing its occurrence.

The most rational implementation mode for applying this invention is to use a mixture of water, a water-soluble lubricant, or rolling oil, and a phosphate or oxalate as a lubricant in rolling multi-pass rolling. and applied to steel strips in a similar manner.

This point will be specifically explained using an example where water and a phosphate or oxalate solution are used together. In order to accelerate the chemical reaction with the steel strip, disodic phosphate (Na ₂ HPO ₄ ) is added to water heated to about 60° at a concentration of about 2% (depending on the target coating weight). Mix the desired amount and stir. In addition, at this time, the solution in which the phosphate is dissolved in water is
The pH is adjusted to about 6.5 to promote chemical reaction with the steel strip. For example, an aqueous solution so prepared in the main tank of a conventional circulating rolling lube supply system is supplied to the steel strip surface from a rolling lube supply nozzle connected to the tank. The aqueous solution supplied to the steel strip chemically reacts with the iron, forming a film of iron phosphate (FePO ₄ ) on the surface of the strip in a short period of time. This film is formed not only up to the entrance of the roll bite of the rolling mill, but also within the roll bite, where a chemical reaction occurs with the new surface of the steel strip produced by rolling, and the film is formed. In this way a phosphate coating is formed on the surface of the steel strip.

Furthermore, in order to increase the rolling lubrication effect, if an emulsion rolling lubricating oil using an aqueous solution containing a water-soluble lubricant or rolling oil instead of water is used in combination with a phosphate or oxalate solution, the lubrication effect can be improved. further improves.

In this way, there is no need to separately provide a chemical supply system for forming a phosphate film, etc., and a supply system for water-soluble lubricants, etc., and there is an advantage that it can be a simple hardware system. .

One of the features of the method of the present invention is that the amount of fine iron powder generated during rolling is much smaller than in conventional methods, and at the same time, the amount of wear on the rolling rolls is also small. Therefore, in the rolling oil emulsion type, which is used repeatedly for the same amount of rolling, there is very little contamination of the water-soluble lubricating oil by generated iron powder. In addition, the part of the chemical conversion coating that is peeled off during rolling has a lower surface energy than the iron powder generated during conventional rolling.
Since it does not form a stable composite emulsion like iron powder forms when mixed into rolling oil emulsion or water-soluble lubricating oil, it is easily separated and rarely produces so-called rolling oil scum.

After rolling, the chemical conversion coating can be easily removed by a conventional electrolytic degreasing process. For example, the original sheet before rolling is 3.2mm
When a 0.4 mm rolled sheet was obtained by two-pass rolling, a 2 g/m ² zinc phosphate film was formed on the original sheet, and a 0.12 g/m ² phosphate film was formed on the steel sheet surface after rolling. remained. Almost no phosphate remained on the surface of the steel sheet that had passed through the conventional alkaline electrolytic degreasing line. Furthermore, when box annealing is performed without going through a degreasing process, annealing at a relatively high temperature causes a so-called seizure phenomenon, resulting in a decrease in product yield. According to the method of the present invention, the phosphate film remaining after rolling has a good anti-seizure effect during box annealing, so it is possible to increase the winding tension during rolling, and also to reduce the roughness of the steel sheet. However, if the box is annealed with the phosphate film still attached, the seizure phenomenon can be prevented.

Next, the results of experiments conducted to confirm the effects of the present invention will be explained.

FIG. 1 and FIG. 2 respectively show the results of experiments on the relationship between rolling load and rolling power consumption with respect to rolling reduction using three types of lubricants. In the figure,
The solid line indicates 1-stand 3-pass rolling, and the broken line indicates 1-stand 1-pass rolling. In the figure, the x mark indicates that the beef tallow-based rolling lubricant commonly used in conventional cold rolling mills has been changed to an emulsion rolling lubricant with a concentration of 5% and a temperature of 60°C.
It shows the rolling load or rolling power consumption when pass rolling and one-stand one-pass rolling shown in FIG. 4 are performed.

○ and △ marks are the cases where the iron-based phosphate film and the zinc-based phosphate film of the present invention were formed, respectively. In other words, using the same rolling lubricating oil supply system used in the experiment marked with an X, the concentrations were prepared by mixing and stirring iron-based phosphates and zinc-based phosphates into water at a temperature of 60°C in the main tank. A 3% aqueous phosphate solution was applied to the strip to form 1 shown in Figure 3.
It shows the rolling load or rolling power consumption when three-stand rolling and one-stand one-pass rolling shown in FIG. 4 are performed. In addition, the basis weight of both the iron-based phosphate coating and the zinc-based phosphate coating at this time was 0.6 to 1 g/ ^m2 when the basis weight of the plate after rolling was converted to the basis weight of the plate thickness before rolling. .

The roll configuration of the rolling stand used in the above experiment is shown in FIGS. 3 and 4. Figure 3 shows a 1-stand 3-pass rolling stand, with work rolls 1, 2, 3, 4 and back-up rolls 5.
The strip S is wound around the work rolls 2 and 3 over approximately half a circumference. Fourth
The figure shows a one-stand, one-pass rolling stand, which is a six-high rolling mill consisting of work rolls 6, intermediate rolls 7, and back-up rolls 8. The work rolls of both rolling stands have a diameter of 300 mm and a length of 800 mm.

The steel plate used in the experiment was 2.6 mm thick and 600 mm wide. The steel plate has a rolling speed of 100 m/min and an entry tension of approximately 5.
It was rolled under conditions of Kg/mm ² and exit tension of about 20 Kg/mm ² .

The following is clear from Figure 1.

(1) In one-stand three-pass rolling, the rolling load of the product coated with the film of the present invention is about 10 to 15% lower than that of the product lubricated with tallow-based emulsion.

(2) The rolling load of 1-stand 3-pass rolling is less than 1/2 that of 1-stand 1-pass rolling. This is not simply due to the effect of single-stand multi-pass rolling. That is, in the case of one-stand three-pass rolling, the film is made uniform in the first rolling pass, and the friction between the roll and strip is reduced in the second and subsequent rolling passes.

Furthermore, the following is clear from FIG.

(1) In one-stand three-pass rolling, the rolling power consumption of the product coated with the film of the present invention is about 20 to 40% lower than that of the product lubricated with tallow-based emulsion.

(2) The rolling power consumption of 1-stand 3-pass rolling is approximately 35% smaller than that of 1-stand 1-pass rolling. The reason why the rolling power consumption becomes smaller is the same as in the case of rolling load.

In the above experiment, in the case of tallow-based emulsion lubrication, seizing defects occurred when the rolling reduction exceeded 60%. However, in the case where a phosphate film or an oxalate film was formed, no seizure defects occurred even when the rolling reduction exceeded 70%.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are graphs showing the relationship between rolling reduction, rolling load, and rolling power consumption, respectively, using the lubricant as a parameter. FIGS. 3 and 4 are schematic diagrams showing examples of roll configurations of a one-stand multi-pass rolling stand and a one-stand one-pass rolling stand, respectively. 1, 2, 3, 4, 6...work roll, 5, 8...
Back-up roll, 7...middle roll.

Claims (1)

[Claims] 1 Work rolls are arranged in multiples, and a metal strip is wound around the work rolls so as to pass continuously, and the strip is rolled between a pair of adjacent work rolls in one stand. In the pass cold rolling method, a phosphate or oxalate solution is supplied to the strip surface immediately before rolling, and a basis weight of 0.01 to 10 g/m is applied to the strip surface during cold rolling.
A cold rolling method characterized by forming a phosphate film or an oxalate film of ^m2 . 2. The cold rolling method according to claim 1, wherein water, a water-soluble lubricant, or rolling oil is used in combination with a phosphate or oxalate solution during cold rolling.