JPS5926363B2 - Manufacturing method of cold rolled steel sheet - Google Patents

Description

[Detailed Description of the Invention] The purpose of the present invention is to directly annealing a cold-rolled steel plate without a cleaning process such as electrolytic cleaning to produce a steel plate with a clean surface (hereinafter referred to as a mill-clean sheet). .

In general, rolling oil used in cold rolling, fine iron powder generated during rolling, and other dirt adhere to the surface of a steel plate after cold rolling.

If this steel plate is annealed as is, carbon, iron powder, etc. will remain even after annealing, making it difficult to produce a steel plate with a clean surface.

Therefore, in cases where a high level of surface cleanliness is required, such as with steel plates for plating, in most cases electrolytic cleaning is performed to remove rolling oil, iron powder, etc. from the surface.

By the way, for non-plated steel sheets that do not require a very high level of cleanliness, milk-clean sheets are manufactured in some cases.

Conventionally, when manufacturing Mill Clean sheets, most of the rolling oil composition uses mineral oil as the main component, which easily decomposes and evaporates during annealing, and also contains an emulsifier to create a low concentration emulsion of a few percent or less. I am using it.

Furthermore, since fats and oils such as beef tallow have a lot of residue during annealing, even when blended as a rolling oil composition, care is taken to keep the amount blended as small as possible (so that the amount of residual oil after rolling is reduced).

In addition to the above, in order to produce a mill clean sheet, rolling is carried out using a mill clean sheet other than emulsion rolling oil in the final stand of a continuous rolling mill.

The present invention relates to a method for manufacturing the above-mentioned mill clean sheet, and its characteristics are as follows: In the conventional method, rolling is performed using a low concentration emulsion oil containing less oil and fat and containing an emulsifier as the rolling oil. On the other hand, in the present invention, a non-emulsifying polar compound containing no emulsifier is pre-coated on the steel sheet before rolling, and is used as a lubricating and cooling fluid during rolling.

Use water alone or an aqueous liquid that dissolves or disperses in water.

Therefore, the effects of the present invention can be roughly summarized into the following three types.

(1) Since it is pre-coated with a non-emulsifying polar compound that does not contain an emulsifier, it is difficult to remove the emulsification with coolant during rolling, and the lubricity is far superior to conventional emulsion-type rolling oil, so it can be used in rolling mills. It is possible to obtain a large rolling reduction rate in the first half of the stands (especially the first stand).

Therefore, the adhesion amount of the pre-coat compound is reduced (by rolling with a smaller rolling reduction in the latter half of the stand),
In the second half, the amount of iron powder generated decreases.

As a result, the amount of iron powder generated during rolling and directly attached to the steel sheet after cold rolling can be reduced.

(2) By using water alone or a water-soluble or water-dispersible lubricant as a lubrication and cooling fluid during cold rolling,
It assists in lubrication in the latter half of the continuous rolling mill, where the amount of pre-coat compound adhesion is reduced, and at the same time, when the final stand uses only water, water-soluble or water-dispersible lubricants can be easily washed with water. , the amount of residual rolling oil can be reduced compared to conventional emulsion rolling oil.

Furthermore, by using an aqueous solution or aqueous dispersion with a low concentration (2% or less), the residual amount can be reduced without washing with water.

(3) Since only water or a lubricant/coolant that is soluble or dispersible in water is used, it takes time and effort to manage the coolant, and scum and iron powder are easily separated.

That is, since it is a water-based coolant, unlike emulsion rolling oil, there is no change in concentration due to separation of oil, and it is stable.

Furthermore, the precoat compound separated from the steel sheet during rolling is difficult to emulsify, so it floats and is easily separated.

Furthermore, with conventional emulsion-type rolling oil, it is difficult to trap and separate fine iron powder generated during rolling into the emulsion, so as the rolling oil ages due to the use of recirculate, the amount of iron powder in the emulsion oil increases. There is a tendency for it to re-deposit on the surface of the steel sheet during rolling.

- Iron powder can be easily separated with a magnetic filter using power water or a water-soluble or water-dispersible coolant;
Re-adhesion of iron powder to the steel plate by using recirculate can be reduced.

As described above, in the present invention, most of the lubrication effect during rolling is carried out by the non-emulsifying polar compound that does not contain an emulsifier, but as the rolling continues from the first stand, the precoat compound Since the amount of adhesion gradually decreases and the number of subsequent stands decreases, it is desirable to shift the rolling schedule so that the maximum rolling reduction is achieved in the first stand and the rolling reduction is sequentially reduced.

Furthermore, as the number of subsequent stands increases, the amount of pre-coat compound deposited decreases, and the lubricity decreases accordingly.
In order to supplement the lubricity in this case, rolling can be carried out without any practical problems by using a rolling lubricant and coolant that is water-only or is soluble or dispersible in water.

In other words, if the plate thickness is relatively thick, it is possible to roll with water alone, but if the plate thickness is slightly thin (water alone does not provide enough lubrication), use a lubricant that dissolves or disperses in ζ water. Depending on the situation, it may be difficult (rolling can be performed.

The polar compound for precoating used in the present invention includes:
For example, organic phosphorus compounds, organic boron compounds, amines, fatty acids, alcohols, fatty acid partial esters and saturated esters of polyols having three or more OH groups in one molecule, fatty acid partial esters of polyalkylene glycols, and fatty acid esters of saturated ester monools. , etc. are easily available at economical prices.

Other organic polar compounds mentioned above that have good lubricity can also be used in the same way.

A pre-coat amount of 0.0117m2 or more is good from the lubricity point of view, but economically it is 0.01r~
2 S'/m2 is preferred.

That is, even if it is deposited in excess, it is uneconomical because the parts other than those deposited on the steel plate during rolling and those deposited on the rolls separate and float in the coolant as scum.

Next, the lubricant that dissolves or disperses in water, which is used as a rolling lubricant and coolant in the present invention, is used to compensate for the lack of lubricity of the pre-coated polar compound as described above, and is used as a lubricant with water alone. Since it is used when lubricity is insufficient, it must have better lubricity than water alone.

Lubricants used for such purposes include & Water-soluble sugars, fatty acid alkaline soaps, etc. are easily available at economical prices.

Materials other than these can be similarly used as long as they are soluble or dispersible in water and have better lubricity than water.

When using these additives, the higher the concentration, the better the lubricity will be, but if the final stand is not washed with water, they will remain on the steel plate, so it is desirable to use them at a concentration of 3% or less.

Further, when washing with water at the final stand, it is possible to use a higher concentration, but from the economic point of view it is desirable to use it at a concentration of 10% or less.

As explained above, in the present invention, rolling is performed using a non-emulsifying type precoat polar compound, and in order to take advantage of its characteristics, the rolling reduction schedule during rolling is shifted, and
By using a water-based lubricant and coolant to assist rolling lubricity, iron powder and
The amount of residual rolling oil is reduced compared to the conventional emulsion rolling method.

Therefore, a milk clean sheet can be manufactured by directly annealing a cold rolled steel plate as it is.

Note that even when the steel strip that has been rolled using the method of the present invention is not annealed directly but is annealed through a degreasing process such as electrolytic cleaning, brushing cleaning, spray cleaning, etc., the residual amount of iron powder and rolling lubricant remains small.・This greatly improves the efficiency and cleanliness of degreasing and cleaning work.

Next, examples of the present invention will be described.

The test method was conducted under the conditions described below.

Rolling material: 2.3 m (thickness) x 150 M (width) x coil (low carbon steel, pickled strip steel) Rolling machine: Work roll diameter 200 TIJ 114-high lever/gum mill Rolling speed: 200 m/min Oil supply device: Tank capacity 2001 rolling Two rolling schedules with an hourly supply rate of 601/min were set as shown in Table 1 below.

Rolling was performed four times using a reversing mill according to the above schedule.

In addition, in order to examine the influence of accumulation of iron powder in the rolling lubricant for each example, 1 ton of each material was rolled and the adhesion of iron powder and rolling oil was measured at the rear end of the rolled steel strip. The amount was measured.

The measurement method is to take a sample of a certain area, and the amount of iron powder is determined by wiping the surface of the sample with cotton soaked in acetone to clean it, and quantitatively analyzing the amount of Fe in the cleaning solution using chemical analysis. Ta.

As for the amount of rolling oil, extraction with normal hexane and then extraction with etal were performed using the Soxhlet method, and the total amount was determined.

In addition, the cleanliness of the above-mentioned rolled steel plate was examined when it was directly annealed without being washed.

The measurement method was to adhere cellophane tape to the surface of the sample steel plate, peel it off, and paste it onto white coat paper, which was used as a judgment material.

As a standard material, sellotape directly attached to white coat paper was used, and this was set as 100, and the above-mentioned judgment material was observed with the naked eye to compare and evaluate the degree of staining.

In this evaluation method, a score of 90 or higher was conveniently adopted as a passing score for the Milk Clean Sheet.

The test results are shown in Table 2. As can be seen from the example results in Table 2, rolling the steel strip coated with a polar compound using only water or a coolant that is soluble or dispersible in water compared to the conventional method in the comparative example. This greatly reduces the amount of rolling oil and iron powder deposited.

Furthermore, when rolling is performed using a coolant that is soluble or dispersible in water and rinsed with water in the final pass, the amount of iron powder adhering to the steel plate is significantly reduced compared to rolling with water, and as a result, the cleanliness of the steel plate after annealing is reduced. will improve.

Claims (1)

[Claims] 1. When cold rolling a steel plate, the surface of the steel plate is pre-coated with a non-emulsifying polar substance that does not contain an emulsifier, and then water or a lubricant dissolved or dispersed in water is applied and rolled, followed by a cleaning process. A method for producing a cold-rolled steel sheet, characterized in that it is annealed without passing through the annealing process.