KR100361619B1 - A method of alkaline cleaning for cold-rolled steel - Google Patents

Abstract

The present invention relates to an alkali cleaning method of a cold rolled steel sheet, and more specifically, can be degreased at a lower temperature than in the case of using a caustic soda, a conventional degreasing liquid, and without forming an oil layer on the surface of the steel sheet It is about the method of degreasing.

According to the present invention, when the cold rolled steel sheet is immersed in a cleaning solution containing a caustic soda solution, and degreased, the cleaning solution is 0.25 g of diethylene glycol butyl ether and sodium gluconate in a caustic soda solution, respectively, based on the total weight of the cleaning solution. An alkali degreasing method of a cold rolled sheet is provided by adding within a range of -0.45% by weight and comprising depositing and degreasing the cold rolled sheet in the cleaning solution at 45-55 ° C.

According to the present invention, by adding diethylene glycol butyl ether and sodium gluconate to the caustic soda solution which is an alkaline degreasing solution, it is possible to degrease at a lower temperature and to prevent the formation of an oil layer on the surface of the solution.

Description

Alkaline cleaning method of cold rolled steel sheet {A METHOD OF ALKALINE CLEANING FOR COLD-ROLLED STEEL}

The present invention relates to an alkali cleaning method of a cold rolled steel sheet, and more specifically, can be degreased at a lower temperature than in the case of using a caustic soda, a conventional degreasing liquid, and without forming an oil layer on the surface of the steel sheet It is about the method of degreasing.

Generally, foreign materials such as rolling oil, dust, and machine oil are attached to the surface of cold rolled steel sheet at about 200mg / square meter, and these materials form carbides due to incomplete combustion during annealing, causing defects in the process after annealing. In addition, since it deteriorates the aesthetics of the surface, it is cleaned by chemical and mechanical methods during degreasing. The allowable amount of residual oil after this degreasing process depends on the type of rolled oil and the treatment process after degreasing.

This degreasing process is a method of depositing a steel plate in an alkaline solution (for example, sodium hydroxide or sodium ortho-sodium silicate) in a range of 80-85 ° C. to degreaser it, which is generated by electrolysis of water after passing the steel plate through an alkali tank. Oxygen and hydrogen gas to pass through the electrolytic cleaning tank for removing foreign matter on the surface of the steel sheet.

The strip of cold rolled steel sheet degreased in the electrolytic cleaning tank passes through a hot water cleaning tank for cleaning the residue on the surface of the steel sheet by water, and then sprays hot air onto the surface to remove moisture from the surface. To dry.

In this degreasing process, the degreasing process is performed at a relatively high temperature of 80-85 ° C., which adversely affects the environment and has a problem in that a considerable amount of energy is consumed.

Therefore, the present inventors have invented and applied a technology capable of performing a degreasing process at 50 ° C. with an alkaline solution containing 0.25-0.45% by weight of dodecyl alcohol ethoxylate and sodium gluconate, respectively. : 1998-48447).

However, when degreasing the cold rolled steel sheet with a degreasing solution containing dodecyl alcohol ethoxylate and sodium gluconate, it was found that when left for several hours or when degreasing with the same solution, an oil layer was formed on the surface of the solution. This oil layer may reattach to the surface of the degreased steel sheet, which may cause surface defects. Thus, the inventors have studied and studied diethylene glycol butyl ether in the same concentration instead of dodecyl alcohol ethoxylate. When used as, it was proved that no oil layer was formed on the surface and a good degreasing effect was obtained at low temperature.

The present invention has been made to solve the above problems,

It is an object of the present invention to provide a degreasing method in which no oil is generated in the surface layer of the degreasing solution while degreasing foreign substances in the cold rolled steel sheet at a lower temperature that can reduce the energy consumption of the degreasing process and improve the degreasing environment.

According to the present invention, when the cold rolled steel sheet is immersed in a cleaning solution containing a caustic soda solution, and degreased, the cleaning solution is 0.25 g of diethylene glycol butyl ether and sodium gluconate in a caustic soda solution, respectively, based on the total weight of the cleaning solution. An alkali degreasing method of a cold rolled sheet is provided by adding within a range of -0.45% by weight and comprising depositing and degreasing the cold rolled sheet in the cleaning solution at 45-55 ° C.

Hereinafter, the present invention will be described in more detail.

In the present invention, diethylene glycol butyl ether and sodium gluconate are added to a caustic soda solution to prepare an alkaline degreasing cleaning solution at a temperature of 45-55 ° C. at a relatively low temperature, and then cold rolled steel sheet is deposited on the cleaning solution to degrease the diluent. Ethylene glycol butyl ether and sodium gluconate are both water-soluble compounds having a high affinity for water and have a property of lowering the surface tension, and are well in contact with the rolling oil on the surface of the cold rolled steel to promote emulsification, and The saponification reaction also takes place, and has a special effect of smoothing degreasing of cold rolled steel sheet even at low temperatures.

The amount of diethylene glycol butyl ether and sodium gluconate added in the alkaline solution is preferably in the range of 0.25-0.45% by weight based on the degreasing cleaning liquid. If the amount is less than 0.25% by weight, the degreasing effect is not very good. If it exceeds 0.3% by weight, the degreasing effect reaches an almost constant level, which is not economically desirable.

Hereinafter will be described in more detail through embodiments of the present invention.

<Example>

The rolled oil remaining on the surface of the steel sheet was degreased by depositing a cold rolled steel sheet having a size of 10 cm X 10 cm in a degreasing solution as shown in Table 1 for 20 seconds. The degreased cold rolled steel sheet was washed with distilled water to completely remove the degreasing solution remaining on the surface and dried with hot air. As a result of measuring the weight change of the dried cold rolled steel sheet and examining the weight change after degreasing and leaving the degreasing test solution intact, after several hours, the presence of an oil layer on the surface of the degreasing solution was confirmed and the degreasing test was performed again. Is shown in Table 2.

<Table 1>

Caustic Soda (W%) Diethylene glycol butyl ether (W%) Sodium Gluconate (W%) Degreasing solution temperature (℃) Example 1 3 0.25 0.25 50 Example 2 3 0.25 0.30 50 Example 3 3 0.30 0.30 50 Example 4 3 0.30 0.30 45 Example 5 3 0.30 0.30 55 Example 6 3 0.40 0.30 50 Example 7 3 0.30 0.40 50 Example 8 3 0.20 0.15 50 Comparative Example 1 3 - - 80 Comparative Example 2 3 Dodecyl Alcohol Ethoxylate0.25 0.25 50

<Table 2>

Weight change after degreasing (g) Presence of oil layer Degreasing effect Example 1 -0.0040 none Good Example 1 -0.0040 none Good Example 1 -0.0041 none Good Example 1 -0.0040 none Good Example 1 -0.0041 none Good Example 1 -0.0041 none Good Example 1 -0.0041 none Good Example 1 -0.0039 none Good Comparative Example 1 -0.0036 none Relatively good Comparative Example 2 -0.0044 has exist Poor Reuse after Degreasing

As shown in Tables 1 and 2 above, in the degreasing solution (Examples 1 to 8) of the present invention to which diethylene glycol butyl ether and sodium gluconate were added, the degreasing of the cold rolled steel sheet at a relatively low temperature of 45 to 55 ° C. It was found that the effect was good, and since there is no oil layer in the degreasing solution after degreasing, it can be evaluated to have a good degreasing effect even after repeated use.

On the other hand, in the degreasing solution of Comparative Example 1 showed a relatively good degreasing effect when degreasing at a relatively high temperature of 80 ~ 85 ℃ and Comparative Example 2 was left as a solution after using the degreasing solution as a selection example of the inventors mentioned above When the degreasing experiment was attempted again after several hours, the oil component was formed in the surface layer, and thus the degreasing experiment could not be performed.

According to the present invention, by adding diethylene glycol butyl ether and sodium gluconate to the caustic soda solution which is an alkaline degreasing solution, it is possible to degrease at a lower temperature and to prevent the formation of an oil layer on the surface of the solution.

Claims (1)

When the cold rolled steel sheet is degreased by dipping in a cleaning solution containing a caustic soda solution, the cleaning solution is in the range of 0.25-0.45% by weight, respectively, based on the total weight of the degreasing cleaning solution of diethylene glycol butyl ether and sodium gluconate in the caustic soda solution. Alkali degreasing method of the cold rolled steel sheet, characterized in that the addition is carried out, and degreased by depositing cold rolled steel sheet in the cleaning liquid at 45-55 ℃.