JPH0689417B2 - Dezincification method for zinc plated steel sheet scrap - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for dezincing a galvanized steel sheet, and in particular, for removing zinc deposited on the galvanized steel scrap in order to regenerate a zinc-free steel material. It is about the method.

(Prior Art) For example, galvanized steel sheets are used for various purposes such as inner and outer plates of an automobile body for the purpose of rust prevention, and the amount thereof has been increasing in recent years. Since the galvanized steel sheet is used after being cut, pressed, etc., a considerable amount of scrap (used residue, steel plate scrap) is generated during the process. If such scrap can be effectively utilized by recycling it into steel, etc., resource saving,
This will lead to cost savings and will be extremely beneficial in the industry.

By the way, it is known that the following problems occur when galvanized steel scrap is used as a melting raw material.

B) Due to the presence of Zn, the obtained steel material becomes a base ferrite and pinholes, which causes deterioration of cast iron material and casting defects.

B) The melting furnace lining (furnace lining for heat resistance) is adversely affected. That is, abnormal wear of the silica lining and Zn infiltration into the back of the lining occur, and in severe cases, the lining is destroyed → contact between molten metal and the electric / cooling water system of the furnace → steam explosion.

C) Zn easily evaporates and easily oxidizes, so white smoke of ZnO is trapped and adversely affects the work environment.

In order to avoid the above adverse effects, it is necessary to remove Zn from the Zn-plated steel plate scrap before throwing it into the melting furnace.

Conventionally, as such a method, a method of dissolving Zn plating using hydrochloric acid, a method of electrolyzing Zn in an alkaline solution to remove Zn, and a method of evaporating surface Zn by heating (JP-A-57-85936). (See Japanese Patent Publication).

(Problems to be Solved by the Invention) However, the methods 1 to 3 have the following problems.

That is, although the above chemical and electrical methods are satisfactory in the effect of removing Zn, they require a large amount of water and electricity in addition to special equipment and complicated treatment operations, which results in a significant cost increase. However, this method cannot be used as an industrial dezincification method.

Further, although the above method can be performed very easily, there is a problem that the effect of removing Zn cannot be expected. That is, generally when heated at about 490 ° C, surface-attached Zn diffuses into the rigid plate,
Since an alloy of -Zn is formed, even if it is heated more than that, oxidation or sublimation of Zn is not promoted, and it is said that it is almost impossible to remove Zn.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a dezincification method of scrap, which can be easily and inexpensively performed in order to effectively use the scrap of Zn-plated steel sheet.

(Means for Solving Problems) A method for dezincing a galvanized steel sheet according to the present invention to achieve the above object is to remove galvanized steel scrap from 700 to 900.
Heat to ℃ and keep it in the above temperature range for more than 5 minutes,
Next, the scrap is subjected to shot blasting.

Unexpectedly, the present invention holds a galvanized steel sheet at 700 to 900 ° C. for 5 minutes or more, and a certain amount of zinc is desorbed from the galvanized steel sheet, and the galvanized steel sheet held in the temperature range is used as a conventional galvanizing removal method. Was completed by discovering that most zinc was removed by a shot blasting treatment that was not known.

In maintaining the above high temperature, the effect is reduced at 700 ° C or lower, and the steel sheet itself is easily oxidized at 900 ° C or higher. Therefore, it is preferable to keep the temperature at 750 to 850 ° C. Regarding the holding time, if the holding time is short, the effect of removing zinc is small, and it is important to hold for 5 minutes or more. Further, if the holding time is long, the steel sheet is oxidized, so about 20 minutes is preferable.

And when heating the galvanized steel scrap from room temperature to the holding temperature of 700 to 900 ° C, the faster the temperature rising speed, that is, the faster the heating, the better, 50 ° C / min.
It suffices to heat at the above temperature rising speed, and it is important to avoid the temperature range of 450 to 550 ° C in which the deposited zinc easily melts and diffuses in the steel sheet as soon as possible.

The conditions for shot blasting are not particularly limited,
When the conditions are used for surface cleaning of ordinary metal products, most of the zinc is removed in about 2 to 5 minutes, and even if it is performed more than necessary, it is only wasteful.

Further, in treating the galvanized steel plate scrap according to the method of the present invention, it is preferable to shred the scrap beforehand with a shredder machine or the like. By doing so, the bulkiness can be reduced, a large amount of scrap can be processed at one time, and work efficiency can be improved.

(Function) By keeping the galvanized steel scrap at 700 to 900 ° C, the zinc on the surface is oxidized or sublimated. Particularly, by increasing the temperature rising speed, the diffusion of zinc into the steel sheet can be reduced, and the amount of zinc that can be removed increases.

Furthermore, by applying shot blasting, oxidized and deteriorated zinc still adhering to the surface is mechanically removed, the zinc removal rate is increased, and some surface iron oxide generated in some cases is also removed. The quality of the treated steel material becomes good.

Examples of the method for dezincing zinc-plated steel sheet scrap according to the present invention will be described in more detail below.

Example 1 200 kg of press scraps of automobile galvanized steel sheet (plate thickness 0.9 mm, zinc adhesion amount per m ² = 45 g / one side) were shredded into pieces of 5 cm x 5 cm x 5 cm or less by a shredder machine, and then cut into pieces. It was heated in a gas-fired steel belt type continuous heating furnace. The heating was performed by adjusting the furnace temperature and the belt moving speed so that the press waste was heated at a temperature rising rate of 50 ° C./min until the temperature reached 700 ° C. and then held at about 750 ° C. for 20 minutes. .
FIG. 1 shows the temperature change of the press waste and the temperature change in the furnace measured by setting the thermocouple at this time.

Next, the air-cooled press waste was treated for 5 minutes by a batch type of 200 kg with a shot blast machine of type: drum blast, capacity: 0.3 m ³ , shot material: steel, shot capacity: 400 kg / min, impeller capacity: 30 kw. . From the component analysis, it was confirmed that about 85% of the initially deposited zinc was removed from the press waste after the treatment.

Example 2 and Reference Example The heating temperature was raised to 800 ° C. and the temperature was kept for 5 minutes, 10 minutes or 20 minutes.
The dezincification operation was performed in the same manner as in Example 1 except that the holding time was maintained, and the effect of removing zinc was examined every holding time.

As a reference example, the effect of removing zinc when held at 600 ° C. and 1000 ° C. was also examined in the same manner.

The above results are summarized in FIG. As can be seen from the figure, the zinc removal rate of 62 to 85% was obtained in Example 2 at 800 ° C., whereas the zinc removal rate was low at 600 ° C. and the zinc removal rate at 1000 ° C. Although the removal rate was slightly higher, the steel sheet was oxidized. Further, the longer the holding time was, the higher the zinc removal rate was, but there was a tendency that the degree of oxidation of the steel sheet was increased accordingly.

Examples 3 and 4 and Comparative Examples 1 and 2 As Example 3, 400 kg of galvanized steel plate scrap shredded by a shredder machine was passed through a continuous heavy oil-fired heating furnace (800 ° C) for 20 minutes to form a truck. Place and heat, then continuously process with a continuous steel shot machine using an oscillating conveyor for 5 minutes, 400k of remaining hot water while still hot
It was put into a low frequency furnace containing g. Analytical samples were collected at the time of all the scrap burned out and at the time of tapping at 1500 ° after 15 minutes, and changes in the zinc content in the molten metal in the furnace were investigated.

While applying the operation of Example 3 above, the shot blasting treatment was performed for 2 minutes instead of 5 minutes (Example 4), the one subjected to vibration sieving instead of the shot blasting treatment (Comparative Example 1), and the shredder machine. After being shredded, those that were not subjected to any treatment (Comparative Example 2) were placed in the furnace in the same manner as in Example 3, and the change in zinc content was examined.

The above results are summarized in FIG. From the figure, it can be seen that the dezincified products of Examples 3 and 4 are more advantageous in obtaining a molten metal containing less zinc than the molten raw material, as compared with that of the comparative example.

(Effects of the Invention) As can be seen from the above description, according to the method of the present invention, it is possible to easily and inexpensively and efficiently remove the zinc deposited on the galvanized steel plate scrap without requiring new equipment investment. Therefore, the scrap can be effectively used, and the amount of expensive zinc-free iron material can be reduced.

Further, according to the method of the present invention, since the scrap that can be used as the melting raw material is also preheated, the melting energy can be remarkably saved by charging the scrap into the melting furnace while it is hot.

Further, it significantly improves the problems of a casting defect product caused by zinc, bad influence on the melting furnace lining, and bad influence on the working environment, which have been problems in a foundry using galvanized steel scrap as a raw material for melting. It also has the effect.

[Brief description of drawings]

FIG. 1 is a graph showing a time-dependent temperature rising pattern of galvanized steel plate press scraps in a heating furnace according to one embodiment of the method of the present invention, and FIG. 2 shows heating retention temperature / time of press scraps and zinc removal rate. Fig. 3 is a graph showing the relationship, and Fig. 3 is a graph showing changes in the zinc content in the molten metal when the scraps subjected to the dezincification treatment are dissolved in the same amount of molten metal, for each treatment method.

Claims (2)

[Claims] Claim: What is claimed is: 1. Galvanized steel scrap is heated to 700 to 900 [deg.] C. and kept within the above temperature range for 5 minutes or more, and then the scrap is subjected to shot blasting. Zinc method. 2. The method according to claim 1, wherein in heating the galvanized steel scrap, the scrap is heated to 700 ° C. or higher at a heating rate of 50 ° C./min or higher.