JPS634490B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recoating plastic-coated steel pipes, and more specifically, the present invention relates to a method for recoating plastic-coated steel pipes, and more specifically, the present invention relates to a method for recoating plastic-coated steel pipes, and more specifically, the present invention relates to a method for recoating plastic-coated steel pipes. The present invention relates to a method of sequentially performing stripping and recoating.

Plastic-coated steel pipes, for example, those coated with polyolefin, are widely used because they protect the steel pipes from corrosion and have excellent durability.

However, no matter how excellent the corrosion resistance or durability is, if a pinhole exists in a part of the product, it will be off-spec and cannot be used as a product. Such off-spec products require manual labor and or Currently, the coating is removed using mechanical forces such as cranes. This method can be applied within a range where the peel strength of plastic is approximately 3 kg/cm.

However, recently, adhesive-type plastic-coated steel pipes have appeared in which the adhesive layer is thermosetting, the upper layer is adhesive polyolefin, and the outermost layer is a polyolefin layer for corrosion prevention and protection.In this case, the peel strength is At room temperature, it is about 15 kg/cm, so trying to deal with it using conventional methods would be extremely time consuming and inefficient.

In view of these circumstances, the inventors of the present invention have conducted studies to organically combine the simplification of the stripping work of coated steel pipes and the subsequent reuse of the steel pipes. When the polyolefin layer is removed and recoated from a plastic-coated steel pipe in which an adhesive-modified polyolefin and a polyolefin are sequentially laminated, the treated steel pipe is heated in an induction heating furnace to adjust the temperature of the adhesive-modified polyolefin layer to the melting point of the adhesive-modified polyolefin. The adhesive-modified polyolefin and the polyolefin are heated in the following step while being heated to maintain the temperature below the melting point of the polyolefin, and then peeling off the skin from the incisions made in advance or just before the work in appropriate areas of the coated area. A method for recoating plastic-coated steel pipes has been achieved, which is characterized by simultaneously extruding and cooling plastic-coated steel pipes using an extruder.

By implementing the present invention having such a configuration, the treatment of off-spec coated steel pipes can be directly connected to the manufacture of products, and the entire process can be carried out in a manner that is included in the production line. It has the advantage of being able to perform tasks extremely efficiently.

To explain each step of the present invention in more detail with reference to the drawings, first, the coated portion of the coated steel pipe 1 is heated in an induction heating furnace 2 set at a predetermined temperature, thereby changing its adhesive properties. The polyolefin layer begins to soften or melt. Therefore, the bonding force between the adhesive layer, which is the skin part of the steel pipe, and the adhesive modified polyolefin layer weakens or disappears, and when the peeling operation begins in this state, it is necessary to remove the By moving the polyolefin layer in the advancing direction while peeling from an appropriate number of cut portions 3, the polyolefin layer to be peeled can be peeled while curling outward.

The temperature of the steel pipe to be treated heated by the induction heating furnace 2 used at this time is maintained only at the melting point of the adhesive modified polyolefin that is the inner skin, and reaches a temperature that softens the polyolefin that is the outermost skin. You must be careful not to do this. If the temperature of the induction heating furnace is insufficiently controlled and the outermost polyolefin begins to soften, the resin becomes less stiff during peeling, and sometimes breaks, making peeling difficult.

As described above, in the present invention, since strict temperature control is required during the peeling operation, generally known heating means such as burners and hot air heating cannot precisely control the temperature and take time. This conducts heat to the polyolefin coating and softens the coating, making it difficult to use in the present invention.

The steel pipe that has been peeled as described above has not had the adhesive layer covering its surface removed and its temperature is above the melting point of the adhesive-modified polyolefin, so the adhesive layer has not been removed. The recoating of the plastic-coated steel pipe is completed by sending the polyolefin and polyolefin to the coextrusion die 4, coating the surface again, and cooling the polyolefin in the ring-shaped cooler 5 or the one-way injection cooler 6. Separate extruders 7 and 8 are installed in the coextrusion die 4.
Adhesive modified polyolefin and polyolefin have been extruded from coextrusion die 4.
The two are now polymerized.

A steel pipe whose surface is coated with plastic as described above is no different from a plastic-coated steel pipe obtained through normal production, and therefore can be shipped immediately as a product.

[Brief explanation of the drawing]

The figure is an explanatory view showing the arrangement of equipment for re-coating plastic-coated steel pipes. 1... Coated steel pipe, 2... Induction heating furnace, 3... Notch, 4... Coextrusion die, 5, 6... Water cooling device.

Claims (1)

[Claims] 1. When removing the polyolefin layer from a plastic-coated steel pipe in which a thermosetting adhesive, an adhesive modified polyolefin, and a polyolefin are laminated in order on the surface of the steel pipe and recoating it, the treated steel pipe is coated with an adhesive modified polyolefin layer in an induction heating furnace. The temperature of the polyolefin is heated to a temperature higher than the melting point of the adhesive modified polyolefin and lower than the melting point of the polyolefin, and then the skin is peeled off from the incisions made in advance or just before the work on the appropriate part of the coated part. A method for recoating a plastic-coated steel pipe, which comprises simultaneously extruding and cooling an adhesive modified polyolefin and a polyolefin in an extruder and cooling the same.