JPS58167118A - Manufacture of metal tube having resin covered inner face and plated outer face - Google Patents

Abstract

PURPOSE:To manufacture the titled metal tube without stripping off the plating layer of an outer face, by inserting a resin tube into the metal tube having a plated outer face via an adhesive, then drawing it with the die having a specified approach angle. CONSTITUTION:A diameter reduction is done by using the tapered die having the approach angle of 15 deg. and below or the R type die corresponding to this. that is, a resin tube 1 is inserted into the metal tube having a plated outer face (e.g., a galvanized steel tube) 2 via an adhesive (e.g., an aqueous rubber adhesive), then the metal tube 2 is contacted to the resin tube 1 by reducing the diameter of the metal tube 2 with said die 3 and the metal tube having a resin covered inner face and the plated outer face is shaped.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a metal tube whose inner surface is coated with a resin such as vinyl chloride and whose outer surface is coated with metal plating such as zinc. Such metal pipes are mainly used for water pipes buried in soil or concrete.

When metal pipes are used as water pipes, it is customary to coat the inner surface of the metal pipes with a resin in order to protect the tap water from contamination due to corrosion of the metal pipes. In this case, as a means of resin coating, insertion of an FJJ resin tube is generally used, which is said to be more reliable than powder lining.

On the other hand, when metal water pipes are buried in concrete, it is recommended that the outer surface of the water pipes be plated with a highly corrosion-resistant metal such as zinc in order to protect the water pipes from corrosion due to residual moisture in the concrete. There is. Furthermore, even when the water pipe is buried in the ground, plating the outer surface of the water pipe is effective in protecting the pipe surface from damage caused by construction work.

For this reason, water pipes buried in concrete are metal pipes whose inner surfaces are coated with resin and whose outer surfaces are plated with metal (hereinafter referred to as inner resin-coated/outer plated metal pipes).
are widely used, and demand is increasing for water pipes that can be buried underground.

When manufacturing metal tubes with resin coating on the inner surface and plating on the outer surface, it is important to be careful when plating the surface after coating the inner surface with resin. Plating must be performed prior to resin coating.

After inserting a resin tube through adhesive into a metal tube whose outer surface is metal plated (hereinafter referred to as outer surface plated metal tube), the diameter of this tube is reduced by drawing with a die.
One such method is to adhere a resin tube to the inner surface of the externally plated metal tube, but it has the disadvantage that the plating layer of the externally plated metal tube is strongly rubbed by a die, causing the plating layer to peel off.

An object of the present invention is to provide a method for manufacturing a metal tube with an inner surface coated with resin and an outer surface plated, which eliminates this drawback.

By the way, in the production of metal tubes with inner resin coating and outer surface plating using conventional pultrusion diameter reduction processing using dies, a die with an approach angle of around 25 degrees, which is similar to general pultrusion diameter reduction processing, is used without considering the plating layer. was using.

The peeling of the plated layer caused by the drawing process is due to the low ductility of the alloy N (Fe-Zn alloy layer in the case of ZN plating) that occurs between the metal tube and the metal tube during the plating process. The cause is that the tube breaks in the axial direction when it is pulled out. It may be possible to prevent this breakage by reducing the diameter reduction ratio of the outer plated metal tube, but reducing the diameter reduction ratio means a decrease in the contact M strength of the resin tube, which is not preferable.

The present inventors found that in order to prevent peeling of the plating layer without reducing the diameter reduction ratio of the externally plated metal tube, it is a good idea to find a die hole shape that can suppress only the elongation of the alloy layer in the tube axis direction. Considering this, we investigated the relationship between the approach angle of the die hole and the elongation of the metal tube in the tube axis direction when drawing the metal tube. As a result, when the approach angle is 15 degrees or less, which is smaller than conventionally used ones, the elongation of the metal tube in the tube axis direction is suppressed, and in the case of externally plated metal tubes, the elongation of the alloy layer is suppressed, and the plated It has been found that peeling of the layers can be prevented.

The present invention was made based on this knowledge, and includes an outer plated metal tube with a resin tube inserted through an adhesive.
An inner resin coating characterized in that the resin tube is bonded to the inner surface of the outer plated metal tube by reducing the diameter by drawing with a Taber type die having an approach angle of 15 degrees or less or an equivalent R type die. The gist of this article is a method for manufacturing a metal tube with a plated outer surface.

Hereinafter, the method of the present invention will be explained in more detail with reference to the drawings.

First, prepare an externally plated metal tube.

The material of the metal tube is generally steel, but is not limited to this.

Zinc is also the most common plated metal.

It is not limited to this.

Once the externally plated metal tube is prepared, adhesive is applied to its inner surface and/or the outer surface of the resin tuner to be inserted.

Examples of adhesives include comb-based water-based adhesives. There are mixed solvent volatile adhesives, etc.

After applying the adhesive, insert the resin tube inside the outer metal pipe.

The outer diameter of the resin tube needs to be as large as possible within a range that does not hinder its insertion into the externally cast metal tube. If there is too much gap between the resin tube and the externally plated metal tube when the resin tube is inserted, there is a risk that the adhesion strength between the two will be insufficient during the next drawing process.

Other dimensions may be determined based on the dimensions of the resin-coated inner surface and outer cast metal tube to be manufactured.

When the resin tube is inserted, as shown in Fig. 1, the outer surface plated metal tube (2) is inserted with the resin tube (1) inserted.
) is reduced in diameter by drawing with a die (3).

If the die (3) is a take type device shown by the solid line in the figure, it is necessary that the approach angle (b) of the die hole (referring to the opening angle of the approach part) be 15 degrees or less. If the force (at the approach angle) is larger than 515 degrees, the outer surface plated metal tube (2) will elongate in the axial direction, causing the alloy layer at the bottom of the plated layer to lengthen by 4 degrees, causing its rupture. , peel off the remecked layer. The lower limit of the approach angle (b) is determined by the approach angle at a constant diameter reduction rate)
Since the thickness of the die (3) increases as the size of the die (3) decreases, this is naturally determined by usage constraints.

If the die (3) is a rounded die shown by the broken line in the figure, it has a die hole corresponding to the die hole of the tapered die. Here, being equivalent does not mean that the two die holes are geometrically similar, but rather that the color tubes that affect the material of both are substantially the same.In other words, the approach angle of the Taber die light) and
Compare the average opening angle of the moving part (X4) (the part that directly contributes to the diameter reduction of the material) of the R-type die, or the opening angle 0 at the midpoint (4) of the moving part (x-y). would be appropriate.

If the diameter reduction rate of the outer plated metal tube (2) is too small, the adhesive strength between the resin tube (1) and the outer plated metal tube (2) will be insufficient, and if it is too large, mechanical damage will occur. Since this brings about a change in physical properties, a range of 3 to 6% is preferable.

The drawing temperature may be either cold or warm (within a range that does not adversely affect the resin tube). Tung lubricating oil is usually required for cold drawing, but no lubricating oil is required for warm drawing.

Other processing conditions may be determined according to general drawing diameter reduction processing.

When the drawing process of the externally plated metal tube is completed, the mouth portion at the tip of the tube and the rear end portion are cut off to obtain a resin-coated internally and externally plated metal tube.

Next, the implementation effects of the method of the present invention will be explained in comparison with the conventional method.

Five types of externally galvanized steel pipes (8) to (g) shown in Table 1
was drawn using various tapered dies with a blow angle of 1 to 25 degrees. In both cases, the diameter reduction rate is 5.7%,
The drawing speed was 80%.

Table 1 shows the percentage of steel pipes with peeling in the plating layer, based on the number of pipes pulled out, by approach angle. It can be seen that the danger is greatly reduced and peeling of the plating layer is almost completely prevented when the approach angle is 8 degrees or less.

Table 2 Also, Fig. 2 shows a case where the outer diameter is 29fi and the wall thickness is 3. Off steel pipe (Material J Engineering S-8GP) with an approach angle of 1 to 25.
The approach of the die hole when drawing with various Taber type dies at a diameter reduction rate of 5.7%. As seen in this figure, as the approach angle decreases, the elongation rate of the steel pipe in the tube axis direction decreases, and the reason why peeling of the plating layer is prevented in the method of the present invention is that It can be seen that the elongation rate of the alloy layer decreased due to the regulation.

Incidentally, the present inventors obtained similar results in experiments using R-type dice.

As is clear from the above description, the present invention has the effect of preventing peeling of the plating layer during drawing of an externally plated metal tube, and thereby stably manufacturing high quality internally resin-coated and externally plated metal tubes. There is.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the drawing step of the method of the present invention;
FIG. 2 is a graph showing the relationship between the approach angle of the die and the elongation rate of the steel pipe in the axial direction when the steel pipe is subjected to drawing processing. In the figure, l: resin tube, 2: outer plated metal tube, 3:
dice.

Claims (1)

[Claims] (1) The diameter of an externally plated metal tube into which a resin tube is inserted via adhesive is reduced by drawing with a tapered die with an approach angle of 15 degrees or less or an equivalent rounded die, and the outer surface is plated. A method for producing a metal tube with an inner surface coated with resin and an outer surface plated, the method comprising adhering the resin tube to the inner surface of the metal tube.