JPS591911B2 - Manufacturing method of small diameter double-wound steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a double-wound steel pipe having a relatively small diameter.

Double-wound steel pipes are relatively small steel pipes with an outer diameter of about 20 mm or less, which are often used to connect automobile brake pipes, fuel pipes, various supply pipes, and refrigerator condenser pipes. The pipes were made using steel strips with copper plating on both sides.

Therefore, under line speeds of around 150 meters per minute during double-wrap forming, the copper plating film often melts due to the generation of frictional heat caused by the continuous passage between multiple rolls due to the use of internal plugs, which causes the plugs to melt. A seizing accident occurred on the inner peripheral surface of the pipe, which naturally forced the temporary suspension of pipe-making operations.Furthermore, due to such seizing accidents, line speed was restricted during pipe-making, which generally reduced productivity. They tended to be scarce.

On the other hand, when using piping, for example, when it is used as a brake pipe or fuel pipe for an automobile, the copper plating film on the inner peripheral surface is melted by impurities such as sulfur compounds or organic acids contained in the internal fluid. There is a drawback that the molten fluid causes electrolytic corrosion to other parts made of aluminum, aluminum alloy, etc. in the same flow path.

The present invention eliminates these conventional drawbacks, and includes a steel strip having a copper plating film on one surface and a chemical conversion coating made of phosphate, iron oxalate, or triiron tetroxide on the other surface. The pipe is manufactured with the copper plating film side positioned on the outer peripheral surface side.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a reduced plan view of a steel strip for making a small-diameter double-wound steel pipe according to the present invention, and FIG. 2 is an enlarged sectional view taken along the line A--A in FIG. 1.

In the figure, 1 is a steel strip plate with a wall thickness of 0.3 to 1.0 millimeter, and one surface is pre-plated with a copper plating film of about 2 to 5 micrometers.
After that, the other surface is coated with an aqueous solution of zinc phosphate with an oxidizing agent added, an aqueous solution of a concentrated caustic alkaline solution with an oxidizing agent added, or a mixed solution of ferric oxalate dissolved in a saturated aqueous solution of oxalic acid, etc. in the temperature range of 600 to 150℃
A chemical conversion film 3 of about 2μ to 8μ is formed by immersion for about 0 to 30 minutes, and after processing both sides of the width into parallel slopes /1 and /2 consisting of edges, the dull plating film 2 is As shown in Figure 3, by continuous passage through a multi-stage roll pipe making machine by using a plug inside with the side facing the outer circumferential surface, a double winding is formed in the width direction as shown in Fig. 3, and this At the same time, the parallel slopes A and /2 on both sides are butted together through the center offset part 4, and they are mutually heated to a temperature higher than the melting temperature of the dull plating film 2 through continuous passage in an atmospheric furnace. At the same time, the chemical conversion coating 3 is removed from the inner circumferential surface 5 side as shown in FIG. 4 due to the thermal influence of these heat treatments, and the inner circumferential surface 5 is formed into a copper plate. It was forced upon me.

Note that the chemical conversion coating 3 does not need to be applied to the entire surface of one side, and may be provided only within the range of the inner circumferential surface 5 (see FIG. 4) as shown in FIG.

In this way, when the double-wrap is formed by continuous passage between multiple rolls during pipe making, the chemical conversion coating 3 present on the inner peripheral wall surface permeates through the crystal interfaces on these peripheral surfaces, resulting in reduction. In order to fully demonstrate the lubricating effect with the abrasive agent,
It is possible to prevent seizure accidents on the inner peripheral surface due to frictional heat with the plug.

Therefore, it is possible to further increase the line speed as necessary, making it easier to improve productivity, and to simultaneously form a chemical coating on the inner circumferential surface 5 during heating during the subsequent soldering process 6 (see Fig. 4). The coating 3 can be made to disappear and formed into a copper dish.

As explained in detail above, according to the present invention, seizing on the inner circumferential surface due to frictional heat with the plug used inside due to double-wound forming due to continuous passage between multistage rolls during pipe making is prevented. This not only simplifies pipe-making work but also increases productivity by increasing line speed as needed. This has the effect of simultaneously solving problems on both sides.

[Brief explanation of the drawing]

Fig. 1 is a reduced plan view of a steel strip for pipe making used in the method of the present invention, Fig. 2 is an enlarged sectional view taken along line A-A in Fig. 1, and Fig. 3 is a simple double winding of the steel strip before soldering in the method of the present invention. FIG. 4 is an enlarged cross-sectional view showing an example of a small-diameter double-walled steel pipe manufactured according to the present invention; FIG. FIG. 2 is an enlarged cross-sectional view of a steel strip for pipe making, which is partially flattened on the inner circumferential surface during forming. 1... Thin steel strip plate, 2... Copper plating film,
3... Chemical conversion coating, 4... Center offset portion, 5... Inner peripheral surface, 6... Brazed portion.

Claims (1)

[Claims] 1. Use a thin strip steel sheet that has been previously coated with a copper plating film on one surface and a chemical conversion film made of phosphate, iron oxalate, or triiron tetroxide on the other surface, with the copper plating film side facing the outer peripheral surface. and align the double windings in the width direction, parallel to this alignment, butt the parallel slopes of the edge portions on both sides through the center offset portion,
The overlapped peripheral surfaces of the double windings are soldered with the copper plating film, and at the same time, the chemical conversion coating on the inner peripheral surface disappears due to the thermal effect of heating during this soldering, and the inner peripheral surface is A method for manufacturing a small-diameter double-wound steel pipe, characterized in that it is formed on a steel skin.