JP3267185B2 - Cold drawing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cold drawing a steel pipe, for example.

[0002]

2. Description of the Related Art The cold drawing method has developed a unique field which is not hot, in the elimination of steps in a dimensional range, the dimensional accuracy thereof, and the surface gloss finishing by cold finishing. Taking advantage of these features, the material to which cold drawing is applied is a wide range of materials from mechanical steel to carbon steel to bearing steel and Cr-Mo steel, and boiler material from carbon steel to Cr-Mo steel. Material.

[0003] By the way, general pretreatment steps of the cold drawing method are roughly classified into two types, a phosphate coating method and an oil lubrication method. Oil lubrication methods of this is present in bullion surface, wustite (FeO), magnetite (Fe ₂ O
₃ ) Removes black scale (hereinafter simply referred to as “scale”) made of hematite (Fe ₃ O ₄ ) and roughens the surface of the base metal, facilitating subsequent adhesion of coatings and oil For this purpose, after pickling with sulfuric acid or hydrochloric acid of about 5% at 80 ° C., the base metal is neutralized with a solution containing phosphate so as not to rust, and dried. After that, cold drawing is performed while applying a lubricating oil whose main component is a sulfurized oil or fat to a steel pipe.

[0004]

SUMMARY OF THE INVENTION For the purpose of streamlining work and improving the working environment, there is a demand for the latter oil lubrication method to omit steps from pickling to drying, which are pretreatments for cold drawing. However, if these steps are omitted, the metal and tool can easily come into contact with each other without lubricant (oil). The possibility of occurrence of defects increases.

That is, the disadvantage of omitting the above-described steps is caused by the presence of a scale of several μm to several tens μm on the base metal. For example, in the case of a scale of several tens of μm, peeling of the scale occurs at the time of cold drawing, and the metal that has appeared due to the peeling of the tool and the scale directly contacts the tool. In addition, when cold drawing a steel pipe with a scale of several tens of μm attached, the unevenness of the scale and the base metal becomes too large, the base noise in ultrasonic flaw detection becomes large, and flaw detection in a normal state cannot be performed. Occurs. In addition, UV (Ultra Viol
et) In the case of painting (painting using a paint that solidifies oil by irradiating ultraviolet rays), the coating may not adhere well if the irregularities are too large.

An object of the present invention is to provide a cold drawing method which does not cause the above-mentioned problems even by oil lubrication in which steps from pickling to drying are omitted.

[0007]

In order to achieve the above-mentioned object, a cold drawing method of the present invention is to provide a method of forming a crack in a steel pipe with scale attached to the scale, the oil pool being formed on the scale. Is to be caused. Then, at the time of cold drawing by oil lubrication, since lubricating oil accumulates in the cracks described above, even if a scale of several tens of μm adheres to the steel pipe, direct contact between the scale and the base metal can be prevented,
Cold drawing can be performed without causing a seizure defect.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The cold drawing method of the present invention comprises:
Oil sump on the scale of the steel pipe with the scale attached
After causing Ritonaru cracks, and performs cold drawing according to oil lubrication. In the present invention, the scale refers to the Mannesmann mandrel mill method (hereinafter, referred to as “mannesmann mandrel mill method”).
This refers to the scale generated when the tube is produced by the “M / M method”) or the scale generated when the tube is heat-treated in a bright furnace. Its composition is wustite (FeO), magnetite (Fe ₂ O ₃ ) and hematite (Fe ₃ O ₄ ), the thickness of which varies slightly depending on the state of occurrence.

In the present invention, the means for generating cracks in the scale is not particularly limited as long as the generated cracks can be used as oil pools. A straightening machine such as a 2-2-1 type straightener or a multi-stage straightener, a shot blast, or the like is employed. In addition, 1 in FIG. 1 shows a bending roll, 2 shows a steel pipe.

According to the cold drawing method of the present invention, as shown in FIG. 2, cracks 3 formed on the scale 2a on the inner and outer surfaces of the steel pipe 2 become oil pools, and the tools (plugs, dies) and the ground are grounded. Direct contact with gold can be prevented, and the oil pool makes it easy for the scale 2a to peel off at the time of drawing. Therefore, even in the steel pipe 2 to which the scale 2a of several tens of μm having poor adhesion is adhered, there is no seizure defect. Cold drawing becomes possible. For the same reason, the conventional unevenness can be reduced by half, so that normal flaw detection by ultrasonic waves and formation of a normal film by UV coating can be promoted.

According to the cold drawing method of the present invention, as shown in FIG. 3, the scale 2a of several tens of μm that adheres to the inner surface of the steel pipe 2 is attached to the plug 4 and the outer surface of the steel pipe 2 At the very moment when it is squeezed by the die 5, it is separated from the inner and outer surfaces of the steel pipe 2 and collected together with the lubricating oil 6 injected toward the inner and outer surfaces of the steel pipe 2. The recovered oil is supplied again as an oil lubricant via a suitable iron removing device such as a magnet separator.

Since the scale of several μm has good adhesion, the thickness of the scale is changed even after cold drawing to adhere to the inner and outer surfaces of the steel pipe. However, not all scales are peeled or adhered, but a scale with a small thickness has a high probability of remaining on the inner and outer surfaces of the steel pipe after cold drawing, and conversely, a thicker scale The scale is stochastically less likely to remain on the inner and outer surfaces of the steel pipe after cold drawing. Actually, the thickness of the scale is not uniform, and the thin scale and the thick scale are in a mixed state.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The results of experiments conducted to confirm the effects of the cold drawing method of the present invention will be described below. As shown in FIG. 1, various scale pipes (0.25% C steel) having an outer diameter of 30 to 120 mm and a wall thickness of 3 to 10 mm to which scale was attached while being heat-treated in a bright furnace were subjected to 2-2 as shown in FIG. -2-
After passing through a type 1 straightener to cause cracks on the scale, cold drawing by oil lubrication (die: SD type, plug: SF type, drawing degree: 20 to 35)
%, Drawing speed: up to 30 m / min) and the outer diameter is 20 to 1
Various steel pipes having a thickness of 10 mm and a thickness of 2 to 9 mm were prepared.

Table 1 shows the results of an examination of the occurrence of seizure during cold drawing, ultrasonic flaw detection, UV paint adhesion, and surface roughness (Rmax) after cold drawing in these steel pipes.
In addition, Table 1 shows that when cold drawing by oil lubrication is performed while the tube is manufactured by the M / M method (referred to as “M / M method” in Table 1), after the pickling-drying step, the oil lubrication is performed. (In Table 1, referred to as "conventional method 1"), and when conducting cold drawing by the phosphate coating method (in Table 1, referred to as "conventional method 2"), the same results are also included. Is shown.

[0015]

[Table 1] Note 1) Regarding the flaw detection properties of ultrasonic waves, good means a state where there is almost no base noise, and acceptable means a state where there is considerable base noise but somehow flaw detection is possible. Note 2) Regarding the adhesion of the UV paint, good means a state where a uniform paint film is adhered, and bad means a state where only a non-uniform paint film is adhered.

As apparent from Table 1 above, according to the method of the present invention, although the steps of pickling and drying are omitted,
As in the case of the conventional method 1, it was possible to obtain the same seizure generation rate at the time of cold drawing, the flaw detection property of ultrasonic waves, and the adhesion of UV paint. The surface roughness after the cold drawing was the same as that of the conventional method 1.

[0017]

As described above, according to the cold drawing method of the present invention, the scale and the base metal can be formed by the lubricating oil accumulated in the cracks even by the oil lubrication in which the steps from pickling to drying are omitted. Several tens μm
Even with a steel pipe to which an m-scale is attached, there is little seizure defect and cold drawing is possible. Further, according to the cold drawing method of the present invention, since the steps from pickling to drying can be omitted, material costs can be reduced accordingly.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of a bending straightening machine used in the cold drawing method of the present invention.

FIG. 2 is an explanatory view of a steel pipe in which a scale has cracked by the cold drawing method of the present invention.

FIG. 3 is an explanatory view of a state in which a steel pipe having cracks on a scale is cold drawn by a cold drawing method of the present invention.

[Explanation of symbols]

 2 Steel pipe 2a Scale 3 Crack 6 Lubricating oil

Claims (1)

(57) [Claims] 1. A cold drawing method comprising the steps of: forming a crack that becomes an oil reservoir on the black scale of a steel pipe with the black scale attached to the steel pipe; and performing cold drawing by oil lubrication. .