JPS58202915A - Manufacture of pipe and bar by cold drawing - Google Patents

Abstract

PURPOSE:To eliminate annealing and relubrication treatment and reduce manufacturing cost, by straightening a pipe or bar material continuously and in sequence, directly after its cold drawing, at the temperature higher than its transition temperature of brittleness. CONSTITUTION:When a material is drawn through a die, the temperature of the material rises due to a working heat, resulting from the deformation of the material and the friction between the material and tools, to the temperature higher than its transition temperature of brittleness. Accordingly, when the drawn material is straightened continuously in sequence directly after its drawing, the processing is performed naturally in the temperature region higher than its transition temperature of brittleness, and the annealing and relubrication treatment of the material can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a tube bar by cold drawing through a die 7 to obtain a tube bar of desired dimensions.

For example, when manufacturing a pipe using this method, the degree of work allowed for one drawing is expressed as the ratio of the cross-sectional area of the outer periphery (hereinafter referred to simply as the degree of work), which corresponds to the area reduction rate of the bar material. 4
The limit is set at 5%.

Therefore, if the dimensional difference between the material and the product is small, it may be possible to complete the process in one drawing process, but in general, the process is divided into multiple steps to gradually bring the material dimensions closer to the product dimensions. be exposed. FIG. 1 shows an example of the work order when the drawing process is performed in multiple steps.

When the drawing process is performed in multiple steps, work hardening and bending occur in the material each time the drawing process is performed.

Regarding work hardening, if left untreated, the next drawing process will become difficult, so it is said that it is better to perform a softening annealing called intermediate annealing between the end of processing and the next processing. (See Figure 1).

Regarding bending, if a bend occurs in the material, ■ it becomes difficult to handle it. ■Materials are not properly aligned in the furnace during intermediate annealing or heat treatment of finished products, which deteriorates the storage efficiency of the furnace.

If zero bending is accumulated, the material will be subjected to severe processing during finishing work after heat treatment of the finished product, and the yield strength (
This may lead to a decrease in Y, P) and an increase in hardness, resulting in dimensional changes.

For this reason, it is customary to straighten the material after each drawing process (see Figure 1).

However, this straightening process often causes internal cracks in the material.

The purpose of the present invention is to prevent inner surface cracking of the pipe material caused by straightening the bend, and also to eliminate the need for intermediate annealing between drawing processes, as well as to perform recleaning and relubrication treatment on the surface of the pipe material after the intermediate annealing. The purpose of the present invention is to provide a method of manufacturing a pipe material that eliminates the need for.

It should be noted that internal cracks do not occur in bar materials as they do in tube materials. However, it is true that work hardening of the bar material occurs due to bending straightening even if it does not lead to cracking.

Another object of the present invention is to prevent work hardening and/or brittle fracture of the bar material caused by straightening the bending material, thereby eliminating the need for intermediate annealing, recleaning treatment, and relubrication treatment of the bar material. The purpose is to provide a manufacturing method.

Hereinafter, the first invention will be explained in detail regarding the tube material.

This occurs when conventional pipe materials undergo bend straightening after drawing. This processing has conventionally been carried out mostly cold. This is because the conventional manufacturing method for pipe materials by cold drawing was a batch method. In other words, in the past, after drawing a predetermined number of materials, they were bundled together and sent to the bend straightening process, so the material heated up by drawing was cooled down before bend straightening, and as a result, it was The bend will be corrected. However, materials that have been subjected to drawing processing have a brittle transition temperature raised by the processing, making them extremely brittle at room temperature. The reason that internal cracks occur in the material during conventional bend straightening is that the material is extremely brittle at room temperature, and the bend straightening is performed in this brittle room temperature range. This inner surface cracking is more likely to occur in materials that have undergone intense drawing processing.

On the other hand, the degree of processing per drawing process is limited to 45% as described above. Although it is true that the so-called general workability such as hardness is involved, the reason for this is mainly due to the above-mentioned internal cracking. In other words, materials that have undergone a drawing process of more than 45% have an extremely high risk of causing internal surface cracks when subjected to bend straightening without intermediate annealing. In other words, the intermediate annealing is
Its original purpose is to remove the work hardening of the material and improve its workability, but directly, it plays the role of preventing internal cracks in the material. If this is the case, if internal cracking of the material can be prevented by means other than intermediate annealing, intermediate annealing will actually become unnecessary.

Based on this premise, the present inventors conducted various experimental studies, and as a result, the present inventors performed straightening of curvature after cold drawing in a temperature range above the brittle transition temperature of the material, and It has been found that as long as the inner surface cracks of the material are prevented, intermediate annealing of the material can be omitted, and at the same time, recleaning and relubrication of the material surface accompanying intermediate annealing can be omitted.

The method of the present invention has been made based on the above knowledge, and involves straightening the bend after cold drawing in a temperature range above the brittle transition temperature of the material, thereby making it possible to straighten the bend of the pipe material. This prevents the inner surface W'l from warping and prevents the work hardening of bar materials due to bend straightening, thereby eliminating the need for intermediate annealing of these materials, as well as re-cleaning and re-cleaning the material surface due to intermediate annealing. This is a method for manufacturing tube and bar materials by cold drawing that eliminates the need for lubrication treatment.

The reason why the recleaning treatment and relubrication treatment of the material surface can be omitted in the method of the present invention is as follows.

In the manufacturing method of pipe and bar materials by cold drawing, lubrication treatment is applied separately from intermediate annealing and bend straightening (first step).
(see figure). This is a process in which a chemical conversion coating is formed on the inner and outer surfaces of the pipe material and the outer surface of the bar using a sintered salt film, oxalate film, etc. as a base, in order to extend the lifespan of the pipe and further improve the quality of the product. done before. The film formed on the surface of the material, for example, in the case of a phosphate film, is said to be able to withstand about 8 drawings, but in the past, intermediate annealing was performed between drawings, so the film was formed each time. I had to fix it. This is the relubrication process. In addition, it is necessary to clean the material surface before lubrication treatment, and recleaning treatment is always performed before relubrication treatment (see Figure 1).
. However, if intermediate annealing is omitted, there is no need to re-form the film. As a result, re-lubrication treatment is no longer necessary, and accordingly, re-cleaning treatment is also no longer necessary.

The fact that the lifetime of the chemical conversion coating can be maximized by omitting intermediate annealing is one of the major features of the present invention, as well as the ability to omit intermediate annealing.

In addition, in cold drawing of tube and bar materials, lubricating oil is supplied directly to the material surface during drawing instead of lubrication treatment using a chemical conversion coating, but even when this lubrication treatment is performed, the main The invention is applicable. In this case, the lubrication treatment cannot be omitted, but the effects of the present invention are not limited to the omission of this lubrication treatment, but have many other effects, and these effects are not present in the case of lubrication treatment using lubricating oil. It's definitely something you can get a laugh out of.

In the method of the present invention, in order to straighten the bend in the temperature range above the brittle transition temperature of the material, it is possible to forcibly heat the material after drawing, or use the processing heat generated by drawing. However, the latter method is preferable in terms of thermal economy and work efficiency.

That is, when the material is drawn through the die, the temperature of the material increases due to processing heat due to deformation of the material, friction between the material and the tool, and the like. Figure 2 shows the relationship between workability and material temperature when a raw tube made of low carbon steel with an outer diameter of 8411 and a wall thickness of 8.5W is drawn, together with the brittle transition temperature of the material. It is. This figure reveals the very interesting fact that a material that has undergone pultrusion has a material temperature that is higher than its brittle transition temperature. Therefore, if the drawn material is straightened one after another, processing will naturally occur in a temperature range above its brittle transition temperature, and this type of manufacturing method can be made continuous. The reason why this has not been known in the past is thought to be because the method of manufacturing tube and bar materials by cold drawing was carried out in a batch-wise manner, as described above.

This point, that is, the fact that the material can be straightened at temperatures above its brittle transition temperature without requiring any heat source, and that the manufacturing method can be made continuous is also a major feature of the present invention.

Figure 8 shows an example of the equipment between the drawing machine and the bend straightening machine when straightening the bend using drawing process heat, so (1)
(2) represents a drawing machine frame, and (2) a carriage. The material that has been drawn in the drawing machine is received by the carriage (2) and the glue craft table (3).1. , and then traversed by the delivery chain transfer (4). Next, the tray transfer (5) is used to straighten the bend (
It is scooped up into the inlet cheeple of 6) and conveyed by a cross-feeding chain (7) to the charging port of the straightener (6) while the material temperature does not fall below the material temperature or its brittle transition temperature.

It goes without saying that even when processing heat of the material is used, an auxiliary heat source may be used to prevent the temperature from decreasing.

Furthermore, in the case of forcibly heating the material after drawing, a batch-type manufacturing method is of course possible.

In the method of the present invention, the upper limit of the bend straightening processing temperature is 30
The temperature should be around 0℃.

This is because if the material is heated to a higher temperature than this, thermal decomposition of the lubricating film will occur, and there will be no difference from performing intermediate annealing.

Other manufacturing conditions may be determined according to general conditions for this type of manufacturing method.

Next, an embodiment of the present invention will be described in comparison with a conventional example.

[Comparative Test 1] A low carbon Si, -At killed m steel pipe with an outer diameter of 84fi and a wall thickness of 8.5fi was used as a raw pipe, and was tested by the conventional method, the comparative method, and the method of the present invention to have an outer diameter of 19.05ff and a wall thickness of 2.5fi. 114 general heat exchange tubes were manufactured. The manufacturing procedure and manufacturing results of each method are shown in Table 1.

In the conventional method, after cleaning and lubricating the raw pipe,
The first drawing process was performed. The processing degree in this processing is 37%, and the material dimensions after processing are outer diameter 26u and wall thickness 2.
It was 9fl. Next, in order to remove the bends caused by this drawing process, the bends are straightened by cold, and after that,
Intermediate annealing, recleaning treatment, and relubrication treatment were performed, and product dimensions were obtained by the second drawing process. The working degree in the second drawing process was 48%, and the total working degree from the first drawing process was 63%. After the second drawing process, the material was straightened by a "cold" process, and then heat treated and refined.

Because the degree of work in the first and second drawing processes is kept to 45% or less, and annealing is performed in between the two processes,
Although no internal cracks occurred in the material, the intermediate annealing, as well as the recleaning and relubrication treatments to re-form the chemical conversion coating that was lost due to this, required 20% of the cold work cost.
0% spent.

In the comparative method, after the first drawing process, the material is straightened by "cold" and then directly subjected to the second drawing process, omitting intermediate annealing, recleaning, and relubrication. After that, a second bend straightening was performed in a "cold" manner.

Since the degree of work in the first drawing process was kept to 45% or less, no internal cracks occurred in the first bend straightening process, but after that, the intermediate annealing was omitted and the second drawing process was performed. Since the workability was 64% without annealing and exceeded 45%, internal cracking occurred during the second bend straightening.

In the method of the present invention, intermediate annealing, recleaning treatment, and relubrication treatment were omitted, and the bending straightening was performed twice at 130°C, which exceeded 95°C, which is the brittle transition temperature of the material. As a result, not only the first bend correction, but also the second bend correction in which the intermediate annealing was omitted, did not cause any internal cracks. Furthermore, by omitting intermediate annealing, recleaning treatment, and relubrication treatment, cold work costs could be reduced by 20% compared to the conventional example.

1 Table 1 Table 2 [Comparative Test 2] A low iron killed steel pipe with an outer diameter of 42.7 m and a wall thickness of 3.21 mm was used as a base pipe, and the conventional method, the comparative method, and the method of the present invention were used.
Table 2 shows the manufacturing procedure and manufacturing results of each method that produced a low-temperature heat exchange tube with an outer diameter of 25.4a and a wall thickness of 2.114mm.In this comparative test, the method of the present invention also showed that the method of the present invention did not require intermediate annealing. Despite the omission, no internal cracking occurred and it was confirmed that it was significantly superior in terms of manufacturing cost.

In addition, the present inventor has discovered that in a method for manufacturing a bar material by cold drawing, by straightening the material at a temperature above its brittle transition temperature, intermediate annealing, recleaning treatment, and relubrication treatment can be omitted. has also been confirmed.

As is clear from the above description, the present invention eliminates intermediate steps such as annealing, relubrication, etc. in the production of pipe and bar materials by cold drawing, thereby significantly reducing manufacturing costs. . ■Inner surface cracking and work hardening of the material due to bending correction can be prevented, and the degree of processing of the material can be increased. ■No heating source is required for the material during bend straightening, and the manufacturing process can be made continuous. ■Since the number of lubrication treatments is reduced, the amount of chemical conversion coating remaining after drawing process is reduced, improving the surface cleanliness of the finished product, etc.
It will have a great industrial effect, 6゜

[Brief explanation of drawings]

Figure 1 is a flow sheet illustrating the work order of a method for manufacturing pipe materials by cold drawing, and Figure 2 shows the relationship between the degree of work and material temperature when a pipe is drawn, together with the brittle transition temperature of the material. Graph, Figure 8 is a schematic diagram showing an example of equipment between a drawing machine and a bend straightening machine when straightening a bend using drawing process heat, l: drawing machine frame, 2: carriage, 8: refraft table. , 4: Delivery chain transfer 15: Trait funnel, 6: Straightening machine, 7: Transverse feed chain. (5 11!l 2!I Fig. 3

Claims (1)

[Claims] (1) A method for producing a pipe bar material by cold drawing, characterized in that straightening of the bend after cold drawing is performed in a temperature range equal to or higher than the brittle transition temperature of the material.