JP6443398B2 - Plug mill plug bar - Google Patents

Description

  The present invention relates to a plug bar used in a plug mill in a series of rolling equipment installed in a seamless steel pipe production line.

  In a seamless steel pipe production line, a solid round bar (so-called billet) is first heated to a high temperature in a heating furnace, and further pierced and rolled with a piercer to form a hollow pipe (hereinafter referred to as a raw pipe). The raw tube is drawn and rolled with a plug mill. After that, the raw pipe passes through a reheating furnace, a sizer, and the like to become a seamless steel pipe having a predetermined size. In such a seamless steel pipe manufacturing process, the drawing and rolling performed by a plug mill is performed by inserting a plug into the base pipe and applying a reduction with a rolling roll located outside the base pipe and a plug inserted inside. It is a rolling technique that stretches a tube.

Since the rolling roll is driven to rotate, the friction with the raw tube is relatively small. However, since the plug slides on the inner surface of the raw tube, a large friction is generated. As a result, the plug mill has a problem that surface defects (for example, scratches) occur on the inner surface of the raw tube. Moreover, since the raw pipe supplied to the plug mill is hot, seizure is likely to occur on the inner surface due to friction with the plug.
In view of this, a technique for preventing surface defects and seizure from occurring on the inner surface of an element pipe by a plug mill has been studied.

  For example, Patent Document 1 discloses a technique for reducing the friction of a plug by injecting a lubricant onto the inner surface of the raw tube with a plug mill, thereby preventing surface defects and seizure on the inner surface of the raw tube. .

  When this technology is applied to the operation of a plug mill, as shown in FIG. 2, a steel tube 7 (hereinafter referred to as a built-in tube) is disposed inside the plug bar 3, and the tip of the plug bar 3 (that is, the plug) The built-in tube 7 is connected to a steel conduit 10 (hereinafter referred to as a steel conduit) provided in the end fitting 4 disposed on the end 2 on the side where the 2 is mounted. Then, the lubricant 6 is supplied from the rear end of the plug bar 3 (that is, the end opposite to the front end) through the built-in tube 7 and the steel conduit 10, and the lubricant 6 is supplied from the injection hole 11 of the plug 2. Stretch rolling is performed while spraying on the inner surface of 1. As already described, since the raw tube 1 supplied to the plug mill is hot, the plug bar 3 is exposed to high temperature. On the other hand, since the inside of the plug bar 3 is cooled by the cooling water 5, the built-in tube 7 which becomes the flow path of the lubricant 6 is kept at a low temperature. Such a temperature difference between the plug bar 3 and the built-in tube 7 causes a difference in expansion amount.

  That is, the expansion amount of the high-temperature plug bar 3 is large, and the expansion amount of the low-temperature internal tube 7 is small. As a result, the expanding plug bar 3 is restrained by the internal tube 7 and deformed (for example, bent) , Meandering, etc.) occurs. If the expansion amounts are significantly different, the joint between the built-in tube 7 and the steel conduit 10 may be damaged, making it difficult to supply the lubricant 6. The breakage of the joint portion is caused not only by the bending of the plug bar 3 caused by the load during rolling, but also by the concentration of stress on the joint portion due to the deflection due to the thermal expansion of the internal tube 7. In particular, since the built-in tube 7 and the steel conduit 10 are joined by welding, there is a problem in that the weld metal at the joint causes metal fatigue during the operation of the plug mill and promotes breakage of the joint.

If the plug bar 3 is deformed during the operation of the plug mill, or if the joint between the built-in tube 7 and the steel conduit 10 is damaged, the plug bar 3 must be replaced. Decrease in productivity).
If the life of the plug bar is extended, it is possible to prevent a decrease in the operating rate of the plug mill, but technology has been established to reliably and stably extend the life of the plug bar with a built-in lubricant flow path. Absent.

Japanese Patent Publication No.2-29402

  An object of the present invention is to solve the problems of the prior art and to provide a plug bar having a built-in lubricant flow path and having a long life so that it can be suitably used in a plug mill.

The present inventor not only swells when the plug bar is exposed to high temperature when the plug mill is operated, but also cannot be avoided by bending due to the rolling load. The present inventors have found that the above-described problems can be solved by using a cylindrical tubular body (hereinafter referred to as an elastic tube) having elasticity instead of a steel built-in tube. In other words, elastic tubes (for example, rubber hoses, polyvinyl chloride hoses, etc.)
(A) Since the inside of the plug bar is cooled with cooling water, a commercially available elastic tube can be used without any trouble.
(B) Since the elastic tube is easily bent, an elastic tube having a length that takes into account the amount of expansion and bending of the plug bar (ie longer than the plug bar at the time of manufacture) can be easily stored in the plug bar in advance.
(C) When the plug bar significantly expands (or bends) and exceeds the amount of expansion (or the amount of bending) assumed in (B) above, the elastic tube follows the plug bar and extends.
(D) It has an advantage that the steel conduit and the elastic tube of the end fitting of the plug bar can be connected by means other than welding.

  In this way, the plug bar expands (or bends) without being restrained by the elastic tube during operation of the plug mill, so that the deformation of the plug bar and the breakage of the joint with the elastic tube can be prevented. The life of the plug bar can be extended.

The present invention has been made based on such knowledge.
That is, the present invention relates to a plug bar in which a plug is mounted in a plug mill that performs stretching and rolling by inserting a plug into a previously drilled base pipe to produce a seamless steel pipe, and a steel conduit is attached to the tip of the plug bar. The plug bar is a plug bar of a plug mill having an attached tip fitting and an elastic tube extending from the rear end of the plug bar to the tip fitting and having means for connecting the elastic tube and the steel conduit.

  In the plug bar of the present invention, it is preferable that the means for connecting the elastic tube and the steel conduit is a screw provided so as to be screwed together or a connecting tool provided so as to be fitted to each other. The elastic tube is preferably a rubber hose.

  Since the plug bar of the present invention has a built-in lubricant flow path and has a long life, it can be suitably used in a plug mill, and thus has a remarkable industrial effect.

It is sectional drawing which shows the example of the plug bar of this invention typically. It is sectional drawing which shows the example of the conventional plug bar typically.

FIG. 1 is a cross-sectional view schematically showing an enlarged example of the plug bar of the present invention. In FIG. 1, illustration of the raw tube and the plug is omitted.
In the present invention, the elastic tube 8 incorporated in the plug bar 3 is used as a flow path for the lubricant 6. Since the inside of the plug bar 3 is cooled by the cooling water 5, the elastic tube 8 can be used without any trouble.

Means for connecting the elastic tube 8 to the steel conduit 10 in the end fitting 4 is, for example,
(a) A cylindrical metal fitting is fixed to the elastic tube 8 with an adhesive, and a screw is provided on the metal fitting and the steel conduit 10 (see FIG. 1).
(b) The elastic tube 8 and the steel conduit 10 are connected by attaching and fitting connecting jigs (so-called couplers), respectively. In this way, the elastic tube 8 and the steel conduit 10 can be connected without welding.

  Since the elastic tube 8 is soft and bends easily, when the plug bar 3 is manufactured, the elastic tube 8 which is longer than the plug bar in consideration of the expansion amount and the bending amount of the plug bar 3 is provided inside the plug bar 3. It can be easily stored (see FIG. 1). By doing so, the plug bar 3 expands (or bends) without being restrained by the elastic tube 8 during operation of the plug mill. In addition, when the plug bar 3 significantly expands (or bends) and exceeds the amount of expansion (or the amount of bending) assumed in advance, the soft elastic tube 8 follows the plug bar 3 and easily extends. The plug bar 3 can expand (or bend) without being restricted by the elastic tube 8. Therefore, deformation of the plug bar 3 can be prevented, and damage to the connecting portion between the elastic tube 8 and the steel conduit 10 can be prevented, so that the life of the plug bar 3 can be extended.

  As the lubricant 6, a solid lubricant (for example, graphite, boron nitride, molybdenum disulfide, etc.) or a liquid lubricant (for example, mineral lubricating oil, synthetic oil, etc.) is used. When a solid lubricant is used, it is finely divided into granules or powders and pumped with air. When using a liquid lubricant, drop it into a mist and pump it with air.

  In the plug mill of the seamless steel pipe production line, the drawing and rolling was performed using the plug bar 3 having the elastic pipe 8 shown in FIG. The elastic tube 8 and the steel conduit 10 were screwed together with a screw 9 as described in (a) above. As the lubricant 6, powdery graphite was used, and it was pumped from the elastic tube 8 through the steel conduit 10 together with air at a pressure of 3.0 MPa, and sprayed from the plug injection hole onto the inner surface of the raw tube. The elastic tube 8 used has a pressure resistance of a maximum of 3.5 MPa. An example in which a rubber hose is used as the elastic tube 8 is an invention example 1, and an example in which a polyvinyl chloride hose is used is an invention example 2.

  On the other hand, conventionally, drawing and rolling was performed using a plug bar 3 having a built-in steel tube 7 shown in FIG. In the operation, the built-in tube 7 and the steel conduit 10 were connected by welding. As the lubricant 6, powdered graphite was used, and the inside of the built-in tube 7 was pumped together with air at a pressure of 3.0 MPa, and sprayed from the spray hole 11 of the plug 2 to the inner surface of the raw tube. This is a conventional example.

The average rolling which can be stretch-rolled with one plug bar using the number M of the raw tubes subjected to the stretching rolling and the number N of the plug bars used during the operation of the invention example 1 for 3 months. When the number of times M / N was calculated, it was M / N = 3200.
The operation of Invention Example 2 was carried out for 3 months, and the average number of rolling operations M / N was calculated in the same manner as in Invention Example 1. The result was M / N = 3100.
On the other hand, when the conventional operation performance was analyzed and the average number of rolling operations of the plug bar of the conventional example was determined, M / N = 1500.
That is, it was confirmed that the life of the plug bars of Invention Examples 1 and 2 can be greatly extended compared to the conventional example.

DESCRIPTION OF SYMBOLS 1 Elementary pipe 2 Plug 3 Plug bar 4 Tip metal fitting 5 Cooling water 6 Lubricant 7 Built-in tube 8 Elastic pipe 9 Screw
10 Steel conduit
11 Injection hole

Claims (3)

A plug bar in which the plug is mounted in a plug mill that inserts and inserts a plug into a previously drilled base pipe to produce a seamless steel pipe, and the steel pipe is attached to the tip of the plug bar. A means for connecting the elastic tube and the steel conduit, as well as providing an elastic tube longer than the plug bar at the time of manufacture as a tube from the rear end of the plug bar to the tip metal fitting. A plug bar for a plug mill, comprising:   The means for connecting the elastic tube and the steel conduit is a screw provided so as to be screwed together or a connecting tool provided so as to be fitted to each other. Plug bar for plug mill.   The plug bar of a plug mill according to claim 1 or 2, wherein the elastic tube is a rubber hose.

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