JPS6235843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing seamless pipes.

In the Mannesmann drilling method, which has been commonly used in the past, a biasing bar is inserted between two rolls whose axes are tilted, and the rolls are rotated in the same direction to give the bar forward motion. The bar is formed into a tubular shape by creating cracks inside the bar while applying pressure, and by placing the tip of the metal core at the location where the crack occurs and drilling a hole.

In this case, at the start of machining, the diameter of the tip of the bar material is reduced in advance and pre-machining is applied to the bar material to form an angle corresponding to the inclined surface of the roll. Since the product shape cannot be obtained, the rear end of the tube is cut off.

However, the length of the tube material manufactured by this method is limited by the length of the core metal, and it is not possible to obtain a desired seamless tube.

The method of the present invention makes it possible to manufacture such seamless pipes in extremely long lengths, and involves feeding a metal bar heated to a high temperature in the axial direction while reducing its diameter with three rolls. A spindle-shaped core metal is placed in a floating state at the center of the bar on the exit side of the roll, and the bar material is wound around the core metal, thereby cooling the hollow bar. After increasing the strength by drawing the pipe through a drawing die or drawing roll and the rear end of the core metal, it is possible to manufacture seamless pipes without being affected by the length of the core metal. It has characteristics.

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

As shown in FIG. 1, a metal bar 1 as a tube material is first heated by a heating device 2 and inserted between three rolls 3. These three rolls 3 have a tapered surface 4 for narrowing the diameter of the supplied bar material 1 and a tapered surface 5 for winding the material around a core metal 6, which will be described later. is shifted in a certain direction with respect to the bar 1. Therefore,
When these rolls 3 are rotated, the bar 1 inserted between the rolls is sent in the axial direction while rotating around its axis.

On the exit side of the roll 3, the tip of a spindle-shaped core bar 6 is arranged to face the center of the bar material 1 to be fed out, and the bar material to be fed out from the roll is placed between the core bar 6 and the center of the bar material 1 to be fed out.
Wrap it around. The thus hollow bar or tube material is pulled in the axial direction while being cooled by water injection in the cooling device 7 and drawn through the drawing die 8, thereby making it possible to obtain a very long seamless tube 10. As the tensioning mechanism for pulling the seamless pipe 10, a known tensioning mechanism that grips the pipe with rolls or chucks can be employed.

In manufacturing the seamless pipe described above, in the process of reducing the diameter of the bar 1 using three rolls, the bar 1 is heated to a high temperature by the heating device 2, but this temperature improves the ductility of the bar. , and it is necessary to lower the deformation resistance. For example, in the case of carbon steel, the temperature is preferably about 1100 to 1200°C.

In addition, the diameter of the tube material wound around the core metal 6 in a tubular shape is reduced by squeezing between the drawing die 8 and the rear end of the core metal 6. The core bar 6 is pressed against the drawing die 8 through the tube material due to the load acting on the side end. As the temperature of the tube material increases, it becomes softer. Therefore, if the temperature of the tube material is high between the drawing die 8 and the core bar 6, the rear end of the core bar will push through the material, or the drawing die 8 will break. It also comes into contact with the inner surface. Therefore, in order to effectively utilize the machining load acting on the core metal for drawing and to draw the tube material smoothly in the gap between the core metal and the drawing die, the cooling device 7 cools the tube material. It is necessary to have a sufficiently high hardness; for example, in the case of carbon steel, it is desirable that the temperature of the tube material just before it comes into contact with the drawing die 8 is about 600 to 800°C. By cooling the tube material in this manner, it is possible to apply a tensile action to the heated portion near the tip of the core metal, and at the same time, it is possible to provide the cooled portion with sufficient strength to withstand the tension.

Incidentally, instead of the drawing die 8 described above, a drawing roll may be used to draw the tube material.

When starting the production of the seamless pipe described above, the core bar 6 is temporarily held in a required position by an appropriate holding means, the bar material is wound around the core bar, and then a drawing die is used. 8, it is necessary to temporarily push the core bar 6 in the opposite direction to the direction in which the tube is pulled out when starting the drawing process of the material tube.

As explained in connection with the prior art example, such processing of the front end of the material and cutting off of the rear end portion are operations that are normally performed in plastic working, and in the present invention, following these examples, the processing is also carried out. Although this is a matter of course, one example will be briefly explained below based on FIGS. 2A and 2B.

In the tipping process performed at the start of processing, first, a metal bar 1 as a tube material is heated with a heating device 2 and inserted between three rolls 3. Therefore, when these rolls 3 are rotated, the bar 1 inserted between the rolls is rotated around its axis, its diameter is reduced, and it is sent in the axial direction.

On the exit side of the roll 3, the tip of the core bar 6 or a tip of a tip core bar 6a having a similar shape is arranged opposite to the center of the bar material 1 to be fed out (FIG. 2A).
A hollow portion is formed by winding the bar material 1 sent out from the roll around the tipped core bar 6a. Next, the rod material 1 whose tip is partially hollow is returned to its initial position, and the spindle-shaped core metal 6 is inserted deep into the hollow portion.

In this way, by passing the bar 1 with the hollow part holding the core metal 6 inside again through the gap between the rolls 3, the hollow part at the tip of the bar 1 is compressed, and the hollow part as shown in FIG. 2B is compressed. A bar material containing the core metal 6 inside is obtained. Next, the gap between the rolls 3 is widened to the extent that the bar holding the core metal 6 inside can be fed, and the tip of the bar is fed to the hole of the drawing die 8, and the temperature of the bar is properly controlled while being rolled. By continuing the rotation of step 3, the bar can be pulled out through the drawing die 8.

When manufacturing the seamless tube is finished, the core bar 6 is taken out from the tube 10 by pulling the tube 10 out of the drawing die 8. In this case, the vicinity of the end of the tube 10 is cut off due to errors in size and shape.

The shape of the core metal may be a spindle shape with a tapered tip, and a shape that is used in the conventionally known hole-punching method may be selected.

Next, experimental examples related to the present invention will be explained.

A metal bar is inserted between multiple rolls with a feed angle on the axis, and these rolls reduce the diameter of the bar while feeding it in the axial direction, forming a spindle shape at the center of the bar at the exit side of the rolls. By arranging the core metal and wrapping the bar material around the core metal, a hole can be drilled in the center of the bar material. This method has been known for a long time, and various experimental examples have been reported (for example, TZ
Blazynski: “An assessment of a
Combined Rotary Piercing and Elongating
“Process for Tube Making”, JOURNAL OF
THE INSTITUTE OF METALS, 1967
Vol.95). Therefore, in the present invention, the processing conditions in those experimental examples can be used as the processing conditions when drilling a hole in a bar material.

In experiments conducted by the present inventor using lead round rods of 20φmm, core metals with diameters of 8, 10, 12, and 13 mm were used, and by feeding the round rods with a feed angle of 14° on the roll, It was possible to obtain tubes with outer diameters of 18, 16, and 14 mm and inner diameters of 8 to 13 mm, which corresponded to the diameter of the core metal.

On the other hand, it has been known for some time that drawing is performed by drawing the tube material through the space between the drawing die and the end of the core metal, and various experimental examples have been reported (for example, TZBLAZYNSKI:
“Theoretical method of designing tools for
METAL
FORMING, MAY 1967, Vol.34, No.5). As for the processing conditions when drawing the tube material in the present invention, almost the processing conditions in those experimental examples can be used.

Therefore, the biggest problem lies in the processing conditions to keep the core metal in a floating state, that is, how to maintain the temperature distribution of the bar.More specifically, the three rolls are used to At the same time as reducing the diameter of the hollow bar, the heating temperature for drilling holes in the bar is limited to a certain temperature range determined by the material, resulting in the problem of how much to cool the hollow bar. Since the strength of the material is determined by the degree of cooling of the rod, a simulation was conducted using a model as shown in Figure 3. Figure 3 shows two round lead bars with different strengths.
1 and 12 are separately formed into hollow shapes in advance, the end surfaces of both are joined by appropriate means, and this is used as a tube material.The core bar 6 is inserted inside, and the lead round with greater strength is formed. The rod 12 is shown facing the drawing die 8, set between the rolls 3, and pulled out by gripping the end with a drawing chuck. According to the results of this simulation, it was confirmed that it was possible to maintain the core metal in a floating state within the tube material and process the lead round bar 12, which had greater strength, into the desired seamless tube. Therefore, by confirming the appropriate cooling mode depending on the material and performing appropriate cooling, it is possible to obtain the infinite length seamless pipe according to the present invention.

As detailed above, according to the method of the present invention, an infinite length seamless pipe can be manufactured without being constrained by the length of the core metal.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing an embodiment of the present invention, FIGS. 2A and 2B are explanatory views of pre-processing, and FIG. 3 is an explanatory view of simulation related to the present invention. DESCRIPTION OF SYMBOLS 1... Bar material, 2... Heating device, 3... Roll, 6... Core metal, 7... Cooling device, 8... Drawing die, 10... Seamless pipe.

Claims (1)

[Claims] 1 A metal bar heated to a high temperature is inserted between three rolls whose axes are shifted, and the rolls rotate to reduce the diameter of the bar while sending it out in the axial direction. A spindle-shaped core metal is placed in a floating state at the center of the core metal, and the bar material is wound around the core metal, thereby forming the bar material into a hollow shape.At the same time, the roll side of the core metal The core metal is pressed against a drawing die or a drawing roll through a hollow bar by the load acting on the end of the hollow bar, the hollow bar is cooled to increase its strength, and then the hollow bar is drawn. A method for producing a seamless pipe, which comprises drawing the pipe through a space between a die or a drawing roll and the rear end of a core metal.