FR2467644A1 - Reducing tube dia. and wall thickness - by drawing through die using self-centring core formed as truncated cones connected at small ends - Google Patents

Abstract

The arrangement is intended for drawing a tube to reduce its dia. and wall thickness using a drawing die and a self-centering drawing core. The core is so arranged that, after being reduced in the die, the tube dia. is increased by passing over a further portion of the same core. The first portion of the core is pref. frusto conical with its larger dia. pointing against the direction of tube movement and slightly smaller than the inner tube dia., whilst its second portion is also truncated conical with its smaller dia. equal to and fixed to that of the cone and out of contact with the tube wall.

Description

The present invention relates to the manufacture of tubes by drawing, and more precisely to a method of drawing tubes and to a self-adjusting mandrel serving to ensure the implementation of this method.

The invention can find the widest application in the drawing in reels or rolls of steel tubes made of non-ferrous metals and alloys. By drawing is meant work of the tubes by deformation carried out by pulling the tubes through a die, from which it follows that the geometric parameters of the tubes change.

Anyone skilled in the art working in this field knows that the term "roll drawing of the tubes means drawing of blanks of tubes wound beforehand in the form of a roll or coil, and obtaining after drawing also tubes in the form of a roll, by their winding on a drum.

A method of drawing tubes is known comprising a reduction of the tube in a die according to the diameter and the wall thickness, on a self-adjusting mandrel composed of two parts arranged coaxially with respect to each other and contiguous one to the other, one of which is produced in the form of a truncated cone and the other in the form of a cylinder.

Before drawing, the end of the tube blank is forged. During forging, the end of the tube blank is reduced according to the outside diameter, and this to ensure its free passage through the die and its subsequent clamping by pliers or by other clamping means of the bench drawing.

According to the known method of stretching on a self-adjusting mandrel, the tube blank is reduced any port following the diameter in the die, and S from the moment of contacting the surf: internal xoe of the blank - tube head rec has the surface to the conical part of the self-adjusting mandrel; thanks to the common effect of the die and the self-adjusting mandrel, the tube blank is reduced according to the wall thickness. When the tube blank in the die comes into contact with the cylindrical part of the self-adjusting mandrel, thanks to the common effect of the die and the cylindrical part of the self-adjusting mandrel, an intense subsequent reduction of the tube blank according to the thickness of the wall up to the predetermined value a location. After the passage of the tube blank between the die and the cylindrical part of the mandrel, the tube acquires the required dimensions according to the diameter and thickness of the wall and leaves the die.

According to the known method of drawing tubes on a self-adjusting mandrel, after the reduction of the tube blank according to the diameter, it is necessary to carry out an intense reduction of the tube blank according to the thickness of the wall.

This is necessary in order to eliminate tangential tensile stresses appearing in the blank of pipe during the process of its reduction according to the diameter in the die, until the moment of the coming into contact of the interior surface of the blank of tube with the conical part of the self-adjusting mandrel. If the tangential tensile stresses emerging in the tube are not eliminated, they can lead to deterioration of the tube after it has been stretched.

The need to achieve a considerable reduction in the tube blank according to the thickness of the wall, in the known method, leads to the need for tube blanks for the manufacture of the tubes by several draws. , and tubes of intermediate dimensions, having a large wall thickness and, consequently, a greater mass of metal.

Since after each stretch the forged end of the tube blank must be cut in order to ensure the possibility of carrying out the subsequent work of the tube (annealing, chemical attack, etc.), when using blanks of tube having a large wall thickness, the losses of the metal increase, especially when cutting the forged ends, which is disadvantageous from the economic point of view.

In addition, the need to use tube blanks having a large wall thickness does not ensure a sufficient value of deformation depending on the diameter of the tube when drawing the tubes on a self-adjusting mandrel according to the known method, being given that at the same time as the wall thickness of the tube blanks, the values of the tangential tensile stresses increase.

When using tube blanks having a thin wall to draw tubes of required dimensions, it is necessary to carry out, after drawing by the known method on a self-adjusting mandrel, several additional drawing without using the mandrel, during which the tubes are reduced only according to the diameter. During the drawing of tubes without a mandrel, tangential tensile stresses appear in the tubes which can, during large reductions of the tubes according to the diameter, cause cracking of the tubes after drawing.

In addition, when drawing the tubes without a mandrel, the inner surface of the tabs becomes worse, that is, on this surface may form folds, roughness, etc. The stretching of the tubes without the use of a mandrel, during which a free movement of metal takes place towards the longitudinal axis of the tube, does not make it possible to obtain tubes having the required wall thickness
The carrying out of the additional drawing of the tubes without the use of a chuck leads to additional losses of metal during the cutting of the forged ends of the tubes carried out after each drawing.

Thus, the drawing of the tubes according to the known method on self-adjusting mandrel ensured an insufficiently high productivity and required a high consumption of the metal and other materials (technological lubricant for drawing, electrical energy, etc.) .

A self-adjusting mandrel is known for drawing the tubes. This mandrel is composed of two parts arranged coaxially with respect to each other. One part is made in the form of a truncated cone, and the other in the form of a cylinder. The cylindrical part is adjacent to the small base of the conical part and has a diameter equal to the diameter of this base and to the inside diameter of the tube obtained during the drawing process. The diameter of the large base of the conical part of the mandrel is smaller than the inside diameter of the tube blank. The large base of the conical part is oriented in the opposite direction to the direction of movement of the tube to be worked.

Due to the presence of the cylindrical part of the known self-adjusting mandrel, during the reduction of the tube blank appear the tangential tensile stresses already mentioned in the description of the known process and which can only be eliminated by means of a reduction. intensity of the tube blank according to the wall thickness.

As a result, the drawing process becomes more expensive, since when drawing with an intense reduction of the tube blank according to the wall thickness, it is necessary to use high quality technological lubricants. and more expensive to prevent the adhesion of the metal of the tube blank to the cylindrical part of the self-adjusting mandrel, which would cause the appearance on the inner surface of the defect tubes in the form of longitudinal stripes or ruptures of the tubes behind the die.

The object of the present invention is to remedy the aforementioned drawbacks by providing a method of drawing tubes and a self-adjusting mandrel for implementing this method, making it possible to increase the yield of the process by increasing the deformation. depending on the diameter of the tube blanks and to make the drawing process more economical by reducing metal losses and by using less expensive technological lubricants.

The aim is achieved by a tube drawing process comprising a reduction of the tubes according to the diameter and the thickness of the wall in the die with the use of a self-adjusting mandrel, in which, according to the invention, after the reduction, the tube is widened behind the die on the same mandrel.

The aim is also achieved thanks to a self-adjusting mandrel for the implementation of this method of drawing tubes, of the type comprising two parts arranged coaxially and connected to each other, one of which has the form of '' a truncated cone with a large base oriented against the direction of movement of the tube to be worked and a diameter somewhat smaller than the inside diameter of the tube blank, in which, according to the invention the second part has also the shape of a truncated cone which is connected by its small base to the small base of the truncated cone of the first part and whose large base has a diameter essentially equal to the inside diameter of the tube obtained during the drawing process, while the diameters of the small bases of the truncated cones of the two parts are equal and somewhat smaller than the inside diameter of the tube obtained so as to avoid contact of the tube worked with the mandrel at the junction of its two parts.

Such a technical solution ensures the possibility of drawing the tubes with the use of the self-adjusting mandrel without making considerable reductions depending on the wall thickness of the tube blank.
In addition, the use of the stretching procedure and of the self-adjusting mandrel proposed makes it possible to increase the yield of the process thanks to an increase in deformations during the reduction according to the diameter of the hires of you be, and to make the process d cheaper drawing thanks to the use of thinner-walled tube blanks and reduced metal loss when cutting forged tube ends
In addition, the use of the method and of the self-adjusting mandrel according to the invention gives the possibility of making the drawing process more economical thanks to the use of less expensive technological lubricants.

In the following description is given the description of a non-limiting example of embodiment of the present invention, with reference to the accompanying drawings, in which
- Fig. 1 schematically illustrates, with partial longitudinal cut, the tube to be worked subjected to a stretching in a roll, a self-adjusting mandrel produced according to the invention and a die, intended for the implementation of the method according to the invention;
- Fig. 2 shows on an enlarged scale and in longitudinal section, a tube blank with the self-adjusting mandrel according to the invention, placed in this blank before the work of the tube begins.

The process of drawing tubes is carried out as follows.

A technological lubricant is injected under pressure into the open end 1 (FIG. 1) of the tube blank 3 rolled into a roll or coil 2. Then, from the side of the outer surface of the tube blank 3, at a certain distance from the end 1, a cavity 4 (FIG. 2) is produced by pushing the wall inside the blank 3. In the open end 1 of the tube blank 3 a self-adjusting mandrel 5 is placed 5. The cavity 4 serves to fix the self-adjusting mandrel 5 in this end of the blank 3.

Next, the end 1 of the tube blank is forged by means of an appropriate known mechanism capable of reducing the diameter of the end 1 of the tube blank 3, whereby the front part of the end 1 of the blank 3 acquires the shape shown in FIG. 1 and designated by the reference la. After that, the roller 2 is installed on an unwinding table (not shown) of the drawing bench, this table and this bench having a known construction.

The forged part 1a of the tip 1 of the blank 3 is moved through a die 6 and is clamped by pliers 7 of a drawing drum 8 of known construction. Then, starting from a command (not shown) of known construction, the stretching drum 8 is started, and one begins to stretch the blank 3 through the die 6. During the movement of the blank 3, the cavity 4 abuts against the self-adjusting mandrel 5 and the drive in the die 6.

By stretching the tube blank 3 through the die on the self-adjusting mandrel 5, the stretching process is carried out, which includes a reduction of the tube blank 3 according to the diameter and thickness of the wall. . The operations of the proposed method to be carried out later will be described in more detail in the description of the self-adjusting mandrel produced according to the present invention.

The self-adjusting mandrel 5 (Fig. 1 and 2) is composed of two parts 9 and 10 arranged coaxially and connected to each other. These parts have the shape of truncated canes. The large base 9a of the part 9 is oriented opposite the direction of movement of the tube to be worked. The diameter of the base 9a is somewhat smaller than the inside diameter of the tube blank 3. The part 10 is connected by its small base lob to the small base 9b of the truncated cone of part 9. 9
The diameter of the small base lob 'is equal to that of the small base 9b of the truncated cane of part 9.

The diameter of the large ba lOa of the truncated cane of the part 10 is equal to the inside diameter of the tube obtained during the drawing.

The diameters 9b and 10b are somewhat smaller than the inside diameter of the tube after drawing. The parts 9 and 10 are connected to each other at the yen of an intermediate cylindrical part which is arranged coaxially with respect to the parts 9 and 10.

The operation of the self-adjusting mandrel 5, according to the invention, and the subsequent operations of the proposed stretching process, are carried out as follows.

At the start of the stretching process, the mandrel 5 installed at the end 1 of the tube blank 3 passes through its part 10 through the die 6 and then occupies a position coaxial with respect to the tube blank 3, as shown Fig.l; in this position, the frictional forces arising in contact with the part 9 of the mandrel 5 with the inner surface of the blank 3 and tending to push the mandrel 5 during the die 6 become equal to the frictional forces appearing on the surface of contact of the part 10 of the mandrel 5 with the inner surface of the tube obtained during drawing and tending to pull the mandrel 5 in the die 6. From this moment begins the drawing process, during which a reduction in the tube to be worked, and then a widening of the tube worked behind the die 6 on the same mandrel 5.

By means of the grippers 7 of the drawing drum 8, the tube blank 3 is drawn through the die 6. From the moment the blank 3 comes into contact with the die 6, the blank 3 is reduced according to the outside diameter by means of the die 6, and from the moment of the coming into contact of the inside surface of the blank 3 with the surface of the part 9 of the mandrel 5, serious to the common effect of the die 6 and of the mandrel 5, the reduction of the tube blank 3 takes place according to the thickness of the wall.

After the reduction according to the diameter and the thickness of the wall, the tube leaves the die 6. The inner surface of the tube then ceases to touch the surface of the part 9 of the mandrel 5. As soon as the tube has passed the junction between the two parts of the mandrel 5, from the moment the inner surface of the tube comes into contact with the surface of the part 10 of the mandrel 5, the tube is enlarged. As a result of this widening of the tube, its inside and outside diameters increase.

During the reduction of the blank of tube 3 following the diameter in the die 6 appear in the blank of tangential pulling stresses whose value reaches its maximum at the time of coming into contact with the inner surface of the blank 3 with the surface of the part 9 of the self-adjusting mandrel 5. Following a slight reduction of the blank 3 according to the wall thickness under the common effect of the die 6 and of the part 9 of the mandrel 5, a required thickness of the wall of the tube is obtained.

Furthermore, the tangential tensile stresses decrease somewhat. Following the widening of the tube behind the die 6, the tangential tensile stresses decrease considerably, and, for a sufficient value of the widening, they become tightening stresses, which makes it possible to entirely eliminate the danger of cracking of the tubes.

Following enlargement, the tube acquires the required outside and inside diameters.

Thus, thanks to the use of the method of drawing tubes on a self-adjusting mandrel according to the invention, it is possible to obtain the tubes of required dimensions from blanks of thin-walled tubes. On the other hand, the amount of deformation when reducing the tube blanks along the diameter increases and, therefore, the yield of the process also increases.

Thanks to a saving in metal and the use of cheaper technological lubricants, the drawing process becomes less expensive.

The proposed tube drawing process and the self-adjusting mandrel for implementing this process have been successfully tested under laboratory conditions.
The tests have shown that the application of the process and of the self-adjusting mandrel follow the invention makes it possible to increase the yield of the process thanks to an increase in the value of deformation during the reduction of the tubes according to the diameter during drawing. , and to make the process more economical graA.ce> a reduction in metal losses and the use of less expensive technological lubricants.

Claims (2)

RESELL I CATI 0 NS 1 - Method of drawing tubes comprising a reduction of the tubes according to the diameter and the wall thickness in a die on a self-adjusting mandrel, characterized in that after the reduction, a widening of the tube is carried out behind the die on the same mandrel. 2 - Self-adjusting mandrel for implementing the method according to claim 1, of the type comprising two parts arranged coaxially and connected to each other, one of which has the shape of a truncated cone with a large base oriented against the direction of movement of the tube to be worked and a diameter somewhat smaller than the inside diameter of the tube blank, characterized in that the second part also has the shape of a truncated cane which is connected by its small base to the small base of the truncated cone of the first part and whose large base has a diameter essentially equal to the inside diameter of the tube obtained during the drawing process, while the diameters of the small bases of the truncated cones of the two parts are equal and somewhat smaller than the inside diameter of the tube obtained so as to avoid contact of the working tube with the mandrel at the junction of its two parts.