CN114425570B

CN114425570B - Cold drawing die

Info

Publication number: CN114425570B
Application number: CN202210270601.9A
Authority: CN
Inventors: 潘迪波; 陶修林
Original assignee: Zhejiang Sanji Steel Tube Co ltd
Current assignee: Zhejiang Sanji Steel Tube Co ltd
Priority date: 2022-03-18
Filing date: 2022-03-18
Publication date: 2023-07-14
Anticipated expiration: 2042-03-18
Also published as: CN114425570A

Abstract

The invention discloses a cold drawing die, which comprises: an inner die sleeve; the outer side edge of one end of the inner die sleeve is inwards recessed to form a concave edge; the center of the inner die sleeve is provided with a shaping die hole, the shaping die hole comprises a cylindrical hole positioned in the middle, one side of the cylindrical hole, which is close to the concave edge, is sequentially provided with a first conical hole and a second conical hole, and the maximum inner diameter of the first conical hole is smaller than the minimum inner diameter of the second conical hole; the cylindrical hole is provided with a third conical hole on one side far away from the concave edge, two sides of the section of the third conical hole are arcs which are symmetrically distributed and protrude towards the central axis, the minimum inner diameter of the third conical hole is equal to the inner diameter of the cylindrical hole, and the inner side wall of one end of the third conical hole far away from the concave edge is inwards recessed to form an annular step. The invention realizes one-time cold drawing forming through the cylindrical hole, the first conical hole, the second conical hole and the third conical holes with a plurality of circular arcs and steps in the cylindrical hole, the first conical hole and the second conical hole.

Description

Cold drawing die

Technical Field

The invention relates to the field of cold drawing dies, in particular to a cold drawing die.

Background

At present, various moulds and tools for obtaining required products by injection molding, blow molding, extrusion, die casting or forging, smelting, stamping and other methods are used in industrial production, different moulds are composed of different parts, and the processing of the appearance of an article is realized by changing the physical state of a formed material.

The cold drawing die for manufacturing the section steel is used for heating materials, and stretching the materials through the cold drawing die after the materials are cooled, so that the section steel is formed, the current mode of the cold drawing die is diversified, various section steels can be manufactured and finished due to the variety of the cold drawing die, and the dies of other modes can not be replaced due to the fixation of the cold drawing die when cold drawing operation is performed, so that the manufactured section steel mode is manufactured. The existing steel tube cold drawing needs to be performed twice, annealing is performed after the first cold drawing, and then the second cold drawing is performed, so that time and labor are wasted.

Disclosure of Invention

Aiming at the problems, the invention provides a cold drawing die, which solves the defects that the cold drawing of the existing steel pipe needs to be carried out twice, annealing is carried out after the first cold drawing, and then the second cold drawing is carried out, thereby wasting time and energy.

The technical scheme adopted by the invention is as follows:

a cold drawing die comprising: an inner die sleeve; the outer side edge of one end of the inner die sleeve is inwards sunken to form a concave edge. The center of the inner die sleeve is provided with a shaping die hole, the shaping die hole comprises a cylindrical hole positioned in the middle, one side of the cylindrical hole, which is close to the concave edge, is sequentially provided with a first conical hole and a second conical hole, and the maximum inner diameter of the first conical hole is smaller than the minimum inner diameter of the second conical hole; the cylindrical hole is provided with a third conical hole on one side far away from the concave edge, two sides of the section of the third conical hole are arcs which are symmetrically distributed and protrude towards the central axis, the minimum inner diameter of the third conical hole is equal to the inner diameter of the cylindrical hole, and the inner side wall of one end of the third conical hole far away from the concave edge is inwards recessed to form an annular step.

The invention realizes one-time cold drawing forming through the cylindrical hole, the first conical hole, the second conical hole and the third conical holes with a plurality of circular arcs and steps in the cylindrical hole, the first conical hole and the second conical hole. The invention solves the problem that the cold drawing of the existing steel pipe needs to be performed twice, annealing is performed after the first cold drawing, and then the second cold drawing is performed, thereby wasting time and labor.

Optionally, four groups of fixing pieces are arranged on the outer side of the inner die sleeve, each fixing piece comprises a first adjusting component, a second adjusting component and a first screw, the first adjusting component is abutted against the outer side wall of the concave edge of the inner die sleeve, and the second adjusting component is abutted against the outer side wall of the inner die sleeve located on the outer side of the concave edge; the first adjusting assembly and the second adjusting assembly are respectively provided with a first screw hole, the first screw rod simultaneously penetrates through the first screw holes of the first adjusting assembly and the second adjusting assembly, and nuts are respectively arranged at two ends of the first screw rod.

Optionally, the first adjusting component comprises an abutting adjusting structure, the abutting adjusting structure comprises an outer elastic plate and an elastic membrane, the outer elastic plate and the elastic membrane form a sealed liquid storage cavity, and electrorheological fluid is stored in the liquid storage cavity; the outer elastic sheet comprises an outer baffle sheet abutting against the longitudinal surface of the concave edge and an arc-shaped limiting block positioned at the end part of the outer baffle sheet, the outer baffle sheet is made of a memory metal material, and the outer baffle sheet stretches outwards after the outer baffle sheet reaches the metamorphosis temperature.

Optionally, a first electrode plate is installed on the inner side of the outer baffle, an insulating outer cylinder body is installed on one side, close to the outer baffle, of the first electrode plate, the first electrode plate is inserted into the outer cylinder body, a second spring is arranged between the first electrode plate and the bottom wall of the outer cylinder body, an elastic piece made of conductive materials is installed between the first electrode plate and the top wall of the liquid storage cavity, the elastic piece is electrically connected with the first electrode plate, the elastic piece is used for providing elastic force for enabling the first electrode plate to move downwards, a heating piece is also installed on the inner side wall of the liquid storage cavity, an L-shaped second electrode plate is installed in the liquid storage cavity, the first electrode plate is externally connected with one pole of an external power supply, and the second electrode plate is externally connected with the other pole of the external power supply; the L-shaped second electrode plate comprises a transverse extension part and an abutting part, and the abutting part faces the limiting block.

Optionally, a switch is further installed between the first electrode plate and the external power supply, and the switch is used for controlling the electrifying states of the first electrode plate and the second electrode plate.

Optionally, the second adjusting part includes the medial part that is used for contradicting the lateral wall of the interior die sleeve in concave edge outside and is equipped with the lateral part of first screw, install a plurality of first springs between medial part and the lateral part.

Optionally, be equipped with the installation cavity in the lateral part, be equipped with first conical gear and first conical gear intermeshing's second conical gear in the installation cavity, be equipped with first pivot on the first conical gear, be equipped with the second pivot on the second conical gear, first pivot transversely stretches out the lateral part to be equipped with the rotation handle at the end.

Optionally, the inner side piece and the outer side piece are both provided with second screw holes which are axially arranged, the second rotating shaft longitudinally penetrates into the second screw holes of the inner side piece and the outer side piece, and the first rotating shaft is provided with threads which are matched with the second screw holes. The external fixing piece of the existing cold drawing die can only correspond to the internal die sleeve one by one, and cannot be adjusted according to different sizes. According to the invention, four groups of conditions are respectively fixed at four corners of an inner die sleeve, the four groups of conditions are inserted into first screw holes of a first adjusting component and a second adjusting component through a first screw rod, the first adjusting component is clamped into a concave edge through nut fixation, a first rotating shaft is rotated through rotating a rotating handle, a first bevel gear and a second bevel gear are driven to rotate, and the inner side piece is driven to extrude the inner die sleeve and adapt to the inner die sleeves with different sizes; when the interference adjusting structure interferes with the concave edge, the heating piece heats to enable the temperature of the outer baffle to exceed the metamorphosis temperature of the outer baffle, after the outer baffle reaches the metamorphosis temperature, the outer baffle stretches outwards to drive the elastic membrane to interfere with the concave edge, meanwhile, the switch is turned on to enable the first electrode plate to be connected with one pole of the power supply through the elastic piece, and the second electrode plate is connected with current to enable the electrorheological fluid to be converted from a liquid state to a solid state; at the moment, the abutting adjusting structure abuts against the concave edge and cannot generate flexible deformation, so that the firmness of clamping is guaranteed, the abutting part of the second electrode plate is extruded to become solid electrorheological fluid, and the problem that the second electrode plate is damaged due to the fact that the second electrode plate moves relatively is solved, and the second electrode plate directly abuts against the elastic membrane and the concave edge; when the heating element does not generate heat, the switch is turned off, the electrorheological fluid is in a liquid state, the first electrode plate moves upwards due to the relative extrusion of the concave edges, the first electrode plate is in contact with the adjusting structure and can deform, and at the moment, the first adjusting assembly and the second adjusting assembly are convenient to take down; the outer baffle deflects inwards to be close to the abutting part of the second electrode plate, so that the second electrode plate is protected.

(III) beneficial effects

1. The invention realizes one-time cold drawing forming through the cylindrical hole, the first conical hole, the second conical hole and the third conical holes with a plurality of circular arcs and steps in the cylindrical hole, the first conical hole and the second conical hole. The invention solves the problem that the cold drawing of the existing steel pipe needs to be performed twice, annealing is performed after the first cold drawing, and then the second cold drawing is performed, thereby wasting time and labor.

2. According to the invention, four groups of conditions are respectively fixed at four corners of an inner die sleeve, the four groups of conditions are inserted into first screw holes of a first adjusting component and a second adjusting component through a first screw rod, the first adjusting component is clamped into a concave edge through nut fixation, a first rotating shaft is rotated through rotating a rotating handle, a first bevel gear and a second bevel gear are driven to rotate, and the inner side piece is driven to extrude the inner die sleeve and adapt to the inner die sleeves with different sizes; when the interference adjusting structure interferes with the concave edge, the heating piece heats to enable the temperature of the outer baffle to exceed the metamorphosis temperature of the outer baffle, after the outer baffle reaches the metamorphosis temperature, the outer baffle stretches outwards to drive the elastic membrane to interfere with the concave edge, meanwhile, the switch is turned on to enable the first electrode plate to be connected with one pole of the power supply through the elastic piece, and the second electrode plate is connected with current to enable the electrorheological fluid to be converted from a liquid state to a solid state; at the moment, the abutting adjusting structure abuts against the concave edge and cannot generate flexible deformation, so that the firmness of clamping is guaranteed, the abutting part of the second electrode plate is extruded to become solid electrorheological fluid, and the problem that the second electrode plate is damaged due to the fact that the second electrode plate moves relatively is solved, and the second electrode plate directly abuts against the elastic membrane and the concave edge; when the heating element does not generate heat, the switch is turned off, the electrorheological fluid is in a liquid state, the first electrode plate moves upwards due to the relative extrusion of the concave edges, the first electrode plate is in contact with the adjusting structure and can deform, and at the moment, the first adjusting assembly and the second adjusting assembly are convenient to take down; the outer baffle deflects inwards to be close to the abutting part of the second electrode plate, so that the second electrode plate is protected. The invention is convenient to disassemble and is completely and conveniently adjusted according to the size of the inner die sleeve.

Description of the drawings:

FIG. 1 is a sectional view of a cold drawing die of embodiment 1 of the present invention;

FIG. 2 is a front view of the cold drawing die of embodiment 2 of the present invention;

FIG. 3 is a sectional view showing the assembly of the fixing member and the inner die sleeve of FIG. 2 of the cold drawing die of embodiment 2 of the present invention;

fig. 4 is an enlarged partial view of part a of the outer cylinder of the cold drawing die of example 2 of the present invention.

The reference numerals in the drawings are as follows:

1. the inner die sleeve, 2, a concave edge, 3, a shaping die hole, 4, a cylindrical hole, 5, a first conical hole, 6, a second conical hole, 7, a third conical hole, 8, a step, 9, a fixing piece, 10, a first adjusting component, 11, a second adjusting component, 12, a first screw rod, 13, a first screw hole, 14, a nut, 15, an interference adjusting structure, 16, an outer spring plate, 17, an elastic film, 18, a second screw hole, 19, a liquid storage cavity, 20, an outer baffle, 21, a limiting block, 22, a first electrode plate, 23, an outer cylinder body, 24, a second spring, 25, an elastic piece, 26, a heating piece, 27, a second electrode plate, 28, a transverse extending part, 29, an interference part, 30, an inner piece, 31, an outer piece, 32, a first spring, 33, a mounting cavity, 34, a first conical gear, 35, a second conical gear, 36, a first rotating shaft, 37, a second rotating shaft, 38 and a rotating handle.

The specific implementation formula is as follows:

the following describes in further detail the embodiments of the present invention with reference to the drawings and examples. The following examples are illustrative of the invention and are not intended to limit the scope of the invention.

In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front," "rear," "head," "tail," and the like are used as an orientation or positional relationship based on that shown in the drawings, merely to facilitate description of the invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "connected," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically connected, directly connected or indirectly connected through an intermediate medium. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.

Example 1

The technical scheme adopted by the invention is as follows:

as shown in fig. 1, the present invention discloses a cold drawing die, comprising: an inner die sleeve; the outer side edge of one end of the inner die sleeve is inwards recessed to form a concave edge; the center of the inner die sleeve is provided with a shaping die hole, the shaping die hole comprises a cylindrical hole positioned in the middle, one side of the cylindrical hole, which is close to the concave edge, is sequentially provided with a first conical hole and a second conical hole, and the maximum inner diameter of the first conical hole is smaller than the minimum inner diameter of the second conical hole; the cylindrical hole is provided with a third conical hole on one side far away from the concave edge, two sides of the section of the third conical hole are arcs which are symmetrically distributed and protrude towards the central axis, the minimum inner diameter of the third conical hole is equal to the inner diameter of the cylindrical hole, and the inner side wall of one end of the third conical hole far away from the concave edge is inwards recessed to form an annular step.

When the embodiment is implemented, the cold drawn steel tube is inserted into the inner die sleeve and is formed by one-time cold drawing.

Example 2

The difference between this embodiment 2 and embodiment 1 is that, as shown in fig. 2, 3 and 4, the present invention discloses a cold drawing die, comprising: an inner die sleeve 1; the outer side edge of one end of the inner die sleeve is inwards sunken to form a concave edge 2. The center of the inner die sleeve is provided with a shaping die hole 3, the shaping die hole comprises a cylindrical hole 4 positioned in the middle, one side of the cylindrical hole, which is close to the concave edge, is sequentially provided with a first conical hole 5 and a second conical hole 6, and the maximum inner diameter of the first conical hole is smaller than the minimum inner diameter of the second conical hole; the cylindrical hole is provided with a third conical hole 7 on one side far away from the concave edge, two sides of the section of the third conical hole are arcs which are symmetrically distributed and protrude towards the central axis, the minimum inner diameter of the third conical hole is equal to the inner diameter of the cylindrical hole, and the inner side wall of one end of the third conical hole far away from the concave edge is inwards recessed to form an annular step 8.

Four groups of fixing pieces 9 are arranged on the outer side of the inner die sleeve, each fixing piece comprises a first adjusting component 10, a second adjusting component 11 and a first screw rod 12, the first adjusting component is abutted against the outer side wall of the concave edge of the inner die sleeve, and the second adjusting component is abutted against the outer side wall of the inner die sleeve located on the outer side of the concave edge; the first adjusting component and the second adjusting component are respectively provided with a first screw hole 13, the first screw rod passes through the first screw holes of the first adjusting component and the second adjusting component at the same time, and nuts 14 are respectively arranged at two ends of the first screw rod.

The first adjusting component comprises an abutting adjusting structure 15, wherein the abutting adjusting structure comprises an outer elastic plate 16 and an elastic membrane 17, the outer elastic plate and the elastic membrane form a sealed liquid storage cavity 19, and electrorheological fluid is stored in the liquid storage cavity; the outer elastic sheet comprises an outer baffle 20 abutting against the longitudinal surface of the concave edge and an arc-shaped limiting block 21 positioned at the end part of the outer baffle, the outer baffle is made of a memory metal material, and the outer baffle stretches outwards after the outer baffle reaches the metamorphosis temperature; the inner side of the outer baffle is provided with a first electrode plate 22, one side of the first electrode plate, which is close to the outer baffle, is provided with an insulating outer cylinder 23, the first electrode plate is inserted into the outer cylinder, a second spring 24 is arranged between the first electrode plate and the bottom wall of the outer cylinder, an elastic piece 25 made of conductive materials is arranged between the first electrode plate and the top wall of the liquid storage cavity, the elastic piece is electrically connected with the first electrode plate, the elastic piece is used for providing elastic force for enabling the first electrode plate to move downwards, the inner side wall of the liquid storage cavity is also provided with a heating piece 26, the liquid storage cavity is also provided with an L-shaped second electrode plate 27, the first electrode plate is externally connected with one pole of an external power supply, and the second electrode plate is externally connected with the other pole of the external power supply; the L-shaped second electrode plate comprises a transverse extension part 28 and an abutting part 29, and the abutting part faces the limiting block.

And a switch is also arranged between the first electrode plate and the external power supply and is used for controlling the electrifying states of the first electrode plate and the second electrode plate.

The second adjusting component comprises an inner side part 30 and an outer side part 31, wherein the inner side part is used for abutting against the outer side wall of the inner die sleeve at the outer side of the concave edge, a plurality of first springs 32 are arranged between the inner side part and the outer side part, a mounting cavity 33 is arranged in the outer side part, a first conical gear 34 and a second conical gear 35 meshed with the first conical gear are arranged in the mounting cavity, a first rotating shaft 36 is arranged on the first conical gear, a second rotating shaft 37 is arranged on the second conical gear, the first rotating shaft transversely extends out of the outer side part and is provided with a rotating handle 38 at the tail end, second screw holes 18 which are axially arranged are formed in the inner side part and the outer side part, the second rotating shaft longitudinally penetrates into the second screw holes of the inner side part and the outer side part, and threads matched with the second screw holes are formed in the first rotating shaft.

When the embodiment is implemented, the fixing pieces are fixed by utilizing the external fixing structure, four groups of fixing pieces are respectively fixed at four corners of the inner die sleeve, the fixing pieces are inserted into first screw holes of the first adjusting component and the second adjusting component through first screws, the first adjusting component is clamped into the concave edge through nut fixing, the first rotating shaft is rotated through rotating the rotating handle, the first conical gear and the second conical gear are driven to rotate, and the inner side piece is driven to extrude the inner die sleeve and adapt to the inner die sleeve with different sizes; when the interference adjusting structure interferes with the concave edge, the heating piece heats to enable the temperature of the outer baffle to exceed the metamorphosis temperature of the outer baffle, after the outer baffle reaches the metamorphosis temperature, the outer baffle stretches outwards to drive the elastic membrane to interfere with the concave edge, meanwhile, the switch is turned on to enable the first electrode plate to be connected with one pole of the power supply through the elastic piece, and the second electrode plate is connected with current to enable the electrorheological fluid to be converted from a liquid state to a solid state; at the moment, the abutting adjusting structure abuts against the concave edge and cannot generate flexible deformation, so that the firmness of clamping is guaranteed, the abutting part of the second electrode plate is extruded to become solid electrorheological fluid, and the problem that the second electrode plate is damaged due to the fact that the second electrode plate moves relatively is solved, and the second electrode plate directly abuts against the elastic membrane and the concave edge; when the heating element does not generate heat, the switch is turned off, the electrorheological fluid is in a liquid state, the first electrode plate moves upwards due to the relative extrusion of the concave edges, the first electrode plate is in contact with the adjusting structure and can deform, and at the moment, the first adjusting assembly and the second adjusting assembly are convenient to take down; the outer baffle deflects inwards to be close to the abutting part of the second electrode plate, so that the second electrode plate is protected.

The foregoing description is only of the preferred embodiments of the present invention, and is not intended to limit the scope of the invention, but rather is intended to cover all equivalent structures as modifications within the scope of the invention, either directly or indirectly, as may be contemplated by the present invention.

Claims

1. A cold drawing die, comprising: an inner die sleeve; the outer side edge of one end of the inner die sleeve is inwards recessed to form a concave edge; the center of the inner die sleeve is provided with a shaping die hole, the shaping die hole comprises a cylindrical hole positioned in the middle, one side of the cylindrical hole, which is close to the concave edge, is sequentially provided with a first conical hole and a second conical hole, and the maximum inner diameter of the first conical hole is smaller than the minimum inner diameter of the second conical hole; a third conical hole is formed in one side, far away from the concave edge, of the cylindrical hole, arcs protruding towards the central axis are symmetrically distributed on two sides of the section of the third conical hole, the minimum inner diameter of the third conical hole is equal to the inner diameter of the cylindrical hole, and the inner side wall of one end, far away from the concave edge, of the third conical hole is recessed inwards to form an annular step; the outer side of the inner die sleeve is provided with a plurality of groups of fixing pieces, each fixing piece comprises a first adjusting component, a second adjusting component and a first screw rod, the first adjusting component is abutted against the outer side wall of the concave edge of the inner die sleeve, and the second adjusting component is abutted against the outer side wall of the inner die sleeve positioned at the outer side of the concave edge; the first adjusting assembly and the second adjusting assembly are respectively provided with a first screw hole, the first screw rod simultaneously passes through the first screw holes of the first adjusting assembly and the second adjusting assembly, and nuts are respectively arranged at two ends of the first screw rod; the first adjusting component comprises an abutting adjusting structure, wherein the abutting adjusting structure comprises an outer elastic plate and an elastic membrane, the outer elastic plate and the elastic membrane form a sealed liquid storage cavity, and electrorheological fluid is stored in the liquid storage cavity; the outer spring plate comprises an outer baffle plate which is abutted against the longitudinal surface of the concave edge and an arc-shaped limiting block positioned at the end part of the outer baffle plate, the outer baffle plate is made of a memory metal material, and the outer baffle plate stretches outwards after the outer baffle plate reaches the metamorphosis temperature; the inner side of the outer baffle is provided with a first electrode plate, one side of the first electrode plate, which is close to the outer baffle, is provided with an insulating outer cylinder body, the first electrode plate is inserted into the outer cylinder body, a second spring is arranged between the first electrode plate and the bottom wall of the outer cylinder body, an elastic piece made of conductive materials is arranged between the first electrode plate and the top wall of the liquid storage cavity, the elastic piece is electrically connected with the first electrode plate, the elastic piece is used for providing elasticity for enabling the first electrode plate to move downwards, the liquid storage cavity is also provided with an L-shaped second electrode plate, the first electrode plate is externally connected with one pole of an external power supply, and the second electrode plate is externally connected with the other pole of the external power supply; the L-shaped second electrode plate comprises a transverse extension part and an abutting part, and the abutting part faces the limiting block; the inner side wall of the liquid storage cavity is also provided with a heating element; a switch is also arranged between the first electrode plate and the external power supply and is used for controlling the electrifying states of the first electrode plate and the second electrode plate;

when the interference adjusting structure interferes with the concave edge, the heating piece heats to enable the temperature of the outer baffle to exceed the metamorphosis temperature of the outer baffle, after the outer baffle reaches the metamorphosis temperature, the outer baffle stretches outwards to drive the elastic membrane to interfere with the concave edge, meanwhile, the switch is turned on to enable the first electrode plate to be connected with one pole of the power supply through the elastic piece, and the second electrode plate is connected with current to enable the electrorheological fluid to be converted from a liquid state to a solid state; at the moment, the abutting concave edge of the abutting adjusting structure cannot flexibly deform; when the heating piece does not generate heat, the switch is turned off, the electrorheological fluid is in a liquid state, and the concave edges are extruded relatively, so that the first electrode plate moves upwards and can be deformed by abutting the adjusting structure.

2. A cold drawing die as defined in claim 1, wherein said second adjusting assembly includes an inner member for abutting against the outer wall of the inner jacket outside the concave edge and an outer member provided with a first screw hole, a plurality of first springs being installed between said inner member and said outer member.

3. A cold drawing die as defined in claim 2, wherein the outer member is provided with a mounting cavity, a second bevel gear is provided in the mounting cavity, the first bevel gear is provided with a first rotating shaft, the second bevel gear is provided with a second rotating shaft, the first rotating shaft transversely extends out of the outer member, and a rotating handle is provided at the tail end.

4. A cold drawing die as defined in claim 3, wherein the inner and outer members are provided with second screw holes arranged axially, the second shaft penetrates into the second screw holes of the inner and outer members longitudinally, and the first shaft is provided with threads adapted to the second screw holes.