Die For Hydrostatic Extrusion Of Sections Having Elongated Projections

Abstract

For producing rods having longitudinally or helically extending projections or ribs by hydrostatic extrusion, the billet is extruded through a die having grooves, with the bases of the grooves inclined towards the longitudinal axis of the die so as to cause the material being extruded to fill the grooves of the die completely.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a die for manufacturing sections having longitudinal projections by means of hydrostatic extrusion of a billet through a die orifice of the desired cross section. The projections may be parallel with the section or helical in shape. As examples of products which can be manufactured may be mentioned shafts having splines, toothed gears having straight or oblique teeth, pump rotors, etc.

2. The Prior Art

One problem in the hydrostatic extrusion of sections having elongated projections with grooves between them is to get the billet material to completely fill the grooves in the die which form the ridges along the section so that the projections acquire the intended cross-section and shape. This difficulty is particularly pronounced when the elongated projections are also rather high. Consequently, variations in measurements of the product produce have been considerable. The reason that the billet material does not completely fill out the grooves in the die which are to form the elongated projections is that between the cross-section of the die where the orifice is largest, i.e., the transition between a conical inlet area and the bottom of the grooves forming the projections and the smallest cross-section of the die orifice there is an extreme elongation of the central part of the billet, which causes the part of the projection formed to stretch so that the height and width decrease if the radial displacement of the billet material is insufficient.

SUMMARY OF THE INVENTION

The invention provides a solution to the above-mentioned problem of completely filling the grooves of the die which are to form the elongated projections and thus obtaining the correct measurements for the extruded section. It is characterised in that the grooves in the die to produce the elongated projections on the rod are shaped so that their bases incline towards the longitudinal axis of the die. The grooves may also be shaped so that their width decreases from the inlet side towards the smallest cross-section of the die opening. A radial or a radial and tangential decrease in dimensions is thus obtained. This gives successive radial and/or tangential compensation for the extension of the projections as the material is extended in the central part of the billet. In dies for extruding sections having helical projections it may be suitable or necessary to have a smaller pitch in the first part of the die groove, i.e., the part of the groove lying ahead of the smallest cross section of the die orifice. In certain cases it may also be necessary or suitable to allow the pitch of the die groove to deviate somewhat from the pitch of the elongated projections in order to obtain the desired pitch. In one embodiment the projections between the grooves of the die are bevelled in the area immediately ahead of the smallest cross section of the die orifice so that the stresses in the projections between the grooves of the die can be decreased somewhat, thus decreasing the risk of rupture.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further exemplified with the help of the accompanying drawings.

FIGS. 1 and 2 show two examples of rod shaped products manufactured in dies according to the invention,

FIG. 3 a section of a die previously used together with a billet and the product in the die,

FIG. 4 a view of the die according to FIG. 3 from the inlet side,

FIG. 5 a corresponding view of a die for extruding a section having the same cross-section but with the elongated projections running helically,

FIG. 6 a section extruded in a die of previously known type showing how the measurements of this section differ from the cross-section of the die,

FIG. 7 a section in perspective through a die according to the invention having radial compensation in the grooves,

FIG. 8 a section through a die of the same type as that shown in FIG. 7 for producing a rod having four elongated projections,

FIG. 9 a view from the inlet side of the die shown in FIG. 8, with a billet and the product in the die,

FIG. 10 a section through a rod produced in the die,

FIG. 11 a die having tangential compensation in the grooves which are to form the ridges,

FIG. 12 a view of the die according to FIG. 11 from the inlet side,

FIG. 13 a section through a die having both radial and tangential compensation in the grooves which are to form the ridges,

FIG. 14 a view from the inlet side of the die according to FIG. 13,

FIG. 15 a section through a die for producing a section having helical elongated projections with both radial and tangential compensation in the grooves forming the projections,

FIG. 16 a view from the inlet side of the die according to FIG. 15,

FIG. 17 a section through a die having bevelled projections between the grooves and

FIG. 18 a view from the inlet side of the die according to FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a shaft having elongated projections 1 like splines around a core part 2. The projections 1 are parallel to the shaft itself. FIG. 2 shows a section having helically arranged projections 3 around a core part 4. The projections are shaped so that the section can be used as a rotor in a compressor. The die in FIGS. 3, 4 and 5 is of a type already known. It has a conical inlet part 6 and an opening 7 with grooves 8 and projections 9 between the grooves in order to produce the bar 10 shown in FIG. 6 which consists of a core part 11 and elongated projections 12 projecting from this core. In FIG. 6 the profile of the die is shown by broken lines 13. A billet 14 is shown in the die, and this is shaped to the section 10. The edges of the die hidden by the billet 14 are shown in broken lines. In dies for producing sections having straight projections 1, 12 the sides of the grooves 8 are parallel to the longitudinal axis of the die, as shown in FIGS. 3 and 4. In dies according to FIG. 5 for producing sections having projections 3, 12 running helically, the base of the groove is at a constant distance from the longitudinal axis of the die and the side surfaces of the groove form the same angle to the longitudinal axis of the die along the whole length of the groove. To shape the billet 14 the cross section is decreased uniformly in the conical inlet part 6 of the die from the diameter D.sub.0 to the diameter D.sub.1 which corresponds to the greatest measurement of the die opening, therefore within the vertical section A. Within the vertical section B the material is shaped to the section 10 with the core 11 having diameter D.sub.2 and projections 12. Even in the upper part of setion B the outermost part of the projections 12 are already properly formed. When the cross section within the section B in the die is reduced, an extension is obtained. Even the outermost, finished parts of the projections must be extended to the same extent as the rest of the material. In order to obtain a complete cross section in spite of the extension, a radial material flux is required within the section B to keep the die groove 8 filled. However, in many cases it has been found that this material flux is insufficient and the cross section of the projections 12 is less than the cross section of the grooves 8. As shown in FIG. 6, the tops of the projections have the width H instead of the same width C as the groove 8. Measured across the projections the dimension of the section will be D.sub.1 - 2A = D.sub.3 and not equal to the measurement between the bases of two grooves 8. The width of the projections at the tops will be C - 2K = H and will gradually increase to C towards the base of the projection on the section. The rod will therefore not have the same dimensions as the die opening.

FIGS. 7, 8 and 9 show a method of shaping dies so that a rod is obtained which has the same cross section as the die orifice, for example a rod 10 according to FIG. 10 with four elongated projections 12 around a core 11. In this embodiment the base 15a of the groove 8 in the area L is parallel to the longitudinal axis of the die 5, but the base 15b in the upper area F inclines the amount E towards this axis. The sides 16a and 16b of the groove 8 are parallel to the longitudinal axis. Because the radial distance of the groove to the centre of the die decreases in the direction of extrusion, what might be called a radial compensation is obtained, which gives radial compression of the material in the groove 8 which forms the projections 12 of the section 10.

At the start of the groove 8 the inner diameter of the die is D.sub.4 and the upper part M of the die will therefore have a conical surface against which the front end of the billet 14 may abut before the start of the extrusion process. Obviously the billet must have an outer diameter D.sub.0 which is larger than D.sub.4.

FIGS. 11 and 12 show a die having grooves 8 to produce elongated projections, the bases 15 of the grooves being parallel to the longitudinal axis of the die. On the other hand, the sides of the grooves in the section F of the die above the smallest cross-section of the die orifice incline towards the longitudinal axis of the die so that the width of the groove increases upwardly. In the area F the material is pressed tangentially in towards the centre of the groove and compensation is obtained for the alteration in dimension which is obtained as the projections become extended. This may be called tangential compensation.

FIGS. 13 and 14 show a die constructed in such a way that both tangential and radial compensation are obtained. The side surfaces and base surfaces have the same designations as in the preceding figures.

FIGS. 15 and 16 show a die according to FIGS. 13 and 14 modified to produce a section having four helically arranged elongated projections.

FIGS. 17 and 18 show a die according to FIGS. 13 and 14 which is modified in such a way that the projection 9 between the grooves of the die is somewhat bevelled at the transition from the conical surface of the die to its vertical orifice surface. The projections 9 will therefore acquire a surface 19 which will form a more acute angle with respect to the axis of the die than the conical inlet surface 6.

The die according to the invention is applicable to all types of sections. That a die has been described which produces a section having only four elongated projections with flat sides is purely because the invention can be more clearly explained in this way.

It has been found that the radial compensation, i.e., the embodiment having an inclined groove base but parallel groove sides is most suitable from the lubrication point of view. The radial compensation due to an inclined groove base is limited since at the first part of the die inlet opening within an area M there must be a conical sealing surface of a certain width. When the radial compensation which can be achieved is insufficient, it can be combined with tangential compensation, i.e., the sides of the grooves may be made inclined.

Claims

I claim:

1. Die having an extrusion orifice with a substantially circular central opening and grooves communicating therewith for producing rods having a central core part and elongated projections extending from said core part, by means of hydrostatic extrusion, the bases of the grooves in the die being inclined towards the longitudinal axis of the die.

2. Die according to claim 1, the grooves in the die decreasing in width from the inlet side towards the smallest cross-section of the die opening.

3. Die according to claim 1, in which the grooves are helical in shape.

4. Die according to claim 1 having a conical inlet, in which the projections between the grooves of the die are bevelled nearest to the smallest cross-section of the die so that the surfaces of the projections of the die between the grooves are directed towards the center of the die from a more acute angle to the longitudinal axis of the die than the surface of the inlet.