GB2071543A

GB2071543A - Extrusion Die

Info

Publication number: GB2071543A
Application number: GB8009298A
Authority: GB
Original assignee: Erbsloeh & Co GmbH
Current assignee: Erbsloeh & Co GmbH
Priority date: 1980-03-19
Filing date: 1980-03-19
Publication date: 1981-09-23
Also published as: GB2071543B

Abstract

A two-part extrusion die has a first part (2) provided with one or more passage openings (5) determining the external contour of an extruded product and has a second part (1) provided with at least one mandrel arbor (6) determining the internal cross-section of the product. The side of the die adjacent to the extrusion material container (3) is provided with one or more inlet chambers (8) the floor of which is formed by a front surface (9) of the mandrel arbor (6) and bridge arms (10) connecting the arbor to the second part. The edge regions of the inlet chamber are interspersed by passages (12) which communicate with a chamber (15) located between the parts and about the mandrel arbor. <IMAGE>

Description

SPECIFICATION Extrusion Mold Technical Field of the Invention The invention relates to an extrusion mold, in particular for producing hollow shaped sections of aluminium or alloys thereof, said mold consisting of a two-part female mold or die, one of whose parts has one or more passage openings determining the external contour of the shaped section and whose other part has one or more mandrel arbors joined via bridge arms to a body part, wherein the outer surfaces of the mandrel arbor(s) determine the internal cross-section of the shaped section.

Background Art In the case of the previously known extrusion molds for producing hollow shaped sections it is known to separate the female mold into two parts and to connect the parts to one another by bolts or the like. The female mold part lying in the extrusion direction has a passage whose contour determines the external shape of the extruded profile. The other female mold part consists of a body section that carries, via wings or bridge arms, a mandrel which projects through the passage opening of the female mold counter-part and thereby determines the internal surface of the profile to be extruded. Hollow spaces are provided between the mandrel, wings (bridge arms) and body section, which extend in the extrusion direction and thus permit the material being extruded to flow through the remaining gap between the mandrel and the edge of the passage opening.

The female mold part containing the mandrel experiences a flexural stress which is directed from both ends of the mandrel towards the mandrel and is deflected from the mandrel in the centre region of the latter. This flexural stress also acts on the connection plane of the female mold and bridge. As a result, in the case of fairly long extrusion times the impact surfaces of the female mold and bridge no longer lie flush against one another. Varying lateral forces thus act on the mandrel, which, as a result of the contraction forces exerted during extrusion, thus tends to plastically deform from its central position.

A so-calied weld chamber is located between the two mold parts, which is bounded on the outside by the female mold part with the passage opening, and on the inside by the mandrel. The component streams of the material being extruded rejoin one another in the region of this weld chamber and form a homogeneous material which is forced through the gap between one female mold part and the mandrel. If however the mandrel adopts an out-of-centre position as a result of the deformation forces, the extruded profile will inevitably have varying wall thicknesses.

There is also the additional problem that the lower ends of the wings or bridge arms taper towards one another in a wedge-shaped manner and are rounded off. In practice crack formations often arise at the transition between the wings and the mandrel, thereby producing a shortened working life of the extrusion mold.

The object of the invention is to provide an extrusion mold that will on the one hand substantially reduce the danger of cross-sectional variations in the extruded profile, and will on the other hand increase the working life of the mold.

Disclosure of the Invention On the basis of the type of extrusion mold known in practice and described at the beginning, the essential feature of the invention is that the mold has, on the side facing the extrusion material container, one or more inlet chambers preferably centrally aligned with respect to the passage openings, wherein the floor of the inlet chambers is formed by the front surface of the mandrel arbor, which is backwardly displaced in the extrusion direction, and the adjoining front surfaces of the bridge arm, which are inclined with respect to the inlet side.

The advantage of this feature is that the extrusion pressure of the material forced through the mold has an outwardly directed component which on the one hand prevents the aforementioned damaging flexural stress on the female mold, and on the other hand frees the mandrel arm from stresses that would lead to plastic deformation. Consequently, extruded profiles, in particular hollow shaped sections, can be produced with uniform wall thicknesses, and the working life of the mold is increased.

The reason for this beneficial effect is the fact that the front surface of the bridge arms is inclined outwardly from the centre. This diverts the extrusion pressure outwardly into the corresponding component forces and consequently the two female mold halves remain joined flush to one another for a longer time. In addition, these outwardly directed inclined forces relieve the pressure on the arms in the mandrel arbor region, which is thus not plastically deformed.

Embodiments within the scope of the invention provide that each inlet chamber has, from the inlet side and in the extrusion direction, a crosssection that first of all widens out and then tapers.

Another variant of the invention is for the inlet chamber to have a cross-section that is initially uniform and then tapers from the inlet side in the extrusion direction. In the first case it is recommended to arrange the inlet chamber centrally and form it at least in part from conical surfaces. In the second case the inlet chamber is initially cylindrical and then tapers conically. If the extruded profiles are not intended to have a circular or square cross-section, then the crosssection of the inlet chamber can of course be suitably changed.

A further embodiment of the invention is characterised in that the edge regions of the inlet chamber are interspersed by passages, running parallel to the extrusion direction, in the body part carrying the mandrel, which passages together with a component region on the front surface of the female mold carrying the passage opening and together with another, preferably larger component region, open out into a chamber that is situated between the female mold parts and surrounds the mandrel. This latter chamber, which is also called a weld chamber, is known per se. Its cross-sectional shape is however novel within the context of the invention.

The thick mandrel plate reduces the frictional forces in the critical region and thus reduces the danger of crack formation.

Details of the invention are shown diagrammaticalty and by way of example in the drawings.

Brief Description of the Drawings Fig. 1 is a longitudinal section through an extrusion moid, Fig. 2 is a plan view of the mold according to Fig. 1, Fig. 3 is a section through the mold along the iine 111--ili according to Fig. land Fig. 4 is a section along the line IV--IV through the mold according to Fig. 1.

Best Mode For Carrying Out the Invention The embodiment illustrated in Fig. 1 shows an extrusion mold for producing hollow shaped sections of aluminium, for example aluminium alloys, which consists of the female mold parts 1 (Bridge) and 2 (female mold), which are bolted to one another Both female mold parts 1 and 2 abut one another at the front surface 14 and are centred with respect to one another. The reference numeral 4 denotes the extrusion direction, in which the heated material is forced through the usual container 3 and thence through the extrusion mold 1 , 2. In the embodiment as illustrated it is assumed that a tube of circular cross-uection is to be produced, though the invention is of course not restricted thereto.

An inlet chamber 8 which is arranged in the female mold part 1 is located at the inlet side of the extrusion mold 1, 2. Assuming that an extruded profile of circular or square cross-section is to be produced, the axis of the inlet chamber 8 is concentric with the axis of the profile being extruded.

The bridge 1 has a mandrel arbor 6 connected via bridge arms 7 (wings) to a body part 13. The lower end of the mandrel arbor 6 determines, via its cross-section, the internal surface of the profile being produced.

The female mold part 2 has a passage opening 5 whose edge determines the external surface of the profile being extruded. A chamber 15, which in practice is termed a weld chamber, is located between the female mold parts 1 and 2 bolted to one another.

The material is forced from the container 3 into the inlet chamber 8, and a divided flow of the material then takes place through the passages 12 into the weld chamber 15. As a result of the inclined front surfaces 10 of the arms, which rise outwardly from the centre, a lateral component force is exerted on the circumferential region of the female mold part 1, thus preventing any deflection of this female mold part 1 in the centre region, such as occurs in the previously known molds. At the same time this ensures an intimate and flush engagement between the female mold parts 1, 2 along the common surface 14. The material flows through the passages 12 into the weld chamber 15, combines there, and then flows along the outer surface of the mandrel arbor 6, through the passage opening 5, and thereby forms the cross-section of the profile being extruded.

In the example of Fig. 1 the inlet chamber 8 has a surface 11 that first of all widens out in the extrusion direction, and then has a tapering bridge arm surface 10. This shape of the inlet chamber means that the female mold part 1 in the inlet region experiences an outwardly directed component force which prevents any lateral movement of the mandrel arbor 6 and is moreover absorbed in the region of the common surface 14.

In place of the widening surface 11, a cylindrical surface can also be employed without impairing the desired operation of the extrusion mold.

The outlets of the passages 1 2 meet in a part region on the front surface 14 of the female mold part 2 and there exert a centrally directed pressure. The larger region of the passages 12 opens out into the weld chamber 1 5 located between the two female mold parts 1, 2. In this connection, the passages 12 can be situated so that they engage segmentally in the outer region of the mandrel arbor 6. In this case the passages 1 2 terminate on the outlet side with a widened cross-section, while the mandrel arbor 6 has a widening 1 7 in the region of the passage opening 5. Radial forces are thereby exerted on the mandrel arbor 6, which centre the latter and prevent plastic deformation. A prerequisite is that the passages 1 2 should of course be distributed and arranged uniformly around the mandrel arbor 6.

As in the case of the known extrusion molds, the bridge arms 7 taper in the direction of the female mold part 2 in order that the flow of the material is not interrupted.

Without necessarily limiting the scope of the invention claimed, preferred embodiments of the invention may be summarised as follows.

1 ) An extrusion mold, in particular for producing hollow shaped sections of aluminium or alloys thereof, said mold consisting of a twopart female mold or die, one of whose parts has one or more passage openings determining the external contour of the shaped section and whose other part has one or more mandrel arbors joined via bridge arms to a body part, wherein the outer surfaces of the mandrel arbor(s) determine the internal cross-section of the shaped section, characterised in that the extrusion mold has, on the side facing the extrusion material container (3), one or more inlet chambers (8) preferably centrally aligned with respect to the passage openings, wherein the floor of the inlet chambers is formed by the front surface (9) of the mandrel arbor (6), which is backwardly displaced in the extrusion direction (4), and the adjoining front surfaces of the bridge arm (10), which are inclined with respect to the inlet side.

2) An extrusion mold according to summary 1, characterised in that each inlet chamber (8) has, from the inlet side in the extrusion direction (4), a cross-section (10) that first of all widens out (11) and then tapers inwardly (10).

3) An extrusion moid according to summary 1, characterised in that the inlet chamber (8) has, from the inlet side in the extrusion direction (4), a cross-section that is first of all constant and then tapers inwardly (10).

4) An extrusion mold according to any one of the preceding summaries, characterised in that the internal surface of the inlet chamber (8) is formed at least partially by conical cylindrical surfaces (10,11).

5) An extrusion mold according to any one of the preceding summaries, characterised in that edge regions of the inlet chamber (8) are interspersed by passages (12), running parallel to the extrusion direction, in the body part (13) carrying the mandrel (6), which passages together with a component region on the front surface (14) of the female mold (2) carrying the passage opening (5) and together with another, preferably larger component region, open out into a chamber ( 1 5) that is situated between the female mold parts (1, 2) and surrounds the mandrel (6).

Claims

1. An extrusion mold comprising a two-part female mold having one part provided with one or more passage openings determining the external contour of a shaped section, and having another part provided with at least one mandrel arbor determining the internal cross-section of the shaped section, characterised in that on the side which faces the extrusion material container (3) the mold is provided with one or more inlet chambers (8) the floor of which is formed by a front surface (9) of the mandrel arbor (6) which is backwardly displaced in the extrusion direction (4), and the adjoining front surfaces of the bridge arm (10), are inclined with respect to the inlet side.

2. An extrusion mold as claimed in Claim 1, characterised in that the inlet chambers (8) are centrally aligned with respect to the passage openings (5).

3. An extrusion mold as claimed in Claim 1 or Claim 2, characterised in that each inlet chamber (8) has a cross-section which from the inlet side in the extrusion direction (4) first widens out (11) and then tapers inwardly (10).

4. An extrusion mold as claimed in Claim 1 or Claim 2, characterised in that each inlet chamber (8) has a cross-section which from the inlet side in the extrusion direction (4) is initially constant and then tapers inwardly (10).

5. An extrusion mold as claimed in any preceding claim, characterised in that the internal surface of an inlet chamber (8) is formed at least partially by conical cylindrical surfaces (10, 1 1).

6. An extrusion mold as claimed in any preceding claim, characterised in that the edge regions of the inlet chamber (8) are interspersed by passages (12) in the body part (13) running parallel to the extrusion direction (4), which passages (12) together with a region on the front surface (14) on said one part (2) provided with the passage openings (5) and a further region, open out into a chamber (15) located between the two parts (1 and 2) and surrounding the mandrel arbor (6).

7. An extrusion mold as claimed in any preceding claim, characterised in that the crosssection of the extruded profiles are substantially circular or square.

8. A extrusion mold substantially as hereinbefore described with reference to the accompanying drawings.