GB2081153A

GB2081153A - >Friction-effection Extrusion

Info

Publication number: GB2081153A
Application number: GB8123057A
Authority: GB
Original assignee: Alform Alloys Ltd
Current assignee: Alform Alloys Ltd
Priority date: 1980-07-31
Filing date: 1981-07-27
Publication date: 1982-02-17

Abstract

In an extrusion apparatus, two passages, each defined in part by a groove 5 in wheels 1, 3 and in part by a fixed shoe 7, lead to a common passageway from which a die orifice extends. Material, such as aluminium, is fed in rod form into each of the passageways and it is forced into the common passageway and out of the die 17. The direction of movement of the material through the die is opposite to the direction of the material along the passageways and, in this way, impurity material, which might finish up just under the surface of the product, and thus cause a bad surface finish, is buried towards the centre of the product, thereby avoiding bad surface finish. <IMAGE>

Description

SPECIFICATION Improvements In or Relating to Extrusion This invention relates to the forming of materials by extrusion.

In British Patent Specification No. 1370894, there is described a method of, and apparatus for, continuously extruding material. The process comprises the steps of feeding material to one end of a passageway, formed between first and second members, with the second member having a greater surface area for engaging the material than the first member, said passageway having a blocked end remote from said one end and having at least one die orifice associated with said blocked end and moving the passageway defining surface of the second member relative to the passageway defining surface of the first member in a direction towards the or each die orifice from said one end to said blocked end such that the frictional drag of the passageway defining surface of the second member draws the material substantially in its entirety through the passageway and through the or each die orifice.

The apparatus may comprise a wheel member having an endless groove therein, a shoe member covering part of the length of the groove and forming a passageway therewith, an abutment member projecting from the shoe member into the groove and blocking one end of the passageway, the wheel member being rotatable relative to the shoe member, at least one die orifice associated with the abutment member and means for feeding material to be extruded into the end of the passageway remote from the abutment member so that, upon rotation of the wheel member, the material is carried along in the groove by frictional drag in the direction towards the abutment member and is thereby extruded through the or each die orifice.

In United States Patent Specification No.

4208898, there is described a method of, and apparatus for, continuously extruding composite sections comprising a beam-like section made of a light metal and at least one insert made of another metal which provides a facing on at least one surface of the beam-like section.

The extrusion apparatus comprises two elongate first passageways each defined by a movable member and a fixed member with the passageway defining surface of the movable member being greater than that of the fixed member, each first passageway having an abutment member projecting therein to block off the passageway and said passageways being in communication adjacent the blocked end thereof with a common passageway, and means defining at least one die orifice leading from the common passageway and means for moving the movable members relative to the fixed members such that material fed into the first passageways is urged along these passageways into the common passageway and out of the die orifice.

In the arrangement shown in the abovementioned United States Patent Specification, the movable members comprise two wheels each having a continuous groove therein and a fixed shoe member is associated with the grooves. The flow of material through the die orifice is in substantially the same direction as the flow of material along the two passageways defined by the two wheels and the fixed member. In this way, the material, which is in contact with the base of the groove in either of the wheels, finishes up just beneath the surface of the product which is extruded through the die orifice. Particularly when the material being extruded is aluminium or aluminium alloy, it is very difficult to prevent a surface coating of aluminium oxide being present on the material which is introduced into the two passageways.It follows, therefore, that the impurity from the surface of the material which is adjacent the bottom of the groove in each wheel finishes up close to or just beneath the outer surface of the finished extruded product. This is most undesirable since the outer surface of the extruded product can to be marked and otherwise irregular where the impurity is buried just below the surface of the workpiece. Furthermore, the surface material outwardly of the impurity can break away producing a most unsatisfactory surface finish on the extruded product. This lack of satisfactory surface finish is most important in many products which are extruded and the apparatus of this type has heretofore suffered greatly from the fact that the surface finish of much of the product extruded by it is of unsatisfactory standard.

It is an object of the present invention to provide an apparatus for, and a method of; extruding metal which produces a product having a surface finish which does not suffer from the problem referred to above and which, consequently, is much superior to that obtainable from the prior art machines described above.

According to a first aspect of the invention, a process for continuously extruding metal comprises the steps of feeding material simultaneously into one end of each of a pair of first passageways each having a blocked end remote from said one end and each formed between first and second members with the second member having a greater surface area for engaging the material than the first member, each first passageway adjacent the blocked end thereof being in communication with a common passageway leading to at least one die orifice, moving the passageway defining surface of each of the second members relative to the passageway defining surface of the first members in the direction towards the blocked end of the passageways such that the frictional drag of the passageway defining surface of each of the second members urges the material along the pair of first passageways into the common passageway and extruding the material from the common passageway through said die orifice in the direction opposite to the direction of movement of the material along said first passageways.

According to a second aspect of the invention, extrusion apparatus comprises two elongate first passageways each defined by a movable member and a fixed member with the passageway defining surface of the movable member being greater than that of the fixed member, each first passageway having an abutment member projecting therein to block off the passageway and said passageways being in communication adjacent the blocked ends thereof with a common passageway, means defining at least one die orifice leading from the common passageway and means for moving the movable members relative to the fixed members such that material fed into the first passageways is urged along these passageways into the common passageway, and wherein the die orifice is positioned such that material extruded therethrough from the common passageway is moving in a direction opposite to the direction of movement of the material along said first passageways.

From a design standpoint, it is desirable for the outlet die of a two wheel apparatus to be in the position shown in the United States Specification No. 4208898 since this allows a "straightthrough" movement of the metal and also the position taken up by the die orifice is particularly uncluttered.

Applicant has appreciated that, if this desirable position for the die orifice is changed so that the material extruded through the die orifice is in a direction substantially opposite to the direction of movement of the material along the first passageways, then the surface finish of the product is improved considerably. The reason for this is that the material which is initially present adjacent the bottom of the grooves in the two wheels does not finish up near the surface of the extruded product but is, in fact, buried well below the surface of the extruded product. This means that the surface finish is greatly improved over the product of the known arrangement where, in fact, the impurity is either on the surface or very close to the surface of the extruded product.Applicant has arranged for the die orifice to be positioned such that the material passing through it is moving in an opposite direction to the direction of movement of the material in the passageways and, consequently, the material has to make a turn of approximately 1 800 in its passage through the machine.

As mentioned above, it is not the most desirable place to position the die orifice between the two ingoing passageways since this area contains the fixed shoe which is associated with the two grooves in the wheels but, by so positioning the die orifice, the advantages of Applicant's invention are obtained.

It is, therefore, not an obvious place in which to position the die orifice and it is, in fact, not an obvious step to re-position the die orifice from the position shown in United States Patent Specification No. 4208898.

In order that the invention may be more readily understood it will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic side elevation of apparatus in accordance with the invention, Figure 2 is an enlargement of part of the apparatus shown in Figure 1, Figure 3 is a cross section of a typical product formed in the apparatus of Figure 1, Figure 4 is a cross section of part of apparatus in accordance with the present invention for producing hollow section, and Figure 5 is a sectional side elevation of apparatus for sheathing a core section.

Referring to Figures 1 and 2, a pair of wheels 1, 3 are arranged with their axes parallel and in spaced apart relation and each wheel has a continuous groove 5 extending around its periphery. A part of the periphery of each wheel is closed by a shoe member 7 which overlies part of the groove. The two shoes are formed in integral manner from a single metal body. Each groove is blocked off by means of an abutment 9, a part of which extends into each groove. The walls which define the groove 5 on each wheel and the walls of the shoe 7 form a pair of first passageways each leading from an open end 11 to the end which is blocked by the abutment 9. The part of each groove which defines the first passageway is larger than the part of the passageway defined by the shoe 7.In the vicinity of the abutment 9, the two passageways are in communication with a common passageway 13 and from this passageway an opening 15 extends through the body which defines the shoes 7. A die 17 having an orifice is mounted at the inlet end of the opening.

In use, material, particularly aluminium, in the form of a rod 18 is introduced into each of the first passageways through the open end 11 thereof and, by rotating the wheels in the direction shown in the figures by means of electric drive means, the input rods are forced by the moving wheels against the abutment 9 and the material flows into the common passageway 13. The only way in which the material entering the common passageway from the first passageways can escape therefrom is through the orifice of the die 17 and, consequently, the material is extruded through this die to form a product 1 9 having a cross section defined by the die orifice.

In Figure 2 there are shown, to an enlarged scale, the common passageway 13, the passageway 15 and the die 17. When the apparatus is in use and, as is usual, the feed material 18 is aluminium or an aluminium alloy, the rods 1 8 have a surface layer of impurity mainly aluminium oxide. The oxide which is on the part of the rods 1 8 which are engaged by the shoe 7 tends to remain on the surface of the metal as it passes through the passageway 13 and it remains on the surface of the extruded product 19. On the other hand, however, the impurity which is on the part of the rods 1 8 which comes into contact with the base of the groove 5 is folded slightly inwardly of the surface of the material flowing through the passageway 13, as indicated by the marks 20 in Figure 2.The material entering the common passageway from one of the wheels meets the material entering the passageway from the other wheel and the two flows of material join and are extruded through the orifice of the die 17. The impurities 20 present in each of the two flows of metal are buried towards the centre of the material as it passes through the orifice in the die.

In Figure 3 there is shown a typical cross section of the product extruded through the die and the marks 21 indicate the oxide layers which are trapped in the product towards the centre thereof. These oxide layers are well buried in the product and they are unlikely to cause any surface of the product to break away.Thus, by arranging for the flow of metal through the die 17 to be in the direction substantially opposite to the direction of movement of the material along the first passageways, particularly where the first passageways join the common passageway, the inpurity material is buried towards the centre of the extruded product, whereas, if the die 1 7 were positioned on the opposite side of the passageway 1 3 so that the material leaves the passageway 13 through the die 17 in substantially the same direction as the material is travelling in the first passageways 5, then the impurity material 20 would be just below the surface of the material passing through the die and this causes either a "bubbled" surface on the product, which is not acceptable, or else the "bubbled" portion breaks away leaving a rutted surface on the product.

As shown in Figure 4, a tube may be extruded using a mandrel 22 without a supporting bridge.

The mandrel is mounted on the abutment 9 and projects into the die 1 7. The material from the two first passageways flows into the common passageway and around the mandrel 22 and into the die orifice thus producing the tubular product 23. Although not shown in Figure 4, the impurity from the incoming material which contacts the rotating groove is buried on the inside of the tube 23 so that the surface finish of the tube remains satisfactory.

In the arrangement shown in Figure 5, an opening 25 extends through the abutment 9 in aiignment with the opening 15. A core section 27 is fed through the opening 25 and through the orifice of the die 17. The material from the two first passageways flows into the common passageway and through the orifice of the die to provide a sheathing around the core section 27.

Again, the flow of the material through the die orifice is substantially opposite to the direction of flow of the material in the first passageways, particularly adjacent the abutment 9, and, with this arrangement, the impurity from the feed material which is engaged by the base of the groove in each of the wheels is buried on the inside of the sheathed core so that the surface finish of the sheathed core is satisfactory.

Claims

1. A process for continuously extruding metal comprising the steps of feeding material simultaneously into one end of each of a pair of first passageways each having a blocked end remote from said one end and each formed between first and second members with the second member having a greater surface area for engaging the material than the first member, each first passageway adjacent the blocked end thereof being in communication with a common passageway leading to at least one die orifice, moving the passageway defining surface of each of the second members relative to the passageway defining surface of the first members in the direction towards the blocked end of the passageways such that the frictional drag of the passageway defining surface of each of the second members urges the material along the pair of first passageways into the common passageway and extruding the material from the common passageway through said die orifice in the direction opposite to the direction of movement of the material along said first passageways.

2. Extrusion apparatus comprising two elongate first passageways each defined by a movable member and a fixed member with the passageway defining surface of the movable member being greater than that of the fixed member, each first passageway having an abutment member projecting therein to block off the passageway and said passageways being in communication adjacent the blocked ends thereof with a common passageway, means defining at least one die orifice leading from the common passageway and means for moving the movable members relative to the fixed members such that material fed into the first passageways is urged along these passageways into the common passageway, and wherein the die orifice is positioned such that material extruded therethrough from the common passageway is moving in a direction of movement opposite to the direction of the material along said first passageways.

3. A process as claimed in claim 1, in which the material fed into each of the first passageways is in the form of a rod which is engaged by the first and second members.

4. A process as claimed in claim 1 or 3, in which the die orifice has a mandrel projecting therein to produce a tubular extruded product.

5. A process as claimed in claim 1 or 3, in which the material flowing through the die orifice forms a sheath on a solid core passing continuously through the die orifice.

6. Apparatus as claimed in claim 2, in which the two first passageways are defined by two separate rotatable wheels each having a continuous peripheral groove and a fixed body providing a pair of shoes which overlie a portion of respective grooves.

7. Apparatus as claimed in claim 6, in which an opening extends through the fixed body from the common passageway to the exterior of the body and the die is positioned at the junction of the opening and said common passageway.

8. Apparatus as claimed in claim 7, in which the die has a mandrel associated therewith by which a tubular product is extruded.

9. Extrusion apparatus substantially as hereinbefore described with reference to the accompanying drawings.

1 0. A process for continuously extruding metal substantially as hereinbefore described with reference to the accompanying drawings.