GB2149714A - Extrusion process - Google Patents

Abstract

A process for producing (metal) wire or rod as a continuous extrusion involves the steps of feeding an agglomerated (metal) powder material (50) into one end of a passageway (13) formed between first and second members (10, 14) with the second member having a greater surface area for engaging the material than the first member, the said passageway having a blocked end (16), remote from the said one end and having at least one die orifice (40) associated with the 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 the said one end to the said blocked end such that the material is drawn substantially in its entirety through the passageway, and out through the or each die orifice. The powder material is agglomerated by a lubricant or binder, and the agglomerates present separation of different particulate components of a mixture, and also prevent the development of excessive temperatures during structure. <IMAGE>

Description

SPECIFICATION Extrusion process The present invention relates to extrusion of metallic compositions and to novel feed stocks for use in such processes. It is particularly applicable to the extrusion process known as the CONFORM process, one form of which is described in British Patent Specification No. 1370894. Whilst it will be described with reference to the process and apparatus shown in that specification (which will be referred to hereinafter as the CONFORM process), it is not however limited in its usefulness to the process specifically described in the above specification.

The CONFORM process so far has only found substantial use in the extrusion of malleable metals such as copper and aluminium.

The dry powders or granules even of such malleable metals result in the generation of very high temperatures at the extrusion die and thus problems of die wear and life are limitations on the process.

We are particularly concerned with the production of filler wires for fusion welding e.g. flame or electric arc welding such as gas shielded or self-shielded welding and rods for coating with flux and wires for submerged are welding.

In all arc welding processes the arc is struck between the rod and the work piece at the weld site. The wire or rod melts and forms a pool of molten metal produced from the rod by the arc at the weld site. If the wire or rod is made up from discrete particles, the particle size needs to be small enough to ensure that the molten metal pool becomes homogenized under the welding conditions.

Whilst the CONFORM process initially looked attractive, when we discovered the temperatures generated with malleable metals such as copper, it seemed no longer likely that it could be used with the types of materials with which we were concered such as iron, nickel and chromium and alloys thereof.

We were also concerned with converting blends of powders of different materials into welding wires or rods. These powders often have different particle sizes as well as densities and surface characteristics and we realized that the vibratory feed in the CONFORM process would be liable to cause the powders to segregate resulting in variation in composition along the length of the extrusion and again, this seemed to preclude us from making use of the CONFORM process or indeed any powder extrusion process.

However, we then conceived of the idea of forming crumbs or agglomerates of the particles, in which the proportions of the materials of different particle sizes were maintained against segregation and the particles lubricated in the extrusion process by the presence of a small amount of binder.

Clearly, the binder must not be such as to prevent the CONFORM process cohering the particles into an extrusion which is self supporting nor must it be such as to intefere with the eventual end use to which the extrusion is to be put. The amount and nature of the binder is thus of importance. The CONFORM process is thought to rely on frictional drag and the lubrication must not be such as to prevent this effect occurring. The binder may be one which remains in the extrusion because it does not interfere with the end use or may be one which is removable, in which case the removal process must not interfere with the end use.

According to its broadest aspect the present invention provides a process for producing an extrusion from powder in which the powders are formed into agglomerates prior to being subjected to the extrusion forces.

The present invention is particularly concerned with processes which enable continuous extrusion to be carried out, one form of such a process being the CONFORM process, such process being one which includes the steps of feeding material into 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, the said passageway having a blocked end, remote from the said one end and having at least one die orifice associated with the 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 the said one end to the said blocked end such that the material is drawn substantially in its entirety through the passageway, possible by the frictional drag of the passageway defining surface of the second member, and, thus, through the or each die orifice.

A particularly preferred form of apparatus for carrying out the CONFORM process comprises 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.

The die orifice or orifices are preferably provided in the face of the shoe member in front of the abutment member.

Thus according to the present invention the material which is extruded comprises agglomerates of metallic particles and solid material having a binding or lubricating effect or both and it is these agglomerates which are fed into the end of the passageway. Thus the metallic particles are preferably held together by a binder. The particles may be of the same material or different materials and may be of the same of different particle sizes.

Desirably the solid material has both functions for example it may be an organic polymer e.g. a thermoplastic solvent-soluble material. Another possibility is that it has a purely lubricating function and is coated on or absorbed in the agglomerates which are porous being formed by sintering of small individual particles or may be porous as a result of the method by which the metallic material was prepared.

The invention is particularly useful when the particles are of different sizes because the agglomeration of the particles prevents segregation of the different sizes and thus maintains a higher level of uniformity of composition of the extruded product than would otherwise be the case.

The particles may be powders e.g. having particle sizes 100% less than 500 microns preferably less than 350 microns and 70, 80 or 90% less than 150 microns (as determined by sieving). For production of filler wires for welding, be they flux coated or not, it is preferred that the maximum particle size should not exceed 350 microns so as to permit full dissolution and homogenisation of the molten pool of metal when the filler wire is fused by the arc during welding. Thus the extrusion may not in itself be fully homogeneous and may be porous and may be constituted by compressed agglomerates partly sintered and partly bound by the binder to each other rather than by a single continuous alloy wire.

The particle size of the primary particles may be as low as 20 microns or less but preferably the bulk e.g. at least 50% by weight of the particles will have a particle size in the range 100-150 microns.

These may be converted into agglomerates having sizes of greater than 500,750 or 1000 microns e.g. 1 to 2,3,4 or 5 mm. The particles may be elongated e.g. having L:W ratios in the range 1.1:1 or 1.5:1 to 2:1,3:1 or more. The size of the agglomerates can be measured by drying a sample so as to remove the solvent for the binder and then sieving.

The amount of binder used is that required to produce agglomerates in which the primary particles cohere through the steps of feeding into the extrusion apparatus so that segregation of primary particles is substantially reduced or eliminated as compared with what happens when the same blend of unagglomerated primary particles is used (quite apart from the fact that without the binder and its cohesive and lubricating effect a self supporting rod may not be formed). The amount of binder is preferably less than 1.0% e.g. 0.2 to 0.8% or especially 0.3 to 0.6% by weight (dry basis). The agglomerates may be dried before use or can be used with some of the solvent vehicle for the binder still present so that the agglomerates form a damp crumbly mass. The binder can be water soluble or solvent soluble, e.g. soluble in a ketone, such as acetone.Examples of water-soluble binders are carboxymethyl cellulose e.g. that supplied as CEKOL (Trade Mark) MV, or cellulose ether/methyl cellulose e.g. that supplied as CELAKOL (Trade Mark) M450-P. Examples of solvent-soluble binders are the polybutyl methacrylates, which are soluble in such solvents as methyl ethyl ketone. An example of a commercially available form of such a binder is that supplied as CRANCO (Trade Mark). The amount of solvent may be 2 to 5% or 8% and desirably less than 13% e.g. less than 10% by weight (on a total weight basis).

Particles which have been fabricated by the conventional CONFORM process and which it may be expected could be agglomerated include aluminium, e.g. 97 or 99.5% pure; or copper; or blends of aluminium and copper e.g. 2 to 10% copper; copper-silver-lead alloys; copper-nickel-phosphorous alloys; copper-aluminium oxide alloys; brass (60/40); leaded bronze; magnesium; and magnesium-zirconium alloys.

Particles which the present invention will, it is believed, permit to be extruded as a self-supporting extrusion include higher melting metals the agglomerates being made from metals and alloying elements such as manganese e.g. electrolytic manganese, nickel e.g. carbonyl or atomised nickel, chromium, molybdenum, tungsten, vanadium, copper, silicon, niobium, cobalt, aluminium, titanium or yttrium or any desired metal available in powder form and alloys e.g. iron alloys such as ferro-chromium and ferro-molybdenum alloys, or any other ferro-alloy.

The agglomerates can be made by conventional techniques e.g. by mixing and blending the dry powders in the required proportions and then adding a solution of the binder in the solvent or liquid vehicle for example by spraying the binder solution on the tumbling particles and continuing the mixing until the desired degree of agglomeration has occurred, or, and this is preferred, by dry mixing the particles and dry binder powder until a homogeneous blend is produced and then adding the solvent or liquid vehicle to the blend.

The liquid vehicle need not necessarily be a true solvent and heat could be used to extend the binder sufficiently to produce the required binding and agglomerating effect.

The invention may be put into practice in various ways and two specific embodiments as applied to the production of filler wires forvarioustypes of welding will be described to illustrate the invention with reference to the accompanying examples and drawing which is a diagrammatic side elevational cross-section of extrusion apparatus suitable for carrying out the invention.

The extrusion apparatus shown in the drawing comprises a wheel 10 rotatably mounted on a shaft 12. The wheel 10 has a square cross-section circumferential groove 13 machined around its outer edge, the groove being therefore a square surface of revolution about the axis of the wheel. A shoe member 14 fits closely against the edge 15 of the wheel 10. An abutment member 16 located next to the lower end of the shoe member 14 projects into the circumferential groove 13 and is complementary in shape to the groove cross section so as to block the groove with a sliding fit. An extrusion orifice 40 is formed in a die insert 41, which is held against the surface of the wheel 10 between the abutment 16 and the shoe 14 by a backing member 43 which supports the shoe 14.A driven roll 45 is mounted just above the top end 44 of the shoe member 14, with it's surface in contact with the surface 15 of the wheel 10. The roll 45 has it's axis just to the right of the vertical centre line through the axis of the roll 10. A hopper 46 with it's open lower feed opening 47 in sliding contact with the surface of the wheel 10 is located with the opening 47 just to the left of the vertical centre line through the axis of the wheel 10.

Material 50 to be extruded, in the present invention agglomerates of primary particles, is fed, e.g. by a vibratory feeder, into the hopper 46 and fills that part of the groove 13 in the wheel 10 underneath the shoe member 14 between the abutment member 16 and the feed opening 47 of the hopper 46.

The wheel 10 is rotated clockwise as shown by the arrow 21 in the drawing. The material 51 in the circumferential groove 13 beneath the shoe member 14 is carried forward towards the abutment member 15 by, it is thought, the frictional drag of the walls of the circumferential groove 13. Thus it is thought that pressure is generated in the material in the circumferential groove 13, so that the material is extruded through the orifice 40 in the insert 41. Also the rotation of the wheel 10 aided by the wheel 45 drags material from the hopper so that a continuous extrusion of the material is obtained. Material drawn from the hopper 46 by rotation of the wheel 10 is continually replaced by a continuous feed fresh material into the hopper 46.

With a feed of agglomerated powder the pressure applied on the material in the circumferential groove 13 results in compaction of the agglomerated material. Further compaction of the agglomerated material occurs during extrusion through the extrusion orifice 40 so that a solid or at least self-supporting extruded product is obtained.

The circumferential groove 13 in the wheel 10 in conjunction with the shoe member may be regarded as forming a passageway or channel having four walls. The three walls of the channel defined by the side walls and base of the circumferential groove 13 move continuously towards the abutment member 16. The fourth wall of the channel, defined by the under surface of the shoe member 14 is stationary. As described above the three moving walls of the circumferential groove 13 carry the material 51 towards the abutment member 16. The material slides over the stationary fourth wall formed by the under surface of the shoe member 14.

The frictional coefficients may be the same for all four walls.

Example 1 An Iron-nickel-chromium based filler wire for metal inert gas welding is prepared from the ingredients given in Table 1 below: TABLE 1 Composition Weight % Low carbon (C=0.04% max.) 27.0 Ferro-Chromium (71% chromium) Atomized Nickel 12.5 Ferro-Molybdenum (71% molybdenum) 4.0 Electrolytic Manganese 2.0 Ferro-Silicon (45% silicon) 1.0 Iron powder 53.5 100.00 The ingredients were selected to have all particles less than 350 microns, and generally in the range 100-150 microns.

A filler wire 52 is made from the above ingredients by feeding the agglomerates described below to the hopper 46 of the apparatus shown in the drawing.

The agglomerates are formed by slow dry mixing the above ingredients together with 0.3 to 0.6% of sodium carboxy methyl cellulose powder until a uniform blend is produced. The tumbling powders are then sprayed with water. The mixing and spraying is continued at room temperature until powders are no longer apparent, at which point the mixer speed can be increased and the mixing and spraying continued until a dryish crumbly mass is produced, the individual agglomerates being 1 to 5 mms across (as measured on the dried agglomerates).

Example 2 An aluminium bronze filler wire, useful inter alia in metal inert gas and tungsten inert gas welding and in submerged arc welding is prepared from the ingredients given in Table 2 below: TABLE 2 Composition Weight % Pure Aluminium 9.0 Pure Nickel 4.2 Pure Iron 2.5 Pure Manganese 1.5 Pure Copper 82.8 100.00 The procedure of Example 1 is repeated, the total volume of water used is 210 ml applied to 2 Kg of metal powderwith 8 grams of SCMC.

In another run 12 grams of SCMC were present and then 240 ml of water were required.

When a homogeneous dry blend of this mixture of powders was shaken in a glass beaker segregation of aluminium occurred immediately and was readily apparent.

After agglomeration the blend was visually homogeneous.

Example 3 A Nickel-chromium based filler wire for tungsten inert gas welding is prepared as in Example 1 from the ingredients given in Table 3 below: TABLE 3 Composition Weight % Electrolytic Manganese 3.0 Ferro-Silicon (45% silicon) 0.5 Pure Chromium 20.5 Nickel-Niobium (52%) Alum- 5.3 inium (1.5%) Pure Titanium 0.4 Atomized Nickel 70.3 100.00

Claims (12)

1. A process for producing an extrusion from powder in which the powders are formed into agglomerates prior to being subjected to the extrusion forces.

2. A process for producing wire or rod as a continuous extrusion which includes the steps of feeding agglomerated powder material into 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, the said passageway having a blocked end, remote from the said one end and having at least one die orifice associated with the 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 the said one end to the said blocked end such that the material is drawn substantially in its entirety through the passageway, and out through the or each die orifice.

3. A process as claimed in Claim 2 carried out using an apparatus comprising 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 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 located at or adjacent to the abutment member, and means for feeding the agglomerated powder 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 in the direction towards the abutment member and is thereby extruded through the or each die orifice.

4. A process as claimed in Claim 1 or Claim 2 in which the agglomerates comprise metallic particles and solid materials having a binding or lubricating effect or both.

5. A process as claimed in Claim 1,2,3 or 4 in which the agglomerates are of different materials or of different particle sizes or both.

6. A process as claimed in any one of Claims 1 to 5 in which the particles have particle sizes 100% less than 350 microns.

7. A process as claimed in any one of Claims 1 to 6 in which at least 50% of the particles by weight have a particle size in the range 100-150 microns.

8. A process as claimed in any one of Claims 1 to 7 in which the agglomerates have sizes of greater than 500 microns up to 5 mms.

9. A process as claimed in any one of Claims 4 to 8 in which the amount of binder in the agglomerates is less than 1.0% by weight (dry basis).

10. A process as claimed in any one of Claims 4 to 9 in which the binder is a water soluble carboxymethyl cellulose or cellulose ether/methyl cellulose or a solvent-soluble binder polybutyl methacrylate.

11. A process as claimed in any one of Claims 1 to 10 in which the agglomerates are made from metals and alloying elements consisting of manganese, nickel, chromium, molybdenum, tungsten, vanadium, copper, silicon, niobium, cobalt, aluminium, titanium or yttrium or any desired metal available in powder form or an iron-alloy or mixtures thereof.

12. A process as claimed in Claim 11 in which the iron alloy is a ferro-chromium or a ferro-molybdenum alloy.