Patent GB-544974-A (GB)
Title: Improved method of and apparatus for forming rods, tubes and like articles by extrusion
IPC: B22F3/20
Filed: 1940-11-04
Abstract: 544,974. Moulding by extrusion ; making extruding dies. BRITISH THOMSONHOUSTON CO., Ltd. Nov. 4, 1940, No. 16046. Convention date, Nov. 4, 1939. [Class 87 (ii)] [Also in Group XXII] A plastic mixture is formed into plate-like members, the members are stacked.in an openended tubular container where they are freed from air and other non-condensible gases, and the tubular container is inserted into an extrusion apparatus whence the stack is extruded, e.g. into the form of a rod, tube, spiral, or twist drill. The plastic mixture may contain metals, alloys or porcelain compositions. Powdered tungsten carbide, cobalt, starch or casein, and alcohol, acetone or ether are ball milled, the mixture is dried in an oven to remove the alcohol and a small quantity of a mixture of 80 per cent. alcohol &c. and 20 per cent. glycerine is added to make the mixture cohesive. The mixture is pressed into the shape of flat annular plates 1 which are threaded on a steel rod 3 and inserted into a cylinder 4, the rod being then removed. The loaded cylinder is placed inside concentric containers 11 and 20, where the air is removed from the plates and the starch is cooked by the following operations :-Hot oil is introduced into container 20 by pipe 23<SP>1</SP>, and air is evacuated from containers 4 and 11 through pipe 27, the evacuation being interrupted periodically for the introduction of small quantities of distilled water through pipe 26 into containers 4 and 11, this water being immediately converted into steam. The amount of water injected is preferably such as to give a steam pressure of 100 lbs. per sq. inch. The steam penetrates the intergranular spaces of the plates and purges them of air and other non-condensible gases. The hot oil is drawn off and, with vacuum still on in containers 4 and 11, refrigerated oil is admitted to container 20 through pipe 23<SP>1</SP>. When the discs have been cooled to about - 8‹C. the vacuum is shut off and a mixture of water and glycerine at -9‹C. is admitted through pipe 25. The glycerine lowers the freezing point of the water, facilitates penetration of the water into the plates, permits subsequent uniform drying and hardening, and prevents cracking of the extruded material during drying; when very small rods or tubes having a wall thickness of 1/16 inch or less are to be extruded, the glycerine may be omitted. The rod 3 is reinserted in the holes 2, and the plates are heated to 80-95‹C. to cook the starch, as by heating the oil in container 20 or by replacing the cold oil therein with hot oil. The loaded cylinder 4 is then removed and placed in an extrusion gun 28 where plates are forced by a plunger 30 through wire screen 46 of successively varying mesh, whereby the material becomes progressively more limp and plastic. Water escapes from the compressed mass through longtitudinal openings in the cylinder 4. The extruded paste is received on a carriage comprising parallel adjacent rollers 49 mounted on a platform 50 which is moved on rollers 51 in a straight line to the right at the same speed as that of the paste 48. The paste is dried, as in a graphite boat through which electric current is passed, then further heated, e.g. at 150‹C., to remove the glycerine, placed in a larger graphite boat covered with "Alundum" (Registered Trade Mark) and sintered into a hard dense mass In modifications, (a) a tube-forming die may be substituted for the die 32 in Fig. 4, (b) a spiral-forming die may be used, the rollers 51 being then rotated in the same direction and at the same speed as that of the extruded spiral : such a die may be made by casting fused metal, e.g. type metal, around a twist drill which is removed after the metal has solidified ; (c) the loaded tube 4 may be cooled to -8‹C. without evacuation of air, placed in a jar and slowly wetted from the bottom upwards, to remove the air, by dropping into the jar water-glycerine solution cooled to -8‹C., the heating &c. being then carried out as before ; and (d) the extrusion nozzle is as long as the article to be produced and the paste extruded thereinto is removed therefrom by filling the container 4 with paraffin and extruding the paraffin into the nozzle ; a cork may be placed in the throat of the nozzle to offer resistance and cause the extruded paste to be closely compacted, and another cork may separate the paraffin and paste. An obstruction such as a cork may be placed in the throat of any die used in the process, to cause the paste stream to spead out and fill all spaces in the die.