US2047237A - Extrusion - Google Patents

Description

July 14, 1936.

H. B. UPDEGRAFF EXTRUSION Filed April 12, 1955 INVENTOR Jfi /ws 5 gym m BY M J ATTORNEY Patented July 14, 1936 UNITED STATES PATENT OFFICE EXTRUSION Application April 12, 1935, Serial No. 15,929

11 Claims.

This invention relates to improvements in extrusion and is particularly concerned with nonferrous metals such as aluminum and'its alloys.

In the extrusion of metals, wherein a heated metal billet or charge, suitably confined, is expressed in indefinite lengths by pressure through a die orifice of desired configuration, there are certain factors which limit the number of billets or charges that may be extruded before the quality of the extruded product commences to suffer from inferior quality of surface. Furthermore, the speed at which a metal may be extruded is greatly curtailed by reason of known extrusion methods.

In known extrusion practice each billet or charge expressed through a die, or between a die and mandrel, leaves an indefinite amount of its metal, and any oxide thereof, upon the bearing surface of the die. This metal and/or oxide forms a bond with the die bearing surface as by a welding or alloying action, the pressure exerted on the billet, together with its initial temperature, and the temperature generated by friction of the metal passing through the die orifice, causing the adherence or" the metal of the billet upon the die bearing surface.

Various metals and alloys require different temperatures at the beginning of an extrusion operation in order that they may readily flow under pressure, and these initial temperatures increase 3 or build up during an extrusion operation in view of the friction generated by the metal within its confining cylinder and while passing through the die orifice. It will be manifest, then, that variations in the character of the metals to be extruded,

the temperatures of operation, and the die orifice configuration present factors which are responsible to a great degree for the amount of metal which adheres to the bearing surface of a die.

The metal which adheres to an extrusion die.

in view of the above-mentioned causes, is a vari able quantity and is not predictable because of the numerous variables associated with each metal and die configuration. It is known, however, that the metal, and/or oxide thereof, which bonds itself to a die bearing surface, and hereinafter termed pick-up, militates against the quality of an extruded product, as well as the speed at which a metal may be extruded. In explana- 50 tion of the effect of pick-up on quality and speed, it will be manifest that the pick-up does not accumulate uniformly upon the bearing surface of a die, with the result that surface scratches and blemishes are produced upon the product exud- 55 ing from a die thus contaminated. Also, the

bearing surface is appreciably roughened by pick-up, which, in contrast to a polished die surface, offers increased friction and militates against the speed of an extrusion operation. likewise, pick-up aflects the dimensional size of 5 the finished product, which condition is adverse to one of the desired characteristics for which the extrusion method of producing shaped articles has become famous, namely, dimensional accuracy. m

In present extrusion practices, it is usual to clean the dies to remove pick-up by means of a scraping action such'as is produced by emery cloth or a like polishing action. Another clean- 7 ing procedure resorted to comprises flushing or swabbing the die orifice with a suitable heavy lubricating oil between charges extruded therethrough. Such practices are quite impractical in intricate die shapes in that they do not insure a complete and absolute removal oi the pick-up. Furthermore, the lost time accruing from such die-cleaning procedures, which in most instances requires the removal oi the die from its retaining means, adds greatly to the cost oi operation oi an extrusion mechanism, which increased cost is directly reflected in the cost of the product produced under such operating conditions.

It is an object oi the present invention to proride an improved method of extrusion to overcome the disadvantages caused by pick-up, and W I the invention is predicated upon the fact that if a solvent of the metal, or any oxide thereof, being extruded is applied to the bearing surface of an extrusion die prior to expressing the metal there- 35 through, a product oi superior surface quality is produced at extrusion speeds greatly in excess oi those now possible to obtain. It will be manitest that other objects and advantages accruing from the invention will hereinafter present themselves on consideration of the specification.

It has now been discovered, in the case of extruding aluminum and its alloys, that a suitable caustic coating upon the bearing surface of an extrusion die quickly and readily removes piclr- 45 up and permits the production, at increased speeds, of an extruded product having a surface finish of high quality and polish, free from the, scratches and blemishes so well known in extruded shapes produced in accordance with known practices. In actual practice, three or four charges or billets are usuallyconsidered a maximum before it is necessary to remove pickup, as by the scraping or similar die-polishing operation hereinbeiore described. with a caustie coating applied to the die bearing surface following each billet extruded therethrough, in accordance with the present invention, it has been found that the same die will permit the extrusion of twenty-five to fifty charges through a die before it is necessary to repolish the bearing surface of the die, the surface finish of the product produced from these latter billets being uniform in quality and free from scratches, or similar surface blemish, so common in known extrusion practice.

It has been further discovered that the effect of an application of a caustic coating to the bearing surface of an extrusion die may be appreciably improved when such an application is preceded by coolingthe die. Such a cooling step permits a more uniform thickness of caustic coating and insures complete and absolute coverage of the bearing surface. In explanation of the cooling step, it has been found that a die temperature, substantially that at which an extrusion operation is usually started, permits retention of the caustic applied thereto, the caustic preferably being applied in the form of a solution, and if applied directly to a heated surface, representative of a die temperature at the completion of an extrusion operation, would rebound therefrom until such time as the die reached a temperature more nearly that of the solution.

It will be manifest that the die-cooling step is not essential in the original or first extrusion operation following indefinite inoperation of an extrusion apparatus. In subsequent operations, however, during which the die temperature has been increased, in view of the heat generated by friction of the metal passing through the die and the heated billet's contact with the die, the cooling step is resorted to and preferred.

In practicing the invention the caustic coating may be applied to the die bearing surface by means of a brush, the die preferably being first flushed with water or other suitable cooling medium. Such a procedure is best suited in the case of a simple die orifice where it is possible to reach all portions of the bearing surface with the brush, but is not so successful in instances where a complicated die orifice presents itself. Exemplary of a die orifice that lends itself readily to the application of a caustic coating by means of a brush or the like would be a circular orifice for the production of extruded shapes of circular cross-section.

A more eificient means of applying the caustic coating, and the one which has been accepted from a production and commercial standpoint, embodies a spray apparatus mounted adjacent the die orifice, whereby caustic solution from a suitable supply tank may be sprayed under pres sure, such as compressed air, upon the die bearing surface through a suitable spray gun of any well known construction. The caustic solution in spray form readily enters and reaches all points on the bearing surface of a die, no matter how intricate or complicated it may be. Also, the air pressure employed acts in a capacity to cool the die simultaneously with the coating operation.

Following the application of a coating of caustic by either of the above-mentioned methods, or, in fact, any suitable method, the first portion of the billet exuding from the caustic-coated die removes the dissolved pick-up metal, and/or oxide, together with any excess caustic adhering to the die bearing surface, with the result that the subsequent portion of the extruded billet is free from scratches and surface blemish. The removed caustic and dissolved pick-up usually extend a few inches from the forward or leading end of the extruded shape and are readily dispensed with by removing this portion of the extruded shape. The caustic is obviously discernible on the aluminum in that it appears in the form of a stain, and the removal of the stained portion of the extruded shape is imperative in view of the corrosive action of caustic.

In usual practice, as applied to the extrusion of aluminum and its alloys, the billets are heated to a temperature not lower than 450 Fahrenheit, which, under the usual extrusion pressures em-- ployed, readily causes the bonding of the aluminum to the die surface. It has been found, however, even under these severe conditions, that the application of the caustic coating counteracts the disadvantages accruing from the pick-up accumulated under these working conditions, and very favorable results have been obtained in the further treatment of extruded shapes of strong aluminum alloys subjected to heat-treatment, which treatment ordinarily discloses or opens up any corroded or otherwise pitted or blemished surfaces.

The caustic solutions which have been found economically satisfactory in carrying out the present invention, in its application to aluminum and its alloys, are ten per cent solutions of caustic soda (NaOH) and ten per cent solutions of caustic potash (KOH) but any solvent of aluminum and its alloys which does not have an ailinity for, or corrosive action on, the material of the extrusion die, and its adjacent structure, may be satisfactorily employed. It is to be understood, however, that the concentration of the caustic solution selected is in no way critical to the results of the invention.

Although the invention has been described in its applicability to the extrusion of aluminum and its alloys, and is of great benefit in connection therewith, zinc, copper, and brass form a group of metals the extrusion of which may also be benefited by the use of this invention. A particularly satisfactory solvent for this latter group of metals is concentrated nitric acid, which has no appreciable effect on the usual steel die used in extrusion presses.

In order that the invention may be more readily understood, reference is made to the drawing accompanying this specification in which an extrusion apparatus suitable for carrying out the invention is diagrammatically illustrated in sectional elevation. In the drawing, in represents a billet container of an extrusion press into which a metallic billet II is positioned for extrusion, under the influence of a ram l2 provided with a suitable dummy block i4, through a suitable die I! restrained against the forward end of the billet container. In the particular apparatus shown herein a die I! is suitably mounted within a tool carriage or carrier l8, and a back-up ring l1, adjacent the die and in bearing contact with the die and a shouldered portion of the carriage, maintains the die in pressure-resistant relationship with respect to the cylinder I 0. An aperture ii in the wall of the tool carriage l8 provides for easy assembly of the die and back-up member within the carriage II. A slidable locking plate 20 operating in a slot 2 l, disposed in a housing or platten l9 adjacent the front end of the billet cylinder I0, serves to maintain the tool carrier II with its assembled die in operating position against the cylinder Ill. By vertical reciprocation of the plate 20 and horizontal reciprocation of the carrier i 8, the tool assembly may be moved to a position indicated in the dotted construction.

A supply tank 22, for the particular solvent being employed, is suitably located above the extrusion apparatus adjacent the die end thereof, and a manually manipulated pressure gun 23, connected to said supply tank by means of a fiexible conduit 24, and having a second connection 25 to a suitable source of pressure, such as compressed air, provides means for applying a coating of solvent to the bearing surface 26 of the die It. It will be manifest that the apparatus herein disclosed forms no part of the present invention, and numerous other satisfactory devices may be employed for carrying out the process steps of the invention.

Although specific illustrations of the invention have been used in describing the nature of the contribution to the art represented by this invention, it is to be understood that the invention is not to be interpreted except as defined in the appended claims.

What I claim is:

1. The method of extruding non-ferrous metals having extruded surfaces free from pick-up blemish, comprising providing an extrusion die and coating the die prior to extruding the metals therethrough with a solvent of the metals extruded,

2. The method of extruding metals having extruded surfaces free from pick-up blemish, comprising providing an extrusion die of a metal other than the metals to be extruded, coating the die prior to extruding the metals therethrough with a chemical solvent of the metals extruded, said chemical solvent being inert to the metal of the die.

3. The method of extruding copper having an extruded surface free from pick-up blemish, comprising providing an extrusion die and coating the die prior to extruding the metal therethrough with a concentrated solution of nitric acid.

4. The method of extruding zinc having an extruded surface free from pick-up blemish, comprising providing an extrusion die and coating the die prior to extruding the metal therethrough with a concentrated solution of nitric acid.

5. The method of extruding aluminum having an extruded surface free from pick-up blemish, comprising providing an extrusion die and coating the die prior to extruding the metal therethrough with a caustic solution.

6. The method of extruding aluminum having an extruded surface free from pick-up blemish, comprising providing an extrusion die and coating the die prior to extruding the metal therethrough with sodium hydroxide. '7. The method of extruding aluminum having an extruded surface free from pick-up blemish, comprising providing an extrusion die and coating the die prior to extruding the metal therethrough with potassium hydroxide.

8. The method of extruding aluminum having an extruded surface free from pick-up blemish, comprising providing an extrusion die, coating the die prior to extruding the aluminum therethrough with a caustic soda solution, heating the aluminum to a temperature of at least 450 Fahrenheit, and thereafter applying pressure to extrude the aluminum through said coated die.

9. The method of extruding aluminum having an extruded surface free from pick-up blemish,

comprising providing an extrusion die, coating the die prior to extruding the aluminum therethrough with a ten per cent caustic soda solution, heating the aluminum to a temperature of at least 450 Fahrenheit, and thereafter applying pressure to extrude the aluminum through said coated die.

10. The method of extruding aluminum and its alloys having an extruded surface free'from pickup blemish, comprising providing an extrusion 'die, cooling said extrusion die. and thereafter applying caustic soda to the cooled die prior to extruding the metal therethrough.

11. The method of extruding aluminum having an extruded surface free from pick-up blemish, comprising providing an extrusion die, simultaneously cooling and coating the die prior to extruding the aluminum therethrough with a ten per cent solution of caustic soda, heating the alm'ninum to a temperature of at least 450 Fahrenheit, and thereafter applying pressure to extrude the aluminum. through said cooled and coated die.

HUGHES B'. UPDEGRAFF.

Images