US3153482A

US3153482A - Lubrication of mandrels for tube extrusion

Info

Publication number: US3153482A
Application number: US287161A
Authority: US
Inventors: Billie J Buntz; Lester A Unnerstall
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-06-11
Filing date: 1963-06-11
Publication date: 1964-10-20
Anticipated expiration: 1981-10-20

Description

Oct. 20, 1964 B. J. BUNTZ ETAL 3,153,482

LUBRICATION OF MANDRELS F OR TUBE EXTRUSION Filed June ll, 1963 Wig-1 IEE-E INVETORS ,Bal/ze Z ,Panty [eBsYer-A? Zif/fiefasall M Q. www

Kto/'Wg United States Patent O M 3,153,482 LUBRICATION OF MANDRELS FOR TUBE EXTRUSION Billie J. Kuntz, Cushing, Okla., and Lester A. Unnerstall,

Washington, Mo., assignors, by mesne assignments, to

the United States of America as represented by the United States Atomic Energy Commission Filed .lune 11, 1963, Ser. No. 287,161 2 Cls. (Cl. 207-3) This invention relates to the lubrication of a piercing mandrel used in the extrusion of tubing.

In the extrusion art difficulty is often experienced in centering a piercing mandrel accurately in an extrusion die. An inadequately supported mandrel causes variations in tubing wall thickness. This is referred to as a lack of concentricity. Such variations frequently amount to 10 percent of the wall thickness.

It is important in tubular nuclear fuel elements such as those described in U.S. Patent No.72,992,172, issued July 1l, 1961, to have uniform tubing wall thickness both for uniform heat generation and for uniform transfer of heat to cooling mediums. Extrusions that yield tubing closer to the final machined dimensions are an advantage in that a higher percentage of the tubing will meet strict specilications for acceptability.

Another diiiculty has been that of providing adequate lubrication for the mandrel surfaces which come into contact with a hot billet. Normally a piercing mandrel is lubricated after it passes through its last support, which is at some distance from the piercing end of the mandrel. If the support is placed close to the piercing end of the mandrel, the only lubricant on the mandrel is that which passes through the support. Lubrication provided in this manner is inadequate if the support tits the mandrel closely enough to accurately maintain the position of the mandrel in the extrusion die. Mandrel replacement is costly, yet if not replaced, a Worn mandrel causes inferior inside surface finish in the extruded tubing.

The present invention has resulted in a substantial improvement in concentricity of extruded uranium tubing so that variations in concentricity are consistently less than percent of the tubing wall thickness and are usually in the neighborhood of 3 percent. In addition, mandrel life has been increased by at least a factor of l0 with an associated improvement in smoothness of the inside surfaoes of the tubing.

This has been accomplished by the present invention which includes iilling a piercing cap with lubricant and providing a lubricant well around the mandrel just ahead of a guide bearing positioned close to the billet so that as the mandrel is driven forward the lubricant is forced back into the lubricant well thereby lubricating the mandrel after the mandrel passes through the guide bearing.

It is an object of this invention to minimize variations in tubing concentricity.

It is also an object of this invention to increase mandrel life.

It is a further object of this invention to maintain uniform quality of inner surface smoothness in extruded tubing.

Other advantages of the present invention will be apparent from the following description and accompanying drawing in which:

PIG. 1 is a sectional view taken in elevation of an extrusion set-up preliminary to a piercing operation.

FIG. 2 is a similar view after piercing showing the be ginning of an extrusion operation.

A piercing mandrel is centered in a tubular extrusion ram 12 by a support sleeve 14 which is carried by the forward end 16 of the ram 12. The support sleeve 14 has a guide bearing portion 18 in close-fitting contact 3,153,482v Patented Oct. 20, 1964 ICC with the mandrel 10. A recess 20 in the forward end of the support sleeve 14 receives a piercing cap 22 which, according to this invention, has been iilled with lubricant 24. Between the recess 20 and the bearing portion 18 Vis a lubricant well 26 which receives the lubricant as it is displaced from the piercing cap` 22 by the piercing end 28 of the mandrel 10 as the mandrel moves forward.

The lubricant may be one of several commonly used `types of extrusion lubricant for high temperature use.

The lubricant should be Viscous enough to be retained in the lubricant well 26 and to adhere to the surface of the mandrel 1t? under operating conditions. Grease-base extrusion lubricants containing graphite or aluminum flake are satisfactory, for example, in gamma phase extrusion `of uranium.

`is press-fitted into a die case 36.

As the ram 12 is driven forward the billet 32 is upset to fill a cavity 38 between the die case 36 and a forward face 40 of the dummy block 30, a forward end 42 of the support sleeve 14 and the piercing cap 22. Then, the mandrel 10 is driven through the billet 32 carrying the piercing cap 22 with it until the piercing end 2S of the mandrel 10 extends beyond the die insert opening 34 where the cap 22 ilies off. The mandrel 10 in passing through the lubricant-lilled Well 26 picks up lubricant on its lateral surfaces. The amount of lubricant fed into the lubricant well may be controlled by varying the amount of lubricant placed in the piercing cap prior to extrusion.

As the ram 12 moves forward, it upsets the billet 32, causing the billet metal to close in around the mandrel 10 as the billet material begins to extrude through the die insert opening 34 as shown in FIG. 2. The lubricant 24 adheres to the surface of the mandrel out of direct contact with hot billet material until the extrusion operation is under way. This facilitates horizontal extrusion operations which are difficult in methods where a fluid lubricant such as molten glass is applied to the surface of the hot billet metal itself.

If a mandrel is lubricated before it is driven through the close-fitting guide bearing portion 18, the residual lubricant left on the mandrel is not adequate to protect the mandrel from erosion by the hot metal. Under such conditions a mandrel used for extruding uranium tubing lasts for only about fifteen billets. On the other hand we have found that a mandrel lubricated according to this invention will still be suitable for use after extruding several hundred billets. This represents a considerable saving in mandrel replacement costs. It also represents a great improvement in uniformity of the inside diameter of the extruded tubing as well as in smoothness of the inside surface of the tubing.

In gamma phase extrusion of uranium we have found hot work tool steels such as A.I.S.I. Hll and H12 to be satisfactory for extrusion equipment which comes into contact with hot uranium billets. For the die insert 35, high speed tool steel such as A.I.S.I. T1 has proven satisfactory. The support sleeve 14 was made of A.I.S.I. H13, a hot work tool steel.

This invention is not limited to the exact details disclosed, but may be embodied in other forms within the scope of the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A tube extrusion apparatus comprising: a die case 3 having a cavity adapted to receive a billet of a material to be extruded, said die case having an extrusion opening in one face thereof through which said material may be extruded; a tubular ram positioned to axially enterv the cavity in said dieA case essentially in axial alignment with said extrusion opening; a piercing mandrel extending axially through the tubular ram and adapted to be extended forward through the billet and into the extrusion opening, said mandrel being smaller in diameter thanY the diameter of the extrusion opening; a piercing cap adapted to t over a forward end of said mandrel; a support sleeve positioned in a forward end of the ram and rigidly supported thereby, said sleeve having a rearwardly positioned guide-bearing portion snugly receiving `said piercing mandrel, said sleeve having a recess in a forward end thereof in axial alignment with said guide-bearing portion adapted to receive the piercing cap, said sleeve having a lubricant well between the guide-bearing portion and the said recess, said Wellv being disposed about the mandrel in a lubricant-applying relationship thereto and being of a size suliicient to receive lubricant displaced from the piercing cap as the mandrel is driven forward; and a dummy block positioned between the forwardend of the ram and the billet, said dummy block being centered around and supported by a forward portion of said support sleeve, said dummy block having a forward face essentially in the same plane as the plane of the forward end of the support sleeve.

2. A device for centering and lubricating a piercing mandrel in a tubing extrusion die, comprising: a support sleeve carried by and centered in a forward end of an extrusion ram, said sleeve having a rearwardly positioned guide-bearing portion snugly receiving said piercing mandrel, said sleeve having a recess in a forward end in axial alignment with said guide-bearing portion and adapted to receive a piercing cap positioned over a forward en-d of the piercing mandrel, said sleeve having a lubricant well positioned between said recess and said guide bearing portion, said wellbeingdisposed about lsaid piercing mandrel in a lubricant-applying relationship thereto, said well being of a size suicient to receive at least a major portion of 'a lubricantA displaced from a lubricant-filled piercing cap as the mandrel is driven forward through a billet to be extruded.

Claims

1. A TUBE EXTRUSION APPARATUS COMPRISING: A DIE CASE HAVING A CAVITY ADAPTED TO RECEIVE A BILLET OF A MATERIAL TO BE EXTRUDED, SAID DIE CASE HAVING AN EXTRUSION OPENING IN ONE FACE THEREOF THROUGH WHICH SAID MATERIAL MAY BE EXTRUDED; A TUBULAR RAM POSITIONED TO AXIALLY ENTER THE CAVITY IN SAID DIE CASE ESSENTIALLY IN AXIAL ALIGNMENT WITH SAID EXTRUSION OPENING; A PIERCING MANDREL EXTENDING AXIALLY THROUGH THE TUBULAR RAM AND ADAPTED TO BE EXTENDED FORWARD THROUGH THE BILLET AND INTO THE EXTRUSION OPENING, SAID MANDREL BEING SMALLER IN DIAMETER THAN THE DIAMETER OF THE EXTRUSION OPENING; A PIERCING CAP ADAPTED TO FIT OVER A FORWARD END OF SAID MANDREL; A SUPPORT SLEEVE POSITIONED IN A FORWARD END OF THE RAM AND RIGIDLY SUPPORTED THEREBY, SAID SLEEVE HAVING A REARWARDLY POSITIONED GUIDE-BEARING PORTION SNUGLY RECEIVING SAID PIERCING MANDREL, SAID SLEEVE HAVING A RECESS IN A FORWARD END THEREOF IN AXIAL ALIGNMENT WITH SAID GUIDE-BEARING PORTION ADAPTED TO RECEIVE THE PIERCING CAP, SAID SLEEVE HAVING A LUBRICANT WELL BETWEEN THE GUIDE-BEARING PORTION AND THE SAID RECESS, SAID WELL BEING DISPOSED ABOUT THE MANDREL IN A LUBRICANT-APPLYING RELATIONSHIP THERETO AND BEING OF A SIZE SUFFICIENT TO RECEIVE LUBRICANT DISPLACED FROM THE PIERCING CAP AS THE MANDREL IS DRIVEN FORWARD; AND A DUMMY BLOCK POSITIONED BETWEEN THE FORWARD END OF THE RAM AND THE BILLET, SAID DUMMY BLOCK BEING CENTERED AROUND AND SUPPORTED BY A FORWARD PORTION OF SAID SUPPORT SLEEVE, SAID DUMMY BLOCK HAVING A FORWARD FACE ESSENTIALLY IN THE SAME PLANE AS THE PLANE OF THE FORWARD END OF THE SUPPORT SLEEVE.