Expanding Head And Improved Seal Therefor

Abstract

A sealed expanding head is provided for an expanding mandrel machine tool. The head includes a plurality of radially expansible and contractable die units and an expansion cone drawn between the units to expand them. The space between adjacent units is sealed against the loss of lubricant and the entrance of scale and other debris by an elongate flexible sealing element having a generally U-shaped cross section, with the free ends removably mounted in the adjacent segments.

Description

BACKGROUND AND OBJECTS

This invention relates to expanding mandrel-type machine tools. More particularly, it provides a sealed expanding head for such tools and an improved seal therefor.

Expanding mandrel-type tools stretch-form cylindrical workpieces by radially expanding a head or mandrel within the workpiece and radially stretching the workpiece beyond its yield point. These tools are becoming widely used for a variety of metal forming operations, ranging from pipe sizing to the forming of complex thin metal shapes.

The basic elements common to expanding mandrel tools are a series of radially expansible and contractable die units, the inner sections of which define a polysided wedge-shaped cavity. A mating polysided cone or plug is drawn into the cavity and, as longitudinal movement of the die units is prevented, the cone expands the units radially outward to stretch the workpiece.

As may readily be appreciated, the frictional force applied on the wedge or ramp surfaces of the die units and the cone require careful lubrication. Lubricants, usually heavy-duty greases, must be confined within the expanding head. Concomitantly, metal scale and other debris on the workpiece must be prevented from contacting the grease and penetrating to the lubricated surfaces. An object of the invention is to provide an improved sealing means for confining the grease within the expander head, preventing its contamination by external debris, and achieving both aims without the penalty of inordinately complex grease seals.

Grease seals of various designs have been proposed and used for expanding mandrel tools. In general, however, the more effective seals have proven to be complex and, in any event, to require complete disassembly of the expander head when replacing the seals. Simple compressible seals have also been proposed, but in high output machine tools have proven insufficiently durable. Another object of the invention is to provide expanding mandrel and grease seal therefor which uniquely combines simplicity of construction, ruggedness of operation, and ease of replacement. An associated object is to provide a low cost sealing element which can be replaced without requiring disassembly of the expanding mandrel.

Other and further objects, aims and advantages of the invention will become apparent as the description thereof proceeds.

BRIEF DESCRIPTION OF DRAWINGS

The invention is exemplified in the annexed drawings, wherein:

FIG. 1 is a lateral view of an expanding mandrel machine tool head incorporating the seals of the present invention;

FIG. 2 is a partial sectional view of the expanding head, showing the die units in their retracted position and, in phantom, the units in their radially expanded position; the section is taken to show the construction of replaceable liners on the several die units;

FIG. 3 is another partial sectional view on a plane perpendicular to the draw bar axis of FIG. 1, this time showing the expanding head in its expanded position, and with the plane selected to show the construction of the cone liner with respect to the cone; and

FIG. 4 is a partial elevation of the sealing element according to the invention.

DETAILED DESCRIPTION

While the invention is susceptible of various modifications and alternative forms, certain specific embodiments thereof have been shown by way of example in the drawings which will be described in detail herein. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed but, on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention.

Turning now to the drawings, particularly FIG. 1, a lateral view of the expanding head 11 is depicted. The head 11 in this case is horizontally disposed and is adapted to stretch-form a cylindrical workpiece into a cylinder of generally smooth shape.

The expanding head 11 includes a plurality of radially expansible and contractable die units disposed around the generally conical, or more accurately a polysided wedge-shaped, cone 12, located near the end of a drawbar 14. The tapered surfaces of the cone 12 taper inwardly from the end of the cone towards the drawbar 14 direction. A table, omitted from the drawing, is positioned against the right end (as viewed from the aspect of FIG. 1) of the expander head to prevent axial movement of the several die segments as the drawbar 14 is pulled to the right.

A cover 15, shown removed from the end of the expanding head 11, is secured to the expanding head to prevent discharge of lubricant grease and entrance of mill scale and other debris. The attachment between the cover 15 and the expanding head 11 includes a circumferential gasket 16 provided with radial slots or keyways 17, which match a series of keys 18 on the expanding head and permit the die units to move radially with respect to the cover 15. As best shown in FIG. 2, each die unit comprises a jaw 19 to which is removably secured a replaceable die segment 20. The die segment 20 has an external surface defining a portion of a cylinder wall, with the cylinder radius substantially equal to the final radius of the expanded workpiece. Capscrews 21 arranged centrally along a longitude of each die segment 20 permit the segments to be removed from their respective jaws 19.

On the radially inward face of each jaw 19 is a replaceable jaw liner 22, removably secured to the jaw by cap screws 24, 25. A similar liner, namely cone liner 26, is removably secured to the cone 12 (FIG. 3) by capscrews 27, 28. Thus, sliding surfaces on the cone 12 and on the die jaws 19 are made replaceable.

To restrict movement between the jaw liners 22 and the cone liner 26 to a longitudinal movement only, a longitudinal slot 29 is provided in the cone liners 26, and a key 30 is secured to the die jaw 19 by a bolt 31 (as best shown in FIG. 3). A keyway slot 32 is machined longitudinally in the cone 12 to receive the key 30.

As the cone 12 is drawn axially with respect to the die segments, the wedge or slant surfaces on the cone liner 26 and on the jaw liner 22 cam the die jaws 19 radially outward, from the retracted position shown in FIG. 2 to the expanded position shown in FIG. 3. As this occurs, the adjacent die segments are separated, from the proximate position shown in FIG. 2 to the distal position of FIG. 3. In the absence of a grease seal, grease or other lubricant in the frictional zone between the cone liners 26 and the jaw liners 22, and between the key 30 and the slots 29, would normally be exposed to external contamination from mill scale and other debris. Additionally, the lubricant would escape from the areas between adjacent die segments, where it would contaminate the work area and surrounding equipment components.

Escape of lubricant grease and entrance of debris are simultaneously prevented by the improved grease seals according to the invention. As shown best in FIGS. 3 and 4 conjointly, the seal element 34 comprises a generally U-shaped, or omega-shaped, longitudinally uniform element 34, extending substantially along the entire length of the expanding head 11 (FIG. 1). The seal element 34, as viewed from the end as in FIG. 3, includes a pair of leg portions 35, 36, the free ends of which are removably secured to adjacent die units, e.g., to the die jaws 19. Flanges 38, 39 extend generally outwardly and then toward the arch of the seal element 34 near the respective ends of the leg portions 35, 36. Thus, as the die units of the expanding head 11 are moved from their radial outward position of FIG. 3 to the contracted position of FIG. 2, the seal elements 34 are compressed at their leg portions 35, 36.

The material constituting the seal elements 34 is a resilient nonmetallic material, advantageously an extruded flexible organic plastic such as polyethylene, polypropylene, a nylon, or polytetrafluoroethylene. These materials provide the desired flexibility, grease impermeability, and low cost, as well as virtually complete sealing for the lubricant against contamination from external debris.

Removal of the seal elements 34 is effected by providing an undercut recess 40 (FIG. 3) in the die units, preferably along the joining surfaces between the jaws 19 and the die segment 20. Consequently, and as best shown in FIG. 1, the seal elements 34 may be slid into or out of position with respect to the expanding head 11 without any need for disassembling the head 11 as has usually been the practice with prior grease seals.

The particular structure depicted in FIGS. 2 and 3 affords an additional advantage. As may be seen from FIG. 2, when the die units are in their contracted position, the grease seal elements 34 provide a partially enclosed tubular zone 41 defined by the inner portion of the seal element 34, or, in other words, that portion of the seal element 34 which is not compressed by the retracting die jaws 19. As a result, this can receive and contain debris which has entered the seal 34 while the expanding head 11 is in its expanded position (FIG. 3).

Obviously, the expanding head 11 and the grease seal elements 34 may be of varied sizes, depending upon the size requirements of the workpiece, the expected amount of debris, the expected frequency of seal cleaning and of seal replacement, and the like. Illustratively, for a pipe expander designed to expand a tubular pipe to about 22 to 22 1/2 inches internal diameter, the expanded diameter of the head 11 is about 22 1/2 inches, while the nominal contracted diameter of the head is about 21.375 inches. The seal elements 34 are of polyethylene, 0.032 inch thick at the leg portions 35, 36 (FIG. 3) and a maximum of 0.062 inch at the apex of the arch portion. The flanges 38, 39 are about one-sixteenth inch thick, and their inner sides extend about one-sixteenth inch from the outer surfaces of the leg portions 35, 36.

Thus, it is apparent that there has been provided, according to the invention, a unique expanding head and improved seal therefor which fully satisfy the aims, objects and advantages of the invention as earlier indicated.

Claims

We claim as our invention:

1. A sealing element for use with expanding heads of the type having a plurality of radially expansible and contractable die units, said element being formed of resilient nonmetallic material, longitudinally uniform, and having a generally U-shaped cross-sectional configuration defining a pair of sealing legs for sealing engagement with respective different ones of a pair of adjacent die units, said element including means for securing said legs to respective different ones of a pair of adjacent die units.

2. Sealing element of claim 1 wherein said resilient nonmetallic material is selected from the group consisting of polyethylene, polypropylene, a nylon, and polytetrafluoroethylene.

3. Sealing element of claim 1 wherein said securing means comprises an external flange near the end of each of said legs and receivable in a corresponding undercut in each of said adjacent die units.

4. A sealed expanding head of the type including a plurality of radially expansible and contractable die units together with means for controlled actuation thereof and sealing means interposed between each adjacent pair of die units, said sealing means comprising in combination with said expanding head an elongated resilient sealing element having a generally U-shaped cross-sectional configuration defining a pair of sealing legs, a pair of flanges formed near the free ends of said legs and extending substantially the entire length of said elongated flexible sealing element, and a flange-receiving recess in each of said adjacent die units whereby lubricant is retained within said expanding head and scale and other debris is prevented from entering said head.