GB2268431A

GB2268431A - Method and apparatus for weld flash removal

Info

Publication number: GB2268431A
Application number: GB9214767A
Authority: GB
Inventors: Bruce Albert Humphries
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1992-07-11
Filing date: 1992-07-11
Publication date: 1994-01-12
Also published as: GB9214767D0

Abstract

Friction welded tubes 18, 20 develop flash 32 around the walls of the tube bores. The invention provides pulses of a reactive gas, eg oxygen, to the flash as it forms, thus disintegrating it and spreading it in the form of small pellets 34 long the bore wall of one of the tubes. The tubes remain sufficiently clear as to provide passageways for a flow of cooling fluid in eg. rock drilling operations. The gas may be supplied from a nozzle 22. <IMAGE>

Description

METHOD OF AND APPARATUS FOR WELD FLASH REMOVAL The present invention relates to the removal of flash from a welded joint. The invention particularly relates to the removal of flash from the bore of a structure which is formed by the end to end joining of hollow members. Thus the invention has particular efficacy in the field of friction welding wherein flash is produced as a result of pressing two or more relatively moving hollow metal objects together, the movement effectively occurring in directions laterally of their lengths.

It is known to remove flash from the welded joint in the bore of a hollow welded structure, by drilling and by mechanical ramming with a ramrod. However in some instances both systems require re-setting of the welded structure on a second machine which is capable o; performing those respective operations.

The present invention seeks to provide both an improved method of and apparatus for removing flash from the joint of a hollow welded structure.

According to the present invention a method of removing flash from the bore of a hollow structure which is formed by forcing end portions of at least two relatively rotating hollow sub structure together comprises the steps of first inserting a reactive gas supply tube in one of the sub structures with the nozzle outlet of the tube adjacent the junction of the substructures, effecting relative frictional motion between the substructures and as flash is formed in said bore, emitting a pulse or pulses of gas so as to react with and disintegrate the flash and blow it away from the joint.

Preferably the method includes the step of emitting intermittent pulses of gas during the formation of flash.

The method may further include timing the issue of said pulse or pulses of gas to coincide with a specific point or points in the welding process.

The invention includes apparatus for putting the method into effect and comprises, in combination, a friction welding machine, a source of reactive gas, a tube for conveying said gas to the region of the weld joint in parts to be joined, valve means for controlling the flow of said gas and timing means for effecting actuation of said valve means so as to provide pulses of said gas at a preselected time or times during the flash forming process.

The invention will now be described, by way of example and with reference to the accompanying drawings in which: Fig 1 is a diagrammatic representation of a friction welding system which incorporates the present invention.

Fig 2 is an enlarged cross sectional part view of Fig 1.

Referring to the drawings. A friction welding machine 10 includes a fixed headstock 12 and a rotatable tailstock 14, both being mounted on a common bed 16. A pair of tubes 18,20 to be friction welded, are gripped, one in headstock 12 and the other in tailstock 14, so that they are axially aligned.

A pipe 22 is positioned within the static headstock 12 so that its nozzle is just upstream of the intended joint line 24 between the abutting ends of the tubes 18, 20. That is, upstream relative to the direction of flow of gas through the pipe 22 during operation.

The gas delivery pipe 22 is connected via a valve 26 to an oxygen supply 28. In operation, the friction welding machine 10 functions in known manner, and consequently, the welding of the tubes 18, 20 together is effected in known manner, as is the forming of flash, both internally and externally of the tubes.

The external flash is removed by any conventional means. The internal flash however is removed as follows: The normal step of pressing the tubes together under a small load and relative rotation is effected. When the first stage friction phase is completed, a timer 30 which enables actuation of the valve 28, is energised. After a pre-determined interval of time, which is governed by the area of joining and the materials being joined, the valve 28 is actuated so that a pulse of oxygen is ejected from the pipe 22 onto the forming ring of flash 32 (fig 2). The molten metal immediately oxidises and breaks up into small pellets 34, to be removed from the flash by the force of the gas pulse. The pellets are blown down the tube 20 and some of them, indeed most of them if the tube 20 is long enough, adhere to the wall of the bore.

The blowing step is repeated as often as is necessary through the flash forming part of the welding process, so that minimum flash is left at the joint during the final forging step when no relative rotation of the tubes 18, 20 is occurring.

One successful experiment which has been carried out comprised welding two tubes which were 32 mm outside diameter and had 10 mm diameter bores (a wall thickness to bore diameter of approximately 1.1:1). The oxygen pulses were applied for 0.5 to 1:0 seconds at a pressure of about 60 psi (4.22kg/sq cm). The experiment resulted in the flash being removed from the vicinity of the joint and deposited as a spray of fine oxidised metal droplets over a large area of the bore surface. Whilst this result would not satisfy a requirement that the bore be absolutely clear, it is eminently suitable in a situation where, eg, hollow drills of the kind used in mining are made by welding three to six metre lengths in end to end relationship. The bore in such a drill is used for the passage of cooling and flushing fluid and the droplets would not impede such a flow to the extent that flow would be reduced.

Fig 1 depicts the oxygen flow control system in isolation. However, a production machine would incorporate the system in the main machine control console.

It is thought that an incidental benefit will accrue from the present invention by way of the oxygen causing a thermal cycle which hardens the surface of the bore if utilised on tubes made from hardenable steels. A surface hardened thus can enhance the fatigue performance of the finished assembly by the generation of compressive internal stresses in the hardened region.

Claims

Claims:

1. A method of removing flash from the bore of a hollow structure which is formed by forcing end portions of at least two relatively rotating hollow substructures together comprising the steps of first inserting a reactive gas supply tube in one of the sub structures with the nozzle outlet of the tube adjacent the junction of the substructures, effecting relative frictional motion between the substructures and as flash is formed in said bore, emitting a pulse or pulses of gas so as to react with and disintegrate the flash and blow it away from the joint.

2. A method of removing flash as claimed in claim 1 including the step of emitting intermittent pulses of gas during flash formation.

3. A method of removing flash as claimed in claim 2 including the step of timing the issue of said pulses to coincide with a specific point or points in the welding process.

4. Apparatus comprising a friction welding machine, a source of reactive gas, a tube for conveying said gas to the region of the weld joint in parts to be joined on said machine, valve means for controlling the flow of said gas and timing means for effecting actuation of said valve means so as to provide pulses of gas at preselected time or times during a flash forming welding process.