GB2055066A - Removal of slag from consumable electrode wire in arc welding - Google Patents

Abstract

In consumable electrode, particularly automatic submerged-arc welding, slag is removed from the end of consumable electrode wire 22 between the weld runs by a pair of spring-biased or, as shown, spring arms 14, 17 attached to the A tip 10 of a weld head, wire feed means being arranged to retract the wire past the arms before each weld run. <IMAGE>

Description

SPECIFICATION Welding This invention relates to welding. More particularly the invention is concerned with automatic welding in which welding wire is fed automatically to the site of a weld through a hollow tip of a welding gun.

In effect, all automatic welds are intermittent in that after making a welding run of whatever length there is a time interval before the start of the next welding run. The fabrication of a single article may require a number of welding runs and an example of this is the manufacture of a road wheel for a vehicle which comprises a disc and a rim, the disc having a number of arms whose free ends are welded to the rim. The welding is carried out by causing relative movement between the rim and wheel combination on the one hand and the welding gun on the other, welding taking place along a run consisting of the end of each arm and then being interrupted while further relative movement brings the welding gun to the next arm when a second welding run takes place.

Slag is formed during welding and the slag conglomerates as a tacky mess at the end of the wire at the end of each welding run. In order for welding to be able to be recommenced with certainty, this slag has to be removed. One way in which this is done at present is for the operator to remove it by hand and it is not unknown for the operator to bang the welding wire on the work to remove the slag but this is not good practice.

An object of the invention is to provide welding apparatus which will enable the removal of slag from the end of the welding wire between welding runs. Another object of the invention is to provide a method of welding using such apparatus.

According to one aspect of the invention we provide welding apparatus comprising a welding gun having a tip with a bore through which welding wire can be fed to a weld site from an end of the bore, means to advance and retract welding wire through the bore and spring-biased, slag-stripping means at said end arranged to remove slag from the end of the wire as the wire is retracted into the bore through said end thereof.

The procedure in using the apparatus, therefore, is that between weld runs the wire is retracted into the bore and this retraction causes the slag-stripping means to remove the slag from the end of the wire so that when the wire is next advanced to commence a new welding run, the end of the wire is free from the slag and a certain start to welding is obtained.

Preferably, the stripping means comprises a pair of sprung arms mounted on the nozzle at diametrically opposed positions relative to the bore, the arms being displaced from a rest position when welding wire extends between them and moving to said rest position when the wire is retracted and during said movement stripping any slag on the wire from the ends thereof.

Preferably, the arms themselves are made of spring material. The arms may have, at the ends remote from the nozzle, convergent portions which, in the rest position of the arms, touch one another. In this arrangement the free end of one arm may touch the other arm at a position adjacent to but not at the free end of said other arm in the rest position.

The invention also provides a method of intermittently welding with apparatus described above in which, between welds, the wire is left in a position projecting from the tip beyond said stripping means until the slag has solidified and the wire is then withdrawn into said bore to allow the stripping means to remove the slag before starting the next weld.

This method may advantageously be applied to the manufacture of a road wheel for a vehicle comprising a disc and a rim in which the disc has a number of arms whose ends are welded to the rim.

The invention will now be described in detail by way of example with reference to the accompanying drawings in which:~ Figure 1 is a diagram indicating welding wire feed in apparatus embodying the invention; Figure 2 is a diagram illustrating the relative speed of movement between the work and the welding gun in apparatus embodying the invention; Figure 3 is an elevation of the tip of a nozzle; Figure 4 is a detail of the nozzle of Fig. 3 showing welding wire projecting through the slag-stripping means; and Figure 5 is a diagram showing how a wheel may be welded with the method of the invention.

Referring first to Figs. 3 and 4, these show the tip 10 of a welding gun for automatic, submerged-arc welding. The tip has a bore 11 extending therethrough, the tip being arranged to receive welding wire which can be advanced in the direction of the arrow 12 to a welding site being operated upon and can be retracted in the direction of the arrow 13. The wire is advanced and retracted by a feed mechanism of the welding machine which is not shown.

Two spring arms are attached to the tip.

Thus there is a first arm 14 which is secured at 15 to the nozzle and at its free end has a part 16 which is at an angle to the main part of the arm. There is a second arm 17 which is secured to the nozzle at 18 and has a part 19 which is at an angle to the main part of the arm. The arms 14 and 17 converge and the parts 16 and 19 converge. The arms are shown in their rest position in Fig. 3 and in this position the arms touch and in particular it should be noted that the part 19 touches the part 16 at 20 which is a position spaced away from the free end 21 of the arm 14.

During welding, welding wire 22 projects from the bore 11 as shown in Fig. 4 and deflects the arms 14 and 17 and passes between the parts 16 and 19.

At the end of a welding run, slag adheres to the free end 23 of the wire. It will be understood that during the welding run wire is fed in the direction of the arrow 12 to the weld and at the end of that run the wire feed is stopped and the welding current turned off.

The apparatus is arranged so that the wire can be moved in the direction of the arrow 1 3 which moves the free end 23 of the wire past the free ends of the parts 1 6 and 19 and these parts scrape from the end of the wire any slag which is adhering thereto. For the most efficient operation of the apparatus the slag is allowed to cool before the wire 22 is withdrawn to be acted upon by the arms 14 and 17.

Referring to Fig. 5, this shows diagrammatically a wheel comprising a disc 23 having four arms 24. The ends of these arms are welded to the inner periphery of a rim, such inner periphery being indicated by the circle 25. In the particular example, the circumferential distance along the end of each arm is 4 inches and then there is a circumferential space of 4 inches before the next arm starts so that in welding the disc to the rim there will be four weld runs, each 4 inches long, and between each pair of weld runs there will be a 4 inch space.

Referring now to Fig. 1, this shows the wire feed. During a weld run the wire will be advanced at a speed indicated by the line 26.

At the end of the weld run the feed of the wire will be stopped so that there will be a period 27 when the wire is stationary. During this period the slag on the wire solidifies. The wire is then retracted as indicated at 28, i.e.

in the direction of the arrow 13 in Fig. 3, and by this retraction the slag is removed from the end of the wire. The wire is then fed forward again as indicated at 29. It will be appreciated that the welds along the ends of the arms 24 will be made with the wire being advanced as indicated by the lines 26 and 29. During the movement between the welding gun and the wheel assembly across the 4 inch space, the wire will be stationary during slag solidication and will then be retracted.

Fig. 2 indicates the table speed. During welding, the table carrying the rim and disc assembly will be moving at a relatively slow speed indicated by the line 30. Between welds the table will move at a higher speed as indicated at 31. The time interval for each weld may, for example, amount to 10.5 seconds and the time interval for the movement across the space may be 1.5 seconds. It will be appreciated, therefore, that the retraction as indicated at 28 will have to be effected very rapidly.

We have found that by using this method, each welding run has a certain start and the spring arms effectively remove the slag. By having the arms arranged as shown in Fig. 3 so that the part 19 engages the part 16 midway down its length, each arm has a chance to remove the slag whereas if the arms met, in the rest position, at their free ends the removal of the slag would be less efficient. However, if desired, the arms may be arranged in this way.

As described, the arms themselves are made of spring steel. However it would be possible to have arms made of other material but spring biased to the position shown in Fig. 3.

The end parts 16 and 19 of the arms could be tipped with abrasive material so as to ''file" the end of the wire during the slag removal. Moreover, the ends could be hardened to reduce wear.

The invention is particularly applicable to submerged arc, automatic welding where the wire is a solid wire and the flux is applied externally. However, the invention could be applied to welding methods in which a cored wire is used. Moreover, although the invention is particularly useful in automatic welding it could also be used in semi-automatic welding where the operator himself controls the forward feed of the wire. The arrangement here could be such that, upon each start of a weld, upon the operator signalling for the forward feed of the wire the wire would first retract to remove any slag from the end thereof before being fed forward.

Claims (8)

1. Welding apparatus comprising a welding gun having a tip with a bore through which welding wire can be fed to a weld site from an end of the bore, means to advance and retract welding wire through the bore and spring-biased, slag-stripping means at said end arranged to remove slag from the end of the wire as the wire is retracted into the bore through said end thereof.

2. Apparatus according to Claim 1 wherein said stripping means comprises a pair of spring arms mounted on the tip at diametrically opposed positions relative to the bore, the arms being displaced from a rest position when welding wire extends between them and moving to said rest position when the wire is retracted and during said movement stripping any slag on the wire from the end thereof.

3. Apparatus according to Claim 2 wherein said arms are made of spring material.

4. Apparatus according to Claim 2 or Claim 3 wherein said arms at said ends re mote from the tip have convergent portions which, in the rest position, touch one another.

5. Apparatus according to Claim 4 wherein, in the rest position, the free end of one arm touches the other arm at a position adjacent to, but not at, the free end of said other arm.

6. Apparatus according to any one of Claims 2 to 6 wherein the ends of the arms are formed with abrasive surfaces to scrape the end of the wire as the latter is retracted.

7. A method of intermittently welding with apparatus as claimed in any one of the preceding claims in which, between weld runs, the wire is left in a position projecting from the tip beyond said stripping means until the slag on the wire has solidified and the wire is then withdrawn into said bore to allow the stripping means to remove the slag before starting the next weld.

8. A method according to Claim 6 for welding a wheel disc to a wheel rim in which the disc has a number of radial arms, the end of each of which is welded to the rim.