GB2074069A

GB2074069A - Contact tube for a consumable arc welding electrode

Info

Publication number: GB2074069A
Application number: GB8111066A
Authority: GB
Original assignee: ESAB Ltd
Current assignee: ESAB Ltd
Priority date: 1980-04-18
Filing date: 1981-04-08
Publication date: 1981-10-28
Also published as: SE440617B; SE8002917L; FR2480649B3; GB2074069B; JPS5711674U; IT8121527V0; FR2480649A3

Abstract

A contact tube of a welding torch nozzle is constituted in its front part by a contact nozzle (4) with a straight guide duct (17) and in its rear part by a guide tube (3) the inside diameter of which is greater than the diameter of the guide duct (17). The guide tube (3) is provided on its inside with one or two projections (11, 12) which force the electrode during its passage through the guide tube (3) to changes in direction. In the process, the electrode will be slightly curved before it enters the guide duct (17) where the curvature is straightened out, thereby establishing good contact with the contact nozzle. The electrode is straight when it leaves the contact nozzle. The contact tube is particularly suitable for electrodes with a diameter less than 1.6 mm. <IMAGE>

Description

SPECIFICATION Contact tube for a fusible welding electrode The invention relates to a contact tube of a welding torch nozzle for a fusible wire electrode wherein a contact nozzle with a straight guide duct for the electrode is forming the front part and a guide tube having a larger inside diameter than the contact nozzle is forming the rear part of the contact tube.

The passage of current from the contact tube to the electrde should take place as near to the orifice of the contact nozzle as possible, so that full current only passes through the tip of the electrode sticking out from the contact nozzle, which causes a rapid and strong heating of the electrode owing to the occurence of high current densities. Therefore, a good contact between the fed electrode and the contact nozzle must be provided. In a known contact tube, the guide duct is somewhat curved. When the electrode is pushed through this curved duct, it slides along the inside of the contact nozzle, thereby providing good contact.However, it is unavoidable that the electrode issuing from the nozzle is somewhat bent and the welder must continuously control the position of the welding torch with respect to the welding pool, as the direction of the issuing electrode changes continually because of its bent design.

In fully automatic welding operations, where the movement of the welding torch is controlled by manipulators or robots, it is desirable for the electrode issuing from the contact nozzle to maintain a pre-determined direction, as an additional control of the direction of the electrode stick-out must otherwise be provided to eliminate unpredictable changes of its direction.

For this reason, it is advantageous for the contact nozzle to be provided with a straight guide duct.

However, when using such nozzles, a deficient contact between the electrode and the contact nozzle occurs which ultimately results in a poor weld.

This problem becomes noticeable when welding with electrodes having a diameter of less than 2.4 mm and is particularly striking when the diameter of the electrode is less than 1.6 mm.

A contact tube has been known which is provided with a guide tube having a helical passage extending into a straight guide duct of an electrode nozzle. The diameters of the helical passage and the guide duct are identical. Contact between the electrode and the contact tube is established when the electrode slides against the wall of the helical passage. Therefore, the part of the electrode extending between the helical passage and the tip - thereby including the whole length of the electrode nozzle - is passed through by the full welding current. This relatively long part is subjected to very intensive heat by the current. The electrode tip becomes weak and there is a risk that it cannot maintain the direction of the guide duct when issuing from it.When the electrode is fed through the helical passage, it must overcome a remarkable frictional resistance and the wear of the guide duct is considerably increased.

It is the subject of the present invention to provide a contact tube constituting such a reliable contact between the contact nozzle and the electrode and causing the electrode to be straightened in such a way that the electrode issues from the contact nozzle in a straight line. According to the invention, the contact tube is characterized by the fact that the guide tube is provided with at least one constriction formed by an eccentric projection on the inside of the guide tube. By means of locally limited constrictions in the guide tube, the electrode is imparted to follow a curved path.In the rest of the guide tube, the position of the electrode is quite undetermined as the diameter of the contact tube is greater than the inside diameter of the contact nozzle and consequently substantially greater than the electrode diameter, which in itself is advantageous as the resistance of motion for the electrode when passing the contact tube thereby becomes very low.

The curved electrode is once again bent when it enters the guide duct of the contact nozzle. The electrode which becomes slightly curved when passing the guide tube, is completely straightened during passage through the contact nozzle. On smoothing out its curvature, the required contact pressure is produced between the electrode and the contact nozzle.

For electrodes having a diameter of 1.6 to 2.4 mm, the curvature to which the electrode is subjected during passing a single constriction and the introduction into the contact nozzle, is wholly sufficient for good contact-making in the contact nozzle.

For an electrode with smaller diameter, however, it is advantageous to make it pass through two constrictions arranged one behind the other. In accordance with a preferred embodiment of the invention, these projections are arranged diametrically. When the electrode passes the two constrictions, its curvature will be increased, which improves the contact-making in the contact nozzle.

The invention will now be described in more detail in connection with the accompanying drawing which shows an embodiment of the same.

Figure 1 shows a section through a welding torch nozzle.

Figure 2 is a section along Il-Il, and Figure 3 is a section along Ill-Ill in Figure 1.

An electrode conduit 1 of a welding hose not shown is inserted into a coupling tube 2 through which the welding current is conducted from the welding hose to a contact tube consisting of a guide tube 3 and a contact nozzle 4. The contact nozzle is screwed into the guide tube for the purpose of easy detachment. The coupling tube 2 is provided on its outside with longitudinal ducts 5 for the supply and withdrawal of cooling water for the welding torch nozzle. These ducts 5 are inter-connected at the front end of the coupling tube via an annular duct 6. The coupling tube is surrounded by a concentric outer tube 7, having a shielding gas duct which terminates in a gas nozzle formed by the outer tube 7 and a tip sleeve 9.

The inside wall 10 of the guide tube is provided with two projections 11, 12, which form two constrictions 13, 14, in the course of the duct. The projections have been formed by diametral and radial impressions 15, 16, into the outside of the hexagonal guide tube 3.

An electrode, not shown here, fed through the electrode conduit 1 and the guide tube 3 is bent twice when passing the two constrictions 13, 14.

When entering the guide duct of the contact nozzle, the electrode is bent once again as the feeding direction is changed again. The electrode thus slightly curved, is sliding along the inside wall of the contact nozzle, thereby establishing very good contact. At the same time, the electrode is straightened out in the straight guide duct 17 of the contact nozzle.

The diameter of the guide duct which is only somewhat larger than the electrode diameter, is smaller than the constricted diameter of the guide tube 3. The inside diameter of the guide tube 3 is preferably 1.5 to 5 times as large as the diameter of the guide duct 17.

If the ratio of these diameters is smaller than 1.5, the curvature of the electrode imparted by the constriction may be too small to ascertain a good contact in the contact nozzle. If the ratio is greater than Sit might be difficult to straighten out the curvature of the electrode in the contact nozzle.

As regards electrodes having a diameter of 1.6 mm and more, it is sufficient to let them pass a guide tube having only one constriction. Because of their larger cross-section, these electrodes are quite stiff and therefore the curvature produced when passing through one constriction is distinct enough to make good contact with the contact nozzle. However, when welding with electrodes having a diameter of 1.6 mm or less, it is preferable to use a guide tube with at least two constrictions as described above.

The electrodes straightened out in the contact nozzle leaves the same completely straight and consequently, the electrode can be directed to the weld point with the utmost accuracy.

The realization of the constrictions of the guide tube is very simple. As the depth of impression can be easily pre-determined, the desired cross-section of the duct 10 of the guide tube 3 can be determined with great accuracy.

The welding torch nozzle is intended first and foremost for use in fully automatic welding equipment, e.g. in connection with robots, where the direction of the electrode between the contact nozzle and the weld point is not permitted to alter.

Claims

1. A contact tube of a welding torch nozzle for a fusible wire electrode, wherein a contact nozzle with a straight guide duct for the electrode is forming the front part, and a guide tube having a larger inside diameter than the contact nozzle is forming the rear part of the contact tube, characterized in that the guide tube (3) is provided with at least one constriction (13; 14) formed by an eccentric projection on the inside of the tube.

2. A contact tube in accordance with Claim 1, characterized in that the contact nozzle (4) and the guide tube (3) are detachably connected to each other.

3. A contact tube in accordance with Claim 1 or 2, characterized in that the guide tube (3) is provided with two projections (11; 12) arranged behind each other.

4. A contact tube in accordance with Claim 3, characterized in that the projections (11, 12) are arranged diametrically.

5. A contact tube in accordance with anyone of the Claims 1 to 4, characterized in that the projections (11, 12) are formed by material that is displaced by radially directed impressions (15, 16) on the outside of the guide tube (3).

6. A contact tube in accordance with anyone of the Claims 1 to 5, characterized in that the inside diameter of the guide tube (3) is 1.5 to 5 times as great as the guide duct (17) of the contact nozzle.

7. A contact tube for a fusible welding electrode substantially as herein described with reference to and as shown in the accompanying drawings.