DEVICE FOR PLASMA WELDING HAVING A POWDER DOSING MEMBER

ACTING BY GRAVITY FALL

The subject of the present invention is a device for plasma welding with transferred arc, for surfacing with hard powders on workpieces, including a welding torch, a powder dispenser with dosing member, and means for conveying the powder from the dispenser to the weld region. For the plasma welding with transferred arc are of essential impor¬ tance the torch, the powder dispenser with dosing member and their connec¬ tion means, and the main requirements concern the thickness of the surfac¬ ing and the penetration attained in the workpiece.

The known technique offers for this kind of devices various solutions: all these solutions provide for one or more powder dispensers which are materially separated from the torch and are connected to the same by means of tubes across which runs a gas stream. The dosing, namely the control of the delivered rate of powder, takes place at the dispensers. Then the pow¬ der, pushed by the gas stream, after travel along a certain length in the tubes enters the torch and reaches the welding region where the electric arc is generated.

This structure and its mode of operation involves several disadvan¬ tages, namely:

- there is always a noticeable delay between the moment in which the powder leaves the dispenser, which is the moment in which the dosing is carried out, and the moment in which the powder reaches the weld region;

- along the tubes some temporary powder accumulations may take place, and the powder is then suddenly sprinkled in the weld region;

- the accumulations in the tubes may give rise to obstructions which, when are formed, cause the interruption of the operating cycle and may even cause damages to the workpiece.

These drawbacks, even when they have no heavier consequences, hinder a precise control of the delivered rate of powder, and therefore give rise to incorrect, uneven and not repeatable penetrations and thicknesses of the surfacing.

The object of this invention is to avoid or reduce the cited disadvan¬ tages, by providing a device capable of precisely controlling the delivered rate of powder in the very region of its use, by preventing any possible ac¬ cumulation and the consequent interruptions of the operating cycle or the ir- regularities in the delivered rate of powder.

The device for plasma welding with transferred arc according to the invention is characterized in that the powder dispenser is mounted on the torch itself, and that from the dispenser starts a tube directed downwards, towards the weld region, at the initial portion of which there is provided a dosing member intended for regulating the rate of powder which falls by gravity in the weld region.

Preferably, according to a feature of the invention, said dosing mem¬ ber is embodied by constructing said initial portion of the powder descent tube by means of an elastic material, such as for example rubber, on which acts a shutter which causes a controlled throttle thereof.

Thanks to these features, the distance covered by the powder from the dosing region to the weld region is reduced to a minimum, and the travel of the powder along this distance is due to the gravity, not to a gas stream. As a consequence, the delay from the moment in which the powder is dosed and the moment in which it is applied onto the workpiece becomes negligible, and no temporary accumulation or obstruction may take place.

These and other features, objects and advantages of the invention will be better understood from the following description of an embodiment, having the non limiting character of an example, diagrammatically shown in the sole Figure of the appended drawing, which diagrammatically represents a view of the whole device for plasma welding according to the invention, showing some parts thereof in cross section.

In the Figure, number 1 designates the welding torch, which per se may be of any known or special embodiment, and therefore will not be de- scribed in detail. Number 2 designates the dispenser, which is mounted on the torch 1 itself, and number 3 designates the descent tube for the powder, which is directed downwards from the dispenser 2 to the weld region and has an initial portion formed by an $| stic material of the type of the rubber. Number 4 designates the shutter, which acts on the initial elastic portion of the descent tube 3, and is driven by a motor 7; number 8 designates the

weld region wherein an electric arc is generated, and number 9 designates the workpiece onto which a surfacing should be made by means of the pow¬ der contained in the dispenser 2.

In order to supplying the dispenser 2, the powder arrives from one or more main containers (which are not shown, and may be positioned any¬ where) through a connection tube 5; number 6 designates a level sensor, which measures the powder level in the dispenser 2 and cooperates with means (not shown and per se known) intended for supplying the dispenser 2 in order that it cannot become empty; the flow of the supply of powder is therefore controlled by the level sensor 6.

From the dispenser 2 the powder, falling by gravity along the descent tube 3, arrives to the weld region (8) where, by means of an electric arc, is welded onto the workpiece 9.

The rate of powder which comes down on the workpiece is controlled by the shutter 4 driven by its motor 7, by more or less strangling the initial elastic portion of the descent tube 3. The regulation of the rate of powder by means of the modification of the cross section of the descent tube 3 due to its controlled throttle operated by the shutter 4 is very advantageous, be¬ cause it allows accurately dosing the rate of powder which is forwarded to the weld region, without introducing hindrances which might cause possible obstructions.

As it may be understood, thanks to the application of the invention there is provided a welding torch device of a simple structure, sturdy and re¬ liable, which is capable of operating by avoiding at least most of the disad- vantages of the welding torches according to the former technique.

Although the subject of the invention has been described and shown with reference to a specific embodiment, it should be understood that this latter has the character of a non limiting example, and that different modifi¬ cations may be introduced; for example, the level sensor 6 and the motor 7 may be of any kind and, although the dosing member device consisting of an elastic portion of the descent tube 3 and a shutter which throttles in con¬ trolled manner the same represents a preferred solution, also other dosing means could be used.

These and other modifications, and any replacement by technically equivalent means, may be applied within the scope of the appended Claims