Wooden receptacles – Baskets – Closures
Patent
1997-05-01
1998-05-26
Paschall, Mark H.
Wooden receptacles
Baskets
Closures
219 7616, 21912145, 21912151, B23K 1000
Patent
active
057569584
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an assembly for use in the powder filler material feed system of plasma or laser welding equipment, for instance.
Plasma welding is advantageously carried out using powder filler material in a plurality of welding tasks and particularly in automated welding systems in which the feed of the filler material is otherwise difficult to arrange. Powder filler material has been used for a long time in plasma surfacing and the technology of such equipment is already rather reliable and conventional. Relatively large amounts of powder are consumed in the surfacing process and powder feed to the point being surfaced can be easily arranged with the help of an inert carrier gas, because the feed can be implemented using hoses having a large diameter and usually a short length combined with a high flow rate of the inert gas and the powder. Powder consumption in surfacing may be up to hundreds of grams per minute. In joint welding by a plasma arc, the powder feed rate is very small, typically approx. 15 g/min or even less. The greatest consumption of powder occurs in the fill weldment of a V-butt joint, whereby powder consumption may rise up to 20-50 g/min. As the welding speed with concurrent plasma welding equipment may be as high as 5 m/min, obviously an extremely accurate dosing of filler material into the weldment must be arranged.
The greatest difficulties in powder feed are encountered in feeding the powder to the weld pool via a long and thin channel located inside the welding cable. The diameter of the feed channel in the order of a few millimeters, e.g., 3.5 mm, and the flow resistance of the channel must be overcome by applying a pressure differential between the ends of the powder carrier gas channel inside the cable. Presently, powder-form filler material can be fed over cable lengths of 4 to 5 meters, whereby the required pressure head at the powder entry point into the feed channel is approx. 100-150 mbar. To make the powder flow smoothly through kinks in the welding cable, the carrier gas velocity must be approx. 20 m/s, whereby the powder transfer speed is 5 m/s. In plasma equipment for joint weldments, the volumetric rate of carrier gas required to transfer the powder is approx. 4-5 l/min. A sufficiently high velocity of the powder flow is crucial, because after the plasma arc has been ignited, powder feed into the plasma arc must be commenced rapidly to enable starting the welding without delay. The above-given figures are only exemplifying values for a typical operating environment and subject to variation depending on the dimensions of the welding cable and the actual application. Besides in plasma welding, the same method of powder filler material feed is also employed in laser welding, for instance.
The greatest problem in feeding a powder-form filler material is pulsation of the feed flow which may be related to a number of different reasons. Because of the powder feed via a narrow and bent channel and that the volumetric flow rates of the carrier gas and the powder remain small, the powder tends to accumulate in the bends of the feed channel thus causing pulsation on the flow velocity. Such pulsation of the powder feed flow further causes pulsation of the carrier gas inlet pressure thus degrading the situation. Another factor hindering a steady flow of the powder is the reflection of such pressure pulsations backward via the feed arrangement into the powder hopper. These pressure pulsations promote the flow of the powder from the hopper and also causes bridging of powder to collapse, thus introducing a transient powder pulse of several grams into the feed channel, whereby a weldment defect results and the powder feed rate undergoes a short-term disturbance until the feed system again assumes steady-state operation.
Conventional powder feed assemblies aim at alleviating powder feed problems by using the shortest welding cables possible, whereby the feed channel length is minimized. The channel diameter is made as large as possible and the feed channel infeed point
REFERENCES:
patent: 2851581 (1958-09-01), Libby
patent: 5637242 (1997-06-01), Muehlberger
Paschall Mark H.
Rotaweld Oy
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