On the Effect of Mixture of Helium into Argon on Properties of Plasma Jet

Abstract

The influence of mixing of helium into argon on some characteristics of plasma jet, spraying phenomena and properties of coatings are investigated.
Spraying conditions are;
Operating gas: Ar (100%), Ar (75%) +He (25%), Ar (50%) +He (50%), Flow rate (total) : 40 l/min Electrical output: 21, 28, 35, 42 kW, Spraying distance: 100 mm, Spray powder: Ni-Cr alloy
Main results arc summarized as follows.
(1) Arc voltage becomes higher with the increase of helium into argon.
(2) Thermal efficiency of plasma jet spray torch decreases with the increase of mixing ratio of helium into argon.
(3) Mixture of helium makes plasma jet angle smaller. Therefore in such a case higher temperature of the jet is kept to a wide range.
(4) Plasma jet, which is operated by argon mixed with helium, has higher heating effect to the object in front of torch.
(5) Flying velocity of particles decreases with the addition of helium into argon.
(6) The structure of Ni-Cr alloy coating becomes finer and adhesive strength of coating is improved considerably by addition of helium into argon.