Plasma spray apparatus for coating irregular internal surfaces

A plasma spray apparatus adapted for coating an irregular internal surface of a tubular object in which the spray apparatus has a nozzle for directing the coating material on the internal surface of the object and wherein a central spray axis drawn through the center line of said nozzle is adapted to be maintained perpendicular to an impingement point on the surface of the tubular object being coated, which apparatus comprises;

• (a) a plasma torch for spraying a plasma coating on the internal surface of the tubular object, the torch having a spray nozzle adapted to provide a spray to an impingement point on the internal surface of the tubular object;
• (b) first arm means with an inner end and an outer end, the inner end fixedly attached to the torch, the length of the first arm means being such that the central spray axis drawn through the center line of the nozzle can be disposed perpendicular to the internal surface of the tubular object while the nozzle is maintained a fixed distance from the internal surface of the tubular object without interference with the internal surface of the tubular object as the impingement point moves over the internal surface;
• (c) second arm means with an inner end and an outer end, the inner end fixedly attached to the outer end of the first arm means with the outer end adapted to be outside of the enclosed volume of the tubular object as the impingement point moves over the internal surface of the tubular object;
• (d) third arm means with an inner end and an outer end, the inner end fixedly attached to the outer end of the second arm means with the outer end adapted such that the central spray axis can be disposed perpendicular to the internal surface of the tubular object while the nozzle is maintained a fixed distance from the internal surface of the tubular object without interference of the third arm means with the tubular object as the impingement point moves over the internal surface, wherein the first arm means, the second arm means, and the third arm means are fabricated as a unitary structure;
• (e) moving and rotating means attached to the outer end of the third arm means for moving the first arm means, second arm means, and third arm means to effect movement of the spray nozzle in a direction parallel and in a direction perpendicular to the longitudinal axis of the tubular object, and for rotating the spray nozzle about a rotational axis so that the central spray axis is directed perpendicular to the impingement point on the internal surface of the tubular object;
• and
• (f) coordinating means for coordinating the movement and rotation of the spray nozzle as the object is rotated about its longitudinal axis such that the central spray axis is maintained substantially perpendicular to the internal surface, the distance between the spray nozzle and the impingement point is maintained substantially constant, and the rate at which the impingement point moves over the internal surface is maintained substantially constant.