Abstract:
A method and apparatus for coating the outer surface of a workpiece comprises disposing a workpiece in a fixed position along an axis and rotating a thermal spray gun around the axis on a support with a thermal spray thereof directed towards the axis. The powder, fuel and oxygen are rotatably coupling to the gun and the thermal spray gun and the support are moving along the axis while rotating.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method and apparatus for coating the outer surface of a workpiece. 
     Thermal spraying, also known as flame spraying, involves the heat softening of a heat fusible material, such as a metal or ceramic, and propelling the softened material in particulate form against the surface which is to be coated. In many instances where a three dimensional object is to be coated, the thermal spray gun is held in a fixed position and the object is moved relative to the gun in order to coat the entire outer surface. 
     The ability to move the workpiece while the gun is stationary is possible in many situations, however, it is impractical where the workpiece is large in size or where it is desired to recoat a workpiece while it is still mounted in place, for example, the landing gears for an aircraft. The difficulty of moving the landing gears of an aircraft while connected to the aircraft is evident. 
     There is therefore a need for an apparatus and method for coating the outer surface of a workpiece while the workpiece is held stationary. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to provide an apparatus and method for coating the outer surface of a workpiece wherein a thermal spray gun is rotated around a workpiece disposed at the axis of rotation of the thermal spray gun. 
     Another object of the present invention is to provide a convenient and simple method and apparatus for supplying the oxygen, fuel and powder to the thermal spray gun while it is rotating. 
     These and other objects of the present invention are achieved in accordance with the present invention by an apparatus having a support mounted for rotation about an axis and having a fixture mounting a thermal spray gun with a coating spray thereof directed towards the axis, whereby a workpiece disposed at the axis will be coated thereby. The thermal spray gun has inputs for powder, fuel and oxygen and a supply line for each of the powder, fuel and oxygen is rotatable with the support for supplying the powder, fuel and oxygen to the thermal spray gun. At least one coupling having a first portion rotatable with the support and a second portion having ports for receiving the powder, fuel and oxygen communicates the powder, fuel and oxygen to the corresponding supply lines. A motor rotates the support. 
     In order to coat the outer surface of a workpiece, such as a landing gear which is of substantial length, the apparatus further comprises a mechanism for moving the support, supply lines, coupling and motor parallel to the axis to effect a coating of an outer surface along a length of the workpiece. 
     In accordance with the invention, in a particularly advantageous commercial embodiment of the invention, the thermal spray gun is a high velocity oxy fuel spray gun. Such a gun is disclosed in U.S. Pat. No. 4,865,252, the disclosure of which is incorporated herein by reference. 
     In accordance with the method of the present invention, a workpiece is disposed in a fixed position along an axis and a thermal spray gun is rotated around the axis on a support with the thermal spray thereof directed towards the axis. Powder, fuel and oxygen are rotatably coupled to the gun and the thermal spray gun and the support are moved along the axis while rotating. 
     Another object of the present invention is to provide an apparatus and a method for the rotation of a thermal spray gun with powder injection for the purpose of applying a coating on to a stationary part outer diameter. 
     In accordance with the present invention, a rotary coupling with five channels, including water in, water out, fuel gas, oxygen and air cooling and with an additional center feed-through for powder flow, has a center shaft rotating within a stationary housing. The shaft assembly is driven via a belt drive by an electric motor to create a constant speed rotation. A manifold block attaches to the center shaft to provide a convenient hose connection point. The process gun is fixtured to the device in an arrangement that causes the gun to be aimed towards the center of rotation. The fixturing scheme allows the adjustment of the gun distance from the center line to optimize the spray distance based on a part diameter. 
     A counterbalance is fixtured opposite the gun for dynamic balance while rotating. Powder is delivered through the center of the rotating shaft and a separate stainless steel tube is attached to the manifold connection block. The tube rotates with the device and extends beyond the rotary coupling. The rotary powder feedthrough consists of a two part stationary housing. An O-ring provides a positive gas tight seal and a set of compressed felt packings protect the O-ring from abrasive powders. A port is provided to create a positive gas flow through the felt packings. The end cap includes the hose connection and provides compression and retention for the felt packing. 
     In accordance with the method of the present invention, the device is mounted onto a robot or other device that provides a linear motion along the center of rotation. The device is positioned above the workpiece, for example a shaft, to be coated and the gun is lit. The device is then rotated with the gun lit and powder is introduced and the entire rotating device is advanced slowly over the shaft creating a desired coating. 
     The present invention allows for the thermal spray coating of outer diameters that cannot practicably be rotated. The apparatus and method eliminate the requirement for large complex part handling equipment and related room and exhaust. 
    
    
     These and other features and advantages of the present invention will be disclosed hereinafter in more detail with reference to the attached drawings, wherein, 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of the apparatus according to the present invention for carrying out the method according to the present invention; 
     FIG. 2 is a detailed perspective view of part of the apparatus shown in FIG. 1; and 
     FIG. 3 is a detailed sectional view of the couplings of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, the apparatus according to the present invention for coating a workpiece W comprises a support  5  which supports a thermal spray gun  7  and a counterbalance  8  which is mounted for rotation on a shaft about an axis of rotation x. The support  5  is rotated by motor  2  to rotate about the axis of rotation x. Supplies for the thermal spray gun, as well as cooling air and water, are provided through rotary couplings  3  and  4  and supply lines  6 . A robot  1  is operatively connected to the elements  2 - 8  to move those elements linearly along axis x to effect a coating of the entire desired length of the workpiece W. 
     Referring now to FIG. 2, the apparatus elements  2 - 8  of FIG. 1 are shown in more detail. 
     The motor  2  has a shaft  21  to which a pulley  22  is rotably connected for driving a belt  23  which is connected to pulley  24  and which is connected to support  5  to rotate same relative to the stationary housing portion of the rotary coupling  4 . 
     The rotary powder coupling  3  has a powder input  30  and a connecting line  31  to the rotary coupling  4  which has 5 channel inputs and outputs  40 A- 40 E as will be explained. Channel  40 A is an input for water, channel  40 B is an input for hydrogen fuel gas input, channel  40 C is a water outlet channel, channel  40 D is an oxygen input channel and channel  40 E is an input for cooling air. 
     The support  5  includes a manifold connection block  51  which connects to a tubular support block  52  having tubular members  53  and  54  connected in holes therein and having further tubular support blocks  55  and  56  connected thereto and having tubular fixture members  57  and  58  depending downwardly therefrom. 
     Tubular fixture number  58  is connected to the thermal spray gun  7  and tubular fixture number  57  has counterbalance  8  connected thereto. The counterbalance dynamically balances the gun while rotating. 
     Powder is fed via the tubular numbers  54  and  58  to the thermal spray gun, while lines  6  carry water in, hydrogen fuel gas in, oxygen in and cooling air in and carry water out. 
     Workpiece W is held in place by a fixture  100  at the center of rotation of holder  5  so that the thermal spray gun rotates around the workpiece W spraying the spray S at the outer surface thereof. 
     FIG. 3 shows the rotary couplings  3  and  4  in more detail. 
     The rotary powder coupling  3  has the powder fitting  30  which feeds powder line  31  which rotates within a housing having an upper portion  35  and a lower portion  36  with felt packing  32  therein around the powder line and sealed with an O-ring seal  34 . The coupling also has a seal pressure port  33 . The tube  31  rotates with the device and powder is fed therethrough. The O-ring  34  provides a positive gastight seal and the set of the compressed felt packings protect the O-ring from abrasive powders. Post  33  is provided to create a positive gas flow through the felt packing and the end cap includes a hose connection and provides compression and retention for the felt packing. 
     The rotary coupling  4  has a stationary outer housing  41  and a rotatable inner member  42 , which is rotatable by means of bearings  46  and  47  at either end of the housing  41 . The rotatable member  42  has grooves  43 A- 43 E which are mounted in alignment with connection ports  40 A- 40 E respectively and which are sealed from each other by means of O-rings  40 A- 40 J. 
     Each of the grooved areas  43 A- 43 E are in communication with channels  60 A- 60 E respectively, of which only channels  60 A and  60 E are shown. Channels  60 A- 60 E are in communication with connection ports  61 A- 61 E which are in turn connected to lines  6 . Powder outlet  62  feeds through block  52  and tubular elements  54  and  58  to feed powder to the gun  7 . The rotatable member  42  is connected to the block  51  for rotation therewith using O-rings  63 A- 63 E to maintain a seal along the channels  60 A- 60 E. 
     The housing  41  has weep ports  40 A- 40 D and the tube  31  is connected in the member  42  to stainless steel tube  64 . The tube  64  is connected to manifold connection block  51 . 
     In operation, the device is mounted onto the robot to provide a linear motion along the center of rotation. The device is positioned above the shaft to be coated and the gun is lit. Device is then rotated with the gun lit and powder is introduced and the entire rotating device is advanced slowly over the shaft creating a desired coating. 
     The rotating coupling with the five channels and the additional center feed through for powder supplies the necessary fuels to the gun and provides for a water output. The center shaft rotates within the stationary housing and the shaft assembly is driven via the belt drive to create a constant speed rotation. The manifold block attaches to the center shaft to provide a convenient hose connection point. The process gun is fixtured to the device so that the gun is aimed towards the center of rotation and the fixturing allows the adjustment of the gun distance from the center line to optimize the spray distance based on the part diameter.