Electric heating – Metal heating – For deposition welding
Reexamination Certificate
2001-12-04
2004-01-27
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For deposition welding
C219S137710
Reexamination Certificate
active
06683271
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
None known to inventor.
This invention and research and development leading to this invention was not federally funded.
BACKGROUND
1. Field of Invention
This invention relates to using parallel electrical power from the same source to drive the wire feed motor and melt the spray wires, specifically the automatic wire gap adjustments that result.
2. Description of Prior Art
The twin wire arc thermal spray method (arc spray) feeds two wires into respective contact tips that pass electrical current into the wires. The tips are oriented toward each other so the wires extend toward an intersection. A high power is applied across the wires causing an electrical arc to form across the tips of the wires. The electrical current then melts the feed wire portion in the arc zone. A nozzle is located behind and between the contact tips and oriented to emit a gas stream toward the arc zone. The gas stream sprays the molten metal onto the work surface forming a coating. Prior art twin wire arc spray systems use electric drive motors, and use some type of motor control module to adjust voltage to the motor and therefore regulate speed of the motor, the feed motor power is independent of the spray arc power. The feeding of the two wires that are melted by the dc electric current, to make a coating, is the single most important part of the arc spray process. Prior art systems can malfunction due to voltage changes that occur in the spray voltage that are not compensated for in the wire feed system. Under normal operating condition the arc voltage may vary up to plus or minus 2 volt or more with no compensating change in wire feed rate. This is because, prior art systems spraying energy source, is independent (or isolated from), the wire feed motor energy source, therefore, as the arc voltage varies the wire feed rate remains the same. When the arc voltage decreases the wire gap closes and interferes with the gas flow between the wires, which can cause defect in the coating, or lead to system failure. Conversely, as the voltage increases the wire gap widens changing character of the gas flow, which will cause changes in the coating. A voltage increase is not as process damaging as a voltage decrease and usually does not causes a system failure, however it does make the process such that coating character can not be completely controlled. Additionally, prior art arc spray systems have a narrow window of spraying amperages and voltages that work for each type of wire being sprayed, limiting the ability to control the spraying process and the amount of material being sprayed. Also arc starting is a problem with prior art systems, generally the wires are left touching (shorted) at the end of a spray cycle. These wires require being cut to remove the shorted condition, or the process is started allowing the shorted wires to melt and therefore propelling large chunks of hot wire at whatever the gun is pointed at. One prior art system reverses the wires at the end of the spray cycle to create a gap between the wires, if the spray cycle fails to start and the wires become shorted the system must be turned off for the wires to again retract. Teachings of the present invention shows a new method of arc starting and means to precisely control the wire gap between the two wires as the spraying process is active.
OBJECTS AND ADVANTAGES
This invention is a more, effective, economical, and simple method to produce an arc sprayed coating.
Still another object of the present invention is to provide a method to power the wire feed motor with parallel electrical energy used to melt the spray wires, this enables the wire feed motor speed rate to change as the voltage of the spray process changes. The motor speed will increase, as the spray process voltage increases and the motor speed will decrease, as the spray process voltage decreases, thereby controlling the gap between the wires and holding it at a near constant distant.
Still another object of the present invention is to provide a process to power the wire feed motor with parallel electrical energy used to melt the spray wires, this enables the wire feed motor speed rate to change as the voltage of the spray process changes. The motor speed will increase, as the spray process voltage increases and the motor speed will decrease, as the spray process voltage decreases, thereby controlling the gap between the wires and holding it at a near constant distant.
Still another object of the present invention is to provide an unobstructed wire gap for uniform atomization of the molten metal.
Still another object of the present invention is to provide a method for preventing wire shorting which can leads to equipment failure and shut down.
Still another object of the present invention is to provide a method that allows a wide range of spray rate settings for operations and deposit control.
Still another object of the present invention is to provide a method to part the wires during start up of a spray cycle to establish an arc.
Still another object of the present invention is to provide an automatic start up sequence whereas the wire (if touching) will retract to form a gap in the wire then proceed forward to begin the spray cycle.
Still another object of the present invention is to provide a method of repeating the automatic start up sequence until the spraying operation begins.
REFERENCES:
patent: 2669640 (1954-02-01), Outcalt et al.
patent: 3546415 (1970-12-01), Marantz
patent: 4246463 (1981-01-01), Shutt et al.
patent: 5528010 (1996-06-01), Herwig et al.
patent: 5791560 (1998-08-01), Rogers et al.
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