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Electric Control for the Limiting of Maximum Torque, Specific Application to Rolling-In of Small Condenser Tubes


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An electronic relay for opening the circuit to a universal motor at the time the current reaches a pre-selected value is described. This device serves as a control method for the rolling in of tubes in the process of fabrication and repair of condensers. Because the current to a universal motor depends almost entirely upon the motor load, providing line voltage remains constant, this device permits rolling of the tube until the torque required to rotate the expander reaches a prescribed value, and in this manner produced uniform tube to tube sheet joints. The electronic control consists of a sampling transformer, arranged so that the voltage across its secondary is proportional to the current to the motor. This voltage is applied to ta biased diode which becomes conducting only if the positive passed by the diode is applied to the grid of a gas tube, which upon becoming conducting, is instrumental in operating a relay to open the circuit to the motor. Means are provided for automatically resetting the circuit for subsequent operations. Means are also provided for making adjustments to compensate for differences in tube characteristics when tube replacements are made. The device can be useful in an application where it is desired to limit the maximum torque to be applied.



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