Method of cutting carbon and alloy steel

TLDR: In this paper, a programmable logic controller (PLC) is used to control the load on the blade or spindle motor of a steel-cutting saw for optimizing blade life, while at the same time reducing cutting cycle time and protecting the blade, gearbox and spindle hub from stresses caused by binding and jamming of the blade while cutting into a steel member.

Abstract: The present invention discloses a method and apparatus for controlling the load on the blade or spindle motor of a steel-cutting saw for optimizing blade life, while at the same time reducing cutting cycle time and protecting the blade, gearbox and spindle hub from stresses caused by binding and jamming of the blade while cutting into a steel member. Using a programmable logic controller (PLC) to implement the method, the load current drawn by the spindle motor is sensed and compared to a reference value representing the desired optimum operating current. As the saw cuts through a steel member, variations in hardness cause the spindle motor current to fluctuate accordingly. The blade is advanced into the steel member by an electric servomotor. The rate of advancement of the blade is controlled by the PLC. As the current on the spindle motor increases, the PLC is programmed to reduce the rate of advancement of the blade, thereby reducing the load on the blade. The blade loading and spindle current are directly proportional. The rotational speed (RPM) of the blade is also maintained constant by a variable frequency motor drive that powers the spindle motor. The PLC does not vary the RPM of the blade. The operator selects the blade speed as a value in the range from 3 to 85 RPM, which is the reference value maintained by the variable frequency drive. The feed rate is the variable that is controlled by the PLC, by which the load current of the spindle motor is maintained relatively constant. The PLC also compares the current to a preset maximum value, normally around eighty percent of full load amps of the spindle motor. Upon reaching the preset maximum, the PLC removes the run command signal to the variable frequency drive, causing the spindle motor to stop abruptly. Response time for clearing an overload condition is approximately 10 milliseconds, or one-tenth of the time required to clear the overload using conventional analog current sensing and shut-off devices.