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Torque Talk
Industry: Packaging
Application: Box Taper

In the packaging industry, applications for gearmotors can be found in equipment used to automate the assembly, filling, and closing of cardboard boxes. One of these applications is a machine used to automatically close the top and tape it shut. Two Gearmotors drive opposing conveyor belts that pull the carton through the machines closer and tape head assembly.

Issues to consider when specifying a gearmotor in this application include power analysis, shaft loads (at the output shaft), lubrication and sealing system.

Power Analysis: Boxes with varying sizes and weights generate a range of torque loads. This torque data coupled with a range of belt speeds are used to specify the geartrain and motor.

"Our application engineers use one of our calibrated PMDC gearmotors and drives to assist in the power analysis."

With the calibrated unit running at proper speed, the range of loads are determined by measuring the current at the gearmotor at the various load conditions. PMDC motors have a linear relationship between current and torque, so the supplied speed-torque current curve is quickly referenced for torque loads.

Shaft Loads: Radial loading on the output shaft and resulting life expectancy of the bearings needs analysis. Typically three to five inch timing belts are driven via pulley. These pulleys mount directly on the output shaft. Radial loads come from belt tension, separation forces within the gear case, and loads developed from the cardboard boxes as the belts pull the box through the tape head.

Typically we use full compliment needle bearings for maximum life of the output shaft bearings. Our output shafts are carburized in an inert atmosphere to heat treat to a depth of 0.020". This maximizes operating life of the needle bearings.

Lubrication: Since these gearmotors are running continuously during packaging at customer installations, hours accumulate rapidly. Assuming the motor, geartrain and bearing system were sized properly, the life of the gearmotor depends on the lubrication used and the sealing system to maintain the lubrication.

While our competitors typically specify grease lubrication for applications in this equipment, we specify oil bath. Why? Because bearing and gear life depend on it. Bearings keep our gearing right on pitch line, insuring maximum reliability and quiet power transmission. Bison's entire catalog product offering is oil bath lubricated.

Sealing System: The secret in maintaining the oil within the gearcase is where Bison leads the field. Input and output shafts are heat treated and ground in the seal area. Seals are pressed in with custom assembly tooling to bores that are concentric with the shaft. We even measure the roundness of our ground seal areas to monitor the grinding process and prevent multi-lobed problems that can lead to leaking problems.