Door Manufacturer Saves Big-Time

How One Company’s Belt-Drive Conversion Cut Downtime and Costs

Problem: Hinge Replacement Headaches 

A leading manufacturer of residential, exterior fiberglass doors was having trouble with their dual “lock and hinge” machines. These completely automated machines make precision mortise cuts for the hinges on both sides of their fiberglass-faced doors. Each machine has four cutting heads with 4-inch diameter rotating cutters, an upper and a lower, that simultaneously make the mortise cuts through the fiberglass skin of the door, maintaining equal pressure from both sides to prevent chipping.

These unique machines were custom designed and built. And while they serve their purpose admirably, they also pose some headaches for the plant maintenance staff. The machines’ hinge cutters are powered by an AC motor connected to a belt drive with three driveN sprockets made of aluminum. Being a soft metal, aluminum wears quickly, so the sprockets were being replaced every 4-5 months. This was no easy task, because the sprockets are not OEM parts that can simply be ordered and installed. They are attached with keyless bushings with a bolt and flange insert to secure them. The manufacturer must purchase blank pulleys and have them machined in-house to fit the special keyless bushings, a time-consuming process that draws on the plant’s limited manpower.

Moreover, as the sprocket teeth begin to wear, they start tearing up the belts. So the belts were only lasting a few months before needing replacement. With eight hinge cutters in operation running 20 hours per day, the manufacturer was going through 5 to 6 belts per month, in addition to the cost of replacing the aluminum sprockets on the eight hinge cutters every 4 to 5 months. The annual cost for replacement belts and pulleys on both machines amounted to $5,370 and the labor cost to custom machine the aluminum pulleys was $1,400.

Seeking a solution to the problem, the manufacturer asked Gates to take a look at the equipment and help come up with something a little more robust, keeping in mind that this was a totally unique design.

Solution: Robust Belt Drive Redesign  

A Gates field application engineer was called in to redesign the drive. The goal was to test one drive on a single machine using longer lasting, standard parts that would reduce maintenance time and costs. But there were several constraints standing in the way of achieving that goal, namely:

  • Pulley material
  • Clearance limitations
  • Teeth meshing issues
  • Pulley size
  • Center distance movement
  • Belt length and width

Aluminum pulleys had to go. But there were no steel pulleys available off-the-shelf that would fit the keyless bushing. Pulley size, clearance, and teeth mesh were also issues. In the existing design, the center sprocket meshed with less than six teeth of the timing belt. A larger sprocket would engage more belt teeth, but the sprocket could not exceed the diameter of the cutting blade or it would strike the door as it came through to be cut.

There was also an issue with center distance movement, which amounted to about 1/2″ as the cutting blades moved up and down. That’s too much for a synchronous belt to withstand in order to maintain proper tension. And then there was the challenge of finding a synchronous belt of the proper type and length in a standard, off-the-shelf size. Finally, the belt had to be wide enough to register on the overhead electronic sensors used to detect belt failures.

With the initial design as a focal point, an intense collaborative effort took place between the manufacturer, Gates, and the Gates distributor. Everyone had a chance to discuss all the nuances of the design, giving the manufacturer confidence to give it a try.

Keeping within the required parameters, the new Gates drive incorporated steel sprockets pre-machined by the Gates MTO (Made-to-Order) Metals department to fit the keyless bushings. Eliminating the need to machine pulleys in-house freed up maintenance staff time. And replacing aluminum with steel solved the pulley wear and belt wear problem. The Gates drive incorporated a synchronous PowerGrip® Twin Power® timing belt in a standard off-the-shelf size.

The manufacturer has not had a single belt failure since implementing the new design.

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