For nearly 50 years, AJD Forest Products has been producing top quality industrial lumber for the Lake States region. Located in Grayling, Mich., the company has earned a reputation for supplying high-grade red oak, hard & soft maple, aspen, ash, and basswood.  The mill processes 1,700-2,000 logs, or 70,000-90,000 board feet of lumber a day, but constant maintenance and adjustment on their stacker and chain conveyor brakes were forcing unplanned downtime.  And that was cutting into the sawmill’s profits. Since retrofitting their dry-friction, Stearns brakes with Magnashear motor brakes featuring Oil Shear Technology, AJD has eliminated brake maintenance and adjustment, and thus unplanned downtime.  Now with the mill running smoothly, oil shear brakes are helping AJD Forest Products cut more boards without slashing profits.

A Critical Path Approach

A conveyor chain feeds logs into a sawing station which cuts each side of the log.  The log then continues down a conveyor until reaching a backstop, tripping a sensor that engages the motor and releases the brake on a second conveyor which is perpendicular to the first. This second chain conveyor incorporates lugs. Once engaged, logs travel approximately 4 feet or so to another conveyor which carries the lumber onto further processing.  After depositing the log, the lugs trip another sensor which engages the brake and stops the motor, which in turn stops the chain until the next log strikes the backstop, at which point the process repeats itself.  

The drive motor was originally fitted with a dry-friction Stearns brake. However, continual activation of the brake (1,400 and 2,400 cycles per day) was creating a maintenance nightmare. On average, brake discs were being replaced every three weeks or so. Furthermore, the brakes’ heat of engagement was burning up transformers leading to more failures and unplanned downtime.

“We were burning up the transformer because the brake pads would get so hot that the transformer would melt,” said Electrical/Automation Technician Damian Fleischmann.  “The repetition and the friction were causing so much heat that it was just burning everything up inside.”

Replacing the brake discs was challenging because the discs first needed to cool-off as to not burn the technicians replacing them.  

“We’d wait 5 or 10 minutes at least for them to cool down, “recalls Fleischmann, “then it was another 10 or 15 minutes to swap out the pads. If the transformer that steps down the 480 V from the motor to the 240 V or 120 V for the brake is damaged, then the process takes a lot longer.”

After tallying up the cost of brake pads, the labor to replace them, the inventory cost of stocking complete Stearns brakes in case the entire transformer assembly failed, and the unplanned downtime that resulted from brake failures, the team at AJD began searching for a better braking mechanism. In addition to the cost of brake pads, the labor to replace them, and the cost of complete spare Stearns brakes stocked in case of total failures, unplanned downtime meant lost production. Clearly there had to be a better way.

When considering their options, the mill production manager recalled a Force Control Oil Shear Brake in another location of the mill that was operating smoothly without downtime for maintenance or adjustment.  After conferring with local manufacturer’s representative, Dave Dilworth, they purchased a MSB6 size Magnashear which was quite easy to install.

“We have a mechanical starter on ours,” said Fleischmann. “I wired up the brake through an auxiliary contact with the control voltage, so that once the motor is engaged, the brake is disengaged. It is instantaneous on both.”

Fleischmann recalls that when he first saw the proposal, he was a little worried about the price.  But after six months of continuous uptime, he was convinced.  Although he did not perform a formal ROI calculation, he figures “it was a year payback at most, probably sooner.”  And it is still operating, maintenance-free 3 years later.

“If we ever have another project that requires repetitive braking, we’ll definitely use Force Control” he said.

Stacking Up the Benefits

The installation that Fleischmann’s production manager recalled was a stacker.

“We have the Force Control brake on a lift at our stacking station” recounted Fleischmann. “Boards are presented to the stacker individually, and the stacker slides 6-8 boards onto the lift.”  

The lift then drops down anywhere from an inch and a half to three inches depending upon the height of the boards.  It drops below the sensor to allow space for the next row of boards to slide onto the lift.   

Occasionally, the boards are two-by-fours, sometimes two-by-sixes, or two-by-eights, but they can also handle three-by-sixes and three-by-eights. Therefore, the weight of the lift varies, but the reaction time and positioning of the Force Control brake is precise each time. Depending on the line speed, the lift may cycle 75 - 100 times an hour.  

With the old braking system, engaging the brake would generate heat, causing the friction material to glaze-over. Consequently, this would cause variance on the stopping distance which lead to necessary air gap adjustments. Brake pads would also wear out and require replacement.  All of this maintenance and adjustment meant the stacker was out of commission and the mill would remain shut down until the brake could be repaired or replaced.

The MSB6 currently installed on the lift has been in service since June of 2018 and requires virtually no maintenance.  “Other than changing the fluid every six months, you don’t have to do anything to them,” said Fleischmann.

Eliminating maintenance and increasing uptime is important any time, but it is even more important when faced with worker shortages.

“The maintenance on the old brakes was immense and a huge headache,” recalls Fleischmann, “but since we’ve installed the Force Control Brakes, we haven’t had to touch them.”  That’s high praise from someone who knows that the best kind of maintenance is no maintenance.  

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