Brakes for Cranes0 pages

Overhead Cranes

SITE REVIEW

Brakes
for Cranes

MagnaShear motor brake
from Force Control Industries.

Paint finish company opts for
oil shear brakes to reduce crane
maintenance and downtime.

Linetec previously employed dry brakes in its hoist systems,
which required more than 120 hours per year in maintenance.

Oil shear brake alternative

P

aint finish specialist Linetec, Wausau, Wis., employs a
computer-controlled hoist system to guide material through the anodize
process, eliminating any chance of manual variations in pre-cleaning,
etching, anodizing, coloring, or sealing. Each of the eight cranes in the
plant includes a 3-hp trolley motor and 15-hp hoist motor. Every motor
performs roughly 2,000 moves per shift.
The hoist system’s dry brakes were mounted on each motor for stopping
and positioning. Since these brakes have a sacrificial wear surface—the
disc—each one had to be checked weekly. In addition, each brake was
rebuilt on a quarterly basis, requiring disassembly, replacement of the disc
and solenoid, check the gap, reassembly, and start it running again.
Linetec estimates conservatively it was spending 124 hours per year on
preventive maintenance. In addition to time, the plant was spending about
$8,000 per year on maintenance parts. Because all work on the brakes
was accomplished without removing them from the motors, scissor lifts
were required to reach the motors nearly 30 feet in the air. At that height,
the ambient temperature is elevated throughout the year—especially in
summertime when the heat routinely registers in the triple-digit range.
Most maintenance work was scheduled for the weekend when the
plant was idled, but unscheduled failures while the plant was operational
created problems of another sort.
“If the brakes failed when the line was running, we’d have to shut down
production, then go get a scissor lift and the necessary tools and materials,”
said Jon Brubacher, maintenance supervisor. “Then we’d do the rebuild…It was
quite time consuming, and the line is down throughout the entire process.”
Downtime was calculated at $1,500 per hour, and these costs escalated
quickly for the company.
16 Industrial Lift & Hoist

When Bob Rhode from Linder Electric suggested an alternative
braking technology, Brubacher was intrigued. Rhode and Dave Price
of Industri/Motion brought products from Force Control Industries to
Linetec to demonstrate the differences between traditional brakes and oil
shear technology.
Linetec placed an initial order for a single MagnaShear MSB6 motor
brake, which was put into service as a trial. After six months with virtually
no maintenance and no failures, the Linetec team began formulating a
plan for a capital expenditure to replace all of its dry brakes.
“We’re very pleased with the performance of the Force Control brakes,”
said Brubacher. “We have not had a single issue with them since they
were installed. With oil shear brakes on all of our cranes and hoists, we’ve
reduced downtime significantly and increased our productivity.”

How oil shear technology works

Normal dry clutch brakes employ a brake disc or pad to engage the
load. Having no good way to remove the heat caused from engagement
between the disk and plate, this material must absorb the heat. Extremely
high temperatures will eventually degrade the friction material. As the
surface wears away and begins to glaze, the spring force is also reduced,
causing the ensuing torque fade. This leads to positioning errors, which
require adjustment or replacement of the friction surface.
By comparison, oil-shear technology includes a fluid film that flows
between the friction surfaces. As the brake is engaged, the fluid is compressed.
The automatic transmission fluid (ATF) particles in shear transmit torque to
the other side. This torque transmission causes the stationary surface to turn,
bringing it up to the same relative speed as the moving surface. Since most
of the work is done by the fluid particles in shear, by the time the surfaces
actually meet or “lock up,” wear is virtually eliminated.
In addition to transmitting torque, the ATF also helps to dissipate
heat, due to a patented fluid recirculation system. Along with torque
transmission and heat removal, the fluid also serves to continually lubricate
all components, which extends service life.  Oil shear technology also
provides a “cushioned” stop that reduces shock to the drive system. Unlike
dry clutch brakes, the enclosed oil shear system is impervious to external
elements, such as wet, dusty, or dirty environments. Since the layer of oil
eliminates wear, the MagnaShear motor brake provides a long service life.
For Linetec, replacing its dry brakes with oil shear brakes has eliminated
wear and adjustment, increased uptime, and saved them money.

industrialliftandhoist.com • November 2012