Service Trip to Rebuild and Test Caliper Brakes
DP World operates a potash terminal in Saint John, New Brunswick. The current ship loader at this facility went into operation in the early 1980s, using two Johnson 58HBA caliper brakes on the low-speed side of the winch system. Very limited maintenance had been performed on the brakes over their lifetime, and testing found them to be in a poor state of repair. Time was of the essence, as there was a ship scheduled to arrive in a few weeks. In that short time frame the brakes had to be made functional, load testing had to be done, and the ship loader had to be put back in service.
Due to time constraints, it was decided that the best course of action was a partial rebuild of the brake, leaving the exiting base/frame in place, reusing the existing levers, but replacing the actuators, pins, toggle levers, shoes, and all additional hardware.
The existing brakes were disassembled, and the bases and levers were cleaned up. The bases appeared to be in fair condition for the age, with pin bores being relatively corrosion free and not deformed. It was noted that the old shoes had minimal lining wear, which is to be expected for brakes used only for holding or emergency use. The brake disc had some corrosion and heat checking but was in serviceable condition. The culprit of the partial failure appeared to be the actuators, which were original to the brake and non-functional. This, combined with possible seizing from years without any lubrication, is the likely cause of the brake’s partial failure.
Once parts arrived, work proceeded on rebuilding the brakes. All new parts were lubricated and assembled easily. The brakes were then adjusted so proper air-gaps were achieved, while maintaining correct toggle lever orientation. Once fully assembled, the actuators were uncaged using a portable air tank, as the existing air system was linked to the movement of the winch.
Once the actuators were uncaged, the general function of the brakes was tested. They functioned well without binding, and it was confirmed that they were able to hold the weight of the empty ship loader boom. Using the air pressure regulator on the air line, the pressure was dropped to 75 psi, and the winch was operated in order to burnish the linings. From there, the pressure was further dropped to 60 psi to increase the braking force for further burnishing. Considering the amount of torque being generated at this pressure, it was determined that burnishing was complete and the regulator was returned to the full 120 psi to assure full release of the brakes while the winch is in operation. As a final step, full load testing is necessary to ensure the brakes are providing the correct torque and are able to function in an emergency capacity. Site staff assured that this testing would occur before the ship loader was put unto full operation.
This was a good example of the longevity of Johnson caliper brakes, which also showcased the ability for new parts to be retrofit to an old design to achieve a functional, safe, and reliable emergency braking system. It also highlights the importance of regular maintenance and training of maintenance staff, which can prevent a situation like this entirely. This great result was achieved in a little over a week from when the problem was first noticed, with parts being shipped within a day, a Johnson Industries technician being dispatched a few days later, and a total of 3 days on site to completely rebuild and test the braking system.
Leave a reply