Force Control Gives New Life to Aging Dynamometer

Walk into any manufacturing plant in the United States and you are likely to see 50-year-old men and women working hard. These skilled craftsmen and women have earned the respect of their peers by performing year after year. While 50-year-old workers are commonplace, 50-year-old equipment…not so much. When that equipment happens to be a dynamometer, and it gets shipped back to the manufacturer for review and rebuild, it will invariably get nicknamed “dyno-saur.” This was the scenario that a service center engineer for a gearbox manufacturer found himself in. He inherited the dynamometer when his facility was shipped equipment for the manufacture and testing of gearboxes. His crew used the dynamometer sporadically on smaller projects, but when they tried to load test a cooling tower gearbox, they halted the test due to severe vibration in the dyno. After a complete rebuild, the old dyno (with its new nickname) was better than new, with capabilities that it did not have during its first half-century of work. Upon its return to service, the dyno easily handled the cooling tower gearbox load test, absorbing the full 250 hp at the beginning and ending of the 1-hour test, and absorbing 180 hp throughout the remainder.   A Brief Gearbox History Originally built in 1966, the Force Control dynamometer was used until about 2000 at the company’s main gearbox manufacturing facility. The centralized location handled all aspects of gearbox manufacturing, casting, heat treating, metal cutting, and gear cutting. Pretty much everything that went into a gearbox was manufactured within this facility, and completed gearboxes were load tested with the Force Control dyno. Given the wide range of industries served and sizes of gearboxes manufactured, there is no telling how many load tests it performed in its first 30+ years, but it likely tested products destined for bridges, steel plants, assembly lines, military applications, and more. When the company decided to decentralize operations, the manufacturing and test equipment was shipped to their five regional service centers, including the northeastern US facility, when the service center engineer and his team “inherited” the dyno.    “It was pretty lightly used since 2000,” said a company representative. While load tests were the norm in the 60’s through the 90’s, they are not widely requested anymore. “Most of the industry does a no-load spin test.  This was a 250 hp gearbox, so the customer wanted assurance that it could absorb 250 hp, which this dyno would be ideal for. We want to use it at the limits of its ability, but initially it wasn’t up to the task. We realized that it needed to be serviced, so we called Force Control.” He sent the unit for inspection, and it didn’t take long for the Fairfield, OH team at Force Control to give the brake a new moniker - "dyno-saur." They installed new bearings, seals, drive plates, friction discs, and even added separator springs which will allow the unit to be mounted vertically rather than its normal horizontal orientation.

How Oil Shear Technology Works  Oil Shear Technology is a system of providing a film of transmission fluid between the friction discs and drive plates of a mechanical, multi-disc style friction brake. As the discs and plates are brought together, squeezing the fluid film, it goes into hydroviscous shear. This phenomenon transmits torque through the fluid through laminar flow. This phenomenon is based on the laminar flow of the fluid film between the friction discs and drive plates. The fluid tends to flow in layers with each layer moving at consistently different speeds between the rotating friction disc and the static drive plate. As the pneumatic or hydraulic pressure squeezing the disc and plate together increases, the hydroviscous force of the molecules sliding past each other increases. In other words, torque is directly proportional to pressure on the brake stack. This pressure can be provided by a proportional regulator for pneumatically actuated units, or a proportional regulator or servo valve in hydraulically actuated, more responsive systems. With the fluid layer between the friction disc and drive plate, there is no tendency to stick slip or chatter at very low differential speed, providing a smooth transfer of torque down to zero RPM. The second part of the equation is heat energy that must be dissipated from the system. Using Oil Shear Technology, the fluid is circulated through the friction stack and is cycled out of the brake to a forced lube cooling system. The cooled fluid cools the brake components including the friction material, eliminating the typical degradation found in dry friction brakes. This also allows for a more compact load brake that can, in many cases, be directly mounted to the axle, or output of the test device. The cooling system typically includes cooling oil pumps, motors, filters, over temperature switches, optional hydraulic actuation pump and motor, flow switches, fluid level sight gauge, optional tank heater, and heat exchangers. Heat exchangers can be oil-to-water or oil-to-air. The cooling system can be designed for one load brake or several. Some cooling systems are designed multiple load brakes, such as 4-wheel vehicles utilizing 4 brakes. The hydraulic actuation system can be built into the cooling unit utilizing the same fluid. The rebuild project called for a complete overhaul, replacing virtually all components aside from housings, frame, torque arm, hub and shaft extension.  The brake has 2 brake stacks (tandem stack) where each friction stack has a dynamic brake torque of 3,600 lb. ft. (4,880 Nm) and can absorb up to 225 thermal hp (168 Kw). Separator springs were added to the brake stack to reduce residual drag when oriented vertically.  The dyno was received in Fairfield on March 9 and was shipped back out to the customer on March 26, a turnaround of two and a half weeks.   A Brand New 56-Year-Old Workhorse The service center engineer was impressed with the team at Force Control throughout the process. From the first call through the final delivery, “they were very prompt in replying, gave good answers, and asked good questions to better understand the situation.” Those questions were not only key to understanding how the dyno was to be used, but they also led to some modifications that the equipment did not have in its first half-century of service. While the engineer described how the gearbox load testing would occur, FCII engineers realized that a vertical orientation of the dyno would be most effective. So, they modified the unit during the rebuild, adding separator springs between the friction disc and drive plates to reduce residual drag on the brake stack induced by gravity. With the load applied at a right angle, company employees can now easily position the gearboxes to be tested into position, connect the load to the dyno and commence load testing.   In addition to asking the right questions, the FCII team also gave the right answers. Like when a speedier delivery was requested. “We asked them to expedite the repair, and they were willing to come in on a Saturday to get it done for us and push this project over the finish line.” With the dyno-saur back home, the factory team have not only completed the initial 250 hp gearbox testing, but they’ve accomplished some others as well.  They’re preparing to test a 40 hp unit with the dyno configured horizontally when the gearbox is complete.   Though the manufacture and testing of gearboxes is much different than it was in 1966, these workhorses of American industry are still used across virtually all areas of manufacturing. There are still critical projects - whether they are for bridges, steel mills, stadium domes, or any other heavy load projects that specify a full load test prior to shipment.  The rebuilt Force Control Dyno, aka the dyno-saur, is ready to perform load testing for the next half-century.