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Actuator in the Mix
Provides enhanced performance, reliability for volumetric mixer
Al Presher, Contributing Editor -- Design News, June 23, 2008
Mobile volumetric mixers from Reimer International (http://rbi.ims.ca/5716-558) are capitalizing on rotary actuator technology to reduce maintenance and increase the effectiveness of systems used for cost-effective, on-site production of concrete. All of the components in the mix, including stone, sand, cement and water, are loaded into separate compartments on one truck-mounted unit. Components are then metered and mixed into fresh concrete in a special auger as the mobile mixer unit is being discharged.
A helical hydraulic rotary actuator from Helac Corp. (http://rbi.ims.ca/5716-559) is part of the lifting mechanism that lifts the auger and carries a discharge chute on the end. The auger rotates a full 180 degrees and provides greater speed of movement compared to the previous system that utilized a cylinder with a chain and sprocket linkage assembly.
Allan Spreeman, a production engineer at Reimer, says the company used several methods to control the auger and discharge chute. It started with a manual system, changed to a system that utilized chains and motors and finally settled on a double-rodded cylinder mechanism and assembly. Due to the corrosive environment of the application related to mixing concrete and the fact that many linkage points in the cylinder created wear points, maintenance issues continued to be a problem.
“Chains stretch, sprockets wear and with the cylinder rod exposed to the concrete grit, we encountered a series of ongoing field maintenance problems,” says Spreeman. Scratched cylinder rods could also introduce debris which would contaminate the hydraulic circuit and potentially create other leakage problems.
An important benefit of the new rotary actuator system included the full 180-degree rotation of the chute, what Reimer calls “power swing,” compared to 140-degree rotation with the older system. But even more importantly, the speed and responsiveness of the power swing makes it easier and more convenient for the operator, compared to the cylinder-based system which slowed the movement of the chute. And although the price of the actuator reflects higher initial system costs, there is less installation labor required and the total number of parts in the system is dramatically reduced.
System reliability is key for Reimer, since its goal is to create an efficient, load-sensing hydraulic system, using a simple design and constant flows to ensure a consistent mix. The system also provides a wireless remote control that allows a single operator to adjust both the mix and discharge rates with ease. One operator does the work of a batch plant operator and mixer operator.
After the initial phases of the project where Reimer provided basic application data including weights, pressure readings and mounting information, the process of integrating the rotary actuator proved to be extremely straightforward. Compared to the design of the previous system, which included a variety of mechanical components, the rotary actuator provided a turnkey solution by comparison.
The Helac L20 series actuator used in the system uses sliding spline technology that offers high load-carrying ability, high torque output, shock resistance and zero leakage in a compact package. Maximum corrosion protection for vertical-mounted applications is achieved using an exclusion seal and thrust bearing configuration.
After initial testing and adjustments to size the system properly, it has performed almost flawlessly and the new system has helped eliminate expensive maintenance issues in the field. Since ordering the first actuators in November 2003, the return rate on the rotary actuators has been less than 1 percent.
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