Overhung load adaptors, inset, help ensure the life and reliability of hydraulic pumps in Roadtec's asphalt repaving machines, such as this RX 50B, their largest.
Repaving asphalt roadways requires stripping off the old layers of asphalt before the new surface can be laid. A machine for accomplishing this is the RX 50B cold planer from Roadtec, Chattanooga, Tenn., a leading manufacturer of pavement placement equipment for more than 30 years. The RX 50B cuts an 8-ft wide swath up to 12-in. deep in removing layers of old asphalt at speeds as high as 4 ft per minute. After the old surface has been stripped away, the RX 50B reduces it to granular form and conveys the loose material into waiting trucks for recycling.
The RX 50B is Roadtec's largest cold planer, and it operates on three D-4 size tracks with crab steer, front-track steer, and rear-track steer. Power from the main shaft of the RX 50B's 600-hp Caterpillar diesel engine is transmitted through a hydraulic clutch to a grinding drum through a belt drive. Two hydraulic pumps provide power — one for propulsion, and one for all other hydraulic functions.
To ensure smooth, trouble-free operation of the auxiliary hydraulic systems, two overhung load adaptors (OHLAs) from Zero-Max, Inc., Plymouth, Minn., are employed — one mounted on each side of the engine. OHLAs contain heavy-duty bearings that accommodate side load often present in belt drives. Eliminating side load at the pump shaft can increase pump life and performance. In the RX 50B, one OHLA transmits power to the pump supplying the components that move the ground asphalt to the conveyor. A smaller OHLA drives a hydraulic pump for steering, discharge conveyors, and auxiliary functions.
Chris McSharry, design engineer for Roadtec, reports, "Without the overhung load adaptors, too much stress was transmitted to the pumps' bearings, which could result in premature and costly pump failure." The drive setup McSharry and the Roadtec engineers devised positions the OHLAs 180° from each other. This balances the force applied to the front of the engine's crankshaft.
"The OHLAs give us a solid, permanent mounting surface, which aids in the overall stability of the system," adds McSharry. "By eliminating the stress and overhung loading, both the pump and bearings perform nicely without any threat of failure. The entire drive system runs more freely with the OHLAs and with less power utilized. These cold planers put out a lot of power, so the added stability from the OHLAs really promotes a smoother operating system."
Sensor is ideal for short strokes
A new sensor for feedback of linear position relies on magneto-inductive sensing technology, which makes it compact and ideal for short -stroke applications. Balluff's BIL magneto-inductive linear position sensor provides highly accurate, non-contact continuous positioning information for displacements to 60 mm (2.4 in.). The versatile sensor allows existing motion control systems to be affordably upgraded from end-of-stroke to the flexibility and precision of continuous absolute positioning feedback.
The sensor's magneto-inductive analog technology uses a triangleshaped coil and an associated magnet to provides an accurate, continuous position signal. Because it uses non-contact sensing, it serves as a cost-effective replacement for contact devices, such as potentiometers. At 95-mm long, and with a cross-section of only 10-mm square, the sensor fits into confined areas.
Temperature compensation allows the sensor to provide a linear, analog output signal-for up to 50 mm, or non-linearized for strokes to 60 mm. Voltage and current-output versions are available. Because the sensor head and processing elements are potted, the BIL sensor exhibits high resistance to shock, vibration, and moisture. These characteristics make it ideal for harsh industrial applications where potentiometers and photoelectric sensors would become fouled.