Overhung load adapters keep roadworks to a minimum

To ensure smooth, trouble free operation of the auxiliary hydraulic systems in its cold planers, Roadtec uses overhung load adapters from Zero-Max.

Repaving asphalt streets and highways requires heavy equipment including cold planers, which cut 2.5m wide by 300mm deep swaths in old asphalt surfaces in order to remove them.

These cold planer systems work at speeds up to 125cm/min cutting, granulating and conveying the loose asphalt into waiting trucks for recycling.

By necessity, the power transmission systems in these cold planers are ruggedly designed to handle large amounts of asphalt and to operate for long periods without service or maintenance.

Roadtec, An Astec Company, is a world leading manufacturer of pavement placement equipment for over 30 years.

Used for asphalt removal, its cold planers are designed to provide the optimum balance between horsepower, production and manoeuvrability.

These are versatile machines capable of cutting depths to 30cm and widths from 0.2 to 2.5m.

They also provide side-cutting operations and have bidirectional operation capabilities to achieve down cutting in the reverse direction of travel.

Roadtec's largest cold planer, the RX 50B, operates on three D-4 size tracks providing a 2.5m cutting radius with crab steer, front-track steer and rear-track steer.

It has a two stage covered 86.4cm-wide front load-out conveyor with 50-degree swing to either side providing high volume loading capacity.

Power from the main shaft of the 600HP Caterpillar diesel engine travels into a hydraulic clutch and then to the grinding drum by belt drive.

A second pump on the same shaft provides the hydraulics for propulsion.

To ensure smooth, trouble free operation of the auxiliary hydraulic systems in these cold planers, two overhung load adapters (OHLAs) from Zero-Max are employed, one mounted on each side of the engine.

The larger OHLA (800 series) drives the pump that provides hydraulic pressure to operate the components that move the ground asphalt to the conveyor.

The smaller OHLA (600 series) drives a pump that provides hydraulic pressure for other system operations such as steering and discharge conveyors.

"Without the overhung load adapters, too much stress was transmitted to the pump's bearings which could result in premature and costly pump failure", reports Chris McSharry, Design Engineer for Roadtec.

"We'd heard about the overhung load adapters and did a bearing life scenario for our system using Zero-Max's estimated working life formula from their online catalogue.

The numbers looked good, plus we liked the idea of using a proven off-the-shelf module rather than trying to design a bearing support setup or our own from scratch, which would have been more expensive and time consuming".

The drive setup McSharry and the Roadtec engineers devised positions the OHLA units at 180 degrees from each other.

This balances the force applied to the front of the engine's crankshaft.

The model 600 has two V-belts on one pulley connecting it from the engine, while the model 800 has three V-belts on one pulley connecting it to the engine.

By choosing just the OHLA size needed to do the job, only essential space and weight was used in the engine compartment.

The OHLA 600 used in Roadtec's system has an SAE-B face mount and weighs 13.5kg, and the 800 has an SAE-C face mount and weighs 25kg.

Both sizes feature rugged housings made from 25,000lb/in2 tensile cast iron with shafts of 130,000lb/in2 stress-proof steel.

Both have heavy-duty tapered roller bearings and operate the Roadtec system at a 1-to-1 ratio at speeds up to 2100rev/min.

"The OHLAs give us a solid, permanent mounting surface, which aids in the overall stability of the system", reported McSharry.

"By eliminating the stress and overhung loading, both the pump motor and bearings perform nicely without any threat of failure for either.

The entire drive system runs freer with the OHLAs, and with less power used.

These cold planers put out a lot of power so the added stability from the OHLAs really promotes a smoother operating system".

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