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Coil Handling & Compacting Machine Required Redesign & Reconfiguration
When a major US machine manufacturer experienced a challenge at its China wire drawing mill from a malfunctioning coil compacting system, the engineers at The Hope Group responded with a machine assessment that led to a redesign and reconfiguration to bring the equipment into its original design specifications.
The coil handling and compacting machine, which compresses large coils of wire and then secures them with either wire binding or steel strapping, was not working correctly. The machine had developed an inconsistent compacting force and coil positioning. In describing the problem, the chief engineer at The Hope Group described the problem as “the ‘hands’ of the compactor would come together to squeeze the coil, but the force of the one ‘hand’ would push the other out of position.”
Client engineers and the engineering team at The Hope Group worked together designing needed changes to the hydraulic control system used on the compactor. Both sides of the compactor would come together to squeeze the coil, but the force of one side would periodically push the other out of position. Additionally, force control was erratic due to inconsistent pressure control. Both issues combined to produce coils with inconsistent compaction and resultant potential damage to the coil.
After analyzing the circuit and the power unit, the first issue of inconsistent positioning was determined to be a result of using large DIN cartridge valves, whose performance is susceptible to dirt and debris in the system. To match the filtration level of the hydraulic power unit, the team chose low leakage poppet style pilot operated check valves to replace the DIN valves. In order to meet the expected flow rate requirements two poppet PO checks were installed in parallel for each DIN valve.
Inconsistent Pressure Control
The issue of inconsistent pressure control was found to be caused by over pressurization of the system during initial cylinder approach. Specifically, the cylinders were run in regeneration mode for the initial approach and dropped out of regeneration mode for final compaction. However, due to system resistance the pressure required for regeneration mode was greater than that required for final compaction. Because control of pressure was being accomplished by a proportional pressure relief valve – lowering the pressure set point at the time of compaction resulted in periods of instability as the valve attempted to lower the system pressure to the desired level – adversely affecting compaction force.
The solution was achieved with the replacement of the existing valves with faster, larger Parker proportional directional and relief valves, along with a wholesale redesign of the manifold, simplification of the hydraulic circuitry, and enlargement of associated piping and hoses, which resulted in lowering regeneration system pressure to levels well below compaction pressure, greatly improving compaction reliability. Once the redesign was completed, the hydraulic control system was assembled, tested and packed for shipment to Shanghai, China.