|This illustration shows the points of entry for leaking shot that can damage a mechanical valve. |
At an iron foundry in Australia, maintenance engineers had been frustrated by the frequent breakdowns of the grit valves on their monorail, eight-wheel shot-blast machines. They diagnosed the breakdowns as resulting from two weaknesses in the design of the valves: the mechanical shot control/shut off valves were seizing when the moving parts were clogged by metal dust; and shot leaking into the valves during shut down.
Leaking valves can fill a blast cleaning machine’s wheel assembly with shot, making it impossible to restart the motor until the wheel housing is cleaned out — an effort that takes the shot-blast machine out of service.
At this automotive foundry near Melbourne, the valve seizures were putting the shot-blast machine out of service as often as two or three times every week. Each breakdown required many hours of labor to get the valve operational, and the foundry lost valuable production time while the machine stood idle. As a manufacturer of four-cylinder engine blocks, the plant had been designed to run several shifts a day, making the shutdown an expensive problem.
|The MagnaValve uses a permanent magnet and electro-magnet to regulate the flow of steel shot for blast cleaning and shot peening machines. |
Seeking a resolution to the problem, the foundry’s maintenance team contacted Blastmaster, a local distributor of Magna- Valve® media flow valves. MagnaValve is manufactured by Electronics Inc.
MagnaValve is a steel media valve that uses a strong permanent magnet and electro-magnet to regulate the flow of steel shot in blast cleaning and shot peening machines. When no power is applied to the MagnaValve, the permanent magnet stops all flow of the shot into the working part. If power to the valve is interrupted for any reason, the valve’s permanent magnet securely holds shot without the need for a secondary mechanical shut-off valve. With power applied, the magnetic field is neutralized and shot is allowed to flow through the valve. After a successful in-house trial period with the Magna- Valve, the foundry ordered eight of the magnetic valves for installation on its shot-blast machines. Blastmaster designed the first retrofit kit for the valves and the foundry built the remaining retrofit kits.
“The customer found the Magna- Valve installation easy and straightforward,” according to Blastmaster’s Nathan Dalton.
Seven months after the installation, Blastmaster reported that the foundry had endured no machine stops or equipment breakdowns; shot flow rate to each wheel was “highly controllable”; and consistent wheel motor loadings ensured shot intensity is always reliable and effective. Also, the operators found that precision electronic flow rate adjustment was possible, as needed, and there were no incidents of shot flooding the wheel housing, nor was there any wear to the valve due to shot flow. Finally, electrical interference from other metalcasting equipment in the plant had not affected the valve or controller functions in any way.