TL;DR
Low roller grinding force means the hydraulic tensioning system has a leak or the accumulator nitrogen charge is low. Check the accumulator pre-charge before looking at the cylinder seals.
What you might see
- roller grinding force below setpoint
- hydraulic accumulator pressure dropping fast
- oil leak detected at tensioning cylinder seal
- one roller not making full contact with table
Likely causes
Hydraulic accumulator nitrogen pre-charge pressure below the required value
Tensioning cylinder rod seal leaking, causing oil loss and pressure drop
Hydraulic pump delivering below the rated pressure
Tensioning system control valve sticking or leaking by
Required tools
- Nitrogen charge kit with regulator
- Calibrated hydraulic pressure gauge
- Cylinder seal replacement kit
- LOTO kit
Safety first
- Use only dry nitrogen for accumulator pre-charge. Never use air or oxygen.
- Lock out the hydraulic power unit and bleed all pressure before opening any tensioning cylinder fitting.
- High-pressure hydraulic oil can inject through skin. Never use bare hands to find leaks.
Procedure
- 1
Read the tensioning hydraulic pressure from the circuit gauge. Compare to the setpoint and the accumulator working range.[1]
- 2
Check the accumulator nitrogen pre-charge pressure with a nitrogen charge kit. Pre-charge must be above the minimum specified value.[1]
- 3
If the pre-charge is low, recharge the accumulator with dry nitrogen to the specified value using a calibrated regulator.
Warning: Use only dry nitrogen for accumulator pre-charge. Oxygen or air in the hydraulic accumulator is an explosion risk. - 4
Inspect the tensioning cylinder rod and seal area for oil seeping. A wet rod confirms a seal failure.
- 5
If the cylinder seal is leaking, stop the mill and lock out the hydraulic power unit. Replace the cylinder seal.
- 6
After repair, pressurize the tensioning system and hold for 30 minutes. Confirm no pressure drop before restarting.
Sources
Loesche Loesche LM Series Vertical Roller Mill (VRM) general technical documentation, Loesche
Loesche VRM hydraulic system and accumulator maintenance documentation (general)
More guides for Loesche Loesche LM Series
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VRM vibration almost always means the material bed on the grinding table is too thin. Increase the dam ring height or reduce the separator speed to build the bed before increasing feed rate.
How to assess roller tire wear on a Loesche LM Series VRM
Worn roller tires increase specific power consumption and degrade product fineness. Measure the tire profile with a profile gauge during a planned stop and schedule replacement when wear reaches the minimum profile depth.
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