McLanahan Corporation's Horizontal Screen Troubleshooting Guide offers corrective actions to situations such as blinded decks, excessive vibration and low output to decrease downtime.
Horizontal Screen Maintenance
What should I inspect before startup?
Before starting up the screen each day, check the following items:
- Check the oil level in the gear and impulse cases. Unscrew the oil-level plugs in the case covers to see that oil reaches the holes. Note: Do not allow the breather caps to plug. Clean filter regularly. Running the screen with plugged breathers risks damage to the driveshaft seal, case covers and bearings. If you lose the breather cap, do not replace it with an airtight cap.
- Check the breather cap on both impulse and gear case covers. Keep dirt buildup away from breather caps.
- Check the condition of the feed box and discharge-lip liner. Note any excessive wear in your log book and replace the affected parts as soon as possible.
- Check the wire cloth for holes or excessive wear.
- Keep the wire cloth taut between the screen-side plates. Tighten new wire cloth, as needed, after the first one or two days of operation. Whipping, caused by loose wire cloth, greatly reduces the life of the wire.
- Inspect the drive assembly for signs of V-belt stretching or cracking.
- Make sure all coil springs are free of rock and other foreign material.
- Make sure all guards are in place and in good condition.
Why the violent startup and shutdown?
When starting or stopping the inclined screen, the screen basket has a tendency to surge on its supports during the interval of slow vibrator-shaft speed. This is a normal action that stops when the vibrator unit reaches operating speed or stops completely.
How important is the feed box?
The feed box is designed to receive material and spread it across the full width of the screen. To increase the efficiency of the screen and allow more uniform wear, maintain a uniform feed rate to the center of the feed box.
What do I check during normal operation?
During daily operation, check for unusual sounds or signs of excessive vibration. Make sure you know the cause of any abnormality. Correcting problems when they first appear can often save you expensive downtime later.
Watch for product spillage due to damage or wear in the feed-end curtain, feed box or discharge-lip liner. Record any observations about the system in your log book.
What should I do at shutdown?
Before shutting down, always clear the system of product. Stop the feed and watch the system run until all material cycles through the screen and is discharged. Then, shut down the screen.
Observe surging as the screen basket decelerates. If surging is extreme, the rubber snubbers may need adjusted. Turn the snubber adjusting bolts clockwise an equal amount at each corner to force the snubbers tight against the screen basket. Be sure the screen basket stays centered in the frame.
Important: For any new V-belts or sheaves, check the belt tension after two, eight and 40 hours of operation. Adjust to the V-belt manufacturer’s specifications. Failure to do so may result in the belt being damaged beyond use, and costly downtime.
When starting or stopping, screen baskets are prone to surge on their supports during the interval of slow shaft speed. This is a normal action that stops when the screen either reaches operating speed or stops completely.
The feed box is designed to receive material and spread it across the full width of the screen. To increase the efficiency of the screen and obtain more uniform wear, maintain a steady feed rate to the center of feed box.
Keep the discharge end of the feed conveyor as close as possible to the screen feed box while allowing adequate clearance for the screen basket to vibrate. Material dropped into the feed box from too great a distance causes excessive wear and damage.
Operational Best Practices
Can I cut or weld on a screen box?
Cutting or welding on a screen box is not recommended.
How can I maximise the performance of my screen?
Make sure the feed is spread evenly across the screen width to maximise screen performance.
What is important for startup and shutdown?
Allowing clearance around the screen is especially important in initial startup and during shutdown.
How much water do I need?
The water volume for wash applications should be 3-5 gallons for every ton of material that is to be washed.
How deep should the material bed be?
Bed depth should not exceed four times the screen opening at the discharge end of the deck.
How often should I check the screen's speed and throw?