Most operator's mechanical equipment on sites has been procured from a variety of manufacturers over years of operations. The operating instructions and site knowledge may have been lost over the years but simple maintenance and overhaul techniques can be used to maximize the life of the asset and minimize the total costs. As company who manufacture replacement screens, refurbish existing machines and maintain screens I thought I would write down some of the common issues we see within the industry and some simple solutions.

• Roller/Ball Bearings all need regular lubrication. Bearings on screens are operating in one of the harshest environments and the key to the screen operating efficiently and effectively is ensuring the bearings receive enough lubrication with the motto being "little and often" with a little being 2 - 6 shots per day per bearing dependent on size. Vibrating screen bearings generally need lubricating with a Lithium based grease whereas other plantbearings normal EP grease is fine. As plant managers it is worth checking that fresh grease is visible on grease nipples during walk-arounds. Oil lubricated screens need to have the oil regularly checked for contaminants by taking a sample and getting it analysed by your lubricate supplier to determine the life of the lubricant and the state of the bearing. More automated solutions for both grease and oil lubricated screens are available which can dramatically reduce the maintenance time plus give the site manager piece of mind that the bearings will only fail when they reach the end of their useful life but there is an initial capital cost (for the unit, for installation and potentially integration with control system) and also power cost.
  
  
• If you have indications that the bearing is about to fail such as increased heat, noise or amps required, managers should schedule the bearing change as soon as possible as the potential damage caused by a total failure can increase the repair bill by a factor of 3. Changing Bearings in screens can be difficult if you have not done it before or don't undertake it regularly. Ideally bearings should be pressed out of the housings using a hydraulic press which will minimize the chance of damaging the housings and the shaft. Before installing new bearings the existing area should be cleaned to remove any debris and degreased. The bearing should be pressed in to the housings being careful to ensure that the alignment of the bearing is correct as misaligned bearings will fail quickly plus damage housings and shaft. When reassembling the remaining components of the shaft assembly it is key that the correct torque settings are used and that the maintenance engineer checks that the shaft assembly is able to rotate prior to testing under load.
  
  
• Changing from woven wire to modular polyurethane screen media is often done when a second hand machine is utilized on a quarry to replace an existing machine. It is key when you do this to have the deck frames modified or replaced as the deck frame construction is generally different for both screen media's. Unfortunately we have seen machines with cracked side plates and broken deck frames within weeks when the screen has been modified to go from woven wire to polyurethane.
  
  
• Support Structures - Vibrating screens should vibrate the load going over the screen decks not the entire screen house or screen structure. Causes of high vibration in structures can be as simple as the springs have reached the end of their useful life and need replacing. Other simple causes can be bolts coming loose in the support structure or parts of the support structure being removed following overhaul and not being replaced. The high residual vibration can cause damage to the screen itself and/or cause damage to the support work. During regular walk-arounds attention should be paid to vibration in the flooring or hand railing to see if there has been a change.