Maintenance and replacement advice

Screening is a tough business, so for most operations replacing wear parts and screening media is a fairly frequent event. Sometimes it is self-evident when replacement parts are needed – for instance, if a wire mesh has a gaping hole in it – but at other times, the signs of wear are a bit subtler and harder to identify. To keep screening at an optimal level, you need to be able to recognize the types of wear and damage that can affect performance. Read on for information about some of the most harmful wear and maintenance issues and how to resolve them.

Monitoring and maintaining screening media

It is normally apparent when screening media is severely damaged or worn. If holes have formed in the mesh or modular panels, this is often visible to the naked eye. The contamination of your product is also likely to be clear. Screening media that is blown-out in this way should be replaced immediately – not only do they harm your product, they can also damage lower screen decks or cause problems downstream in the plant.

Of course, you should ideally replace screening media before it gets to this level of disrepair. Regular sieve analyses or other quality control measures can give insight into the condition of screening media, and following up with visual inspections can confirm when action is required. The image below shows a screen panel that should be replaced. There are two visible indicators. Firstly, the steel frame is exposed in places, and secondly, the bridges between holes are thinning and taking on a concave shape.

The screening media shows signs of thinning bridges and the steel frame has becoming exposed in places.

Modular screening media that isn’t reinforced by steel can sag in the middle if overloaded. Over time the membrane can stretch and dip if the feed material is too dense, or if the material bed is too deep. These modules should be replaced, of course, but it is advisable to switch to a stiffer screening media or ensure that your screen is used only for appropriate purposes in future.

Installing tensioned screening media

The cloth or mesh of tensioned screening media can break if stretched unevenly or if the tension is too high or too low. It’s important, therefore, to adhere to manufacturers’ installation instructions. For Sandvik’s rubber and polyurethane tensioned screening media, proper tension is achieved when it is possible to lift the cloth with light force (between 5N and 20N) until there is a 5mm to 8mm space between the cloth and the capping rubber underneath. Bolts should be tightened gradually, just a few turns at a time, and locked with a counter nut or a spring lock washer to maintain the correct tension.

Broken frames

Self-supporting panels are intended for heavy-duty use, but they aren’t indestructible. Screening media normally has maximum bulk density and maximum particle size limitations. Piling on heavier, larger rocks is likely to cause premature damage, from the impact when they land at the feed end or from the excessive weight bearing down on the panels throughout. Sometimes, one or more of the steel frames in the self-supporting panels can snap, and require immediate replacement.

Center hold down bar

Center hold down bars are important components that hold screening media in place. The movement of the screen can cause them to loosen, so it is important to regularly check their bolts to make sure they are properly tensioned. New bolts should always be used when replacing center hold down bars.

Camber supports

When using screens and screening media with a camber (crown), it’s vital that all of the support bars are utilized. If not, the screening media is likely to break prematurely. Therefore, make sure that the screening media touches the capping rubber on all of the support bars. This should be checked during installation and periodically.

In the bottom example, the cambered screening media is supported by all of the support bars.

Additional wear parts that need attention

The rubber capping that sits on the support bars plays an important role in protecting the screening media. The capping should be monitored as regularly as possible, and replaced whenever the screening media is changed. When checking for wear, bear in mind that the underside of the rubber capping can deteriorate as well as the top side.

The liners on the feed box and discharge lip should also be checked regularly for wear. Replacing steel liners with rubber or ceramic alternatives can significantly extend wear life and service intervals.