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Tips for avoiding premature screen media failure

Here are installation tips for two common types of tensioned screen media: Flex-Mat-type and woven wire.


Prior to installation:

? Check for proper tensioning system and correct installation of tension bar.
? Ensure the crown bar is engaged in ?U? channel rubber and is consistent in height.
? Ensure clamp rails are not deformed and are the same length as the screen media.
? In bolt-type tensioning systems:
    – Check the rail design and height of bolt holes and check for missing bolts.
? Clean the rail and hook edge thoroughly.
? Check for cracks, broken welds and loose bolts on screen box or deck (fix if necessary).

During installation:

? Ensure clamp rails do not overlap multiple panels, but fit each panel.
? Ensure that in side-tension systems there is a 19mm space between the wall and the outside of the hooks.
? Align polyurethane strips perfectly on all crown bar supports.
? Place overlaps (if applicable) on top of preceding screen media at discharge end.
? Stretch Flex-Mat screen media tightly.
? Do not over-tighten when using an impact wrench on wire diameters less than 4mm.
? Check tension. A screwdriver or hammer should bounce easily on the screen media.

{{image2-a:r-w:250}}None of these tips help with a faulty screen box. Before you install your screen media, make sure your unit passes inspection.

Do not install:

? If crown bar supports do not create a consistent crown curve or are worn or bent.
? If screen media is too flat, lacks a proper crown curve, or does not fit tight against all crown bar supports.
? If polyurethane strips do not line up perfectly on all crown bar supports.
? If ?J? bolts are not in use (these indicate a problem with the crown which must be fixed).

The string test
New crown bar rubber should be installed with each new set of Flex-Mat screen media. To install correctly, perform the string test, ie run a string from sideplate to sideplate over the crown bars and pull tight, then check for gaps between the string and crown bars to see if the screen media will sit on them properly. Correct the height of the crown bars to reduce gaps.

Before you install:

? Look for significant damage to crown bars and screen decks.
? I nspect the crown bar rubber for damage and wear (replace if necessary) and ensure it is the same type and height and covers all of the crown rails. Check crown bar height with the string test.
? Make sure side clamp rails are not worn thin, bent, do not have ?dimples? where the clamp rail bolts come through, and equal the length of the screen media.
? Remove all material build-up from the hook ledge on the screen box?s pan side and/or the crown bar rubber.
For proper installation:
? Make sure screen media has the correct outside and inside hook width for the deck.
? Ensure that the ends of the screen media panels fit together tightly and the ?tail ends? do not exceed more than 50 per cent of the opening size where they meet.
? Side-tension screen boxes. Position the screen media so clearance from the pan side to the hook is even on both sides.
? Tension your screen media by tightening the bolts intermittently from both sides.
? Once installed, make sure all screen media is seated properly on all crown bar tops and the side clamp rails match the length of the screen media once it is installed.

Source: Major Wire Industries/Nepean Rubber & Plastics

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