Avoid Premature Screen Media Failure for Improved Productivity
Tips from an expert on how to get more from your screen media.
December 14, 2011 By Gary Pederson
No matter what kind of screen media you choose, proper installation is crucial.
No matter what kind of screen media you choose, proper installation is crucial. Poorly installed screen media can slow down your operation and hurt your product quality, production and profit. Produce material that meets specification, achieve longer screen media wear life and generate the tonnage your operation was designed to produce by installing your screen media right the first time.
|Improper installation can lead to premature wire breakage.
The two most common types of screen media are Flex-Mat-type and woven wire. Here are some installation tips for each:
|A curved tension bar decreases screen media wear life.|
Prior to installation:
- Check for proper tensioning system and correct installation of tension bar
- Ensure that crown bar is fully engaged in “U” channel rubber and is consistent in height
- Ensure clamp rails are not worn thin, bent or deformed
- Ensure clamp rails are the same length as the screen media
- In bolt-type tensioning systems:
- Check the rail design and height of bolt holes
- Check for missing bolts (replace if broken or missing)
- Clean the rail and hook edge thoroughly
- Check for cracks, broken welds and loose bolts on screen box or deck (fix if necessary)
- Ensure clamp rails are not overlapping multiple panels, but fit each panel
- Side-tension systems: Ensure there is a .750-inch space between the wall and the outside of the hooks
- Align polyurethane strips perfectly on all crown bar supports, making sure they lie flat on the bars when tightened
- If equipped with overlaps, place overlaps on top of preceding screen media starting at the discharge end
- Stretch Flex-Mat-type screen media “tight as a drum”
- Do not over-tighten when using an impact wrench on wire diameters less than .148 inches
- Check tension: the heavy end of a screwdriver or hammer should bounce easily on the screen media
None of these tips means anything if you are operating a faulty screen box. Placing screen media in an inadequate screen box will almost certainly result in premature failure. Before you install your screen media, make sure your unit passes inspection.
|Properly tensioned Flex-Mat-type screen media.
Do not install:
- If crown bar supports do not create a consistent crown curve
- If crown bars are worn or bent
- If screen media is too flat – lacking a proper crown curve
- If screen media does not fit tight against all crown bar supports
- If polyurethane strips do not line up perfectly on all crown bar supports
- Check for use of “J” bolts (these indicate a problem with the crown that must be fixed)
Do the String Test:
New crown bar rubber should be installed with each new set of Flex-Mat-type screen media. To see if you have installed it correctly, perform the string test. First, run a string from sideplate to sideplate over the crown bars and pull the string tight. Next, check for gaps between the string and the crown bars to see if the screen media will sit on them properly. If there are gaps, then the height of the crown bars must be corrected or breakage will occur.
Prior to installation:
- Look for significant damage to crown bars and screen decks
- Inspect the crown bar rubber for damage and wear (replace if necessary)
- Ensure the crown bar rubber is the same type and height and covers all of the crown rails
- Make sure side clamp rails are not worn thin, bent or have curves or “dimples” where the clamp rail bolts come through
- Ensure the side clamp rails equal the length of the screen media or they will cause uneven tensioning
- Check crown bar height by doing the string test
- Remove all material buildup from the hook ledge on the pan side of the screen box and/or the crown bar rubber
For proper installation:
- Make sure the 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 to prevent the passing of oversize material
- Make sure the lengths of all screen media “tail ends” don’t exceed more than 50% 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
Conduct Habitual Inspections
|Make sure crown bar rubber is not missing, damaged or worn.
Once you have properly installed your screen media, conduct daily inspections before startup and after shutdown. Make sure that your screen media and screen boxes are free of unnecessary wear, breakage or damage. Catching problems ahead of time can save costly fixes later.
If you need a second opinion, Major Wire and your local authorized dealer can provide a free screening plant audit. During an audit, a dealer representative will review the screening plant and compile a detailed report of findings with photographs and clear recommendations of adjustments that will help the operator maximize the screening operation.
This article was produced by Major Wire for Aggregates & Roadbuilding by Gary Pederson at Major Wire in Candiac, Que.
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