Not many screens in the Mobile Market offer Cross Tensioning for the bottom deck. The majority of screens utilise End Tensioning for the bottom deck. The bottom deck is usually the most important deck as it determines how clean the aggregate will be and bears a large factor in the ultimate production achieved. If it blinds off, the aggregate becomes "dirty" and of lessor value, it may require cleaning and result in lost production. This is only possible for finished products that do not have a cubical shape requirement - sand, soil, aglime, mulch for example. If there is a shape requirement then triangle or diamond harps will achieve the desired outcome.
Advantages we see that SIDE tensioned 45 Degree hooked screens (CROSS-FLOW slot = cross harp screen) have over END tensioned 180 Degree hooked screens (WITH-FLOW slot = harp screen) include;
Fitting/installation and handling benefits of Cross Flow
Tend to have more panels that are smaller and lighter, so easier to handle. ( OHS )
Simpler to install (hard to get wrong), we see end tensioned (piano wire/harp screens especially) regularly wrecked due to incorrect fitting - hooks open up or screens run loose etc.
Don’t have issues with oversize material getting past media at walls of screen box - especially in fine apertures under 5mm - screen panel overlaps solve this or for (Cross-flow) harps a joining strip can be supplied.
No need for Silastic or Foam to fill gaps down sides.
No issue with dirt buildup or stones in bottom clamp area that can cause the hooks to bend if not properly cleaned out before hand.
It can be difficult to slide end tensioned mesh along bottom deck with bolts and protrusions causing clearance problems.
Different angle Banana Bars are required when changing between very fine aperture mesh and very large aperture mesh with thick wire or tension problems will occur.
Much easier tensioning with side tensioning as compared to end tensioning – especially for 1 man.
End tensioning clamps can be difficult to get ratchet drive sockets onto due to clearance issues and can often only be done with a spanner taking more time.
No potential of material running backwards between the end tensioned meshes and contaminating the next product with oversize.
Problems and issues reduced or eliminated
(Cross-flow) harp screens suffer much less from pegging as stringer bars are not in the path of flow and the slot is cross-flow.
Tend to have more stringer support bars, closer together = screens are better supported (especially harp screens = better aperture integrity).
Less material blinding or clinging to stringers as stringers not in path of flow.
(Cross-flow) harp screens tend to suffer less contamination from elongated particles e.g. sticks (though not immune).
Superior performance and more operator control
(Cross-flow) harp screens provide significantly better productivity in many applications but not all
(Cross-flow) harp screens provide significantly better wear life and can also be supplied in stainless for longer life and less build up.
(Cross-flow) harp screens provide operator with the option to fine tune the cut/effective aperture by steepening/flattening the slope of the screen deck.
Better suited to running varied specs down the deck, e.g. heavy spec at the feed/higher wear area, this feed panel can be changed out more often rather than throwing out a larger panel with inconsistent wear.
With more panels per deck there can be varied apertures/wire diameters from panel to panel for fine tuning product.
OHS issues reduced due to smaller panels.
Better suited to higher clay and moisture contents than square mesh
If you are experiencing blinding, pegging, fines carry over, low production etc. feel free to call Onetrak or Symphony Wire to discuss your application and see if we can provide a solution.
The Striker Mobile Screens are quite unique in that they do have cross tension on all decks and that the decks are all the same size - the bottom deck is not shorter than the top deck like most competitors incline screens.
A big thanks to Jon and Marc at Symphony Wire for their ongoing help and product knowledge with square mesh, triangle harps, diamond harps, mega cross harps and standard harps.
Written by Jason MacDonald, Product Manager - Crushing and Screening