Dust control is critical in increasing production as well as reducing maintenance costs. Its importance ranges from improved productivity, due to less unscheduled downtime, to increased performance of equipment, reducing maintenance cost. More importantly is the long term effects fugitive dust and spillage has on the human element. Studies reflect significant savings in medical costs as well as worker’s compensation costs when effective dust control measures are implemented. When considering dust control methods, whether it is dust collection (use of air) or dust suppression (the use of water or chemicals), containment is the foundation to success of most applications. Without proper containment, neither dust collection nor dust suppression systems will be effective. However, it is important to note that containment is not as critical with the use of foams or chemical surfactants, though the trade off is increased future operating costs. Therefore, containment issues must be addressed when discussing dust control. Containment of transfer points and head chutes of conveyors are the focus of this pamphlet.   The following applied principals have proven success to all transfer points:

1. Proper belt support to prevent belt sag is accomplished with the use of;
• impact cradles and sealing cradles
• Installation of said cradles with idlers (steel cans as specified by CEMA) at each end to minimize belt drag and reduce horsepower requirements. Standard impact idlers are suggested with minimum CEMA C specifications.
• As an alternative the use of idlers either standard or impact at 8-12” centers, although it may not eliminate all sag but they can be relatively effective.
• Belt supports that cover actual impact/load areas as well as a distance equal to three times the belt width from impact area to ensure proper sealing.

 

2. Proper chute design:
• Determine length, usually 4-5 times belt width, and also design such that the side chutes are easily replaced. One method is to flange side chutes just above the area required for skirting.
• Chute height minimum of 18” to help reduce velocities (if room permits higher is usually better), the use of dust curtains can assist with air velocity reductions (if room permits). The curtains can be made of various materials such as nylon strips or old belting slit at ½” increments. The purpose is to allow material to accumulate and then drop to the belt. The larger the slits the more likely build-up will occur due to less movement, where as narrower slits will create its own vibration (movement) to release the attached particulate back onto the belt. In addition the use of dust curtains, as stated, reduces the velocity of the air, thus allows dust collector or dust suppression system to be more effective as well as minimizing the particulate size for the collector or suppression to contend with. The collector can be a centralized unit or a self-contained single pick-up point unit.
• Chute width to allow proper skirting system, usually 3-4” on each side. There are number of variations of skirting available, the two piece Apron Seal™ is our recommended style
• Install tailgate 24”- 48” long, 18”-24” in height to help prevent rear spillage and dusting, install with access door at top of unit to assist with clean-up for unexpected occurrences, also install deflection plate to prevent airborne product to reach back of tailgate.
• Minimize impact by use of deflector plates, rock boxes, etc.
• keep chutes in-line for proper loading, if not possible the use of deflectors, liners, baffles, shapers, screens, grizzly bars, horseshoe plates and training gates can assist with ensuring balanced loading pattern.
• Use of wear liners to help prevent product from spilling and assist with material containment. Install liner to start as close as 3/16″ above belt (at back of chute beginning of wear plate) and increase to as much as ¾” –1” above belt (at exit point). This is to prevent material from being lodged between belt and wearliner.

 

3. Proper Skirting:
• There is a variety of sealing systems available such as rubber, urethane and UHMW, all have advantages and disadvantages. It is important to evaluate based on customer’s specific application.
• dual seal products are also recommended and are available in either rubber or urethane
• Use clamps, which are easy to install and to replace. Match clamp length with side chute length. Be cautious as to the durability for the specified application. Size of clamps should take tonnage and belt speed into consideration.

 

4. Proper Head Chute/Tail Pulley Design:
• Design should be such as to allow for multiple belt cleaners, this pertains to both installation and required future maintenance. If room does not allow for dual system, then place single belt cleaner such that it removes a majority of the carryback within the head chute, the secondary should be mounted in such a manner as the debris removed drops to an area accessible for easy clean up outside the head chute area. Also install a push down roller above contact point of cleaner to belt to promote maximum contact between belt and blade.
• Design of chute back plate should be a minimum of 9” behind point of contact of secondary cleaner to allow for maximum flowability of product removed from top cover belt.
• Use of wing style tail pulley with straps limit vibration, however drum pulley is preferred.
• New style trackers should be considered if belt misalignment is present.
• Installation of V-Plow or Diagonal Plow to protect tail pulley from any unexpected debris which may have fallen onto the underside of belt and could damage said tail pulley.
• When necessary consider using liner to increase wearlife as well as flow.
• chute angle should be greater the angle of repose of said material
• Though not specifically related to sealing of transfer point it is important to make sure the transition from the tail pulley to the transfer chute is set not to cause stress to belting. One rule is to allow transition to be two times the belt width.
• Design with access cover which is easily sealed.
• Seal all open holes, especially at points where cleaner’s mainframe exit chutes. One easy and economical method is to cut rubber pieces to seal around the mainframe and attach with silicon. This procedure allows for easily removal and replacement when maintenance is required.