Conveyors are an integral part of most materials-handling operations. When they operate well, material moves efficiently. But conveying problems apply a stranglehold to productivity and profitability. Keeping conveyors efficient is essential. Here are some thoughts on improving conveyor operations.

DON'T be "penny-wise and pound-foolish" If history has taught any lesson in solids handling, it is that demands on conveying systems only increase. Material volumes are raised, belt speeds are increased, additional loading areas are added, and expectations are raised (often while equipment maintenance schedules are allowed to deteriorate).

The result is that in many cases "saving money" on initial design proves costly in the long run as adverse conditions arise and system demands increase.

The answer is to "overdesign" the system when it is new, which allows "room to grow" to accommodate (with minimum expense and discomfort) later variations in conditions and increases in demand.

DO plan for the "worst case" The conveyor must be designed not only for routine operations, but also for worst cases. This means the system must continue to operate when faced with the worst possible environmental conditions, material conditions, material rates, state of maintenance, and other considerations.

Adverse conditions must be anticipated. For example, virtually any material will handle differently when wet than when dry. The conveying system-including loading and discharge hoppers, belts, rolling components, and other systems-needs to be able to accommodate both, because while it is likely to see the typical more often, it is probable the conveyor will see the worst extreme as well.

Other considerations include chutes and skirtboards wide enough to accommodate two of the largest lumps locked together, cleaning systems adequate to remove sticky materials and return that carryback to the main material body, and tracking systems to keep the belt away from the conveyor's structural steel.

When the conveyor is designed for the worst case, it will be a case of "overkill" during normal operating conditions. But this overdesign is likely to provide the benefits of improved wear life and reduced service requirements when conditions are as anticipated. Also, when the material or conditions do change, the conveyor will be able to stand up to the challenge.

DO install multiple belt-cleaner systems The key to controlling carryback is the installation and maintenance of an effective belt cleaning system. It is a sound practice to use a multiple cleaner system to provide "more than one pass" at removing the material. These systems are typically composed of a precleaner on the face of the head pull ey to remove the majority of material, and one or more secondary cleaners installed further along the belt return to remove residual fines. Tertiary or follow-up cleaners can be positioned even further back along the conveyor return to remove any last material. Criteria to consider in the selection and placement of a belt cleaning system include:

Far forward-Installation should be on the conveyor return as close to the face of the head pulley as possible to remove material as close to the original material trajectory as possible.

Out of the flow-The cleaners should be installed below the material trajectory, so they are not barraged by lumps.

Safe for the belt-Use systems that minimize or eliminate any risk of damage to the belt, splices, or to themselves. They should clean at low pressure and incorporate a method of relief for the passage of splices and other obstructions.

With multiple-cleaner installations, it may be necessary to add systems-an expanded dribble chute or a scavenger conveyor-to return the material removed by follow-up cleaners to the main material flow.

DO control the belt's tracking Proper tracking will improve the service life of belting and the conveyor's efficiency. Belt wander can arise in many ways: from off-center loading; from stringers misaligned by a shift in their foundation or by impact from mining equipment; from pulleys and idlers with material buildups; or from faults with the belt or splices.

There are a number of techniques for keeping a belt in alignment, from "knocking" the idlers to introducing a deliberate mistracking to compensate for the wander, to training idlers and multiple-pivot belt steering mechanisms. A survey of the conveyor structure can be performed with laser equipment, a conventional transit, or piano wire to determine where mistracking arises and what adjustments can be made.

The belt should be kept in the center, or the damage to belt edges and to structural steel will become apparent (and expensive).

DON'T load off-center Off-center loading can cause a number of problems, including mistracking and spillage. The solution, of course, is to load the belt in the center. This is easier said than done, particularly in the case of angular or non-in-line transfer points.

Systems to direct the material flow into the center of the belt include properly adjusted deflectors, liners, baffles, screens, grizzly bars, or curved loading gates. These devices must be installed with the understanding that the mission of any transfer point is to direct the material onto the belt in the same direction and speed as the receiving belt.

When a problem is solved, detailed records of the solution should be kept, i.e., the design and placement of the deflector. These records will provide an answer when wear has altered the shape of the deflector.

DO stabilize the belt's line of travel The key to reducing fugitive material, controlling tracking, ensuring safety for the belt, and efficient operations is to stabilize the belt's line of travel. That means it runs smoothly, as across a table top, particularly through a load zone.

There are many systems available to control a conveyor belt's line of travel, ranging from closely-spaced idlers, to impact cradles that absorb the force of material loading, and "side-rail" belt support cradles that stabilize the belt edges to minimize material entrapment and improve sealing. Each conveyor is different and requires an individual treatment.

The belt support structure should extend down the belt, from before the point where the load is introduced to the belt, until the load has settled into the profile it will keep for the remainder of its journey. Belt support is similar to money: it is better to have a little extra than to fall a little short.

Wing-style tail pulleys are often used as a way to prevent the entrapment of material lumps between the pulley and the belt. However, the "paddle wheel" design of these pulleys can bounce the belt, destabilizing the line of travel and defeating the belt support and sealing systems. Wrapping these pull eys with a band of steel preserves the self-cleaning function while minimizing the "bounce" imparted to the belt.

DON'T allow "pinch points" All skirtboard (and the liner systems inside the skirtboard) should be installed to offer relief in the direction of belt travel. That is, they gradually open in both vertical and horizontal planes toward the exit area of the transfer point. This prevents the creation of pinch points, where lumps of material can become wedged in by belt motion and then abrade the belt cover.

When placing steel or ceramic walls or liners adjacent, care must be taken to prevent any "sawtooth" pattern. If the bottom edges are not precisely aligned, entrapment points will be created, which will catch material lumps and quickly damage the belt.

DON'T expect component to perform like new if they are not properly serviced Under the stress of day-to-day operations, no system-no matter how well designed-can sustain high performance levels if it does not receive proper maintenance.

Maintenance people must be properly equipped, trained, managed, and motivated. More importantly, they must be aware of the service requirements and of the consequences of a lack of service to conveyor components.

Outside maintenance services can provide skilled maintenance on specialized systems. The use of these outside services offers two benefits: it provides skilled specialists to focus on specific identified projects, and it allows in-house personnel to focus on other priorities.

DON'T expect elastomer seals to contain the full material load Rubber or urethane strips are installed along the bottom of the steel skirtboard as a seal to keep material on the belt. But in many cases, these elastomer strips are expected to contain the side forces of the belt's cargo. This is unreasonable; no simple elastomer strip can contain this weight of material.

For a reasonable expectation of success in the control of fugitive material, use skirtboard and replaceable liners inside the skirtboard to keep the pressure of the main material body away from the sealing strips. With the material load away from the edge, the sealing strips can do the job for which they are best suited, keeping stray fines and dust on the belt.

DO install a multiple-barrier defense against loading zone spillage Wear liners installed inside the skirtboard and effective seals attached to the outside create an effective multiple-layer system to control spillage.

Using a sealing system composed of two layers would be beneficial. These layers would be a primary seal clamped against the chute wall to keep lumps in the main material body, and a secondary seal that lays on the belt to contain any fines or dust that have been pushed underneath the primary seal.

Dust curtains inside the enclosed skirtboard slow down the movement of dust-laden air, giving this material a chance to fall back to the moving belt before escaping to the outside. A tail sealing box could be used to form a one-way seal that prevents material rollback out the back of the loading zone.

DO protect the tail pulley Lumps of material caught on the return side of the belt can be carried into the tail pulley, where they will damage the belt and cause mistracking. To prevent this material impingement, install a tail plow to remove this material from the belt. Most coal mines use V-plows underground.

DO specify systems that simplify maintenance When considering the installation of conveyors and their subsystems, the designers should review the entire system's maintenance requirements. It's the mark of good engineering when service activities are considered during the design stage, as far as what work is required and what efforts are required to do the work.

Does service require the maintenance worker to lie down on a dust-covered floor, or can it be done standing? Can components be serviced without removing other systems? Must the conveyor be shut down to allow safe service, or is there any method to allow the work duringoperation or with minimal downtime? Does the manufacturer have realistic expectations of the operating conditions and the service timetables available in the operation?

It is designed-in ease of service that simplifies (and hence, encourages) routine maintenance.

DON'T allow the belt to rise off the idlers If the belt rises up off the idlers at start-up or when unloaded, it is in danger of damage from the steel skirtboard. This is especially true if the skirtboard is close to the belt, as is required in a low-spillage transfer point. Belt rising also can lead to belt wander and make it difficult to seal the belt effectively.

To prevent this problem, avoid the "half-trough" technique sometimes used to shorten the transition distance required for troughing the belt prior to introducing the cargo. This technique raises the tail pulley to reduce the transition distance, at the cost of increasing the likelihood that the belt will rise off the idlers. It also is possible to install hold-down rollers to position the belt as it enters the transition area and the loading zone. Other possible ideas include checking to make sure the belt tensioning and take-up systems are properly adjusted and installing a "soft start" function in the conveyor drive.

DO protect your investment The conveyor represents a significant investment in structural steel, belting, idlers, and other components. And more importantly, it is a critical ingredient in the efficiency of any operation. If the conveyor goes down, so does the rest of the mine or prep plant (and profitability too).

Consequently, it makes sense to undertake all measures that will protect and improve the investment, from the installation of monitors and belt alignment switches, to proper maintenance and service.