The Life Rule That Doesn’t Always Apply to Conveying Material

At some point, everyone learns that the shortest distance between two points is a straight line. The ancient Greek mathematician Archimedes is credited with first articulating this concept, which has since become not only an accepted geometric fact when applied to flat surfaces or planes, but a general rule of life.

However, his statement doesn’t necessarily hold true in every material handling situation for two reasons:

  1. Conveying distances aren’t always short.
  2. Facilities aren’t always able to convey materials in a straight, horizontal line.

That’s why CDM offers several types of conveyors that can handle a variety of material handling needs. The ideal choice for a particular application depends on the 18 pieces of data we require to properly specify an equipment solution. The first two on our list—the horizontal length of the conveyor and the inclined degree of the conveyor—are extremely important to determining which is the best material handling option: a drag chain conveyor or a screw conveyor (which coincidentally was invented by Archimedes).

Horizontal Length
Once a screw conveyor exceeds 20-30 feet in length, hanger bearings are required within the conveyor t

ube to support the screw sections. For example, if an operation calls for a 50-foot conveying distance, there will need to be a hanger bearing every 12 feet or so to support the coupling between the two screws. This becomes a potential maintenance headache as the hangers are susceptible to failure due to dust and contamination. Eliminating the use of hanger bearings makes screw conveyors much more reliable, but doing so also limits the length.

Many applications accept this maintenance issue because a screw conveyor is the best solution for the product they are handling (material that is consistently sized, non-corrosive or abrasive, low temperature or non-friable). But drag chain or en-masse conveyors offer a viable alternative for longer conveying paths, as this equipment does not require additional support bearings that must be replaced frequently. These conveyors also deliver dependable performance in more severe-duty applications and minimize product degradation because they do not exert pressure on the material or subject it to a tumbling, scraping or dragging action.

Degree of Incline
Screw conveyors and drag chain/en-masse conveyors are each capable of moving material on an incline. However, once the incline exceeds approximately 20 degrees, screw conveyors quickly lose efficiency and the screw must be significantly oversized to handle the load. For steep incline conveying, the better solution is generally an en-masse or drag conveyor, which utilizes up to 90% of the cross-sectional area of the housing for horizontal and shallow incline applications, and up to 50% of the cross-sectional area for severe incline configurations. This typically results in a smaller piece of equipment that, in some cases, can offer increased capacities over the common alternative, a belt conveyor.

Another advantage of an en-masse conveyor is the dust-tight operation. The enclosed design of this material handling equipment means no housekeeping, which is an inherent concern associated with incline conveying and conventional belt conveyors. This can improve profitability while also eliminating exposed rotating parts, inhalation hazards and other major safety concerns associated with belt conveyors that can compromise employee health and workplace safety.

Other Configurations
Screw conveyors can only handle shallow bends in a conveying path if they have lighter-gauge, shaftless screws or if a horizontal screw conveyor feeds an inclined screw conveyor. Neither option is as effective as an en-masse conveyor, which offers the flexibility to move bulk materials in various configurations: horizontal, inclined, L-path, Z-path and loop.

For straight vertical lifts and high volumes, our bucket elevators are the ideal conveying solution. To best suit your specific application, our bucket elevators are available with your choice of centrifugal or continuous discharge and a single- or dual-strand drive mechanism that moves the buckets with a chain or belt.

Archimedes was definitely onto something when he said, “the shortest distance between two points is a straight line.” However, the concept simply isn’t practical or possible in some conveying situations—not even with his own invention, the screw conveyor. Fortunately, there are several conveying methods available, each optimized for specific material characteristics and plant layouts. With more than 40 years of experience in providing our customers with the longest lasting, most efficient conveyor systems for their specific applications, we can help you achieve the shortest distance to your ideal equipment solution.