The concept of moving material via screws, or helix, is not new or recent. Historically, the concept of the helix goes back to the ancient Greeks, such as Archimedes and Vitruvius. Industrial uses for lifting and conveying (via screws) in this country is generally credited to Oliver Evans, who wrote and published ‘”The Young Millwright and Miller’s Guide” in 1795. This is considered the first reference source for flour milling and production processes, which was later used in other industries. Ever since the early days of industrial manufacturing, basic equipment, such as screw conveyors and screw feeders, has been improved upon by others. With improvements comes variety. Today there are probably a dozen or more reputable companies manufacturing screw feeders here in the United States alone. It is also fair to state that each will submit for consideration their design that falls into the category of ‘A better Mouse Trap’!

In my opinion, there is little or no difference between a single screw and a so called ‘dual screw’. As I recall, the ‘dual screw’ concept was publicized/advertised as being designed to handle adhesive or cohesive powders, and could do so based on the two intermeshing, self-cleaning screws.

In fact, Class 4 materials (powder sluggish, adhesive-cohesive) are being handled with single screws probably more often than a dual-screw configuration due primarily to the sheer number of single-screw feeders working in industry today!

What is more important in selecting a screw feeder, other than a single-helix or dual-helix design, are the variables that must be considered in basic selection. Some of these are:
1. Material: Properties and Classification. Standards that apply to the material.
2. Performance requirements: feed rates, accuracy, and life cycle.
3. Environment/Ambient conditions: indoors or outdoors, food plant, pharma plant, foundry, etc.
4. Maintenance: spare part availability and COST, the number of moving parts to wear and break.
5. Manufacturer’s Integrity: ability to provide convenient field service, long term solvency,
and business philosophy.
6. Historical Experience: actual field installations and experience with your material, in your
industry (i.e., reference list), test lab services.
7. Cost: initial cost, cost to operate, manufacturer’s commercial terms, and warranty.