Frequently Asked Questions

Q:

What is the main difference between a screw conveyor and a screw feeder?

A:

Screw conveyors normally run 15, 30, to 45-percent full. Screw feeders run 100-percent full and are designed to meter the flow of material. Screw conveyors are basically for moving from one location to another.

Q:

Name three (3) limiting factors when determining if a screw conveyor is appropriate for a bulk material handling application.

A:

  1. Capacity exceeds maximum recommended for screw conveyors.
  2. Lump size exceeds maximum recommended for screw conveyors.
  3. Products easily degrade.

Q:

What are three (3) advantages of screw conveyors over the other types of bulk material handling conveyors?

A:

  1. Totally enclosed housing to prevent leakage.
  2. Compact design allows for easy installation.
  3. Economical means for conveying many bulk materials.

Q:

What is the difference between angle flange and form flange troughs? Are they interchangeable?

A:

Angle flange trough has an angle welded to the top to provide more rigidity. Form flange trough is made from one (1) piece of sheet metal. Both trough types are interchangeable. KWS Manufacturing stocks both angle and form flange troughs.

Q:

How much greater is the radius of a trough than the screw it fits?

A:

Standard clearance between the screw and the trough is 1/2 inch.

Q:

What is the advantage of curved bottom slide gate vs. flat bottom?

A:

Flat bottom slide gates allow build up in the void area under the trough. Curved bottom slide gates match the curve of the trough and have more of a self-cleaning effect.

Q:

What is a pedestal or outboard bearing trough end and why is it used in place of a standard end plate?

A:

It is a trough end with a shelf for the pillow block bearing. The pedestal moves the bearing away from the end of the conveyor and away from the product.

Q:

What type of shaft seal requires a pedestal or outboard bearing trough end plate?

A:

Split gland seal, packing gland seal, and most mechanical seals require a pedestal trough end.

Q:

How is thrust developed in a screw conveyor and how do we design to compensate for it?

A:

Thrust is back force of material against the screw. The direction of the force is opposite the direction of material flow. It is compensated for by using a thrust unit. The thrust unit is usually located on the drive end.

Q:

What is a thrust unit?

A:

A thrust unit "fixes" one end of the screw/shaft by use of roller bearing, snap rings or set collars. The thrust unit can also be located in the screw conveyor drive.

Q:

Why must the type of flange bearing required be specified when ordering a plate or waste pack seal?

A:

The bolt pattern for the flange bearing is different for ball and roller bearings.

Q:

Why and where are trough saddles and feet used?

A:

Trough saddles and feet are used for intermediate support, and are normally located at 10 to 12-foot intervals.

Q:

What are the two (2) types of flight construction? What are the advantages of each? Which is stocked?

A:

The two types of flight construction are helicoid and sectional. The advantages of using helicoid flighting are one-piece construction, availability and helicoid flighting costs less than sectional flighting. The advantages of using sectional flighting are unlimited variations of materials, pitch, thickness and diameter can be used. Both helicoid and sectional flighting is stocked at KWS Manufacturing. Non-standard sectional flights are made to order.

Q:

How do you determine if a screw has right or left hand flighting?

A:

Standing at the end, if the flight tails off to the right, then it is right-hand flighting. If the flight tails off to the left, then it is left-hand flighting.

Q:

How can the life of the conveyor screw be improved?

A:

The flighting can be constructed of abrasion resistant materials. The flight face can be hard-surfaced with a weld-on hard-surfacing material. A bolt-on wear shoe can be added to the face of the flights.

Q:

What letter is added to the screw part number to indicate loose flighting, not mounted on the pipe? What information is necessary to quote loose flighting?

A:

The letter F is added to the part number to designate loose flighting. The information required to quote loose flighting is screw pitch, screw diameter, flight thickness and pipe size.

Q:

Why are screws shorter than the troughs they fit?

A:

Clearance is required at each end and for each hanger bearing.

Q:

When is it necessary to use a hardened coupling shaft?

A:

Hardened coupling shafts are used with hard iron bearings. The hardened coupling shafts have a higher torque rating and longer wear life than standard coupling shafts.

Q:

What do the letters at the end of the part number on the end shaft tell us?

A:

The letters at the end of the part number on the end shaft designate the length of shaft used based on bearing used, and if hardened.

Q:

When would you use Style 216 Hangers vs. 226 Hangers in an application?

A:

Style 216 hangers are more rigid for supporting larger diameter screws and for handling dense, abrasive materials.

Q:

Which hanger bearing insert requires a hanger with a grease pipe?

A:

Typically, hard iron, babbitted and bronze require a grease pipe for external lubrication.

Q:

What are the types of trough covers and which are most commonly used?

A:

  1. Flanged - is the most common
  2. Semi-flanged
  3. Flat
  4. Hip roof
  5. Shroud

Q:

What type of drive is most commonly used on a screw conveyor?

A:

The screw conveyor drive is specifically designed for screw conveyors.

Q:

When using a screw conveyor drive, is a separate thrust unit required?

A:

The thrust unit is an integral part of the screw conveyor drive.


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