I will start by saying the number one cause, except for wear, of screw conveyor failure, is a failure to discharge properly. Discharge plugging, whether a result of poor conveyor discharge design or failure of the downstream equipment to take the flow, may cause failure in several components. This can include thrust bearings, hanger bearings, screw center pipe, bending of the flights and bolt breakage. A properly designed discharge will include ample size to discharge, reversed flighting to keep product from building up on the opposite side of the discharge and some sort of sensory device to stop the conveyor when this occurs. Most often this is a proximity sensor on a door above the discharge.

Another very common cause of failure is product overload due to incorrect sizing or improperly designed inlets and screws under the inlet. The overload can cause an overload on the drive which will draw too much current. It will also cause rapid hanger bearing wear and hanger failures. Screw gudgeon collars will also wear rapidly. The first sign of the gudgeon wear will be bolt failures.

Collar wear, hanger bearing wear, bolt breakage and shaft wear are also common and unavoidable as the conveyor ages. However, careful design can greatly increase the life of these components.

Other common screw conveyor failures occur due to incorrect hanger bearing selection, which varies according to product and bearing failures due to seal failure. The best seals for keeping product in the screw conveyor are the Grease purge seals, such as those from Conveyor Eng and Mfg, or the air-purged seals marketed by several manufacturers. These seals all follow shaft run-out well. Waste pack seals work well with some products, allowing some space for product drop-out. Seal failures can lead to bearing failures or failure of screw conveyor drives. If this is suspected as being a problem for an installation, the use of pillowblock bearings will allow clearance for product drop-out.

There are many design modifications that can be made to ensure that screw conveyors are highly reliable pieces of equipment. Many are subtle changes that cost very little to implement. Most will save considerable money in the long run.

We have not done any statistical data on these causes. These are observations made from my experience of over 25 years.

The parts to be kept in stock depends on how critical the conveyor is to your operation. Certainly, you should keep all bearings in stock, as well as gudgeon bolts, seals and a minimum of one of each type of shaft. If you can't have the conveyor shut down for even a few hours, you should also include parts for the entire drive unit and one of each different screws found in that conveyor.

There are many design tips which can drastically improve conveyor life and decrease down-time, but that is more of a book length answer. Which parts will fail first, and most often, is dependant highly on the initial design, or design shortcomings.

I have a definite bias on the manufacturer, since I am a designer for Conveyor Eng and Mfg Co.

Let me know if you need additional info. ■

Originally Posted by DickVH

I have a definite bias on the manufacturer, since I am a designer for Conveyor Eng and Mfg Co.

Nice to have a bit of up front honesty ■

DickVH has put together a nice summary of common problems that may arise. two others that can be awkward is trapping of hard components in the fllight tip clearance and flight tip binding on a caked layer in the clearance. I would strongly endorse his comment that there are many specialised techniques available to the specialists to overcome many problems. The apparent simplicity of screw equipment can lure many to seek cheap suppliers when a bit of experience may save considerable heartache.

This list of potential problems should not deter users as screws are a solid workhorse of industrial handling and, properly specified, offer great reliability. ■