Page 134 - Root Cause Failure Analysis

122 Root Cause Failure Analysis

In addition, the product-feed system must prevent entrainment of contaminates in the
incoming product. Normally, this requires an enclosure that seals the product from
outside contaminants.

Operating Methods
As previously discussed, screw conveyors are sensitive to variations in incoming
product properties and the operating environment. Therefore, the primary operating
concern is to maintain a uniform operating envelope at all times, in particular by con-
trolling variations in incoming product and operating environment.

Incoming-Product Variations Any measurable change in the properties of the
incoming product directly affects the performance of a screw conveyor. Therefore, the
operating practices should limit variations in product density, temperature, and vis-
cosity. If they occur, the conveyor’s speed should be adjusted to compensate for them.

For property changes directly related to product temperature, preheaters or coolers
can be used in the incoming-feed hopper and heating or cooling traces can be used on
the conveyor’s barrel. These systems provide a means of achieving optimum conveyor
performance despite variations in incoming product.

Operating-Environment Variations Changes in the ambient conditions surrounding
the conveyor system may also cause deviations in performance. A controlled environ-
ment will substantially improve the conveyor’s efficiency and overall performance.
Therefore, operating practices should include ways to adjust conveyor speed and output
to compensate for variations. The conveyor should be protected from wind chill, radical
variations in temperature and humidity, and any other environment-related variables.