Knauf Fiber Glass blends glass batch in an aerating blender and then pneumatically conveys it to a bin above each of several furnaces at their Shelbyville, Indiana plant. When the original furnace feed bins were kept full, few, if any, handling problems were experienced. However, when a bin emptied due to upstream mechanical problems with the batching system, stable ratholes formed above each of the three chute legs, resulting in occasional loss of feed to the furnace.

Even worse, as the ratholes collapsed the material fluidized and flushed through the chutes to the furnace. Fine material which had been stagnant in the bin was then able to move, resulting in a high percentage of fines in the feed to the furnace. The fines typically melted at a lower temperature than the normal batch and produced a glass with radically different physical properties. Each of these changes resulted in a major disruption to the manufacturing process, with the disruptions lasting for about 24 to 36 hours.

More severe flow problems were anticipated on a production line with similarly designed equipment that was to be put into production.

A Jenike & Johanson engineer was asked to visit the plant to observe the operation of the bins, run laboratory tests on the glass batch to determine its flow properties, and make functional design recommendations for modifications to alleviate the problems. Jenike & Johanson also performed the design and engineering of the final modifications. Time was of the essence.

It was necessary to change the bin's flow pattern to mass flow from the funnel flow which had developed due to the shallow hopper wall angles and surface finish. This involved building a new hopper section with steeper and smoother walls. These modifications eliminated ratholes and stagnant regions, developed a first-in-first-out flow sequence, and minimized segregation [220K QuickTime video].

Jenike & Johanson personnel completed the laboratory tests and functional bin design recommendations within a week of receipt of the sample. Next, they completed detailed drawings and structural engineering within two weeks. Finally, the retrofit for the new line was fabricated and installed within 11 days.

The modifications have met all of Knauf's expectations. Ratholing has been eliminated, resulting in a much more uniform furnace feed.