Operators had to constantly adjust the feed rate of each charger so that all four cans would empty at the same time. As production increased over the years, it became more and more difficult to maintain a constant delivery of batch to the furnaces.

Beginning in 1980 and continuing through 1984, a total of six bins (two for each furnace) were installed to store mixed batch and feed it directly to the batch chargers. The bins were expected to provide six to eight hours of storage capacity, which would allow plant operators much needed time for maintenance and flexibility in dealing with expected breakdowns in the batch house.

After the bins were installed, operators found that they could not use all of the new storage capacity because glass quality deteriorated when the bins were drawn down. Upon investigation, plant engineers determined that the problems were the result of changes in batch composition that could be traced to segregation [220K QuickTime video] in the batch storage bins. To avoid production problems, the bins had to be kept at least 50% full, and operators attempted to keep the bins topped off to maximize the available surge capacity.

After reading an article in one of our newsletters describing the BINSERT® and how it can be used to control segregation, an engineer in Owens-Illinois' Toledo office contacted us for assistance in solving the segregation problem. One of our engineers visited the plant to investigate the problem firsthand. Each of the existing storage bins consisted of an 8 ft. diameter by 17 ft. tall cylinder on top of a conical hopper that converged at 20° from vertical to a 16 in. diameter opening. The hopper contained an inverted conical insert located just below the cylinder-to-hopper transition (see sketch).

Observation of the top surface of the material in one of the bins revealed a fast, central flow channel typical of a funnel flow pattern. Inverted inserts, such as the one used in these bins, are often used to expand the flow channel in a bin in an effort to achieve more uniform flow. In this case, however, the insert was too small and placed too far from the outlet to be of any benefit.

The glass batch handled at the plant is a mixture of sand, cullet, and other ingredients with a wide particle size range. Since the batch is free-flowing, it is a prime example of material that segregates by the classic sifting mechanism. Sifting, one of the most common mechanisms of particle segregation, often occurs at the top surface of a pile of material as fine particles sift through the voids between larger particles. Center filling a bin results in a radial segregation pattern with coarse material near the outside wall and finer material at the center. If the flow pattern in the bin is funnel flow, the predominantly fine material in the center will be withdrawn first, followed by coarser material.

Our technicians collected and tested samples of batch. Our test results confirmed that the existing carbon steel hopper wall was not steep and smooth enough for material to slide along it. Recognizing the severe abrasive character of this batch, we also ran wear tests to estimate the wear rate for exposed internal components.

The proposed modifications had to meet several important criteria:

1. minimize segregated discharge of batch;
2. fit within the space occupied by the existing conical hopper;
3. accommodate occasional large lumps of cullet, stray pieces of 2x4 lumber, paper, rags, etc.; and
4. be robust enough to withstand the highly abrasive glass batch.

Our engineers studied the problem and formulated various solutions. They recommended the design shown in the sketch. A BINSERT® hopper system was chosen because it offers excellent velocity control—a key element in eliminating problems due to sifting segregation—and allows a shallower outer hopper to be used.

We constructed and tested a quarter-scale model in our San Luis Obispo, California laboratory to verify the design. The model was tested with samples of glass batch from the plant which contained scaled large particles to confirm that they would pass through the BINSERT® without plugging. A full scale model of the inlet chute and top of the bin was also tested to refine the design of the inlet distributor.

Next we prepared detailed engineering design drawings and fabricated the equipment. Retrofit installations require special care because equipment in the field is often different from what is shown on available drawings, and the effect of modifications on the existing structure must be considered.

Before starting any design work, one of our engineers made another visit to the plant to collect detailed field measurements. Based on the field measurements and drawings of the existing equipment, we designed the new equipment as a combination of bolted and field welded assemblies that would allow easy field installation. We designed critical structural members, such as the cross beams supporting the inner cone, with rock-boxes to prevent sliding contact between the steel and glass batch.

Components for two of the six bins were initially fabricated and installed. One of our engineers inspected the work during installation and again after the bins were put into operation. Two more bins were modified the following year, and modifications to the last two bins were completed about a year later.

We provided a performance warranty, which guaranteed non-segregated discharge from the bins, as part of the equipment supply contract. According to Jim Phillips, Batch and Furnace Supervisor at the Oakland plant, "The performance of the bins has been excellent. Glass quality problems attributed to batch segregation have been virtually eliminated."