Dust-extraction systems were attached to the packaging machines, the sugar screening equipment, and the mills for powdered-sugar production, to remove sugar dust. The dust-extraction ducts were connected to dry dust collectors. However, it was found that the maintenance of the dust-collection system had been poor. In addition, some equipment was significantly undersized or incorrectly installed. Some dust ducts were found to be partially, and in some locations, completely filled with sugar dust.
The plant had hired an outside consultant to evaluate airflows, pressure drops, and other operating parameters on both the dry and the wet dust-collection systems. The report identified numerous design and maintenance deficiencies. Because the report was delivered only a few days before the 2008 catastrophe, there had been no opportunity to review or act on it.
In addition, during the investigation following the 2008 catastrophe, it was found that sugar conveying and processing equipment were not adequately sealed to prevent spillage of significant quantities of sugar onto the adjacent floors. Less than 2 months before the catastrophe, an internal inspection by company supervisors and quality assurance personnel learnt that many tonnes of spilled sugar had to be removed from the floors at intervals and returned to the refinery for reprocessing. Packaging operators and other employees also reported significant amounts of sugar dust escaping the packaging equipment into the working areas.
The systems for conveying maize starch to be mixed with the granulated sugar, the grinding mills, and the powdered-sugar vertical packing machine all generated significant quantities of sugar dust and maize starch in the work area. Workers reported that airborne sugar dust and spilled sugar in the powdered-sugar processing and packaging work areas were a constant problem and that significant accumulations were often seen on equipment and on the floor. One worker told that he used a squeegee to clear a path on the floor through spilled powdered sugar to get to equipment he operated during his shift.
Packaging equipment unwinds materials from its roll, forms it into the shape of a container, fills it with product, and seals the container. Printed material should, of course, reflect the container’s length (the “cutoff”) and its width (the “web”). Web and cutoff can be no more precise than as initially printed, but any subsequent web handling can introduce additional variability to both. Slitting defines a roll’s edge that must parallel to the machine direction of the printing process. Figure 6.1 suggests the challenge. Three impressions on the right have a light-colored border and three on the left have a darker border. Slitting between the third and fourth impressions (cut No. 3) is likely to produce a wavy line with alternating strips of either color. They would appear on the right edge of the third roll and left edge of the fourth roll. When print extends to (and through) a slit edge as in Figure 6.1 (called a “bleeding edge”) its color must be uniform for a width at least as great as the side-to-side tolerance of the slitting operation.
Once the contract has been agreed, the processes of design and construction may commence. These lead to the manufacturing site acceptance trials, which would include a full validation of all the operational requirements of the machine. The final stage is delivery, installation and commissioning, at which the performance of the machine is assessed to ensure that the required operational performance has been achieved.
A rather unusual application of rigid PVC involves building apparatus from machined parts, largely because the polymer is very easy to machine into complex and intricate components. A company in Coventry had the idea of building a type of transparent film packaging machine using such PVC components to produce the wrapping action needed. Their concept included incorporating water-cooling channels within the PVC parts to control the process. They built a working prototype using a combination of light alloy components, slab PVC and acetal bearings (Fig. 6.17), and relied on a toolmaker to machine the various PVC parts and solvent welding the parts together to make the inner water-cooling channels. However, when the wrapping machine was first switched on in 1998, numerous leaks occurred from the PVC components and rendered the process inoperable.
The forming process on a horizontal packing machine requires conformance of printing to the expected machine sequence. The issue is a recurring one for printed rolls of any material for any handling process. To communicate expectations, the printing industry (not only flexible packaging) uses standard designations for print orientation on a roll (Figure 6.2). Eight orientations are described. Numbers one through four refer to printing wound to read from the outside of the roll; five through eight refer to printing wound inside of the roll. The four numbers of each set refer to the orientation of the printing relative to the leading edge of the unwinding roll, top, bottom, right, or left.
The plastic packaging company sued the toolmaker for their losses. I was asked to examine various parts and report on the root cause of the problem. One particular part was chosen for close scrutiny. It was a bar 640 mm long with a section of 39 by 20 mm and when examined, proved to be slightly curved, being about 2 mm out of true. The bar had been solvent welded to form the water channel which ran along its length and was drilled at either end (inner diameter about 8.5 mm) to accept the water supply. Macroscopic inspection showed that the joint between the two halves exhibited a small gap of about 0.6 mm (Fig. 6.18). The same picture shows cross-threading on the upper part of the screw thread, which no doubt was caused by numerous attempts to discover the source of the leak or disconnect the supply to stop the leakage. Since the water pressure was about 2.6 bar or 38 psi, the inner source of the leak was established. External examination showed a similar problem, with similar sized gaps in the joint (Fig. 6.19), and since the bar had leaked here in service, a path between the two gaps was present. No doubt the many other leaks in the system were caused in a similar way by poor joints.
After pressing, the garment should be free from wrinkle and creases, and have a good shape. Apparel needs to be stored and packed for delivery to the potential customers. Nowadays, there are manual or semi-automatic small packing machine available in the industry, but careless or inappropriate storage and packaging will cause a deterioration in the appearance of the final product.