Designing WIP Systems (CONT’D FROM PAGE 66)
should be long enough that transfer cars can always dis- charge several full car loads even when the machine is down. Control algorithms typically try to place material on lines directly opposite the converting equipment on which they will be processed. Discipline is required when using an automated sys- tem. For one thing, bottom and tie sheets will, in most cases, prevent automated systems from separating stacks as necessary to build car loads and should be avoided. For another, don’t push material off the corrugator in an attempt to keep it running if it can’t be processed in a reasonable time, since doing so can overpower the WIP system. Furthermore, over-riding the system by manual- ly packing stacks together may cause the system to lose track of material. Although WIP systems don’t get the same attention as corrugators and converting machines, failure to design them properly, will prevent your plant from fully getting the benefit of your investment in equipment. Richard Etra is a 47-year veteran of the corrugated indus- try with extensive experience in all aspects of box plant operations. He was a principal of Star Corrugated Box Company, and subsequently Manager of Special Projects and Technology at Cascades Containerboard Packaging. He is currently the principal of Etra Corrugated Solutions, LLC and can be reached at richard_etra@etracorrugated- solutions.com.
be accommodated, and their length. Sheet size distribution and quantity per stack, dictated by flutes and stability, can be used to calculate the quantity of conveyors needed to store that MSF of product. Take into account how densely the controls allow material to be packed on the conveyors; capacity is not 100 percent of the conveyor length.
Corrugator discharge lines should be able to hold multiple carloads to ensure that the transfer car or cars can travel to the furthest WIP conveyor and back in time to remove corrugator output when running at top speed with low stacks. Similarly, converting machine infeed lines
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April 4, 2022
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