The Impact of Vacuum-Drying on Efficiency of Hardwood Products Manufacturing

Abstract

Increasing global competition, high stumpage and energy prices, and the slowing housing market have challenged the U.S. hardwood lumber industry during the past several years. Many wood product manufactures are trying to remain in business by implementing continuous improvement programs like lean manufacturing. However, the lumber drying process where lumber is kiln-dried in large batches, can significantly increase manufacturing and inventory lead-time; and is a process that tends to limit how lean the remaining process can become. Vacuum drying has the potential to reduce drying times, reduce batch sizes and achieve product quality comparable or superior to conventional drying. The overall goal of this research was to evaluate how vacuum-drying technology could support further lean implementation in manufacturing of hardwood products. Specifically, to estimate conventional and vacuum drying times, quality, and costs for drying 4/4 red oak lumber; to determine by the use of feasibility analysis (cash flow, net present value, and internal rate of return) differences between conventional and vacuum drying for 4/4 red oak lumber; and to determine if the high capital cost of vacuum drying equipment can be justified with the reduction of WIP and cycle time, while meeting desired throughput. The study includes a cost analysis of vacuum and conventional drying, and a determination of the potential financial gains associated with the reduced drying times via vacuum drying. It was determined that vacuum drying quality was equal or better than conventional drying with less checking, end splits, drying stress and shrinkage. Compared to conventional drying, vacuum drying times with air drying and without air drying were 67% less and 70% less, respectively. Conventional and vacuum with no air drying scenarios were determined to be financially feasible when compared using Net Present Value and Internal Rate of Return analysis. However, vacuum drying with no air drying had better NPV and IRR values than conventional drying. The scenario of vacuum with air drying was not feasible. Two case studies, each employing the three drying scenarios (conventional drying, vacuum with air drying, and vacuum without air drying), were used to determine the impact of cycle times and work in process. It was determined that the cycle times for vacuum drying were 87% and 95% less than conventional drying for the first case study and 51% and 90% less than conventional drying for the second. WIP was 48% and 84% less in the first case study and 43% and 92% less than conventional drying for the second. Cycle time was reduced by 87% and 51% for Plant C and D, respectively. Finally it was determined that the reduction of WIP represented a cost saving of 73% and 76% for the two case studies. The reduction in costs, faster drying rates, and equal quality, and reduced cycle times make vacuum drying a potential technology available for improvement of the competitiveness for flooring manufacturers.