Statistical process control for residential treated wood

Patricia K. Lebow; Timothy M. Young; Stan Lebow

Treesearch

Statistical process control for residential treated wood

Informally Refereed

Authors:

Patricia K. Lebow, Timothy M. Young, Stan Lebow

Year:

2017

Type:

Paper

Station:

Forest Products Laboratory

Source:

In: McCowan, C.; Gothard, T.; Staula, B., eds. Proceedings, One hundred thirteenth annual meeting of the American wood protection association. Birmingham, AL: American Wood Protection Association: 234-247.

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Abstract

This paper is the first stage of a study that attempts to improve the process of manufacturing treated lumber through the use of statistical process control (SPC). Analysis of industrial and auditing agency data sets revealed there are differences between the industry and agency probability density functions (pdf) for normalized retention data. Resampling of batches of treated wood without replacement appears to affect the pdf of the industrial data. The best-fitting pdf for the agency data is the Largest Extreme Value (LEV) pdf. Assumptions of a normal or a Gaussian pdf may not be valid. The process of treated residential lumber is hard to predict due to special-cause variation. A capability analysis revealed that from 2.25% to 3.16% of the charges are below the AWPA Lower Confidence Limit (LCL) for an industrial data set and 1.57% to 6.63% are below the LCL for an agency data set, with both varying by product type.

Keywords

Residential treated lumber, statistical process control, probability density function, largest Extreme Value, natural variation, capability analysis

Citation

Lebow, Patricia K.; Young, Timothy M.; Lebow, Stan. 2017. Statistical process control for residential treated wood. In: McCowan, C.; Gothard, T.; Staula, B., eds. Proceedings, One hundred thirteenth annual meeting of the American wood protection association. Birmingham, AL: American Wood Protection Association: 234-247.