Western mills keep up with MSR technology

f Ufnf'S anew aspecrro lumber r quality control beyond the "grading" manufacturers and retail lumbermen have become accustomed to over the generations. Technological advances have resulted in new approaches to traditional products and a matching level of quality control has evolved.

Machine stress rate lumber is one of these products. In 1983, it is estimated 180 million board feet of machine stress-rated lumber will be manufactured by Western lumber producers. There are 16 "machines" already installed in the West with more on the way.

MSR material is increasingly sought for engineered uses in residential and non-residential construction design calling for explicit.single-

Story at a Glance

Quality control keeps up with technological advances . . .stringent procedures. . Machine and visual testang required. .product reliability stressed.

member values. As MSR technology has developed, WWPA mills have played a key role in development of quality control disciplines governing the product.

Stringent procedures cover each mill's initial certification and daily quality control. Samples of every grade/ size/ species combination are pulled out of ongoing production by WWPA inspectors. Each sample piece is individuallytested in a special device that applies 2.1 times the "load" its design values prescribe. The procedures provide that no lumber in a run represented by a sample can be shipped from the mill improperly labeled.

MSR stock also is visually-graded by mill graders in accordance with rules written especially for it. Most in-plant quality control testing is done by plant personnel, but is later reviewed by WWPA.

WWPA inspectors check MSR grades for visual accuracy. Four times a year, a WWPA MSR technologist makes a spot "service check" of available shipping grades at each mill. He conducts tests independent of mill tests and checks test equipment to assure its accuracy.

Glue products also have brought about new approaches to quality control testing. New adhesives have made it possible to assemble pieces of wood into larger members. WWPA has quality procedures that apply to end-and-face-glued products as well as finger-jointed framing lumber.

Visual grading of finger-jointed dimension, while considering joint appearance and quality, considers grade-limiting characteristics the same as those imposed upon solid lumber. The performance of each glue-joint earns special additional quality control attention. Every six months a WWPA mill's gluedproduct production is certified for each glue formula and joint configuration.

Samples typical of production selected by WWPA lumber inspectors are taken off theproduction line, shipped to an independent laboratory and subjected to intensive durability and bending tests. This provides a periodic third-party technical check of each mill's performance. Meanwhile, each mill conducts daily quality control. Samples are pulled hourly from current production. Each is "loaded" to double the assigned design values ofits particular grade as a test.

If the grade is STUD, using different glues than those with certified exterior joints, the same durability test is conducted by specialist mill personnel as in laboratory certification. The hourly samples are placed in a special chamber where intense vacuum saturates the glued joint area far beyond the norms expected in actual use. Then it is dried in an oven, approximately to its original moisture content.

This wet/dry process places the glue line under extraordinary stresses. When broken under doubleload static bending tests at the mill, examination of the finger-joint must reveal that the wood, not the glue, is what gave way most. Production which meets this criteria may be grade stamped accordingly and shipped. The objective of testing and quality control is aproductwhich can be used with confidence.