When Plum Creek Timber Company's plywood mill was built in Columbia Falls Montana, US, in 1964, it was one of the many commodity mills producing sheathing which rose up in US softwood plywood's heyday, but many have gone. It is specialities that have kept many of the remaining mills - including Plum Creek's - in business, and keeping up with the latest time and labour-saving innovations is a big part of it, along with methods and equipment giving better-quality output. Encouraging employees to do their best is another big feature in Plum Creek's mills. These three philosophies have kept Plum Creek plywood right up there in an industry declining in numbers. One of the latest innovations is robot-controlled panel patching, or plugging. Plant Manager Rick Nelson said his mill has been heavily into industrial panels for more than 20 years and overlays have become more important, particularly in concrete form stock using Dynea and Paneltech overlays. The Columbia Falls mill's output is entirely in exterior grades. As an example, Marine tech grade plywood is one speciality. This is designed for rigorous marine use with Superior 'B' face grades. It is all structural 1, group 1 species construction, produced with 'ultra core' tight, 'high c' grade cross-bands and centres. A preponderance of Plum Creek plywood's logs come from the company's own timberlands since it is the nation's largest private timberland owner. The plywood mill uses primarily Douglas fir and western larch. Present log diameter averages 9.5in (diameters are gradually decreasing) with a minimum diameter of 7.5in. The lathes peel down to a 3.25in core which a local mill buys, squares two sides, and sells for landscaping timbers. The plywood plant shares a log yard with Plum Creek's adjoining sawmill and MDF mill and the entire site is one mile wide. A LeTourneau machine unloads trucks while a Caterpillar 980 decks logs, serves the conditioning vats and feeds the mill. A 36in Salem ring debarker skins the logs, which then proceed to a 72in double circular saw built by Plum Creek. It cuts them to 8ft peeler lengths. Next they go to the 12 hot water conditioning vats for up to 24 hours, depending on conditions, to achieve a 110ºF core temperature. The blocks come up to the 250hp Coe lathe installation. The Coe 765 x-y charger works through the scanner to the lathe, which has three retractable spindles. The automated system peels seven to eight blocks per minute, primarily in 1'10in and 1'7in. The veneer offbears to four 90ft trays with Lloyd controls. A Ventek scanner and moisture detector precedes the Durand-Raute rotary clipper, which offbears to a CTC diverter and 10-bin stacker that can stack random and 27s in two bins each. The other bins take full sheets. There are four moisture sorts. A short green chain pulls remaining random strip and there is a centre-cut fishtail at the end of the line. Two Coe jet tube direct-fired dryers with Sweed automatic feeders are heated by a Wellons fuel cell which burns residuals, bark, sander dust and plywood trim. The second dryer has a rather unusual set-up with six steam sections heated from a central boiler for the complex and the others heated by a cell reheating dryer air. To solve a dryer dust-plugging problem, Plum Creek installed a PPC Industries electrostatic precipitator. Hot gases from a blending chamber go through a Zurn Industries multicyclone to remove larger particulate and wood fibre picked up in the recirculated air. The dried veneer goes through Ventek GS2000 scanners and sorting to CTC and Braun-Cardin 10-bin stackers. With declining grades because of smaller wood, this accurate sorting is particularly important. The mill had seven manually-operated Raimann patchers. Robotic controls have already been added to two of these. Two more are slated to be added this autumn, leaving two manual machines remaining. The veneer goes under a Ventek scanner which locates defects. This information goes into computer memory for each sheet as it is transferred to the patch line. The sheets are automatically placed on the patcher's table with the accuracy required to ensure accurate patching as the computer controls the travel of each sheet. Maintaining positive control, vacuum heads on Panuc M-410 robots move sheets around under the patcher heads in the computer-controlled patching pattern. The system is being supplied by Ventek and the Precision Technologies division of Willamette Valley Co, Eugene, Oregon, US. Two Raute composers with Ventek scanning systems serve a Durand five-feeder lay-up line installed eight years ago. The line can handle lay-ups from 0.25in to 1.5in. From lay-up the panels go to a pre-press and two 36-opening Williams White hot presses with Raute and Spartek unloaders. Offbearing, they go to a pie rack for cooling and to a Willamette Valley Co synthetic patching putty line as required. A Globe saw line is followed by a Coe Tidland six-head sander. A rebuilt six-head Kimwood will be added. The mill produces 120 million ft², 3'8in basis, or 480,000ft² per day, with a total workforce of 200. The green end runs two shifts with three shifts on dryers, pluggers and composers and two shifts on lay-up through the finish end.