Computer Control in a Dry-Formed Fiberboard Process

A computer process control system was installed on a dry-formed hardboard siding process. The system includes: 1) a traversing weight sensor located after the prepress, 2) three moisture sensors located after the filter heads which receive fiber from the three dryers, 3) an operator’s station, and 4) a printer/plotter. The computer controls dry fiber weight by adjusting the final shave-off height. Fiber moisture content (MC) is controlled by adjusting the outlet dryer temperature. In addition the computer optimizes line speed based on the press cycle time and fiber availability and controls the resin flow to maintain the target resin-to-wood ratio. Under computer control the hourly average weight variability about target was reduced 95 percent and short term scan-to-scan weight variability was reduced 39 percent. Short term MC variability was reduced 43 percent. Economic results achieved with the tighter computer control included a 2.5 percent raw material savings, a 30 percent reduction in rejects, a 57 precent reduction in dryer fires, and a 715,000 SCF reduction in natural gas usage per month.

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