Particleboard Blow Detector

A non-contacting ultrasonic inspection system has been developed to detect laminar imperfections in composite panels fabricated from wood laminates, chips, or fibers. The prototype blow detector consisted of a single channel transmitter-receiver, and an electronic gating and monitoring system. Signal levels were recorded on a strip chart recorder. The transmitter, placed above the board, emits a sound burst which travels across an air gap, through the board, across an air gap below the board, to the receiver. A distinct drop in the average signal amplitude picked up by the receiver indicates a blow. Other signals which momentarily drop to low levels indicate weak bonds or low density areas approaching blow conditions. Good panels show a consistent signal amplitude along the full length of the board. During the 6-month production test, little maintenance was required on either the electronic or sensor hardware of the system. The Sondictor blow detector may be used on panel products varying in thickness from 3/16 to 1-3/16 inches and in specific gravity from 0.6 to 1.0 and on all board widths Presently manufactured. Defects can be detected in any thickness, and between any ply or veneer. Materials which are not suited to this type of inspection include door cores and extremely high density. hardboard with a glossy surface. The best location for a blow detector is just after the board has been pressed, so that the process variables that are causing the defects can be corrected.

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