Tilt hoist with multiple independent rotatable masts

Abstract

A tilt hoist for breaking down a lumber stack has an inclined face such that a lumber stack may be translated by sliding upwards over the inclined face. The tilt hoist includes a plurality of tilt masts having translatable hoist arms for receiving the lumber stack from a stack transfer device such as an infeed chain. The tilt masts and corresponding hoist arms are pivotally mounted to the support frame at the pivot points located at the bottom of the tilt masts. A selected first group of tilt masts (the number depending on the tiered material length) are rotated into a stack receiving position where the hoist arms engage the underside of a first lumber stack which has been advanced by an infeed chain to a stack transfer position. The selected first group of tilt masts and corresponding hoist arms are rotated back, lifting the first lumber stack and positioning the first lumber stack into slidable engagement on the inclined face, that is, so that the first lumber stack lies flush on its side on the inclined face. The hoist arms translate the first lumber stack by sliding the stack upwards over the inclined face in a direction towards and over the shear point of the inclined face. Immediately after discharging the first lumber stack, the first group of tilt masts and corresponding hoist arms are rotated downwards to a recessed position where they are recessed beneath the inclined face so as to allow a second, subsequent, lumber stack to pass over.