Plywood QC Inspection Checklist : Part 13 warping and twisting
When inspect plywood ,normally the first top piece of plywood always have a little warpping,not just because of the manufacturing factory ,maybe the packing and conditioning problems or bottom pallets problems .
Wood warping is a deviation from flatness in plywood as a result of stresses and uneven shrinkage. Warping can also occur in plywood considered “dry” (plywood can take up and release moisture indefinitely), when it takes up moisture unevenly, or – especially – is allowed to return to its “dry” equilibrium state unevenly, too slowly, or too quickly. Many factors can contribute to plywood warp; wood species, grain orientation, air flow, sunlight, uneven finishing, temperature – even cutting season and the moon’s gravitational pull are taken into account in some traditions .
The types of wood warping include:
- bow: a warp along the length of the face of the plywood
- crook: (also called wain) a warp along the length of the edge of the plywood
- kink: a localized crook, often due to a knot
- cup: a warp across the width of the face, in which the edges are higher or lower than the center of the plywood
- twist or wind: a distortion in which the two ends do not lie on the same plane. Winding sticks assist in viewing this defect.
Plywood warping costs the wood industry in the world millions of dollars per year. The qc can check how is the warpping and twist happened and try to help manufacturers make changes in the manufacturing process so that wood doesn’t arrive at its destination warped after it leaves the mill or factory.