Parquet Surface Crack Causes And Process Improvement Research

Multi-ply parquets(MPP) with their perpendicular grain each other layer overcome the anisotropy of natural lumber, also enhance the balance and stability of products. Therefore, MPP are more and more paved in heat radiant environment. However, not all the wood species for MPP suitable to be used in this entironment. Some wood species for MPP's surfaces appear checks less than a week after they were paved and seriously affect the decoration effect. Also some parquets are extremely perfect in the south, but will crack when paved in the north. Therefore, it is necessary to study the properties of surface resisting cold and hot circulation(CHC) of MPP thoroughly.The CHC test result of MPP which surface layers were teak,black walnut,mongolian oak,maple,jatoba veneer of thickness 0.6mm, 2.0mm and 4.0mm showed that: the 2.0mm and 4.0mm jatoba tangential veneer and half tangential veneer appeared checks, and the former was more serious than the latter, other parquets surfaces'effect were perfect, did not appear checks.After thorough research about remaining dry stress, coefficient of shrinkage, tensile strength perpendicular to grain of wood as well as moisture content'change of parquets surface layers in the hot pressing and the use process (simulation). Conclusions as follow: the interior reason why jatoba parquets surface layers easy to crack is that, jatoba veneer tangential's coefficient of shrinkage is bigger, but the tangential tensile strength perpendicular to grain of wood is relatively smaller; The external causes is that, in the parquets hot pressing and use process, moisture content of parquets surface layers reduced with transverse shrinkage, then resulted in shrink stress.The adoption of cold pressing technics can't solve the question of jatoba parquets surface's checks. Before pressed with plywood, moisture content of jatoba veneers adjusted to 6%～7%, the effect of CHC on parquet was improved, but the surface layers cracked all the same. Before pressed with plywood, moisture content of jatoba veneer adjusted to 5%～6%, the effect of CHC on parquet was very good and the surface didn't appear checks. but parquets would bow bend because of moisture absorption.Before pressed with plywood, jatoba veneers impregnated with melamine modified formaldehyde resin, then moisture content adjusted to 6%～7%, the effect of CHC on parquet was very good and the surface didn't appear checks. It can meet the need of state standard GB/T17657-2000"Test methods of evaluating the properties of wood-based panels and surface decorated wood-based panels".The study showed that, the gluebond strength and painting properties of jatoba parquets with 2.0mm and the 4.0mm thickness of jatoba veneer impregnated with resin can reach the state standard GB/T18103-2000"Parquet".