Individuals in the woodworking field such as furniture, cabinetry, and flooring manufacturers often encounter manufacturing issued caused by dry air. These issues can include warping, shrinkage and other dimensional problems with painting, finishing and gluing; and a variety of static electricity-based problems. All can affect product quality, part reject rates, throughput speeds, run times and overtime, which all cut into profits.
Maintaining proper relative humidity (RH) throughout the entire cycle of transportation, storage, manufacturing, finishing and finished goods storage will have a substantial impact on the moisture content of the wood you use in your manufacturing and finishing operations.
Most woodworking begins with kiln-dried lumber containing 6% to 11% moisture content. Wood is hydroscopic in nature, readily absorbing and releasing moisture, depending on humidity levels. Wood that is stored and worked on in environemnts with stable humidity levels, ensures that the wood stays dimensionally stable and should give you relatively few manufacturing problems. However, retaining 11% moisture content in kiln-dried wood requires an RH level of 55% to 60%.
When air is heated, humidity levels often drop to as little as 10% RH or less. RH levels under 40% reduce moisture content in wood and lead to changes in wood dimensions, including shrinking or swelling, cupping or warping, and checking or splitting. Once the damage is done, it is usually impossible to correct it.
Machine stops and reduced machine speeds, problems with settings and production quality are likely results. This leads to predictable drops in production efficiency, increased machine and tool wear and tear, and a higher number of part rejects.
Static electricity problems in a woodworking environment occur when dry air causes surfaces to become charged with static electricity. It causes a variety of problems including dust fires and static explosions. In some cases, static electricity can also affect the way paints and finishes adhere to wood.
Dimensional changes can affect all aspects of a wood’s size. Dried-out wood blanks or parts can shrink, cup or warp, check and split causing a host of problems when the wood’s shape or size no longer fits proper dimensions for planing, shaping or assembly.
Gluing and laminating issues are common. Glues often do not cure as completely and uniformly in dry conditions. Ill-fitting pieces also are frequently subject to gluing problems. Dry air can often lead to glue joints separating or veneers popping off the base wood as dimensions change or pieces twist or “pop.”