Relative humidity along with time and temperature affect wood drying. Normally these parameters are based on previous drying experience, with the goal being to optimize drying time while minimizing wood cracking. The process parameters are unique to the system used, with different woods and seasonal variations affecting the result. This makes wood drying a demanding process. To achieve the best results, relative humidity needs to be continuously monitored.
Wood is a porous material, i.e. it is hygroscopic, absorbing moisture to reach an equilibrium with the ambient environment. The mechanical properties of wood vary with the temperature, pressure and moisture content. In most applications the moisture in the wood cells must be removed to allow further processing and to protect wood from blue stain, fungi and mold, as well as from cracks and checks. The initial moisture content of green wood, i.e. freshly sawn timber, varies from 50 to 100%, depending on the species. When used as a construction material in, for instance, a normal temperate zone climate, the timber is dried to a moisture content of 18%, while for joinery and carpentry a moisture content of 10% to 15% is ideal.
The accuracy of relative humidity measurements really matters. It directly affects the quality of the drying process and indirectly affects facility capacity. Inaccurate measurements can cause the following problems:
Three main factors help to keep measurements accurate: use of the appropriate sensor, ensuring that the measurement device is installed correctly and regular calibration of the measurement device.
During manufacturing, veneer is dried in a drier circulating hot and humid air. This is a demanding processing step, and accurate dewpoint control is essential in obtaining the best quality veneer for demanding wood products and long-lasting finishes.
There are many probe options to choose from measuring several parameters: humidity, temperature, dew point, CO2, moisture in oil, and vaporized hydrogen peroxide. The probes can be attached to Indigo500 or Indigo200 series transmitter. When is a probe sufficient on its own – and when do you need both a probe and a transmitter?
Some of our customers have applications that require measurement transmitters to be installed outside, so the Vaisala Indigo500 and its family of smart probes have been designed to be durable enough for these kinds of rough, tough conditions.
Learn about the benefits of using two probes measuring either the same parameter or two different ones.
Taking measurements in environments with high relative humidity (over 90%) is always a challenge because the environment is so close to saturation.
As a natural product, wood has a unique set of characteristics that can make drying a challenging and complex process – one where relative humidity (RH) plays a critical role.
In order to run efficiently, the Korkeakoski sawmill seeks to minimize the drying time for timber goods. Therefore the drying temperatures must be very high, which creates very specific requirements for the humidity conditions in the chambers.