Expert Article

Bringing out the beauty of wood: Veneer drying with humidity control

Juhani Lehto

Juhani Lehto

Product Manager for high-end products


Industrial Manufacturing and Processes
Industrial Measurements

Wood is an incredible and unique material with stunning visual appearance. Wood as a material is strong and versatile while being renewable and sustainable.  

A veneer is a thin slice of wood, typically between 0.5 and 3.0 mm, often used to cover or wrap core panels of different materials. Veneers are commonly used in furniture making, cabinetry, doors, and interior design applications. Wood veneers are often preferred over solid wood because they can be more economical, more flexible, and more environmentally friendly. 

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. The drying process domineers the veneer manufacturing efficiency and can be a bottleneck if not optimized. 

Veneer making step-by-step

In veneer production, one of the first steps is cooking the log. Next, the wet log is flat sliced, much like salami is sliced at the delicatessen. Veneer is fed into a press dryer, where it travels between two conveyors through the high-temperature dryer. The dryer air temperature fluctuates between 180 – 190 °C depending on humidity and moisture. 

In modern dryers, separate zones allow tight control and adjustment of the internal temperature and humidity of the dryer. The veneer exits the dyer, sheet by sheet, ready to be glued, graded, cut into matching size sheets, and bundled.

Quality through dewpoint control

The veneer must be dried well for it to be flat, flexible, and suitable for further processing, for example, splice the veneer into sheets. Yet, the veneer moisture content must be at a suitable and even level across the product, and according to different product specification, which varies. The final moisture content has a tight specification and if that is not met, the next processing part, gluing, might not be successful. Usually, this means that the whole batch is ruined.

Drying is a delicate process, and the biggest issue in manufacturing usually relates to moisture content fluctuation in veneer. Too dry veneer may cause problems in splicing because it becomes brittle and may break. Over-drying is uneconomical as it overuses energy and time, decline veneer quality and capacity, and occupy the drier unnecessarily. 

The main components that have an effect on veneer moisture content include natural variations in raw wood moisture content, variations in the humidity of the drying air, different dryer filling grades, and changes in drying temperature.

Therefore, the manufacturers will benefit greatly from online measurement data, which gives a whole new basis for controlling the drying process. 

Direct installation with no sampling systems

The humidity inside a dryer is measured with Vaisala DRYCAP® Dewpoint Transmitters, such as Vaisala DMP5, DMP6 and HMP7, which are directly installed into different zones of the dryer. No complicated sampling systems are needed. The warmed probe technology minimizes the risk of condensation accumulating on the sensor. If the DRYCAP® sensor does get wet, it dries rapidly and recovers its swift response time.

The measurement data flows to the operating system of the dryer, which connects all relevant information needed to control the dryer's operation. The data of this PLC-based system may be accessed from remote monitors at the operator’s location and changes to operating procedures are made on touch screens. 

Quality matters 

Producing on-spec veneer consistently requires a drying process that can be measured and adjusted, with online data provided by quality measurement that can take the process heat and humidity. Additionally, energy efficiency, yield, and quality can increase, bringing favorable results to manufacturing and customers. 

Go to wood drying page

Juhani Lehto

Juhani Lehto

Product Manager for high-end products


Juhani Lehto has over ten years of experience in industrial measurements and sensor technology. He holds a Master of Science degree in Technology from the Aalto University of Espoo, Finland.