Image: Graph of the process
The production process of Frøslev Heatwood is based on the use of high temperatures and water vapour preventing the wood from burning. The process removes sugary substances from the wood, and the cellular structure is altered. Rot and fungi can therefore not settle in the tree, and the finished product becomes very dimensionally stable. Frøslev Heatwood is very suitable for use in the Nordic climate, especially during humid seasons.
Frøslev Heatwood is a very sustainable product as no chemicals are used at any point during the process. Moreover, energy consumption during production is very low.
The process can be divided into three steps.
Phase 1 - Increase in temperature and kiln desiccation
The air temperature in the oven is rapidly increased by using heat and steam until it reaches a temperature of about 100 °C. The wood reaches the same temperature. The temperature is then gradually increased to 130 °C, and kiln drying takes place. Steam is used as a moisture barrier to prevent the wood from splitting. The vapour also causes cellular structure changes in the wood.
After this phase, the moisture content of the tree is reduced to almost zero.
Phase 2 - Intensive heat treatment
During the intensive heat treatment phase, the air and wood temperature is increased to between 185 and 225 °C. The highest final temperature depends on the requested use of the wood.
When the requested final temperature has been reached, the temperature is kept constant for 2-3 hours. Steam is used to prevent the wood from burning and splitting and continues to be part of altering the cellular structure of the wood.
Phase 3 - Cooling and adding moisture
During the final phase, the temperature is reduced by using a water spraying system. The moisture content of the wood is raised to just above 4%, so work can still be done on the wood.
Heat-treated wood is available in two versions: Class D for outdoor use where the wood is heated up to 212 °C and Class S for indoor use
Frøslev only sells Class D for outdoor cladding and terraces. The profiles are not processed till after the heat treatment.