Autoclave treatments

Among the autoclave treatments, the most commonly used process these days is the injection treatment called the Bethell process. At the beginning it consists of filling all the cells of the wood with product until full saturation (filled cells process).
Whatever may be the cycle adjustment, it is the same at the beginning:

• Before the treatment, the pieces of wood should be imperatively dry, at a humidity rate less than 25%).
• Insertion of the wood load into the autoclave.
• Initial vacuuming to take out the air contained in the cells (vacuuming of at least 85% during 30 to 60 minutes at least).
• Refilling the autoclave with treatment product, maintaining the vacuum.
• Stopping the vacuum and applying pressure from 10 to 12 bars: the wood, vacuumed out of its air, spontaneously absorbs the product and the applied pressure allows speeding the absorption. This pressure is maintained until full saturation that corresponds to the total filling of the accessible vacuumed cells. According to the species and the sections, this phase could last from 30 minutes to 3 hours and sometimes more
• Vacuuming the product.
• Final vacuum application, destined to rebalance the internal pressures in the wood, to stop the reach of air that had been compressed during the pressure phase and to get a moisturized wood surface, without a leaking coming out of the autoclave.

The next figure illustrates the successive phases of an injection autoclave treatment (Bethell process).