Pressure Treatment
At 7:20 in
How Wood Fence Posts are Made
What happens here
Once the posts are air-dried to below 30% moisture content, they are prepared for pressure treatment. Bundles of posts are loaded onto a tram, resembling a train rail, and securely chained together. This entire tram is then pushed deep into a massive pressure tank, also known as an autoclave. Inside the autoclave, the magic happens: a computerized system controls the injection of a chemical preservative (like chromated copper arsenate - CCA, or similar alternatives) at approximately 150 PSI (pounds per square inch). This high pressure forces the treatment chemicals into the empty air gaps created by the drying process within the wood's cellular structure, saturating it completely for long-lasting protection.
Goal: Impregnate dried posts with chemical preservatives for durability.
Tools and materials
- Chains — Securing posts onto the tram
- Computerized Control System — Monitoring and controlling the pressure treatment process
- Personal Protective Equipment — Ensuring worker safety during handling of chemicals and machinery
- Pressure Tank — Applying chemical treatment under high pressure
- Tram/Rail System — Transporting bundles of posts into the pressure tank
- Chemical Wood Preservative — Protecting wood from rot and insects