The manufacturing process for OSB subflooring starts in the log yard. Pines and hardwoods are purchased from local wood baskets (1-4 hours away from mill). Logs arrive at the mill in 40-60% of water. Logs remain in wood stack from 1-12 days on average where some drying takes place. Logs species are typically kept together where possible because stranding operation is sensitive to species.
The next step for creating OSB subfloors is the creation of flakes. The process is like a giant deli slicer that cuts thin slices out of log. Scoring tips are knives that simultaneously cut the slice into 4-6" strands. Widths are actually controlled by counter knives that "break" the strand along growth rings. OSB Flake thickness target for all mills is between .027"-.030".
The drying and screen process for creating OSB subfloors starts when the furnaces blow hot, dry air into rotating drums to dry the OSB flakes from 40% moisture to 4-9%. The fuel is the bark from the trees. The OSB goes through single pass or triple pass dryers. Typically one dryer is dedicated to core moistures (~4.0%) while remaining dryers produce surface moistures (~9.0%). Once dry, OSB strands are sent to screeners that separate fines from stands. Hot, moist air is sent through RTOs that use natural gas to breakdown organic VOCs.
This brings us to the stage where the rotary blending begins in the blender. PF (phenolformaldehyde) and wax are added to most OSB subflooring. PF powder is used to stop curl OSB flakes from popping. Wax helps PF powder bond and provides modest moisture resistance. MDI (Methylene diphenyl diisocyanate)is the key ingredient. MDI is used in the core for most OSB subfloors for speed benefits. AdvanTech is unique in the quantities of MDI used in the surface.
Typical OSB resins like PF simply glue strands together with physical bonds (like velcro). PF and the wood remain chemically the same after pressing. MDI (Methylene diphenyl diisocyanate)reacts with the water in the wood transforming it to polyurea. The bond is a chemical bond which is very strong and highly resistant to water. Smaller amounts of the MDI may react with the wood transforming it to polyurethane. Polyurea has the same water resistance properties as polyurethane We prefer polyurea because it is known for its "stiff" properties, polyurethane is known for flexibility.
You probably had no idea the amount of detail that goes into creating OSB subfloors. That is just the process to prepare the wood and flakes before forming the actual OSB boards. Learn about the next phase of forming OSB subflooring