Drying Quality: The Importance of Proper Baffling
Baffles are an integral part of lumber drying. They are used to close off all unwanted openings in the kiln. Such openings are, over the top and underneath the stacks, and around the ends of the cars. Air takes the path of least resistance. So any openings in the kiln, the air will go there instead of going through the sticker spaces, where we want it to go.
These baffles keep the air from going over the top of the cars. Two of the most critical areas for these baffles to perform correctly are uniform stack heights and the structural condition of the baffles. In order for the baffles to sit tightly down on the outer edge of the stacks, all stacks must be uniform in height. Baffles that are damaged should be repaired as soon as possible so that they sit evenly on the lumber with no gaps. Often these baffles are made from thin sheet metal or aluminum. If they are too light, the air flow in the kiln could lift them up, creating an opening where the air can go over the car. When this occurs, you’ll need to add weight to the outer edge of the baffle to hold it down. Another problem often found is the cable used to raise and lower the baffles is restricted from falling while the lumber dries. The kiln stack can shrink in height as much as one foot. If the cables are tight at the beginning of the schedule, then by the end you could have as much as a foot opening between the top of the car and the top baffles.
The result from any of these scenarios will be losing air flow over the top of the stacks, over drying the top 1/3 of the stack, and under drying the bottom 1/3 of the stack due to low air flow at the bottom. We degrade our lumber by over drying, and by being wet.
End or door baffles, prevent the air from escaping around the end of the load at the doors. If you are not using these baffles correctly, it will result in over dry lumber right on the end, and wet lumber in the pack away from the door. This is because you’ll have insufficient air in the end pack due to the air choosing the path of least resistance around the end.
Floor baffles provide the same function as top and end baffles. They keep the air from going through an opening underneath the car and direct it through the lumber.
Plenum baffles are also used for directing air flow. This type of baffle is mounted to the kiln walls and captures air coming from overhead and directs some of it down through the lower part of the stack.
To ensure good quality, always remember, proper baffling is important. Baffles will direct air uniformly through the sticker spaces where we need it to go. Drying with uniform air flow causes fewer defects and produces a better quality product.