New Lumber Mill Spray System Reduces Rejection Rate and Chemical Usage, Improves Customer Satisfaction and Virtually Eliminates Downtime
 Application Could Benefit Any Mill Applying Sapstain Control Chemical, Paint or Stain to Lumber, Siding or Molding
Sapstain control chemical - an anti-stain/anti-mildew/anti-fungus chemical - is applied to lumber to prevent fungal growth during transport or storage. If the chemical is applied too heavily, expensive chemical is wasted. Too lightly and fungus grows.
PROBLEM: Years ago, a major Pacific Northwest lumber mill used open hoses to spray the sapstain control chemical and then switched to a more efficient system using Spraying Systems Co.'s FloodJet® spray nozzles. Because of the use of a recirculating system, sawdust impeded the system causing frequent downtime. The entire line needed to be shut down while maintenance crews spent up to 30 minutes cleaning and replacing nozzles. The line had to be shut down almost every two hours.
The FloodJet spray nozzles were superior to the spray hoses that were previously being used. However, higher spray impact was necessary because the sapstain control chemical did not penetrate into the lumber. Low retention onto the lumber resulted in fungal growth and a rejection rate between 40% and 50%. Over applying the chemical is not a viable alternative since the chemical is so costly.
SOLUTION: Spraying Systems Co.'s sales engineer designed a spray system which incorporates the use of: WindJet® blow-off nozzles to help reduce sawdust from contaminating the system and to blow-off excess chemical back into the spray booth; a parallel self-cleaning line strainer system to protect the nozzles from clogging; and Quick VeeJet® spray nozzles to lower maintenance costs.
Here's how the system works: As the lumber enters the spray booth on a conveyor, WindJet nozzles mounted at the outside entrance of the spray booth blow sawdust off of the incoming lumber. This reduces the amount of sawdust entering the recirculating system. Once inside the spray booth, the lumber is sprayed with the sapstain control chemical by Quick VeeJet spray nozzles. Depending on the dimensions of the lumber, the system can be switched to accommodate 2" x 4" up to 14" x 16" (5.1 cm x 10.2 cm up to 35.6 cm x 40.6 cm) lumber. Two, two-way solenoid valves control which of the spray rings is activated. As the lumber begins to exit the spray booth, another bank of WindJet nozzles blow the excess chemical back into the spray booth. This saves on chemical usage and also allows the lumber to dry quicker as it progresses down the line.
The parallel self-cleaning line strainers are used in increasing smaller mesh sizes to strain out sawdust and wood flour from the recirculating system, further protecting the nozzles.
By installing pressure gauges before and after each strainer, the operator can tell at once if a particular strainer needs to be purged and they can do so without disassembling the strainer.
The rejection rate has been decreased from 50 percent to less than 10 percent (and the 10 percent is due to other factors, not inadequacies of the spray system). Plus, the system requires only routine maintenance once every couple of days versus every couple of hours. Chemical usage is reduced since the coating is being applied more precisely and with higher impact and since the WindJet® nozzles blow the residual chemical back into the spray booth for re-use.
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