Board selection and sorting throughout the milling process assists sawmills in selecting cutting patterns and products standards for their market segments and is essential for quality assurance. Unfortunately, the sorting method often damages boards and reduces efficiencies.
The most common sorting method is to grade boards and direct them to a specific storage area to fall into bins until needed. The bins are usually filled from the bottom up, increasing the risk of boards breaking and inventory loss.
USNR, the world’s largest supplier of equipment and technologies for the wood processing industry, manufactures a range of wet and drymill lumber handling equipment and systems, including top-loading sling sorters.
Neil Murray and his company, Pinnacle-SA, supply USNR products in Africa. Murray says a sorter-top sling bay system in the drymill handles premium boards and other high-quality niche products gently.
Nylon straps or slings are suspended transversely to form a “cradle” that catches and supports the boards released by the top-sorter. While the dropping boards fill the sling cradle, the hydraulic let-down system slowly extends the cradle downwards. The distance between the top of the package and the sorter remains constant.
When ready, the package lowers until it reaches the floor chains. One end of the sling is released, and the boards offload and travel along the chains. The slings retract, reattach, and the sorting bay is ready for the next load.
USNR manufactures different sorter tops, including pusher-lug, drag-chain and J-bar sorters.
The pusher-lug design is ideal for high-speed applications and sorting random thickness products. The pusher lug sorter’s chain cannot leave marks because it does not touch the boards. It is capable of up to 160 lugs/min in wetmill applications and 250 lugs/min in planer/dry mills.
The drag-chain sorter is also suitable for high-speed wetmill and planer/dry mill applications. The chain lies flat on the boards, facilitating stable sorting and control during sudden stops. It handles poor quality (twisted, bowed) lumber well. The drag-chain sorter can achieve up to 160 lugs/min in wetmill applications and 250 lugs/min in planer/dry mills.
The J-Bar sorter design is robust and reliable. It can reach speeds up to 120 lugs/min and handles poor quality (twisted, bowed) lumber or boards well.
Murray says a sling sorter can be less capital intensive than bin sorters because it contains less structural steel than a typical bin sorter design. The advantage of sling sorters include:
- Wetmill or drymill applications
- Pusher- lug or drag-chain feeding
- Gentle nylon webbing slings
- Single or double packs
- Hydraulic let-down system
- Low-cost installation
CANFOR ORDERS 50 SORTERS
Canfor recently ordered 50 new sorter-top sling bay assemblies from USNR. Canfor is one of the largest producers of sustainable lumber, pulp and paper and is upgrading its planer mill facility in Graham, North Carolina, USA.
The new sorter top assemblies will be fitted to the existing structural steel frame, offering a faster and more reliable sorting operation and product throughput. USNR expects to commission the system in the third quarter of 2022.