X-ray sensors and Whirlwind mills represent advances in woodworking equipment design. This week Allison and Vince explore several such advances, with their trademark tongue-in-cheek perspective.
Wood processing mills are large grinding machines which are designed to break down large pieces of wood into smaller pieces. In the past mills have been wind powered, animal driven, and mortar and pestle driven. Today, large electric powered and CNC controlled mills are used for the grinding of many materials including plastics, non-metallic minerals, food, and wood.
Many wood processing mills defibrate their wood, which means they have to break the wood into its fibre components. These small wood fibres are most commonly used in thermal insulation of residential buildings. This is traditionally done using the impact force of a beater mill. Designers at Grenzebach have created Whirlwind Mills that can take more than twice the input of conventional mills while using the same amount of energy.
In a whirlwind mill the wood is first crushed into large pieces by beating tools. These large pieces are accelerated and ôfluidizedö in air. This flow is then pulverized by grinding tools. The rotor component of the mill generates air ôwhirlsö which increase the number of collisions of the particles as well as the shearing forces. The particle size can be adjusted by changing the grinding rotor clearance, air flow, and rotor speed. The biggest design challenge in milling is how to separate the particles which will usually have some variance in size. The Whirlwind millÆs thorough pulverization of the material creates only one uniform, controlled grain size which eliminates the need for any further sorting.
TodayÆs woodworking industry features highly automated production lines. These lines can be slowed down because there is a manual step of inspecting and classifying lumber before it is cut. This inspection step is necessary, because knot locations, size, color, texture and defects determine the end use of the lumber. Designers at Weinig have developed a scanner system that can scan any type or size of wood almost instantly. By communicating that information automatically, the saw cuts can be automated to maximize the value of the lumber. The scanner completes these tasks in a fraction of a second, thus not slowing down the production speed.
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