PANELS & FURNITURE ASIA • Issue 1 • January / February 2019 PANELS MANUFACTURING 27 In the grinding chamber, the rotor blades guide the pre-cleaned chips to the knives of the non-rotable knife ring to produce thin uniform chips. The non-rotable centred knife ring together with the precise bearing system of the rotor create a narrow gap which can accurately cut chips on high rotation speeds of the rotor. This reduces power consumption and improves the quality of the chips produced. Ready chips can be removed from the machine both mechanically or pneumatically. It is, in fact, advisable to purchase an MRM machine to clean knife rings that have a ring extension and rotation device. A high- pressure cleaning and drying system (to ensure an environmentally safe cleaning of all common types of knife rings) and an automatic knife sharpening machine MSA also ensure an automated, precise and cost-effective grinding and setting of knives in the knife rings. The knife ring can also be replaced easily as the crane is mounted on the machine, and features a swivel arm and a transport trolley. Additionally, wood flakes used for the outer layers of the chipboards can be further grounded using mills or refiners as the grinding process also involves the abrasion of large particles of chips. Needle-shaped chips are made using centrifugal machines to divide the chips along the fibres, with a coarse fraction re-grounded using mills or refiners. An example of the equipment used is the MPM impact mill, which is recommended in manufacturing the outer layers of the chipboards. This equipment recycles soft and medium-hard materials into small cubic flakes or wood powder. After passing through the vibrating chute, magnetic drum and HPS heavy particle separator, chips are fed through the back wall into the grinding chamber and grounded between the rotor's impact beams and the mill's grinding plates. The materials are then finally grounded and calibrated in a special built-in finely perforated screen. For the processing of soft and medium- hard materials into fine chips or wood powder, an MPF impact refiner is used as it has similar operation as the MPM impact mill. The difference is that the final product is removed through a hatch. To clean the fine fraction of the wood board’s outer layer, an MVS vibrating separation table is recommended as it can efficiently clean dry or semi-moist fine material from mineral impurities, heavy contaminants, dust and film. The material to be cleaned is loaded from the top and light fraction is separated by a stream of air blowing fromunder the inclined screen. Due to the vibration of the screen, heavy particles move to the upper discharge outlet, and dust and film are sucked into the cyclone. Factories producing OSBs often used specialised shredders to make strands, such as the SmartRING Stranders. Such equipment produces high quality strands and features design making, hence, they are easily adjustable. The maintenance of the machine is simple and worn out components can be easily replaced, which minimises the machine's idle time. In addition, wood board (chipboards, MDF, OSBs) production lines can use a SE air separator to clean chips and flakes from metal, heavy particles and light impurities. The equipment consists of a vibration chute, magnetic drum, an HPS heavy particle separator and a cyclone with a built-in rotary gate valve installed on the supporting frame. The material can be fed to individual machines and/or the grading section using a VC vibratory chute that enables uniform in-feed of various bulk materials. Depending on the application, material in-feed can be combined with grading or a separate screening module. Choppers designed for processing wood wastes, sleepers, pallets, old furniture, stumps, power transmission lines, and more, belong to a separate class. These raw materials are usually not processed using wood preparation equipment. However, if needed to process them into chips, an MGB large crusher can be used. In the crusher, raw materials are fed directly to the machine through a feed hopper, and crushed between a slowly rotating large-size splined shaft and crushing plates installed on the floor of the chopping chamber. This equipment is also insensitive to foreign bodies or contaminants. The use of the SRH impact rotor crusher is possible too. Its feeding rollers grab the materials horizontally with special teeth, and crush them with high kinetic energy between the rapidly rotating heavy hammer rotors and an anvil-type knife. The ground materials are then processed to the required size by a re-grinding screen. This crusher is also insensitive to foreign bodies or contaminants. Wood materials crushed in a large MGB crusher or SRH impact crusher is fed into the SRV impact rotor crusher, which is designed to produce chips from pre-chopped recovered wood. The raw materials in it are crushedwith high kinetic energy between the rapidly rotating heavy impact hammers of the rotor and the impact plate. The grounded materials are then processed to the required size by a re-grinding screen. The one-stage grinding of raw materials is done by ClassiSizer. Materials are fed from the top to the impact chamber where they are grounded by the impact action of a rapidly rotating rotor and interaction between individual particles of the materials with each other. The materials are then finally calibrated using screens whose perforation size is selected depending on future application. The product is then collected in two collecting tanks and removed using discharge augers. ℗ Criteria for choosing re-grinding equipment: • Screen and hole dimensions • Power • Hammer replacement speed • Adjustable gap between the screen and hammers • Uniformity of resulting fraction This was first published in Lesnaya Industriya.