A screening apparatus has a screening surface comprising at least one group of elongate, mutually parallel and mutually adjacent screening elements, the size of the mesh defined by adjacent elements being varied by moving the elements of one and the same group transversally of their longitudinal axes while maintaining an equal distance between all said elements. Each screening element of a particular group of said elements is mounted on an associated arm arrangement which can be swung about an axis extending parallel to the long axis of an associated screening element. Planes containing the pivot axis of a respective arm arrangement and the longitudinal axis of its associated screening element are parallel to one another while the distance between said axes decreases from arm arrangement to arm arrangement in direct proportion to the distance between the pivot axes of the arm arrangements. One advantage afforded hereby is that the force required to shift the screening elements, to change the mesh size, is smaller than with known apparatus.
Wood chips having an acceptable thickness pass between the rollers of a roller screen for collection and over-thick chips discharge from one end of the roller screen for recycling. The rollers have chip agitating protuberances, preferably of pyramidal shape or in the form of spiral ridges. A second roller screen with pyramidal protuberances on its rollers and with its rollers closer together is used to screen out fines, preferably after the fines and acceptable chips pass through the first roller screen. Some of the fines pass through the second roller screen by occupying the valleys between the pyramidal protuberances.
The present invention concerns a screening method and apparatus for sorting wood chips into three categories, namely, accept chips, overthick and/or overlong chips requiring further processing and reject fines. The chips are fed onto a disc screen. A major portion of fines and a portion of accepts fall by gravity through clearances between the discs (1) of the disc screen and a portion of the chips travels over the disc screen. Screening of chips on the disc screen is cut short before all accept chips have fallen through the disc screen. Chips travelling over the discharge end of the disc screen are routed onto a roller screen (10), whereby the remaining portion of accepts can fall by gravity through the roller screen while overthick and/or overlong chunky chips are conveyed over the discharge end of the roller screen.
A screen roller is provided, configured to rotate as one of a plurality of rollers in a roller screen. The roller may include left hand spiral grooves formed in a first region of the surface of the roller, extending from one end of the roller toward the center, and right hand spiral grooves formed in a second region of the surface of the roller, extending from the other end of the roller toward the center of the roller. The roller may include a bumper strip around the central portion of the roller and configured to protect the roller from damage in the event the roller strikes a neighboring roller. The features on the surface of the roller may be formed on a sleeve that slides onto a shaft. The sleeve may be the length of the roller or may be one of a plurality of sleeves on the shaft.
The invention relates to a roll screen having variable screening apertures having axle-fitted rolls which are spaced at adjustable distances apart and a device for adjusting this spacing. The roll spacing adjusting device functions to act on all rolls simultaneously, so that the spacing change will be the same for all rolls. The device includes two parallel running tracks (10, 11) and the distance between these tracks can be varied. A change in the distance between the running tracks causes the roll axle housings (6) to rotate and move the axles (2). This roll screen also includes a device for adjusting the individual distance between two consecutive rolls without affecting the distances between the remaining rolls. This device includes a spacer (32) which is inserted between the housings of the two rolls in which the roll axles are journalled. The roll screen is also provided with a separate elastic sealing element between the roll axle and the roll drive arrangement.
Fines are separated from wood chips by feeding the chips onto the infeed end of a bed formed by a plurality of knurled rollers separated by narrow gaps and rotated in the same direction. The chips are tumbled by the knurls, and the fines settle into the spaces between the knurls and in the gaps to pass downwardly out of the bed for collection. As the chips tumble, they gradually move to a discharge end of the bed and discharge for further processing.
