TECHNICAL REPORT 9172 Published 1987-12-15 Continuous mechanical handling equipment -- Safety code for screw conveyors -- Examples of guards for trapping and shearing points Engins de manutention continue Code de securité des transporteurs.a vis Exemples de protection des points de coincement et de cisaillement ANsl Internrt Doc Sect ISo (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing international Standards is normaily carried out through IsO technical committees. Each member body International organizations, governmental and non-governmental, in liaison with iso, also take part in the work. The main task of Iso technical committees is to prepare International Standards. In exceptional circumstances a technical committee may propose the publication of a technical report of one of the following types type 1, when the necessary support within the technical committee cannot be obtained for the publication of an Internationa! Standard, despite repeated efforts; type 2, when the subject is still under technical development requiring wider exposure; type 3, when a technical committee has collected data of a different kind from that which is normally published as an International Standard ("state of the art", for example). necessarily have to be reviewed until the data they provide are considered to be no longer valid or useful. ISO/TR 9172 was prepared by Technical Committee ISO/TC 101, Continuous mechanical handling equipment. Introduction. 0 Introduction This Technical Report supplements the various safety standards for conveyors for loose bulk materials. It gives examples of the many kinds of hazards connected with screw conveyors at trapping and shearing points; it incorporates illustrative examples which show in principle how sufficient safety can be achieved, without excluding other methods which give the same level of safety. SO/TR 9172 : 1987 (E) UDC 621.867.4-783.3 Ref. No. ISO/TR 9172 : 1987 (E) Descriptors: handling equipment, continuous handling, continuous safety requirements. screwconveyors, @ International Organization for Standardization, 1987 Price based on 16 pages Notfor Resale ISO/TR 9172 : 1987 (E) Scope and field of application and shearing points located between the moving screw and the fixed parts of the conveyor or surrounding structures. It describes different safety devices, ilustrated by examples of design sheets, capable of meeting safety requirements specified in ISO 1819 and ISO 7149. References 2 ISo 1819, Continuous mechanical handling equipment -- Safety code - General rules: Iso 7149, Continuous mechanical handling equipment - - Safety code - Special rules. 3 Danger points 3.1 . Trapping points Trapping points occur where the outer edge of the screw approaches a fixed part with a steadily decreasing distance; examples of danger points where this hazard occurs are given in 3.1.1 to 3.1.5. 3.1.1 Between screw and trough As the distance between the outer edge of the screw blade and the trough decreases down to the operating clearance, there is a danger of limbs being pulled in (see figure 1). In the case of large screw conveyors, the whole body may be pulled in. Figure 1 3.1.2 Between screw and screw protection plate A trapping point will occur on the running area under the protection plate (usually made from angle steel or shaped tike a roof) if the clearance c (see figure 2) is less than 50 mm. Figure 2 mIHS ISO/TR 9172 : 1987 (E) 3.1.3Betweenmultiplescrews Trapping points will occur between adjacent screws [see figures 3a) and 3c] or on one [see figure 3c] or both [see figure 3b] of the trough walls depending on the direction of rotation and the pitch of the screw helix. The trapping points at the trough sides are the same as in 3.1.1; between the screws, trapping points may occur depending on the distance between the screw blades and the friction generated at the blades. b) c) ar Figure 3