Issue 41

F. Chebat et alii, Frattura ed Integrità Strutturale, 41 (2017) 447-455; DOI: 10.3221/IGF-ESIS.41.56 451 - A spindle which sustains the roller when it is assembled into the troughing set supports. It is made from drawn steel, cut and machined by automatic numerically controlled machines. The spindle is ground to a precision tolerance, to guarantee a perfect match of bearings, seals. Spindle tolerance, together with bearing housing tolerances, functionally guarantees the autoalignment of the internal and outer bearing rings of the ball race resulting in a good performance even when the spindle deflection is extreme due to overloading. - The seals components, which are meant to protect the bearing from harmful elements that may impinge from the outside or the inside of the roller, made of three main sections: Figure 1: Scheme showing the main geometrical parameters at the weld root and an example of lack of penetration. - Two bearing housing made by a steel monolithic structure (in agreement with UNI EN 10111 characterized by a yield strength 170< σ y <330 MPa), deep drawn and sized to a forced fixed tolerance (ISO M7) at the bearing position. The thickness of the housings is proportional to the spindle diameter and to the bearing type, with thicknesses that are up to 5 mm, to guarantee the maximum strength for each application, including the heaviest. - A spindle which sustains the roller when it is assembled into the troughing set supports. It is made from drawn steel, cut and machined by automatic numerically controlled machines. The spindle is ground to a precision tolerance, to guarantee a perfect match of bearings, seals. Spindle tolerance, together with bearing housing tolerances, functionally guarantees the autoalignment of the internal and outer bearing rings of the ball race resulting in a good performance even when the spindle deflection is extreme due to overloading. - The seals components, which are meant to protect the bearing from harmful elements that may impinge from the outside or the inside of the roller, made of three main sections: 1. external section: made of an external stone guard, a lip ring made from soft anti-abrasive rubber with a large contact surface onto a metal cover cap; that forms a self-cleaning stage of seal in that it centrifugally repels water and dust naturally towards the outside; 2. outward bearing protection: triple lip labyrinth in nylon PA6 greased to give further bearing protection; 3. inward bearing protection, made of a sealing ring in nylon PA6 is positioned that provides an ample grease reservoir and also retains the grease near to the bearing even when there is a depression due to an abrupt change in temperature (pumping effect). - Locking system: provided by means of the correctly located cir-clip, which is the most effective and the strongest system implemented in heavy rollers for belt conveyors. The feature under investigation in this paper is the joint between tube and bearing housing. The bearing housings of the PSV rollers are welded to the tube body using autocentralising automatic welding machines utilising a continuous wire feed. Tube and bearing housing form a monolithic structure of exceptional strength which itself reduces to the minimum any imbalance in the roller. This guarantees the alignment and concentricity with respect to the external diameter of the component parts of the sealing system. The optimum balance and concentricity thus obtained allows these rollers to be used at the highest speeds, eliminating harmful vibration to the conveyor structure and the “hammer effect” on the bearings of the rollers. From the point of view of the fatigue behavior under loading, the weakest point of the entire structure is the lack of penetration of the weld root. Therefore, if the roller is loaded well above its declared nominal admitted load [26] it would experience fatigue failure starting at the level of the weld root. A detail of the weld root is shown in Fig. 1, where the lack