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Layout design of printing machine bearings

by:JNSN     2021-12-29
Design requirements for adjacent structures: Printing machine bearings are very robust mechanical components, and the surrounding structures are required to have high precision, which can be fully achieved by modern processing equipment. The most important requirements for the surrounding structure are high-precision shaft diameters and precision-machined wallboard holes. Usually, the journal needs to be ground, the wall plate hole needs to be finished, and if necessary, it is honed, as shown in Figure 1. The internal radial clearance of the cylindrical bore bearing is specially designed according to the specific application. The swing bearing in the three-ring and four-ring bearings has zero clearance or light preload, which has been set before the bearing leaves the factory. No customer adjustments are required. Schaeffler Group has advanced calculation software to assist design. In order to achieve the best function, all tolerances must be carefully determined. Axial positioning of printing machine bearings The positioning of the outer ring of printing machine bearings DML is very simple, because it does not bear axial forces during work. The eccentric middle ring and outer ring of the three-ring and four-ring bearings are axially positioned by the bearing shoulder and the retaining ring. Therefore, for bearing units DML3E, DML3D and DMLD, there is no need for axial positioning through peripheral structures. Generally, fixing the eccentric ring to the wall panel with peripheral parts can be sufficient to achieve axial positioning, page 37, Figure 1. Thrust bearing arrangement If cylindrical roller bearings are used at both ends of the drum, then another rolling bearing is required to bear the axial force. Since the axial force in the printing press is usually very low, economical standard bearings can meet the requirements. The proven reliable types include two zero-clearance angular contact ball bearings, double-direction thrust needle roller bearings or double-direction thrust cylindrical roller bearings, see page 98. Tolerance of shaft and bearing seat hole In order to minimize the working clearance tolerance of the bearing, the tolerance of cylindrical shaft diameter should be as small as possible. The prerequisite for optimization is that the tolerance level of the shaft must reach IT4. However, the most commonly used shaft fit k5 can meet all requirements. For tapered shafts, since the working clearance of the bearing can be adjusted, the tolerance can be slightly larger. In this case, js6 is commonly used for shaft coordination. Tolerances of wallboard holes For printing press bearings, the wallboard hole and the outer ring of the bearing are usually a transition fit or a tight fit. When using the bearing unit DMLE or DML3D, if the outer eccentricity needs to be moved during work, a certain fit clearance is required. In order to minimize the possible deformation of the components, the tolerance band should be as narrow as possible. This can be achieved by appropriately fitting the bearing into the wallboard hole or by high-precision machining methods, such as honing. In order to facilitate the selection and installation, the bearings of the printing press are measured before they leave the factory, and the actual outer diameter is recorded on the bearing. For situations that often require mass production such as sheet-fed offset printing presses, it is more economical to design the outer diameter of the bearing in groups. In this way, the diameter tolerance of the wallboard hole can be relatively large, which is very beneficial to mass production. Geometric tolerances of bearing mating surfaces. If the bearing arrangement meets the requirements of running accuracy, rigidity, zero clearance, working temperature and guaranteeing excellent printing quality, then the adjacent structures must meet certain minimum requirements. The geometric deviation of adjacent parts must be controlled to a minimum. In order to achieve the required fit, the mating surface of the shaft and the bearing seat hole must meet certain tolerances, see Figure 2, Figure 3 and page 42, and note the requirements for the roughness of the bearing mating surface, page 43. Accuracy of the bearing mating surface For the tolerance of the shaft and the bearing seat hole mating surface, the allowable geometric deviations are listed here, please refer to the table. Accuracy grades can be viewed in accordance with ISO basic tolerances in accordance with ISO 286, see page 43. The allowable geometric deviation value must be determined according to the relevant shaft diameter and seat hole diameter. Example: If the tolerance level of the shaft bearing is P5 and the shaft diameter is 90 mm, the tolerance value of the shaft is as follows, see the table: ■ Roundness t u003d IT3 · 1/2 u003d 6 · 1/2 u003d 3 m. The roughness of the bearing mating surface The roughness of the bearing mating surface must match the tolerance level of the bearing. The average roughness Ra should not be too large to ensure a limited reduction in interference, please see the table. The shaft needs to be ground and the bearing seat hole needs to be finished. The design and safety guidelines in the product chapter also give tolerances and allowable roughness for holes and shafts.
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