FLENDER Standard Couplings Technical Information © Siemens AG 2015 ■ Overview Shaft misalignment Furthermore, because individual components of the drive train heat up differently during operation, heat expansion of the ma- chine housings causes shaft misalignment. 2 Shaft misalignment is the result of displacement during assem- bly and operation and, where machines constructed with two ra- dial bearings each are rigidly coupled, will cause high loads be- ing placed on the bearings. Elastic deformation of base frame, foundation and machine housing will lead to shaft misalignment which cannot be prevented, even by precise alignment.
Poorly aligned drives are often the cause of seal, rolling bearing or coupling failure. Alignment should be carried out by specialist personnel in accordance with Siemens operating instructions. Depending on the direction of the effective shaft misalignment a distinction is made between: . U . D . Z *B0'B;;B *B0'B;;B *B0'B;;B Axial misalignment Radial misalignment Angular misalignment Couplings can be categorized into one of the following groups: • Single-joint couplings Couplings with flexible elements mainly made of elastomer materials. Shaft misalignment results in deformation of the elastomer elements.
The elastomer elements can absorb shaft misalignment as deformations in an axial, radial and angular direction. The degree of permissible misalignment depends on the coupling size, the speed and the type of elastomer element. Single-joint couplings do not require an adapter and are there- fore short versions. • Two-joint couplings Two-joint couplings are always designed with an adapter. The two joint levels are able to absorb axial and angular misalign- ment. Radial misalignment occurs via the gap between the two joint levels and the angular displacement of the joint lev- els. The permitted angular misalignment per joint level is fre- quently about 0.5°.
The permitted shaft misalignment of the coupling can be adjusted via the length of the adapter. If there are more than two joint levels, it is not possible to define the position of the coupling parts relative to the axis of rotation. (The less frequently used parallel-crank couplings are an ex- ception). • Example: ARPEX ARS-6 NEN 210-6 coupling with a shaft distance of 160 mm with a permitted radial misalignment of Δ K r = 1.77 mm (angle per joint level 0.7°). • Example: In the case of a RUPEX RWN 198 coupling with an outer diam- eter of 198 mm and a speed of 1500 rpm, the permitted radial misalignment is Δ K r = 0.3 mm.
G_MD10_XX_00014 K r *B0'B;;B Restorative forces Shaft misalignment causes restorative forces to act on the cou- pled shafts which are determined by the displacement stiffness of the coupling. These restorative forces are frequently compar- atively weak and can usually be disregarded. Where bearings or shafts are under heavy loads, the restorative forces should be taken into account. 2/2 Siemens MD 10.1 · 2015