(September 19, 2011)
The increasing importance of regenerative energy production, particularly by means of wind turbines, is resulting in a growing demand for production machinery which is capable of producing the large-size components used in such turbines in a reliable and efficient manner. In combination with a wide product portfolio, Schaeffler Group Industrial has an extensive level of application, production and service know-how to offer where large machining centers are concerned. In addition to single bearing solutions, which offer a good compromise between performance, design outlay and price for the majority of standard applications, two or three bearing solutions are frequently being used, which permit a design which is specifically tailored to the requirements of the machine tool.
In particular, the turning of large and heavy components represents a particular challenge when designing machine tools on account of the long duty cycle at correspondingly high speeds. The bearing support in the faceplate, which acts as the mount for the workpiece, has a significant effect on the performance of the machine. In addition to accuracy and rigidity, speed suitability is a critical factor where these applications are concerned.
The economical 1-bearing solution
The simplest mechanical design for a bearing support is the use of a single bearing. It supports forces and moments from all directions and offers favorable relubrication options. In this instance, for example, the screw-mountable bearing units of the series YRTS and ZKLDF are used. Their size range is restricted to a maximum bore diameter of 460 mm and 725 mm respectively. Crossed roller bearings, which have been developed specifically for these applications, are available in a diameter range of 457.2 mm to 2100 mm and thus provide a simple bearing option even for larger tables. For the majority of standard applications, these one-bearing solutions offer a good compromise between performance, design outlay and price.
1-bearing solution with crossed roller bearings for the rotary table used in vertical lathes: For the majority of standard applications, this economical solution offers a good compromise between performance, design outlay and price.
Optimum performance with a multiple bearing solution
Specifically matched pairs of bearings can be used if several bearings are used for the bearing support of a rotary table. In principle, this means that each bearing can be selected according to its load carrying capacity, rigidity and in terms of its speed capacity. With a multiple bearing solution, the main bearing makes up the core piece in the form of an axial bearing. Its characteristics have a decisive influence on the machine’s performance.
Two design variants have proven themselves: The 2-bearing solution, comprising an axial bearing (axial deep groove ball bearing or axial cylindrical roller bearing) and an angular contact bearing (angular contact ball bearing or tapered roller bearing): The axial runout is determined by the axial bearing and the radial runout is determined by the angular contact bearing. The axial bearing usually limits the speed as a result of the larger diameter and is preloaded with the angular contact bearing in order to guarantee defined kinematic conditions in the rolling contact in each load case. The 3-bearing solution, comprising two axial bearings paired with a radial bearing: The larger axial bearing supports the main load of the table plate and the workpiece and the smaller axial bearing provides axial preload for the bearing support and acts as an outer support bearing when tilting moments are supported. Radial guidance is provided by the radial cylindrical roller bearing.
For extremely high speed requirements and an optimum price/performance ratio for rotary tables used in vertical lathes: 2-bearing solution with ball bearings.
As a general rule, the design variants comprising ball bearings are able to achieve higher speeds and the design variants comprising cylindrical roller bearings are able to achieve higher rigidity values and load-carrying capacities. The axial deep groove ball bearings achieve speed parameters of up to 460,000 mm•min-1 compared with 270,000 mm•min-1 by cylindrical roller bearings. The highest load ratings are achieved by axial cylindrical roller bearings with a diameter of up to 3,830 mm. The achievable accuracies, even with larger bearing diameters, are impressive and consequently make a valuable contribution to the machining quality.
Achieve extremely high rigidity values and load carrying capacities: 3-bearing solution with roller bearings.
An extensive range of services tops off the Schaeffler Group Industrial's product portfolio. This begins with the engineering service we provide at the customer’s premises and the substantiated bearing design performed with the calculation software Bearinx which has been developed by Schaeffler and is used to calculate defined states in rolling contact for all load cases. The support provided by the Industrial Aftermarket’s service departments during assembly ensures that the individual bearings are carefully and correctly aligned in cases where elaborate multiple bearing solutions are used. Further advice and services relating to operation, lubrication, maintenance and extending to reconditioning, can lower operating costs and downtimes.
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