Linear bearings are bearing elements for translation type motion. As in the case of rotary bearings, a distinction is drawn as to whether the forces occurring are transmitted by means of rolling or sliding elements.
The requirements placed on linear components are as varied as the applications in which they are used. In transport and feed systems, it is mainly speed and accuracy that are required while, in measuring machines for example, the emphasis is more on precision and rigidity. In order to find the right linear guidance system for the specific task, both a sophisticated product range and detailed consultation are important. INA offers both: a wide range of linear products, combined with expert service. Furthermore, a range of accessories precisely matched to applications allow even greater optimisation of the comprehensive standard versions of guidance systems.
Each linear design has particular characteristics that make it especially suitable for particular bearing arrangements. Generally applicable rules for selecting the type of guidance system can only be formulated up to a point, since more and more factors must be taken into consideration and weighed up against each other. Apart from load, acceleration, speed and stroke, factors including temperature, lubrication, vibration, mounting, maintenance etc. must be taken into consideration.
Linear rolling bearings
Linear rolling bearings are available as monorail guidance systems, track roller guidance systems, shaft guidance systems with linear ball bearings, flat cage guidance systems, guidance systems with linear recirculating roller or ball bearing units and as driven units (actuators and tables). Furthermore, INA also manufactures special miniature guidance systems for small design envelopes such as those in mechatronics and precision engineering. These very compact elements with very high load capacity, low friction and high rigidity are available as cage or recirculating systems. Due to their compact design, they can often replace solutions requiring significantly greater space.
The guidance systems comprise a guideway/carriage unit, a linear bearing/shaft system or are guideway/guideway units with roller or ball flat cages between them. Driven linear units are single-axis or multi-axis complete systems with a mechanical guidance system, an electric motor and a controller matched to the system.
Linear guidance systems are ready-to-fit locating bearings predominantly for unlimited stroke lengths. Flat cage guidance systems and linear guidance sets are, with a few exceptions, used for restricted stroke lengths due to the cage kinematics. The bearings support forces from all direction - except the direction of motion - and moments about all axes. Shaft guidance systems with linear ball bearings are suitable for loads from two directions and can compensate for static shaft misalignment. For the high rigidity and accuracy often required in operation, most units are supplied ex works preloaded or can be preloaded at fitting. Due to the various accuracy and preload classes, applications can easily be realised with high guidance and positional requirements.
In order to determine the size of guidance system, attention is paid primarily to the magnitude and type of load and the requirements for operating life and operational reliability of the bearing arrangement. In general, roller bearings can be subjected to higher loads than ball guidance systems of comparable external dimensions. Ball guidance systems are therefore normally used for small to moderate loads and highly dynamic motion, while roller guidance systems are used for high loads. If particularly high loads must be supported, flat cage and recirculating roller guidance systems are particularly suitable.
Linear plain bearings
While in rolling bearing arrangements the bearing elements are separated by rolling parts (the rolling elements), in plain guidance systems the movable component slides on a static guideway or shaft. Depending on the type of guidance system, the sliding layer is applied to the movable or the rigid component. Lubrication is carried out by means of lubricants embedded in the sliding layer.
Linear plain bearings are linear locating bearings for unlimited stroke lengths. These linear guidance systems are available as a miniature plain guidance system, Permaglide® linear plain bearings and Permaglide® linear plain bearing units as well as a flat guidance system. Miniature plain guidance systems comprise a guideway/carriage system with a maintenance-free sliding layer, Permaglide® linear plain bearing units with a low-maintenance Permaglide® bush seated in a light metal ring. Flat guidance systems are guideway systems in which the sliding surface is provided on the guideway by means of a low-maintenance sliding layer.
Plain bearing guidance systems have low wear and high static load capacity, are insensitive to shocks and contamination, make little noise and operate substantially free from stick-slip. Maintenance-free plain guidance systems do not require lubrication, and low-maintenance materials have good emergency running characteristics. Due to their versatile specific characteristics, plain guidance systems are used in many areas, especially where the bearing position must be maintenance-free or low-maintenance, there is a risk of inadequate lubrication or where lubricant is either undesirable or impermissible.
The life of a linear plain guidance system depends essentially on the load, sliding speed, temperature and operating duration. There are additional limiting factors including contamination, corrosion in dry running or possible ageing of lubricant if lubrication is not sufficient. The basic rating life is therefore only ever a guide value.
Many external influences on linear plain bearings cannot be included in calculation. Tests under operating conditions therefore give the most reliable information on the use and life of the guidance system in the specific application. |
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