MAHR - Шариковые направляющие Marmotion - 2010 Английский язык
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MarMotion. High-precision rotary stroke bearings +
35 Mahr
2. Design, Functions, Features
2.1 Design and functions
MarMotion high-precision rotary stroke bearings consist of the cylindrical shaft and
bush, which act as guiding elements, and the steel balls, which act as the rolling bearing
elements. The balls are held in a brass or plastic smooth-moving tube where they roll
easily.
The guide shaft, balls and guide bush are specially hardened and micro-finished. The
structure is stabilized through careful application of heat treatment.
The balls roll non-positively between the bush and shaft under a preloading tension.
Linear, rotary and combined movements are possible. The frictional connection of the
balls means the cage moves in accordance with the laws of kinematics.
2.2 Preloading Fig. 1
Preloading must be set with great precision to ensure problem-free operation. This is v = dw + 2·k – d1 [mm]
d1 = dw + 2·k – v [mm]
achieved and defined using the manufacturing tolerances. Preloading value v is the
Fig. 2
difference between the size of the inside diameter of the guide bush d1 and the
distance between two balls lying opposite each other and touching the shaft. Stationary guide bush
PR = radial force acting on the shaft
Recommended preloading P0 = force acting on the ball at
The preloading values given in the following table are recommended for most the load apex
applications. These values are based on theoretical knowledge and practical Pi = force on a ball outside
experience.
the load apex
Preloading values v [m] dw [mm] v [m] dR = radial offset of the bush and
dw [mm] 0.5 - 2 14/ 25 4- 7 shaft axes
1-3 30/ 42 4- 8 v = preloading
2.5/ 3 2-4 50/ 63 6 - 10
4/ 5 3-5 80/100 8 - 12 Fig. 3
6/ 8
10/12
These preloading values ensure that the rotary stroke bearing has both excellent
rigidity and smooth running. In the case of orders for complete rotary stroke bearings
consisting of a guide shaft, ball cage and guide bush, the components are paired in
the factory. This ensures optimum and uniform preloading.
Due to the range of scatter of the manufacturing tolerances (IT 3), indiscriminate
pairing of shafts, ball cages and bushes can result in unfavorable preloading values
which deviate from those listed in the table. The rotary stroke bearings of the Mini Range
should always be ordered in pairs.
The significance of preloading
Preloading guarantees that the MarMotion high-precision rotary stroke bearing has
absolutely no backlash. In the case of applications where special conditions have to be
satisfied, the required preloading value can be specified at the time of ordering.
A very low preloading value means that the rotary stroke bearing runs smoothly but
rigidity is limited. A higher preloading value increases loading capacity and rigidity.
A very high preloading value leads to the rotary stroke bearing running less smoothly.
If the preloading value is too high, the run will be rough and stiff. The rotary stroke
bearing can also be overloaded by excessive surface pressure. This is prevented by
the narrow manufacturing tolerances of the rotary stroke bearing. It must therefore be
ensured that the guide bush is not deformed when being installed. The guide bush
should thus not be pressed into the location bore or secured with pressure screws.
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