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Figure 10.3 Scheme of rotaprint lubrication.
1 - shaft, 2 - bearing, 3 - solid lubricant roller, 4 - holder
In rare cases, lubrication is carried out periodically while the machines are stopped.


Lecture No. 12
Rolling friction.
The rolling friction force is an order of magnitude or more less than the sliding friction force. Rolling resistance is attributed to deformation losses in the underlying solid. In the absence of plastic deformation, friction is due to hysteresis losses in the solid. With rolling friction, mutual slippage of surfaces occurs, which can be represented when considering the rolling of the ball (Figure 12.1.). The circle AB of the ball moves in the middle of the groove, and the circle CD touches its edge. Circle AB travels a greater distance in one revolution of the ball than circle CD . This difference determines the sliding of friction surfaces.
Let us explain the hysteresis losses during rolling friction using Figure 12.2

Figure - 12.1 Figure - 12.2

Even O. Reynolds noted that when a cylinder of solid material rolls on a flat surface of rubber, then with each revolution it passes a path less than the circumference of the cylinder. He suggested that the rubber is stretched at point C differently than at points B and D , and as a result, as already mentioned, slippage occurs with a corresponding dissipation of energy. Figure 12.2 shows that a recess is formed under the ball in front of the ball at point E , and behind the ball at point A the deformable material is completely (rubber) or partially (metal) restored under the action of elastic forces or elastic hysteresis; in addition, due to irreversible plastic deformation, the reaction forces behind the ball are less than the pressure forces in front of it. As a result, the ball performs deformation work.

During rolling friction in the case of solids, surface deformations are small, and the oxide films present on the friction surface do not undergo significant destruction. The sliding of surfaces therefore occurs not over metal, but over oxide films, which can wear out.
For the run-in state of surfaces, according to experimental data, the rolling friction force ,

Where k is a material dependent constant;
N is the load on the ball;
D is the diameter of the ball;
n , m - exponents - n = 1.7 ... 1.85; m = 1.5…1.6
The friction force in rolling bearings at high speeds depends on the viscosity of the lubricant and can reach large values. The friction force in rolling bearings is affected by the viscosity of the lubricant, friction in the bearing cage, ball size, surface roughness, etc.

Friction moment in rolling bearings or , Ututr - friction coefficients for radial and axial loads related to the shaft diameter d ; Q and T – radial and axial loads. The friction force in rolling bearings increases in the case of technological and installation errors, increased speeds and friction in the seals. The values of friction coefficients in various types of rolling bearings are in the range of 0.002…0.008.