139
If we express the surface of the trace left by the
ball on the metal by the
diameter of the ball "D" and the depth of the trace "h", then the surface of the trace
will be as follows:
Figure 1.
Brinell method
Since it is difficult to measure the depth of the trace, F is filled from the following
formula:
The sign of
hardness
N
is the initial letter of the English word Nagdness. The
letters after
N
indicate the corresponding hardness test methods, such as
V
- Brinell,
R
- Rockwell and
V - Winkers.
It usually takes the form of the Brinell hardness of the metal:
where: D is the diameter of the sphere, (mm).
d—diameter of the trace
left by the ball on the metal, (mm).
The diameter of the track is measured with a special caliper.
In order to quickly determine the hardness of the sample, special tables are
used in practice. Hardness (NV) in these tables
140
the values corresponding to the force (R) and the diameter of the trace (d) are
given (Appendix 1).
Balls are made of solid steel of SHX15 grade. They have a hardness of at least
8500 Vickers units after hardening and then releasing at low temperatures.
should not exceed 450 N/mm
2
according to Brinell, that is, the hardness of
the tested metals and the hardness of the sheet materials with a thickness of less than
1 mm are determined by this method. determination will not be appropriate. This is
considered a disadvantage of the Brinell method. The Brinell method has a number
of advantages as well as disadvantages.
They are the simplicity of the press and the approximation
of the hardness
value (NV) determined by this method to the tensile strength limit ( d
v
); ie
In this formula, K
is a dimensionless coefficient, which is determined by
experiment. For example, the value of K for steel is from 0.34 to 0.36.
Usually, before testing the sample, its surface to be tested is smoothed and
brought to a flat state. In the standard test, the load for a ball with a diameter of 10
mm is always 30 kN (3000 kg). The standard conditions for determining the Brinell
hardness of materials are listed in Table 1.
Brinell
test conditions include load, ball diameter, and load exposure time.
For example, in NV 10 (3000)10-2500, the first number (10) is the diameter of the
ball, the second number (3000) is the load, the third number (10) is the time the load
is applied, and the fourth number (2500) is Brinell. represents hardness.
The scheme of the Brinell press is shown in Fig. 2. The sample or part to be
tested is placed on the base (1), and when the spindle (2) is rotated clockwise, the
ball rises to (3). After that, the electric motor (4) is activated, and the motor, in turn,
activates the system of levers in the press. When the lever system is activated, the
ball begins to sink into the sample under the influence of the pressure (5).