354
M. Fenchea
If the expression (5) and (9) are equalized, it is obtained the existence conditions
J yz = 0
( 1 0 )
and the equations of the support of percussion
x A =
J Z
mx G
(11)
and
z A =
J xz
mx G
(12)
which define the centre of percussion [6].
Particular, the usual case of the hammer in the form of a plane which presents the
axis of longitudinal symmetry can be taken J xz = 0 and J yz = 0. This thing shows
the existence of a centre of percussion, and z A = 0.
Consequently, for the joint percussions to be null, it is sufficient to be verified the
(11).
3 Experimental Determinations
The accelerometer KD 35 (piezoelectric transducer), mounted of the bearings of
the mill, put in evidence the perturbations of the rotor as a result of the unbalances.
Transducer receives these perturbations, which generate a tension signal, proportional
to the acceleration.
If the rotor is considered well-balanced, the signal in the time domain was
sinusoidal (see Fig. 2), and the frequency spectrum is shown in Fig. 3.
For put in evidence, the dependence between different tips of hammer and wellbalanced rotor, it’s made experimental determinations with two tips of hammer where
the differences between the values of the real parameter of the hammer used for
determinations and the calculated ones for the same types of hammers (x A ) are:
• Hammer set 1: 1,9290 mm (see Figs. 4 and 5)
• Hammer set 2: 15,7411 mm (see Figs. 6 and 7).
4 Conclusions
In practice, the existence conditions of the percussion centre are not always satisfied.
In consequence, unbalances depending on the connection percussions appear, having
as effect supplementary perturbations in the mills with hammers.
M. Fenchea
If the expression (5) and (9) are equalized, it is obtained the existence conditions
J yz = 0
( 1 0 )
and the equations of the support of percussion
x A =
J Z
mx G
(11)
and
z A =
J xz
mx G
(12)
which define the centre of percussion [6].
Particular, the usual case of the hammer in the form of a plane which presents the
axis of longitudinal symmetry can be taken J xz = 0 and J yz = 0. This thing shows
the existence of a centre of percussion, and z A = 0.
Consequently, for the joint percussions to be null, it is sufficient to be verified the
(11).
3 Experimental Determinations
The accelerometer KD 35 (piezoelectric transducer), mounted of the bearings of
the mill, put in evidence the perturbations of the rotor as a result of the unbalances.
Transducer receives these perturbations, which generate a tension signal, proportional
to the acceleration.
If the rotor is considered well-balanced, the signal in the time domain was
sinusoidal (see Fig. 2), and the frequency spectrum is shown in Fig. 3.
For put in evidence, the dependence between different tips of hammer and wellbalanced rotor, it’s made experimental determinations with two tips of hammer where
the differences between the values of the real parameter of the hammer used for
determinations and the calculated ones for the same types of hammers (x A ) are:
• Hammer set 1: 1,9290 mm (see Figs. 4 and 5)
• Hammer set 2: 15,7411 mm (see Figs. 6 and 7).
4 Conclusions
In practice, the existence conditions of the percussion centre are not always satisfied.
In consequence, unbalances depending on the connection percussions appear, having
as effect supplementary perturbations in the mills with hammers.