Fig. 14-4
Fig. 14-5
14.5
In order to get a soft conversion between
START
and
STOP
of the wrapping arm, the speed is
divided in two steps. (This happens automatically).
At ½ speed the magnet valve, (pos. 5, fig. 14-2), opens for oil to the wrapping arm, but it goes
through a nozzle that limits the oil amount.
At full speed also the magnet valve on the tower of the machine, (pos. 6, fig. 14-3), is opening, so
that the oil goes outside the nozzle.
14.6
All three oil motors on the machine are serial-connected. At first the oil runs through the wrapping
arm motor, then to the control valve for roller-speed, through each of the roller motors and returns
to tank.
14.7
WRAPPING ARM VALVE BLOCK.
The wrapping arm valve block is attached to the wrapping arm motor, and includes 4 valves.
When the wrapping arm starts, the oil pressure also goes to the brake so it is released. But we want
a little delay here to prevent a too hard stop when the brake goes on. This is obtained by the
mounting of a nozzle inside the fitting to the brake.
a)
Non return valve.
It shall prevent the oil of going back to the control valve for wrapping arm speed. It is placed
inside the block, and can only be reached by removing the whole block from the motor.
b)
Safety valve on the plus side.
(S4, fig. 14-4).
This valve shall provide a gradual stop of the wrapping arm and prevent accumulation of
pressure on the motor's outlet side when the arm stops. The valve lets the oil flow from the
outlet side of the motor to the input side.
c)
Safety valve on the minus side.
(S3, fig. 14-5).
This valve limits the max. torque of the wrapping arm. The valve lets the additional oil over
to the motors' outlet side. It is adjusted so that the pull force on the far end of the arm is
approx. 35 KP.
d)
Holding valve.
(Pos. 1, fig. 14-5).
This valve regulates the oil flow on the outlet side to be able to hold a constant input
pressure to the wrapping arm motor. This makes the motor go smooth, and the brake is not
activated even if the wrapping arm rotates easy "downwards". (If the machine is in an
oblique position while wrapping).
* Emergency stop: see chapter 2.1
35
