Fronius VR 4040, Operating Instructions Manual

Page: 36 / 56

36
Increase in ten -
sile force as a
function of wire -
feed speed
When accelerating, the unreeling device generates an increased tensile load on the wire
and releases the brake at the same time. This ensures optimum acceleration of the wire
spool.
The aim of timely acceleration is to prevent the “lever + drawback pulley” unit (1) from
reaching the top mechanical limit-stop.
With full wire spools, the travel range of the “lever + drawback pulley” unit (1) should be
utilised as completely as possible, in order to keep the acceleration of the wire spool (and
the resultant increase in the tensile load on the wire) as small as possible.
Limiting the ten -
sile load on the
wire
The VR 4040 unreeling device offers the facility to limit the increased tensile load on the
wire during acceleration by means of an overload coupling (11). This limitation feature is
factory-set to a wire load of 15 N.
Equilibrium and
working position
In equilibrium, the wire being fed by the wirefeeder and the wire at the periphery of the wire
spool both have the same speed. After briefly swinging back and forward before reaching
the working position, the “lever + drawback pulley” unit (1) no longer moves, and stays in
the working position.
The “lever + drawback pulley” unit (1) is suspended in a loop of welding wire (pulley prin -
ciple). For this reason, the tensile load on the wire is half of the effective weight of the “lever
+ drawback pulley” unit.
In all three conditions of the unreeling device - equilibrium, idling and decelerating - the ten -
sile load on the wire is approx. 6 N.
When heavy wire spools are being used and a higher braking force has been set, the “lever
+ drawback pulley” unit assumes a slightly higher working position.
This allows for the longer deceleration time that is needed for heavy wire spools. In such
a case, then, do not attempt to correct the working position.
Decelerating
When welding is stopped, the welding wire is also stopped immediately. Because the wire
spool cannot brake to a standstill instantaneously, the excess wire must be collected by
lowering the “lever + drawback pulley” unit (1).
The braking lever (3) is moved by means of spring (2) and spring (6). The brake block (4)
is applied to the brake wheel (5), and the wire spool is braked to a standstill.
In all three conditions of the unreeling device - equilibrium, idling and decelerating - the ten -
sile load on the wire is approx. 6 N.
The factory-set braking force for the wire spool is such that even at a wirefeed speed of 22
m/min, a 40 kg spool can easily be braked down to zero.
At the end of deceleration, the “lever + drawback pulley” unit (1) reaches the bottom posi -
tion. Make sure here that the “lever + drawback pulley” unit (1) is not resting on the bottom
mechanical limit-stop, as this would mean that it would no longer be applying any tension
to the welding wire.