Stand by mode. Monitoring pulses.
Under certain conditions, sealing is also possible with the
so-called
procedure. In this mode, the
remaining heat in a sealing element is calculated to be
just enough for the sealing process. This means that in
the timing process, the temperature drops in phase 4 .
The current is cut off when the jaws touch. The heat flows
into the film and "unloads" the heat stored in the heatseal
element, which results in a faster cooling. For this method
to be effective the thickness, therefore the mass, of the
heatseal element must be great enough to hold the
required total heat.
rest-heat
The pre-set temperature should always be attained
before the sealing jaws make contact. This allows the
sealing element to expand without constraint and
eliminates stressing of the heatseal element ends
(phase 2 ).
R O P E X
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R O P E X
R O P E X
INDUSTRIE - ELEKTRONIK GmbH
Page 11
9. IMPULSE SEALING
When the impulse sealing method is employed the start
signal is synchronized with the operating cycles of the
machine. Every heating cycle is followed by a cooling
cycle
. It is Important that the cooling is
effected with jaws closed so that the seal can set and
gain strength and good appearance befor the jaws are
opened. This method is preferred if adequate sealing
time is availabel because the strength and appearance
of the seal are optimized.
Since the heat sealing is a thermodynamically reversible
procedure and is often influenced by time constraints, it
is very important that the relevant parameters; tempera-
ture, time and pressure are very carefully synchronized.
The following diagram shows an example of the timely
setting of each parameter.
Basic rules for Impulse Heatsealing:
A.
with jaws closed
B.
PRECISION TIMING FOR PERFECT HEATSEALS
High performance productivity with perfection
requires coordinated timing between the heatseal
impulse and the jaw action.
The timing chart below describes the relationship of (A) Heating and cooling
cycles. (B) Heatseal Band temperature. (C) Heatseal Jaw action. (D) Power Output.
START
HEATING CYCLE TIME
COOLING CYCLE TIME
TEMP.
SET POINT
COOLING
Phase
1
1
2
2
3
3
4
4
4
5
5
6
6
t
t
t
JAW ACTION
S
S
OPEN
OPEN
CL
OSING
CLOSED
OPENING
CURRENT
(= LED OUTPUT)
I
2
I
MAX
MONITORING
PULSE
MONITORING
PULSE
A
B
C
D
Phase :
Jaws are opening.
Cooling phase:
set-up
Start of cooling time. Time must be allowed for the
seal to
befor jaws are opened.
Power output is
. Temperature remains at set point.
controlled
While jaws are closing, the heatseal band temperature rises to the set
point so that full temperature is reached befor the jaws closed.
START is "OFF"
open
. Jaws are
and the heatseal band is cooling
from the previous cycle. (Monitoring Mode)
Diagram D
shows the rate of current flow during a sealing phase.
This can also be measured with an amp-meter.
Phase
:
1
Phase
:
2
Phase
:
3
Phase
:
4
Phase
und
:
Phase
5
6
Heatseal process:
Start of sealing time. Time must be allowed for the
heat to full penetrate the material to be sealed.
9.1
The system should be designed to drive the heatseal
element to the preset temperature in minimum time.
The total system, principally the secondary voltage,
must be optimized to achieve the best result.
.
C.
Our application service will give you the necessary
data for your special application
The cool down of the heatseal element while still
under the force of the jaws is the main advantage of
impulse sealing (phase 5 ). At the completion of the
heatseal cycle, most of the excess heat will be
absorbed by the jaws. Cooling of the jaws is
sometimes recommended so that they can absorb
enough heat from the heatseal element quickly.
Contrary to the constant heat mode, good thermal
conductivity between the sealing element and the
jaws must be assured by using a thin backup material
behind the heatseal element.
Notice that it is possible to energize the heatseal band
prior to jaw closing because the temperature controller
eliminates the risk of overheating.
Controller "ON" heating up with full secondary voltage,
maximum power.
Controller "ON" and regulating to maintain the preset
temperature while the jaws are still open.
Controller "ON" and regulating. Increased power is
being supplied to maintain the preset temperature
during the sealing process.
Controller "OFF" and the heatseal band is cooling,
