DE2356373A1 - Welding thermoplastics packaging of large articles - using heavy welding band with current switched off during waiting times to prevent overheating - Google Patents

Abstract

A method of welding thermoplastics sheet, esp. for packaging large articles discontinuously, is as follows: the welding band is first at constant temp., then is cooled during the welding stage by interrupting the heat supply, then is rapidly reheated to welding temp., and then is kept at the temp. Pref. a constant current is used for the first and last stages, with much higher current pulse for the reheating.

Description

Method and circuit arrangement for welding and separating thermoplastic Foils The invention relates to a storage and a circuit arrangement for welding and cutting thermoplastic films for relatively wide and discontinuous webs of film Working cycles in which the heat of separation is applied to the separation welding element in a pulsed manner is fed.

Cut-off welding processes in which cut-off welding heat is pulsed in a separation welding element is generated, generally so that the foils be brought between the welding bars of a separation welding device. Thereafter the sealing bars move towards each other and initially clamp the foils by clamping elements resiliently arranged on the welding bars.

At around this time, a current pulse is sent to a between the Clamping elements of the welding bars arranged separation welding element applied, whereby the necessary separation welding heat generated in the separation welding element will.

The moving separating welding element is affected by the in the plane of movement clamped film through, separates; these, also being at the same time the edges are welded.

(DT-GM 1 942 723) It is also known that the separating welding element is flush to be arranged with the clamping plane of the welding jaws and the Tronn welding elements so to heat that the radiant heat is sufficient to separate and weld the foils. The ßschweißnällte are mostly still cooled after decl welding.

(DT-P 1 213 596) These methods are generally very suitable for welding relatively thin foils and small bags. but packs relatively large widths are welded and separated, and then the case occurs that the pace of work is different, for example when packing in bulk, these methods are no longer suitable. Due to the relatively large mass of the separating welding element always a certain amount of heat remains in this element, which is from the between time is dependent on two pulses. In the case of short cycle times, the belt is overheated several cycles and burns at the welding point. at longer cycle times the required temperature in the separating welding element not achieved with the same impulse line and faulty welds would occur.

With changing pack lengths, readjustment would therefore always be necessary the impulse line necessary.

The purpose of the invention is to provide a method and a circuit arrangement for the welding and cutting of thermoplastic foils, which at all package widths and lengths without readjustment of the once set Optimal values works safely.

The invention is based on the object of a separation welding process to develop at which the optimal cut-off welding temperature in the cut-off welding element is always present at the start of the cut-off welding process.

According to the invention the object is achieved in that in a sweatband a constant welding temperature is generated, the supply of heat during the welding process interrupted, the sweatband temperature, which has decreased due to the welding process the welding process by briefly increased heat supply back to welding temperature brought and is kept on this by subsequent uniform supply of heat.

In another inventive solution to the problem is in the Welding band creates a constant welding temperature due to the welding process Lowered sweatband temperature after the welding process due to briefly increased Heat supply brought back to welding temperature and then uniform Heat supply kept on this.

The heat generation in the sweatband takes place in that a constant Heating current applied to the sweatband, this heating current during the welding process switched off, a higher current than the heating current in terms of pulses after the welding process applied to the sweatband so that when the welding temperature is reached, the current pulse switched off and the heating current is switched on again.

In the second variant, a constant heating current is applied to the sweatband applied, this switched off after the welding process, one opposite the Ileizstrom higher current applied in pulses, when the welding temperature is reached the current pulse switched off and the heating current switched on again.

A circuit arrangement for implementing the method is like this built that in an excitation circuit of a contactor at the beginning of Welding process off and arranged switchable switch at the end of the welding process is that in an excitation circuit of a contactor and in the heating circuit for Applying the heating current switches are arranged on the heating tape, which can be switched on or off by the contactor that gerstromkreis in the excitation the contactor and an excitation circuit of a switch-on delayed timing relay a switch is arranged at the end of the welding process and at the latest at the beginning of the next welding process can be switched off that in the excitation circuit of the contactor and the pulse circuit for applying the current pulse to the -Swiss tape switches are arranged, which can be switched on or off by the contactor are and that a switch arranged in the excitation circuit of the circuit protection can be switched by the timing relay Another circuit arrangement is designed in such a way that that in an excitation circuit of a contactor an excitation circuit of a On-delayed time relay a switch is arranged, which is at the end of the welding process can be switched on and switched off at the latest at the start of the next welding process that one in the excitation circuit of the contactor and in the heating circuit to apply of the heating current to the sweatband switches are arranged through a contactor can be switched on or off that in an excitation circuit of the contactor and the pulse circuit for applying the current pulse to the sweatband switch are ,, -which can be switched on or off by the contactor, that one in the excitation circuit of the contactor 5 close or dna ter switch by the time relay and one in the excitation circuit of the contactor arranged switch can be switched by the auxiliary contactor.

In both variants, a self-holding circuit is arranged, the by one in the excitation circuit of the switch-on delayed timing relay and one in the excitation circuit A switch arranged in an auxiliary clip can be switched off or one can be switched off.

Because in the transwelding element up to the beginning of the separating welding process a current always flows that creates the separation welding temperature and that the cut-off welding element again after the cut-off welding process by means of a current pulse heated to the separation welding temperature is a safe 2rennschv: eißen too guaranteed with the different work cycle sequences.

The invention is to be described in more detail below using an exemplary embodiment explains vjerden.

The accompanying drawings show: FIG. 1: a part of a welding bar by means of which the method is implemented FIG. 2: a section through the welding bar according to Fig. 1 and the corresponding counter rail Fig. 3: a circuit arrangement, , in which the power supply is switched off before the welding process. Fig. 4: a Circuit arrangement in which the power supply increases to a higher level after the welding process pulsed current value is switched.

Known welding devices can be used to implement the specified methods be used for welding thermoplastic foils. In this version s example was a welding device consisting of a relatively large welding bar length consisting of an upper welding bar 1 and a lower welding bar 2 are used.

The upper welding bar 1 has a longitudinal groove 3 and is made of silicone rubber 4 occupied. On the lower welding bar 2 hold-down devices 5 are resilient and a Schxeißband 6 arranged. The sweatband 6 is through ceramic pins 7 in relative large distances to avoid sagging during the welding process. For faster cooling of the weld seam, there are 5 coolant pipes under the hold-down devices 8 arranged. The sweatband 6 is designed in its section so that the heat content is sufficient for welding and separating the thermoplastic film. In the present For example, it is made of Kanthal and has a single cross-section of 3 x 1 mm.

At the beginning of the work cycle is in the solution shown in FIG the excitation circuit a of the contactor is closed - this closes the contactor 9 energized, switch 91 is closed and switch 911 is open.

Thus the circuit b; b '; b '' closed and one on one The voltage set at the control point 10 is applied to a welding point 11. Of the Current transformed in the welding spot 11 is applied to the sweatband 6 and is produced represents the heating current for generating the constant welding temperature. This heating current may depending on the packaging conditions via the variable transformer 10 to be changed.

At the time when the hold-down device 5 hits the silicone rubber 4 in the course of the closing movement of the welding channels 1; 2 becomes one with the hold-down interacting contact actuated by which a relay is energized.

(Not shown). The switched on in the excitation circuit a Switch 12, which is a contact of this relay, is opened, the excitation circuit a interrupted and the contactor 9 drops out. This opens the switch 9 ' and the switch 9 ″ closed. The heating circuit is interrupted and the sweatband 6 is not heated. At the end of the welding process, i. i.e. when the welding bars 1; 2 have reached their lowest position, and the hold-down devices 5 have their dashed lines in FIG occupy the position shown, another relay via a second with energized the hold-down cooperating contact (not shown). One in that Excitation circuit c of a contactor 13 arranged switch 14 which has a contact this relay is closed.

If the switch 14 and thus also the circuit c is closed, is the contactor 13 excites and picks up, a contactor 13 actuated switch 13 ', switched and a circuit b; closed at b ''. the full primary voltage is applied to the welding transformer 11 and an opposite to the Iieizstrom higher current is applied to the heating band 6. This will be back on in no time Welding temperature heated up.

Of the contactor 13 are still two; further switches 13 '' and 13 '' ', the function of which will be explained elsewhere.

To limit the intensive heating time is in the excitation circuit c @ a switch 151 actuated by a delayed-on time relay 15 in the excitation current circle c arranged. The delayed-on timing relay 15 is; in an excitation circuit c; d and thus becomes; also energized at the same time as the switch 14 closes.

After a time set on the time relay 15, the heating up of the sweatband 6 isb sufficient to sweat temperature, the time relay pulls 15 on, the switch 15t is opened, the excitation circuit c interrupted and the contactor 13 is de-energized.

Due to the fact that the welding bars are in the fully closed position 1; 2 occurring opening movement, the switch 14 is only closed for a relatively short time. This has the consequence that the excitation circuit c is immediately interrupted again, the contactor 13 drops out and the. Switch 131 is already opened when the Sweatband 6 has not yet heated up sufficiently. To avoid this is a Latch circuit d; f provided, in which the timing relay 15 is and that of a switch 13 ″ can be closed. If the switch 14 and thus the Excitation circuit c closed, the contactor 13 is energized. It attracts and thus closes in circuit b; b '' '; b '' arranged switch 13 'and the in the Latch circuit d; f lying switch 1311.

If the switch 14 is opened again, the timing relay now remains in the excitation circuit d f and the contactor 13 now in the excitation circuit f; d; c lying under, tension. Only when the timing relay 15 picks up, the excitation circuit is c interrupted by the switch 151, the contactor 13 drops out and the switch 13 '; 13 '' open. Thus, the pulse duration is greater than that of the heating current Sbromwert determined safely by the timing relay 15. In the meantime, the the hold-down device 5 actuated first contact released, excited by the di.esem Relay de-energized and switch 12 was closed again, in the present example the contact arrangement was chosen so that the switch 12 in the time between the closing of the switch 14 and the opening of the switch 15s closed again In this case, however, the excitation circuit a is already closed again, hen the switch 13 'and thus the pulse circuit b; b '' '; b '' still closed is. Since the contactor 9 is energized when the excitation circuit a is closed, is also the switch 9 'and thus also the circuit b; b 'bcc closed. In this Trap, two dependent circuits are closed at the same time and a short circuit would be the result. To avoid this short circuit is one of the contactors 13 actuated switch 13111 is arranged in the excitation circuit a of the contactor 9. Only when the excitation circuit c by means of the Switch 15 'unserbro Chen is, the switch 13 is de-energized, the switch 13 '' 'closes and the Switch 13 'opens. Now circuit is b; b '' '; b '' and the excitation circuit a closed, the contactor 9 is energized and the switch 9 'closes the circuit b; b '; b ''. A new work cycle can begin.

In the circuit arrangement according to FIG. 4, the excitation circuit is a closed at the beginning of the work cycle.

The contactor 9 arranged in the excitation circuit a is energized, whereby the switch 9 'in the heating circuit b; b '; b '' closed and the one in the excitation circuit c of the contactor 13 arranged switch 9 ″ opened i st.

The sweatband 6 is thus heated. At the end of the welding process, d. ho, at the time of the complete closing of the welding bars 1; -2 becomes a Contact actuated by the hold-down device 5, which energizes a relay. (Both not shown). This relay closes the switch 14, whereby the excitation circuit c; e for a Auxiliary contactor 16 and the excitation circuit c; d for the delayed timer relay 15 is closed 0 The auxiliary contactor 16 picks up, and the in the excitation circuit a switch 16 'arranged for the contactor 9 is opened. This will make that Contactor 9 de-energizes and drops out. The switch 9 'in the heating circuit b; b '; bii will opened and the switch 9s in the excitation circuit c of the contactor 13 is closed. As a result, the contactor 13 is energized and it pulls at. The switches 13t and 13 "actuated by the contactor 13 are closed and the switch 13 '' 'is opened 0 This creates the pulse circuit bt b £' '; btt closed.

The switch 13 ″ closes an auxiliary circuit c; d; f who the has the same task as described in the first example. The switch 13 '' 'is as already described, to avoid a short circuit in the excitation current circle a arranged.

After a pulse time set on the timing relay 15, it pulls on, the switch 15t is opened, the excitation circuit c and the excitation circuit c; e are interrupted and the contactor 13 and the auxiliary contactor 16 drop ab0 The switches 13 'in the pulse circuit b; b '' '; b '' and 13 '' in the self-holding circuit c; d; f open, the current pulse is switched off. The ones in the excitation circuit a arranged switches 13 '' 'and 16' close, the contactor 9 is energized and attracts Thus the circuit b; bt; b '' closed again for the heating current and a new cycle of work can begin.

It is also possible to use both circuit arrangements described here to combine so that either the first or second method is used can be. For this purpose, the switch 12 shown in FIG. 3 is the same Job to be arranged in the circuit arrangement according to FIG.

In the case of working according to the method described first the switch 16 ', in the case of working with the method described last the switch 12 is bridged.

Claims (2)

P a t e n t a n s p r ü c h e (1, Method of welding thermoplastic films during packaging relatively broad ge,; arises with discontinuous work cycles, characterized by that creates a constant welding temperature in a sweatband, which supplies heat v: interrupted during the welding process, the one which has decreased due to the welding process Sweat band temperature after the welding process due to briefly increased heat supply brought back to welding temperature and then by applying uniform heat is held on this. 2. Process for welding thermoplastic films during packaging relatively wide objects with discontinuous work cycles, characterized in that that in the sweatband a constant welding temperature is generated by the welding process Lower sweatband temperature after the welding process due to brief increases Heat supply brought back to welding temperature and then uniform Heat supply uaf this is kept. 3. The method according to claim 1, characterized in that a constant Heating current applied to the sweatband, this heating current during the welding process switched off, a higher current than the heating current in terms of pulses after the welding process Applied to the sweatband so that when the welding temperature is reached, the current pulse switched off and the heating current is switched on again. 4. The method according to claim 2, characterized in that a constant Heating current is applied to the sweatband, which is switched off after the welding process, a higher current than the heating current is applied in pulses when the Welding temperature, the current pulse is switched off and the heating current is switched on again vjird0 5. Circuit arrangement for implementing the method according to the claims 1 and 3, characterized in that in an excitation circuit (a) of a contactor (9) one that can be switched off at the beginning of the welding process and switched on at the end of the welding process Switch (12) -arranged that in an excitation circuit (c) of a contactor (13) and in the heating circuit (b; b '; b' ') for applying the Iieizstromes to the heating tape ) 6) switches (9 ''; 9 ') are arranged, which are switched on or off by the contactor (9). can be switched off that in the excitation circuit (c) of the contactor (13) and one Exciter current circuit (c ;. d) of a delayed time relay (15) a switch (14) is arranged at the end of the Welding process one and at the latest at the beginning of the next welding process can be switched off that in the excitation circuit (a) the contactor (9) and the pulse circuit (b; b '' '; b' ') for applying the Current pulse to the Schwaißband (6) switch (13 '' '; 131) are arranged, the can be switched off or on by the contactor (13) and that one is in the excitation circuit (c) the contactor (13) arranged switch C15 ') through the timing relay (15) is switchable. 6. Circuit 5 arrangement for realizing the process to, J after the Claims 2 and 4, characterized in that in an excitation circuit (c) one Contactor (13) an excitation circuit (c; d) of a delayed timer relay (15) a switch (14) is arranged which switches on and off at the end of the welding process at the latest at the beginning of the next welding process can be switched off that an in the excitation circuit (c) of the contactor (13) and in the heating circuit (b; b '; b ″) for applying the heating current to the sweat band (6) switches (9 ″; 9 ′) are, which can be switched on or off by a contactor (9), that in an excitation circuit (a) of the contactor (9) and the pulse circuit (b; b '' '; bit) to apply the Current pulse to the Schwaißband (6) switches (13 '' '; 13') are arranged, the can be switched on or off by the contactor (13) that a switch (15g) arranged in the excitation circuit (4) of the contactor (13) through the time relay (15) and one in the excitation circuit (a) of the contactor (9) arranged switch (16 ') can be switched by the auxiliary contactor (16). 70 circuit arrangement according to claims 5 and 6, characterized in that that a self-holding circuit (c; d; £) is arranged by the in the excitation circuit (c; d) of the delayed time relay (15) and one in the excitation circuit (c; e) Auxiliary contactor (16) arranged switch (14) can be switched off or on.