DE1246219B - Heat pulse bar for welding devices for welding thermoplastics - Google Patents

Description

Heat pulse bars for welding devices for welding thermoplastic Plastics The invention relates to a heat pulse bar for welding devices for Welding of thermoplastic plastics, the heating element of which by means of an am Beam attached film is covered from heat-resistant insulating material, on which liquid plastic does not adhere.

In known machines for the production of bags from thermoplastic Material, a working cylinder with preferably six welding tongs is used, which extend axially parallel to the circumference of the cylinder. Each welding gun of the continuously rotating cylinder detects the end of a to be welded to the Cylinder brought tube piece and welds it while continuing to run of the cylinder. To be provided with bottom welding at its trailing end Plastic hose sections are placed on the outside of the welding cylinder Ribbons and held by suction air.

Each welding gun consists of a fixed and a movable one Jaw, the fixed jaw carrying a resistance band that is covered by a foil is covered from insulating material to which liquid plastic does not adhere. the Foil usually consists of glass fiber coated with polytetrafluoroethylene. The movable jaw of the pliers is not heated and it is useful to have an elastic one Effective area on, z. B. an inserted silicone rubber strip to a good contact pressure ensure over their entire length, even if the number of each other layers to be welded changes, as is the case, for example, with gusseted bags the case is.

Used to heat the resistance band to the welding temperature one current pulse each.

After each welding process, however, it remains in the resistance band residual heat that heats up the resistance band more and more over time. For longer The operating time also heats up the welding jaw carrying the resistance band. As a result, the welding temperature changes with the pulse power remaining the same increased more and more, so that it is too high after just a few welds and there is a risk of burning the weld seams. To an approximately constant To ensure welding temperature, one is therefore forced with the known machines, the pulse power after which it was correctly set when the machine was started up after the resistance band has been heated by the remaining in it Regulate residual heat.

This readjustment makes the operation of the machine extraordinary difficult. In addition, it is not always possible to produce welds that are more consistent and good quality and there is occasional scrap. A Another disadvantage of the known welding device is that for the required Cooling down after welding is required a relatively long time, so that the actual welding time can only be very short, which in turn is a relative one requires large pulse power. This particularly applies to processing If the material is thick, there is a risk that the layers will not be welded through in the short welding time and thus the bags do not leak. The workpieces are only about one Arches from 270 to 300 degrees are transported on the cylinder and the cylinder must Rotate as fast as possible to achieve a large output. The result of it the resulting working time is to be used for heating and cooling; there the cooling can not be forced in the known machines, you have to as much as possible of the available commute to work thus a maximum of circumferential speed of the welding cylinder and thus of output to receive finished pouch. However, this can only be done at the expense of the heating-up time, which forces an increase in the welding temperature, which finds its limit there, where the material starts to burn.

Especially with thicker foils, the one that burns against the heated one Position of the welding jaw in contact with the other, while the other is not warm enough.

In addition, it is significantly above the melting temperature at such of the plastic lying welding temperatures the correct allocation of the welding time essential and critical to the welding temperature. Since the machine starts up and over- Especially useful welds at different machine speeds must perform, the electrical welding energy is dependent on the number of revolutions controlled by the machine. This regulation is due to the different characteristics the control elements for the speed on the one hand and the electrical energy on the other hand, it cannot be carried out with sufficient accuracy, so that this also results in faulty welds or the need for manual readjustment.

From the German utility model 1742559 are hot jaw and heat impulse welding devices with sweat organs that od in the processing of foils into bags. Like. With coatings preventing the foils from sticking to one or both welding jaws, for example made of silicone rubber or Teflon glass silk fabric, are known, in which a resistance band serves as a sweat organ. In this reference is also indicated in general terms that welding stamp and foil for the purpose Cooling can be blown. The special heat pulse bar described below according to the present invention, which is associated with considerable advantages however, in no way suggested by the citation.

In French patent specification 1 164707 there is an impulse welding device described in the between the weld metal lying on the support jaw and the Heating element an inflatable bellows is arranged. This bellows is after the actual Welding process inflated by compressed air, which on the one hand is necessary for maintained pressure on the weld seam during cooling and on the other hand the heating element with its support structure is lifted against the pressure of two springs will. On the side of the weld metal, the bellows is soaked in silicone oil Glass silk covered.

The device according to said French patent has the disadvantage that an effective cooling of the resistance band of the thermal pulse Baikens not or only inadequately achieved, since it does the job of the mentioned inflatable element is a cooling of the welding point after the welding process to convey and at the same time a considerable contact pressure on the weld maintain. There must therefore be an appreciable internal pressure in the bellows mentioned be maintained, causing a significant throttling of air circulation the bellows requires, if any: air control is carried out. It kicks that is, according to this prior art and in contrast to that described below Arrangement according to the invention a cooling of the heating element of the welding device only to a very small extent. The one from the aforementioned French patent known welding device is also disadvantageous in that the welding heat must pass through both bellows walls and a glass silk layer. Through this insulating Intermediate layers increase the time it takes to heat the weld, which leads to the Reduced output of the device per unit of time. In addition, the heating temperature of the welding element to be determined on the material of the bellows so that this does not burn. This limitation of the heating temperature to the bellows material decreased the heat gradient, so that the heating time continues to increase, whereby the output of the Device per unit of time is further reduced.

The invention is based on the object described above To avoid disadvantages and also to provide a device in a further embodiment create that not only no longer has these disadvantages, but also for education better welds than the known arrangements.

According to the invention, the heat pulse bar for welding devices is for welding thermoplastics, the heating element of which is attached to the beam by means of a Foil made of heat-resistant insulating material is covered on which liquid plastic does not adhere, characterized in that the film loosely over the active surface of the Heating element is and that at least one coolant supply line for a gaseous Coolant opens into the space delimited by the heating element and the film, the is provided with at least one outlet opening for the coolant, wherein in In the cooling position, the film is lifted from the heating elements by the coolant pressure is. This arrangement means that the heat pulse bar absorbs the residual heat after the welding process is completely withdrawn by the coolant flow, this can also take place over a longer period of time Operation of the device no longer heats up, so that the pulse power once set does not have to be readjusted during operation and there is no risk of formation there are defective welds. Air is expediently used as the coolant.

The heat pulse bar expediently has a cross-section U-shaped support piece, in the base of which a coolant feed opening opens, and between its legs a rail made of insulating material and carrying the heating element is arranged, which with the legs and the base one in the longitudinal direction of the beam extending longitudinal channel limited, both legs with a number are provided by transverse to the longitudinal direction of the beam extending channels, which at one leg, the longitudinal channel with that delimited by the bar and the film Room and with the other leg this room with the outside air or at least a coolant discharge channel connects. The channels are advantageous here of one leg opposite the channels of the other leg in the longitudinal direction offset.

In a particularly advantageous embodiment, the with the Heat pulse bar provided with a heating element is a support piece with a rectangular cross-section through which the coolant supply line is centered in the area delimited by bars and foil Space is led, and this space is at the ends of the beam with the outside air or each connected to a coolant discharge channel.

Since the device according to the invention loosely over the Effective area of the heating element lying film after the end of the welding process lifts off the heating element under the pressure of the coolant, thereby opening the coolant duct forms, the welding point is advantageously also when the film is lifted off of the bag raised.

The welding point can through the cooling air guided under the film Cool down very quickly when the welding gun is open. The cooling takes place in contrast to the known versions, not under pressure on the weld, whereby the weld seam is given the opportunity to cool down to shrink, which leads to greater strength in the seam. This solidification the weld seam through shrinkage was previously not achievable. To get the seam in yet Not to destroy or impair the unsolidified state was a contact pressure on the weld until the material has solidified sufficiently. With the device according to the invention is the opening of the welding gun without destruction the seam is possible if that. Opening at the latest when the current pulse is switched off takes place because the plastic in the liquid state is not on the opening jaw hold remains.

As a result of the intense possible with the device according to the invention Cooling the heating element and the weld seam can increase the welding time and the Heating power can be reduced. It has been shown that on the basis of the same times for a work cycle when using the device according to the invention the cooling time can be reduced so that for welding four times what it was before available time can be spent. The heating power can therefore can be reduced to a quarter of the previous output. The welding temperature in the resistance band of the heat pulse bar does not decrease in the same proportion, because on the one hand it is not in a proportional relationship to this anyway and on the other hand, due to the previous short pulse duration, that of the electrical Power corresponding final temperature was not reached at all. The in the application the device according to the invention possible significant reduction in heating power has the added advantage that the electrical parts are much weaker can be dimensioned. In addition, the welding temperature can now be significant are less above the melting temperature of the plastic, so that the assignment the welding time is no longer so critical to the welding temperature and on a manual basis Adjustment in the event of speed changes can be dispensed with. Also occurs no scrap formation with the automatic speed / welding temperature control more on.

The invention is illustrated in the following description with reference to the drawing explained in more detail in which two exemplary embodiments are shown. In the drawing shows Fig.1 i g. 1 shows a sealing bar according to a first embodiment, namely the left part in the view, the middle part in the section along the line B-B and the right part in section along the line C-C of FIG. 2, fig. 2 one Section along the line II-II of FIG. 1, F i g. 3 shows a sealing bar according to one second embodiment with partially cut-off insulating film, FIG. 4 a Section along the line IV-IV of FIGS. 3 and F i g. 5 one of FIG. 4 corresponding Section through the welding bar according to FIG. 3 at the moment of welding, wherein also indicated the material layers to be welded together and a press beam are.

The first embodiment of the welding bar, that in the. Fig. 1 and 2 is shown, has a cross-sectionally U-shaped support piece 1, whose The web has a hole 2 in the middle, into which an air line 3 opens. One Rail 4 made of insulating material, which between the legs 5, 6 of the support piece 1 is pushed, limited with the insides of the legs and with the base of the support piece an air duct 7. This air duct is provided with a sealing piece 8 at both ends closed, one of which is indicated in Fig. 1 on the left. the Rail 4 carries a switched on in a manner not shown in a circuit Resistance band 9.

Above the resistance band there is a loose one on the outer surfaces of the legs 5, 6 fastened by means of rails 10 film 11 made of coated with polytetrafluoroethylene Glass silk stretched. In the leg 5 of the support piece 1 recesses 12 are incorporated, which, in conjunction with the strip, form 4 air ducts. The leg 6 has a Row of bores 13 also forming air channels. The one through the line 3 air conveyed into the channel 7 passes through the channels 12 under the film 1.1 and flows over the heating tape 9 and then through the bores 13 to the outside. The holes 13 can be offset relative to the recesses 12 in the longitudinal direction of the welding bar to be more intensive cooling at the outlet openings of the recesses 12 and thus to prevent irregular weld seam formation as far as possible.

The particularly useful embodiment of the welding bar according to 3 to 5 has a support piece 15 which, with the interposition of a bar 16 carries a resistance band 17 made of insulating material. Same as in the first embodiment is on the resistance band by means of rails 18 on the side walls of the support piece 15 attached insulating film 19 loosely stretched. The support piece 15 has a transverse bore, into which an air line 20 opens and which is connected to an air duct 21. The air duct opens in the middle of the welding bar 1 under the foil 19. A through The air flow guided under the film arches the film and spreads out to both sides. It finds practically no resistance and flows over it Resistance band 17 on both sides into the open (see arrow at the right end in FIG. 3).

5 shows the welding bar in cooperation with a press bar 22 at the moment of welding. The welding bar 22 carries on its active surface a silicone tunnel bar 23. While in the illustrated embodiment of Welding bar forms the fixed jaw of welding tongs, forms the press bar the movable jaw, which after the introduction of the material layers 24, 25 against the fixed jaw is pressed.

Here, the loosely presses itself over the resistance band. 17 lying Slide 19 a little to both sides.

After closing the pliers, there is a brief current surge the resistance band 17 is heated and causes the layers 24, 25 to be welded together together. Immediately after the end of the impulse, the pliers are opened so far that that the film 19 comes free from the resistance band 17 and under the pressure of the fed Air also lifts the welded layers. Here the weld seam cool faster than before and also shrink. The one about the Resistance League 17 flowing air leads into this remaining heat completely away. This causes the resistance band and thus also the welding bar to heat up certainly avoided.

Appropriately, the air flow to the sealing bar is only in the stage of Cooling supplied. But it is also possible to supply the air to the welding bar to be carried out continuously, as the film is firmly attached to the Resistance band is pressed and therefore no impermissible cooling can occur, because the air does not go to the effective surface of the resistance band, but only to its narrow one Side edges can get.

Claims (4)

Claims: 1. Heat pulse bars for welding devices for welding thermoplastics, the heating element of which was fastened by means of a be on the beam Foil made of heat-resistant insulating material is covered on which liquid plastic does not adhere, characterized in that the film (11, 19) loosely over the active surface of the heating element (9, 17) and that at least one coolant supply line (3, 7, 12 or 20, 21) for a gaseous coolant in the through the heating element and the film opens into a limited space, which with at least one outlet opening (e. B. 13) is provided for the coolant, the film through in the cooling position the coolant pressure is lifted from the heating element. 2. heat pulse bar according to claim 1, characterized in that the beam (1) has a cross-sectionally U-shaped support piece (2) knows in whose Base a coolant supply opening (3) opens and between its legs (5, 6) a rail (4) made of insulating material and carrying the heating element (9) is arranged is that with the legs and the base one in the longitudinal direction of the beam extending longitudinal channel (7) limited, both legs with a number of channels (12, 13) running transversely to the longitudinal direction of the beam are provided, the one at one leg (5) the longitudinal channel with the one through the bar and the film limited space and with the other leg (6) this space with the outside air or connect at least one coolant discharge channel. 3. heat pulse bar according to claim 2, characterized in that the channels (12) of one leg (S) opposite the channels (13) of the other leg (6) are offset in the longitudinal direction. 4. heat pulse bar according to claim 1, characterized in that the bar (1) provided with the heating element (17) has a rectangular cross-section Has support piece (15), through which the coolant supply line (20, 21) centrally in the is guided by bars and foil (19) limited space and that this space to the Ends of the beam connected to the outside air or a coolant discharge channel each is. Considered publications: German utility model no. 1 742559; French patent specification No. 1 164707.