EP2173533A2

EP2173533A2 - Method for producing blow-moulded hollow bodies

Info

Publication number: EP2173533A2
Application number: EP08773753A
Authority: EP
Inventors: Günther KAPPEN; Rolf Kappen-Feuerherm; Horst Deckwerth
Original assignee: Individual
Current assignee: FEUERHERM, MAX
Priority date: 2007-06-29
Filing date: 2008-06-30
Publication date: 2010-04-14
Also published as: WO2009003662A2; DE102007030369A1; DE102007030369B4; WO2009003662A3

Abstract

The invention relates to a method for producing blow-moulded hollow bodies. Flat preforms are produced during the working cycle of a blow-moulding installation, said preforms emerging from wide-slit nozzles, and being connected, while still in the thermoplasticised state in the blow-moulding installation, along a pinch-off weld formed by the closing of the blow-mould, and expanded to form a hollow body. So that the flat preforms assume a reproducible position both in relation to the respective blow-moulding half and to each other, a plurality of measures according to the invention are carried out alone or as a group. The synchronism of the preforms emerging from the wide-slit nozzles is monitored. If there are variations in the synchronism behaviour, the flow resistance is modified in order to correct the synchronism by heating the flow channels differently and/or by actuating a throttle element acting on one of the partial flows, or the transport power of a plasticising unit is adapted. Furthermore, the course of the preforms emerging from the wide-slit nozzles is monitored, and differences between the courses created by local variations of the flow resistance in the flow channels are corrected. In order to ensure the synchronism of the preforms and a straight course therefor, the preforms can be controlled by a mechanical device once they have emerged from the wide-slit nozzles, said mechanical device moving downstream at a pre-determined speed and guiding the preforms until they have been transferred into the blow-moulding halves.

Description

Process for producing blow-molded hollow bodies

Description:

The invention relates to a method for producing blow-molded hollow body, being produced in the working cycle of a blow molding sheet preforms, which emerge from slot dies and connected in the thermoplasticized state in the blow molding along a squeeze formed by closing a blow mold and endgeformt to a hollow body. It tabular preforms are formed, which may optionally have a curved profile. The preforms can be continuously extruded or batch produced in the discharge operation.

Such a method is known from DE 20 2006 013 751 U1. The method opens up the possibility to position almost any inserts between the sheet preforms before the blow mold is closed. In this way, blow-molded hollow bodies can be produced in which, for example, prefabricated assemblies of several parts are integrated. However, there is the problem in this method of simultaneously positioning the preforms emerging from slot dies independently both relative to one another and with respect to the blow mold halves, before the blow mold is closed. A possible misalignment of the preforms, deviations with regard to the synchronous behavior as well as viscoelastic effects have the result that the preforms in the blow mold are not connected in the correct assignment to one another.

The procedure is such that the blow-molded hollow bodies have a predetermined net weight, a given wall thickness and wall thickness distribution, predetermined dimensions and no distortion. These quality features must be adhered to within the narrowest possible limits. Against this background, the object of the invention is to guide the method so that the flat preforms both assume a reproducible position relative to the respective blow mold half and to one another. The independent claims 1, 6, 9 and 12 solve this problem. The methods according to claims 9 and 12 can also be realized in combination with the methods according to claim 1 or 6. The dependent claims represent preferred embodiments of the method according to the invention.

A first embodiment of the method according to the invention provides that a melt stream of thermoplasticized plastic is divided into at least two sub-streams, from which the preforms are formed, that the preforms emerging from the slot dies are monitored with respect to their synchronization and that in case of deviations in the synchronous behavior for correcting Concurrently, the flow resistance in the flow channels through which the partial flows flow is varied by varying the temperature of the flow channels and / or by actuating a throttle element which acts on one of the partial flows. The term "tempering" includes measures for heating as well as for cooling.

It should be noted that the melt strand coming from a plasticizing unit is divided into at least two partial streams. The partial flows are transformed in the flow channels to flat melt webs, which emerge through the slot dies as flat or tabular preforms. Since approximately the same melt pressure prevails at the dividing point for the partial flows and the incoming mass flow, the incoming mass flow is divided in such a way that the same pressure loss builds up over the remaining flow channel length. The pressure loss in the flow channel depends essentially on its geometry, the gap width of the slot dies and the local throughput. The gap width of the slot dies is changed during the extrusion of the preforms according to a wall thickness program which proceeds with the preform extrusion, so that the preforms have thick and thin locations in the longitudinal direction. The wall thickness profile thus influences the flow resistance. If a larger gap width is set at the nozzle outlet, the flow resistance of the respective side is reduced and vice versa. Pressure loss and flow resistance depend directly on each other. With the same flow resistance in the flow channels, the throughput is divided into equally sized partial flows. With different flow resistances in the flow channels connected in parallel, the partial flows are distributed in the opposite proportion to the flow resistances. To make matters worse, that the partial flows behave through a common feed as communicating tubes. This means that a changing flow resistance in the first flow channel results in a throughput change in the parallel-connected second flow channel. The flow resistance is essentially dependent on the flow channel cross section, the flow behavior of the melt and the temperature of the flow channel. All these influencing factors have an effect on the extrusion process and can contribute to the fact that the flat preforms do not assume the desired position when closing the blow mold and / or have the desired mass distribution. In order to compensate for this, the synchronization of the preforms emerging from the slot dies is monitored according to the invention, and appropriate corrective measures are carried out in the case of deviations in the synchronization behavior. In the case of a correction, the manipulated variable is preferably positive for one flow channel and negative for the other flow channel at the same time. For synchronism control, the extrusion speeds of the preforms emerging simultaneously from the slot dies are recorded. The measurement of the extrusion time is expedient in that at one or more points the time is measured when the preform lower edge or a mark applied to the preform reaches the measuring point. It goes without saying that the greater the number of measuring points, the more effective is the synchronization control. It makes most sense to record the sheet-like preforms in several places during extrusion in order to then activate the correct manipulated variables. A correction of the synchronization is generally carried out in the next possible power stroke of the system. But it is also possible a synchronization correction already during the preform extrusion, which is still effective in the same working cycle, ie before molding the preforms in the blow mold. With regard to the location and the time for the smelting division, there are several possibilities. It is within the scope of the invention that the melt stream is first converted into a tubular melt flow, which is then divided into the part streams. A further, preferred embodiment of the method provides that the melt stream emerging as a strand from a plasticizing unit is subdivided into the part streams and that the part streams are subsequently shaped into sheet-like melt webs in separate flow channels. Finally, it is within the scope of the invention, the possibility that the exiting as a strand of a plasticizing melt stream is formed in a flow channel in a flat melt web, which is then divided into the partial streams. When producing multilayer preforms, the layers can be combined before or after division.

An alternative embodiment of the method according to the invention provides that the preforms are formed from melt streams which are produced by separate plasticizing units and formed into sheet-like melt paths in separate flow channels, that the preforms emerging from the slot dies are monitored for their synchronization and that deviations in the synchronous behavior the capacities of the plasticizing units are adjusted to correct the synchronization. The adaptation of the delivery rate is done for example by changing the speed of at least one extruder. In order to determine the rotational speed adaptation, it is expedient to use measured values from measuring devices with which, for example, the net weight of the hollow bodies, the weight of waste slugs, the length of the preforms, viscoelastic effects (swelling, relaxation, sagging) and the like are detected. The method is also suitable for the production of multilayer preforms. It is within the scope of the invention that one or more layers are formed by dividing a melt strand conveyed by a plasticizing unit and the sub-stream is assigned in each case a further plasticizing unit, which delivers the plastic melt for only one layer whose conveying powers be regulated to compensate for deviations in the synchronous behavior. In the production of, for example, six-layer preforms, five layers can each be formed by dividing a melt stream, while for the extrusion of the sixth layers separate plasticizing units are used whose delivery rates are controlled to compensate for deviations in the synchronous behavior. For synchronism control, it makes sense to record the extrusion speeds of the preforms emerging simultaneously from the slot dies.

In the case of deviations in the synchronous behavior, a suitable adaptation of a wall thickness program controlling the preform extrusion can also be carried out in the above-described methods for correcting the synchronization of the preforms. By adapting the wall thickness program, the wall thickness of the preforms is changed to preform sections which form waste slugs during the blow molding. This measure can be carried out in addition to the measures described above, for example, for fine correction. It also lends itself to a quick, preliminary correction before the corrective action on flow resistance becomes effective.

Another aspect of the invention relates to any misalignment of the preforms. Since in the production method according to the invention two or more sheet-like preforms are connected to one another over the entire circumference, it is important that the sheet-like preforms are each positioned in the blow mold half in such a way that they can form fault-free connection zones over the circumference. If, for example, a preform were to go so wrong that it does not overlap the edges of the cavity during molding, this would mean that the half-shells would not be able to be welded together and scrap would be created. But even at a lower level of skew or a non-uniform preform run quality loss are the result. They can affect a delay. You can be the reason that the wall thickness distribution in one or both Halves of the blow-molded hollow body deviate from standard values. Causes of a misalignment are, for example, rheological influences or changing sagging of the preforms due to procedural factors such as throughput changes, viscosity changes and the like. Further, a wall thickness varying across the preform width dictated by a horizontal wall thickness control may cause skewing or uneven running of the preform.

According to the invention, the trajectory of the preforms emerging from the slot dies is monitored and deviations of the trajectory are corrected by local changes in the flow resistance in the flow channels of the extrusion dies forming the preforms. To record the trajectory, methods of image acquisition, photoelectric sensors or photocells can be used. It can be continuously created digital images, which are compared with reference images. It is also within the scope of the invention that the preforms are imaged at certain times, for example immediately after the extrusion of a preform, and that the images are compared with an underlying reference image. The images can be evaluated computer-aided. The digital image analysis can be easily integrated into a control loop that controls the flow resistance in the flow channels. To correct any skewing of the preforms separate tempering are used according to the invention, which are preferably arranged in the walls of the flow channels and / or segmentally on the circumference of the extrusion die on both sides of the melt stream and transverse to the flow direction. Temperature control devices include heating and cooling devices. With these tempering devices, different temperatures can be set transversely to the flow direction and / or on both sides of the melt paths flowing through the flow channels in order to locally change the flow resistance. According to a further aspect of the invention, the sheet-like melt webs are formed in flow channels whose flow channel geometry transversely to Flow direction is changeable. In order to correct a trajectory deviating from standard values or uneven trajectory, the thickness of the melt web can be changed by adjusting the flow channel geometry in sections corresponding to an upper waste slug, a lower waste slug or lateral waste slugs of the blow-molded hollow body. For example, if the preforms have thick-walled and thin-walled sections that extend over a great length of the preform, this can lead to skewing or at least an uneven lower edge of the preforms. This is due to the fact that thick-walled Preform- lingsabschnitte run ahead and run after preform sections, which are extruded with a smaller die gap. The described effect can be at least partly compensated for by adjusting an inverse profile of the nozzle gap during the extrusion of preform sections, which are formed into an upper or lower waste slug. In zones that are leading, a thin nozzle gap is set. In zones where the melt strand is sagging, the die gap becomes more open during extrusion of preform sections that are formed into scrap pieces.

The flat melt webs can be formed in flow channels whose width is changeable transversely to the flow direction. The width of the flow channels can be changed in order to correct a sagging of the preforms that deviates from the preset values or to correct a trajectory deviating from standard values. By sagging is meant a Auslängung the not yet solidified thermoplastic preforms due to their own weight. For example, in order to reduce sag, the preforms may be extruded at a smaller width in areas forming the lower scrap. Preform sections that are formed into a top scrap can be extruded with the same objective with a greater melt bandwidth. To measure the amount of sag, the preforms are conveniently marked during preform extrusion. The distances between the marks are measured and compared with default values to detect sagging of the preforms.

In the previously described embodiments of the method according to the invention, the preforms are extruded downwards into the open without support on the underside. The problems of synchronism and misalignment can also be achieved according to a further embodiment of the method according to the invention, that the preforms are detected after emerging from the slot dies of at least one mechanical device which is moved downwards with a predetermined speed profile and the preforms preferably leads to the transfer in the blow mold halves. To guide the preforms, a device may be used which has surfaces for supporting the preform lower edges and / or clamping elements for detecting the preforms. The device may be formed as a separate device or be integrated in a carrier for the transfer of the preforms to the blow mold. The support can also be carried out on two independent devices, wherein between the devices a carrier for the transfer of the preforms can be arranged to the blow mold. When using separate and independently controlled devices, each detecting a preform, the wall thickness profile of the preforms can be influenced by controlling the downward speed.

In all the methods described, the gap width of the slot dies is changed regularly during the extrusion of the preforms according to a wall thickness program which proceeds with the preform extrusion. Preferably, each slot die is assigned a separate wall thickness program which controls the gap of the slot die. In order to produce the preforms, it is possible to use slot dies which have a nozzle element which is flexible transverse to the flow direction or a nozzle element comprising a plurality of segments arranged next to one another in the flow direction, the segments being relatively close together for the purpose of changing the flow channel geometry. other are adjustable. Preferably, the segments are assigned adjusting devices which are each controlled by an associated wall thickness program. To adjust a flexible nozzle element, this can be assigned to a plurality of adjusting devices, which are also each controlled by a separate wall thickness program.

According to a preferred embodiment of the method according to the invention, wall thickness programs are used which subdivide the volume of the plastic melt required for a preform or a preform section into a predetermined number (n) of volume sections and assign setting values for adjusting the nozzle gap to these volume sections. On the basis of at least one measured variable, the material distribution in the preforms or in the hollow body is detected and compared with a specification. For the purpose of triggering a deviation from the default values caused by viscoelastic effects, the control values for adjusting the nozzle gap are applied with correction values which influence the sagging, the swelling and / or the relaxation of the preform. The control values form a program curve plotted over the number (n) of volume sections, which is composed of at least one base gap and one profile curve. The base gap or another part of the program curve is expediently adjusted when the correction values are applied so that the amount of melt, the wall thickness and the wall thickness distribution remain constant. The method according to the invention is primarily used to compensate for fluctuations caused by changes in the material behavior, eg. As melt index, Plaszifizierverhalten, threshold behavior, viscosity of the melt and the like result. Furthermore, it can be used to stabilize a manufacturing process as quickly as possible after longer downtimes. However, the control method according to the invention presupposes that the net weight of the hollow body, the desired wall thickness distribution, the desired position of the preforms are defined relative to the respective blow mold half and the nominal throughput. Viscoelastic effects and other interference can lead to the net weight of the blow molded hollow body, the wall thickness and wall thickness distribution of the hollow body or the preforms, and the dimensions of the preform differ from standard values. The deviations can be corrected by correcting the program curve. To record and determine the necessary corrections, suitable measured values must be recorded. Preferably, the weight of the planar preforms and / or the weight of the blow-molded hollow body and / or the weight of one or more hollow body sections of the blow-molded hollow body is measured. By measuring the net weight and weight of the lower and upper garbage, viscoelastic effects, e.g. B. a changing threshold behavior and deviations in terms of sagging, are detected. Another way to detect viscoelastic effects is to mark the preforms emerging from the slot dies in at least two places and to measure the distance between the marks. Preferably, the markings are applied to preform areas which form side debris after blow molding and are separated from the blow molded hollow body. It is also expedient to arrange the markings on preform areas in which the wall thickness profile changes significantly. Deviations of the distance from a setpoint at constant net weight are a direct measure of viscoelastic effects.

Preferably, both flat preforms are detected by image technology and the images are compared with reference images. If several images are taken in an extrusion cycle, it is possible to intervene in the ongoing extrusion during the extrusion cycle, if deviations from the reference images are detected. Furthermore, wall thickness measurements can be made on the preforms or on the blow-molded hollow bodies. Preferably, the wall thickness of the hollow body is measured by suitable sensors already in the blow mold. Deviations from nominal values indicate that the preforms did not assume the specified position when they were transferred to the blow molds. Another method of capture of disturbance variables is the measurement of the temperature distribution of the preforms or the measurement of the temperature in a defined preform area.

A blow molding plant can be operated with a variable or constant cycle time. In the first case, the molding process of the preforms is triggered in the blow mold halves when the preform has reached a certain length, which is detected for example by means of a photocell in the extrusion space. According to a preferred embodiment of the method according to the invention, the extrusion times of the preforms are measured and compared with nominal values. If the measured extrusion time deviates from the standard value, corrective measures must be taken. If the blow molding machine is operated with a constant cycle time, it is expedient to measure the length of the extruded preforms while specifying an extrusion time and to compare them with a standard value. In the event of deviations, corrective measures must be initiated.

With regard to an optimal mode of operation, it is furthermore advantageous if at least one marking is applied to the preforms emerging from the slot dies whose positions on the preforms or on the hollow body are measured. Also suitable as marking is a significant feature of the preform made by extrusion, e.g. B. an extremely set point of the wall thickness profile.

The synchronization and / or the course of the track and / or the suspension of the preforms can also be detected using image acquisition methods, light barriers or photocells.

The measured values described above are compared with setpoints. To correct subsequently produced hollow bodies, the delivery rate of at least one plasticizing unit, the temperature, the gap geometry of the slot dies or the gap width of the slot dies can be changed as corrective measures. In addition to simple adjustment of also cascade controls and multi-variable control, which take into account the dependencies of the disturbances, are used. Preferably, a corrective action is executed only when a combination of at least two controlled variables have been detected and evaluated. For example, the length of the preforms and the net weight of the blow-molded hollow body or the net weight of the blow-molded hollow body in combination with the weights of the upper waste casing and the lower waste casing or a measured variable relating to the position of the preforms relative to the blow mold are used in combination with the control variable combinations the net weight of the hollow body into consideration. In addition, an interference signal can be emitted if the deviation of the measured values from the assigned desired value leaves an allowable tolerance range. It is understood that the interference signals can be used to eject defective hollow bodies from the manufacturing process.

In the context of the method according to the invention, it is essential that the sheet preforms are brought into a defined position relative to the blow mold and then taken directly from the blow mold halves or fed to the blow mold halves by the use of grippers and / or carriers. According to a further embodiment of the method according to the invention, the position of the preforms is detected metrologically and any positional deviations of the preforms are determined by a desired value. Then the trajectories of the gripper or carrier can be changed to correct these bearing deviations. Preferably, two carriers are used, which simultaneously supply the flat preforms to the blow mold halves. In the context of the invention, however, it is also the case that the preforms are fed in succession to the blow mold halves. Furthermore, there is the possibility that the blow mold halves travel to transfer the preforms against a carrier, which has previously taken up both preforms. The sheet-like preforms are supported under vacuum and / or with blown air and introduced into the blow mold of the blow molding. Before closing the blow mold inserts can be positioned between the sheet preforms. These can be introduced into the cavity of a carrier or into a preform preformed in a blow mold half. It is understood that inserts can also be inserted into a plurality of preforms or cavities of the carrier.

The method according to the invention includes that the preforms introduced or assigned in pairs into the blow mold differ in material terms and / or in terms of their material distribution and / or layer thickness or are colored differently. The preforms can then be combined in the blow mold along a squeezing seam formed by closing the blow mold and shaped into a hollow body whose housing halves differ, for example, in terms of material, material thickness, layer structure or color.

In the following, the invention will be explained with reference to exemplary embodiments. They show schematically:

1 shows a plant for carrying out the method according to the invention in a side view,

2 is a plan view of the system shown in Fig. 1,

3 to 5 further embodiments of the system with associated measuring and control devices,

Fig. 6 shows the head of an extrusion die in a section through the

Flow channel in the sectional plane B-B of Fig. 7,

7 shows the section AA of FIG. 6, 8 and 9 constructive embodiments of a slot die for carrying out the method.

The systems and devices shown in the figures are used for the production of blow-molded hollow bodies, eg. B. plastic fuel containers. In the working cycle of a blow molding plant, pairs of sheet-like preforms 1, 1 'are produced, which exit from slot dies 2 and are joined in the thermoplasticized state in the blow molding plant along a squeezing seam formed by closing a blow mold 3 and are finally formed into a hollow body 4. In their basic structure, the systems each consist of an extruder with one or more plasticizing units 5, at least one extrusion die 6 for the production of sheet preforms 1, 1 'and a blow molding machine with at least one blow mold 3. The blow mold can be stationary under or next to the extrusion die 6 be arranged or drive to take over the preforms under the extrusion die 6.

The sheet-like preforms 1, 1 'emerging from the slot dies 2 are single or multilayered. They are extruded down into the open and connected in the blow molding plant still in the thermoplastic state materially or positively and finally to a hollow body 4. For the extrusion of the preforms 1, 1 'separate flow channels 7 are preferably used, each forming an incoming melt strand into a sheet-like melt web and end in a slot-shaped outlet cross-section of a slot die 2. The gap width of the slot die 2 is changed during the preform extrusion according to a wall thickness program 8, which runs with the preform extrusion and controls actuators. The sheet-like preforms 1, 1 'have in the preform longitudinal direction and possibly also in the horizontal direction (transverse direction) on a changing wall thickness, thick points are assigned to the areas which are subject to strong stretching in the blow mold 3 or require a greater wall thickness. The flow channel geometry is located in the exit section or in one or more sections before the Outlet cross section changed. The wall thickness distribution of the preforms in the width direction also depends on the geometry of the blow-molded hollow body 4.

The sheet-like preforms 1, 1 'are brought into a defined position relative to the blow mold 3. The takeover of the preforms 1, 1 'by the blow mold can take place directly through the blow mold itself or through the use of grippers and / or carriers 9. The operation with two carriers 9 is shown by way of example in FIG. 2. The blow mold halves 10 of the blow molding machine are arranged with lateral offset below the extrusion die 6. The preforms emerging from the slot dies 2 on the underside are grasped by carriers 9 and in each case fed to a blow mold half 10. The carriers 9 travel during or before extrusion between the preforms. Each sheet preform is taken after reaching the individual hose length of the associated carrier 9, which clamp the preform so that forms a closed cavity. The carriers 9 separate the preforms and move to the blow molding position. There, the preforms are aligned with the blow mold half 10. About the cavity of the carrier 9 can be pre-blown. After a first shaping by pre-blowing, the preforms 1, 1 'are taken over by the associated blow mold half 10. Thereafter, the two carriers 9 drive out of the blow molding area. The blow mold 3 is closed and the preforms placed in the blow mold halves 10 are inflated to form a hollow body 4. In the embodiment, two separately movable support 9 are provided, which simultaneously supply the sheet preforms to the blow mold halves 10. It is also within the scope of the invention to use only one carrier 9, which feeds the preforms in succession to the blow mold halves 10 or receives two preforms and positions them between the blow mold halves. The blow mold halves are moved against the carrier and the preforms molded by means of vacuum and / or with blown air support in the blow mold halves. The blow mold is opened and the carrier removed. Then the blowing mold halves together and the preforms are connected to form a hollow body.

In the embodiment of FIGS. 1 and 2, the extrusion tool is fed by different plasticizing units 5. The pairs introduced into the blow mold preforms 1, V may differ in material terms, in terms of their material distribution and / or layer thickness or colored differently. The method according to the invention can be used to produce hollow bodies whose housing halves differ, for example, with respect to the coloring and / or the material composition and / or their wall thickness.

The extrusion die 6, which may also consist of two parts 6a, 6b, has two flow channels each with a melt inlet 12 for a melt strand emerging from a plasticizing unit 5, a distributor channel 13 and a choke field 14 for uniform spreading of the flat melt web. As a distribution channel 13, for example, the usual in the flat film or panel extrusion distribution channel forms, z. B. so-called coat hanger nozzles, fishtail nozzles or the like can be used. The gap width of the slot die 2 is adjustable and has, for example, an adjustable bar 15. The adjustment takes place by means of conventional actuators 16, which are controlled by the wall thickness program 8. In the flow direction in front of the outlet cross section, a throttle element 17 is provided. The actuation of the throttle element 17 is preferably carried out by actuators 18, which are also controlled by a program.

The extrusion tools shown in FIGS. 3 to 5 for carrying out the method described comprise a head element with two slot dies 2 and adjusting devices for actuating a respective nozzle element 19 of the slot dies 2. The gap width of the slot dies 2 can be changed by the movable nozzle element 19 in the outlet cross section. The actuating device 20 for actuating the nozzle element 19 is a program control assigned, which controls the gap width of the outlet cross section of the slot die according to a running with the preform extrusion wall thickness program 8, that the emerging from the slot die 2 planar preform 1, 1 'thick and thin in preform longitudinal direction. The preforms 1, 1 'can have different wall thickness distributions.

The gap width of the choke field 14 can be changed by adjusting elements 18. According to the exemplary embodiments illustrated in FIGS. 6 and 7, the extrusion tool 6 has wall segments 21 which can be adjusted in the throttle field. Further, the width of the distribution channel 13 is changed by slide 22. The slide 22 have a slide plate, which can be adjusted in the flow direction and a part of the distribution channel 13 shuts off. The choke field 14 is variously adjustable with the described devices. On the one hand, the flow resistance can be changed by adjusting the segments 21. Furthermore, by means of the segments 21 and slide 22, the flow channel in the edge regions can be completely closed so that an adaptation of the extrusion width can be achieved. The segments 21 and slide 22 may be equipped with actuators. Finally, by shutting off the flow channel through one or more inner wall segments 21 of the choke field, the melt coming from the distributor channel can also be divided into several partial flows. This allows the extrusion of at least two preforms 1, 1 'side by side.

According to an embodiment shown in Fig. 8, the nozzle member 19 of the slot die 2 is composed of a plurality of juxtaposed in the flow direction of segments 23, which are adjustable relative to each other for the purpose of changing the flow channel geometry. The adjustment of the segments 23 relative to one another takes place by means of actuators, which can be integrated in a still-explained measurement and control scheme. Furthermore, the slot die 2 can be equipped with an adjustable throttle element 17, which is arranged in the flow direction in front of the nozzle element. The slot die 2 can also be equipped with heating and / or cooling devices 25, which are arranged on both sides of the flow channel. By setting different temperatures, a skew of the preforms 1, 1 'can be counteracted. Also, transversely to the direction of flow, a plurality of separately controllable heating / cooling devices can be arranged next to each other for the correction of any skewing of the melt web.

The blow-molded hollow body 4 must have a predetermined net weight, a predetermined wall thickness and wall thickness distribution and predetermined dimensions. You must also have no delay. The quality features must be adhered to within the narrowest possible limits. The method must therefore be performed so that the sheet-like preforms 1, 1 'occupy both a reproducible position relative to the respective blow mold half and each other. The methods explained below with reference to FIGS. 3 to 5 solve this problem.

In a method illustrated in FIG. 3, a melt stream of thermally plasticized plastic is divided into two partial streams, from which the preforms 1, 1 'are formed. The emerging from the slot dies 2 preforms 1, 1 'are monitored for their synchronization. In the event of deviations in the synchronous behavior, the flow resistance in the flow channels through which the partial flows flow is varied by different temperature control of the flow channels and / or by actuation of a throttle element which acts on one of the partial flows to correct the synchronization. Furthermore, the distribution of the mass flow can be changed by means of an adjustable distributor 33. Finally, a suitable adaptation of a wall thickness program controlling the preform extrusion is considered as a corrective measure, wherein the adaptation of the wall thickness program changes the wall thickness of the preforms into preform sections which form waste slugs during the blow molding. The adaptation of the wall thickness program and / or a change in the In particular, the distribution of the mass flows can be carried out as preliminary, quick-acting corrective measures before the corrections concerning the flow resistance take effect. During the synchronism control, the extrusion speeds of the preforms 1, 1 'emerging simultaneously from the slot dies 2 are detected by means of a measuring device 26. The measurement of the extrusion time is expedient in that at one or more points the time is measured when the preform bottom edge or a mark applied to the preform reaches the measuring point. The measured extrusion times of the two preforms 1, 1 'are compared. If deviations occur, one of the two throttle elements 17 is changed or regulates the heating power acting on the heating element 24.

In the method illustrated in FIG. 4, the preforms 1, 1 'are formed from melt streams which are produced by separate plasticizing units 5 and converted into sheet-like melt webs in separate flow channels. The emerging from the slot dies 2 preforms 1, 1 'are monitored for their synchronization. In case of deviations in the synchronous behavior, the delivery rates of the plasticizing units 5 are adjusted to correct the synchronization.

Another aspect of the invention relates to a possible skew of the preforms 1, 1 ¹ . Since, in the production method according to the invention, preforms 1, 1 'are extruded in pairs and joined to one another over the entire circumference, it is important that the planar preforms 1, 1' are respectively positioned in the blow mold half 10 so that they are free of defects over the circumference Can form connection zones. If, for example, a preform were to go so wrong that it does not overlap when molding the cavity, this would mean that the half shells would not be welded together and scrap would arise. But even with a lesser degree of skew over a non-uniform hose run quality loss are the result. They can affect a default or cause Be sure that the wall thickness distribution in one or both halves of the blow-molded hollow body 4 deviates from default values. In the method shown in FIGS. 3 and 4, therefore, the web run of the emerging from the slot dies preforms 1, 1 'by measuring devices 27, z. B. methods of image capture, photocells, photocells and the like detected. Deviations of the given trajectory are corrected by local changes of the flow resistance in the flow channels of the slot dies. To correct any skewing of the preforms 1, 1 ¹ separately controllable tempering 25 are used, which are arranged in the walls of the flow channels on both sides of the melt stream and also transversely to the flow direction. With these tempering devices 25, different temperatures can be set transversely to the flow direction and / or on both sides of the melt web flowing through the flow channels in order to locally change the flow resistance. When using the extrusion dies shown in FIGS. 6 to 8, the flow resistance transverse to the flow direction can also be effectively changed. To correct an oblique or irregular course of the web, the thickness of the melt web is changed in sections corresponding to an upper waste slug, a lower waste slug or lateral waste slug of the blow-molded hollow body by adjusting the flow channel geometry.

In the method shown in FIG. 5, the preforms 1, 1 ^* after exiting the slot dies 2 are detected by a mechanical device 28 which is moved downwards at a predetermined speed and the preforms 1, 1 'until they are transferred to the blow mold halves 10 leads. By using such a device 28 an exact synchronization of the preforms 1, 1 'is guaranteed. Also, a misalignment of the preforms 1, 1 ', which affects the molding of the preforms in the blow mold halves, no longer occur. Additional control measures, which will be explained below, can be used to ensure that the wall thickness and wall thickness distribution comply with standard values. The device 28 has Areas for supporting the Vorformlingunterkanten and / or clamping elements 29 for detecting the preforms 1, 1 ^* on.

The gap width of the slot dies 2 is changed during the extrusion of the preforms 1, 1 'according to a wall thickness program 8, which proceeds with the preform extrusion. If slot dies 2 are used for the production of the preforms, which have a nozzle element 19 of a plurality of segments 23 arranged side by side in the flow direction (FIG. 8), the segments 23 can be assigned adjusting devices, which are each controlled by a separate wall thickness program 8. It is expedient to use a wall thickness program 8 which subdivides the volume of the plastic melt required for a preform or a preform section into a predetermined number (n) of volume sections and assigns these volume sections control values for setting the nozzle gap. Based on at least one size, the material distribution in the preforms or in the hollow body is compared with a specification. For the purpose of triggering a deviation from the specification caused by viscoelastic effects, correction values 30 are applied to the control values for setting the nozzle gap, which influence the sagging of the preform. The control values form a program curve plotted over the number (n) of volume sections, which is composed of at least one base gap and one profile curve. The base gap or another part of the program curve is expediently adjusted in such a way that the amount of melt remains constant when the correction values are applied.

As measured variables, a large number of variables can be used. Weight measurements are preferably carried out on one or more hollow body sections of the blow-molded hollow bodies. By measuring the net weight and weight of the lower and upper garbage, viscoelastic effects, e.g. B. a changing threshold behavior and deviations are detected with respect to the sag. Another possibility for detecting viscoelastic effects is that the preforms emerging from the slot dies are marked in at least two places and the distance between the marks is measured using measuring means 31. Deviations of the distance from a setpoint at constant net weight are a direct measure of viscoelastic effects. Furthermore, 32 wall thickness measurements can be performed on the preforms or on the blow-molded hollow body with a non-contact measuring device. Deviations from nominal values indicate that the preforms 1, V did not assume the predetermined position when they were transferred to the blow mold halves 10. Another method for detecting disturbance variables is the measurement of the temperature distribution of the preforms or the measurement of the temperature in a defined preform area.

According to a preferred embodiment of the method according to the invention, the extrusion times are measured for both preforms 1, 1 ¹ and compared with default values. Further, during extrusion of the preforms, markings are made on the preforms and the distances of the marks are measured. The net weight of the blow-molded hollow bodies is measured. Taking into account the weight measurements, the control analyzes the deviations of the markings from the default values and outputs the required corrective measures as a manipulated variable.

A blow molding plant can be operated with a variable or constant cycle time. In the first case, the molding process of the preforms is triggered in the blow mold halves when the preforms have reached a certain length, which is detected for example by means of a photocell in the extrusion space. According to a preferred embodiment of the method according to the invention, the extrusion times of the preforms are measured and compared with basic values. If the measured extrusion time deviates from the standard value, corrective measures must be taken. If the blow molding machine is operated with a constant cycle time, the length of the extruder is expediently diert preforms measured under the specification of an extrusion time and compared with a default value. In case of deviations, corrective measures must be taken.

All measured values are compared with setpoints. To correct subsequently produced hollow bodies, the delivery rate of at least one pasting unit, the temperature control in the flow channel, the gap geometry of the slot dies or the gap width of the slot dies can be changed. In addition, an interference signal can be emitted if the deviations of the measured values from the assigned desired value exceed a permissible tolerance range. The interference signals can be used to eject defective hollow bodies from the manufacturing process.

Claims

claims:

1. A process for producing blow-molded hollow body, wherein in the working cycle of a blow molding sheet preforms are produced, which emerge from wide slot dies and connected in the thermoplastic state in the blow molding along a squeeze formed by the closing of a blow mold and are finally formed into a hollow body, characterized that a melt stream of thermo-plasticized plastic is divided into at least two partial streams, from which the preforms are formed, that the preforms emerging from the slot dies are monitored with respect to their synchronization and that in case of deviations in the synchronous behavior to correct the synchronism of the flow resistance in the Partial flows flowed through flow channels by different temperature of the flow channels and / or by actuation of a throttle element which acts on one of the partial flows, is changed.

2. The method according to claim 1, characterized in that the melt stream is formed into a tubular melt flow, which is then divided into the partial streams.

3. The method according to claim 1, characterized in that the emerging as a strand from a plasticizing melt stream is divided into the sub-streams and that the sub-streams are then transformed into separate flow channels to flat melt webs.

4. The method according to claim 1, characterized in that the emerging as a strand of a plasticizing melt stream is formed in a flow channel in a flat melt web, which is then divided into the partial streams.

5. The method according to any one of claims 1 to 4, characterized in that in case of deviations in the tracking behavior for correcting the synchronization, the distribution of the mass flows is changed.

6. A process for producing blow-molded hollow bodies, wherein in the working cycle of a blow molding unit preforms are produced which emerge from slot dies and are connected in the thermoplasticized state of the blow molding plant along a squeezing seam formed by closing a blow mold and are finally formed into a hollow body, characterized in that the preforms are formed from melt streams which are produced by separate plasticizing units and transformed into sheet-like melt paths in separate flow channels, that the preforms emerging from the slot dies are monitored for their synchronism and that in case of deviations in the synchronous behavior, the conveying powers of the plasticizing units for correcting the synchronization - be fitted.

7. The method according to any one of claims 1 to 6, characterized in that the extrusion speeds of the simultaneously emerging from the slot dies preforms are recorded for the purpose of synchronization control.

8. The method according to any one of claims 1 to 7, characterized in that in case of deviations in the tracking behavior for correcting the synchronization a suitable adaptation of the preform extrusion controlling wall thickness program is made, which is changed by adapting the wall thickness program, the wall thickness of the preforms in preform sections which form waste slugs during blow molding.

9. A process for producing blow-molded hollow body, being produced in the working cycle of a blow molding sheet preforms, which emerge from slot dies and formed in the thermoplasticized state in the blow molding along a by closing a blow mold Quetschnaht connected and are finally formed into a hollow body, characterized in that the trajectory of emerging from the slot dies preforms is monitored and that deviations of the trajectory are corrected by local changes in the flow resistance in the flow channels of the preforms forming extrusion dies.

10. The method according to any one of claims 1 to 9, characterized in that the flow channels are equipped with separately controllable tempering and that transversely to the flow direction and / or on both sides of the flow channels flowing through melt webs different temperatures are set to the flow resistance locally to change.

11. The method according to any one of claims 1 to 10, characterized in that the sheet-like melt webs are formed in flow channels whose

Flow channel geometry is changeable transversely to the flow direction, and that to correct a non-standard or non-uniform trajectory, the thickness of the melt paths in sections corresponding to a top waste, a bottom waste or side waste slugs of the blow-molded hollow body is changed by adjusting the flow channel geometry.

12. A method for producing blow-molded hollow body, wherein in the working cycle of a blow molding planar preforms are produced, which emerge from wide slot dies and connected in the thermoplastic form in the blow molding along a squeeze formed by the closing of the blow mold and finally formed into a hollow body, characterized that the preforms, after emerging from the slot dies, are detected by at least one mechanical device, which is moved downwards with a given speed profile.

13. The method according to claim 12, characterized in that the preforms are guided by the device to the transfer in the blow mold halves.

14. The method according to claim 12 or 13, characterized in that for guiding the preforms, a device is used which have surfaces for support in the region of the preform lower edges and / or clamping elements for detecting the preforms.

15. The method according to any one of claims 1 to 14, characterized in that the gap width of the slot dies during the extrusion of the preforms for a wall thickness program, which runs with the preform extrusion, is changed.

16. The method according to claim 15, characterized in that the gap width of each slot die is controlled by one of these slot die associated wall thickness program.

17. The method according to any one of claims 15 or 16, characterized in that for producing the preforms slot dies are used which have a transverse to the flow direction flexible nozzle member or a nozzle element of a plurality of juxtaposed in the flow direction segments, wherein the segments for the purpose of changing the Flow channel geometry are adjustable relative to each other, and that the segments are associated with adjusting devices or the flexible nozzle member are assigned a plurality of actuating devices, which are each controlled by an associated wall thickness program.

18. The method according to any one of claims 1 to 17, characterized in that the sheet-like preforms placed in a defined position relative to the blow mold and then taken directly from the blow mold halves or be fed through the use of grippers and / or carriers the blow mold halves.

19. The method according to claim 18, characterized in that the position of the preforms detected by measurement and any positional deviations of the preforms are determined by a desired value and that the trajectories of the gripper or carrier to correct these positional deviations are changed.

20. The method according to claim 18 or 19, characterized in that two carriers are used, which simultaneously supply the sheet preforms to the blow mold halves.

21. The method according to claim 18 or 19, characterized in that only one carrier is used, which feeds the preforms in succession to the blow mold halves.

22. The method according to any one of claims 1 to 21, characterized in that the sheet-like preforms are introduced under vacuum and / or with Blasluftunterstüt- tion in the blow mold of the blow molding machine.

23. The method according to any one of claims 1 to 22, characterized in that are positioned before closing the blow mold inserts between the sheet preforms.

24. The method according to any one of claims 1 to 23, characterized in that the pairs introduced into the blow mold or mutually associated preforms differ in material terms and / or in terms of their material distribution and / or thickness or are colored differently.