DE2429203A1 - Extrusion of elastomers - with automatic regulation of feed by sensors - Google Patents

Abstract

In the continuous extrusion of elastomers, e.g. silicone rubber, into tubes, profiles, cable coverings etc, the material passes from a limited-capacity container and then for a free distance before being extruded, this distance being at least equal to the product of the extrusion process speed and the time for periodical replacement of the container with fresh material.

Description

Password: Prefeeder method and apparatus for continuous Extrusion of elastomeric compositions The invention relates first of all to a method for the continuous extrusion of elastomeric materials such as silicone rubber, to continuous hoses, profile strips, cable sheaths or the like.

Elastomeric compounds, such as silicone rubber, cannot be easily removed in the form of granules to the processing tray, because the particles are added tend to stick to each other and thereby a smooth further movement itself hinder. The supply of the silicone rubber in the form of prepared strands must done carefully so as not only to use the processing machine with the correct volume per unit of time to load, but above all to the draft-sensitive pieces of material as possible can be handled without tensile stress. Also a compression of the material in the Feeding is to be avoided because of the accumulation of excess material. Hence was it has hitherto been necessary to carry out the feeding of these masses to the extrusion process manually and to control what caused high operating costs.

The invention is initially based on the object of providing a method of To develop the type mentioned at the beginning, that a trouble-free automatic extrusion such masses guaranteed.

The inventive method proposes to this mass behind their storage, which has a limited capacity, but move a section of the way as a free strand before their processing extrusion, this path length being at least equal to the product of the extrusion-related Processing speed of the strand and the time for periodic replenishment the stocking with new mass.

Due to the free guidance within the section of the route, there is an impairment of the material by pulling or pressure is avoided. By measuring this path length it is easily possible to periodically add new filling masses to the To give stock while the continuous extrusion continues to run smoothly.

During the replenishment of the #orratung the end of the previous one runs Strand over the free path according to the processing speed of the Strand continues continuously and the beginning of a new strand can be forehead-shaped mutual contact against the previous end of the strand, so that still within This length of the path creates a coherent strand at this transition point. For the processing extrusion there is always a continuous, constant, warp-free strand available.

The regulation of this process can run automatically, with a It is possible to make the cross-sectional thickness of the strand adjustable. In terms of the process, it is easier to determine the exit speed of the strand the supply depending on the extent of a bulging of the strand in the course to make his free path adjustable. If the transport of the strand is too great, in this way, in the area of the free path, a strand length is created that is greater than this path length is formed, which is why the strand bulges. The extent of this bulge can now be used as a control variable for the exit speed of the strand can be used. This regulation of the exit speed as a function the curvature of the strand can be positive or negative. Would the curvature of the bulge too big, so leave the exit speed the strand from the supply become smaller; conversely, the bulge becomes fall below a lower value, i.e. a stretching of the strand over a certain amount Enter the extent, the exit speed of the strand is increased again. This allows the bulge to be scanned and controlled accordingly the exit speed a problem-free, simple automation of the process achieve. Without cumbersome changes, this control can be used for a wide Use a range of different extrusion processes, in which different Material breakup takes place.

With the method according to the invention it is easily possible to capture all of these cases. When exceeding a maximum curvature of the bulge In the line, for safety reasons, the Occurring exit of the strand from the supply, which even in extreme cases Difficulties are avoided.

However, the invention is also directed to a device for implementation of the method, wherein a storage device for receiving a supply of any kind of elastomeric mass is provided. The output of this storage device is connected to the inlet of a downstream, uniformly operating extruder.

The device according to the invention is characterized in that between the output of the memory and the input of the extruder one of guide surfaces for the elastomeric mass is arranged in a gap that is kept free. The gap length allows a change in the storage tank filling, even before the previous end of the strand in the Extruder arrives.

The device can be designed in a wide variety of ways, each of which has its own particular advantages.

In the simplest case, the storage device becomes a simple one Use wraps where the elastomeric compound has already been applied in the form of a strand is and is now only fed to the extruder with an adapted take-off speed must become. However, it is more cost-effective to use a vacuum-loaded storage device as the storage device To use pressure cylinders with pressure pistons, the diameter of which is sufficiently large, to pick up a rolled-up sheet of material. Sufficient for simple control it is necessary to regulate the cross-sectional thickness of the strand in the gap area accordingly. This can be done through a fixed, one-time adjustability of the cross-sectional thickness on the Exit of the strand from its storage device happen. To an even more precise one It is also possible to control it continuously by means of control elements that act like a diaphragm the cross-sectional thickness of the strand in adaptation to the respective volume requirements to change.

Instead of this regulation, however, it would also be possible in the gap area the device to arrange a sensing element, which on a lateral deviation of the elastomeric masses from the line connecting the accumulator outlet and responds to the extruder inlet.

This sensing element is connected to an actuator which is based on the Acts drive the accumulator emptying. The masses are expediently scanned on a strand into which these masses are formed within the storage device will. The sensory link responds to a bulging of the cord. So that the control is simplified and the bulge is targeted in one direction, recommends the strand has the lowest section modulus in this desired direction to arrange its strand cross-section. It is sufficient for this to have a single-sided strand or elliptical profile.

A wide variety of components can be used as the sensing element, such as mechanical ones and optical sensors. The feeler speaks to the boundary edge of the cord and gives the above-mentioned actuator a control pulse corresponding to occurring bending of the strand in the gap area. As an optical one A light barrier consisting of a light transmitter and light receiver is suitable for the sensing element. Depending on the shadowing, such an optical sensing element can switch on and off the cylinder-piston device on the accumulator side.

But it would also be possible to have a number of adjacent to provide optical sensing elements, which in an individual way the drive speed control for the exit of the strand from the storage device. It can thus a number of sensing members may be provided.

In order to take into account a deflection of the strand in every direction, it is recommended that the feeler element or the feeler elements surround the cord on more than one side allow. In the mechanical case, it is sufficient to use the feeler element as a scanning fork to train. Instead of a fork, a ring-shaped body could also be useful, the strand is passed through its opening.

For further automatic operation, it is recommended to use the device to provide with a signal element, which with a minimum supply amount in Memory takes effect. If the signal element responds, either automatically, from a feeder, or by hand, i.e. semi-automatically, a new supply quantity be introduced into the storage device.

For exact handling it is important to be in the upper area of the Gap to provide a cutting mechanism on the device, which is used to cut off the strand is useful and automatic when there is a minimal supply in the memory is triggered. This creates a smooth end on the strand, making it a good one form-fitting connection for the beginning of the following strand with the new one Stock mass is given. This is the trouble-free continuous operation the device also guaranteed in this regard.

In the drawing, the invention is in several exemplary embodiments shown. 1 shows a longitudinal sectional view through a schematic Representation of a first embodiment of the invention, FIG. 2 is a sectional view Transverse view through the device of FIG. 1 along the cutting line shown there II-II.

3, 4 and 5 different working stages of the device compared to one another Fig. 1 modified embodiment, Fig. 6 is a side view through a last embodiment the device.

In the first embodiment of FIGS. 1 and 2, the device comprises an extruder 10 and a storage device 20.

The extruder 10 comprises an inlet 11 for feeding in the silicone rubber masses in the form of a strand. Inside a housing 12 in the extruder is the in the sectional view of FIG. 1 recognizable screw 13, which in the masses its front end towards / into the shaping space 14 recognizable from FIG. 2. In this space 14 is from one side, through an opening in the present case a copper wire 15 continuously fed through inside this space not shown in detail, known per se shaping channels with the extruded mass is surrounded, so that on the other side of a mold opening 17 is a semi-finished electrical cable in the form of a cable core made of copper wire 15 and an insulating one Serving 16 comes out. The subsequent heat zones for vulcanization the masses are not shown in detail.

The masses enter the entrance 11 of the extruder 10 in the form of a Strand 30. The shaping of these masses takes place here in the storage device 20th

This storage device 20 comprises a printing cylinder 21, which is shown in its interior receives the masses 31 to be treated and in which for expulsion the masses from the cylinder space a 'vertically movable pressure piston 22 moves. An air discharge line 23 is connected to the pressure cylinder and leads to a pump 24 performs, which generates a suction in the cylinder 21 with a motor 25 by which unwanted air inclusions are continuously removed from the mass 31 form. The pressure piston 22 is driven by the one shown in the upper region of FIG. 1 Drive 26.

The drive 26 for emptying the memory 20 includes a the piston rod 27 connected working piston 28, which is in an associated working cylinder 29 can be controlled hydraulically. The control device and the pressure medium source are arranged in the schematically indicated control unit 40, from which the working cylinder 29 at both ends via a line 41, 42 with the pressure medium is supplied. The direction and the extent of the flow rate of the pressure medium is determined by the control unit 40. The mode of operation of the control device 40 can be preprogrammed be. In addition, limit switches and sensing elements are provided, which the each required mode of operation of the control device 40 regulating and controlling.

This includes first of all an end position control of the drive 26.

For this purpose, the working piston 28 is provided with a control rod 43 extended, which engages longitudinally displaceably in a control tube 44. In this Control tube 44 are at a distance that corresponds to the desired end position of the pressure piston 22 in the storage device 20 in the upper and lower reversal point corresponds to two Limit sensor 45, 46 provided. Reached the end of the control rod 43 where the relevant tax stamp is provided, the lower limit sensor 46, the control unit 40 interrupts the further supply of pressure medium through the upper line 41 into the working cylinder 29. The pressure piston 22 thus remains in the lower position, as follows will be explained in more detail in FIG. 3. At the same time, when the limit sensor responds 46 triggered a certain control program in device 40, which, as shown later in Fig. 4 will be explained, a cutting unit 32 via a control line indicated in FIG. 1 33 can be effective and at the same time the pressure piston 22 from the pressure cylinder 21 leads out. The cutter 32 includes a blade 34 which the strand 30 on Output 47 of storage device 20 cuts off.

In the aforementioned on driving movement of the plunger 22 arrives the end of the control rod 43 carrying the mark into the area of the upper limit sensor 45, where the upward movement of the pressure piston 22 is ended. In this position the pressure piston 22 is held until a new piece of storage material 35, as explained in FIG. 4, has entered the printing cylinder 21, whereupon only the further operation of the control device 40 either automatically or by manual triggering goes on. The on driving movement and the downward movement of the plunger 22 to to touch the strand ends 54, 56 is expediently carried out in rapid traverse.

There is a gap between the storage device 20 and the extruder 10 18 arranged, through which the strand 30 runs freely for a distance. As long as the exit speed 36 of the strand 30 from the memory 20 is the same indicated processing speed 37 of this strand 30 in the extruder 10, the shape of the guided strand 30 in the aforementioned gap 18 remains unchanged. The output 47 in the memory profiles the cross section of the strand 30 in a certain way Way. The shape of the exit 47 can be made adjustable. In the present case, as shown in FIG. 2, the strand is elliptical Cross-section, as a result of which in the arrow direction 38 indicated in FIG. 2 the least Moment of resistance of the strand 30 is present and at any excess length of the Strand 30 in the region of the gap in this direction can be seen from FIG. 1 Bulging of the strand 30 takes place, the deviation of which from that in FIG. 1 is shown in dashed lines indicated. extended connecting line 19 can serve as a measure of how strong the exit speed 36 depends on the processing speed of the strand 30 differs. For this purpose, in the gap area 18, expediently in the middle, where the greatest deviation ~ 39 is noticeable, a feeler 48 is arranged, which in the present case mechanically causes the bulging of the strand 30 scans. For this purpose, as shown in FIG. 2, one with its prongs serves the strand 30 on both sides surrounding fork 49, which with normal agreement between exit speed 36 and processing speed 37 allows the strand 30 to pass through unhindered and thereby expediently already a slight bulge in the gap area 18 allows.

If the exit speed 36 is too great, the curvature decreases the bulge 39 to, whereby the fork 49 because of the entering contact easily is taken and triggers a control pulse in the sensing element 48, which is transmitted via the control line 50 a compensating pulse in the above-mentioned control unit 40 for the drive 26 of the memory 20 delivers. This increases the exit speed of the strand throttled from the memory 20, so that the deflection of the strand is reduced. A regulation of the exit speed in the opposite sense results when the exit speed 36 is less than the processing speed 37 becomes, which is caused by an excessive stretching of the strand 30 in the gap area 18 affects. The fork 49 also provides this Position fixed and granted from the sensing element 48 a compensating control pulse via the control line 50 the Control unit 40, which accelerates the drive 26 again somewhat, whereby the exit speed 36 is regulated up to the optimal value. It would be easier, however, instead this continuous control to use an on-off circuit for control purposes.

This ensures that the device works automatically, which is steered by the control unit 40 with the aid of the above-mentioned Limit sensors 45, 46 on the one hand, which are connected to the control unit 40 via a line 51 are and via the aforementioned sensing member 48 on the other hand, which has a connection via has the control line 50 on the device 40 and finally also the cutting unit 42 comprises, which has the control line 33 as a connecting element. The one to be overmolded Wire is in Fig. 1 in its course to the extruder 10 dash-dotted line 52 indicated.

In the embodiment of the device according to FIGS. 3 to 5 there are sensing elements omitted and in different working positions the importance and size of the Gap 18 clarified in more detail. To designate the same components, however, are the the same reference numerals are used as in the previous exemplary embodiment, which is why insofar as the previous description is valid.

In the working position of FIG. 3, the supply amount has 31 in the memory 20 has reached its minimum value, which is why, as already mentioned, the cutting unit 32 cuts off the strand at the output 47 of the store 20 via its blade 34. Thereupon the pressure piston 22 occurs, as illustrated in the next working position of FIG is in its extended position, creating space for a new piece to be introduced Storage mass 35 is possible, as indicated by the schematic introduction arrow 53 in Fig. 4 can be seen.

The smooth end 54 of the strand 30 moves with the Processing speed 37 indicated in FIG. 4 in the free path segment 18 Further.

In the last working position according to FIG. 5, the drive is again of the memory 20 has become effective and the pressure piston 22 to squeeze out the new one The cutting unit 32 has long been in its rest position, whereby a new strand section 30 'is created, which initially with a higher Initial speed 55, as indicated in FIG. 5, is expelled until its smooth front 56 with the aforementioned front end 54 of the preceding strand 30 touched. From this point on, the further movement of the new strand 30 ' again adapted to the processing speed 37 in the extruder 10. The size of the Gap 18, plus a safety piece, is dimensioned so large that during the duration of the refilling of the memory 20 with new storage masses 35 and the faster extension 55 of the new strand beginning 30 ', the front end 54 is not yet has entered the extruder 10. The contact 54, 56 of the two strands 30, Rather, 30 ′ still takes place in the region of the gap 18, as a result of which, from the extruder 10 from the point of view of a continuous, form-wise constant strand is supplied will.

In the exemplary embodiment in FIG. 6, identical components are used for naming the same reference numerals are used as in the previous embodiments. Here is the memory 20 in the form of a roll 60, where the silicone rubber masses to be processed are wound in strand form. The coil 60 rests on a shaft 59. The strand 30 is withdrawn from the roll 60 via a pair of take-off rollers 57, 58, of which the a roller 58 is connected to a controllable drive 26. Also here is between the take-off rollers 57, 58 on the one hand and the extruder 10 on the other hand a gap 18 of sufficient length is provided, wherein the strand 30 is already related with the bulge explained in the first exemplary embodiment experiences the deviation thereof 39 of the dash-dotted straight connecting line is a measure for represents the regulation of the drive 26. In the present case, it serves as a feeler an optical device responsive to shadowing by strand 30. In the present In the case of this, a number of photocells 61 are provided which, depending on which is shaded by them, in a certain way via the control line 62 one that increases or decreases the exit speed of the strand from the reservoir 20. convey a lowering control pulse to the drive 26. Assume that the photocell 61 'which becomes visible in the bulge of the strand 30 of FIG. 6 the one that, in the event of blackout, is the normal drive speed the take-off rollers 57, 58 adjusts. Should be caused by minor discrepancies Finally, between the exit and processing speed of the strand 30 result in a bulge which, according to FIG. 6, shadows the neighboring photocell 61 '' while the previous photocell 61 'is uncovered, so becomes at these shading conditions triggered a control pulse in the sensing element 48, the causes a slower withdrawal, which again the strand 30 for shading the the first-mentioned photocell 61 'comes. Eventually the bulge becomes due to inconsistencies so large that the outermost photocell is activated, the drive 26 can thereby be stopped completely. Conversely, if a thinner photocell controls it experiences, the withdrawal speed of the strand 30 is increased again. It understands that the last-mentioned version of course auckboit a cutting knife can be provided and that this embodiment also in the sense of the in Fig. 3 to 5 explained device can be effective.

These measures are analogous to the stipulated statements to be transferred to the latter. If, for example, in the execution 6, the end of the roll 60 has passed through the rollers 57, 58, a control pulse can be emitted by the limit switch via the line 63 activates a signal element 64 which indicates the emptying of the cylinder. The signal member 64 can also act as a trigger member for the actuation of a automatic feeder that puts a new roll on the Pull-off shaft 59 touches down. Here, the pair of rollers 57, 58 takes over the function of a monitoring element.

However, this function could also be taken over by the sensing device 48 which, after the end of the roll has passed, all photocells 61 releases and thus triggers the described mode of operation. Should be within the sufficient, available distance 18 the exchange of the stock do not proceed satisfactorily or some other defect occurs that affects the strand 30 interrupts, it is easily possible with the means described, finally also to stop the extruder 10 and thus the processing operation as a makeshift completely, because a standstill of the working method is more favorable in many cases than producing defective goods.

Claims (13)

Password: Prefeeder Claims: ~ 1. experienced in the continuous extrusion of elastomers Masses, such as silicone rubber, for continuous hoses, profile strips, cable sheaths or the like., d u r c h ge k e n nz e i c h n e t that the crowd is behind its one limited storage capacity, but before their processing-extrusion, a stretch of path is moved long as a free strand, this path length at least is equal to the product of the extrusion-related processing speed of the line and the time to periodically replenish the supply with new ones Dimensions. 2. The method according to claim 1, characterized in that the exit speed of the strand from the supply depending on the extent of a bulging of the Strand can be regulated in the course of its free path. 3. The method according to claim 2, characterized in that when exceeded a maximum curvature of its bulge, the exit of the strand from the supply is stopped. 4. Device for performing the method according to one or more of claims 1 to 3, comprising a storage device for receiving a supply amount of elastomeric masses, e.g. a vacuum-pressurized pressure cylinder with pressure piston, its output connected to the input of a downstream, uniformly operating extruder is, d u r ch e k e n n -z e i c h n e t, that between the output of the memory and the inlet of the extruder one kept free of guide surfaces for the elastomeric mass Gap is arranged. 5. Apparatus according to claim 4, characterized in that in the gap area a sensing member is arranged, which on a lateral deviation of the elastomer Masses from the connecting line between the storage outlet and the extruder inlet responds, wherein the sensing element with one on the drive of the storage emptying acting actuator is connected. 6.Vorrichtung according to claim 4 or 5, characterized in that the elastomeric masses in strand form leave the store and enter the gap area arrive, the cross-sectional thickness of the strand being adjustable. 7. ' Device according to claim 6, characterized in that the profile of the strand has a lower section modulus in one direction than in all others Has directions of the strand cross-section. 8. Apparatus according to claim 7, characterized in that the strand has a rectangular or elliptical profile. 9. Device according to one or more of claims 4-8, characterized characterized in that the sensing element responds to the boundary edge of the strand. lO.Vorrichtung according to claim 9, characterized in that the sensing element surrounds the strand on several sides. 11. The device according to claim 10, characterized in that the Feeler element consists of a fork that mechanically scans the strand and which is connected to a electrical control and switching device is connected. 12. The device according to one or more of claims 4-11, characterized characterized in that the memory is provided with a signal element which at responds to a minimum supply in the memory. 13.Vorrichtung according to one or more of claims 4-12, through this characterized in that in the upper region of the gap a cutter for separating the Strand is arranged, which can be triggered with a minimal supply in the memory is.