DE2308284A1 - PROCESS FOR THE CONTINUOUS PROCESSING OF PLASTICS OR ELASTOMERS - Google Patents

Description

FRIED. KRUPP GESELLSCHAFT LIMITED LIABILITY in Essen

Process for the continuous processing of plastics or elastomers

The invention relates to a method for continuous Processing of plastics or elastomers e.g. in an extruder. The method is intended in particular when processing crosslinkable substances are used.

When processing rubber and plastics, for example As a rule, the following four functional stages have to be passed through during extrusion:

"Feed"

"Collect"

"Processing"

"Support financially",

then "Shapes" afterwards.

With conventional extruders the functions are:

"Collect"

"Prepare" and

"Support financially"

combined in one zone. In modern extruders a separation of functions is carried out in such a way that the processing of the material takes place in a zone, and behind this - seen in the direction of material flow - comes the zone, in which the material is measured and conveyed into the tool. This last zone * A * d usually "metering zone"

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called. The problems with this sequence of functions are that the high amount associated with the preparation of the material Temperature is already present before the material enters the measuring and conveying zone. This is especially so then disadvantageous if the processed material is temperature-sensitive, e.g. cross-linked polyethylene or sulphurized rubber compounds. All of these materials play a role the temperature dwell time plays an important role, which reduces the remaining vulcanization time. As a rule, it should be in the Processing machine must be kept as short as possible} because the temperature dwell time in the processing machine reduces the processing reserves that arise during molding and vulcanizing are available. Another disadvantage of this functional sequence is the dependence of the temperature of the material when it enters the mold the speed of the machine, the consistency of the feeding, the toughness of the incoming material and the cooling system. All of these factors influence each other} in particular, however, the metering function is also influenced by it.

In the known methods of the type mentioned, it is difficult to prepare the substances to be used uniformly and uniformly over their entire cross-section. When extruding crosslinkable materials, it is extremely important, these substances at a certain point near the exit side of the extruder on certain Bringing temperatures and keeping them exactly at this temperature for a certain period of time. Here comes it is essential that these conditions are achieved at all points of the fabric cross-section.

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The invention is now based on the object of showing a method in which the requirements mentioned can be fully met with the help of simple, essentially mechanical, measures.

The teaching according to the invention which solves this problem consists primarily in the fact that in the processing of the plastics or elastomers within, for example, extruders, have mechanical forces acting on them, their size while the process is running, regardless of a specified flow rate of the substances to be treated can be varied. These forces, the size of which can be varied, are caused by the relative movement of parts which creates the walls surrounding the substances to be treated. The relative movement comes from rotation and / or Oscillation of the wall parts comprising the substances to be treated. The change in the magnitude of the mechanical forces takes place by a corresponding change in the relative speed between the substances to be treated Wall parts. However, there is also the possibility of reducing the mechanical forces by changing the space to change between the relatively moving wall parts. According to the invention it is intended that the The mechanical forces acting on the substances to be treated represent at least a considerable part of the forces required to process them Supply the required thermal energy. In particular, it is possible to use all of the thermal energy to be expended to be generated by the mechanical forces acting on the substances to be treated.

The teaching according to the invention is based on what is described below known physical circumstance. A

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elastic or plastic material that sticks between surfaces that are set in motion relative to each other will try to compensate for this relative motion by frictional forces inside the material between the walls. Shear forces. With a homogeneous material and uniform wall adhesion, the frictional energy is generated simultaneously and evenly at all points of the material to be treated as a result of the shear forces that arise. The intensity of the energy generation depends only on the size of the relative movement of the moving walls and the viscous properties of the material to be treated. The shear forces acting inside the material to be treated convert a large part of the mechanical energy used into thermal energy. This treatment zone, in which you work with short dwell times and high Sbherenergie, is intended as a so-called. Intensive shear zone . When preparing the substances to be treated in the extruder, this has the great advantage that the heat energy is always evenly distributed within the substance to be treated. When the substance to be treated is heated, this favorable heat distribution cannot be achieved, since the heat only reaches the outer surfaces of the substance to be treated locally and can only be distributed over the entire cross section from there. In this way, especially in the case of poorly thermally conductive materials such as plastics, overheating on those surfaces to which heat is transferred from outside can never be completely avoided. When processing crosslinkable substances, however, this fact has an extremely disadvantageous effect. Because just at

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In the recently developed extrusion processes, efforts are being made to place the beginning of the crosslinking phase in the forming zone of the extruder in terms of location and time in the case of crosslinking substances. However, care must be taken to ensure that the crosslinkable substance is in the forming zone leaves in a state, especially on the surface, in which the actual crosslinking has not yet started, i.e. in a deformation zone only the so-called. Start-up phase of the crosslinking reaction can be set. A prerequisite for such a procedure, however, is that exact compliance with the temperatures and dwell times of the substance to be treated is possible within the extruder or the downstream molding tool. This is the case with the method according to the invention. Through the Achieving diner even temperature distribution over the entire cross-section of the substance to be treated can In particular, premature crosslinking of the substance on its outer surface, as is usually the case with decays that work with external heating, can be avoided. According to the method according to the invention, it is even possible to cool the layers of the material to be processed which adjoin the walls. A premature networking on the surface of the substances emerging from the extruder has the consequence that the surfaces during the molding process experiences permanent damage such as scoring.

In the method according to the invention, the energies required for processing are applied independently of the amount of substances conveyed in the extruder. The mechanical forces that can be varied according to the invention for processing therefore do not have to actively participate in the conveyance of the substances to be treated in the extruder. To carry out the

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The method according to the invention are therefore advantageous Extruders are used, which have separate areas for conveying and processing the material to be treated exhibit. The feeding of the extruder and the metering of the substances to be introduced also take place in the conveying area. The preparation area according to the invention downstream of the conveyor area is located in the exit area of the extruder or it can also be moved into the mold. In both cases, however, he practically provides the last function of the manufacturing process before the deformation. With a view to the fact that the preparation is independent depends on the delivery rate that can be achieved in the extruder, large amounts of energy can be used with short dwell times can be transferred to the substances to be treated. There is a further advantage of the method according to the invention in that the preparation area has no influence on the metering of the substance to be treated. In this way the preparation area can be controlled independently of all other functions, i.e. the temperature can be very high set exactly to the desired setpoint and maintained over a certain period of time. Through the Conversion of mechanical energy into thermal energy through frictional forces (intensive shear) within the area to be treated Substance can be an exact temporal and spatial fixation of the temperature rise, especially when the temperature is reached critical temperature for the crosslinking reaction can be reached.

In the case of crosslinkable substances, there is on the one hand a close relationship between the temperature level and the temperature residence time and the rate of reaction initiated thereby on the other hand. A higher temperature can get through a shorter dwell time can be compensated. At fixed

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geometric relationships of an extruder, the dwell time is inversely proportional to the throughput. The temperature control independent of the throughput by converting mechanical energy into thermal energy internal friction can therefore be used to optimize the process determined by the reaction kinetics can be used. With the help of the energy generated by internal friction in the substances to be treated also by changing the kinetic energy of the internal frictional forces moving parts an instantaneous adjustment of the energy supply to changes in the throughput, such as when starting up the extruder. In this respect, the method according to the invention is also more dynamic View extremely good properties.

The fact that in the method according to the invention no Heat must be brought from outside to the substance to be treated by heat transfer, has with crosslinkable substances the great advantage that the risk of crosslinking within the extruder can be kept very low. This is further promoted by the fact that in the temperature-critical area of the extruder, in particular in the downstream Mold, the material to be treated is cooled can be. Furthermore, a process management is also possible in which the outer surface of the extruder or its Downstream molding tool already formed leaving substance on a compared to the inner fabric parts bring lower temperature. Compared to the other pieces of fabric on the outer ura trap, this is low Temperature has the great advantage that the part to be molded does not damage its outer surface during the molding process

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because there has been no crosslinking because of the relatively low temperature.

The uniform heating of the substance to be treated according to the invention over its entire cross-section provides also sure that not with regard to the poor thermal conductivity properties, especially of plastics and Elastomers, excess heat energy must be supplied to keep all parts safe to a certain minimum temperature to be able to bring.

Compliance with certain temperatures and dwell times is particularly important when processing crosslinkable substances important. With the method according to the invention it is possible to determine the magnitude of the mechanical forces that affect the frictional energy inside the substances to be treated in the extruder generate, depending on the temperature of the substances to be treated at the exit of the extruder or one downstream of it To regulate the molding tool. In this way, the temperature at said point can be on a predetermined Setpoint are maintained. This control option is particularly valuable for an exact control of the crosslinking reaction in the shaping phase.

Those causing the internal friction in the fabrics to be treated mechanical forces can also be dependent on the flow rate passing through the extruder be managed.

An advantageous preparation consists, for example, in the fact that the parts leave the extruder or the molding tool as finished parts With the exception of their surface, substances are already

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are essentially networked. Xn expediently can the process can also be designed in such a way that the substances to be treated are already inside the extruder or of this downstream molding tool are essentially networked and there still from one to another Place generated mass flow of uncrosslinked or non-crosslinkable substances are encased and in this form emerge as a finished part.

The preparation according to the invention can be carried out, for example, in a device that consists of a shaft and a the shaft consists of a distance coaxially surrounding the jacket. The fabric to be treated is between the wave and the mantle. The mechanical forces acting on and within the substance to be treated are generated by the fact that the shaft and shell move relative to each other. This can be done, for example, by that the jacket is stationary and the shaft rotates or vice versa, in that the shaft is stationary and the shaft surrounding coat turns. It goes without saying that the shaft and the jacket can each be separated, however, relative to one another move. Wave and jacket also need only relative Execute mutually directed rotary movements, but they can also oscillate relative to each other in the longitudinal direction move towards each other. Of course, the rotational movements exerted relative to one another can also be oscillating take place.

In a particularly expedient embodiment of the invention The shaft and jacket, between which the preparation of the substance to be treated takes place, are each conical. With this configuration, it is possible to run

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Process operation also vary the volume of the space available for processing. The one for them The space available for preparation can also be changed in size by adding the treatment room Slide can be introduced from the outside.

The type of preparation according to the invention is of course not limited to use in extruder processes limited. The process can also be used to pelletize plastic liquids, for example or to granulate. In addition, the process can also be used to preheat plastic masses, in particular elastomers, can be used. Furthermore, substances prepared according to the invention can also be a conveying element, for example a Screw extruder, are supplied, this conveyor element being the one required for loading a molding tool Pressure builds up and thus takes over the promotion of the processed material into the molding tool.

Devices for carrying out the method according to the invention are shown in the drawing, namely show:

1 shows an extruder with a screw conveyor in the conveying area and a roller connected in the axial direction of the screw conveyor in the processing section,

Fig. 2 shows the temperature versus time in the extruder Fig. 1,

3 shows an extruder with a conically designed processing space,

Fig. 4a, b each have an extruder with mutually perpendicular

-10 -

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net processing and conveying area, Fig. 5 an extruder for cable sheathing,

6 shows an extruder in which the material to be treated is conveyed through a standing mandrel into the preparation area,

7a and b preparation areas of an extruder which can be varied in terms of volume.

8a, b devices for carrying out the method according to claim 21.

The extruder shown in Fig. 1 is composed of a conventional screw extruder 1 for feeding and metering the substances to be treated and a subsequent processing part 2 for processing these substances. This processing part is composed of a cylindrical shaft 3 and a jacket k which surrounds this shaft coaxially at some distance. The preparation of the substances according to the invention takes place in the annular space between the shaft 3 and the jacket k. From the preparation part, the substances for shaping pass through the opening 5 to a shaping tool (not shown). The screw extruder 1 used for conveying can, since no preparation has to take place in it, be significantly shorter than in the cases in which the preparation must also take place there at the same time. FIG. 2 schematically shows the temperature-time curve in an extruder constructed according to FIG. 1. The figure shows the individual areas of the temperature profile: conveying, processing, shaping and cooling

- 11 -

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-IX-

specified after the shaping. Like the curve
clearly shows, the temperature in the conveying area rises only very gradually, then increases suddenly within a relatively very short period of time
the preparation area and then assumes a constant value in the shaping area in order to then gradually decrease in the cooling area. The schematic representation of the temperature profile clearly shows that in the preparation part, the crosslinking of the
substances to be treated or those for the start-up reaction
the networking, the required temperature can be precisely fixed in terms of location and time. The steep rise in temperature in the preparation area is caused by a rapid rotary movement of the shaft 3i, which can be set independently of the volume flow to be conveyed.

3 shows an extruder in which, in the processing part 6, a conically shaped shaft 7 rotates in a casing 8 which conically surrounds this shaft. The shaft 7 can be moved in the axial direction, whereby the volume of the processing space can be changed. The shafts 3 and 7 can in addition to their rotating movement at the same time
perform an oscillating movement in the axial direction. The oscillation frequency should be selected so high that no noticeable pulsations occur when the material is applied.

In the extruder according to FIG. K , the substances to be treated are conveyed in a screw extruder 9 arranged perpendicular to the direction of extrusion. The processing takes place essentially in an annular space between a rotating shaft 10 and a concentrically surrounding the shaft

- 12 -

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Jacket 11. The shown extruder is to be used to extrude tubes will. The shaft 10 also serves as a mandrel for the hose.

Fig. 5 shows only the preparation part of an extruder. The substances to be treated are brought up to a standing mandrel 13 through the opening 12. This mandrel 13 is surrounded by a rotating jacket 14. The materials are processed in the annular space between the mandrel 13 and the jacket Ik. The extruder shown in Fig. 5 is intended to sheath cable material. Such cables 15 are guided through the mandrel 13 into the preparation section of the extruder. In this embodiment, the molding tool is practically part of the extruder.

In the embodiment according to FIG. 6, the to be treated arrives Substance from a screw conveyor l6 through the interior of a fixed dome 17 into a conically narrowing one circular processing room 18. The outer wall this preparation space forms a rotating jacket 19 · This extruder shape is for the production of Suitable for smart profiles.

7a and 7b show processing rooms 20 and 21, the volume of which can be changed by slide 22 and 23, respectively.

Claims :

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Claims (1)

P a tentana claims; 1. Process for the continuous processing of plastics or elastomers, especially those which can be crosslinked, characterized in that during processing of the substances mentioned, mechanical forces act on them, the magnitude of which during the ongoing process operation is independent of a given quantity substances to be treated can be varied. 2. The method according to claim 1, characterized in that it takes place in extrusion devices. 3. The method according to claim 1 or 2, characterized in that the acting on the substances to be treated variable Forces are generated by relative movements of parts of the walls surrounding the substances to be treated. 4. The method according to claim 3i, characterized in that the relative movement takes place by rotation and / or oscillation of the wall parts comprising the substances to be treated. 5. The method according to any one of the preceding claims, characterized in that the size of the mechanical forces by Change in the relative speed between the wall parts comprising the substances to be treated can be changed. 6. The method according to any one of claims 1 to k, characterized in that the mechanical forces by a change - Ik - 409836/0488 of the space between the wall parts moving relative to one another are changeable. 7. The method according to any one of the preceding claims, characterized in that- on the to be treated Substances acting mechanical forces at least a considerable part of the necessary for the processing of these substances Deliver thermal energy. 8. The method according to claim 7, characterized in that the mechanical forces acting on the substances to be treated cover the entire TeD. supply the thermal energy required to process these substances. 9 · Method according to one of the preceding claims, characterized characterized in that the size of the variable mechanical forces as a function of the temperature of the substances to be treated automatically at the exit of the extruder or a downstream molding tool is regulated. 10. The method according to claim 9i, characterized in that the The size of the variable forces is also regulated as a function of the flow rate passing through the extruder will. 11. The method according to claim 9 or 10, characterized in that the size of the effective variable mechanical forces depends at least on the temperature of the substances to be treated in a molding tool downstream of the extruder is and is regulated in such a way that in the case of the substances leaving the molding tool as finished parts, at least the - 15 - 409836 / UA88 The start of the reaction start-up phase, which initiates crosslinking, is already reached at a point in time when the substances have not yet left the forming tool. 12 · Method according to claim 9 or 10, characterized in that the size of the effective variable mechanical Forces at least from the temperature of the substances to be treated in a molding tool downstream of the extruder is dependent and is regulated in such a way that the substances leaving the molding tool as a finished part with the exception their surface are already essentially networked. 13. The method according to claim 9 or 10, characterized in that the size of the variable forces is regulated in such a way that the substances to be treated are already essentially crosslinked in a molding tool downstream of the extruder pass through and there uramantel from a mass flow of uncrosslinked or uncrosslinkable substances generated elsewhere will. 14. Device for performing one of the methods according to the preceding claims, characterized in that the wall parts, which comprise the substances to be treated and move relative to one another, come together of a shaft and a casing coaxially surrounding the shaft at a distance. 15. Device according to claim 14, characterized in that the shaft and cylinder jacket are cylindrical. l6. Device according to claim 14, characterized in that the shaft and cylinder are conical. - 16 - A09836 / UA88 17 · Device according to claim lA, characterized in that the shaft and / or the casing surrounding the shaft rotating and / or oscillating in the axial direction of movement or movements · _o performs or perform. l8. Device for carrying out the method according to Claim 6, characterized in that slides projecting adjustably into the treatment room are provided in order to change the volume of the preparation space for the substances to be treated. 19 · Method according to one of the preceding claims, characterized in that the frequency of the driven part a device used to carry out the process is significantly higher than the usual extruder speeds, so that the use of support gears, especially in the case of multi-stage with electric motor drive, not applicable. 20. The method according to any one of the preceding claims, especially for processing, e.g. pelletizing, granulating, characterized in that the part of the plant used for processing is taken from one of the preceding claims described zones of intense shear exists. 21. The method according to any one of the preceding claims, for processing plastic masses, especially for the extrusion part in the production of profiles, hollow bodies and injection molding unwinding according to claim 20, characterized in that the material from the zone of intense shear (2, 2k) in a conveyor element, For example, the extruder (25) opens - FIGS. 8a and 8b - which builds up the pressure required for loading the molding tool and thus takes over the conveyance of the material into the molding tool. - 17 - Blank page