DE2329754A1 - FEEDER SCREW FOR EXTRUSION MACHINES AND THE LIKE - Google Patents

Description

KR Matthews & Company (Worcester) Limited Hallow, Near Worcester / England

Conveyor nook for extrusion machines and the like.

The invention relates to a screw conveyor for extrusion machines and the like for conveying plastic material that is to be melted by heat while conveying, which is fed through an interface within a heating zone extending in the axial direction, the The screw conveyor has a Sennecken or screw thread that essentially sealing inside halo exner .bore egg machine lies and delimits a substantially spiral conveyor trough.

With conventional strand molding machines for plastics this will be solid raw material, usually in the form of granules or powder, through a funnel into a housing or Tube supplied in which a rotating screw conveyor is housed is that feeds the material to a spray head or a discharge opening, the plastic material during of the conveying process is melted by in a regulated

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Catfish is supplied with heat through the housing or pipe.

With regard to the construction of the screw conveyors, the greatest value is generally placed on obtaining a good degree of efficiency, in that the plastic material is conveyed by the screw at a maximum speed on the one hand and complete melting of the same takes place on the other hand. In practice , however, considerable problems arise in attaining this aim, the particular difficulties encountered depending on the nature of the plastic material used.

Thus, the processing ability of the different plastics varies considerably, depending both on the chemical composition and the physical state of the raw material, the conditions in which the raw material melts, are extremely critical. For example, although some materials such as polyethylene are easily meltable and very flowable, and can withstand considerable temperatures above their melting range, other materials such as polyvinyl chloride, and in particular so-called hard PVC, can only be melted and treated within a very narrow temperature range, since at too Complete melting does not occur at a lower temperature, while decomposition begins at a temperature that is too high.

When using extrusion or conveyor screws in In extrusion molding machines, the heating of the raw material and the temperature control take place mainly in the area of an interface, usually the inner surface of the screw receiving housing or tube. The melting process also preferably takes place in a boundary layer, a particular problem being effective mixing of the molten and unmelted material fractions as the raw material passes through the heating zone. If such a mixing does not take place, it occurs

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high temperature gradients in the partially melted material with the risk of either decomposition causing overheating takes place or the material is only imperfectly melted. Either way, it is an effective one Mixing and achieving a high degree of homogeneity of the material during the melting process are essential Prerequisite for a good result, i.e. a good level of efficiency.

There are various modifications to a simple, catchy, continuous helical or worm thread shape for such Screw conveyors have been proposed in order to obtain better efficiency, taking into account the above requirements. However, the proposed designs have not proven to be satisfactory to the extent desired, namely due to an undesirably high back pressure or counter pressure and a harmful, in particular locally limited high compression of the cloth material so that the need of improved screw conveyor designs has persisted.

The invention is based on the object of designing an extrusion or screw conveyor so that with minimal stress of the material a good mixing of molten and unmelted material parts and thus a complete Melting of the starting material is guaranteed.

To solve this problem is for an extrusion or screw conveyor a helix shape and a Proposed conveyor trough shape, which in certain cases even up to a complete reversal to a significant extent ongoing redistribution or redeployment of the relative position of melted and unmelted material layers or partially cause molten material, which is conveyed by the screw through the heating zone.

Such a redistribution or redeployment and reversal

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can arise from molten material of the boundary layer or boundary layers is preferably conveyed or moved forward through the conveyor trough before a Forward movement or conveyance of the remaining unmelted material over the previously conveyed molten material connects away. Such a conveying process is carried out according to the invention by changing the conveying channel width in Connection with a change in the depth of the conveyor trough is achieved in at least one intermediate section of the conveyor screw, these width and depth changes being present relative to the rear and front sections of the conveyor chute,

According to the invention, the screw or worm thread and the conveyor trough bounded by it are shaped such that from the Total mass of partially melted plastic material, which moves through the conveyor chute in the area of the heating zone, with melted and unmelted material move through the conveyor chute with different average speeds, the molten ones being preferred first Material portions and then preferably the unmelted material portions are moved forward or conveyed. Through this there is at least a temporary substantial redistribution or redeployment or even reversal of the overlapping layers of the respective melted and unmelted material proportions with regard to their relative position within the Caused conveyor trough, whereby an intimate mixing and the complete melting of the material is guaranteed.

The extrusion or conveyor screw according to the invention is characterized in that the width of the conveyor trough in the area at least one axially extending intermediate section of the screw length located in the heating zone Progressive changes in the pitch angle of the screw thread in the area of the intermediate section in the conveying direction first increases to a maximum value and then decreases again, and that the conveyor trough section of changing width

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has adjacent, relative to one another front and rear conveyor chute parts, of which the rear conveyor chute part has a core diameter that progressively increases to the outer diameter of the associated screw thread section, such that a substantial redistribution or redeployment of the melted and unmelted material portions of a partially melted plastic mass is caused, which is promoted in the area of the heating zone through the conveyor trough or is moved forward.

According to a further invention it is provided that the core diameter of the front conveyor chute part progressively from a value corresponding to the outer diameter of the associated screw thread section decreases to a value which in the substantially corresponds to the initial minimum core diameter of the rear conveyor chute part, so that molten Material proportions from the boundary layer or the boundary layers of the partially melted plastic compound are preferred are first moved in the axial direction in the conveyor trough section of the intermediate section, before then a preferred Movement of the remaining not yet melted material portions in the axial direction over the previously preferred promoted molten material portions takes place, so that an intimate mixing and complete melting of the whole Material is facilitated.

In the screw conveyor according to the invention, the screw or Screw thread with at least one screw thread turn provided, which has a larger pitch angle and replaces a section of the normal screw thread, the one has a smaller pitch and a uniform pitch angle. The front and rear conveyor chute parts are according to the invention separated from one another by a step running transversely to the conveyor chute section, which essentially follows a helix with a constant pitch angle parallel to the above-mentioned helical sections. These Level leads to height and depth differences between each other

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adjacent conveyor trough parts.

According to the invention, the screw conveyor has a spiral-shaped screw or screw flight which extends continuously over the entire length of the screw conveyor over three successive sections, namely an inner or rear inlet section, an intermediate section forming the melting zone and an outer or front outlet section. This screw or worm thread delimits a continuous helical conveyor trough, the width of which is determined by the successive turns of the screw thread. The helical thread comprises turns which have a uniform pitch angle and lie in the inlet section and in the outlet section, and at least one turn with a larger pitch angle in the area of the intermediate section. The conveyor trough located in the area of the intermediate section thus has a width that gradually increases up to a maximum value and then decreases again, with a step running transversely to the conveyor trough in the areas of increasing and decreasing width, which forms a dividing line between the different depths that adjoin one another Forms front and rear conveyor trough parts, the depths of which progressively increase in the conveying direction over the length of the conveyor trough and then decrease again, causing the above-described shifting or redistribution of melted and not yet melted material components in the area of the intermediate section .

The invention is described in more detail below with reference to the exemplary embodiment shown in the drawing. Show it:

Fig. 1 is a side view of a normal extrusion machine equipped with the extrusion or screw conveyor according to the invention is provided, with some parts of the machine housing broken away;

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Fig. 2 shows, on an enlarged scale, a side view of the invention Auger;

3 is a sectional view showing the progressive change in diameter of a rear section of the screw conveyor trough between points A1 and A2 in FIG. 2;

4 is a sectional view showing the progressive change in diameter of a front section the screw conveyor chute between points B1 and B2 in Fig. 2;

Fig. 5 is a partial sectional view according to the line V-V in Fig. 2, and

6 shows, in an enlarged illustration, a sectional view along the line VI-VI in FIG. 2.

The extrusion molding machine 10 shown in Fig. 1 for thermoplastic materials is with the exception of the subject of the present invention forming extrusion or conveyor screw 11 of conventional design.

The screw conveyor 11 is rotatably mounted in a cylindrical housing 12 which is provided with heating elements 13 (for example electrical heating elements not shown in detail) is provided. The heating elements allow the temperature in the individual areas that follow one another over the length of the housing. At the front end of the Housing 12 can be attached to a conventional spray head 14 of the shape desired in each case; in the area of the rear end of the housing is a filling opening with a hopper 15 attached to solid thermoplastic raw material in powder or To feed the machine in granulate form or in another form,

The screw conveyor 11 is with the interposition of a suitable Reduction gear with gear box 16 driven by an electric motor in the lower part of the machine housing is housed. The machine can be equipped with various additional units such as adjustable cooling devices

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for the cylindrical tube and the screw.

The Extrusion ™ or screw conveyor 11, the core of which can be either full or pierced to one or more axial To form channels for cooling or heating medium is with a single helical worm gear or. Screw thread 20, the cross-sectional profile of which is shown in FIG. The screw or worm thread profile has a uniform one Outer diameter of such a size that this profile with a minimal working clearance of the inner surface of the tube 12 opposite to produce a sealing effect. Of the The helical thread 20 delimits a helical conveyor chute 22 between its adjacent turns,

The screw conveyor is both in the area of its inner or rear inlet section X and in the area of its outer or front output section Y of conventional design, and the sections 20a and 20c of the screw thread 20 have in the area of these sections X and Y a uniform slope and a uniform angle of inclination, which is described below is referred to as the base pitch angle. Sections 22a and 22c of the helical conveyor chute 22 have a constant width in the area of these sections X and Y, respectively. The inner or rear entrance section X, which lies below the inlet opening of the hopper 15 and extends to the coupling end 18 of the screw, has in the shown embodiment has a uniform core diameter in accordance with common practice. Of the outer or front output section Y, which is located in the area of the discharge end 19 of the screw and in operation on the In the manner shown, the extrusion head 14 has a core diameter that increases continuously in the conveying direction.

Between the input section X and the output section Y is the intermediate section Z, in which the screw profile is designed in the manner according to the invention. Of the

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Section Z lies within or extends through a heating zone of the tube 12 of the extrusion molding machine. Of the Intermediate section Z has a length which corresponds to the space of four turns or threads with the base pitch angle is occupied, i.e. the length of the intermediate zone Z corresponds to the length of four full turns of a Helical thread shape as it is realized in sections X and Y. is.

If you follow the screw thread along the conveyor chute 22 in the conveying direction from the inner entrance section X to the center of the Following intermediate section Z, the effective total width of the conveyor trough begins in the axial direction from that through the point A1 on the helical center line of this conveyor chute 22 to become progressively larger at a certain point, as a result of the change in the pitch angle of the screw thread section 20b beginning at point B2, which is shown in FIG the intermediate section Z lies. Point B2 is on the front side of the conveyor chute area described. At the same time, the core diameter increases along an intermediate section in a region that is an imaginary continuation of the original conveyor chute section 22a corresponds to a constant width, this continuation now being a represents the rear part t_ of the section 22b of the widening conveyor trough lying in the intermediate section Z, continuously so that the depth of this rear part of the conveyor trough, based on the outer diameter of the screw threads decreases.

In contrast to this, the front conveyor chute part 11 begins the width of which increases progressively, at point B2 of the outer surface of the screw passage 20 with a minimum width and a core diameter equal to the outer diameter of the turns. After that, the core diameter of the front increases Conveyor chute part 1 progressively so that the depth of this conveyor chute part along the spiral path increases.

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As can be seen from Fig. 6, the depth of the conveyor trough section 22b changes in this area over the entire axial extent, although the cross-sectional area of the trough formed thereby essentially maintains its size, the above-mentioned rear and front conveyor trough parts t and .1 are separated from one another by a step S which forms a dividing line which delimits the different depths or height levels of these parts t and 1_ and which follows a helical line which is essentially a continuation of the screw thread section 20a of the rear input section X.

In the middle of the intermediate section Z, namely at point M, which is reached by following the conveyor trough starting at point A1 by an angle of 360 °, the rear conveyor trough part _t and the front conveyor trough part I _{1 have} risen to a common level or fallen off, so that these two conveyor trough parts have the same depth at this point M and the step S disappears. At point M, the total axial width of the conveyor trough has also increased to slightly more than twice the initial value in accordance with the line A2-B2 in FIG. 2.

Behind the middle of the intermediate section Z, the total axial width of the conveyor track section 22b begins to decrease progressively towards the output section Y due to the change in the pitch angle of the screw thread beginning at point A2; From point A2 on, the pitch angle towards the end 19 has the same size as the pitch angle of the entrance section X. The core diameter of the rear conveyor chute part t begins, however, to become progressively larger, while the core diameter of the front conveyor chute part 1 progressively decreases, the dividing line between the rear conveyor chute Conveyor chute part t and the front ^{conveyor chute part 1 is} formed by a step S 1, which also delimits the various height and depth levels from one another.

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The step S 'follows a helical line which is essentially a rearward continuation of the helical line
of the screw thread portion 20c of the outer output portion Y represents. The starting point of stage S ¹ is
offset slightly forward relative to the line determined by step S by a distance equal to the width of the
Screw thread corresponds.

In this area of the intermediate section Z, ie behind the point M, the width of the front conveyor chute part 1 of the conveyor chute remains constant. At the point determined by point B1, the core diameter is the same again
Value decreased as at point A1, but with the
Width of the rear conveyor trough part t progressively decreases and reaches a minimum at point A2, at which the core diameter has increased to the outer diameter of the screw thread turns, so that the rear conveyor trough part t essentially merges into the outer surface of the screw thread.

In this way, a complete profile reversal between the rear conveyor chute part t and the front conveyor chute part 1 of the conveyor chute section 22b of the conveyor chute in
Area of the intermediate zone Z took place; as far as the
Concerning screw thread, two full turns are the
The base forming the screw thread form by a single full
The turn of a screw thread replaces the double
Has the pitch of the screw thread forming the base.

Such a configuration leads in practice to an improved mode of operation of the screw conveyor, such as the
the following theory can be used as a basis.

When operating the extrusion machine that is through the
Funnel 1! ^^ guided, solid, granular or powdery plastic raw material conveyed forward by the rotating screw conveyor in the housing or pipe 12. When reaching the intermediate section Z, this material is through the

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Regulated heating of the pipe (and also by frictional action) partially melted so that there is a mixture of melted and unmelted material. The unmelted material has the tendency in the area of the bottom of the To remain the conveyor trough while the molten material lies mainly in an overlying boundary layer, namely adjacent to the inner surface of the pipe through which the main amount of heat is supplied.

After entering the intermediate portion Z the already molten material layer preferably has the tendency to spread into the front conveyor chute portion 1 of the conveyor trough in, since the width of the front conveyor trough part I ₁ increases, with the unmelted material gradually on the leading ramp surface of the rear conveyor trough part t nearer is brought to the heated tube inner surface, so that the melting process is continued. It must be taken into account that, due to the increasing overall width of the conveyor trough, the decreasing depth of the rear conveyor trough part t is compensated, so that there is no substantial creature with regard to the volumetric cross-section of the conveyor trough, so that the plastic material in this area is not significantly compressed, which may result forward-looking promotion could be hindered.

The remaining, unmelted material is gradually conveyed to the front conveyor chute part 1, the conveyor chute, in particular after passing the center point M of the intermediate section Z, with it on the already conveyed there molten material is deposited so that the not yet melted material is still closer to the heated one inner boundary layer of the tube 12 lies, as the majority of the already melted material. The melting process will consequently continued and largely relieved, so that at the time when the material is the front end of the Intermediate section Z is reached, a complete melting of the material can be expected without higher temperatures

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ture gradients have arisen in the material mass, and without that an additional compression reducing the conveying speed has taken place.

The process that takes place in the intermediate section Z can largely be regarded as turning, reversing or rearranging the Mixture of melted and unmelted layers of material which are present in the entrance section X after the initial partial melting. There no substantial reduction in the cross-sectional area formed by the conveyor chute section 22b in the intermediate section Z. Channel is present, and because the plastic material is not pressed through small gaps along the length of the screw must be, the process of turning or shifting the mixture without increasing the pressure and without high localized Shear forces take place, which generate high internal friction and reduce output, as is the case with many previously existing screw conveyors. It should be pointed out that there is no physical separation of the mixture of molten and unmelted material, since the Mixing always remains within the limits of the changing total total width of the channel that runs through the only one Conveyor trough is formed.

When the conditions for the treatment of certain, especially difficult-to-process plastic raw materials are such that the passage of the material through a single section corresponding to the intermediate section Z. is not sufficient to achieve complete melting, the screw conveyors with two or more consecutive Be provided sections which correspond to the described intermediate section Z, so that the material along the screw conveyor is turned over or rearranged more than once.

The invention also relates to further modifications within the scope of the invention, for example the

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Transfer the thread course to multi-thread screws can be.

Although the above-described shape of the intermediate section Z represents a preferred solution, it can be assumed that the essential characteristics are the progressive successive widening and narrowing of the conveyor trough in connection with the progressive decrease in the depth of the rear conveyor chute part over the entire length of the Intermediate section or the progressive increase in the depth of the front conveyor trough part over the front half of the intermediate section Z are. In a further modified embodiment of the invention, if desired, the front conveyor trough part of the conveyor trough over the rear half of a finished intermediate section the same level and have the same decreasing depth as the rear conveyor chute part, so that with increasing width it is up to the center of the intermediate section becomes progressively flatter before it is then, as already described, at a constant width becomes progressively deeper.

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Claims (4)

7329754 Claims 1J screw conveyor for extrusion machines and the like for conveying of plastic material that passes through while conveying Heat is to be melted within an axially extending heating zone by a Interface is fed, wherein the screw conveyor has a screw or screw flight, which is substantially lies in a sealed manner within a bore of the machine and delimits an essentially spiral-shaped conveyor trough, characterized in that the width of the conveyor trough (22) in the region of at least one is in operation in the heating zone located, axially extending intermediate section (Z) of the screw length by changing the pitch angle of the screw thread (20a, 20b, 20c) in the area of the intermediate section (Z) progressively first in the conveying direction increases up to a maximum value and then decreases again, and that the conveyor trough section (22b) changes Width adjoining, relative to each other front and rear conveyor chute parts (t, 1), of which the rear conveyor chute part (t) has a core diameter which progressively up to the outer diameter of the associated Screw thread section (20b) increases, while the core diameter of the following front conveyor chute part (1) progressively from a value corresponding to the outer diameter of the associated screw thread section (20b) decreases to a value which is substantially the initial minimum core diameter of the rear conveyor chute part (t) corresponds in such a way that molten material fractions from the boundary layer or the boundary layers of the partially melted plastic mass, which in the intermediate section (Z) and in the area of the heating zone through the conveyor trough is conveyed, preferably first moved in the axial direction in the conveyor trough section (22b) before then a preferred movement of the rest 309881/0899 7329754 non-melted material portions in the axial direction over the previously preferably conveyed melted Material proportions take place so that complete melting and thorough mixing of the entire material is facilitated will. 2. A screw conveyor according to claim 1, characterized in that the rear conveyor trough part (t) over the length of the conveyor trough section (22b) forms a continuously increasing ramp surface, the width of which decreases progressively behind the point (M) corresponding to the maximum value of the width of the conveyor trough, that the front conveyor chute part (1) forms a continuously sloping ramp surface, the width of which increases progressively up to the point (M), and that the front and rear conveyor chute parts (1, t) through a step (S, S) running transversely to the conveyor chute section (22b) ¹ ) are separated from each other, which essentially follows a helical line with a constant pitch angle parallel to the screw thread sections (20a, 20c) which delimit opposite side edges of the conveyor chute section (22b) which extends through the associated section of the conveyor screw « 3. A screw conveyor according to claim 2, characterized in that the screw thread (20b) in the region of the intermediate section (Z) comprises only a single screw turn, the axial length of which is equal to an integral multiple of the axial length of a single screw turn of the screw threads (20a) which have a uniform pitch angle , 20c) of the rear input section (X) or of the front output portion (Y) of the screw, and in that the step (S, S ¹⁾ in the region of the intermediate section (Z) is substantially of the helix of an imaginary continuation of the screw threads (20a, 20c) follows. 309881/0899 4. Conveyor screw according to one of claims 1 to 3t thereby characterized in that the cross-sectional area of the conveyor chute section (22b) at least in the area of the intermediate section (Z) is essentially constant. 309881/089 *