DE2241111C2 - Double or multi-screw press for processing powdery plasticizable compounds - Google Patents

Description

a) the lower opening of the hopper (5) in the direction of the screw axes is at least equal to or greater than the pitch (b) of the screws (2, 3) and is at least equal to the width (c) of the intermeshing screws when leased across the screw axis (2,3),

b) the filling funnel (5) is shaped so that at the transition point (6) of the funnel wall into the cylindrical wall of the screw housing (1) the tangent (T) to the screw housing (1) is at least perpendicular (7 b in Fig. 5 ) or is inclined outwards (7c in Fig. 6, Td in Fig. 7).

2. Double or multi-screw press according to claim 1, characterized in that the opening of the hopper (5) in the direction of the screw axes is at least equal to 1.5 times the pitch (b) of the screws (2,3)

3. Double or multi-screw press according to claim 1 or 2, characterized in that the lower opening of the hopper (5) is at least approximately rectangular

The invention relates to an improvement in a twin or multi-screw press for processing of powdery plasticizable masses, the mutually engaging screws of which are in the opposite direction Sense of rotation are rotatable, the screws at the point of engagement in the area of the opening of the hopper in the direction of the hopper.

Twin screw presses are often used because they are larger compared to single screw presses Ability to convey amounts of material and the material in the twin screw press is better worked through and is plasticized than in a single screw press. But it has long been known that the double or Multi-screw presses have the disadvantage that the degree of filling, d. H. the ratio of the absorbed per revolution The amount of powder to the delivery volume is unsatisfactory and is only about 33%. To this difficulty is pointed out, among other things, in DE-AS 10 07 499, column 1, lines 6 to 9. Despite many attempts at improvement however, a degree of filling of 100% has not yet been achieved. In the aforementioned In DE-AS 10 07 499, a filling funnel was used, the lower opening of which is larger in the axial direction is than corresponds to the pitch of the screw. But since the two screws rotate in the same direction and the Width of the opening of the hopper is smaller than that Width of the intermeshing screws, a high degree of filling was not achieved, especially since the funnel through a storage rib is subdivided. In particular, the two augers are filled unevenly in this device the screw, which moves with its upper side towards the other screw, can hardly pick up material, so that even with a good filling level of this other screw a total filling level of 50% can hardly be achieved is

Attempts have been made to increase the degree of filling by adding screw feeders or similar in the filling funnel Conveyor devices were provided. Apart from the fact that an additional, energy-consuming Device is required, no higher degree of filling than about 50% was achieved in this way, too 100% horizontal filling level, d. H. an incomplete filling the screw not only has the disadvantage that the output of the plasticizing unit, which is an extrusion press, Extruder or for feeding plastic injection molding equipment is used, correspondingly reduced there are other disadvantages.

Due to the incomplete filling of the screw, air is also taken up in the unfilled spaces must be extracted in addition to the air contained in the bulk material and the resulting gases. By the incomplete filling resulting cavities result in pulsations, as well as increased zones Friction and affect the mixing effect and thus the homogenization of the material, which as a result only relatively late is fully plasticized, which again has the consequence that, since the promotion of Powder requires more energy than the conveyance of the plasticized material, an increased expenditure of energy is required and there is increased axial pressure in the screw bearings. Incomplete filling but has the further disadvantageous consequence that, since the material, following the rotation of the screws, in the Gathered in the middle under the screws, in this way a one-sided radial pressure is exerted on the screws is, so that the screws are also subjected to bending stress and increased wear and a There is increased radial pressure in the screw shaft bearings, and the material in the lower part moves faster is conveyed than in the upper part, which means that the output is uneven and, under certain circumstances, the mass comes to a standstill at the top, so that temperatures that are too high may occur locally, resulting in decomposition of the material and when processing polyvinyl chloride leads to the formation of hydrochloric acid, which again has a corrosive effect

The invention is based on the problem of creating a screw press which, when it is constantly filled Working funnel without additional device, the shortcomings occurring in the known screw presses According to the invention, this problem is avoided by the characteristics specified in claim 1 solved. A particularly good effect is achieved by adding what is described in claims 2 and 3 specified further characteristics.

Extrusion presses are known in which the length of the lower opening of the filling funnel is in the axial direction is greater than the pitch of the screw (DE-PS 9 38 441 and DE-AS 10 38 268). It is about however, it is about single-screw presses, in which the effect according to the invention cannot be achieved anyway, especially since According to these proposals, the width of the opening of the filling funnel is significantly smaller than the width of the

Slug.

A screw extruder with several intermeshed screw shafts, in which the opening of the filling funnel is slightly longer in the axial direction than the pitch of the screw, is known (DE-AS 15 54 751). In this screw extruder, however, the Material to be conveyed is provided with a perforated disc with narrow passage openings. In this known screw extruder Therefore, a 100% filling level must not be aimed for, because otherwise on the perforated disc too high a back pressure would occur. To avoid material jams and the resulting Excessive pressures must always be a metering device for input of the material in such extrusion presses be used. This known screw press also does not have those specified in claim 1 further characteristics.

It is also known in single screw presses to use a hopper which is shaped so that on the The transition point of the funnel wall into the cylindrical wall of the screw housing is the tangent to the The screw housing is at least vertical or inclined outwards (DE-OS 20 03 078 and DE-PS 9 38 441). The effect sought after according to the invention is not achieved in any case with single-screw presses and is not aimed for there either

In none of the known double or multi-screw presses is a 100% filling level achieved and none of these known presses has those specified in claim 1 or in the subclaims License plate on. The length of the lower opening of the filling funnel required to achieve this effect in the direction of the screw axes depends on the pourability of the material introduced. With very good Free-flowing material can already have a good effect if the funnel is only a little longer than corresponds to the pitch, while in the case of poorly free-flowing material a length of 1.5 times to 2 1/2 times the pitch and more can be beneficial.

The lower opening of the filling funnel can be as with the known arrangements can be round or oval. The proposed, approximately rectangular shape has the advantage of that the condition on the shape of the lower opening of the hopper is not just in the middle, but is fulfilled over the entire length and width

Because the subject of the invention achieves a degree of filling of 100% or approximately 100%, the delivery rate is increased, which in itself would have to result in an increased expenditure of mechanical energy to drive the screws. However, it has been found that the increase in energy consumption does not increase proportionally to the output quantity after a relatively short time there are no more nests with powdery material, and the energy expenditure for shearing is much lower, so that the material is mainly heated by heating and only to a very small extent by shearing. The result is that materials with very different shear strengths can be processed in the same press without changing the screw. The even filling also eliminates the radial stresses on the screws, so that the radial pressure in the bearings is also reduced. The rapid and thorough mixing of the material and the good heat transfer mean that no excessive temperatures and local overheating occur and enable the press to be heated up at the beginning of the screw so that the material is heated quickly and evenly
The twin or multi-screw press according to the invention is particularly suitable for processing powdery, plasticizable compounds, but under comparable conditions it is also suitable for other purposes, e.g. B. for processing other pulverulent masses or granulates.

The figures show schematically exemplary embodiments of the subject matter of the invention.

F i g. Fig. 1 shows a twin screw press seen from above;
FIG. 2 shows the same exemplary embodiment as FIG. 1 in longitudinal section along the line H-II in F i g. 1;

3 shows the same embodiment as FIG. 1 in cross section along the line IH-III in F i g. 1;

the F i g. 4 to 7 show in cross section the influence of the shape of the funnel on the degree of filling.

The in the F i g. 1 to 3 shown double screw press contains in the housing 1 the two mutually engaged single or multi-start screws 2 and 3, which, like the arrows 4 in F i g. 3 show, rotate in opposite directions so that they move at the point of engagement in the direction of the hopper 5, that is, upwards. The length a of the lower opening of the hopper is greater and, as shown, about twice as long as the pitch b of the worm thread. The width of the lower opening of the funnel 5 is, in particular, as shown in FIG. 3 shows, greater than the width c of the intermeshing screws, the side walls of the funnel being shaped so that at the transition point 6, where the wall of the funnel 5 merges into the cylindrical wall of the screw housing 1, the tangent 7 is inclined outward.

The effect of the width and shape of the funnel in cross section is illustrated in FIGS. 4 to 7 explained in more detail The arrows 11 indicate the pressure in the funnel Powder mass.

F i g. 4 shows a shape of the funnel in which the tangent 7a at the transition point of the funnel wall in FIG the housing wall is inclined inwards rather than outwards. The width of the funnel is smaller than the width of the intermeshing screws 2, 3, the powder mass mainly presses on the center of the Snails. The result is that the hatched part of the worm thread that is not or is poorly filled, is relatively large, because the powder is indeed carried away by the snails to the outside will, but not be sufficient to fill the entire lower space of the worm thread.

5 shows an embodiment in which the filling funnel is just as wide as the interlocking screws, the straight funnel walls merging into the cylindrical wall of the housing at the point of greatest width of the screw, ie here the tangent Tb coincides with the vertical funnel wall together. The spaces 8 that are not or poorly filled, shown hatched, are significantly smaller than in the case of the funnel shape shown in FIG. 4.

In the embodiment according to FIG. 6, the funnel is shaped so that the transition point 6 from the housing wall in the funnel below the largest

Width of the screw is, the tangent Tc at the transition point 6 is inclined outward. Here one can no longer speak of a lower opening of the funnel in the strict sense. The width of the lower opening of the funnel within the meaning of the invention is in this case the width of the funnel in the cutting plane 9 formed by the axes of rotation of the screws, that is to say the width d in FIG. 6, which is greater than the width c of the intermeshing screws. The insufficiently filled space 8 is opposite to the funnel shape according to FIG. 5 still significantly reduced.

The advantage of the shape according to FIG. 6, as in FIG. 7, achieved in an even better manner if the funnel walls are curved so that they merge from the direction of the tangent Td into the vertical. As a result, the powder is pressed by its pressure - arrow 11 - into the pockets between the funnel and the screws, which are completely filled.

In the F i g. 4 to 7 the filling of the funnel is shown in order to influence the width and shape of the To explain side walls of the funnel. Characterized in that, according to the characteristics of the invention, the length of the The funnel opening in the direction of the screw axes is greater than the thread pitch, the screw will be at filled with the first rotation, the material compacted and refilled with the following rotation, and thereby a degree of filling of practically approx. 100% is achieved. The hopper 5 is to be charged so that at least the snails are always fully covered, expediently the funnel is completely filled, d. H. it is neither a dosing device that limits the amount of powder fed, nor a plug screw that the the amount of powder fed into the screw conveyor is required.

To achieve an approx. 100% filling of the snails and to maintain it in the long run, care must be taken that the funnel wall and the adjoining it Section of the screw housing and the screws are smooth. About sticking the powder material The funnel walls and the adjoining sections are to be avoided at these points of the screw housing appropriately cooled so that it does not reach a temperature at which the Powder begins to soften, can heat up, which would result in powder grains sticking to the walls, and it is useful, especially for processing poorly free-flowing material, the Hopper walls and the housing and the screw under the hopper by appropriate surface treatment, z. B. by chrome plating to smooth.

Increasing the degree of filling from approx. 35% to 100%, with the hopper always full, would lead to an overload of the machine if only the hopper shape is changed in accordance with the invention on a known machine. Experiments have shown, however, that the drive energy does not increase proportionally to the output, but would correspond less than the proportional increase. The much higher degree of filling of the screws, however, gives the possibility of reducing the feed volume, i.e. the total volume available between the screws and the housing wall, by reducing the flight depth and the flight height of the screw conveyors, and still achieve an increased material output or the effort with the same material output to reduce mechanical energy and to make the machine simpler and cheaper and to increase its service life. The reinforcement of the core diameter, which is identical to the reduction in the flight depth, strengthens the screws and, if necessary, allows an increase in the driving force, while on the other hand, the uniform filling and rapid plasticization of the material largely avoid radial forces acting on the screws, which in turn leads to wear is decreased. The complete filling also has the consequence that the compression takes place uniformly from the beginning of the screws to their end. No blockages occur and should not be caused by perforated disks or the like. The compacted material emerges evenly without pulsations.

Thanks to the reduction in the heating caused by the shear and kneading forces, the mass warms up in the main thing is through the external heat input, which is very effective as the material is everywhere on the housing wall or rests against the screw. This external heat supply can thereby be achieved in a manner known per se be designed evenly that in the screw holes 10 are provided through which a liquid, for example oil, which is kept at a certain temperature, is passed, so that on the one hand the The screw is heated, but on the other hand the occurrence of excess temperatures is prevented because the oil at the same time acts as a coolant when temperatures above the oil temperature occur the housing 1 in a manner known per se electrically or also through a, through holes not shown directed liquid can be heated.

The length and width of the lower opening of the filling funnel is understood to mean its total length or width, no matter whether it is divided by ribs or spaces or not

1 sheet of drawings

Claims (1)

Patent claims: 1. Double or multi-screw press for processing powdery plasticizable compounds, whose mutually engaging screws can be rotated in the opposite direction of rotation, wherein the worms at the point of engagement in the area of the opening of the filling funnel in the direction of To move the hopper is characterized by the combination of the following, e.g. T. better known per se Characteristics: