EP0048952A1 - Method of mixing asphalt-aggregate compositions in drum mixers, as well as an apparatus for carrying out the method - Google Patents

Abstract

The prior art discloses drum mixer developments which virtually uniformly strive for the criterion of a cross-sectionally uniform distribution of the aggregates/asphalt mixture in discharge cascades, sliding off lifting paddles, over the drum cross-section. It is shown that a uniform distribution of the mixture over the drum cross-section is not possible and that the formation of discharge cascades severely impairs the aim generally sought with drum mixing of achieving a low-dust preparation by partial distribution of the material in discharge cascades. As a result, a method is proposed which permits the preparation of asphalt-aggregate compositions in a drum mixer while avoiding any notable dust formation and providing optimum thermal efficiency. The solution provides that, during its passage, the material be raised in a constantly repetitive manner along the inner wall of the rising drum until the frictional forces are overcome by the force of gravity, and guided back again to the bottom of the drum. The material travels as a circulating mass through the drum, which mass describes a segment of a circle deformed at the edges in its cross-section, and absorbs radiant heat across its surface and convected heat via the drum wall. An improvement in the mixing intensity and the heat absorption is achieved, with constant drum diameter, by enlarging the heat-transferring inner surface, in conjunction with a positive material guide, which is slidingly inclined to the bottom of the drum and is preferably sill-shaped, and at the same time the mixing intensity is promoted. This guide is preferably supported by mixing tools (2/3) of wedge-shaped design inclined relative to the rising drum (1), these tools being assigned radial rods (4) as required. <IMAGE>

Description

The invention relates to a process for the preparation of a bituminous mixture in drum mixers, in particular for road construction, in which the aggregates, which are not yet pre-dried by drying devices and removed from the mineral landfill, are generally surface-dry to moist, via intermediate storage of a heated drum mixer arranged inclined in the outlet direction abandoned, in or before this, mixed with bituminous binder at low temperature and the good parts are then - with strong heat supply by heating gases - heated and mixed further and the mix is continuously discharged, the heating gases, after they emerge from the drum, in are generally discharged from fine particles and pollutants separated from the goods as well as devices for their exercise.

Systems of this type are known, reference being made in this connection to US Pat. No. 3,832,201 and DE-OS 2 606 422.

In LUEGER, Gesamtlexikon der Technik, roro edition 1972, volume 37, page 511, it is stated that the installations in drying drums have the purpose of mixing the material and distributing it evenly over the drum cross-section in small portions, the material at Use of lifting blades, sometimes trickles back onto the subsequent internals when the drum is turned.

According to the classification given there, a distinction is made between lifting vane internals, simplex internals, cross internals and quadrant internals. Here, of the internals, which become more complex in the order of their enumeration, for the group of "coarse-grained or pulpy materials" - into which the aggregates to be processed or the mix to be processed are classified - lifting blades, i.e. the simplest form of installation, primarily suitable. The selected cross section of the lifting blades, e.g. semicircular troughs, isosceles or isosceles, radially directed 90 ° angle profiles or equally directed, but having a larger angle than 90 °, may vary from case to case.

U-profiles that are radially directed with one of their flanges on the inner periphery with their web are often used.

However, all lifting vane internals of this type basically have the same discharge characteristics.

On the basis of the slope angle that is constant for each bulk material and on the basis of a constant peripheral speed, only the maximum filling volume between two subsequent installations and the shape of these installations can have a slight influence on the density of the discharge cascade that is formed.

However, the finding made in the cited reference that the material is distributed evenly over the drum cross-section in small quantities must be disputed. It is not possible to distribute the bulk material evenly over the drum cross-section with lifting vane components. This is just one of all drum designers working in this sector that has always been a desire.

In this context, an in-depth examination of the state-of-the-art statement cannot be avoided. Here the question is in particular what proportion of the drum filling, i.e. of the mixed material to be prepared, directed, mixed, heated and conveyed against the drum wall, and which parts of the material are distributed over the drum cross section or a part of this cross section and fall back to the part moving on the drum wall.

The investigation is based on the diagram shown below in FIG. 15 about the ejection behavior of the goods in a drum cross section equipped with angular profiles as lifting blades and the assumed drum dimensions, performance data and other practical, fixed assumptions which are subsequently recorded.

• - Leistung 120 t/h Durchmesser der Trommel (lichter Durchmesser) Δ = 2 m
• - Zahl der gleichmäßig über den Umfang verteilten Hubelemente n = 10;
• - Form der Hubelemente sind ungleichschenklige Winkel, wobei der lange Schenkel jeweils radial zum Trommelzentrum gerichtet ist
  
• - Drehzahl der Trommel
  
• - Volumen einer Alveole, zwei aufeinanderfolgende Hubschaufeln bilden eine Alveole, deren Volumen bei dieser Rechnung, für eine Länge von 1 m, durch den Abstand zwischen zwei radial gerichteten, aufeinanderfolgende, der Trommel angeschlossene Schenkel der Winkelpro- .file und durch deren Hüllkreis-Durchmesser δ = 1,5 m bestimmt ist. Das Volumen einer Alveole ist
  
• - Böschungswinkel des nach Trennung von den abrutschenden Materialien in den Alveolen verbleibenden Materials wird mit α nach Praxiserfahrung angenommen
  
• - Länge der aktiven Mischzone der Trommel ist
  
• - Verweilzeit des Gutes in der aktiven Mischzone ist
  
• - Schüttgewicht der in den Alveolen geförderten ruhenden Zuschlagstoffen
  
• - spezifisches Gewicht der getrennten, d.h. im Freifall sich befindenden Granulate
  

The following should apply in detail to the following consideration:

• - Output 120 t / h diameter of the drum (clear diameter) Δ = 2 m
• - Number of lifting elements evenly distributed over the circumference n = 10;
• - The shape of the lifting elements are unequal legs, with the long leg directed radially to the drum center
  
• - drum speed
  
• - Volume of an alveolus, two consecutive lifting vanes form an alveolus, the volume of which, for this calculation, for a length of 1 m, by the distance between two radially directed, consecutive legs of the angular profiles connected to the drum and by their enveloping circle diameter δ = 1.5 m is determined. The volume of an alveolus is
  
• - The angle of repose of the material remaining in the alveoli after separation from the slipping materials is assumed to be α according to practical experience
  
• - The length of the active mixing zone of the drum
  
• - Dwell time of the goods in the active mixing zone
  
• - Bulk weight of the resting aggregates conveyed in the alveoli
  
• - Specific weight of the separated, ie free-falling granules
  

If you now in the by Δ, i.e. by the clear drum diameter, the envelope circle δ determined by the ends of the radially directed webs of the lifting blades, and the slope angle α resulting from the slipping material in the alveoli - the reference line r-r; to the one that runs through the center and is directed from the vertical towards the rising part of the drum - and leads parallel lines to this reference line to the boundary edges of the short legs that determine the height of the lifting blades and the diameter of the enveloping circle Δ, so that is Slope line can be represented precisely in each individual alveolus. In this context, reference is made to the parallels to r-r, namely to the lines r'-r 'and r "-r".

For the sake of explanation, it should be noted once again that the mixture enclosed in the alveoli is raised by the rotation of the drum and that the filler portion lying above the slope line defined above slips, ie slides downward in a slightly parabolic case. This proportion is now recorded on the drum base by the lifting vane internals and partially raised again.

When the aggregates circulate in the drum, however, a remainder of the aggregates, possibly up to that defined by r '' -r '', i.e. to the tangent of the enveloping circle δ. do not cross this outermost line since no material can remain in the socket in this position.

The empty alveoli are continuously loaded and filled again by the good task and by the portion in free fall.

If, at an assumed moment of absolute standstill of the rotating drum, one considers the distribution state in the drum cross-section given for this moment and one assumes that the lower alveoli have their maximum degree of filling, with an increase in the drum wall, it can be seen that the Alveoli have progressively emptied in their circulation - depending on the phase they are currently taking up on the inner circumference of the drum - taking into account the internal friction of the material and the resulting angle of repose α or

if one takes the delay of inertia into account, they are about to empty themselves up to the angle of repose given by the internal friction of the material, whereby the parts in free fall assume a parabolic, slightly fanned, expanded position.

From the diagram inserted in the text to facilitate the explanation of the situation, it can be seen that the lifting elements achieve a good distribution of the material over the drum cross-section, which is not even approximately sufficient. First, on the rising side, i.e. in the direction of rotation of the drum, before reaching the parallels r'-r 'to the reference line r-r - which is identical to the tangent to the enveloping circle δ - no goods emerge from the alveoli, which are positioned with the numbers 1 to 10, rotating to the right starting from the drum base.

This exit only takes place successively with its further increase, whereby after reaching the envelope circle, which further delimits the envelope circle in the descending phase, to the reference line rr, parallel tangent r '' -r '', the remaining small amount of residual material can no longer assume an undisturbed free-fall position , but, disturbed by the leading lifting blade essentially, and that is transferred together with the seizure from the alveoli 6 and 7 into the subsequent alveolus.

The alveoli spread its contents across the cross-section of the drum according to the drawing graph wherein the remaining quantity of material circulation in the respective _P OSI shown in dotted lines and the quantity has slid is shown blackened. The alveolus 9, which is directed towards the base of the drum in the descending phase, experiences a first partial filling, which increases via the alveoli 10, 1 and 2 to full filling. From alveolus 3, the partial delivery of the alveolar volume V takes place, indicated by positions a to f, while the remaining alveoli are identified by positions A to E. So much for the explanation of the inserted diagram.

The frequency of the distribution is determined by the drum speed N - 6 rpm, the distribution being able to be influenced only to a small extent by the shape and height of the lifting blades. The throughput capacity required is determined by appropriate dimensioning of the dimensions of the drum, in particular its inclination and its speed, this capacity being variable in relation to the instantaneous moisture content of the material as a function of the possible burner output.

A largely balanced vote based on the given situation must therefore be found here.

• a) Die Alveolen, welche in die ansteigende Trommelwand eingehen, sind gerade voll gefüllt.
• b) Es besteht ein Überschuß an Mischgut, welcher von den Alveolen nicht eingeschlossen wird und der in der im wesent--lichen von der Trommelneigung und von der Reibung zwischen der Alveolenfüllung und dem Überschuß bestimmten Geschwindigkeit bewegt wird. Bei funktionsfähiger Trommel muß die Geschwindigkeit beider Anteile gleich sein.
• c) Es besteht ein Fehlen von Mischgut, so daß die Alveolen nur teilweise gefüllt ansteigen.

Depending on the setting of the feed performance in the drum, three cases can occur:

• a) The alveoli that enter the rising wall of the drum are just full.
• b) There is an excess of mixed material which is not enclosed by the alveoli and which is moved at a speed which is essentially determined by the inclination of the drum and by the friction between the alveolar filling and the excess. If the drum is working, the speed of both parts must be the same.
• c) There is a lack of mixed material, so that the alveoli rise only partially filled.

In the following, only cases a) and b) should be taken into account, since only they can guarantee the expected even distribution of the mixed material thrown off in the drum cross section and the expected additional intake. It should be noted here in principle that an excess of mix in relation to the capacity of the alveoli does not change the amount of mix to be distributed in the cross section of the drum; it remains unaffected by drum performance and drum fill level and other factors.

As already mentioned at the beginning, the goal aimed at by the designers is the best possible, i.e. to achieve even distribution of the raised mix over the cross-sectional area of the drum with maximum use of thermal energy, combined with a low dust discharge.

A uniform distribution of the respectively increased proportion of the mixed material in the drum cross-section during its free fall could - with an exactly horizontally oriented drum - be compared with an almost stationary shaft or roller made of a disperse material distributed in the gaseous medium; it would thus satisfy cases a) and b).

However, as already mentioned at the beginning, this is not possible.

If you look at the actual distribution of the material in the drum based on the data selected for the diagram, ie at a capacity of 120 t / h, an active drum length of 6 m and a dwell time of 4 min, this results in a constant occupancy of the drum per minute with 120: 60 x 4: 6 = 1.33 t per running meter of the active drum length. Since the drum is fed continuously and the finished mix continuously exits, the calculation of the distribution of the mix in cross-section of the drum can be based on the hypothesis with sufficient accuracy, as if the drum had been placed in a horizontal position and the proportion of the total occupancy increased by 1 per meter of drum length. 33 t also correspond in practice to the individual filling diagrams shown by the diagram.

bleibt, d.h. der vollständigen Füllung der in einzelnen Kaskaden über einen Teilumfang verteilten Alveole entspricht nach Einsetzen der genannten Daten einem freifallenden Mischgutvolumen von

Der partielle Abwurf des Mischgutanteiles a bis f, d.h. aus einer Alveole, wiederholt sich entsprechend der Anzahl der über den Trommelumfang gleichmäßig verteilten Einbauten während einer Trommelumdrehung 10 mal; bezogen auf die Drehzahl bedeutet dies, daß der Abwurf aus

den jeweiligen Mischgutabwurf pro Sekunde bestimmt.Regardless of whether the mix is in excess or just enough to fill the rising alveoli, it should be noted that the proportionate amount of the total quantity per time and length unit / n / min distributed over the drum cross section is always given by the formula

remains, ie the complete filling of the alveolus distributed in individual cascades over a part of the circumference corresponds to a free-falling mix volume of after inserting the data mentioned

The partial dropping of the mixed material portion a to f, ie from an alveolus, is repeated 10 times during a drum revolution according to the number of internals evenly distributed over the drum circumference; based on the speed, this means that the dropping off

determines the respective mix discharge per second.

If one looks at the emptying from the individual alveoli, starting with alveolus 3, and if the volume is delimited by the slope angle α in accordance with the earlier explanations, then the remaining volume A remains Parts b to f or remaining parts B to E. It can be seen from the diagram that the volume b cannot yet be involved in the formation of a cascade veil because it practically does not leave the left side of the rising drum wall. The same applies even more extreme for the volume a. Only from volume c is there a sufficiently open field directed towards the inside of the drum, so that one can speak of a free fall of the material sliding here, the discharge from c and the subsequent positions being essentially perpendicular,
Because of the low peripheral speed, which is only about 0.625 m / sec in relation to the clear diameter of 2 m and a speed of 6 rpm, no significant acceleration of the goods is to be expected.

entspricht dabei, wie bereits vorher ausgeführt, dem Inhalt einer Alveole.The total of the discarded shares

corresponds to the content of an alveolus, as already explained earlier.

d.h. es werden 137,4 1/sec, d.h. der Inhalt einer Alveole pro Sekunde in den freien Querschnitt abgeworfen.The individual contents of the dropping sections are

ie 137.4 1 / sec, ie the content of an alveolus per second are thrown into the free cross-section.

As already mentioned above, however, the total volume does not participate in the formation of the cascade veil, but at least the material (a / b) released from the alveoli 3 and 4 must be subtracted, so that only 84 1 / sec for the formation of the cascade veil be available.

Die mittlere Fallzeit kann für eine mittlere Fallhöhe von

angenommen werden, was einer Raumprozentbelastung von _i

für den im freien Fall sich befindenden Gutanteil entspricht,.wobei in diesem Zusammenhang bemerkt werden soll, daß sich dieser Prozentwert auf den durch die Einbauten bestimmten Hüllkreisdurchmesser δ bezieh t.Since this bed no longer has a bulk density of 1.7 when it emerges from the alveolus, but the specific weight of 2.7 is to be used in free fall, the volume of space displaced by the free fall is only

The mean fall time can be for a mean fall height of

can be assumed, which is a space percentage of _i

corresponds to the proportion of good that is in free fall, whereby it should be noted in this connection that this percentage value relates to the enveloping circle diameter δ determined by the internals.

Converted to the entire inner drum space, this consideration would be even more unfavorable, since if you repeat the calculation, only about 1.18% of the volume will be moved as a free-falling material.

Regardless of this, it must be remembered that the inside of the drum, which is not occupied by the mix, also has absolute gaps that cannot be covered by a discharge cascade, since gaps or gaps that cannot be closed between the individual discharge cascades slowly formed with the circumferential speed of the drum across the drum cross-section Shafts exist through which the major portions of the heating gases flow at high speed, with this discharge cascade only undergoing a somewhat more intensive heat exchange when the heating gases strike the relatively narrow transverse profiles.

In this context, the large differences in volume and thus also the density of the individual discharge cascades should be pointed out again.

Setzt man hierfür die bereits errechneten Werte ein, so ergibt sich bei dem gewählten Beispiel ein Leervolumen in den sogenannten aktiven Alveolenräumen von insgesamt 491 Liter.If the free alveolar spaces not used for the formation of a cascade are called "absolutely empty", the following individual volumes add up as empty volumes:

If one uses the already calculated values for this, the selected example results in an empty volume in the so-called active alveolar spaces of a total of 491 liters.

In addition there are the empty spaces of the inactive alveolar spaces, i.e. the free spaces of the descending drum phase, which cannot be fully occupied by the mix in free fall;

If one estimates this free space on the content of an alveolus, i.e. approx. 137 1, then these empty spaces with 491 + 137 = 628 liters, i.e. rounded off with 600 liters. This 600 liters of absolute empty space per running meter corresponds to a cylindrical free passage with a diameter of 0.85 m, i.e. an opening that offers no resistance to the heating gases and that is practically passed freely through the drum into the chimney and thus into the open.

Ultimately, this high-speed gas stream is essentially only suitable for transferring convection heat to the metal parts in contact with it.

Some constructions are therefore provided with an annular disc at the end of the burnout zone of the flame, the external dimension of which is determined approximately by the inside diameter of the drum and the internal dimension of which is determined by the enveloping circle of the internals. The resulting narrowing of the cross section leads to a corresponding acceleration of the heating gases, so that their tendency to separate the saft parts from the material is promoted.

Other constructions, e.g. see DE-OS 26 45 344..deflectors arranged concentrically in the end region of the drum,

on which the gas stream loaded with dust particles impacts. Here, the dust particles are only excreted to a very small extent, while a strong acceleration of the gases occurs due to the annular gap formed between the light drum diameter and the reflector, so that their tendency toward sweeping dust transport is further increased here.

• Die schwache Dichte der Abwurfkaskaden und die absoluten, d.h. durch die Abwurfkaskaden nicht belegten Freiräume im Trommelvolumen, sind nicht zu beseitigende Nachteile, die man zwar durch Anordnung und Ausbildung der Trommeleinbauten in geringem Umfang abmindern kann aber niemals ganz beseitigen kann.
• Weiterführende Maßnahmen, insbesondere kompliziertere Einbauten, wie die eingangs erwähnten Simplexeinbauten oder Quadranteneinbauten, sind mit anderen Nachteilen verbunden, wobei insbesondere, in diesem Zusammenhang, neben dem konstruktiven Aufwand die wesentlich höhere thermische Beanspruchung dieser Einbauten und das erhebliche Mehrgewicht anzusprechen sind.

To summarize here:

• The weak density of the discharge cascades and the absolute, that is to say vacancies in the drum volume not occupied by the discharge cascades, are disadvantages which cannot be eliminated, which can be reduced to a small extent by arranging and forming the drum internals, but can never be completely eliminated.
• Further measures, in particular more complicated internals, such as the simplex internals or quadrant internals mentioned at the outset, are associated with other disadvantages, in particular, in this context, apart from the structural outlay, the significantly higher thermal stress on these internals and the considerable additional weight being mentioned.

The only decisive factors for reducing dust discharge are the coordinated interaction of water (moisture) and bituminous binder, Simultaneously with the additives, and according to this analysis, not, as is generally assumed, the need for a distributed free fall of the cascade drops, but the effort to improve the heating and the mixing of the bulk of the mix on the drum wall.

In addition to the revelation given here of an extremely weak and very irregular density of the discharge cascades, an important principle emerges on the basis of the previous analysis, namely the fact that, regardless of the degree of filling of the drum with filled alveoli or with excess material, the density and structure of the dropping cascades remains constant. It was also found that the possibility of distributing the discharge cascades is limited to the cross section represented by the envelope of the drum internals. The analysis also basically confirms that the discharge cascades can never completely cover all or part of the interior.

In addition, the situation with a reduction in the height of the lifting elements is briefly examined and the case of a practical reduction in the radially measured height of the lifting elements from 0.25 m to 0.15 m is examined.

In this case, the room load determined above must be multiplied by a proportionality factor due to the free-falling quantity of material of 1.18%.

Proportionalitätsfaktor, so daß das freifallende Gut nur noch 1,18 x 0,63 = 0,74 % des Raumvolumens beansprucht.The enveloping circle diameter δ must be assumed to be 1.7 instead of 1.5, the drum diameter Δ is 2 m in both cases. Taking these values into account, we get

Proportionality factor, so that the free-falling material only takes up 1.18 x 0.63 = 0.74% of the room volume.

Since the free volume of space per meter of drum length - without taking into account the volume of the internals minus the volume of the good weight - and minus the volume of a free-falling alveolus distributed over the circumference, this is about 2360 1. If one now takes into account the calculated proportionality factor and the specific weight of the falling goods with 2.7, the weight of the free-falling discharge cascades, when using the smaller internals, should be set at approx. 47 kg per second.

It follows that - with the original installation heights mentioned in the example, about 5.6% and with the reduced installations around 3.5% of the mix conveyed by the drum is in free fall, while the main part with 94.4% or 96.5% of the mix weight is in constant movement and mixing as well as in constant heat absorption through contact with the drum wall and the internals connected with it.

If one follows the course of a grain from the mixed material from its entry into the drum to the drum outlet, it can be found, based on the previous analysis, that each time the probability of falling in a discharge cascade occurs, it only takes about 0.5 seconds remains in suspension to be taken up again by the main mass of the material mixing against the drum wall. Here it will, as a rule, remain for at least half a turn or several turns before it is used again for cascading.

There is hardly a possibility that the grain residence time in the cascade is more than 10 seconds, i.e. that this is thrown off more than twenty times during the passage of the material.

This assumption seems to be objective and underpins the thesis that the main part of the drying and heating work with constant exchanging and revolving grain movement is mainly directed against the drum wall, while obviously a vanishingly small part of the good during the free fall in the discharge cascades dust releases to the gas stream.

The resulting discharge cascades are therefore an obstacle to the low-dust operation of a drum mixer. _D .a that in a drop cascade is exploiting Dende Good during the freefall neither envelop by the binder still can absorb heat to any significant extent, the cascading is to question fundamentally.

• - Einfachste Laborversuche, bei denen die in ein Mischgefäß (Metalltopf) eingebrachten feuchten Zuschlagstoffe durch einen Brenner oder eine Heizplatte erhitzt werden, zeigen, daß bei der gleichzeitigen Zuführung des Bitumens -selbst in erstarrter, nicht angewärmter Form - bei Umwälzen des Inhaltes mit einem gewöhnlichen.Spachtel, bereits bei Temperaturen über 80° gut umhülltes Mischgut gebildet wird. Die Notwendigkeit der Kaskadenbildung muß nicht gegeben sein.
• - Derselbe Erfolg stellt sich in der einfachsten .Betonmaschine (Freifallmischer) ein, wenn man eine Brennerflamme auf die feuchten, mit dosiertem bituminösem Bindemittel versetzten Zuschlagstoffe richtet.
• - Die Art und Form der Zugabe des Bitumens beim Trommelmischverfahren ist, und zwar unabhängig von der Temperatur im Augenblick der Zugabe, nicht bestimmend für die Erreichung einer guten Umhüllung und für die Verteilung des Bindemittels im Mischgut, und zwar auch unabhängig von der Größe des Fülleranteiles. Es bilden sich ohne Anwendung besonderer "Kunstgriffe" homogene Mischungen, wenn man das Bitumen auf das feuchte und im wesentlichen kalte Gestein aufgibt und das Gemenge anschließend in die heiße Zone der Flamme einbringt.
• - Auch wenn in einem Trommelmischer die Alveolen so verstopft sind, daß sie nicht mehr imstande sind das Gut anzuheben, so zeigt sich, daß davon die Herstellung eines guten Mischgutes praktisch nicht beeinflußt wird.
• - Die Anordnung von Ketten-anstelle der normalen Einbauten in Trommelmischern ist, wie durch das Deutsche Patent 21 43 975 ausgewiesen, für die Aufbereitung eines guten Mischgutes vollständig ausreichend, ohne daß auch nur entfernt eine Kaskadenbildung gegeben wäre.

From the experience and observation, the process of wrapping should be recorded:

• - Simplest laboratory tests, in which the moist aggregates introduced into a mixing vessel (metal pot) are heated by a burner or a heating plate, show that when the bitumen is supplied at the same time - even in a solidified, unheated form - when the contents are circulated with an ordinary one Spatula, well-mixed mix is formed even at temperatures above 80 °. The need for cascading does not have to exist.
• - The same success is achieved in the simplest concrete machine (free-fall mixer) when a burner flame is directed at the moist aggregates mixed with dosed bituminous binder.
• - The type and form of adding the bitumen in the drum mixing process, regardless of the temperature at the moment of addition, is not decisive for achieving a good coating and for the distribution of the binder in the mix, regardless of the size of the filler content . Homogeneous mixtures are formed without the use of special "tricks" if the bitumen is applied to the moist and essentially cold rock and the mixture is then introduced into the hot zone of the flame.
• - Even if the alveoli in a drum mixer are so blocked that they are no longer able to lift the material, it can be seen that the production of a good mixture is practically not affected.
• - The arrangement of chains instead of the normal internals in drum mixers, as shown by German Patent 21 43 975, is completely sufficient for the preparation of a good mix, without even cascading.

Based on this state of affairs and the experience and knowledge mentioned, it is an object of this invention to name a method of the type described at the outset, which processes bituminous mix in a drum mixer while avoiding any dust development worth mentioning during the application phase of the still cold, i.e. Additives having outside temperature and the usually heated bituminous binder in the drum and during the passage of the batch and its conversion into a bituminous mixture is guaranteed and furthermore at least an optimal use of the convection of the drum walls and the here Possibly connected internals is given to the heat that can be transferred.

The solution to this problem according to the invention provides that the mixture consisting of additives and binders, due to the friction existing between it and the drum wall on the one hand and the internal friction of the material on the other hand, constantly repeats itself during its passage through the drum mixer into a hot mixture until the frictional forces overcome the frictional forces along or parallel to the inner wall of the rising drum mixer and return it to the drum base.

Such a process avoids the formation of dropping cascades and thus the main cause of the construction contract. The material travels back and forth in the lower drum area as a constantly moving flow of material through the drum mixer, the volume of material lying on the base of the drum, the cross-section of which is to be regarded as a circular section distorted in particular at the lateral boundaries, and its free surface due to the length of the constantly oscillating position the chord of this segment of the circle and the drum length is determined. Part of the radiant heat present in the drum space is then directly absorbed by the material via this surface, while the majority of the radiant heat is absorbed by the periphery not covered by the material, and — if the environment is neglected, most of the radiation is neglected good insulation, unavoidable radiation losses - as convection heat via the contact surface between the goods and the drum, which is determined by the length of the bend and the drum, is supplied to the goods, the heat absorption being additionally accelerated by the exchange of particles within the material mass.

A further improvement of the positive results of the invention described here is achieved while maintaining the selected clear drum diameter when the heat transfer from the drum wall to the material by enlarging the heat-transferring inner surface of the drum mixer - combined with a forcibly sliding sleeper-shaped guide of the drum base Good - increased and at the same time the mixing intensity is promoted, whereby it is proposed that the circulating, material and heat exchanging mixing process by mixing tools directed essentially inclined to the ascending radial, while maintaining the connection of the good, ie without dropping or free-fall phenomena of subsets.

The mix in the form of a loose pile can practically not leave the drum wall; With this type of guidance, however, an even more intensive circulation of the material within the pile is achieved, with a simultaneous increase in the contact area with the drum wall.

The device for performing this method provides that the mixing tools, viewed in the direction of rotation of the drum mixer, the inner wall of which are adjoining elements which are inclined to the radial and formed by flat profiles, which are essentially arranged in a radially directed plane leading back to the drum wall and transferred into it support.

The internals thus formed practically form wedges pointing in the direction of rotation and promote the desirable threshold-shaped movement of the goods.

An additional distributing effect is achieved in that the radially directed flat webs also run in the radial direction, i.e. rods directed to the center of the drum mixer are assigned, wherein the rods, gap-to-gap, are connected to the flat webs between two rows of rods which are directed towards one another, and preferably the rods forming or supplementing the mixing tools are profiled in the drive direction in a ploughshare manner.

It can also be provided that the rods are either directly connected to the inner periphery of the drum mixer - without the previously mentioned, additional internals - or that the rods are arranged in one or more rows on exchangeable, flat or curved drum wear plates that are adapted to the drum radius are, wherein the flat wear plates are supported on the inner periphery of the drum mixer and are attached to this.

This proposal takes into account the fact that the technical requirements for the processing of bituminous mixes are often dependent on the recipe and not all mixing problems can be solved optimally with drum internals of the same type.

However, since the basic principle of the invention, i.e. the completion of the mixture by forming a back and forth sloshing bed with intensive particle exchange within the goods, avoiding the formation of discharge cascades and enabling large contact areas between the drum wall and goods for the transmission of convection heat remains untouched in this context, should only be mentioned in this context, that it is easier to encase or mix a well-graded fine asphalt concrete than, for example, a coarse binder.

The technical effort can therefore be graded.

In the case of mobile or highly mobile systems, the transport weight of the facility must also be taken into account in some cases.

The last proposed solution, i.e. the arrangement of the bars on flat wear plates supporting the inner periphery of the drum mixer is particularly interesting. The conversion of the originally cylindrical drum cross-section into a polygonal cross-section creates an excellent self-cleaning effect, while at the same time the mixing of the material is still activated, since the corners of the polygonal cross-section increase its circulation while at the same time supporting the heat exchange between the drum wall thus formed and the material :

In addition, such a design already avoids any approach to alveolus formation and only ever offers the flame and its radiation moving material for heat absorption.

In contrast to lifting shovels according to the state of the art mentioned at the outset, no unmixed mix can be stored on the internals and, in connection with this storage, baked here, which, as a rule, causes damage to the binder due to overheating.

A further embodiment of the device, which also enables compliance with the principles of the invention which have already been emphasized, provides for

that the rods are replaced at least over a partial length of the drum mixer by radially directed, at a substantially uniform angle to the drum axis over the width of the wear plates, rows forming conveyor webs and - viewed in the direction of rotation - the conveyor webs of the subsequent series offset to the conveyor webs of the lead row, and that occasionally in each row of conveyor webs are provided in pairs at a distance from each other associated webs.

In the case of conveyor bridges in the same direction, an interrupted screw is created, which increases the propulsion of the material which is predetermined by the drum inclination.

In the case of an alternative embodiment, which provides for the paired arrangement of conveyor webs arranged at a distance from one another, a rectified row of conveyor webs counteracts the main flow direction and thus promotes the mixing intensity at a reduced passage speed through the drum, which would lead to zero if the drum were in a horizontal position.

In some cases, it may be advisable to attach the wear plates to the periphery of the drum mixer with a small insulation distance.

The process can be carried out both in a drum mixer in which the burner is used for either cocurrent or countercurrent firing
- arranged in relation to the direction of the material flow through the drum.

According to the customary view, the thermal stress on the binder is lower in direct current operation, while in counter current operation there is a better thermal efficiency.

In view of the good distribution of the drum cross-section explained in the context of the prior art, it is proposed that the burner muffle is in each case a wide-dimensioned tube with an insulated jacket region, which is offset axially parallel in its position relative to the drum cross-section so that it is on the one hand in the is essentially outside of the material being moved and, on the other hand, is able to dissipate radiant heat to a large extent to the zone of the inner drum periphery not acted on by material to be mixed and to the mixing tools arranged here.

This means that the burner muffle must be arranged in the upper, descending area of the moving drum wall.

In addition, it can be provided in this connection to insulate the outer surface of the burner muffle in such a way that the major part of its radiant heat is emitted essentially from approximately 50% of its circumference, and this partial circumference is assigned to the region of the drum inner periphery which is initially located.

Regarding the arrangement of the burner muffles, it can generally be stated that the radiant heat is transmitted particularly effectively to the wall area which is only little affected by the additives. The arrangement is, however geeig especially for the counterflow _- net, as the already largely and completely enveloped in a muffle-area aggregates can be conducted under the burner muffle without damaging influence of temperature through and as a ready mix to the discharge chute.

The directional insulation of the burner muffle further supports the desired protection of the goods.

To equip the drum mixer with internals, it should be noted that, as a rule, the mixing tools are designed uniformly over the length of the mixing and heating section of the drum, although a mixed arrangement may be appropriate depending on the task.

To improve the overall efficiency, it is provided that limited to the outlet-side third of the drum mixer, a plurality of spaced-apart, segment-shaped recesses connected to the drum are arranged, the recesses of the deflectors being gap after gap.

This proposal is based on the observation result of a test carried out with a transparent model and is intended to alleviate the mismatch between the flow velocity of the heating gases and that of the mixed material through the drum mixer - which, according to current experience and knowledge, cannot be eliminated in principle - and contribute to improving heat utilization . The flow velocity is reduced due to the arrangement of the deflectors, limited to the actual mixing area of the drum. Due to the constantly repetitive immersion of the deflectors in the flow of material, additional heat is supplied to the latter and, through the impact on the deflectors and the deflecting effect between them, any remaining free dust which may still be present is essentially separated.

For loading with additives, it is proposed that the task of different grain-graded additives is made possible by a multi-cell rotary silo which can be predetermined in its delivery setting for the drum mixer.

By means of this device, aggregates of different grain sizes can be stored according to the number of cells and, according to the required recipe, added to the drum mixer.

A further development of the device provides that a trickle filter designed as an intermediate bunker is provided for the feed of the aggregates, a closed exhaust gas duct is the exhaust gases emerging from the drum mixer between this and the trickle filter to the chimney.

This combination enables the residual heat still contained in the outflowing heating gases to be used largely by transferring this heat to the additives added via the trickle filter.

In conclusion, it should be noted that when the method according to the invention is practiced with the proposed devices, exhausters for the exhaust gas discharge can generally be dispensed with, unless special internals or devices which increase the resistance in the gas duct are provided. In this context, reference should be made to the trickle filter.

• Figur 1 zeigt den Querschnitt durch einen Trommelmischer, dessen Innenwandung mit zum Trommelgrund geneigten, schwellenförmigen Einbauten versehen ist, wobei diesen Einbauten, in radialer Richtung weisend, Lücke auf Lücke stehende Stäbe zugeordnet sind.
• Figur 2 zeigt eine partielle Abwicklung einer Teillänge der Trommel aus Figur 1.
• Figur 3 zeigt im Aufriß Figur 2.
• Figur 4 zeigt einen Querschnitt durch den Trommelmischer entsprechend Figur 1. Die hier dargestellten Stäbe sind jedoch durch über die Breite der Verschleißbleche greifende Förderstege bestückt.
• Figur 5 zeigt die Abwicklung der Trommel in Schnittrichtung III-III bei einheitlich nach einer Richtung winklig angeordneten Förderstegen.
• Figur 6 zeigt eine Darstellung nach Figur 5, jedoch mit der zusätzlichen Anordnung einer Gegenstromreihe der Förderstege.
• Figur 7 zeigt einen im Gleichstrom befeuerten Trommelmischer.
• Figur 8 zeigt den Schnitt I-I, die Lage der Aufgabeschurre, wobei die Aufgabe alternativ durch ein Drehsilo gemäß Figur 12 und 13 erfolgen kann.
• Figur 9 zeigt einen im Gegenstrom befeuerten . Trommelmischer, dem alternativ ebenfalls ein Drehsilo gemäß Figur 12 und 13 zugeordnet werden kann.
• Figur 10 zeigt den Schnitt II-II durch Figur 9. Der Trommelmischer ist lediglich mit radial gerichteten, auf Verschleißblechen angeordneten Stäben besetzt.
• Figur 11 zeigt einen ebenfalls im Gegenstrom befeuerten Trommelmischer, der durch Beistellung eines Verladesilos zu einer Gesamtanlage ergänzt wurde. Die Aufgabe des Gutes erfolgt hierbei über einen Rieselfilter, der eine Nutzung der in den Heizgasen enthaltenen Restwärme zuläßt.
• Figur 12 zeigt ein mehrtaschiges Drehsilo, dem verschiedene Rezepturen aufgebbar sind, so daß bei Rezeptwechsel das Silo lediglich um ein oder mehrere Segment(e) weiter gedreht werden muß.
• Figur 13 zeigt das Drehsilo im Grundriß.
• Figur 14 zeigt die Ausbildung eines der für die Anordnung im auslaufseitigen Drittel vorgeschlagenen Deflektors, wobei die Ausnehmungen der in Richtung der Trommelachse mit Abstand voneinander vorgesehenen weiteren Deflektoren Lücke auf Lücke stehen. Die Anordnung der Deflektoren im Trommelmischer wird durch Figur 7 verdeutlicht.

The invention is explained in more detail with reference to the accompanying drawings in exemplary embodiments.

• FIG. 1 shows the cross section through a drum mixer, the inner wall of which is provided with sleeper-shaped internals inclined towards the drum base, these internals, pointing in the radial direction, being assigned gaps to gaps.
• FIG. 2 shows a partial development of a partial length of the drum from FIG. 1.
• Figure 3 shows an elevation of Figure 2.
• FIG. 4 shows a cross section through the drum mixer corresponding to FIG. 1. However, the rods shown here are equipped with conveyor webs that extend across the width of the wear plates.
• FIG. 5 shows the development of the drum in the cutting direction III-III with conveyor webs arranged angularly in one direction.
• FIG. 6 shows an illustration according to FIG. 5, but with the additional arrangement of a counterflow row of the conveyor webs.
• FIG. 7 shows a drum mixer fired in direct current.
• Figure 8 shows section II, the position of the feed chute, the task can alternatively be carried out by a rotary silo according to Figures 12 and 13.
• Figure 9 shows a counter-current fired. Drum mixer, which can alternatively also be assigned a rotary silo according to FIGS. 12 and 13.
• Figure 10 shows the section II-II through Figure 9. The drum mixer is only populated with radially directed rods arranged on wear plates.
• FIG. 11 shows a drum mixer which is also fired in countercurrent and which has been supplemented to provide an overall system by providing a loading silo. The task of the goods is carried out via a trickle filter, which allows the residual heat contained in the heating gases to be used.
• FIG. 12 shows a multi-pocket rotary silo to which different recipes can be applied, so that when changing the recipe, the silo only has to be rotated one or more segments.
• Figure 13 shows the rotary silo in plan.
• FIG. 14 shows the design of one of the deflectors proposed for the arrangement in the third on the outlet side, the recesses of the further deflectors which are provided at a distance from one another in the direction of the drum axis standing gap after gap. The arrangement of the deflectors in the drum mixer is illustrated by FIG. 7.

FIGS. 1 to 3 show an example of a cross section through a drum mixer 1, in which internals which are effective evenly over the circumference are provided as heat exchange surfaces and mixing tools. The internals, viewed in the direction of rotation of the drum, are formed by flat profiles 2 inclined to the radial, which are supported on the flat webs 3 leading back to the drum wall.

The internals 2, 3 formed in this way are - due to the inclination of the flat profiles 2 to the radial - not suitable for lifting the mix to such an extent that it can fall freely in separate grain sizes.

The intensity of the movement and thus the exchange along the drum wall is improved by the flat webs 3 connected, also pointing in the radial direction, rods 4, wherein, as shown in FIG. 2, these rods 4 are staggered in the development of the drum, gap to gap . The profile of these rods pointing in the drive direction is shaped like a ploughshare and, as shown in the drawing, can be a square rod, the cross section of which has a point, i.e. Edge pointing in the direction of rotation.

The burner muffle 5 is arranged in accordance with the general statements already given in the descending region of the drum wall.

Due to the inclination of the flat profiles 2, the material slides back into the drum base after a short lift.

The distance between the individual bars or the ploughshare-shaped edges can generally be chosen between 5 cm and 25 cm and, in some cases, higher.

A greatly simplified embodiment provides that the internals formed from parts 2 and 3 are dispensed with, and the rods 4 are arranged either directly on the inner periphery of the drum or on wear plates 22 which are flat in their width, with the wear plates 22 on the drum wall are screwed on.

Of particular interest are drum mixers, the burners 9 and 9 'of which are offset axially parallel to the center of the drum and arranged in the descending part of the drum wall, preferably in the third cross-section quadrant (clockwise rotation). The burners 9 and 9 'are encompassed by relatively wide tubes each designed as a burner muffle 5 and 5'. The burner muffles 5 and 5 'are inserted into the interior of the drum and either arranged on the fixed end wall of the drum 1 or slidably mounted in an opening provided in this end wall.

Finally, on the question of the alternatively possible design of the internals, reference is made to the concept shown by FIGS. 4 to 6, FIG. 4 showing the drum cross section.

In this embodiment, the rods 4 are arranged in offset rows by radially directed conveyor webs 4 ', which lead at an angle to the drum axis over the width of the wear plates 22, the angle of attack to the drum axis in the case of FIG. 5 being about 15 ° and the amount of the row offset half distance between the conveyor webs 4 '.

In the case of an embodiment according to FIG. 6, the conveyor webs 4 'of each row are arrow-shaped, also at an angle of approximately 15 °, i.e. enclosing them at an angle of approximately 60 °.

The distance between the conveyor webs 4 'in the case of the example according to FIG. 5 is between 20 and 40 cm. However, it can also be chosen larger.

The same applies to an arrangement according to FIG. 6 for the average distance to be taken into account here.

The webs 4 'have a height of 10 to 25 cm, the height dimension ultimately being determined by the intended filling, since it should have at least the height of the good position in the drum base.

FIGS. 7 to 11 show the device and the method. their training explained.

FIG. 7 shows a drum mixer 8 operated in direct current, a feed chute 10 for the additives, burner 9 with burner muffle 5, and the bitumen feed 23 attached in the usual high position of the drum 1. This section shows the position of the deflectors 26/27, the actual deflector design 14 can be seen.

From Figure 8, which shows a section in the direction I-I through Figure 7, the arrangement of the. through the conveyor belt 10 'loaded feed chute 10 and the location of the burner muffle. 5 in the drum cross section.

FIG. 9 shows a drum mixer 11, which, in contrast to the embodiment according to FIG. 7, is operated in countercurrent. In this case, the mix and bitumen are added 12 and 23 in the region of the high drum position, while the burner 9 'with the burner muffle 5' is arranged in the low drum position.

FIG. 10 shows in a section II-II through FIG. 9 the position of the burner muffle 6 'in the drum cross section.

FIG. 11 shows a drum mixing system which has been further developed by combining a drum mixer 11 according to FIG. 9 with a trickle filter 16 and is operated in countercurrent to the mixing process and, as usual, is supplemented by a mix loading silo 31, the trickle filter 16 connected to the drum mixer 1 in the extended chimney 15 is arranged for transfer (e.g. FR-PS 79 24 572 in connection with FR-PS 79 21 118).

FIGS. 12 and 13 represent a device which is also known, namely a rotating silo 17 which is fed by conveyor belt 17 ¹ and consists of at least four silo cells 18, 19, 20 and 21 which, for example, make it possible to change under four different recipes without the feeder with the previously processed aggregate recipe must be emptied before the new recipe is started.

The control of the setting of the silo cells 18 - 20 is usually connected to the program control of the entire system and can be preselected at the same time - if the correct proportion of binder is set. The known possibilities of program control are diverse and are not the subject of this analysis.

The assignment of the rotary silo 17 to the drum mixers 8 and 11 is indicated in FIGS. 7 and 9. Of course, the rotary silo 17 can also be assigned to the feed belt 24 of the elevator 25 leading to the trickle filter 16.

The design of the deflectors 26/27 already mentioned, identified by FIG. 14 and arranged in the drum mixer 1 according to FIG. 7, is based on the observation result of an experiment carried out with a transparent model. The ratio of the area of the cutout 27 to the remaining area of the deflector 26 and the number and spacing of the deflectors 26 to be installed must be determined on a case-by-case basis.

Claims (18)

1.Process for the preparation of a bituminous mix in drum mixers, in particular for road construction, in which the generally surface-dry to moist aggregates, which have not yet been pre-dried by drying devices and removed from the mineral landfill, are continuously fed into a heated drum mixer inclined in the outlet direction, in or before this at a low temperature with bituminous binder and the good parts then - with strong heat _. supply by heating gases - are heated and mixed further and the mix is continuously discharged, the heating gases being discharged from the drum as a rule from fine particles and pollutants separated from the goods, characterized in that
da ß the mixture consisting of additives and binders, due to the friction existing between it and the drum wall on the one hand and the internal friction of the material on the other hand, during its passage into a hot mixture through the drum mixer, constantly repeating itself until gravity-related overcoming of the friction forces along or approximately parallel to the inner wall of the rising drum mixer and is returned to the drum base. 2. The method according to claim 1, characterized in that
da ß the heat transfer from the drum wall to the good, while maintaining the clear diameter, by increasing the heat-transferring inner surface of the drum mixer - combined with a forcibly inclined to the drum base slidable guide of the good - is increased. 3. The method according to claim 2, characterized in
da ß the circulating, material and heat exchanging mixing process by mixing tools oriented essentially inclined to the ascending radial, while maintaining the connection of the goods, ie without dropping or free-fall phenomena of subsets, is supported. 4. Device for carrying out the method according to claims 1-3, characterized in that
da ß the mixing tools (2/3), viewed in the direction of rotation of the drum mixer (1), the inner wall of which are adjacent, inclined to the radial, formed by flat profiles (2), which are essentially arranged in a radially directed plane leading back to the drum wall and in support them over flat webs (3). 5. The device according to claim 4, characterized in
that the radially directed flat webs (3) also extending in the radial direction, ie to the center of the drum mixer (1) directed rods (4) are assigned, the rods (4), gap to gap, the flat webs between two mutually facing rows of rods (3) are connected. 6. The device according to claim 5, characterized in that
da ß the forming the mixing tools or these additional rods (4) are profiled in the drive direction ploughshare. 7. The device according to claim 6, characterized in
that the rods (4) are connected directly to the inner periphery of the drum mixer (1) without any additional internals. 8. Device according to claims 5 and 6, characterized in
da ß the rods (4) on interchangeable, flat or the drum radius, curved wear plates (22) are each arranged in one or more rows, the flat wear plates (22) on the inner periphery of the drum mixer (1), supported and on this are attached. 9. The device according to claim 8, characterized in
da ß the rods (4) at least over a partial length of the drum mixer (1) by radially directed, at a substantially uniform angle to the drum axis across the width of the wear plates (22), rows forming conveyor webs (4 ') are replaced and - in Direction of rotation considered - the conveyor webs (4 ') of the following row offset to the conveyor webs (4') of the leading row stand, and ß occasionally in each row of conveyor webs in pairs at a distance from each other associated webs (4 ') are provided. 10. The device according to claim 8 and 9, characterized in
that the wear plates (22) are attached to the periphery of the drum mixer (1) with a small insulation distance. 11. Device for carrying out the method according to claims 1 to 3, characterized in
that ß the burner (9/9 ') is arranged either for the cocurrent or countercurrent firing of the drum mixer (1) - based on the direction of the material flow through the drum. 12. The apparatus according to claim 11, characterized in
da ß the burner muffle (5/5 ') is in each case a wide-dimensioned tube with an insulated jacket area, which is offset so axially parallel in its position to the drum cross section that it is on the one hand essentially outside of the moving material and on the other hand, it can dissipate radiant heat to a large extent to the zone of the inner drum bead not affected by the mix and to the mixing tools arranged here. 13. Device according to claims 11 and 12, characterized in that
da ß the burner muffle (5/5 ') is arranged in the upper descending area of the moving drum wall. 14. Device according to claims 12 and 13, characterized in
since B the outer surface of the burner muffle (5/5 ') is insulated in such a way that the major part of its radiant heat is emitted essentially from approximately 50% of its circumference, and this partial circumference is assigned to the region of the drum inner periphery located initially. 15. Device according to claims 4 to 10, characterized in
da ß the mixing tools (2/3/4) or (4) or (4 ') are uniform or mixed over the length of the mixing and heating section of the drum. 16. The apparatus according to claim 4 to 10 and 15, characterized in
da ß approximately to the outlet-side third of the drum mixer (1) limited, spaced apart, with segment-shaped recesses (27) provided with the drum connected deflectors (26) are arranged, the recesses (27) of the deflectors (26) Gap to gap. 17. Device for carrying out the method according to claim 1 to 3, characterized in that
da ß the task of different grain-graded additives by a multi-cell, in its delivery setting to the drum mixer (1) predeterminable rotary silo (17) is made possible. 18. Device for carrying out the method according to claim 1 to 3, characterized in that
da ß for the task of the additives, a trickle filter designed as an intermediate bunker (16) is provided, with a closed exhaust gas duct for the exhaust gases emerging from the drum mixer (1) between the drum mixer (1) and the trickle filter (16) to the chimney (15) is.

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