EP0442790A1 - Apparatus for the continuous or discontinuous production of bitumen coated products with aggregates and bitumen - Google Patents

Abstract

Cold and wet aggregates (4) are continuously introduced into a drying zone (7). The aggregates and hot gases are circulated countercurrentwise in the drying zone (7). The dried and heated aggregates are continuously introduced into a mixing zone (16) through which the hot gases do not travel. Liquid bitumen is incorporated into the aggregates in the mixing zone (16). The aggregates are circulated and they are mixed with the bitumen during their circulation in the mixing zone (16). During coating, the aggregates are kept in the mixing zone (16) during certain phases at least of production, by closure of a discharge means (21) communicating with the exit from the mixing zone (16). <IMAGE>

Description

The invention relates to a process and a device for the production of bituminous coated products continuously or discontinuously, from aggregates and bitumen and optionally, recycled used bituminous products.

The production of bituminous coated products, for example for road surfaces, from aggregates, liquid bitumen and pulverulent is very often carried out hot, the cold and wet starting aggregates being first of all dried and heated, before d '' be added bitumen and then kneaded with liquid bitumen which ensures the coating of aggregates. A pulverulent or filler material can be added to the mixture, in the kneading phase, in order to adjust the content of fine-grained material of the coated products.

It is also known to add to the aggregates a certain proportion of recycled materials constituted by used crushed bituminous coatings.

The oldest technique consists in carrying out the drying and heating of the aggregates in a first device such as a drum-dryer and the mixing, in a second device such as a mixer with parallel shafts or a rotary mixer.

The most recent technique consists in carrying out the drying, heating and kneading operations in the same device generally consisting of a cylindrical drum mounted to rotate around its axis slightly inclined relative to the horizontal plane, such a device being generally designated as a drying drum and wrapper.

This technique using a drying and coating drum is particularly well suited in the case of production of bituminous mixes in large quantities, for large road or motorway construction sites.

On the other hand, the coating dryer drums which are continuously supplied with aggregates and liquid bitumen prove to be unsuitable for the production of small quantities of bituminous mixes insofar as the flows of materials inside the drum are likely to deviate from the values required to obtain a perfect mix of asphalt mixes, when starting or stopping a production. It is then necessary to reject a portion of the coated products whose composition is not satisfactory.

In the case where the quantities of coated materials which are produced are very large, the proportions of materials rejected at the "head" and "tail" of production are small compared to the quantities produced and practically negligible.

It is not the same when the quantities of coated materials to be produced are low, since then the quantities of materials produced in the transitional phases at the end and at the start of manufacture can become very large, even even preponderant compared to the quantities of materials produced under normal conditions and having a satisfactory composition.

It is therefore preferable to use an essentially discontinuous manufacturing process, the necessary quantities of materials being produced by mixing in a single operation or during several successive operations.

Devices and methods have therefore been proposed for manufacturing bituminous coated materials by mixing using certain principles or materials known in the case of conventional coating plants intended for the production of large quantities of coated materials.

Some of these methods and devices use a separate dryer and kneader making it possible to prepare successive loads of materials. Such a process can consist in initially making a mixture of cold aggregates, by means of dosing hoppers such as those which are used on a conventional coating station. The mixture of cold and wet aggregates is transported in a buffer hopper which feeds a weighing hopper.

Loading is carried out by batch of a dryer constituted by a drum having a horizontal axis which dries and heats the aggregates by means of a burner. After drying, the dryer is tilted, so as to empty its load in a mixer such as those used on batch plants. The aggregates are then kneaded with the addition of filler and binder inside the mixer.

In French patent n ° 1.477.016, a process for the production of coated materials by mixing has been described which consists in preparing a mixture of cold aggregates by means of dosing hoppers, in carrying out the drying and the heating of the aggregates in a dryer. conventional, to transport the dry aggregates in a weighing hopper and to feed by batch, from the weighing hopper, a rotary mixer at variable speed and slope which evacuates the mixes via a buffer hopper.

It has also been proposed to use a single drum carrying out the drying and coating of the materials and which can work by tempering. For example, it has been proposed to use a drum with two compartments, one of the compartments drying the aggregates and the other compartment coating by mixing.

More recently, it has also been proposed to use a drying and coating drum with parallel currents. of the conventional type, the slope and speed of which are adjustable, for producing bituminous mixes by mixing. The drum has a movable ring with two positions arranged at the end of the drum and intended to prevent materials from leaving the drum at its end, when the system is working in a tempered fashion.

This device can also operate continuously, the movable ring being placed in a position allowing the material to exit continuously at the end of the drum.

Such devices using parallel current drums have the drawback that both the drying zone and the mixing zone are continuously swept by hot gases from the burner located at the inlet end of the drum.

When the drum is operating in a discontinuous regime, the materials being coated in the mixing zone are subjected to a flow of hot gases, throughout the duration of the mixing, so that it is difficult to control their temperature and avoid overheating of the bitumen covering the aggregates.

Coating dryer drums are also known in which the hot gases and the aggregates circulate in opposite directions, inside the drum drying zone.

In a first type of installation, the counter-current drum comprises a cylindrical casing rotatably mounted around its axis inclined relative to the horizontal plane and has an inlet end into which opens a device for feeding and introducing d cold and wet aggregates and an outlet end opposite the inlet end and located at a level below the level of the inlet end. A burner having an elongated body is introduced axially into the drum through its outlet end, so that the burner flame develops in an area of the drum remote from its ends. The drum has on its internal surface blades for lifting aggregates during the rotation of the drum, over at least part of its length corresponding to the drying zone which is located between the flame zone and the entry end of the drum. .

A mixing zone in which the dried and heated aggregates are mixed with liquid bitumen and coated is arranged around the burner at the rear of the flame zone. Stirring and mixing of the materials is ensured in this area by mixing blades fixed to the wall of the drum.

The mixing zone can be located inside the drum itself which has, in this zone, blades on its internal wall or delimited by a fixed mixer envelope disposed around the end of the drum whose wall carries mixing blades on its external surface. At the exit from the mixing zone, a device for removing the bituminous coated materials produced by the drum is placed.

The flow of hot gases circulating between the flame zone and the inlet end of the drum is not caused to pass through the mixing zone.

Such drums can also include a recycling ring making it possible to introduce, inside the drum, in the flame zone or near the end of the burner, bituminous recycled materials which are incorporated into the dried aggregates and heated in the drying area.

A second type of installation uses a drum dryer in which the hot gases and the virgin aggregates circulate against the current. At the outlet of the dryer drum, the dried and heated aggregates pour continuously into a mixer constituted by a rotary drum independent of the dryer and comprising mixing blades on its internal surface. The mixing zone, inside the drum, in which liquid bitumen is incorporated into hot and dry aggregates and possibly recycled used bituminous materials, is not traversed by a current of hot gases. The coated materials continuously exit through the outlet end of the mixer drum.

In a third type of installation, a double drum is used comprising two coaxial envelopes arranged one inside the other. The internal casing, which is rotatably mounted, constitutes a drum-dryer into which the virgin aggregates are introduced which circulate against the current with respect to the hot gases coming from a burner. The dried and heated aggregates are poured into the outer envelope in which the aggregates are kneaded with liquid bitumen and possibly recycled materials or other heat-sensitive additives. Mixing is ensured by blades integral with the internal envelope. The coated materials continuously exit from the external envelope delimiting the mixing zone around the internal envelope. In this case, as in the case of the installations according to the first and the second type, the mixing zone is not swept by hot gases.

In the three types of installation described, the drying is carried out by circulation of gases against the current of the aggregates and the mixing in an area which is not traversed by any current of hot gases.

In addition, the volume of the kneading zone is significantly greater than the volume of the materials present at a given time in this zone. The mixing is carried out by blades integral with a rotary drum the axis of rotation of which is directed in the direction of circulation of the materials.

However, such installations have never been used to implement a process for the production of bituminous mixes by tempering or so as to maintain the materials being coated for a certain period of time, inside the mixing zone.

The object of the invention is therefore to propose a process for manufacturing bituminous coated products from aggregates and bitumen, in particular for paving roads, which consists in continuously introducing cold aggregates into a drying zone. and humid, to circulate the aggregates and hot gases, against the current with respect to each other in the drying zone, to introduce continuously, without intermediate storage, the dried and heated aggregates leaving the drying zone in a mixing zone not traversed by hot gases, to incorporate liquid bitumen into the aggregates in the mixing zone, to circulate the aggregates in the mixing zone, and to mix them with the liquid bitumen during their circulation towards one end of exit from the kneading zone thanks to kneading members secured to a wall mounted to rotate about an axis directed in the direction of circulation of the aggregates, in the mixing zone, this process being able to be implemented in a completely continuous manner, with maintenance of the materials in the mixing zone during certain phases of the manufacture or alternatively batchwise.

For this purpose, at least during certain stages of the production, the aggregates are maintained during coating in the mixing zone by closing a means of evacuation communicating with the exit from the mixing zone.

The invention also relates to a device for the continuous or batch production of bituminous coated products, from aggregates, bitumen, powders and possibly recycled materials.

In order to clearly understand the invention, a description will now be given, by way of nonlimiting example, with reference to the attached figures, of a method according to the invention using an installation of the first type described above, for the manufacture of bituminous coated products continuously or discontinuously.

FIG. 1 is a schematic view in axial section of a counter-current coating dryer drum.

FIG. 2 is a view in axial section of the mixing zone and of an evacuation device provided with a means for closing a counter-current drum allowing the implementation of the invention.

Figure 3 is a cross-sectional view along 3-3 of Figure 2.

Figure 4 is a schematic view of a coating station implementing the invention for the manufacture of bituminous coated products continuously or discontinuously.

In FIG. 1, we see a coating dryer drum of the countercurrent circulation type constituted by a cylindrical casing 2 mounted on a platform 1 so that the axis of the cylindrical casing is slightly inclined relative to the horizontal plane. The inlet end 2a of the drum through which an introduction device 3 for cold and wet aggregates 4 enters is at a level higher than the outlet end 2b through which a burner enters 5 having an elongated body 5a disposed axially inside the drum 2.

The inner surface of the casing of the drum 2 is provided with vanes for transporting and / or lifting solid materials in the drum.

In a first zone, the drum comprises fins 6 for introducing the material in a helical shape and ensuring rapid transport without lifting the cold and wet aggregates 4 to the drying zone 7 of the drum in which the inner surface of the envelope the drum is lined with material lifting vanes.

The elongated body 5a of the burner 5 is disposed inside a cylindrical casing 8 secured to the drum 2 and fixed coaxially with respect to this casing.

The end of the burner body 5a from which the flame 9 develops is placed substantially in accordance with the end of the casing 8 around which fins 11 are fixed inclined with respect to the longitudinal axis of the drum and placed in radial directions relative to the casing of the drum, so as to constitute a turbine during the rotation of the casing of the drum 2 about its axis.

In the zone 10 of the drum or flame zone in which the flame 9 develops, the interior surface of the drum casing is lined with screen vanes 12 making it possible to transport the solid materials in contact with the wall of the drum and isolated from the flame which they avoid direct contact and radiation.

The drum 2 is surrounded in the zone 10 by a recycling ring 13 making it possible to introduce recycled bituminous materials 14 in the flame zone 10 of the drum.

Following the flame zone 10, in the direction of the outlet end 2b, the casing of the drum 2 carries, on its internal surface, material lifting vanes up to the upper level of the drum, during its rotation . The solid materials lifted by the lifting vanes fall back across the entire section of the drum to form a dense curtain of materials in zone 15.

Following zone 15, the drum 2 has, on the internal surface of its envelope, stirring vanes over the entire length of a zone 16 constituting the kneading zone of the drum, at the entrance of which a lance launches. bitumen injection 17.

A screw conveyor 19 makes it possible to introduce a pulverulent material into the kneading zone 16 in order to adjust the content of fine-grained materials of the coated materials produced.

The mixing zone 16 extends to the outlet end 2b of the drum which opens into a device 20 for evacuating coated bituminous products 21. The evacuation device 20 communicates, by means of a chute, with the inlet end of a scraper conveyor 22 ensuring the transfer of the coated materials to a storage silo.

The hot gases from the flame zone 10 circulate in the drying zone 7 in the direction of the inlet end 2a of the drum, in the direction of the arrow 22, to reach a manifold 23 ensuring the evacuation of the gases to a filtration installation.

The cold and wet aggregates are introduced into the drying zone 7 by the fins 6 and then flow against the current with respect to the hot gases in this area so as to be gradually dried and heated (direction of flow given by arrow 24).

The dried and heated virgin aggregates are then transported by the screen vanes 12, along the length of the flame zone 10 in which they are overheated then mixed with the recycled materials 14 before being introduced into the zone 15 where the solid materials fall back down. throughout the drum section constitute a dense curtain isolating the mixing zone 16 from the flame zone 10.

The point of introduction of the bitumen by the lance 17, at the entrance to the mixing zone 16, is thus protected against the radiation of the flame.

If bitumen vapors are formed in the mixing zone, these vapors are sucked in by the fins 11 constituting a turbine and discharged into the flame zone 10 where they undergo complete combustion.

In the part of the flame zone 10 located downstream of the recycling ring 13, the overheated virgin materials are mixed with the recycled material particles 14, so that the bitumen of the recycled material particles begins to melt and makes a pre - coating of virgin aggregates mixed with recycled materials.

The solid materials introduced at the entrance to the kneading zone 16 therefore consist of pre-coated and hot particles in which liquid bitumen introduced by the lance 17 is incorporated.

The mixing zone 16 is not traversed by hot gases, the gases from the flame zone being directed towards the inlet end 2a of the drum.

In addition, the presence of zone 15 in which a curtain of materials is made up makes it possible to perfectly isolate the kneading zone 16 from the zone flame and to avoid degradation of the bitumen under the effect of heat and radiation of the flame.

In counter-current drums known from the prior art, the coated materials 21 leaving the drum are continuously discharged

Referring to Figures 2 and 3, we will now describe a closure means associated with the discharge device of a counter-current drum for discharging the materials at the outlet of the mixing zone of the drum, so continuous or discontinuous.

In Figures 2 and 3, there is shown the outlet end of a coating dryer drum 30 against the current, this outlet end opening into a manifold 31 connected to a chute 32 at an opening 31a passing through the manifold wall 31.

A burner 35 comprising an elongated body penetrates axially into the drum 30 by its outlet end opening into the manifold 31. The burner 35 is capable of developing a flame inside the drum 30, in a zone remote from the ends of the drum, as in the case of the counter-current drum shown in Figure 1 which has been described above. The mixing zone 33 is arranged inside the end part of the drum 30 shown in FIG. 2.

A liquid bitumen injection lance 36 is also engaged in the drum by its outlet end, the end 36a of this lance ensuring the spraying and spreading of the liquid bitumen being arranged at the entrance to the mixing zone 33, considering the direction of circulation of the solid materials in the drum (arrow 34).

A screw device 37 penetrating through the outlet end of the drum makes it possible to introduce pulverulent materials into the mixing zone of the drum. slightly downstream from the end 36a of the bitumen injection lance 36. It is thus possible to adjust the content of fine-grained elements of the mixes produced in the drum.

In the mixing zone, the casing of the drum carries on its inner surface, mixing and mixing fins 39 ensuring the mixing of the solid materials entering the zone 33 and the liquid bitumen, so as to achieve an effective coating of the particles. solid by bitumen.

The solid particles arriving in the zone 33 are preferably constituted, as in the case of the drum shown in FIG. 1, by pre-coated aggregates mixed with particles of recycled materials whose bitumen has been remelted under the effect of the heat of the flame and by mixing with overheated virgin aggregates.

Preferably, the mixing zone 33 is isolated from the flame zone, by a zone of the drum disposed upstream from the end 36a of the bitumen lance 36 and comprising lifting vanes, so as to constitute a dense curtain of particles falling throughout the drum section, during its rotation. In this way, the bitumen introduction point and the mixing zone 33 are perfectly isolated from the burner flame. In addition, when the burner 35 is placed inside an envelope integral with the drum 30 and carrying turbine blades at its end, these turbine blades provide additional insulation of the mixing zone with respect to the mixing zone. flame and ensure the extraction of vapors of bitumen possibly formed in the mixing zone 33.

The coating of the solid particles 40 in the mixing zone 33, by mixing these particles with the liquid bitumen and mixing by the mixing blades 39, is carried out under good conditions, although no external heat source such as a flow of hot gases is not present in the zone 33, thanks to the fact that the solid particles are at a high temperature at the entrance to the zone 33. These particles store an amount of heat which is sufficient to ensure a good coating by kneading with liquid bitumen in zone 33, for a sufficient time to ensure a perfectly homogeneous composition of the mixes.

The outlet end of the drum 30 disposed inside the collector 31 carries discharge blades 41 carrying out a slight lifting of the coated materials 40 when the drum is rotating in the direction of the arrow 42 (FIG. 3), so as to ensure the evacuation of these coated products 40 via the opening 31a of the collector 31 and of the chute 32.

According to the invention, a closing means 45 is disposed at the opening 31a, so as to ensure the retention of solid materials 40 in the mixing zone 33, that is to say throughout the duration of the manufacture of these products (manufacture by batch), or during certain phases of manufacturing (continuous drum operation).

The device 45 comprises a hatch 46 of the guillotine type which is applied, in the closed position, to the external surface of the manifold 31, at the opening 31a. The hatch 46 constituted by a flat plate is integral with the end of the rod 47 of an actuating cylinder 48 of the device closing. The body of the actuator 48 is fixed by a lug 49 on the manifold 31. The hatch 46 is mounted movable in translation inside the chute 32, by means of slides 44 fixed on the interior wall of the chute.

In its position shown in Figure 3, the closure means 45 ensures the closure of the opening 31a of the manifold 31, the cylinder rod being in its extracted position. By actuating the jack 48 in the direction of retraction of its rod inside the jack body, the hatch 46 can be moved, so as to release the opening 31a. The coated materials 40 raised by the discharge blades 41 can then be poured into the chute 32 in which the flow of particles of coated materials is slowed down and regulated by a blade made of flexible material 51.

The device according to the invention thus makes it possible to operate the drum with a continuous evacuation of the bituminous coated products or with a retention of these products in the mixing zone, during at least certain phases of manufacturing.

In FIG. 4, there is shown a counter-current coating dryer drum 50 according to the invention comprising a closure means 52 associated with the device for removing the coated products disposed at the outlet of the mixing zone 53 of the drum.

The closure means 52 with two positions makes it possible to ensure either the continuous evacuation of the coated products in its open position, or a retention of the coated products in the mixing zone 53, in its closed position.

The coating station in which the drum 50 is used conventionally comprises a set of metering hoppers 54 consisting of four hoppers 54a, 54b, 54c and 54d arranged one after the other above a handling means 55, in the direction of circulation of this handling means ensuring the supply of the device 56 for introducing cold and wet aggregates into the drum 50. The introduction device 56 is produced under the shape of a weighing conveyor equipped with a weighing table 57.

The coating station also includes at least one storage hopper for recycled materials 58 connected by a handling device to the recycling ring of the drum 50, a storage hopper 59 for powdery products connected by means of a hopper weighing machine 60 and a handling means to the device for introducing pulverulent materials into the mixing zone of the drum as well as a tank for storing and maintaining the temperature of the liquid bitumen 62 connected via a pipe on which is arranged a pump 63 and an indicator 64 of the quantities of bitumen supplied to the lance for injecting bitumen into the drum.

The hoppers 54 and 58 have, at their lower part, devices for extracting particles, the flow rate of which can be adjusted by controlling a motor, by means of a computer 65 ensuring the control and adjustment of the coating station. .

The computer 65 receives, as permanent input data, before an asphalt production operation, the formula for the asphalt mixes whose manufacture is started, the quantity to be produced and possibly the flow rate of the installation in the case of operation. continuously (arrows 66, 67 and 68 respectively).

The computer 65 also receives, as variable input data, the instant indication of the weighing table 57.

The computer 65 controls the organ closure 52 located at the outlet of the mixing zone of the drum 50.

In the case of a continuous manufacturing operation of coated products, using the coating station shown diagrammatically in FIG. 4, the drum is supplied with cold and wet aggregates, the particle size composition of which is perfectly defined, by mixing of aggregates having different particle size compositions contained in the hoppers 54a, 54b, 54c and 54d.

The computer controls the output flow as well as the start time of each of the metering hoppers containing aggregates of defined particle size. The particle size composition is introduced into the computer 55 at the same time as the mix formula (arrow 66).

At the start of the installation, the device for extracting the dosing hopper 54a is started first, the device for extracting the second dosing hopper 54b being put into operation after a time T1 following the start of the device for extracting the metering hopper 54a. The time T1 corresponds to the time taken by the aggregates coming from the hopper 54a to arrive below the dosing hopper 54b.

Likewise, the hopper 54c is put into operation at the end of a time T2 following the start of the hopper 54b and the hopper 54d is put into operation after a time T3 following the start of the hopper 54c .

The sequential operation of the metering hoppers ensures a correct composition of the mixture of aggregates from the start.

The metering of the binder introduced into the injection lance by the pump 63 is carried out according to the indications of the weighing table 57 transmitted to the computer 65. The bitumen flow rate to be supplied at any time is determined according to the indication on the weighing table, taking into account the estimated water content of the aggregates, the proportion of bitumen being defined relative to the aggregate flow rate dry.

The recycled materials and the pulverulent materials are introduced into the drum in metered quantities, according to the formula of the coated materials introduced into the computer 65 and independently with respect to the dosage of the aggregates. The computer controls the motor of the device for extracting the hopper for storage of recycled materials 58 and a motor for controlling a device for extracting from the weighing hopper 60 receiving the pulverulent materials.

In the manufacturing start-up and shutdown phases, the device for extracting recycled materials and the device for extracting pulverulent materials are put into operation or stopped, at a determined time, depending on their position in the station. material storage and transport time, so that the material flows meet in the drum at the desired time to ensure a satisfactory and constant composition of the mixture.

Depending on the overall flow rate requested by the operator (arrow 68), the computer defines the flow rate of the extraction device of each of the dosing hoppers as well as the operating time of each of the extraction devices to obtain the quantity of coated products wanted.

Transient regimes are observed at the start and at the end of manufacturing which are due to the volume effect of the drum and which result in deviations in the composition of the mixes produced during these manufacturing phases compared to the composition formula. desired. Therefore, it is necessary to reject a certain quantity of products at the start and at the end of manufacture because, in these phases, the materials do not all advance at the same speed in the drum, the outlet of which is free.

When the coating plant operates in continuous mode, the quantities to be manufactured are very large and the manufacturing "head" and "tail" effects are proportionately negligible.

When the coating station is used to produce small quantities of coated materials, the control and regulation of the material flows is carried out in the same way as in the case of continuous production of large quantities of coated materials. The operating time of the coating plant is however much shorter, so that the effects of the transient regimes at the start and at the end of manufacture become very significant or even preponderant.

By implementing the process according to the invention, large quantities of material are avoided, these quantities possibly being equivalent to or even greater than the quantities of materials having a given composition, the manufacture of which is ensured.

At the start of manufacturing, the computer 65 controls the closing position 52 of the closing member 52 located at the outlet of the mixing zone 53. The function of the closing member 52 is to prevent the materials from leaving the drum before they are completely coated and homogenized. The solid materials arriving first in the mixing zone are retained until the arrival of the following materials, the composition of which may be different, under transient conditions.

The closing time of the member 52 is adjusted to a value such that the coated materials produced and retained in the mixing zone 53 have a perfectly homogeneous composition and in accordance with the chosen formula. This operation is similar to the operation of mixers of batch type coating devices.

To switch from an operating mode with continuous material evacuation to an operating mode with material retention in the mixing zone, it is therefore sufficient to command the closing of the guillotine register such as the register 46 shown in FIGS. 2 and 3 constituting the closing member 52. The adjustment and the control of the coating station is also quite similar in the case of an operation with continuous evacuation and in the case of an operation with retention of materials. coated in the mixing area.

At the end of manufacture, when the materials are perfectly coated and have a completely homogeneous composition, the closing member 52 is placed in the open position and the materials are evacuated via the outlet chute of the collector into which the end of the drum opens.

This avoids any manufacturing rejection in the event that the quantities of coated materials to be produced are low.

When the member 52 is placed in its closed position, throughout the manufacturing (supply of materials, drying and kneading) the drum 50 operates so as to produce coated materials batchwise and by tempering.

The counter-current drum 50 of the device according to the invention also has the advantage of comprising a kneading zone which is not traversed by hot gases and which is completely isolated from the flame zone. The quantities of heat brought into this mixing zone therefore correspond only to the heat stored by the solid materials entering the mixing zone.

The mixing zone of the drum therefore functions in the same way as a batch mixer into which heated and dried aggregates and liquid bitumen are introduced.

In the case of continuous operation of the coating station, it may be advantageous to place the member 52 in its closed position, during certain stages of manufacture.

For example, if the member 52 is closed for a certain time at the start of production, it is possible to eliminate the losses of materials due to the rejections of the mixes produced in transient regime, during the start-up phase.

Likewise, if the member 52 is closed before the end of the period of continuous operation of the installation, the "tail" part of the production constitutes a waste which is homogenized in the kneading zone, which eliminates a manufacturing loss due to rejection of this terminal part of manufacturing.

It is also possible to envisage an operation of the drum by successive mixes circulating one after the other inside the drum. In this case, it is necessary to provide sufficient spacing between two batches to avoid any mixing between successive batches which may have different compositions.

The device according to the invention therefore makes it possible to use a coating station of the conventional type, usually reserved for the manufacture of large quantities of coated materials, for the production by mixing of small quantities of coated materials.

The invention is not limited to the embodiment which has been described.

Thus the mixing zone isolated from the burner flame can be delimited by an envelope different from the envelope of the drum itself. This mixing zone can be delimited by a fixed mixer envelope disposed around an end portion of the drum carrying mixing blades directed towards the outside.

The closing means of the evacuation device placed at the outlet of the mixing zone can be produced in a different form from a movable register in translation of the guillotine type. This closing means can be constituted for example by a register in the form of a portion of a cylinder mounted to pivot and associated with a control device such as a jack.

The counter-current drum of the device according to the invention may have a shape different from that which has been described and include means for isolating the mixing zone from the flame zone different from those which have been described. In all cases, however, the flame zone must be arranged upstream of the mixing zone, so that this mixing zone is not traversed by a current of hot gases.

The invention can be applied not only in the case of an installation comprising a single counter-current drum into which a burner having an elongated body penetrates, as has just been described, but also in the case of installations of the second and third types described above.

In the case of an installation of the second type comprising a dryer drum and a mixing drum, the outlet of the mixing drum is equipped with a closing device making it possible to achieve a more or less prolonged maintenance of the materials in the mixing zone.

In the case of an installation of the third type comprising a double-envelope drum, the outlet of the fixed external envelope in which the kneading takes place can be closed by a hatch preventing, in at least certain phases of manufacture, the outlet coated products. It is thus possible to adjust the mixing time so as to obtain coated products of perfectly homogeneous composition, in the case of production by tempering as well as during the initial and final transient phases, in the case of continuous production.

The process according to the invention can be used for the production of bituminous coated products in large quantities, continuously, or in small quantities, by mixing.

This process makes it possible to manufacture bituminous coated products from virgin aggregates, liquid bitumen and pulverulent in any dosage, with or without the addition of recycled used bituminous materials.

Claims (12)

1.- Process for the production of bituminous coated products from aggregates and bitumen, in particular for paving roads, consisting of continuously introducing cold and wet aggregates (4) into a drying zone (7) , to circulate aggregates and hot gases, against the current with each other in the drying zone, to introduce continuously, without intermediate storage, the dried and heated aggregates leaving the drying zone (7) in a mixing zone (16, 33, 53) not traversed by hot gases, incorporating liquid bitumen into the aggregates in the mixing zone (16, 33, 53), circulating the aggregates in the mixing zone ( 16, 33, 53), and kneading them with liquid bitumen during their circulation towards an outlet end of the kneading zone thanks to kneading members secured to a wall mounted to rotate around an axis directed in the direction circulation of ag regattas, in the mixing zone (16, 33, 53), characterized in that, at least during certain phases of production, the aggregates are maintained during coating in the mixing zone by closing a means evacuation (20, 21, 31, 32) communicating with the outlet of the mixing zone (16, 33, 53). 2.- Manufacturing process according to claim 1, characterized in that the cold and wet virgin aggregates (4) are introduced into the drying zone (7) and the liquid bitumen and possibly a pulverulent product and used bituminous materials recycled in the mixing zone (16, 33, 53), continuously and in metered quantity, for a period of time sufficient to ensure production a determined quantity of coated products and that the products are kept in the mixing zone (16, 33, 53) throughout the introduction period and for a sufficient time to ensure the production of a load of coated products of homogeneous composition. 3.- Manufacturing process according to claim 1, wherein the cold and wet virgin aggregates (4) are introduced into the drying zone (7) and the liquid bitumen and optionally a pulverulent material and used bituminous materials recycled in the zone mixing (16, 33, 53), continuously and in metered quantities, the coated products being continuously discharged at the outlet of the mixing zone (16, 33, 53) during manufacture, characterized in that, in certain phases of manufacture, in transient mode, the means for removing coated products (20, 21, 31, 32) are closed, so as to homogenize the products being coated in the mixing zone (16 , 33, 53). 4.- Method according to claim 3, characterized in that the phases in transient mode during which the means for removing coated products (20, 21, 31, 32) is closed correspond to the phases of production start. 5.- Method according to claim 3, characterized in that the phases in transient mode during which the means for removing coated products (20, 21, 31, 32) is closed correspond to the phases of production stop. 6.- Device for the production of bituminous coated products from aggregates and bitumen, in particular for paving roads, comprising a drying and coating drum (2) having a cylindrical envelope (2, 30) rotatably mounted around its axis slightly inclined with respect to the horizontal plane and comprising an inlet end (2a) into which opens a device (3) for supplying cold and wet aggregates (4) and an outlet end (2b) situated at a level below the level of the end d inlet (2a), a burner (5, 35) having an elongated body introduced axially by the outlet end (2b) of the drum (2), so that its end from which a flame develops ( 9) is located in a zone remote from the ends of the drum (2, 30), blades for lifting aggregates in the drum during its rotation fixed on the internal wall of the drum (3) in a drying zone (7) located between the end of the burner (5) and the inlet end (2a) of the drum as well as mixing blades (39) fixed to the wall of the drum (2) in a mixing zone (16, 33, 53) opening into a device (20, 21, 31, 32) for evacuating bituminous coated products (40), characterized in that e the mixing zone (16, 33, 53) is isolated from the flame (9) and from the hot gases circulating against the current of the aggregates in the drying zone (7) and that the device (20, 21, 31, 32) for evacuating bituminous products (40) at the exit from the mixing zone (16, 33) comprises a closure means (46, 52) with two positions associated with control means (48) for its movement between a first closed position and a second open position allowing the evacuation of the products (40), either discontinuously, the closing means (46, 52) remaining in its closed position during at least certain phases of the operation of manufacturing of bituminous products, either continuously, the closure means (46, 52) being constantly in its open position. 7.- Device according to claim 6, characterized in that the drum (2) comprises in a zone (15) located between the flame zone (10) and the mixing zone (16), lifting vanes making it possible to produce a dense curtain of materials throughout the section of the drum insulating the mixing zone (16) from the flame zone (10). 8.- Device according to any one of claims 6 and 7, characterized in that the closing means (46) of the discharge device (31, 32) located at the outlet of the mixing zone (33) is constituted by a guillotine type register, movable in translation between the closed position in which the register (46) covers an opening (31a) for passage of the coated products (40) and an open position in which the register (46) releases the opening (31a) for passage of the coated products (40). 9.- Device according to any one of claims 6 to 8, characterized in that the device for removing the coated products (40) is constituted by a collector (31) of cylindrical shape in which is engaged the end of outlet of the drum (30) and comprising an opening (31a) passing through its wall and via a discharge chute (32) communicating with the internal volume of the collector (31) via the opening (31a), the closing member (46) being constituted by a movable register between a closed position and an open position of the opening (31a) putting the collector (31) into communication with the chute (32). 10.- Device according to claim 9, characterized in that the drum (30) carries at its outlet end engaged in the manifold (31), discharge blades (41) of the coated products (40), by lifting of these products in the collector, up to the level of the opening (31a). 11.- Device according to any one of claims 6 to 10, characterized in that it further comprises a device (19, 37) for introducing pulverulent materials into the mixing zone (16, 33). 12.- Device according to any one of claims 6 to 11, characterized in that a recycling ring for used bituminous materials (13) is arranged around the casing of the drum (2) in a zone located downstream of the drying area (7) for the virgin aggregates.

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