FR2682308A1 - Method and station for coating aggregates with bitumen and fibres, especially glass fibres, and device for incorporating a particular product into the bitumen - Google Patents

Abstract

The glass fibres are incorporated with the hot bitumen just before it is injected onto the aggregates. In order to do this, the bitumen is injected as a cone in a cylindrical box (21) into which is introduced tangentially a flow of air containing the fibres. Applications to the preparation of bitumen-coated chippings intended for surfacing (carpeting) roadways.

Description

 The present invention relates to the preparation of bituminous mixes used for coating pavements.

This preparation can be carried out in two different types of coating stations:
(a) on the one hand, discontinuous stations, where a load of hot and dry aggregates is poured into a mixer, then a metered amount of hot bitumen is injected onto these aggregates, and the assembly is mixed for a predetermined time then removed from the mixer;
(b) on the other hand, continuous stations, comprising an inclined rotary drum with lifting vanes divided into two successive zones by a diaphragm. The aggregates, introduced at the upper end of the drum, are heated and dried in the upstream zone, and the hot bitumen is injected just behind the diaphragm, the downstream zone carrying out the mixing.

 It is known that the addition of fibers makes it possible to increase the quantity of bitumen which can coat a given quantity of aggregates, and consequently to improve certain mechanical properties of the coated materials.

 In the usual technique, asbestos fibers are used, which mix easily with hot and dry aggregates.

 Environmental problems linked to asbestos have led the Applicant to raise the problem of replacing asbestos fibers with other fibers having similar mechanical properties, in particular glass fibers.

 However, tests have shown that instead of mixing uniformly with the aggregates, the glass fibers gather in lumps, which makes it impossible to obtain a homogeneous distribution of the fibers in the mixes.

 The invention aims to allow the coating of aggregates with bitumen and glass fibers.

 To this end, the subject of the invention is a process for coating aggregates with bitumen and fibers, in particular glass fibers, characterized in that the fibers are incorporated into the hot bitumen, then the bitumen mixture is injected -fibers on the aggregates, then we knead everything.

According to other characteristics
- The fibers are incorporated into the bitumen just before said injection;
- The fibers are transported pneumatically to the point of incorporation of the fibers in the bitumen, the transport air possibly being heated;
- The process being of the intermittent type, the air flow without fibers is maintained beyond the bitumen injection time, this air flow possibly being maintained permanently.

 The invention also relates to a station for coating aggregates with bitumen and fibers, in particular glass fibers, intended for the implementation of such a process. This station, of the type comprising a mixer, means for projecting aggregates into this mixer, and means for projecting hot bitumen onto the aggregates, is characterized in that the projection means comprise a box for incorporating fibers into hot bitumen with a bitumen supply and a fiber supply.

According to other characteristics
- the fiber supply is connected to a pneumatic transport pipe, possibly supplied with hot air;
the fiber supply opens tangentially into the incorporation box, which is cylindrical and open downwards;
- the bitumen supply includes a central nozzle producing a bitumen jet roughly in the form of a cone coaxial with the box;
- the bitumen supply comprises an axial pipe which opens onto the top of a conical deflector, a free annular space being delimited between the base of this deflector and the cylindrical wall of the incorporation box;
- the coating station being of the intermittent type with two parallel kneading screws, this station comprises a row of incorporation boxes above each screw;
- the coating station being of the continuous type in which the mixer is an inclined rotary drum with lifting vanes divided into two successive zones by a diaphragm, the incorporation box is mounted in a fixed position a short distance downstream of the diaphragm.

 The invention also relates to a device for incorporating a particulate product into bitumen which can be fitted to a coating station as defined above.

In a first embodiment, more particularly suitable for a discontinuous coating station, this device comprises
- a cylindrical box open downwards;
- a bitumen supply line connected to a source of bitumen and opening axially downwards into this box, this line ending with a nozzle adapted to produce a jet of bitumen of roughly conical shape; and
a pneumatic pipe opening tangentially into the box, this pipe being connected to a source of compressed air and being equipped with means for metered and selective introduction of said particulate product.

In a second embodiment, more particularly suitable for a discontinuous coating station, the incorporating device comprises
- a cylindrical box open downwards;
- a bitumen supply line connected to a source of bitumen and opening axially downwards in this box opposite the top of a deflector cone fixed in the box, the base of this cone delimiting with the cylindrical wall of the box a free annular space; and
a pneumatic pipe opening tangentially into the box, this pipe being connected to a source of compressed air and being equipped with means for metered and selective introduction of said particulate product.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which
- Figure 1 is a schematic top view of a discontinuous coating station according to the invention;
- Figure 2 is a sectional view along the line II-II of Figure 1;
- Figure 3 is a schematic view in longitudinal and vertical section of a continuous coating station according to the invention; and
FIG. 4 is a view in axial section, on a larger scale, of the device for incorporating the fibers in the bitumen used in the coating station of FIG. 3.

 FIGS. 1 and 2 show a coating station of the discontinuous type comprising two kneading screws 1, 2 which interpenetrate and rotate around respective parallel horizontal axes 3, 4 inside a casing 5. These screws are shown schematically only by their axes in Figure 1 for clarity of the drawing.

 The bottom of the casing 5 forms two channels 6, 7 to match the lower region of the two screws, and is provided along its axis of symmetry with a shutter 8 having a quarter disc section and rotatably mounted around its axis 9, which is parallel to axes 3 and 4. When this flap is in its closed position illustrated in solid lines in Figure 2, its cylindrical surface 10 connects approximately tangentially the inner edges of the two channels 6 and 7 .

Devices 11, 12 for injecting bitumen and glass fibers, associated respectively with the two screws 1 and 2, are mounted in the casing 5. Each of these devices comprises
- A ramp 13 for spraying hot liquid bitumen extending parallel to the respective axis 3, 4 and located in the vicinity of the vertical alignment of this axis, but somewhat offset towards the outside with respect to this vertical alignment. The ramp 13 comprises at regular intervals nozzles 14 directed approximately towards the axis 3, 4. The two ramps 13 are connected, outside the casing 5, to a pipe 15 for supplying bitumen itself connected via a pump 16 to a bitumen tank 17;
- A ramp 18 for feeding glass fibers pneumatically. This ramp comprises a horizontal manifold 19 which runs along the corresponding side wall of the casing 5, and, for each nozzle 14 of the corresponding ramp 13, a pipe 20 which leaves at an acute angle from this manifold and opens tangentially in a cylindrical box 21 coaxial with the sprinkler. The box 21 is open at the bottom, and its upper bottom is crossed in its center by the nozzle, which therefore opens into the inside of this box. Line 20 opens near this upper bottom.

 The two collectors 19 are connected, outside the casing 5, to a common supply line 22 equipped with an air compressor 23. Downstream of this, a hopper 24 containing glass fibers 25 can deliver in line 22, via a motorized metering device 26, for example of the cell type, a metered flow rate of glass fibers in the air stream.

 The operation of the discontinuous coating station thus described is as follows.

 At the start of a cycle, the casing 5 is empty, the flap 8 is in its closed position shown in solid lines in FIG. 2, and the pump 16, the compressor 25 and the metering device 26 are stopped.

 The screws 1 and 2 being in rotation, an appropriate aggregate load, for example of 2 tonnes, is poured into the casing 5 by known means not shown. The pump, compressor and metering device are started.

 Each nozzle 14 then projects a jet of hot liquid bitumen which, by virtue of the constitution of the nozzle, substantially forms a cone whose diameter, at its outlet from the box 21, is close to the inside diameter of the latter. Simultaneously, a stream of air and glass fibers tangentially enters the box 21 via the line 20 and, following a helical path therein, is incorporated into the sprayed bitumen. The bitumen-fibers mixture is thus projected onto the aggregates, and screws 1 and 2 knead everything.

 After a predetermined time, the pump and the metering device are stopped, then the flap 8 is tilted from 1800 to its open position shown in phantom in Figure 2, in order to evacuate from the casing 5 the mix charge thus prepared. Finally, the flap 8 is returned to its closed position, and a new mix preparation cycle can begin.

 To avoid any accumulation of fibers in the lines 19, 20 and 22, the air flow is maintained for a certain period after the metering device 26 has stopped. Optionally, this air flow is maintained permanently, and the fibers They are simply introduced there during the bitumen injection periods.

 It was found that a substantially homogeneous, and in any case entirely satisfactory, distribution of the glass fibers in the mix was obtained in this way.

 Figures 3 and 4 show the application of the invention to a coating station of the continuous type.

 Such a station comprises a large drum 27, for example 12 meters long and 2.5 meters in diameter, open at its two ends and having an inclined X-X axis. This drum is rotated at constant speed (arrow F1) by means not shown.

 The drum 27 has internally, over its entire length, lifting vanes 28, and, at an intermediate point of its length, an annular throttle diaphragm 29. A fixed burner 30 of axis XX is mounted at the upper end of the drum, and a box 21A for injecting bitumen and glass fibers is fixedly mounted a short distance downstream of the diaphragm 29.

 Box 21A, shown in Figure 4, has the same general construction as box 21 in Figures 1 and 2, and is supplied with hot liquid bitumen and glass fibers by the same means 15 to 17 and 22 to 26.

However, the bitumen pipe 13A which penetrates axially into the box 21 is devoid of nozzles and opens opposite the top 31 of a conical deflector 32 positioned coaxially in the box by support rods 33. At its lower end, this cone has a diameter smaller than the inside diameter of the box 21A, so that there is a free annular space 34 between these two members. The pneumatic glass fiber supply line 20A opens tangentially into the box 21A at an intermediate level of the cone 32.

 This difference in structure between the boxes 21 and 21A is explained by the fact that in the continuous station, there is provided a single box, which is therefore of dimension considerably greater than the multiple boxes of Figures 1 and 2. It is therefore preferable to positively create a cone of liquid bitumen, rather than creating such a cone by means of a nozzle producing a flared jet.

 In operation, the aggregates are introduced continuously into the upper end of the drum 27 (arrow F2). During their passage through the upstream part of the drum, that is to say to the diaphragm 29, these aggregates are dried and heated by the flame 35 of the burner 30. The box 21A injects these dry and hot aggregates, at a short distance after the diaphragm, the bitumen-glass fiber mixture, and the whole is kneaded in the downstream part of the drum, until forming a mix which is continuously poured out by its lower end (arrow F3).

 Of course, in the case of such a continuous station, the supply of the box 21A with bitumen and glass fibers conveyed by air is carried out continuously.

 The diaphragm 29 has the functions on the one hand of densifying the aggregates before they are coated, and on the other hand of protecting the box 21A and the products leaving it from the flame 25.

 It should be noted that the air transporting the glass fibers can be at room temperature or heated.

Claims (13)

 1 - Process for coating aggregates with bitumen and fibers, in particular glass fibers, characterized in that the fibers are incorporated into the hot bitumen, then the bitumen-fibers mixture is injected onto the aggregates, then kneading the whole thing.  2 - Process according to claim 1, characterized in that the fibers are incorporated into the bitumen just before said injection.  3 - Process according to claim 1 or 2, characterized in that the fibers are transported pneumatically to the point of incorporation of the fibers in the bitumen, the transport air being optionally heated.  4 - Process according to claim 3, of the intermittent type, characterized in that the air flow without fibers is maintained beyond the time of injection of the bitumen, this air flow possibly being maintained permanently.  5 - Station for coating aggregates with bitumen and fibers, in particular glass fibers, of the type comprising a mixer (5), means for introducing aggregates into this mixer, and means for spraying bitumen hot on the aggregates, characterized in that the projection means comprise a box (21; 21A) for incorporating fibers into the hot bitumen provided with a bitumen feed (13; 13A) and a feed (20; 20A) in fibers.  6 - Coating station according to claim 5, characterized in that the fiber supply (20; 20A) is connected to a pipe (22) for pneumatic transport, possibly supplied with hot air.  7 - Coating station according to claim 6, characterized in that the fiber supply (20; 20A) opens tangentially in the incorporation box (21; 21A), which is cylindrical and open downwards.  8 - Coating station according to claim 7, characterized in that the bitumen supply (13) comprises a central nozzle (14) producing a bitumen jet roughly cone-shaped coaxial with the box.  9 - Coating station according to claim 7, characterized in that the bitumen supply (13A) comprises an axial pipe which opens onto the top of a conical deflector (32), a free annular space (34) being delimited between the base of this deflector and the cylindrical wall of the incorporation box (21A).  10 - Coating station according to any one of claims 5 to 9, of the intermittent type with two parallel kneading screws (1, 2), characterized in that T it comprises a row of incorporation boxes (21) above each screw.  11 - coating plant according to any one of claims 5 to 9, of the continuous type in which the mixer is an inclined rotary drum (27) with lifting vanes (28) divided into two successive zones by a diaphragm (29), characterized in that the incorporation box (21A) is mounted in a fixed position a short distance downstream of the diaphragm.  12 - Coating station according to any one of claims 5 to 11, characterized in that the box for incorporating fibers in the hot bitumen comprises  - a cylindrical box (21) open downwards;  - a pipe (13) for supplying bitumen connected to a source of bitumen (17) and opening axially downward in this box, this pipe ending in a nozzle (14) adapted to produce a jet of bitumen in the form of almost conical; and  - A pneumatic line (20) opening tangentially into the box, this line being connected to a source of compressed air (23) and being equipped with means (24 to 26) for metered and selective introduction of said particulate product (25).  13 - Coating station according to any one of claims 5 to 11, characterized in that the box for incorporating fibers in the hot bitumen comprises  - a cylindrical box (21A) open at the bottom;  - a pipe (13A) for supplying bitumen connected to a source of bitumen (17) and opening axially downwards in this box opposite the top of a deflector cone (32) fixed in the box, the base of this cone delimiting with the cylindrical wall of the box a free annular space (34); and  - A pneumatic line (20A) opening tangentially into the box, this line being connected to a source of compressed air (23) and being equipped with means (24 to 26) for metered and selective introduction of said particulate product (25).