METHOD FOR PREVENTING SEPARATION DURING HANDLING OF MECHANICAL MIXTURES

TECHNICAL AREA The present invention relates to handling and prevention /limitation of separation of granular, mechanical mixtures during free fall loading or silos and in particular a method for designing and dimensioning of a unloading device so that optimal conditions regarding preventing/ limiting of separation, adherence and bridging are obtained.

The present invention also relates to a system for preventing separation of asphalt during the whole line from manufacturing to paving of a roadbed.

TECHNICAL BACKGROUND

Separation in technical sense is a process that in different ways and in different forms is activated in connection with handling of mechanical mixtures, such as for example asphalt compositions, dry mixes, fodder mixtures, containing material granulate of varying size, hereafter named material.

Separation leads to that different subsets of a manufactured and handled amount of material, e.g. a loading deck of a truck, will have different compositions regarding granular size, and that the composition will exceed the tolerance limits of the material receipt.

Regarding asphalt, separated asphalt compositions provide a result in paved roadway where fractions with larger stones are gathered in areas /spots /strips with a deficit of binder while other areas of the roadway to varying extent have a surplus of gravel/ filler/ binder.

The main deterioration and damages originating from separated asphalt compositions in paved and compacted roadway, specifically connected

to separation, relates to wear/ tracking where variations spot- wise and strip-wise depend on variations/ deviations of the composition of the material, local damages of the asphalt due to local accumulation of coarser granular material in combination with a deficit of binder, plastic deformation where variations usually depend on separation of the roadbed masses as well as uneven and/or reduced friction values.

Separation of material arises in varying extent in the different handling steps that can comprise mixer at the producer, transport from the mixer to a silo, free-fall loading to the silo, loading from silo to transport vehicle, loading from transport vehicle to silo at a user site as well as paving on roadway. The largest separation usually occurs during free- fall loading to silo at the producer where the material falls freely down into the silo.

In this context, falling height, the compartment in the silo perpendicular to the fall direction, the kinetic energy of the granular, differences in granular size, are decisive for the occurrence of separation. During free-fall loading to silo, this is done in a so called radial separation during build-up of a sloping slide surface with a cone centre in the middle of the silo. Larger, heavier granulates and particles slide, due to the larger kinetic energy and size, down along the cone surface and are placed further out as seen radially than the smaller and lighter granulates and particles. The movement of the latter is stopped along the cone surface closer to the centre due to lower kinetic energy and due to that the smaller granulates are stuck earlier in cavities in the cone surface.

In order to prevent or limit this radial separation during loading of a silo, a strive is to limit the radial dimension of the silo across the fall direction. A well functioning solution of this is described in the patent with publication number SE 0467215 where a silo is divided into a number of concentric compartments, each with a limited compartment

radially, i.e. across the fall direction. These concentric compartments block the material radially and prevent building of conical sloping surfaces.

Another problem that often occurs during unloading of the silo is that the material drops starting from the centre of the silo, vertically over the unloading opening. During continued unloading, the material is fed to the middle from the peripheral areas of the silo by material flows radially inward and downward, whereby very little "sliding" or movement is occurring along the inner wall of the silo. At the end of the unloading there is thus a risk that material remains at the lower part of the silo due to adherence against the wall and/ or due to bridging over the unloading opening. Such adherence /bridging increases the amount of reject material and requires maintenance and cleaning.

Regarding handling of asphalt to be used for paving roadways, it is not only a problem of separation during unloading of the silo. Separation is likely to occur as described above when the asphalt is tipped onto a deck of a truck for transportation to the road construction site.

Another situation where further separation is likely to occur is when the truck tips the asphalt into the hopper of the paver in the same way as described above. In all there are several occasions where separation is likely to occur, leading to inferior quality of the roadbed.

Another problem in connection with asphalt paving is that the asphalt is cooled, and in particular in the paver. The conventional paver hoppers have side walls that are pivotable from an inwardly inclined position to an outwardly inclined position, a sort of "wings". When the asphalt is to be tipped into the hopper, the side walls are pivoted into the outwardly inclined position in order to receive the asphalt. The feeding bands in the bottom of the hopper preferably feed the asphalt that is tipped above the bands. This means that a large extent of the

asphalt that were tipped on the sides of the feeding bands are fed to the bands later. These areas with asphalt will cool down and also form lumps. When the tipping of asphalt takes time, for instance due to change of truck in front of the paver, cool surfaces will occur in the hopper and sometimes the personnel controlling the paver folds the side walls in order to reduce the amount of cooled asphalt. However, this is not allowed since it creates a damage to the paved surface.

The cooled asphalt will then be fed by the feeding bands, which negatively affects the paved surface, giving a damaged paving. After a working day, there could be between 1 - 2 tons of asphalt remaining on the side surfaces of the hopper as "cold asphalt", which is completely unsuitable for use.

BRIEF DESCRIPTION OF THE INVENTION

One aim of the present invention is to further improve the above mentioned solution with a number of concentric compartments in order to obtain optimal quality of delivered mechanical mixes as well as reducing the maintenance costs.

Another aim of the present invention is to minimize separation along the whole asphalt handling line from production of asphalt to the paver.

The aims are obtained by a system according to the independent patent claim. Preferable embodiments of the invention are subject of the dependent patent claims.

According to a main aspect of the invention it comprises a system for preventing separation of asphalt compositions, comprising separation preventing compartments arranged in a silo, intended for loading of asphalt onto vehicles, separation preventing compartments intended to be arranged to a deck of a vehicle to be loaded with asphalt, and

separation preventing means arranged in a hopper of a paver to be loaded with asphalt from a vehicle.

According to another aspect of the invention, said separation preventing compartments of said silo comprises at least one compartment open in both ends and arranged centrally in said silo. Preferably the compartments comprise a number of tubular compartments arranged concentrically outside each other.

According to yet an aspect of the invention, said separation preventing compartments for a deck comprises a plurality of vertically arranged mainly longitudinally and transversally dividing walls forming a mesh of compartments .

Preferably said transversally extending dividing walls are arranged pivo tally around their upper edges.

Also preferably, it further comprises a cover capable of covering the asphalt when loaded onto the deck.

According to a further aspect of the invention, said separation preventing means arranged in a hopper of a paver, comprises side walls of said hopper that are inclined towards the bottom of said hopper.

Said hopper could either have a rectangular shape or circular shape as seen from above.

According to a further aspect of the invention, it further comprises guide means arranged in the upper opening of said hopper, capable of guiding asphalt that is loaded into said hopper through said opening towards the inclined side walls.

I could also have mainly vertically arranged guide plates arranged to said side wall.

The hopper could further be rotatably arranged to said paver.

According to yet an aspect of the invention, it comprises a method for dimensioning at least one separation preventing compartment used in the system according to claim 1 , which compartment is open in opposite ends thereof and intended to be placed in a silo comprising and upper opening and a conical lower part with at least one outlet opening, which method comprises dimensioning a compartment, intended to be arranged centrally in the silo, such that its diameter for a cylindrical silo is mainly between 1/5 to ¹ A of the diameter of the silo, alternatively between 1/5 to ¹ A of the side width of the silo for quadratic silo.

A great advantage with the present invention is that separation is prevented throughout the whole handling and transport line from producer to the paving site. This ensures a high quality of the asphalt that is paved on the roadway and the problems that conventional methods entail regarding inferior quality of the paved road is eliminated.

Thus the life of a road paved according to the present invention is greatly prolonged, leading to reduced costs for maintaining the roads in good condition. Since most roads are maintained and handled by government owned companies financed by different taxes, the cost for the whole society and country could be reduced with the present invention.

Further, due to the design of the paver hopper with sloping surfaces towards the feeding bands and the inclination of guide plates above the feeding bands, the risk of cold asphalt is eliminated in that no cool

surfaces can occur. The same applies for the circular hopper where the movement of the hopper in relation to a stationary guide plate adjacent the inner surface of the hopper "scrapes off' possible asphalt stuck there and onto the feeding bands.

These and other aspects of and advantages with the present invention will become apparent from the following detailed description and from the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed description of the invention, reference will be made to the accompanying drawings, of which

Fig. 1 shows schematically a longitudinal cross-section of a silo arranged with a number of concentrically arranged compartments according to one aspect of the invention,

Fig. 2a, b show cross-sections taken along line II-II of Fig. 1 , where Fig. 2a is a cylindrical silo and Fig. 2b is a quadratic silo,

Fig. 3 shows schematically a detailed view of an upper part of a silo comprising concentric central compartments,

Fig. 4 shows schematically the length relations between the length of the silo and the distance of the concentric central compartments to the upper part of the silo,

Fig. 5 shows schematically a detailed view of a lower part of a silo comprising concentric central compartments,

Fig. 6 shows the unloading of a silo arranged according to the invention,

Figs. 7a-c show a truck arranged with a separation preventing means according to another aspect of the present invention,

Figs. 8a-d show a cover that can be used in connection the separation preventing means according to Fig. 7,

Figs. 9a-b show a separation preventing means to be used with a paver having a rectangular hopper, and

Figs. 10a-b show a separation preventing means to be used with a paver having a circular hopper.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is intended to be used in for example a silo with optional circular or rectangular cross-section and with a central opening at the top for filling of material as well as at least one central opening at the bottom for unloading of material.

The silo 10, Fig. 1 is arranged with a number, at least one, concentrically arranged compartment 12, in the shown cases concentric tubes open in both ends, the longitudinal axes of which coincide with the longitudinal axis of the silo. The number of tubes depend on the size of the silo, such as will be apparent below.

During development of the above device for preventing separation of material, certain relations have been obtained that improve and/ or maintain the favourable features of the device regarding prevention of separation, adherence and bridging during both loading and unloading of material.

Preferably the silo is arranged with a trough-shaped or conical centrally placed inlet 14. The position of the upper ends of the tubes shall preferably start from the radius of the central tube. According to Fig. 3,

if the radius R of the tube is set as 1 , preferably the distance from the inlet of the silo to the upper edge of the central tube should be between 0,5 - 1,5 * R, more preferably between 0,7 - l,0*R and optimally 0,8*R. Further tubes placed concentrically outside the central tube shall have the upper edge between 0,4 - l,0*R, more preferably 0,5 - 0,7*R and optimally 0,6*R below the upper edge of the central tube. The same applies to further tubes that are placed 0,6*R below the upper edge of the adjacent inner tube.

Another way of dimensioning the length RL of the central tube is to start from the total length of the silo L, Fig. 4, where the length of the central compartment is adapted so that when placed in the silo, the upper edge of the central compartment is arranged at a distance X from the upper edge of the silo that is within an area in relation to the total length L between 1/ 17 and 1/2,75.

When a further concentric compartment is used, this is adapted such that when placed in the silo, the upper edge of the further concentric compartment is arranged at a distance Y from the upper edge of the central compartment that is mainly 0,75 times the distance between the upper edge pf the central compartment and the upper edge of the silo.

If one start with that the diameter and side of the silo respectively is SD, then the diameter of the central tube shall be dimensioned such that it is within an interval of mainly between 1/5 to ¹ A of the diameter SD of the silo for a cylindrical silo, alternatively between 1/5 to ¹ A of the width SD of the silo for quadratic silo.

More preferably the diameter of the central compartment is mainly 1/3 of the diameter SD of the silo for cylindrical silo, alternatively mainly 1/3 of the side width for quadratic silo.

The diameter of the further tube is dimensioned such that its diameter is mainly between 4/3 to 8/3 of the diameter of the central concentric compartment.

More preferably the diameter of the further tube twice as large as the diameter of the central concentric compartment.

Regarding the lower parts of the concentric tubes, Fig. 5, a start point is to take the distances E between the lower edges of the tube and the conical part of the silo measured in a direction perpendicular to the generatrices shall not be smaller than the horizontal distance D between the outer wall of the silo and the most adjacent tube.

Figure 2a,b show preferable assemblies of the concentric tubes in a silo. The concentric tubes are first joined to a unit with three cross-bars 20 placed 120° in relation to each other. With a circular silo, Fig. 2a, then three further cross-bars 22 can be utilized for attachment to the inner wall of the silo. In the case with a rectangular silo, Fig. 2b, preferably four cross-bars are used. Alternatively the package with concentric tubes can be arranged hanging in the silo.

With the above dimensioning guidelines a very good function is obtained regarding prevention of separation of compounds. With the solution of using concentric tubes according to the invention a better unloading of the silo is further obtained, which is shown in Fig. 6 as well as preventing of adherence and bridging in that the compound sinks during "sliding" along the tube surfaces and the inner wall of the silo, which also makes there surfaces free from coating, without need of cleaning. It is to be understood that the above indicated ranges during dimensioning can be modified so that desired functions are obtained. For example, when handling temperature sensitive material, it may be desirable to empty the outer parts of the silo before the inner parts, due to that the outer parts are cooled faster. The measurement ranges

indicated herein may therefore be modified and combined in different ways so that another emptying process is obtained than the one shown in Fig. 7. Numerous modifications of the dimensions may be made in order to obtain the desired result depending on type of material.

Regarding handling of asphalt for paving of roadways, the present invention presents a solution for minimizing separation along the whole asphalt handling line from production of asphalt to the paver.

According to the present invention a silo equipped with compartments as described above is utilized. This ensures that the asphalt unloaded from the silo will not be subjected to separation but will continue to have a good homogeneity.

In order to ensure the homogeneity when loading a truck from the silo, according to the present invention a separation preventing means for the deck 30 of a truck 32 is provided, see Figs. 7a-c. It comprises a "cassette" 34 removably arranged to the deck of a truck. The cassette comprises a number of dividing walls forming a mesh as seen from above in Fig. 7a. The longitudinally extending dividing walls 36 are preferably fixed and attached via cross-bars 38 to an outer frame 40 of the cassette. On the cross-bars shafts are pivotally arranged onto which shafts transversally extending dividing walls 42 are attached so that the transverse walls can pivot. The shafts could be interconnected by suitable levers and arms, in turn connected to a power source, such as a hydraulic cylinder, whereby the pivoting movement is controlled by the hydraulic cylinder when operated. The transverse walls are pivoted when the deck is to be unloaded at the pavement site. Each square of the cassette preferably maximally covers approximately 0,36 square meters. The relation of the cassette to the upper edge of the deck side and the bottom of the deck should preferably be about 2/3 of the total height of the deck as seen from its upper part to its bottom.

The cassette is adapted in size to the sized of the decks of particular trucks. Either the cassette is removably attached to the deck or the cassette could be a stationary part of the asphalt plant. In that case, when a deck is to be loaded, the cassette is lifted onto the deck and the deck is loaded. Thereafter the cassette is removed from the deck, i.e. the deck is lifted onto and off during each loading occurrence. In this case the transverse dividing walls need not be pivotable, but could be fixed as the longitudinal dividing walls.

Further, as seen in detail in Figs. 8, the deck and cassette could be arranged with a foldable, hydraulically driven insulated cover 50. The cover comprises two halves 52, 54, pivotally arranged via a shaft 56 to the longitudinally extending parts of the frame. Each cover is foldable along a longitudinal hinge 58 from a closed position in Fig. 8b to an open position in Fig. 8c. Fig. 8a shows a stop member 60 between the cover halves, and Fig- 8d show a transversily extending part of the frame arranged with guide slits 62 for guide pins 64 arranged at the ends of the cover halves.

Further, according to the invention, in order to further reduce the separation of asphalt, a paver is arranged with separation preventing means, as seen in Figs. 9 and 10. Instead of the conventional type of hopper, which is open towards the front of the paver, and two movable side walls "wings", a hopper according to the present invention is attached to the paver. It comprises a rectangular hopper 70, Fig. 9a-b, with fixed side walls 72, preferably having the same height as the conventional hopper. The side walls of the rectangular hopper slope towards the asphalt feeding bands that pulls the asphalt towards the asphalt spreading equipment, which bands are arranged in the bottom of the hopper. Further, the hopper according to the invention is arranged with guide plates 74, which limit the area over the feeding bands, and lead the asphalt out towards the sides of the hopper. By

adapting angle of the guide plates, the asphalt is forced to a faster movement at the outer sides.

As an alternative, the hopper according to the present invention could be circular, as seen in Fig. 10. The circular or round hopper 80 is arranged rotatable on the paver, preferably via suitable transmission between the hopper and the power source of the paver, whereby the rotation preferably is slow. Inside the hopper stationary arranged vertical guide plates 82 are placed adjacent to the side walls 84 of the hopper, which guide plates scrape asphalt from the inner surface and force the asphalt towards the centre of the hopper above the feeding bands. It is to be understood that instead of the hopper being rotatable, other parts, like the bottom of the hopper, the guide plates or other components can be rotatable in order to obtain the desired function of the paver hopper and to minimize the cooling surfaces and thereby cooling of the asphalt.

For both embodiments of hopper according to the present invention, cooling surfaces are minimized.

It is to be understood that the invention described above and shown in the drawings is only to be regarded as non-limiting examples of the invention and that it can be designed in a number of ways within the scope of protection as defined by the patent claims.