Coating processes – Particles – flakes – or granules coated or encapsulated
Reexamination Certificate
2002-11-04
2004-09-21
Tsoy, Elena (Department: 1762)
Coating processes
Particles, flakes, or granules coated or encapsulated
C427S213300, C427S215000, C427S220000, C366S336000, C366S337000, C366S338000
Reexamination Certificate
active
06793964
ABSTRACT:
The present invention relates to bitumen coating of particulate material and particularly, although not exclusively, relates to a method of and apparatus for bitumen coating particulate materials, for example stone.
Conventional methods for bitumen coating stone involve feeding particulate stone aggregate onto a conveyor and mixing the stone with a foamed bitumen binder. Suitable mixing methods include use of an archimedian screw apparatus set in a trough of a conveyor and/or use of a pugmill mixer. Methods of foaming bitumen binders are well known, and any suitable method can be used.
Use of a foamed bitumen binder aids the distribution of the binder throughout the particulate stone material. However, distribution of the binder is affected by variations in temperature and moisture content of the stone and variations in stone grading and its dust/filler content. For example, when foamed bitumen binder contacts cold stone, the foam rapidly collapses causing a decrease in the volume of the binder and “balling” which leads to poor distribution of the binder throughout the stone.
At relatively low temperatures, efficient binder distribution can be difficult with traditional mixers because binder flow over the surface of stone is a function of viscosity of the binder, which is related to temperature of the stone. Cold or low temperature coating requires a low viscosity binder, resulting in a correspondingly low stability of the final product, for example, when used as a pathway or roadway.
High stability of the final product can be achieved by use of a high viscosity binder. In order to effect appropriate binder flow, the binder is applied to hot graded stone. A bitumen formulation having a kinematic conventional viscosity range of 100-400 centistokes, would require the stone to be heated to around 120-180° C. However, heating of stone involves expensive and inefficient use of energy. Furthermore, stone dries out on heating and stone dust is released into the operating atmosphere. Such dust causes environmental and health and safety problems for the operators.
Specially formulated bitumen emulsions of low viscosity can be employed in cold stone coating. However, emulsions are not sufficiently adaptable and versatile to be useful in all stone coating techniques.
When using a bitumen emulsion to coat stone, the emulsion formulation and stone origin and characteristics, including water content, are important factors in determining the ease of production and the performance of the emulsion coated stone.
It is an object of preferred embodiments of the present invention to provide an improved method of and apparatus for bitumen coating particulate material.
SUMMARY OF THE INVENTION
The present invention provides a method of bitumen coating particulate material, wherein a foamed bitumen formulation is dispersed and contacted with particulate material to be coated.
The particulate material is preferably stone. The stone material may be the particulate stone material commonly known as “aggregate”.
Any suitable means of contacting the particulate material and the bituminous formulation may be used. For example, the particulate material may be fed to a conventional archimedian screw apparatus and the bituminous formulation may be sprayed onto the particulate stone material as the particulate material passes through the archimedian screw apparatus.
An alternative, and preferred, embodiment of the present invention involves separating the particulate material and contacting the separated particulate material with the dispersed foamed bituminous formulation.
The foamed bitumen formulation is preferably contacted with said particulate material in a chamber. Said particulate material may be introduced into said chamber via an inlet, which is suitably at an upper end thereof. The temperature of the particulate material prior to introduction into said chamber may be less than 50° C., preferably less than 40° C., more preferably less than 30° C. Preferably, said particulate material is within about 10% of ambient temperature. Especially preferred is the case wherein said particulate material is at ambient temperature prior to introduction into said chamber. Advantageously therefore, said particulate material need not be heated prior to introduction into said chamber.
Preferably, the particulate material is arranged to flow in a convoluted flow path after introduction into said chamber and, suitably, before contact with said foamed bitumen formulation. Thus, components of the particulate material are preferably caused to move relative to one another and, more preferably, turbulent flow of the particulate material is effected as is passes to a region wherein it is contacted with said foamed bitumen formulation.
Preferably, in the method, components of the particulate material are caused to be separated slightly from one another prior to contact with said foamed bitumen formulation. Preferably, the particulate material is arranged to pass into or through said chamber under the influence of gravity to a region wherein it is contacted with said foamed bitumen formulation. Preferably, no other motive means for causing the particulate material to pass through said region is provided. Preferably, however, the method involves arresting the velocity of the particulate material as it passes towards and/or within said region. Preferably, the method may involve suspending particulate material in said region thereby to increase the time over which it may be contacted with said foamed bitumen.
The velocity of the particulate material may be arrested by one or more baffles arranged within said chamber. Alternatively and/or additionally, the method may involve directing a fluid into said chamber in order to arrest the velocity and/or suspend the particulate material in said chamber. Preferably, said fluid is a gas (which term includes steam), more preferably, it is air.
Suitably, the particulate material remains in said region for a period of time sufficient to enable a proportion of the particulate material, preferably the majority of the particulate material and more preferably substantially all of the particulate material, to be contacted by the dispersed, foamed bituminous formulation.
Suitably, the particulate material is maintained in said region for an average period of at least 5 seconds, preferably at least 10 seconds, more preferably at least 15 seconds and especially at least 20 seconds. Suitably, the particulate stone material is maintained in said region for an average period of less than 120 seconds, preferably less than 80 seconds, more preferably less than 60 seconds and especially less than 45 seconds.
Different sized particles of particulate material may pass at different rates through the region wherein the material is contacted with the foamed bitumen formulation.
The method may include applying heat to the particulate material within said chamber (when provided), preferably within a region wherein it is contacted with said foamed bitumen formulation. Heat may be applied when it is contacted with said foamed bitumen. Heat may be applied to raise the temperature of the surface of the particulate material, suitably, to enable foamed bitumen to flow over the particulate material more easily. Internal regions of the particles of particulate material need not be heated, thereby saving energy. Thus, surfaces of components of the particulate material may be at a higher temperature than internal regions thereof.
Heat may be applied to the particulate material by means of a heated fluid. Preferably, said fluid is a gas (which term includes steam); more preferably, it is air. Where the method involves directing a fluid into a said chamber in order to arrest the velocity and/or suspend the particulate material in the chamber, the same fluid may be heated and may therefore also apply heat to the particulate material as described.
The heated fluid may have a temperature of at least 25° C., suitably at least 40° C., preferably at least 60° C. and more preferably at least 80° C. The heated fluid may have a temp
Goodwin & Procter LLP
Totalfinaelf Bitumen Limited
Tsoy Elena
LandOfFree
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