Solid material comminution or disintegration – Processes – With classifying or separating of material
Reexamination Certificate
1999-08-10
2002-11-19
Hong, William (Department: 3725)
Solid material comminution or disintegration
Processes
With classifying or separating of material
C241S081000
Reexamination Certificate
active
06481651
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process and to a plant, in particular operating continuously, for comminuting a raw material in the form of pieces and obtaining a material in the form of grains having a requisite grain size distribution, as well as to an application of the mixture of material in grain form obtained by implementing such a process.
BACKGROUND ART
In the field of fragmentation, one often has occasion to produce, from a materiel in piece form, grains the differences in size whereof comply with a predetermined grain size distribution or range in order, in particular, to permit subsequent a utilization of this material using various means for packing by vibration, compacting or pressing, to minimize the addition of binder that might be required at the time of said utilization and/or to optimize the physical characteristics of the finished part after forming, according to criteria which are also predetermined.
One characteristic that is generally of prime importance in defining this grain size range is the ability of the fine grains to fill in as precisely as possible the intergranular voids between the larger-sized grains, a characteristic which contributes tots optimization of the compactness or density of the finished part, to a reduction in the consumption of any binder required to fill in the voids, as well as to better performance in terms of mechanical strength and/or electrical or thermal conductivity.
Another characteristic that is often sought after in the coarse fractions in this grain size range is optimum compressive strength, so that they do not deteriorate upon subsequent use, and enhance the mechanical properties of the finished part after forming.
At the present time, there is no control over the characteristics of the raw materials used, or over the grain size distribution of the grains directly resulting from fragmentation operations.
To obtain dimensional distribution of the grains in compliance with the requisite grain size range, it thus appears essential to break down the grain size preparation process into two steps.
The first step consists in dividing the material into several grain size fractions by means of grading or classifying apparatus, in reducing any excess amounts of certain fractions by means of breaking or grinding apparatus, in recycling the fragmented products through the classifying apparatus, and in storing the different fractions thus produced in buffer hoppers or silos according to grain size.
The second step consists in reconstituting a mixture of the different grain size fractions produced in the first step, in order to conform to the requisite grain size range, because of controlled extraction of the materials beneath each of the silos using volumetric /and or weight based proportioning systems.
Although plants are known which make use of only one fragmenting apparatus for simultaneously producing the different fractions, these operations as a whole and, more especially, classifying and mixing, necessitate numerous, cumbersome items of equipment, particularly when one wishes to minimize the non-reusable excess quantities of materials. In addition, they operate in a closed circuit and involve recycling of materials. They are thus complex and costly.
The object of the invention is to provide a process and a plant for grain size reduction of a raw material in piece form to obtain a material in grain form that overcome the aforementioned drawbacks and permit the direct production, particularly continuous production, of a requisite grain size distribution without recycling, and without either classifying or re-mixing of all or any of the fragmented products.
Another object of the present invention is to provide a process and a plant for grain size reduction of a raw material in piece form that permit direct use of the material in grain form obtained without having to modify its grain size distribution once again according to the desired application.
A further object of the present invention is to provide an application of the mixture of material in grain form permitting the manufacture of objects having advantageous physical properties.
Further objects and advantages of the present invention will emerge in the course of description that follows, which is provided only by way of illustration and is not intended to limit the invention.
SUMMARY OF THE INVENTION
The present invention relates, first of all, to a process for the grain size reduction of a raw material in piece form to obtain a material in grain form, wherein:
all or part of the material in piece form is subjected to a grinding operation, capable of enabling to be obtained at its output a material in grain form having a requisite grain size distribution, starting out from any given grain size of the material in piece form;
downstream, the material in grain form is directed exclusively towards a common container, whatever the size of the grains, so as to obtain, in a single run, in the container, a mixture of material in grain form having the grain size distribution, for use as such.
The process according to the invention uses a raw starting material the pieces of which have, sizes which are smaller than or equal to 200 mm.
Advantageously, the pieces are subjected to grinding by layer crushing. It has been found, in fact, that, by choosing such a technique, the parameters of the grinding operation can be selected such that the product in grain form obtained conforms to the requisite grain size range, starting out from pieces of any size, and, what is more, in an open circuit.
The term grinding by layer crushing refers to those grinding processes in which a multigranular layer of material for crushing is compressed between two surfaces, sufficient pressure being applied to cause fragmentation of the grains, which are comminuted to form smaller grains.
During the process of grinding by layer crushing, the compressive force exerted is transmitted within the layer of material from grain to grain via inter-grain contact zones.
At the start of this process, owing to the coarse grain size of the material, the intergranular voids are generally large, and the inter-grain contact surfaces are limited, which generates considerable pressure and causes the more fragile grains to break up. The smaller-sized grains thus formed are then re-arranged in the vacant intergranular voids, gradually increasing the inter-grain contact surfaces, and, at the same time, reducing local pressure in the contact zones.
As a result, the process contributes to reducing the volume of the intergranular voids, correspondingly increasing the density of the layer of material, until the proliferation of points of contact between grains causes local pressures to drop below the crushing threshold of the grains.
It can thus be seen that the active parts of the grinder for comminuting the grains possibly have little contact with the material. The material in fact grinds itself through the effect of the pressure transmitted between the grains. Abrasive materials can thus be processed, while limiting wear on the parts used.
Because of to this technique, it is also possible to obtain a relatively wide grain size range, for example 0 to 30 mm or more.
Such processes can be used to obtain a grain size distribution that is substantially independent of the initial size of the pieces used. To vary the distribution and/or adapt it to the raw material used, it then suffices to act upon the grinding adjustment parameters such as, the fragmentation force and/or the pressure applied.
The latter will depend, in particular, on the subsequent service pressure of the material, and will be greater than, or at least equal to, this pressure in order to avoid deterioration of the grain at this stage.
Apparatus known for carrying out material bed grinding under pressure are, for example, vertical roller mills, vertical ball mills, horizontal roller mills, roller presses, and cone vibrating grinders.
Use can be made, in particular, of a vibrating vertical cone type grinder, that is to say a grinder in which the con
Pinchon Jean-Françis
Pinoncely Andre
FCB Societe Anonyme
Hong William
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