Method and device for determining characteristics of loose material

FIELD: investigating or analysis of material.

SUBSTANCE: method comprises determining the limit value of the stress by measuring the angle of inclination of the surface which is provided with the initial material. The device comprises changeable coating with projections and locking member made of a frame having thin baffles or thin film made of an adhesive agent.

EFFECT: improved method.

2 cl, 3 dwg

 

The invention relates to mining, in particular for enrichment of minerals for studying the mechanical properties of bulk fine-grained materials in the determination of technological modes and geometrical parameters of the processing apparatus, for example when studying the behavior of the sediment layer on an inclined plane.

A known method of determining the mechanical characteristics of the limiting state of the material, including the placement of material in the form of a body on a flat surface in a stable static state, moving it in an unstable state by the inclination of the surface, measuring the resulting minimum surface angle relative to a horizontal plane and defining a calculation of the mechanical characteristics, such as static friction coefficient (see Gernet M. Course of theoretical mechanics. Ed. 3rd revised and enlarged supplementary Textbook for high schools. M.: Higher school, 1973. - 464 S., pp.92...93).

The device includes a flat surface, possibly changing the angle of inclination relative to the horizontal plane (see ibid.).

A disadvantage of the known solutions is limited in application to bulk, especially fine materials and, in particular, by placing them in a liquid medium in a layer of sediment. If on the inclined surface of the base is I loose material, the latter is set in motion by volume gradually: to change the height of the layer due to slipping and rolling of particles, starting from the upper level layer. Change the shape's geometry material time affects the accuracy of the determined characteristics.

The closest to the technical nature of the claimed solution is the method of determining the mechanical characteristics of the limiting state of a granular material according to the natural angle of repose, including the placement of material in a transparent prismatic container in a stable static state, moving it in an unstable state by tilting the vessel, measuring the resulting angle between the upper layer of material and the horizontal plane (see V.D. Lomtadze Physico-mechanical properties of rocks. Methods of laboratory research. Textbook for high schools. - 2nd ed., the processing. and extra - Leningrad: Nedra, 1990. - 328 S., s...293).

The device for implementing the method comprises a transparent prismatic vessel, mounted with the possibility of changing the angle of inclination relative to the horizontal plane, placed inside the investigated material (see Lomtadze E ... s...293).

The disadvantage of this solution is to change the original shape of the distribution of material in size, which limits the study on the impact of the height of the layer of loose what about the material on its marginal status on an inclined plane. Also has low accuracy values of mechanical characteristics, such as limiting tangential shear stresses in the layer at a depth of h normal to the surface of the slope, obtained by analytical dependencies (see below) based on the measured angle. Since the formation of the slope takes place over time due to slipping and rolling of the particles of the upper layers, this angle does not reflect the process shift. In addition, the forming angle is influenced by the additional resistance caused by the frictional forces between particles reaching the lower position, and the bottom of the tank, as well as dynamic factors arising in this area in the process of formation of the slope.

The technical result is to expand the functionality of types of mechanical characteristics of limit state of materials and forms of their existence, as well as improving the accuracy of their values.

The invention consists in that in the method of determining the mechanical characteristics of the limiting state of the bulk material, comprising placing the material in a transparent prismatic container in a stable static state, moving it in an unstable state by tilting the vessel, measuring the resulting angle between the upper layer of material and the horizontal plane, the size of the distribution of material is carried out in the plane of the capacity of a uniform layer of constant height with the application of the locking element on its upper surface, this mechanical characteristic of the limiting state of a material is determined by the limiting value of shear stress formula: air

for liquid media

where h is the height of the cutting layer, g is the acceleration of free fall, ρ is the density of the bulk material, ρT- the density of a solid phase material, ρW- the density of the liquid, m is the volumetric content of solids in the layer of material (in fractions of a unit), α - the measured angle.

The invention also lies in the fact that the device for implementing the method, comprising a transparent prismatic vessel, mounted with the possibility of changing the angle of inclination relative to the horizontal plane, placed inside the investigated material is characterized by the fact that the bottom of the tank in the form of flat bench, provided with a removable cover with the tabs of constant height, and the device is further provided with a locking element, made in the frame of thin walls or in the form of a thin film sprayed adhesive substance located on top of the material under investigation.

The proposed solution is not possible functions of the prototype and analogue, namely the identification of the natural angle of repose of granular mother is La, angle of friction and the static coefficient of friction of a rigid body.

The perform of the bottom of the vessel in the form of a flat bench provides in an inclined position free end of granular material into the cavity of the vessel below the level of the ledge, excluding the impact of the additional resistance of the particles on the bottom of the container.

Installing the replacement of the cover with the tabs of constant height and causing the locking element on top of the material allow you to cut the entire part of the layer according to the level of the projections and to determine additional characteristics of the material ultimate shear stress of the bulk material.

Placement of granular material in the plane of the capacity of a uniform layer of constant height with the application of the locking element on its upper surface provides the opportunity to determine its static coefficient of friction f of the surface-based as f=tgα.

The application of the locking element on the top layer eliminates dynamic factors associated with the shape change layer that brings the process to mechanical shear layer.

The dependencies also allow the angle to be measured to take into account an additional factor is the height of the layer. In addition, they allow you to establish experimentally the relationship between the tilt angle of the layer and its height.

The lling liquid medium expands the scope of IP is the use of technical solutions for determining the mechanical characteristics of the sediment layer.

Thus, the method and apparatus make it possible to determine the angle of friction, static coefficient of friction for the material solids and granular materials. Also allow us to determine the angle of repose, the ultimate shear stress of bulk materials in the dry state and in a liquid medium. The exception of side effects (friction of the particles on the bottom of the tank outlet, the dynamic processes of displacement of the layer, the shape change layer) improves the accuracy of the process.

1 shows a device for the determination of mechanical properties of limit state material; figure 2 is an element a in figure 1, increased; figure 3 - a view B figure 2.

Implementation of the proposed method produces the following way. The bulk of the source material is placed in a transparent container on the surface of the ledge uniform layer of constant height, providing a stable static state, figure 1, is applied on the upper surface of the locking element in the form of a frame or spray adhesive substance relatively thin layer. Tilting capacity, and with it the plane of the ledge, the source material result in an unstable condition in which he starts to move down under the action of gravitational forces. At this point, measure the angle between the top is cut off by a layer of material and the horizontal plane, the which is the end result or an intermediate for subsequent calculations of other mechanical properties. When determining the value of the limiting shear stress pre-measure the height of the layer and the density of the bulk material.

If you select an elementary volume of a layer on an inclined plane at an angle α to the horizontal surface, figure 2, the resulting shear stresses on the plane of shear is defined as

where ΔG - gravity of the selected element at a depth of h normal to the layer; ΔS - area shift; - width layer;- selected by the vertical size of the layer to the plane of the slice.

It follows that the value of shear stress layer is influenced by the density of the bulk material, the height of the layer normal to the plane of the base material and its angle of inclination.

When filling containers with liquid environment appears buoyancy (Archimedes force), while additionally takes into account the density of the fluid and the porosity of the layer in accordance with formula (2).

The measured α, h and known in advance (or ρtthat ρWm in formula (1) or (2) is determined by the limiting value of the shear stress of the layer of bulk material or sludge.

Device for determining the limiting shear stress consists of transparent prismatic container 1 filled with a limited amount of granular material 2, positioned and what about in the form of a layer on the surface of the ledge 3 of the bottom of the tank. In addition, the surface of the ledge may be made removable and consist of plane 4, provided with projections 5 of the same height. On top of the layer of granular material is locking element 6 in the form of a frame of thin partitions. As the locking element can be applied film obtained by spray adhesive.

The operation of the device is performed in the following sequence.

The subject of granular material is placed in the tank with a layer of height h on the surface of the ledge 3 or layer h to the level of the ledges. On top of the layer place the locking element 6. The capacity can be filled with liquid medium. Tilting the container 1 on the corner αand along the plane of the ledge, a layer of granular material is contained in the unstable state, which moves on an inclined plane down, filling particles cavity capacity below the ledge. When this surface shear plane is level thresholds 5. Measured minimum angle of inclination of the plane of the ledge α, which begins to move the layer with the subsequent calculation of mechanical characteristics: maximum shear stress or static coefficient of friction.

Thus, the proposed method is universal: allows you to define a number of mechanical characteristics of the limiting state as solids and granular materials, as in the dry the form and in liquid medium. The device is simple to manufacture and operate. Excludes a number of negative factors affecting the accuracy of the results, allows for the study of dispersed materials additionally take into account the height of the layer. Can be applied in various areas while solving such problems, for example to determine the ultimate mechanical properties of the snow cover on an inclined plane.

1. The method of determining the mechanical characteristics of the limiting state of the bulk material, comprising placing the material in a transparent prismatic container in a stable static state, moving it in an unstable state by tilting the vessel, measuring the resulting angle between the upper layer of material and the horizontal plane, characterized in that the placement of material is carried out in the plane of the capacity of a uniform layer of constant height with the application of the locking element on its upper surface, while the mechanical characteristics of the limiting state of a material is determined by the limiting value of shear stress formula:

for air τ=hgρsinα, (1)

for liquid τ=hgm(ρtW)sinαand, (2)

where h is the height of the cutting layer, g is the acceleration of free fall, ρ - the density with puchero material, ρt- the density of a solid phase material, ρW- the density of the liquid, m is the volumetric content of solids in the layer of material (in fractions of a unit), α - the measured angle.

2. A device for determining mechanical characteristics of the limiting state of a granular material containing a transparent prismatic vessel, mounted with the possibility of changing the angle of inclination relative to the horizontal plane, placed inside the investigated material, characterized in that the bottom of the tank in the form of flat bench, provided with a removable cover with the tabs of constant height, and the device is further provided with a locking element, made in the frame of thin walls or in the form of a thin film sprayed adhesive substance located on top of the material under investigation.



 

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