SU1648561A1 - Grinding unit of air-stream mill - Google Patents

Abstract

The invention relates to devices for jet grinding of material and can be used in the chemical, pharmaceutical, paint and varnish, food industry, construction materials production, etc. areas where fine and superfine ground material is required. The purpose of the invention is to increase the efficiency of work due to the complex effect on the material being milled, sudden changes in temperature, static pressures, acoustic and alternating mechanical and shock loads during the transition of a sound barrier. The essence of the invention consists in the synergistic effect of the physical factors of supersonic flow and the shock wave of the transition of the sound barrier to the material with the aim of its separation and destruction. To do this, in the grinding chamber opposite the chamber of displacement of the ejector, an armored plate with a percussion element is mounted for the length of the grinding chamber, the nozzle is made in the form of a Laval nozzle, and the outlets are located behind the percussion element outside the action of the shock wave. 2 з.п, ф-л, 3 Il.

Description

The invention relates to a device for jet grinding of a material and can be used in the chemical, pharmaceutical, paint and varnish, food industry, construction materials production and similar areas where fine and superfine ground materials are required.

The purpose of the invention is to increase the efficiency of work due to the complex effect on the material being milled, sudden changes in temperature, static pressure, acoustic, alternating mechanical and shock loads during the transition of a sound barrier.

Figure 1 shows the proposed site, a General view; Fig. 2 shows the same embodiment; on fig.Z - section aa in figure 2.

The grinding unit consists of an ejector body 1, a supersonic nozzle 2, a mixing chamber 3, a grinding chamber 4 with outlet openings 5, a percussion element 6 (impact needle of figure 1 or a impact wedge of figure 2) and an armor plate 7. Impact element 6 is mounted on the armor plate 7 with the mixing chamber 3. The outlet openings 5 are placed directly at the armor plate 7 and closed eccentrically mounted on the grinding chamber 4 collector 8 with the exhaust pipe 9 (Fig, 1). In the case of the ejector .1 between the nozzle

00

cl

2m mixing chamber 3, a loading opening 10 is made.

In the high unit power unit (FIG. 2), the supersonic nozzle 2, the mixing chamber of the ejector and the grinding chamber 4 are made flat, and in the supersonic nozzle 2 a shaped body 11 is installed. In this node (FIG. 2) the shock element initiates the shock wave The width of the chamber is three.

 The impactor is designed as a wedge with a sharp edge extending over the entire width of the grinding chamber. The profiled body 11 is fixed in the support 12 so that the plane, dividing it into two parts equal in thickness, is strictly coaxial with the nozzle 2 and coincides with the transverse axis of the nozzle 2,

The cross-sectional shapes of the nozzle 2 and the flat mixing chamber 3 can be different. In the example of the embodiment, the adopted rectangular shape, the width of the cross section of the mixing chamber 3 is slightly greater than the width of the nozzle 2.

The cross section of the grinding chamber 4 is identical to the cross section of the chamber

3 shifts. The internal volume of the grinding chamber is divided by a shock wedge into two equal narrowing slits, spatially representing two flat confuser. Outlets 5, for example, of rectangular shape, are located in the housing of the grinding chamber 4 opposite each plane of the impact wedge 6 directly at the armor plate 7.

Milling site works as follows.

Energy carrier 13, for example compressed air, is supplied from compressor 14 to supersonic nozzle 2. Energy carrier 13 is accelerated in nozzle 2 to supersonic speed. The supersonic jet 15 penetrates into the mixing chamber 3 and carries away (material) to the material 16 supplied through the loading opening 10 into the body of the ejector. The two-phase supersonic flow overcomes the shock wave 17, initiated by the sharp edges of the impact elements 6 (needles, cone), and slows down in the shock wave and confusor 18 formed by the space between the grinding chamber body 4 and the impact member 6. The final deceleration occurs when the two-phase flow hits armor plate 7. The crushed material 19 mixed with the energy carrier gas is withdrawn from the ejector through the outlets 5 and further.

The degree of expansion in the nozzle 2 is chosen such that the temperature in the flow of the formed supersonic jet at

the actual static pressure in the flow was above the liquefaction temperature (Tt Tozh). When using compressed air as an energy carrier, there is a large supply of temperature, since the liquefaction temperature of oxygen, being higher than that of nitrogen, is at 760 mm Hg. - 180 ° С.

The cross-sectional shape of the supersonic nozzle is determined based on a given value of the dimensionless gas velocity at the nozzle exit (Mach number - M) and, in a specific example of design for air, is plotted according to 4 bridges.

F (1 + 0.2 M2) 3

Pip1,73 M.

where Ркр - critical, minimum nozzle section, m2;

F - current nozzle section, m2.

From this dependence it is seen that the nozzle section is characterized by three sections: M 1 dF / F 0 - subsonic part, nozzle section narrows, M 1 dF / F 0 - critical section, M 1 dF / F 0 - supersonic part, nozzle section expands .

Consequently, for a flat supersonic nozzle with a profiled body, the shape of the gas (air) flow channel in the upper and lower slits should follow the shape of the Laval nozzle, i.e. The shape of the shaped body is described by the above dependency.

The static wave of atmospheric pressure, propagating at sonic velocity, is carried by a supersonic flow, so two parallel supersonic flat jets of the second variant of the node on the path between nozzle 2 and mixing chamber 3 do not experience sticking and enter the mixing chamber with two parallel flat flows.

The supersonic jet, the passage of the volume of the housing 1, carries with it (ejects) the layers of air in contact with it and thereby creates a vacuum in the volume of the housing 1. There is a constant fresh air inflow; therefore, the material 16 fed into the body 1 is ejected by a supersonic jet and enters the mixing chamber 3.

The layer of the ejected medium adhering to the supersonic jet as if thickens the supersonic jet, increases its dimensions, therefore, for the unaccented entry of such a jet into the mixing chamber 3, the dimensions of the cross section of the mixing chamber should slightly exceed the dimensions of the output section of the nozzle 2.

The mass of entrained (injected) air depends on the area of contact with the jet. It is known that the circumference is minimal compared to the size of the perimeter of any other figure of the same area. This explains the greater ejection effect of a flat jet compared to a jet of circular cross section. With equal power, the effect of a flat jet leads to an increase in the efficiency of the ejector, which becomes especially noticeable and relevant in installations of high unit power. The efficiency of a flat jet ejector is further increased when using a pack of flat jets. An additional positive effect arises due to the double influence of two neighboring jets 15 on the same elementary volume of the ejected medium 20.

In the mixing chamber 3, a turbulent mixing of two streams occurs - energy carrier and ejected air with the material. The length of the mixing chamber 3 is chosen so that a homogeneous 2-phase mixture is formed at its exit.

Intensive mixing in a supersonic flow with a gradual transition to a supersonic flow regime is already accompanied by a partial crushing of the material. In addition, an intense cold strike leads to deep freezing of the surface layers of a particle of material while maintaining the room temperature inside that particle. This temperature difference creates strong mechanical stresses within the material particle. If it is necessary to grind soft and elastic materials, this circumstance of freezing the material is a decisive factor in the process.

The energy intensity of the carrier, i.e. the initial pressure of the gas is taken to provide a supersonic two-phase flow at the outlet of the mixing chamber 3 with an outflow rate slightly exceeding the speed of sound (M 1), taking into account energy losses in the nozzle 2 and mixing chamber 3.

A two-phase supersonic flow, washing a striking element (wedge) 6, passes through a shock wave (shock front). In the shock wave 17 and in the immediate vicinity of it, the gaseous medium is characterized by sharp vibratory character of temperature differences, static pressures, accelerations against the background of intense acoustic irradiation. Under such conditions, particles of the material are literally broken along the crystal boundaries and split into pieces.

The cross section of the grinding chamber 4 is similar to the cross section of the mixing chamber 3. The internal volume of the grinding chamber 4 of circular cross section, together with the cone 5 of the impactor, form a confuser 18, and in the second version of the assembly, two flat confusors 18.

The supersonic flow at a speed after the mixing chamber 3, slightly exceeding the speed of sound, loses some of its energy as the shock wave 17 passes. The final deceleration, i.e. the transition to the subsonic flow regime occurs in converger 18,

5 In principle, it is possible to use the operating mode of the ejector, in which the two-phase flow at the end of the mixing chamber moves at a speed much higher than the speed of sound. However, the choice of this mode of operation of the ejector is unprofitable due to disproportionately large energy losses, i.e. lower efficiency.

Move further, now subsonic two-phase flow is quenched on armor

5 plate 7. Potentially surviving particles of the material are crushed when colliding with the armor plate 7. From this, the location of the outlet openings 5 is determined only in the area of the subsonic flow mode and after contact with the armor plate 7.

Long-term operation of the unit using abrasive materials leads to intensive wear of the camera surface.

5 mixes of the ejector, the tip of the cone of the impactor and the armor plate. Changing the geometric dimensions of the elements of the ejector leads to a change in the mode of its operation, and rounding the sharp edges "

0 of the impactor can lead to the breakdown of the shock wave or change its characteristics, so the mixing chamber, impactor and armor plate can be made of durable material or

5 have a durable coating.

Further, the ground material 19 is separated from the energy carrier 13. The purified energy carrier 13 can be reused. The coarse fractions from the settling chamber 21 are recycled to the process as material 16.

FIG. 1 shows an example of a process chain separating a two-phase air-mica mixture: precipitation chamber 21,

5 blocks 22 and 23 jet screens and a vacuum pump 24.

The proposed node design is efficient and effective. The known construction gives a crushed material with a spread of particle sizes of more than 60%,

and the proposed solution allows to reduce the dispersion of particles to a practical minimum in the range of 5-8%. It especially effectively destroys mica crystals along the planes of perfect cleavage, i.e. when the particle size is in the area minus 40 microns in thickness of the submidronic. Such a product is especially valuable for the production of decorative paints, varnishes, enamels and other coatings, as well as for obtaining particularly thin and durable paper and luminous papers.

Claims (3)

 Claim 1. Mill unit of the jet mill, including an ejector with a nozzle, a mixing chamber and a grinding chamber with outlet openings, characterized in that, in order to increase work efficiency due to the complex effect on the material being grinded, sudden changes in temperature, static pressures, and acoustic alternating mechanical and shock loads at the transition of the sound barrier, in the grinding chamber opposite the mixing chamber of the ejector an armor plate with a shock element for the length of the grinding chamber oriented along the axis of the chamber against the flow is mounted, the outlets are located behind the impactor outside the impact zone of its shock wave directly at the armored plate, and The nozzle is made in the form of a Lawal nozzle. 2. The grinding unit is populated with differences in that the cross sections of the mixing chamber of the ejector and the grinding chamber are the same. 3. The grinding unit according to claims 1 and 2, is designed in such a way that the ejector nozzle and the mixing chamber are flat, the impactor is made in the form of a wedge, the sharp edge of which is oriented parallel to the transverse axis of the mixing chamber. 10 {b 6 LLA.G1, w 1 X} „.; t 15II / 6 / -fp fig.Z