RU2470760C1 - Abrasive granule - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to machining the parts by granulated abrasive media and may be used for surface finishing in whatever industry. Abrasive granule for 3D machining is composed of plastic shell with core. Said shell represents biconvex body composed by ball segments with common base. Note here that relationship between bulk density of machined parts and abrasive granules is defined by the formula:

where ρ_g is bulk density of abrasive granules, kg/dm³, ρ_p is bulk density of parts, kg/dm³, while diameter D of said ball segments is defined from: 1.8H < D < 2.4H, where H is granule height, mm.

EFFECT: higher efficiency.

1 dwg, 1 tbl, 1 ex

Description

The invention relates to volumetric processing of parts with granular abrasive media and can be used for polishing the surfaces of parts of complex shapes in mechanical engineering, instrumentation and other industries.

Known forms and designs of granules for volumetric processing, which are used to increase the efficiency of grinding and polishing:

A.S. No. 319454 (USSR). Abrasive granules for tumbling / Yu.G. Sergiev, A.G. Varygin. - Publ. in BI No. 33 - 1971;

A.S. No. 804396 (USSR). Granule for vibration processing / L.G. Odintsov. - Publ. in BI No. 6 - 1981;

US Pat. No. 2100175 (RF). Abrasive granule / Z.M.Segal, V.N. Babakhin, V.V. Tribrat, G.M. Mityushkin, L.L. Kuznetsov // 1997.

During the movement of a part in a granular abrasive medium during vibratory volumetric treatment, craters with bulk displaced metal during microcuts are formed on the surface of the part due to numerous impacts of granules on the surface of the part, and metal particles are dispersed and bulk removed, which leads to leveling of the treated surface.

A disadvantage of the application for volumetric processing of abrasive granules produced by the industry is the rapid change in the shape of the granules due to wear on the edges due to the interaction of the granules with each other and with the surface being treated. In addition, a significant drawback of such granules is insufficient penetrating ability when processing hard-to-reach areas of a complex profile of a part.

Closest to the claimed invention is and.with. USSR No. 1675069, MKI ⁵ V24V 31/14. Granule filler for volumetric processing of parts / A.N. Martynov, A.E. Zverovshchikov // Publ. in BI No. 33-1991, according to which the abrasive granule is made in the form of a plastic shell with a core. At the moment of contact with the part, such a granule will reproduce the shape of the surface being treated, which will allow polishing parts of complex shape without local damage to the surface with the formation of deep grooves and craters, due to the absence of sharp peaks and edges in the granule.

The disadvantage of the prototype is the need to increase the pressure to a value sufficient for micro cutting, since due to the increase in the contact area of the granule with the surface of the part, the processing efficiency is significantly reduced.

The technical result of the claimed invention is to increase the productivity of processing hard-to-reach areas of complex profiles of the part.

The technical result is achieved by the fact that the shell is made in the form of a biconvex body formed by two spherical segments with a common base, while the ratio of the bulk density of the workpieces and abrasive granules is determined by the formula

where ρ _g - bulk density of abrasive granules, kg / DM ³ ,

ρ _d - bulk density of parts, kg / dm ³ ,

and the diameter of the common base of the spherical segments D is determined by the ratio of 1.8H <D <2.4H (H is the granule height, mm).

The drawing shows the parameters of the abrasive granules made in the form of a biconvex lens.

If the ratio of the bulk density of parts ρ _d and granules ρ _g is less than the value specified in the formula, then during processing the parts are displaced to the surface of the flow of the processing medium, that is, the effect of "ascent" is manifested, which leads to a sharp decrease in productivity and heterogeneity of quality characteristics at various parts plots.

Exceeding the specified density ratio leads to immersion and grouping of parts in the stagnant zone (relative rest zone), which is formed near the center of mass of the load, making a circulation movement, where the processing intensity decreases sharply.

Obtaining the necessary ratio of the bulk density of parts and granules can be achieved by changing the density of only abrasive granules. In cases where replacement of the material of a bunch of abrasive granules is not possible for technological reasons, it is proposed to mount a foreign body from a material with excellent density into the granule to change the inertial characteristics of the abrasive granules (working bodies).

It is proposed to use a steel ball as a foreign body, the radius of which is determined by calculation in the following sequence.

The bulk densities of parts ρ _d and granules ρ _{g are} found by weighing using a volumetric volumetric capacity, for example, one cubic decimeter. In accordance with relation (1), the required bulk density of abrasive granules ρ _ng is

ρ _ng = ρ _d / 0.75.

The mass of the aggregate of abrasive granules M _ng necessary to ensure the required ratio (1) is determined by the ratio

M _ng = V · ρ _ng .

The difference between the required M _ng and the actual M _g masses (M _g is the mass of abrasive granules in the measured capacity) will be the total mass of steel balls M _w sufficient to achieve the required bulk density

M _W = M _ng -M _g .

Assuming that the number of balls n coincides with the number of abrasive granules of 1 dm ³ (a steel ball is mounted in each granule), we obtain

where m _g is the mass of a single abrasive granule, kg Thus, the mass of one ball m _w will be

Knowing the mass of the ball m _w , we find the radius of the ball R from the relation

where ρ _m is the density of the material, kg / dm ³ (for steel ρ _m = 7.8 kg / dm ³ ).

Then the radius of the steel ball will be

Volumetric processing of parts by granular working media is accompanied not only by deformation and removal of metal from the treated surface, but also by wear of the working fluid. With prolonged use, rounding of the ribs, vertices and wear of the surfaces of the granule occurs, which leads to a change in its geometric shape, size and mass.

To assess the penetrating ability of granules of a working medium of various shapes and increase the resistance of granules with abrasive wear (granules of the same volume or mass are compared), quantitative criteria can be used.

The penetration coefficient K _p granular media can be determined by the ratio

where β _ZOD - the angle between the surfaces of the part, forming a restricted area, deg;

β _i - the angle between the faces (surfaces) forming the edge of the abrasive granules (see Fig.), deg.

From formula (4) it follows that when K _p ≤1 processing of the restricted area does not occur. It is established that reliable access of the cutting elements of the working fluid to such a zone is ensured at K _p > 1.3 ... 1.7.

Due to the wear of the granules during volumetric processing of parts, a change in the shape of the working fluid inevitably occurs. Wear of working fluids during bulk processing leads to rounding and the gradual transformation of any form of working fluids (granules) into spheres.

To quantify the wear of the granules, it is proposed to use the coefficient of wear of the granules K _and , which is determined by the ratio

where V _g is the volume of the granule, m ³ ;

S _g - the surface area of the granules, m ² .

The results of the calculation of parameters for a quantitative assessment of the shape of the granules given in the table show that, with an equal volume (mass) of the working fluid, the granule in the form of a biconvex lens has the largest working surface with a smaller length of the faces.

The results of the calculations shown in the table show that, with high penetration, granules in the form of a biconvex lens will have good wear resistance.

Calculation of quantitative criteria for granules of various shapes Body shape Source Geometric Data Parameter value, mm Volume, mm ³ V _g Area, mm ² S _g Rib length mm l Angle β, degrees Angle β _ZOD , degrees Penetration coefficient, K _p Coefficient nt wear of pellets, K _and Cube Side length a 15.9 4019.68 1516.86 190.8 90 90 one 2.65 Tetrahedron Face length a 33 42373 1886.3 198 60 1,5 2.24 Cone Radius R 12 3995.98 1549,025 75,396 65,4 1,376 2,58 Generator Length L 29,090 Height H 26.5 Cylinder Radius R 8 3920.6 1382.26 100,528 90 one 2,836 Height h 19.5 Lenticular lens Disc Diameter D 32 3714 1734 101 58 1.55 2.14 Height H 9

Therefore, for volumetric centrifugal treatment in containers with planetary rotation, granules in the form of a biconvex lens with an angle β _i between the faces, sufficient for penetration into the restricted access zone of machined surfaces of parts of complex configuration, should be recommended.

It was established that the ratio of the diameter D of the base of the lens to its height H should be in the range of 1.8 ... 2.4. A decrease in the D / H ratio below 1.8 leads to a decrease in penetration to a level insufficient for processing restricted access zones on the surface of the part, and when the ratio of the diameter of the lens base D to the height H exceeds 2.4, the granule shape rapidly changes when wear and tear and its initial penetration.

EXAMPLE

Two types of granules in the form of a biconvex lens were made, characterized by the fact that the first type has a bulk density (ρ _g = 0.75 ... 1 kg / dm ³ ) comparable with the density of polymer granules from Rösler, and the granules of the second type bulk density ρ _{g is} changed due to the introduction of steel ball granules into the body.

As the workpieces used were rings made of steel 45 with a diameter of 30 to 60 mm with a complex profile of the outer surface, the bulk density of the array of which was 0.8 ... 1.5 kg / dm ³ . The processing was carried out by granules on a polymer binder of the Rösler company, bulk density of which is ρ _g = 0.9 ... 1.0 kg / dm ³ , and granules of the first and second types.

The mass of 1 dm ^{3 of} abrasive granules was 0.8 kg, and the details were 1.3 kg. Accordingly, the bulk density of the granules ρ _g is 0.8 kg / dm ³ and the bulk density of the parts ρ _d is 1.3 kg / dm ³ .

Then, in accordance with the calculation according to formula (3), the radius of the steel ball R will be: R = 3.8 mm.

It has been experimentally established that the resistance of Rösler granules is significantly lower compared to the proposed granules in the form of a biconvex lens. When processing restricted access zones with Rösler granules after 30 ... 35 cycles, there appeared a defect in roughness on the cavities of the part profile. When using granules in the form of a biconvex lens of the first type, marriage manifests itself after 45 ... 50 cycles, that is, resistance has increased by 1.5 times. When processing the above zones with granules of the second type, the durability of the working fluid increases 2 times (the marriage appeared after 60 ... 65 cycles) compared with the use of Rösler granules.

Thus, we can conclude that the use of granules with a steel ball embedded in her body can reduce the processing time by 1.5 ... 2 times compared with the processing of granules of the same shape from a solid material.

Claims (1)

An abrasive granule for volumetric processing of parts in the form of a plastic shell with a core, characterized in that the shell is made in the form of a biconvex body formed by two spherical segments with a common base, while the ratio of the bulk density of the processed parts and abrasive granules is determined by the formula:

,
where ρ _g - bulk density of abrasive granules, kg / DM ³ ,
ρ _d - bulk density of parts, kg / dm ³ ,
and the diameter of the common base of the spherical segments D is determined by the ratio:
1.8H <D <2.4H,
where H is the height of the granules, mm