RU1770024C - Method of preparing sand for producing moulds - Google Patents

Abstract

The invention relates to the preparation of quarry sands and can be used in the manufacture of castings by casting according to smelted models. Essence: according to the proposed method, quartz quarry sand is accelerated by compressed air at a pressure of 0.2 ... 0.3 MPa, and the accelerated section from the pipe nozzle to the baffle plate - 100 ... 150 mm. 3 tab.

Description

The invention relates to the preparation of quarry sands and can be used in the manufacture of castings by investment casting.

Known methods for pneumatic regeneration of the molding sand (see the book of IB Zayegrov, Regeneration of waste mixtures in the foundry, - M .: 1961, p. 98-133), based on the use of high-speed flow for separation (by impact and abrasion of the binder films materials from the surface of the grains of sand and air flow to remove these films and other dusty substances from the mixture.

The disadvantage of this method is the difficulty of using for the preparation of fresh quarry sands used for the manufacture of ceramic shells cast on smelted models, because reducible air flow rates provide not only a rupture of the binder films, but also significant grinding of sand.

Meanwhile, quarry sands, due to the presence of internal inclusions in the form of gas or liquid in some quartz grains, do not provide high quality shell molds during the casting process, which leads to defective casting due to shape easor and cracking of the surface of the contact layer of the shell.

The closest to the proposed invention in terms of technical nature and the achieved result is a method of grinding solid bodies, carried out in counter-current jet mills, in which the milled material is transported into a grinding chamber equipped with one ejector; instead of the second ejector, a plug (1) is installed.

The material is crushed by hitting a jet of compressed air against a metal surface at a compressed air pressure of 0.7 MPa and an acceleration pipe length of 170 mm.

A disadvantage of the known method with the described process parameters is the complete grinding of silica sand in dust XJ

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ABOUT

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the left-shaped fraction, which does not meet the requirements of the foundry for grain size of the material.

The aim of the invention is to remedy these drawbacks, i.e. increasing the stability of the physico-mechanical properties of sand and a mixture based on them. This goal is achieved in that in the method for preparing quarry sands, including dispersing silica sand in a horizontal stream in an accelerating tube with air, impinging sand on a baffle screen and sucking off the dust fraction, dispersing sand with air according to the invention is carried out at a pressure of the latter 0.2- 0.3 MPa, while the baffle plate is spaced from the pipe nozzle at a distance of 100 ... 150 mm,

When sand hits a metal surface, in almost all cases only defective grains of sand crack, and destruction occurs due to internal defects or flocs in which a gas or liquid is enclosed. Thereby, gas and liquid inclusions are removed from the sand grains.

Acceleration of sand by air at a pressure of 0.2 ... 0.3 MPa and at a distance of 100 ... 150 mm from the baffle plate allows to eliminate defective grains and stabilize the physicomechanical properties of sand, which ultimately affects the process of manufacturing ceramic .rm when casting according to the smelted models, the ability to significantly improve the quality of casting.

The optimal parameters of the claimed method were established during experimental studies.

When conducting patent research, the authors did not find methods for preparing quarry sands similar to those claimed, which proves that the features of the present invention meet not only the novelty criterion in comparison with the prototype, but also significant differences.

Example. To activate the sand, the sandblasting type laboratory apparatus shown in the drawing was used. Ordinary sand is sucked in by the ejection tube 1 from the hopper 2 and at a speed of 14 m / s, hits a plate (screen) 3, is poured into the hopper 4. Dust and fines, passing through the cover 5, are removed by exhaust ventilation 6.

To determine the optimal sand treatment parameters, i.e. sand acceleration rates and the distance from the nozzle of the booster pipe to the screen, the sands were accelerated with accelerating speeds and different distances, and then checked for changes

particle size distribution of sand and the presence of defective grains in the sand.

The air velocity in the booster pipe was measured at a diameter of 24 mm and a pipe length of 1 m using pneumometric tubes and a U-shaped pressure gauge (see the book of IB Zaigerov. Recycling of waste mixtures in foundry, 1961, p. 124) at pressures of 5.10.15.20.25.25.30 MPa.

In the table. Figure 1 shows the dependence of speed on the applied pressure.

Taking into account the decrease in speed in the accelerating device, after introducing material into it, a coefficient of increase in speed is introduced — 1.72 obtained experimentally.

The change in the granulometric composition of sand was measured using a sieve analysis according to a standard method.

The presence of defective sand, i.e. having internal gas-liquid inclusions, grains were determined by petrographic studies of sand in polished briquettes using an REMMA-200 electron microscope.

For research, the sands of the following quarries and grades were selected: 1. Gusarovsky K 0315A

2.Tamansky K016A

3. Strugokrasnensky KO315A The research results are presented in table.2.

As can be seen from Table 2, the sands of various quarries are infected with gas-liquid inclusions to different degrees.

In these quarries, the number of defective grains ranges from 8 to 16%.

Meanwhile, it is these grains that reduce the strength of ceramic shells and are the cause of casting defects. The elimination of these grains is the activation task.

In the tests, the distance from the nozzle of the ramp pipe to the metal wall of the hopper was 50,100,150,200,250 mm, and the distance for each distance was -9.10,14,16,17,25 m / s.

The data in Table 2 show that, at a distance of up to 100 mm from the screen, regardless of the acceleration speed, the activation is practically

not happening. The number of grains having gas-liquid inclusions varies slightly. It is caused by that. that most sand grains collide with each other and lose energy.

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The most optimal results are obtained at a distance of 100-150 mm and a speed of 10-16 m / s. Defective content

grains is reduced to zero, the main loss

fractions do not exceed 8%, i.e. particle size distribution is practically unchanged.

At a speed of less than 10m / s, activation does not occur. With an increase in speed above 16 m / s, up to 70% of the sand is crushed, and the acute-angled shape of the grains of sand is known to sharply reduce the strength of the shell. In addition, up to 35% of the sand is carried away by exhaust ventilation, which is also economically disadvantageous.

With a further increase in the distance, the speed at the moment the grains of sand hit the screen decreases, and in order to achieve activation, the acceleration speed must be increased. This leads to an overspending of compressed air, which is also not economically feasible.

Thus, the optimum sand acceleration speed is CKopoctb or 10 up to 16 m / s, which is ensured by a compressed air pressure of 0.20-0.30 MPa, as can be seen from the data in Table 1.

Samples were prepared on prepared activated sand for which cold and hot strength were tested.

Next, castings of the sprocket, rocker and valve parts were made, and the percentage of total rejects of castings and litter was determined.

Table 3 shows the comparative results of the hot and cold strength of ceramic shells, as well as the values of the total defect and defect in the ceramic gap of castings obtained by the known and proposed method.

As can be seen from the data in Table 3, the use of shock-activated at a speed of 10-16 m / s and during the acceleration section from the pipe nozzle to the screen mounted on

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a distance of 100-150 mm, under a pressure of 0.2--0.3 MPa of quartz sand, increases the cold strength of pre-calcined ceramic shells when using activated sand by 25-30%, and hot by 40-300% compared to fresh quarry sands and sands activated by a known method.

The table also shows the values of the marriage of castings. As can be seen from the table, when using activated sand according to the proposed method, rejects of castings are reduced by 1.5 times in comparison with unprepared sand.

When using burnt sands, cleaned by a known method, the marriage of castings is 100%, because the cleaned burned sands are not suitable for precision casting due to the formation of burns on castings, since particles of binder remain on the sand grains (water glass, bentonite, etc.).

Claims (1)

The claims A method of preparing quarry sands for manufacturing molds according to investment casting methods, including dispersing silica sand in a horizontal stream in an accelerating tube by air, impacting sand with a baffle screen and suctioning a dust fraction, characterized in that, in order to increase the stability of the physicomechanical properties of the sand and mixtures based on them, sand is accelerated at a pressure of 0.2-0.3 MPa, and sand is hit with a breaker screen at a distance of 100-150 mm from the nozzle by tube distillation. Table t table 2  GU Sarovsky Twianian Strugoksvneky ABOUT fifty fifty fifty fifty fifty fifty 100 too too 100 100 too ISO tso ISO 150 150 ISO 200 200 200 208 200 200 250 250 250 250 250 250 0 fifty fifty fifty fifty fifty fifty 100 100 100 100 too 100 150 ISO 150 150 ISO 150 ioo 200 200 200 200 200 250 250 250 250 250 250 0 fifty SO fifty fifty fifty fifty 0 9 10 14 16 17 25 9 10 14 16 17 25 9 to lit 16 17 25 9 10 111 16 17 25 9 10 14 sixteen 17 25 0 9 10 14 sixteen 17 25 9 ID 14 sixteen 17 25 9 10 eleven) sixteen 17 25 E 10 14 sixteen 17 25 9 10 14 sixteen 17 25 0 9 10 14 sixteen 17 25 10 to 10 10 10 10 10 10 10 ID 10 10 10 10 to to 10 10 40 to 10 10 10 to 10 to 10 10 10 10 10 15 15 15 15 15 15 IS fifteen 15 15 15 15 15 15 15 15 15 IS, 15 15 15 IS 15 IS 15 15 15 15 15 15 IS 16 16 16 16 16 16 16 0 to 0 0 10 0 o 0 o 0 5 2 0 0 9 6 2 2 0 . 1IC04A To "e .It. .H. . . .ti - I. 1L . I. 1K04B 1K04A To me .h. u .. 1l (o4c IK04A.,. .. ... .. .P. at 11. .. .. .eleven. . K016A To the same .i. .It. .H. .11 .1. .11- .11. .eleven. .eleven. .. .1. .eleven. .. .eleven. .. I. SH6A To me .. . .eleven. .to . .it. .1. .eleven. .and. .eleven. GOAT ISA .. . ". .eleven. "N. .. . es as 85 85 65 85 85 85 85 85 85 85 85 85 85 85 85. 85 85 85 85 85 85 85 85 85 85 85 85 85 85 85 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 2b 25 25 25 25 25 25 JO 30 thirty 30 30 30 30 8 $ 85 85 83 82 81 74 81 80 77 76 76 70 81 80 77 76 75 70 82 81 80 80 78 75.5 83 82 81 80.5 80 77 25 25 25 24.5 23 22.5 twenty 21 twenty 18.5 17.5 17 thirteen 21.5 twenty eighteen 17 17 13.5 22 21 20.5 19.5 nineteen sixteen 23 22 21.5 21 20.5 eighteen 30 29 29 28 28 26 26 2 4 6 4 8 10 12 30 4 6 6 10 12 25 2 4 6 6 10 "2.5 at 0 0 2 4 4 5.5 at 8.5 14 at 9 14 sixteen 17 28 at 9 14 sixteen 17 25 at 10 12 thirteen nineteen 6 7 9 YU fifteen 2 g 4 4 15 15 2 4 8 10 4 5 8 9 10 fifteen 5 10 1-2 25 2 4 4  3 4 4, 5 0.5 2 2.5 5 4 5 6.5 7.5 at 12 3,5 5 8 8 11.5 3 4, 5 b5 5 9 2 3 3,5 4 4,5 I I 2 g 3 4 4 5 8 10 fifteen 6 7 9 Yu IS 35 6 8 E 1C fifteen 35 3 4 4 5 fifteen 4 4 5 6 in IS ,5 5 7 8 9 23 4 7 9 10 II 23.5 6 8 to eleven 4 I 8 9 11 4 in 8 And 3, Strugokrasnensky Strength of ceramics on. .1 MZGib, KG / SM2 th re 900.S Prepare according to the Nveston method (prototype) 20 C SOO C Activated by the proposed method 1G 20 C EPA Gusvrov-Ethyl silicate JS 2 JO J5 50 75 13.5 5.3 100. -10.3 2, 9.6 5.1 100 Combined 60 68 60 10 75 25 5.1 6.7 100 -12.5, 10.5 7.2 100 Continuation of table 3 7, 1 2.6 1.1 6.2 100 8, 0 3.1 8, Z 5.2 12, (7.5 100 -9., 5 Continuation of Table 2 Table marriage castings parts, $ the name of detail star rocker hedgehog rye pitch I AM SO1 RU PREPARED to the western way-o (prototype) Ob-I by eotsiy1ru activated by the proposed method .-i-.G .. gospoosotsii | ru beetroot quarry sand obtions BY Litter. prepared according to the mail method 6u (prototype) -1 ob-1 by ratio | RU 8.0 3.1 .V. . , ..- /; H /::.:. . -.  ...: .. V: v: i i: -i: /.- ::; 5 / :: -V /j--../- .. /.;. :.: -l ,, ., 4 - | - “.:;. .  ; 5 / :: -V : /j--../- .. /.;. :.: -l ,, .,