Chemically hardening mixture for the production of casting molds and cores

Abstract

FIELD: foundry production.SUBSTANCE: chemically hardening mixture for the production of casting molds and cores contains a chemically hardening binder, a refractory bulk filler and fractionated magnetite. Fractionated magnetite is introduced into the mixture as a cooling additive, with the refractory bulk filler and fractionated magnetite taken in the following ratio, wt.%: 0.1–77.7 refractory bulk filler, 22.3–99.9 fractionated magnetite. The introduction of a cooling additive with improved temperature-conducting properties allows for an increase in the crystallization rate of the casting metal.EFFECT: reduction of casting defects and increases dimensional accuracy.1 cl, 3 tbl

Description

[0001] Application area

[0002] The invention relates to the metallurgical industry, in particular relates to foundry production.

[0003] Technology Level

[0004] It is known that previously, fractionated minerals (chromite concentrate, distensilimanites, etc., with high thermal conductivity) were used to intensify heat dissipation and to accelerate the crystallization process of the poured metal in order to reduce defects caused by long-term volumetric solidification.

[0005] Also, magnetite (iron oxide Fe3O4) additives were previously used in the core mixture of silica-based refractory filler to prevent defects associated with thermal expansion of silica - not to increase the heat transfer rate.

[0006] A known additive (RU2570680C2 dated 30.12.2010, IPC class B22C 1 / 02) preventing the occurrence of galls is used for the production of casting molds and cores. The additive contains hollow aluminosilicate microspheres in an amount of 90% to 99% and flux from 1% to 10% of the total additive weight. Moreover, the hollow aluminosilicate microspheres contain aluminum oxide in an amount of 15% to 45% by weight.

[0007] The disadvantage is the low thermal conductivity of hollow spheres, which leads to a slowdown in the crystallization process.

[0008] A mixture is known for the production of casting cores (SU668764A1 dated 25.06.1979, IPC class B22C 9 / 10, B22C 1 / 00), used to obtain cavities of gas-turbine blades, including iron, electrocorundum, marshalite, low-melting plasticizer PP-15 (a mixture of paraffin and polyethylene), where in order to increase the strength of the rods, accelerate the sintering process and reduce their cost, as an iron-containing element, the mixture contains an iron derivative in the form of its oxide with the following ratio of ingredients, wt.o / o: marshalite 8-10, light plasticizer PP-15, iron oxide 16-29, electrocorundum.

[0009] The disadvantage is that this mixture is not applicable for chemically hardening mixtures, which makes it impossible to widely use in foundry industry.

[0010] A filler for foundry molding sand (RU2552216 C1 dated 03.04.2014, IPC class B22C 1 / 00) is known, which contains in wt.%: chromite sand 30-70, kyanite-sillimanite 70-30. The chromite sand used is rounded. The average grain size of kyanite-sillimanite ranges from 0.83 to 1.25 of the average grain size of chromite sand.

[0011] The disadvantages include low resistance to nicks and burrs during metal pouring, as well as the relatively high binder consumption required to ensure high strength of the cured mixture. These filler components are expensive and difficult to find on the market, limiting their widespread use in foundries.

[0012] The closest filler composition to the proposed solution is (RU2450885 dated April 12, 2011, IPC class B22C 1 / 00, B22C 3 / 00), which contains, in wt.%: 55-65 chromite sand and 45-35 kyanite-sillimanite, the average grain size of which is 0.3-0.65 of the average grain size of chromite sand. This material increases sintering resistance, and its use reduces surface roughness, increases heat transfer, and improves the processability of cladding application.

[0013] The disadvantages of this material include poor gas permeability and the relatively high binder consumption required to ensure high strength of the cured mixture. These filler components are expensive and difficult to find on the market, limiting their widespread use in foundries.

[0014] The objective of the claimed invention is to develop a chemically hardening mixture for the production of casting molds and cores, which ensures a reduction in defects in castings.

[0015] Disclosure of the essence of the invention

[0016] The technical solution to the above problem is the development of a chemically hardening mixture for the production of casting molds and cores, consisting of a chemically hardening binder and a refractory bulk filler, which, in order to reduce defects in castings by regulating the rate of metal crystallization, contains a cooling additive in the form of fractionated magnetite (iron oxide Fe3O4) in the following ratio:

[0017] 0 - 98% loose filler

[0018] 2-100% fractionated magnetite.

[0019] The specified technical solution, depending on the area of ​​the casting mold and / or rods, ensures an increase in the rate of metal crystallization in the casting, locally or volumetrically, while:

[0020] - reduces the likelihood of defects in the form of shrinkage cavities and porosity;

[0021] - reduces the likelihood of hot crack defect formation;

[0022] - increases the dimensional accuracy of casting due to rapid strength gain and reduction of local deformations

[0023] - improves the mixture's knockout properties.

[0024] Implementation of the invention

[0025] The following terms are used in the claimed technical solution:

[0026] A mixture is a system consisting of two or more substances (mixture components).

[0027] A casting mold is a system of elements that forms the working cavity for forming a casting. The working part of the mold is the cavity in which the metal cools during casting, solidifying and taking the shape of the final product.

[0028] Cast cores are removable forming elements installed in molds, necessary for creating cavities or openings of the desired configuration, as well as other complex contours, including sections of external surfaces. Casting cores are secured using projections that fit into corresponding depressions in the mold and are called core marks. The configuration and dimensions of the core marks should ensure ease of installation and stable attachment of the cores in the mold. Casting Molds and Cores.

[0029] Metal castings are metal products obtained by pouring (casting) molten metal into a special mold.

[0030] Metal defects are deviations in the quality characteristics of the macro- and microstructure of steel, cast iron, and non-ferrous alloys from technical specifications, occurring during the production and manufacture of semi-finished and finished products, storage conditions, and subsequent use of the finished product. GOST 30242-97

[0031] A mixture additive is a powder, granular or liquid substance that can be included in the mixture or coat an already hardened composition, qualitatively changing its properties.

[0032] Magnetite is a widespread black mineral of the oxide class, a natural oxide of iron (II, III).

[0033] Fractionated magnetite is a natural iron oxide that is used as a filler for heavy concrete, masonry and finishing building mixtures.

[0034] The rate of crystallization is the rate of increase of the total volume (mass) of the solid phase during crystallization.

[0035] Chemically hardening mixture for the production of casting molds and cores, consists of a chemically hardening binder and a refractory bulk filler, where

[0036] A chemically hardening binder is an organic or inorganic substance that ensures the binding of grains of bulk filler into a finished form or rod with the required strength.

[0037] The organic substances used in the claimed technical solution are organic phenolic (Alpha-Set) resins with ether hardeners or furan resins with acid catalysts, etc.

[0038] The inorganic substances used in the claimed technical solution are liquid glass (sodium / potassium silicate), phosphate binders.

[0039] Refractory bulk filler is a granular substance of a certain granulometric composition that has fire resistance, for example, quartz sand.

[0040] The claimed chemically hardening mixture is intended for the production of casting molds made in the form of a working cavity for forming castings and cores, and consists of a chemically hardening binder and a refractory bulk filler.

[0041] The chemically hardening binder is:

[0042] - an organic substance in the form of organic phenolic (Alpha-Set) resins with ester hardeners or furan resins with acid catalysts. In the preferred embodiment, phenolic (Alpha-Set) resins are mainly used;

[0043] - or an inorganic substance in the form of liquid glass (sodium / potassium silicate) or phosphate binders. In the preferred embodiment, liquid glass mixtures are primarily used.

[0044] At the same time, the chemically hardening binder itself ensures the binding of grains of loose filler, which contains a cooling additive, into a finished form or rod.

[0045] The specified mixture uses a loose filler in the range of 0-98%. This loose filler is a granular substance with a specific particle size distribution, typically sand (a granular substance) with fire resistance. In the preferred embodiment, quartz sand is used, as this sand, as demonstrated by experience, exhibits high resistance to mechanical, chemical, atmospheric, and water influences.

[0046] A cooling additive has been added to the specified mixture, which increases the thermal diffusivity of the mixture, which characterizes the rate of temperature equalization of a substance in nonequilibrium thermal processes.

[0047] The concept of “cooling” is taken from technological practice and refers to the characteristics of the thermophysical properties of the mixture.

[0048] The cooling additive itself is made in the form of fractionated magnetite (iron oxide Fe3O4) of fraction 01-03 mm in the following ratio: 0 - 98% bulk filler, 2-100% magnetite.

[0049] Fractionated magnetite is chosen for its well-known properties such as increasing density, increasing mass, reducing volume, noise and vibration insulation, radiation protection and reducing cracking.

[0050] The specified magnetite particle size range of 0.1-0.3 mm is chosen due to its similarity to the filler particle size. This magnetite particle size ensures optimal strength while minimizing binder use.

[0051] The resulting mixture has the required strength, which is confirmed by the experiment conducted at different times and with different ratios (in percentage) of the cooling additive:

[0052] Amount of cooling additive, % Tensile strength of a standard specimen (casting) (average value of 3 measurements), MPa, through: 1 hour 2 hours Day 3 0,191 0,240 0,410 5 0,186 0,239 0,389 10 0,183 0,236 0,380 15 0,170 0,226 0,294 25 0,154 0,217 0,264 50 0,214 0,276 0,662 75 0,205 0,272 0,616 100 0,201 0,260 0,585

[0053] The above ratio shows that varying amounts of quenching additive (the experiment was conducted as a percentage of the total mixture weight) increases the tensile strength of the casting. The preferred amount is 25%, as the experiment yielded the best value.

[0054] Metal crystallization rate is regulated by the enhanced thermal conductivity of the quenching additive at varying heating times, ranging between 15 seconds and 240 seconds. Heating temperatures for various fillers range from 35°C to 383°C.

[0055] Heating time, sec. Heating temperature of casting molds and cores, with different amounts of materials in the mixture, °C Refractory filler without additives 50% refractory filler 50% magnetite 25% refractory filler 75% magnetite Magnetite without filler 15 35 36 37 37 30 103 108 110 117 45 149 157 163 169 60 172 187 202 209 75 188 211 225 237 90 204 232 248 262 105 220 254 271 283 120 236 270 284 300 135 245 281 302 314 150 254 291 315 331 165 261 298 323 342 180 269 304 329 352 195 276 309 336 362 210 281 317 345 370 225 287 325 352 376 240 293 334 360 383

[0056] The following ratio shows different heating times ranging from 15 sec to 240 sec, where the relative rate of heat transfer from the mold / core material to the crystallizing metal changes with different mixing ratios.

[0057] According to data from foundries, when producing large steel and cast iron castings, the use of an additive in the mixture based on quartz sand in an amount of 5-15% reduced the volume of shrinkage defects by at least 20% and reduced geometric distortion by 50%.

[0058] Heating time, sec. Relative rate of heat transfer by the mold / core material from the crystallizing metal, relative units. Refractory filler without additives 50% refractory filler / 50% magnetite 25% refractory filler / 75% magnetite Magnetite without filler 15 1 1,02 1,05 1,05 30 1 1,04 1,06 1,13 45 1 1,05 1,09 1,13 60 1 1,08 1,17 1,21 75 1 1,12 1,19 1,26 90 1 1,13 1,21 1,28 105 1 1,15 1,23 1,28 120 1 1,14 1,2 1,27 135 1 1,14 1,23 1,28 150 1 1,14 1,24 1,3 165 1 1,14 1,23 1,31 180 1 1,13 1,22 1,3 195 1 1,11 1,21 1,31 210 1 1,12 1,22 1,31 225 1 1,13 1,22 1,31 240 1 1,13 1,22 1,3

[0059] The claimed chemically hardening mixture for the production of casting molds and cores provides a positive effect:

[0060] - increased rate of heat transfer from the surface of the poured metal, compared to traditional mixtures based on silicon dioxide;

[0061] - reducing the use of expensive and scarce minerals to increase the rate of heat transfer from the surface of the cast metal;

[0062] - availability of source products on the Russian market;

[0063] - The mixture is relatively easy to prepare and use. It can be easily integrated into existing equipment and processes.

Claims

A chemically hardening mixture for the production of casting molds and cores, containing a chemically hardening binder, a refractory bulk filler and fractionated magnetite as a cooling additive, characterized in that the refractory bulk filler and fractionated magnetite are taken in the following ratio, wt. %: refractory bulk filler 0,1-77,7 fractionated magnetite 22,3-99,9