RU2038182C1 - Self-hardening mixture for manufacturing of casting molds and rods - Google Patents

Abstract

FIELD: casting. SUBSTANCE: proposed mixture contains (mass): aqueous solution of alkali metal silicate 2-5, acetates of ethylene glycol or glycerine as hardener 0.2-0.7, additive 0.25-1.25 and fireproof filler on the base of silicium dioxide the rest. Copolymer of maleic anhydride and styrene having SO₃Na group in benzene ring which is saponified by aromatic amine is used as mentioned above additive. EFFECT: improves quality of desired mixture. 6 tbl

Description

 The invention relates to foundry, in particular to compositions of self-hardening molding sand for foundry cores and molds. Self-hardening molding mixtures are known that contain a refractory filler, an aqueous solution of alkali metal silicate and esters as a liquid hardener, such as cyclic ether of propylene glycol and carbonic acid propylene carbonate [1] esters of acetic acid and ethylene glycol (acetic acid glycerol ethylene glycol acetates) or (glycerol acetates triacetin, diacetin and their mixture).

 The disadvantages of mixtures with esters are the difficult knockability from castings despite the low content of liquid glass in the mixtures, as well as the difficulty in controlling the survivability of the mixtures when using the same brand of acetates of ethylene glycol or glycerol. Mixtures with propylene carbonate have limited survivability, making them difficult to use at elevated air temperatures or in the manufacture of large molds and rods.

 Mixtures with acetates of ethylene glycol and glycerol allow for wide control of survivability, however, for this it is necessary to use several brands of hardeners with different fractional compositions.

 A disadvantage of the known mixtures is the relatively low strength at the initial stages of hardening, which determine the cycle of manufacturing molds and rods and the time they reach manipulative strength (the ability to transport rods and molds, their assembly, etc.).

Closest to the proposed is a mixture with esters with the addition of NF, which improves knockability, increases survivability and reduces the tearability of mixtures and is a condensation product of naphthalenesulfonic acid and formaldehyde (NF) [2]
The disadvantage of the mixture with the addition of NF is that the latter slightly increases the survivability and significantly reduces the strength in the initial stages of hardening. When introduced into a mixture containing 2.5 wt. water glass and 0.3 wt. ethylene glycol acetate, NF additives in an amount of from 0.3 to 1.0 wt. the compressive strength of the mixture (MPa) decreases from 0.33 (mixture without additives) to 0.17 (at 1% NF).

 Another disadvantage of this mixture is the strong annoying odor released during the manufacture of the mixture with the addition of NF, which worsens the sanitary and hygienic working conditions.

 The purpose of the invention is the regulation of the survivability of the mixture, increasing the initial strength, improving knockability.

The proposed self-hardening mixture for the manufacture of foundry molds and cores contains a refractory filler based on silicon dioxide, an aqueous solution of alkali metal silicate, an ester (acetates of ethylene glycol or glycerol) as a hardener and, as an additive, styromal, a copolymer of maleic anhydride with alcohol, saponified by aromatic amine, in the benzene ring of which there is a sulfite group SO ₃ Na in the following ratio of components, wt. An aqueous solution of alkali metal silicate 2-5 Ester hardener 0.2-0.7 Styromal 0.25-1.25 Refractory filler based on silicon dioxide Else
The mixture contains ethylene glycol acetate as a hardener.

 The mixture contains glycerol acetate as a hardener.

 The mixture is prepared as follows.

 Pre-mechanically mix the additive with an aqueous solution of alkali metal silicate (liquid glass). Next, a refractory filler, a hardener and then a previously prepared composition consisting of water glass and styromal are successively introduced into the mixer. This composition can be stored for 1-1.5 hours, after which the separation of the components is observed and additional mixing is necessary.

To increase the resistance of its composition is heated to 75-85 ^C with constant stirring, kept at this temperature for 35-40 min. A composition prepared in this way can be stored for 3 hours.

It is also possible to introduce styromal with a density of 1020-1030 kg / m ³ into the autoclave together with a silicate block when cooking liquid glass from a silicate block. Liquid glass prepared in this way can be stored for an unlimited time without delamination of the components.

 Using styromal as an additive allows us to solve several important problems for practice at the same time: to widely regulate the survivability of the mixture using a hardener of the same fractional composition; increase the initial strength of the mixture, reducing the time before opening the core boxes and broaching the model; sharply reduce the complexity of knocking out mixtures from castings. The possibility of increasing the initial strength with the use of styromal and decreasing the crumbling rate allows reducing the content of liquid glass in the mixture to 2.0-2.5 wt. and thereby further improve knockability.

 The optimal content of styromal in mixtures of 2.5 wt. liquid glass 0.7-1.0 wt. the upper limit of 1.25 wt. A further increase in the content of the additive has almost no effect on strength, increases gas production and the cost of the mixture.

 In the table. Figures 1–4 show data on the effect of styromal on the properties of liquid-glass mixtures cured by liquid hardeners based on ethylene glycol acetates. At the same time, 50 M ethylene glycol acetate (very slow) was used, which provides increased survivability of the initial mixtures. A similar effect is exerted by the addition of styromalium on the properties of mixtures cured by glycerol acetates (Table 5.6, mixtures 4 and 5). The same tables provide data on the composition and properties of the mixtures at the limiting values of the content of binder liquid glass and ester hardener. When the content of liquid glass is less than 2.0 wt. the strength properties of the mixture are sharply reduced and there is a large crumble.

 The introduction of a mixture of liquid glass more than 5.0 wt. impractical, since in this case the strength properties change little, and the laboriousness of knocking out greatly increases.

 Usually the ester hardener is given in the mixture in an amount of 10-15% by weight of the binder. With a high content of hardener, strength and other properties hardly change, and the cost of the mixture increases markedly. Therefore, the limit on the content of hardener is limited to 0.7 wt. at 5.0 wt. liquid glass.

 The mixture is prepared from a refractory filler, a binder of liquid glass, a liquid ester hardener and additives that improve the properties of the mixture. As a refractory filler, quartz sand or highly refractory fillers are used: zircon, distensillimanite, rutile, chromite, chromomagnesite, etc.

As a binder aqueous solution of alkali metal silicate, liquid glass of a module of 2.2-3.0 with a density of 1400-1520 kg / m ^{3 is used} . With a module of more than 3.0, the survivability of the mixture is sharply reduced, and the tearability increases to unacceptable values. With a modulus of less than 2.2, the knockability of the mixture deteriorates markedly and volume hardening is reduced. With a decrease in the density of liquid glass, the survivability of the mixture decreases slightly, the initial strengths decrease slightly, the daily strengths remain quite high. When the density of water glass is lower than 1400 kg / m ³ , deformation of molds and cores can occur, and when the density is more than 1520 kg / m ^3, knockability deteriorates and strength decreases. When preparing the mixture using styromal with a density of 1020-1030 kg / m ³ .

 Mixtures were prepared in a paddle mixer as follows.

 A refractory filler was loaded into the mixer, a dose of a liquid hardener was introduced and mixed for 1 min, after which a previously prepared liquid composition consisting of an aqueous solution of sodium silicate was loaded and styromali, after which the mixture was stirred for 45-60 s until it was ready. The specified liquid composition was prepared by mechanical stirring of liquid glass and styromali to a homogeneous state.

 Blocks were packed from the prepared mixture to obtain standard cylindrical samples and to determine the compressive strength and crumbling of the mixture according to the standard method.

 The survivability of the mixture was determined on the device of the TsNIITMASH design, working on the principle of measuring the resistance of a cross-shaped rotor rotating in a freshly prepared mixture.

 The complexity of knocking out the mixtures was determined when casting steel with a technological sample weighing 150 kg with five rods with a cross section of 100x100 mm, a height of 180 mm, made from various tested mixtures. Knocking out the rods was carried out mechanically at the same intensity of impact on the filled rod and was expressed in arbitrary units.

 From the data given in Tables 1 and 2, it can be seen that as the content of styromal in the mixture increases, the survivability of the mixture decreases, the hourly and 3-hour strengths increase, the tearability of the mixture decreases, and the knock-out time drops sharply. From a comparison of mixtures 5 and 8 (prototype) containing the same amount of water glass, styromal and NF, it follows that the mixture with styromal is knocked out much better than the mixture with NF (49 and 67 conventional units, respectively). Thus, the distinctive features of the inventive mixture and the method of its preparation compared to the prototypes are the following: styromal reduces the survivability of the mixture and allows you to adjust it over a wide range using one brand of hardener with increased initial survivability of the mixture, while the addition of NF only slightly increases the survivability of the mixture ; styromal significantly increases the initial strength of the mixture, while NF lowers; styromal to a much greater extent than NF improves the knockability of the mixture (when the content of liquid glass is 3.5 wt.%, the complexity of knocking out when 1 wt. with a liquid glass content of 2.5% by weight 5.7 times and 2.86 times, respectively); styromal is odorless when preparing the mixture, while when using NF an unpleasant pungent odor is released.

 The composition of the mixture are given in table 1.

 The properties of the mixtures are given in table. 2.

Claims (1)

SELF-CURING MIXTURE FOR THE PRODUCTION OF CASTING FORMS AND RODS, containing a silica-based refractory filler, an aqueous solution of alkali metal silicate, ethylene glycol or glycerol acetates, characterized in that it additionally contains a styromal copolymer of maleic benzene amide with an amide with an amide there is a sulfite group SO ₃ Na, in the following ratio of components, wt. Alkali metal silicate aqueous solution 2 5
Ethylene glycol or glycerol acetates 0.2 0.7
Stiromal 0.25 1.25
Silicon Dioxide Refractory Filler

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