SU557858A1 - Mixture for making molds and cores - Google Patents

Description

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The invention relates to a foundry, in particular, to mixture compositions for the manufacture of foundry cores and heat-curable molds.

The known mixture for the manufacture of casting cores and heat-curable forms, besides lignosulfonates based on a refractory filler, and a binder mineral activator, which is used as a slurry of sodium 1. Because of the reversible curing of the lignosulfonates binder, characteristic for this mixture, the latter has a high hygroscopicity, which leads to the softening of the rods and shapes under the influence of moisture coming from the environment.

The closest to the described invention in its technical essence and the achieved result is a mixture for the manufacture of casting cores and heat-curable forms, containing, along with a refractory filler, a binder based on lignosulfonates and a mineral curing activator of the binder, which is used as ammonium mineral salts , for example ammonium sulfate 2. In the process of drying the cores and molds from this mixture at a temperature of 280-300 ° С

irreversible curing of the binder on the basis of lignosulfonates takes place, as a result of which the strength increases and the hygroscopicity of the mixture decreases. However, it is desirable to further improve these properties of mixtures, which will increase the drying speed, increase the output of rods and molds, improve the quality of castings.

The purpose of the invention is to increase the strength of rods and shapes and reduce their hygroscopicity. This is achieved in that the mixture contains phosphorous acid as the mineral curing activator of the binder at the following ratio of ingredients, ree. %:

Binding, it is based on lignosulfonate1,5-10,5

Phosphoric acid 0,15-5,25

Refractory fillerOther

Standard phosphorous acid (MRTU 69-6555-70) is a powdery substance, soluble in water. It can be used both in the initial dry form and in the form of an aqueous solution; chemical formula NZROz. When the content of phosphorous acid in the mixture is below 0.15 weight. % neutralizes its effect as a binder curing activator, and when it contains an acid more than 5.25 weight. % further improvement of properties not. is observed.

An example of a binder based on lignosulfonates is the sulphite-yeast brew {OST-81-79-74).

The activation of lignosulfonate with phosphorous acid is carried out during the preparation of the mixture. Acid may be added to the excipient before or after the introduction of the lignosulfonates. It is also possible to preliminarily introduce phosphorous acid in the form of a powder or an aqueous solution into a binder based on lignosulfonates.

The rods and molds of the proposed mixture are cured by heat treatment in the temperature range of 280-300 ° C. This results in the condensation of lignosulfonates, their transfer from the glassy to the flowable state, and then into the irreversible state. Heat treatment of the rod and its forms at a temperature below 280 ° C does not ensure complete transition of the lignosulphonates to an irreversible state, as a result of which the mixtures have an increased hygroscopicity. It is not advisable to increase the drying temperature over 300 ° C, since the surface strength of the rods and molds is reduced.

The choice of phosphorous acid as an activator of curing lignosulfonates is due to the fact that, along with a high rate of curing of phosphorous acid, it also provides a higher degree of durability of the mixtures after their thermal treatment at 280-300 ° C compared with the use of ammonium mineral salts as activators ( for example ammonium sulfate), and well-known mineral acids (for example, phosphoric or sulfuric).

Example. Mixtures No. 1-3 are prepared, containing phosphorous acid as an activator (according to the invention), and mixture No. 4, containing ammonium sulfate (prototype) as an activator. In addition, to compare the effectiveness of acid activators, mix No. 5 is prepared using orthophosphoric acid as an activator and mixture No. 6, in which sulfuric acid serves as an activator. The compositions of mixtures No. 1-6 are given in table. 1. Contains binder and activators in

Table 1

table 2

Mix x No. 1-6 choose, based on their optimal values.

The order of preparation of the mixtures is as specified. Standard samples are prepared from mixtures and cured at 280-300 ° C for 7.5; 15; thirty; 45; 60 and 75 min. The tensile strength of the mixtures is determined by the standard method, and hygroscopic - by the mass of moisture adsorbed by the hardened samples for 48 hours at 20 ° C and 98% relative humidity.

The strength and hygroscopicity of mixtures No. 1-6 are given in table. 2

From tab. 2 that when using phosphorous acid as an activator, the strength of the mixture rises to 20.60 kgf / cm, and the duration of heat treatment is reduced from 45-60 minutes to 30 minutes. In addition, the hygroscopicity of the mixture is reduced.

In proportion to the increase in curing speed, productivity increases and the costs associated with heat treatment of the cores and molds are reduced. In addition, the tendency of the mixtures to burn through decreases, and the surface strength of the rods increases.

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Claims (2)

1. The author's certificate number 63999, M. Kl.2 V 22C 1/00, 1941. 2. Collector of scientific papers of the Chel Binsk Polytechnic Institute, Chel Binsk, 1975, no. 155, p. 154-159 (prototype).