SU1172146A1 - Self-hardening sand for producing moulds and cores - Google Patents

Abstract

SELF-CONTAINING MIXTURE FOR THE MANUFACTURE OF CASTING FORMS AND RODS, including refractory material based on silica, powdered material based on calcined magnesium oxide, orthophosphoric acid and water, so as to increase the quality of the molds and rods, increase the quality of the molds and rods, and increase the quality of molds and cores. powdered material based on calcined magnesium oxide, pretreated with surfactant of anionic or non-ionic class in an amount of 2, 00% by weight of the aforementioned Oshkoobraznyh material, in the following ratio of ingredients, wt.%: Powdered material based on calcined magnesium oxide, pretreated with anion-active or non-ionic class surfactant in an amount of 0.05-2.00 wt.% 10 by weight of Orthophosphoric material I - 6 Acid 0,25 - 3,00 Water Refractory material based on the rest of silica

Description

1 1 The invention relates to foundry production and, in particular, to compositions of self-hardening mixtures used in the manufacture of molds and cores. The aim of the invention is to improve the quality of the molds and cores by increasing the vivacity of the mixture. The essence of the invention is reduced to the use in the composition of a mixture of a powdered material, based on baked magnesium oxide, previously treated with a surfactant of the anionic or non-ionic classes in the amount of 0.05-2.00% by weight of the powder. The pretreatment of the powdered material based on baked magnesium oxide surfactant consists in applying a surfactant to the surface of said material. This is achieved with, for example, by mixing the powder with the surfactant, however, the best results are achieved with the introduction of the surfactant during the grinding of material based on calcined magnesium oxide in ball vibratory, jet and other types of mills. The specific surface of the powder, determined by air filtration through a layer of material, should be 500-7000 cm / g (according to the ADP-1 device, preferably 2500-5000). As a powdery material based on calcined magnesium oxide, it is intended to use metallurgical or fused magnesite or chromomagnesite. Chromomag nezit is recommended to be introduced into the mixture in higher amounts, than magneite (closer to the upper conditional limit), due to the fact that the content of the active component (magnesium oxide) in chromomagnesite is lower (55–60%), it is in magnesite ( 85 - 95%). Examples of surfactants of the anion-active class are mylonaphs, asidolmilonaphs, and nonionic surfactants of the class - the wetting agent OP-7, as well as synthetic acids with a carbon content of 15-30, for example, oleic acid. When the surfactant content in the powdered material based on calcined magnesium oxide is less than 0.05 wt.%, The technologically required increase in the vitality of the mixture is not achieved, and when its content is 2.00 may,% not 6., a further increase in the vitality of the mixture is observed. When the content in the mixture is less than 1 wt.% Of the mentioned powdered material, pre-treated surfactant, it is impossible to obtain molds with technologically required strength, and when its content is over 10 wt.%, The self-solidification rate of the mixture is too high, which leads to the occurrence of flaking forms. and rods. The content of orthophosphoric acid in the composition of the mixture (1-6 wt.%) Is based on the concentrated acid, but the latter can be used in a wide concentration range of 40 - 80%. A decrease in the concentration of less than 80% is achieved by adding water to the concentrated acid based on the above water content of the mixture (0.25 3, 00 wt.%). The preparation of the mixture according to the invention is carried out as follows. Silica-based refractory material (for example, quartz sand) is mixed for 1–2 minutes with calcined magnesium oxide powder, pretreated with surfactants, then orthophosphoric acid and water are added and mixing is continued for 1–2 minutes. The invention is illustrated by the following examples. Metallurgical and fused magnesite, as well as chromomagnesite of specific surface 4000 (according to ADP-1) were used as the powder material. The OP-7 wetting agent and mylonift were used as surfactants. Prior to use in the blend, the material based on calcined magnesium oxide was ground in a ball mill with a surfactant. The mixture was prepared in a laboratory mixer, the volume of one batch was 10 kg. First, quartz sand was mixed with magnesite for 1–2 min, then phosphoric acid was introduced into water and stirred for an additional 1–2 min. After the mixture was prepared, standard samples with a diameter and a height of 50 mm were made from it by filling in a block of sleeves and manual compaction. The compressive strength of the specimens was determined on a laboratory instrument made by G.Ficher at 0.5, 1, 4 and 24 hours after preparation of the mixture, the vitality was determined visually, friability by the standard procedure 24 hours after preparation, Table 1 Compositions of mixtures 1-8 according to the invention and the composition of mixture 9 according to a known technical solution, adopted as a prototype, are given. From the data table. 2 it follows that the survivability of self-hardening mixtures according to the invention is increased by 17.5 to 100% compared with the known mixture. Naturally, with increased survivability, the initial rate of solidification of the mixture (after 0.5-1 h) decreases, but it remains sufficiently to meet the requirements m technology for the manufacture of medium and large forms and cores in the individual production of castings. At the same time, the daily strengths when using the mixtures according to the invention are 4–23% higher than that of the mixture according to the prototype. The increased survivability of the mixture achieved according to the invention contributes to the improvement of the quality of the forms and rods, especially large forms and rods of complex configurations, which require more than 15 tons to be prepared for 15 to 20 minutes. This is due to the fact that when using a mixture that has lost (partially or completely) its vitality on the surface or in the bulk of the molds and cores, sharply weakened zones appear, which serve as a potential source of scrap castings. It should be noted that, under special production conditions, it is necessary to increase the survivability of the mixtures to 40 - 60 minutes. Such an opportunity is provided by treating powdered magnesium oxide, for example, metallurgical magnesite, silicone surfactants, examples of which are silicone fluids GKZH-10, GKZH-94, as well as representatives of alkylchlorosilanes, alkylaminosilanes or alkylalkoxysilanes. The use of silicone surfactants requires heat treatment of the passivated powder at a temperature of 50 for 0.5-1.5 hours. At the same time, a mixture containing 90.5% by weight of quartz sand, 3% by weight of phosphoric acid (density 1.58 1, 60 g / cm), 5% by weight of metallurgical magnesite, treated with 1% NGL-94, and 1.5% by weight of water, had a durability of 65 minutes, the compressive strength after 2 hours - 1.2 kgf / cm, the strength through day 84 - 90 kgf / cm.

97.75 90.5 81 90.5

13 63

0.25 1.5 3., 1.5

90.5 90.5 90.5 80.5 90.5

33383

1.5 1.5 1.5 1.5 1.5

5 10

Ingredient

PLA magnesite, treated with I wt.X mylonaph

Chromomagnesite, treated with I wt.H

Metallurgical magnesite (cutting processing)

22

33 27

ten

29

26

17

34

thirty

Claims (1)

SELF-CURING MIXTURE FOR THE PRODUCTION OF CASTING FORMS AND RODS, including silica-based refractory material, powdered material based on calcined magnesium oxide, phosphoric acid and water, characterized in that, in order to improve the quality of the molds and cores, the mixture contains quicker material based on calcined magnesium oxide, pretreated with a surface-active substance of the anionic or nonionic class in an amount of 0.05 2.00% by weight of said powder shaped material, with the following ratio of ingredients, wt.%: Powdered material based on calcined magnesium oxide, pretreated with a surface-active substance of anionic or nonionic class in an amount of 0.05-2.00 wt.% By weight of the material Phosphoric acid Water Silica-based refractory material 1 - 10 I - 6 0.25 - 3.00 Other ^{January 1172}