SU1207463A1 - Method of working bars of writing carbonate chalk - Google Patents

Description

I

The invention relates to a method for treating carbonate chalk and can be used, for example, in educational institutions.

The purpose of the invention is to improve the chested surface of the chalk due to the application and prevention of its grinding;

. Example 1, Processing rods writing carbonate chalk are following the technology.

A protective film is applied to the surface of the obese ones produced by the industry of the rods of writing chalk — a double gypsum (CaSO ZHjiO) is impregnated by dipping in 30% sulfuric acid with d 1.219 g / cm and held for 30 s. This forms a film of dihydrate gypsum 0.08 mm thick. The chalk is then washed to remove unreacted sulfuric acid for 3 seconds; subsequent drying of the chalk at 3 minutes (or at room temperature for 1-2 hours).

Example 2 For the manufacture of a non-smudging hand of carbonate chalk, the latter is treated in a 94% solution of sulfuric acid (d 1.831 20 ° C) for 5 seconds. Then it is washed in running water or a bath of water for 10 seconds and the chalk is dried at 150 ° C in an electric oven. for Oh, 1 min (or at room temperature

Thickness of forming coating, mm

The number of layers in the coating

The strength of the coating, the resistance to destruction when the compressive force of 10 N / cm Adhesion of the coating to the surface of the chalk (erase time when processed on a DRSh-200 machine under a pressure of 0.3 N / cm per hour) Solubility in water at 30 ° C, h

Peeling resistance, E / cm

re for 0.5 h). Handless chalk is ready to eat. The thickness of the layer formed is 0.5 mm.

Example 3, Conventional commercially produced carbonate writing. chalk is dipped into 84.48% -s (d "1.780 g / cm) solution of sulfuric acid, in which one molecule of water is used for each HS.SO molecule (ratio: HzSO4: 1: 1). The duration of the treatment of chalk in iJacTBope is 20 s, later on after the formation of the CaSOi protective coating ,. 2 HeO 0.3 mm thick, the chalk is washed in water for 5 seconds and dried in an electric oven for 0.15 hours (or at room temperature for 1 hour),

The cost of chalk with a gypsum coating decreases by more than two times relative to chalk with a silicate coating formed using potassium silicate solution, and more often when using solutions of silicates of other alkali metals Li and Ha,

The table presents data on the properties obtained by the proposed and known methods of chalk with a protective coating.

0.5 1

0.3

one

1.6

3

Not destroyed, Not developed, Not destroyed, Destroyed, destroyed, destroyed

0.5

4.8

12

0.4

5.0

15

0.2 1.2

five

Thus, the application of the proposed method significantly simplifies the technology of making a non-pressing hand of chalk, since the formation of a thick protective (plaster) layer, increases the strength of the coating, due to the fact that the time of erasing the coating when processing the surface of chalk on a DRga-200 machine under pressure .0.3-0.9 N / cm for chalk with a plaster coating is 0.5 h, and for chalk with a silicate coating -0.2 h

As a result of the fact that in a known method a three-layer coating is formed, spontaneous exfoliation often occurs. The gypsum coating practically does not peel off, the chemical resistance of the gypsum coating with respect to water relative to silicate coating will increase by 2-3 times, with respect to alkaline media - by 50-70%, and with respect to acidic media - by 60- 80%,

Claims (2)

1. METHOD FOR PROCESSING ROD WRITING WRITTEN CARBONATE CHALK, including applying a protective film to the surface of the chalk by impregnating it with a solution of a film-forming substance. followed by washing with water and drying, characterized in that, in order to improve the quality of the surface of the chalk due to hardening and prevent chalking, the impregnation is carried out with a 30-94% solution of sulfuric acid with a density of 1.2181.831 g / cm ^g for 5-30 s. 2. The method according to π, 1, about t, l, and that is, drying is carried out at 60-150 ° C for 0.13.0 s. G <o SU, „. 1207463