Sandblasting Apparatus

SANDBLASTING APPARATUS (industrial), an apparatus of various designs in which a jet of sand is set into strong translational motion by air (pneumatic sandblasting apparatus) or water (hydraulic sandblasting apparatus) and directed from a nozzle onto the processed object. Sandblasting apparatuses are used for cleaning metal products from contamination, adhering earth, dust, scale, and the like (for example, for cleaning castings in fettling departments, for removing scale prior to electroplating processes, etc.). For cleaning castings, as well as for cleaning products from scale, depending on their size, sandblasting drums, tables [rotating (Fig. 2) and through-type (Fig. 4)], and sandblasting chambers [closed and open (Figures 1 and 3)] are used; for small castings—drums, for medium ones—tables, and for large ones—chambers. Quartz and river sand are used in sandblasting apparatuses, and recently steel sand (grit) has been finding increasingly wider application. The sizes of sand particles are taken depending on the article being cleaned, with particles from 1 to 2 mm being used for cleaning castings, and particles of 0.75 mm and smaller for scale removal. A portion of the sand (5–8%) when working in a sandblasting apparatus is pulverized and turns into dust. The amount of dust detected at the sandblasting apparatus at the sandblaster's workplace reaches (with satisfactory ventilation) 10–30 mg of dust per 1 m³ of air. With very good ventilation, Beintker detected no dust at all. With insufficient ventilation, Leshchinskaya detected 175 mg, and in individual cases even above 200 mg; Kagan, 133–160 mg; Froboese, 334–453 mg of dust per 1 m³. In the absence of ventilation, Beintker detected 2,690 mg inside the chamber. In terms of size, 92–97% of the dust particles are up to 10 µ. In its chemical composition, the dust during casting cleaning consists of a mixed dust of quartz sand and molding earth. The dust formed by the sandblasting apparatus is non-poisonous, except for the dust during the cleaning

Figure 1. Sandblasting chamber.

of lead products, such as storage battery plates. An example of the composition of dust obtained during casting cleaning: SiO₂—88.3%; Al₂0₃—4%; Fe₂0₃—3.6%, the rest being organic substances. Sandblasting apparatus dust, which is essentially quartz in all cases, can seriously damage the respiratory organs (see Dust, Pneumoconiosis). Working with sandblasting apparatuses has replaced processes previously performed on grinding wheels and accompanied by significant dust generation. The use of sandblasting has a certain positive significance from the standpoint of occupational hygiene, since a) it does not require rough physical strength, as in fettling, and b) provided there is a rational dust-removal system, it makes it possible to protect the worker from significant amounts of dust released during cleaning. The aforementioned significant amounts of dust detected during the operation of sandblasting apparatuses show that the absence of appropriate devices for dust removal and supervision of the operation of sandblasting apparatuses can turn the latter into a source of significant dust generation, and the dust, forcibly ejected from the sandblasting apparatus, not only penetrates the body together with inhaled air, but also strikes the worker, getting into his face, eyes, etc. Hygienic measures that significantly reduce dust emission boil down to: 1) exhausting spent sand and the dust formed thereby by means of an exhaust fan; 2) separating the worker directing the sandblasting nozzle by a partition from the place where the sand jet is sprayed; 3) constantly repairing all cracks in the sandblasting apparatus itself and its pipes that allow sand and dust to escape outward. To ensure the protection of the worker from dust when operating sandblasting drums, hermetic closure of the latter is sufficient; when operating rotating sandblasting tables, it is necessary to cover the workplace (rear part) of the table with a casing (canvas, rubber plates) to protect against scattered particles of dust and sand, as well as their sufficient extraction, leaving small openings only for loading and unloading products; when working with sandblasting chambers (depending on whether they are closed or open): in closed ones—allocation of a special compartment (cabin) for the worker, where the worker is placed in front of a door that has openings allowing him to direct the nozzle and observe the cleaning process; exhaust fans extracting air inside the chamber create a rarefied space in it, as a result of which the draft of air goes from the outside (from the compartment where the worker is located) of the chamber into its interior, and the possibility of air (containing dust) entering from the chamber (where cleaning is underway) through the openings in the door into the worker's cabin is eliminated; in open chambers, where the worker is located inside the chamber itself to direct the nozzle, helmets (Fig. 5) are necessary, with breathing occurring through tubes that discharge exhaled air and supply inhaled air (see Protective devices in industry), and appropriate special clothing with tightly fitting sleeves and trouser cuffs. Recently, hydraulic cleaning of castings in chambers, produced by a water jet under high pressure (35–100 atm), has begun to be used. Hydraulic cleaning is more hygienic than sandblasting, because it is completely free of dust, which in a sandblasting apparatus still pollutes the room air to a certain degree. Abroad, sand-hydraulic cleaning is beginning to be used, in which sand is entrained not by a jet of air, as in a sandblasting apparatus, but by a jet of water under pressure.

Figure 2. Sandblasting floor (rotating).

Figure 3. Sandblasting chamber.

Figure 4. Sandblasting table (through-type).

Fig. 5. Scheme of air supply to lead products...