Grinding

Grinding of metal products in its various modifications pursues three kinds of objectives: 1) removal of excess material from the surfaces of objects being worked (rough grinding); 2) sharpening cutting tools on the edge or at the ends (grinding, honing); 3) imparting smoothness and gloss to the surfaces of objects being worked and their parts (fine grinding, polishing, glazing). The most common instrument for grinding is grinding wheels of mineral composition. Until recently, these wheels, or stones, were made almost exclusively from sandstone—a natural rock consisting mainly of crystalline particles of quartz sand with an admixture of iron oxide, bound together by a cementing substance—carbonic or silicic calcium. At present, natural sandstone grinding stones are gradually being displaced from production by artificial stones, which are distinguished by greater strength and productivity. Artificial stones are made from crushed natural minerals—emery and corundum—and from artificially prepared materials—alundum, carborundum, etc. The main constituent part of emery (50-60%), corundum (75-98%), and alundum (up to 94%) is crystalline aluminum oxide (Al₂O₃), carborundum mainly (90-98%) consists of silicon carbide (SiC). All these substances possess very high grinding qualities, approaching in this respect the most perfect grinding material—diamond. Abrasive materials find application in grinding not only in the form of wheels, but also in the form of fine-grained powders, usually applied either to the peripheral surface of a wheel—wooden, leather, felt, hair, cloth, etc.—or to the surface of the object being ground. As grinding powders are used: emery (the cheapest and most common grinding powder), pumice, crocus and mummy (iron oxide), Vienna lime, kaolin, etc. To enhance or soften the action of grinding and polishing compositions, to wash away spent and worn particles, and finally to cool the object being heated during grinding, recourse is often had to wetting the grinding composition and the object with various liquids, primarily water, which is widely used mainly in grinding and honing on stones, as well as with various oils and fats used exclusively in polishing operations with powder. The main professional hazard in grinding operations is dust, continuously released into the air during the grinding process. The degree of air dustiness and the composition of the dust depend on a number of factors, among which the composition of the material being ground and the method of its use play a decisive role. Of all types of grinding, the greatest importance from a professional-hygienic point of view is grinding on mineral wheels—natural and artificial. As can be seen from Table 1, work on natural stones is associated with significantly greater dust emission than on artificial ones. This is explained by the comparative softness of sandstone stones, due to which they wear out very quickly (the wear rate of natural stone, all other conditions being equal, is 10-15 times greater than that of artificial stone). A special interest is presented by the question of the influence of wetting the stone on the degree of dustiness. From the table it is evident that in this respect there is also a sharp difference between work on natural and artificial stones. While on artificial stones the wet method of work plays a positive role, definitely reducing air dustiness compared to the dry method, wet grinding on natural stones almost invariably gives dustiness indicators exceeding those for similar work by the dry method. Type of grinding Dust found Date of study Author mg/m³ Number of dust particles in 1 cm³ air 1. Grinding of metal products on natural stones (Sheffield, England): b) dry grinding with poorly acting exhaust ........ c) dry grinding with well-acting exhaust ....... d) wet grinding...... 2. Grinding of metal products on natural stones (axe factory, USA): a) dry grinding with exhaust..... 33.1 18.7 - 50.0 0.81-19.6 0.84-28.7 1.94 14.6 9.9 4.5 2.0 13.81 7.82 0.03- 785 1 047-3 272 647-1 150 246- 428 203- 295 1 000-4 060 900-3 495 1922/23 » » » » » » » » ft Ь » » Middleton Winslow Greenburg Teleky and Ro- senthal-Deus- sen TeleKy and Ro- senthal-Deus- sen Pik, Brum- stein et al. Dmitriev 3. Grinding of metal products on natural stones (Solingen, Germany): a) dry grinding with exhaust..... b) wet grinding........... 4. Grinding of metal products on artificial stones (same place): a) dry grinding without exhaust..... c) dry grinding with exhaust..... 5. Grinding of metal products on artificial stones (Moscow, plant 'AMO', 'Vl. Ilyich'): a) dry honing........ b) dry grinding............ 6. Grinding of metal products on artificial stones (Moscow, Tool Plant): b) wet grinding........... 3. As can be seen from Table 1, work on natural stones is associated with significantly greater dust emission than on artificial ones. This is explained by the comparative softness of sandstone stones, due to which they wear out very quickly (the wear rate of natural stone, all other conditions being equal, is 10-15 times greater than that of artificial stone). A special interest is presented by the question of the influence of wetting the stone on the degree of dustiness. From the table it is evident that in this respect there is also a sharp difference between work on natural and artificial stones. While on artificial stones the wet method of work plays a positive role, definitely reducing air dustiness compared to the dry method, wet grinding on natural stones almost invariably gives dustiness indicators exceeding those for similar work by the dry method. No less sharp is the difference between grinding on natural and artificial stones in regard to the chemical composition of the resulting dust: dust from grinding on natural stones consists mainly of mineral particles, mainly of crystalline free silicon oxide (SiO₂), which, as is known, plays the most serious role in the pathogenesis and course of the most common form of pneumoconiosis—silicosis and dust tuberculosis. When grinding on artificial stones, however, metal particles prevail over mineral ones, and the latter consist mainly of aluminates or bound silicates (SiC), which have a much lesser effect on the respiratory organs than SiO₂. Thus, grinding on natural stones is much more harmful, both in terms of the degree of dustiness and the chemical properties of the dust entering the air, than grinding on artificial stones, and the wet method of work does not reduce this harm, but on the contrary, aggravates it. This last circumstance, in combination with other aspects of the work process and its environment—often abnormal, strained body position, dampness and wetness, splashing of open parts of the body and clothing with dirty sludge and dusty water—makes work on natural stones by the wet method the most harmful modification of grinding. Fortunately, in large industry, which very widely uses grinding processes, natural stones have outlived their usefulness and have been almost completely replaced by artificial ones, but in small industry, both in numerous semi-handicraft and handicraft workshops and in large enterprises manufacturing various cutting tools and implements, scythes, shovels, sabers, files, surgical instruments, etc., as well as knives, forks and other metal products of 'wide consumption,' grinding on natural stones is still strongly widespread. In full accordance with this are the data characterizing the mortality and morbidity of grinders. These data, almost exclusively foreign, testifying to the high incidence of diseases among grinders, mainly of the respiratory organs and pulmonary tuberculosis, and thereby confirming the long-established assessment of grinding as one of the most harmful professions, relate mainly to workers on natural stones. Particularly unfavorable, as was to be expected, are the old statistical indicators relating to the second half of the 19th century. Thus, according to Oldendorf's data, mortality among grinders in the Solingen district, this famous center of German small industry, is expressed by the following figures: total mortality—30.4 and from tuberculosis—23.8—(per 1000); corresponding indicators for the rest of the male population—19.6 and 9.0. Also very unfavorable are other indicators: the average age of deceased grinders for 1870-74 is 37.7. Of 256 grinders who died in Solingen and its district in 1848-73, 153 (59.6%) did not live to the age of 40. Later data, relating to the time when, under the influence of technical development on the one hand and the persistent struggle of workers' organizations for improvement of working conditions on the other, health measures were gradually being introduced in enterprises, give somewhat better indicators, however, mortality from tuberculosis remains still very high. Thus, in Sheffield, an English center of the grinding industry, mortality from tuberculosis among grinders in 1905-1907 was 16.3%, among saw filers—7.2%, with the general indicator of mortality from tuberculosis for the entire population being 2.6%. In Solingen, according to data for 1923-27, mortality among the entire population and among grinders gives significantly lower indicators than in the old years (Table 2). However, as can be seen from Table 2, mortality from tuberculosis among grinders remains high, exceeding the average indicator by two times. Unreasonably high are the mortality figures for the same years among grinders in the vicinity of Solingen—Remscheid and Cronenberg, which is explained by the extremely unsanitary condition of the enterprises (Teleky): Table 3. Grinders Total mortality Mortality from tuberculosis Remscheid grinders ..........

Krokenberg grinding - 21.1 16.1 9.7 7.4 From old data on the morbidity of grinders, we cite the figures of Moritz and Ropke, who in 1899 among 1,250 Zolingen grinders they examined found 9% tuberculosis. According to comparatively newer data from the Leipzig hospital fund (1910), grinders show a total number of days of disease 40% higher than average, a tuberculosis indicator 2½ times greater, and diseases of the respiratory organs - almost twice the average. Of great interest are the latest data from Middleton (Middleton, 1923) and Lochtkemper (Lochtkemper, 1929). Middleton among the 269 Sheffield grinders he examined on natural stones - in most cases 'wet' - found 37 cases of tuberculosis and 217 cases of pneumoconiosis, including 159 stage I, 50 stage II, and 8 stage III. Lochtkemper subjected a trained group of 51 Zolingen grinders on natural stones to in-depth clinical examination. The frequency and stages of pneumoconiosis found among them are expressed by the following figures: Table 4. Method of grinding Number examined No signs of pneumoconiosis Stages Dry ...... Wet..... 15 36 d 2 11 As can be seen from the table, the pneumoconiosis indicators in both groups are high, and they are more pronounced among 'wet' grinders. In the USSR, the process of socialist reconstruction of small-scale enterprises creates a solid foundation for the complete elimination of natural stones from grinding workshops, which in combination with the continuously improving working and living conditions of grinders undoubtedly ensures a significant improvement in their health indicators. - A serious hygienic effect of replacing natural stones with artificial ones even in the conditions of capitalist enterprises is evidenced by a number of data. Middleton among 58 grinders on artificial stones he examined found only 1 case of tuberculosis and 3 cases of stage I pneumoconiosis. Nicolson notes as a well-known fact in England the relatively low prevalence of tuberculosis among workers on carborundum wheels. Lochtkemper among 14 grinders with long experience mainly on artificial stones found early stages of pneumoconiosis in 10 and only stage II signs in two. According to his observations, changes in the lungs of grinders on artificial stones are generally not sharp, do not begin earlier than 12-13 years of professional experience, and progress very slowly. It is necessary to emphasize that the morbidity of grinders on artificial stones generally presents a different picture than on natural ones. Along with favorable indicators for tuberculosis and pneumoconiosis, they show a relative frequency of pneumonias (Collis, Vigdorzik), bronchitis, and catarrhs of the upper respiratory tract. - Finally, it is necessary to note the frequency of eye injuries in grinders from flying particles of stone and material being ground; in terms of eye trauma, grinders occupy one of the first places among other professions in metalworks (Glezerov et al.). Radical health improvement measures in grinding shops are: replacement of natural stones with artificial ones and combination of this measure either with well-equipped and rationally operated local ventilation or with the introduction, wherever possible according to production conditions, of the wet method III. The fight against trauma must be carried out first of all by supplying workers with protective glasses, preferably corrective ones, as well as supplying stones with guards, installing transparent protective shields, etc. Only in the conditions of our socialist industry, where these measures are widely implemented in combination with a reduced working day, annual vacations, and other guarantees provided by our labor legislation, are the real prerequisites for the complete improvement of working conditions for grinders first created.