Ceramic Production

Ceramic Production, the manufacture of various articles from clay (see). Clay articles are divided into 2 groups according to the ability of the body to absorb water: 1. Articles with a porous body, characterized by significant permeability to liquids and gases and having an opaque body with an earthy fracture. These include bricks, earthenware (pottery), and faience. Earthenware and faience articles are covered with glaze, making them impermeable to liquids and also serving decorative purposes. 2. Articles with a dense body, impermeable to liquids and gases and having a dense, glossy fracture. These articles are fired at high temperatures. White, glazed articles are called porcelain, and unglazed ones are called biscuit; this also includes the so-called stone ware, which may be either unglazed or glazed. Preparation of articles from clay. Earthenware. Clay of the appropriate grade is mixed with sand (in the manufacture of coarse articles, e.g., pots, often only clay is used), watered, and the mass is kneaded with the feet or in a machine, which is a cylindrical iron box with a rotating shaft on which knives are mounted. In artisanal pottery production, clay is usually kneaded with bare feet on the floor. The resulting homogeneous plastic mass is placed on foot or hand lathes for shaping pots. A foot lathe consists of two disks rigidly connected to each other by an axle passing through the centers of the disks. The lower (larger) disk is set in motion by the potter's right foot after a piece of kneaded clay is placed on the upper disk. With the help of rotational movements of the upper disk and corresponding manipulations with the fingers of the hands, the clay acquires the proper shape. The shaped article is transferred for drying to shelves usually arranged under the ceiling or to a stove. Then the pot is covered with glaze; in the "dry" method of glazing, the pot is coated with resin and sprinkled with crushed dry glaze powder, while in the "wet" method, glaze is applied to the pot with a brush; the inner surface of the pot is coated with liquid glaze. In the "wet" method, the pot is usually subjected to double firing: before and after glazing. Glazes are usually prepared by the potters themselves: lead scrap is melted in special pans; the resulting lead oxide is mixed with sand, the required color is added, the resulting mixture is fused into a glassy mass, broken into small pieces, ground on millstones, and sifted through a hand sieve. The production process in porcelain and faience production. The raw materials in this production are kaolin, quartz, and feldspar. Kaolin is preliminarily washed, i.e., freed from impurities (in mixers, sieves). Feldspar and quartz (in the form of flint or pure white quartz sand) if necessary are washed from dirt (manually or in rotating drums). Flint to achieve brittleness and separation of the flint stone's shell ("crust") is fired in furnaces (at t° 700-900°) usually with manual loading and unloading and then sifted (often on open screens). Both the fired flint and other materials making up the mass are ground on runners, mostly sifted on cylindrical, mechanically rotating sieves, and go into mixers, and before entering the mixer, ground feldspar and quartz are subjected to finer grinding in ball mills. The liquid mass coming from the mixers goes to filter-presses, which are a series of vertically standing frames covered with cloth, through which water seeps through the cloth, while solid particles of the mass are retained on the cloth of the frames in the form of a doughy mass, which is then kneaded in a pug mill. From the resulting plastic homogeneous mass, the required articles are made by molding, casting, or pressing. The most common method is molding articles on lathes or less frequently by hand. Molding lathes are usually driven mechanically. On the disk of a grinding lathe is placed an alabaster mold; inside it or on the surface the worker places the required amount of mass, starts the lathe, lowers the template (a lever equipped with a knife) and presses with one hand on the mass, and with the other hand smooths out the irregularities, "trims". The molded object he places together with the mold on a shelf near himself, and after 15-20 minutes the article is placed on a long board and taken by the molder or assistant for drying on "hor"-a series of shelves usually located in the same room. When insulators are molded, the worker performs a series of operations associated with significant muscular tension. The dried article is again placed on the grinding lathe for "grinding" or rather "smoothing" of the articles, which consists in smoothing roughnesses and irregularities on the surface of the object with sandpaper in the "dry" method of grinding or with a moistened sponge in the "wet" grinding. In addition, sharp edges of the object are scraped off with glass or a metal plate ("key"). In casting articles, the prepared mass is diluted with water in a special drum to the consistency of cream and poured by casters into prepared plaster molds that absorb water. Pressing is used in the manufacture of small electrical insulating parts. Dry porcelain mass is crushed on open rollers and then on disintegrators into the finest porcelain dust, triturated with turpentine and water (Tokarevsky Plant) or with kerosene and resin (Plant "Isolator"). The resulting mass is tamped into a metal matrix and placed under a press of a stamping machine. Auxiliary departments for making plaster molds are the department for "cooking" or firing plaster and the modeling department. When "cooking" plaster, preliminarily crushed on runners, is placed on an iron plate, which is the upper wall of the furnace; when heated, plaster loses part of the water, released in the form of steam bubbles with air. Plaster is also "cooked" in closed boilers. When firing uncrushed plaster is loaded into the furnace through an opening, which is bricked up; firing is carried out at 400° for 10-12 hours. In the modeling department, plaster is diluted with water to the consistency of cream and poured into molds. Auxiliary are also departments for making "capsules", i.e., refractory boxes in which articles are placed in kilns. Molded, dried, and smoothed articles are placed in capsules and go to the first firing (at t° 900° for porcelain articles). Firing of unglazed (utility) goods is usually done in circular kilns (in its upper chamber) or in specially constructed furnaces. After the first firing, articles are cleaned from dust, "de-dusted", which is done either by blowing dust with compressed air or manually with brushes and brushes. Then the articles are covered with glaze. For porcelain articles, glaze is composed of the same materials as the porcelain mass, while for faience articles, lead glazes are usually used, which contain red lead or white lead. First, a frit is prepared: the components of the glaze are weighed, mixed manually in an open box, and fused into glass in a furnace. The resulting mass (frit) is released, hardens, then is broken into pieces, crushed on runners, and sifted. Then from the frit as needed glaze is prepared, and in some cases there is an addition to it of "additive"-red lead. The ready glazing liquid is poured into vats, into which the articles to be glazed are immersed. Glazed porcelain articles are subjected to a second firing at t° 1,300-1,500°; for faience articles the second firing is carried out at a lower t° than the first (1,230-1,330°-first firing; 950-1,150°-second firing). Firing is done either in circular kilns or in tunnel kilns, in which loading is done outside the kiln, and the goods, automatically moving to the unloading opening, are fired and unloaded outside the kiln. In circular kilns, loading and unloading of goods is done by workers entering the kiln at fairly high t° of air in the kiln and significant thermal irradiation. Finished articles are sorted, polished, and transferred to the painting department. Application of paints to articles is done by printing with decals (transferring the design from special paper to the surface of the article), by painting (when applying artistic designs) or with an aerograph (a sprayer connected to a compressor). Painted articles are fired to fix the paint in muffle furnaces. The production process in brick production is similar to the production of coarse earthenware articles. Bricks are molded either in hand molds or in brick-making machines. Firing of bricks is usually done in Hoffmann ring kilns, divided by partitions into compartments, in some of which firing is done, while in others the fired brick is unloaded. Often in this case unloading is done in a compartment not sufficiently cooled, with high t° of air. Occupational hazards of C. p. 1. Danger of lead poisoning.

The widespread use of lead-containing glazes is the cause of numerous poisonings among artisan potters and workers in faience production. Workers handling lead glazes are exposed to inhaling lead dust when uncorking barrels with lead compounds, weighing them out, mixing the components of frit, grinding and sifting frit, as well as during the 'dry method' of applying glaze by dusting or sprinkling with glaze powder; during the 'wet' method of applying glaze, the hands and clothing of potters or glazers in faience factories become contaminated. Hamilton notes that the operation of dry cleaning ('smoothing') excess glaze from products is dangerous in terms of lead poisoning. Schreber points out that cases of lead poisoning have also been observed among persons removing fired glazed goods from the kiln. The working conditions of artisan potters working in a home environment are especially difficult; they are in danger of poisoning not only during the above-mentioned moments but also when breaking down lead scrap and firing lead. Chyzer found among Hungarian potters 986 cases of lead poisoning (of which 114 with paralyses). Hamilton notes in the USA 144 cases of lead poisoning among 1,493 potters examined in 1911. According to a report of the Federal Health Department (1921), a new examination of 1,809 potters revealed 13.5% of them with symptoms of chronic lead poisoning. In the Moscow province, an examination of artisan potters in the Mozhaisk and Zvenigorod districts was undertaken, and among 65% of the examined artisans (and their family members) of the Mozhaisk district, signs of chronic lead intoxication were found, while among 24 examined potters of the Yegoryevsk district, only four showed no signs of lead poisoning. In England, according to the report of the Chief Factory Inspector, 1,831 cases of lead poisoning (or 14% of all cases of lead poisoning in all industries) were registered in ceramic production from 1900 to 1926; the number of cases in recent years has significantly decreased compared to the first years of registration of occupational poisonings (210 - in 1900, 113 - in 1901, 89 - in 1902), but compared to 1915-1920, an increase in the number of cases is observed (from 20 to 40 per year). In Germany in 1927, 190 cases of lead poisoning were registered in ceramic production. Data from an examination of workers engaged in glaze preparation and glazing at the factory named after Kalinin in the former Tver province and at the factory named after the Comintern near the Volkhov station, conducted by the clinic of social and occupational diseases of the 1st Moscow State University, are of interest. At the Tver factory, no clear symptoms of lead intoxication were found among 28 examined workers, while at the Volkhov factory among 26 workers, 3 had lead poisoning and 18 had suspected lead poisoning; at the Volkhov factory, white lead was added to the ready frit, the frit contained 22% lead compounds (at the Tver factory 14-16%), and when treated with 1% hydrochloric acid, this frit released 9.3% soluble lead relative to the weight of lead in the frit (whereas at the Tver factory the frit released 3.2% lead). Measures. The radical measure to combat lead poisoning in ceramic production is the replacement of lead glazes with lead-free glazes. Seger proposed replacing lead glazes with barium glazes. Budnikov points out that bismuth oxide, introduced into the composition of the glaze, acts like lead oxide but gives the glaze greater fusibility. Muller reports that a mixture of 50 parts by weight of borax, 25 parts of quartz, and 25 parts of lime, melted on a weak fire, gives good glass, which, when ground with 5% kaolin, gives a shiny glaze surface on calcium-free clay (which however may have minor cracks). When using lead glazes, the addition of any lead compounds in an unfritted form to the ready glaze is prohibited, and the lead frit itself must be prepared so that it does not release more than 3% of the lead contained in it when treated with a 1% solution of HCl. All processes for the production of lead-containing frit must be mechanized, the supply of liquid glaze to glazing vats must be mechanical, and the application of glaze to products must be organized so as to exclude the possibility of contamination of workers' hands. At the same time, the process of uncorking barrels with lead compounds should be provided with adequate local dust removal equipment. 2. Dust. Processes of grinding, mixing, and sifting raw materials, as well as 'touching' products and cleaning fired products from dust ('whipping') are accompanied by significant dust formation. Unloading kaolin from cars and loading it onto carts are very dusty processes: Kuritsky found 103 mg of dust in 1 m³ of air when unloading kaolin and 58 mg when loading it onto carts. The enormous dustiness of the air is observed when unloading fired flint from the kiln (on average 206 mg per 1 m³) and especially when sifting it through open screens (296 mg per 1 m³). The dustiness of the air during the preparation of the molding mixture, as well as during molding and finishing ('touching') products according to the data of Stozhkova and Kuritsky is given in the following table. Sampling location Amount of dust in mg per 1 m³ Baranovsky plant At runners when moistening material .......... At runners without moistening material .......... At drums ......... When sifting on a manual sieve............. At the molding machine .. . . In the molding shop . . At the grinding machine during dry grinding .......... At the grinding machine during wet grinding.......... 81.0 189.9 59.8 23.4 27.1 118.1 26.9 Buyan- sky plant 132.0 305.0 64.3 Olevsky plant 108.7 197.0 87.4 183.5 36.6 39.6 Tokarev-sky plant 196-397.0 61.2 26.2 38.5-57, 310.5 24.7 From the table, the great importance of moistening the material is visible, which reduces the dustiness of the air during grinding by 2 times or more. The extremely high figures of air dustiness that existed at the 'Isolator' plant are cited by Belikov and Khrustalev: 652 mg at runners and 2,743 mg during sifting. The replacement of manual sieves with mechanical ones, covering the runners with a hood connected to an exhaust fan, and mechanizing the feeding of material to the sieves significantly improved working conditions here. The introduction of 'wet grinding', which sharply reduces air dustiness, requires at the same time careful monitoring of the drying of the material going for 'finishing'. According to Gerchik, the best dust removal effect is obtained when the products going for 'finishing' have 14% to 19% moisture; in this case, not only the 'grinding' process but also the trimming of edges is dust-free. To avoid over-drying of products, it is desirable to divide the labor of the molder and grinder and to establish supervision over the timely and proper drying of products. The dustiness during the actual molding of products is mainly due to the molding mass falling onto the molding machine, drying and then rising into the air in the form of finest dust under the influence of the movement of molding machines and the continuous walking of workers bringing the mass and taking molded products for drying. Among other operations, the crushing of chamotte is particularly dusty. At the unloading point, without ventilation and moistening of the material, the dustiness reaches according to Kuritsky 1,220 mg per 1 m³ of air, and with moistening and the action of ventilation, it remains at a high level (248 mg per 1 m³). High air dustiness is observed during manual 'whipping' of products (123-341 mg) according to Stozhkova. A significant reduction in air dustiness is observed when crushing the mass prepared for stamping in a disintegrator, when the dry mass is pre-mixed with water and turpentine before grinding (from 428 to 113 mg per 1 m³). Dust particles vary greatly in size (according to Belikov and Khrustalev): from 0.5-1.5 μ to 38.7-62.0 μ. Some particles are rounded, some have sharp edges. Koelsch, attaching great importance to the morphological properties of dust, considered quartz and feldspar particles particularly harmful. Recently, increasing importance is attached to the chemical composition of dust and especially - to silicate compounds, which constitute the main part of porcelain and faience dust. According to data from the Ukrainian Institute of Occupational Medicine, the amount of silicates (SiO₂) in the dust of the Buyan faience factory reaches 56.92%. (The effect of silicate dust - see silicosis.) The question of whether colloidal silicates are a cellular poison that causes local destructive action on cells, causing necrotic foci and thereby promoting the development of the tuberculous process, or, conversely, silicate dust promotes the development of connective tissue, encapsulation of foci and delay of the tuberculous process, causes sharp disagreements in the assessment of the harmful effect of ceramic dust. Under the influence of dust inhaled in such large quantities, diseases of the upper respiratory tract develop first.

Temkin, examining 277 grinders from the Dmitrov and Dulev factories in Moscow province, found atrophic processes in the nose in 61.2% of cases, atrophic dry catarrh of the pharynx in 21.3%, and chronic inflammatory processes in the larynx in 36.7%. The almost complete absence of purulent diseases of the nose and accessory cavities led Temkin to conclude that the harmful effect of porcelain dust is due to its morphological properties, whereas silica acid, accelerating the process of scar formation, retards the development of chronic inflammatory phenomena. At the same time, he noted a small percentage of laryngeal tuberculosis (only 10 cases), all of which were of the productive type. Nalétov, in examining 200 workers at the 'Isolator' factory, found a significant number of ethmoiditis cases (22% of all diseases of the nose, throat, and ear). A fairly high percentage (16%) of chronic bronchitis was noted by Ekkel among 430 examined workers in the molding shop of the Budyan faience factory. According to old data, there is a high morbidity and mortality from pulmonary tuberculosis 66 among workers in porcelain and faience production. Sommerfeld indicates that out of 323 cases of death among porcelain workers, in 191 cases (or 60%) the cause of death was pulmonary tuberculosis; the average age of the deceased, according to his data (from 1874 to 1888), was 41 years. According to Bogner, in 67.2% of cases, the cause of death among porcelain workers is tuberculosis. According to Dutch government mortality statistics for 1908-1911, mortality from pulmonary tuberculosis per 1,000 workers in porcelain and faience production is 5.16, compared to 1.69 for all employed workers. Holzmann and Harms believe that the opinion about increased mortality from tuberculosis among porcelain and faience workers is explained by incorrect diagnosis: pneumoconiosis is mistaken for tuberculosis. Through careful clinical and X-ray examination, they found among 41 workers from two porcelain factories 19 cases of coniosis, with pure coniosis occurring without any symptoms. Rossle, in autopsies of 45 porcelain workers, found 'dusty lung' in 20 cases and tuberculosis in 25 cases, but tuberculosis was the cause of death in only 6 cases. According to Rossle, in no case of 'dusty lung' was there an acute pulmonary tuberculosis process. Vollrath believes that tuberculosis among porcelain workers occurs no more frequently than among workers in other industries and has a benign character. Thiele, examining 429 male workers and 231 female workers in porcelain production, found 'dusty lung' in 30% and pulmonary tuberculosis in 5%. On the other hand, it should be noted the data of Kreuser, who found higher mortality from tuberculosis among workers in C. p. (4.4 per 1,000) compared to workers in other industries (1.77 per 1,000), with only those cases considered tuberculous in which the presence of tubercle bacilli was proven during life. In the USSR, old data also paint a very grim picture of the health condition of workers in C. p. (Skibnevsky and others). Gintse, examining 5 porcelain and faience factories in Volyn province, found among the 1,292 workers he examined signs of chalicosis in 15.8%. Karpilovsky, in examining 102 porcelain workers, found 11 cases of pure pneumoconiosis, 49 cases of 'conio-tuberculosis', and 24 cases of tuberculosis without pronounced pneumoconiosis. Sheinin notes that among young faience workers with little seniority, when the 'coniotic' changes are fresh, tuberculosis proceeds according to the subcompensated type with a significant tendency to scar formation. With pronounced 'coniosis', the tuberculous process proceeds benignly according to the cirrhotic form of pulmonary tuberculosis; but gradually, when the developing connective tissue 'compresses blood vessels and lymphatic spaces,' causing impaired nutrition and later destruction of the pulmonary parenchyma, the tuberculous process takes on a malignant course. This author explains the reverse wave of tuberculosis at ages 40-45 among porcelain and faience workers, which he did not encounter in other industries. Measures. Apparatus for grinding materials should be enclosed in tight casings connected with exhaust ventilation, and materials should be moistened before grinding. Mechanization of material transportation from one apparatus to another is necessary. Sieving should be done only mechanically. All apparatus for sieving and mixing materials, as well as apparatus for mechanical transportation of materials, should be tightly enclosed and connected with exhaust ventilation. Finishing of products ('pointing') should be done only by the 'wet' method (i.e., with a wet sponge), and products for finishing should not be overdried. Cleaning of products from dust should be done only mechanically in cabinets equipped with sufficient dust-extracting installations. Departments where dusty processes are carried out should be separated from other departments of the factory, with floors in them being dense and smooth, without cracks. Cleaning of premises in these departments should be done daily by the wet method, and in the grinding shop several times a day as needed. 3. Meteorological conditions. Molding shops differ in high air temperature at increased relative humidity in cases where drying of pottery is carried out in them. In this case, the premises are usually heated by passing flues from kilns. Kuritsky found sharp fluctuations in humidity during the working day in the molding shop of the Budyan factory; room temperature in winter fluctuated between 25-32° with relative humidity of 60-87%. Stozhkova also notes increased relative humidity of air in the molding shops of the Slavutsky, Dobyshevsky, and Olevsky factories, where drying of green products is carried out. Along with this, in the molding department of the Tokarevsky factory, where drying is completely isolated, air temperature and humidity were normal. High temperature can occur during unloading of burned silica from kilns with manual loading and unloading. Extremely high air temperature is noted by several authors during unloading and somewhat lower during loading of round kilns. Thus, Belikov and Khrustalev observed temperatures up to 128° at a height of 2.8 m during kiln unloading at the 'Isolator' factory. Atabekyan observed a case of unloading at 147°, with the pulse of unloaders increasing from 72-76 to 160-180 beats per minute after 13 minutes of work. Work was stopped, and the kiln cooled for another 2 days. Atabekyan observed an increase in body temperature in unloaders after 15 minutes of work to 39.5-40.2°. Yefremov observed an average temperature during kiln unloading at the 'Proletary' factory: 94° at a height of 170 cm from the floor, 79° at 100 cm, and 62° at 15 cm (temperature of a shielded thermometer was 82°, 69°, and 55° respectively); temperatures during loadings were approximately 30% lower than during unloadings. Unloading and loading of the kiln represent heavy muscular work. Measures. Production of drying of molded products in separate dryers. Replacement of round kilns with tunnel kilns of continuous operation. Until this replacement is made, it is necessary to extend the period of natural cooling of the kiln to approximately 60-65 hours and to apply artificial cooling of kilns. By the rules on labor protection in porcelain and faience production of July 12, 1927, the maximum temperature during kiln unloading is set at 40°, with work under the arch not to exceed 15 minutes, after which a rest of 30 minutes is provided. Kilns for firing materials should be equipped with mechanical unloading of materials. 4. Repeated monotonous movements in the left wrist joint and great muscular work performed by the muscles of the thumb during manual brick molding cause tendovaginitis crepitans in molders. It is necessary to regulate their production norm. The problem is radically resolved by the introduction of brick-making machines. 5. Accidents occur at clay mixers, in pressing of small insulators, and in putting on and taking off drive belts in the slip house. The clay mixer should be equipped with a funnel for throwing clay into it, and the lower opening should be guarded to avoid injury to the worker's feet. Presses should be equipped with appropriate guards or devices for mechanical feeding of products under the press. 6. Professional poisoning in the manufacture and application of paints. Painting paints may contain lead, chromium compounds, and antimony. Klyonsky, in examining 8 workers in the laboratory of Porcelaintrust in Kiev who used chromium compounds in the production of ceramic paints, found in one case perforation of the nasal septum, in one case a deep ulcer, and in the others excoriations on one or both sides. In chromolithography at the Dulev factory, 13 cases of lead poisoning were noted among powder girls from 1923-1926. Measures. Mechanization of powdering work. Installation of cabinets equipped with sufficient dust-extracting devices when applying paints by pulverization. 7. Other harmful effects. Skin diseases are noted among stampers due to the use of lubricating oils.

Sharp fluctuations in temperature (especially in the kiln shop), constant contact of hands with cold and damp material during molding, frequent transition from one room to another with sharply differing temperatures or frequent exit from a dark room into the courtyard - all this contributes to the development of lumbago and rheumatism. Constant standing by grinders often causes them, according to Kelsh's data, varicose veins. Labor protection legislation in C. p. in the USSR. 1. Reduction to a 6-hour working day for dry grinding and for workers engaged in preparing and applying lead glaze in porcelain and faience production according to the decree of the NKT USSR of 10/XI 1928, No. 643. 2. Establishment of additional leave for workers in the alabaster department, engaged on runners, at the sieve and in the cooking of alabaster, for selectors and setters at round kilns, and for selectors from carts working in tunnel kilns at a temperature of 40° in the work area, for kiln operators (during manual loading of solid mineral fuel), for workers on open runners for grinding spar, quartz and broken pottery, for pourers, sprayers and cleaners when working with lead-containing glaze; for grinders and their assistants during dry grinding (as well as for those working with them and in the same room as foundry workers), for workers at pulverizers, for engravers, painters and transfer workers in chromolithographs in porcelain and faience production, for workers engaged in glazing and preparing lead-containing glaze mass in the production of refractory-ceramic goods according to the decree of the NKT USSR of 30/VII 1929, No. 156. 3. Prohibition of employment for persons under 18 years of age in porcelain and faience production as glazers when working with lead, in firebrick, red brick and clinker production, non-admission to work involving kiln firing, loading and unloading of furnaces; as clay workers (clay mills, mixing clay with feet) are permitted with the permission of the labor inspection. 4. The legislative consolidation of sanitary requirements for the arrangement and maintenance of work premises and production processes of C. p. is set forth in the mandatory decree of the NKT USSR of 12/VII 1927, No. 170 («Rules on Labor Protection in Porcelain and Faience Production», Izvestia NKT USSR of 30/VII 1927, No. 31).