LABOR PROTECTION AND SAFETY TECHNIQUES IN POWDER METALLURGY

W O R K I N G C O N D I T I O N S IN FE RRITE P R O D U C T I O N

A N D WAYS OF I M P R O V I N G T H E M

G. Yu . R o z i n a . L. S. D u b e i k o v s k a y a , a n d Y a . D. K r a v c h i n s k i i Scientific Research Institute of Labor Hygiene and Occupational Diseases, Leningrad

Translated from Poroshkovaya Metallurgiya, No. 1(7), pp. 97-100, January- February, 1962 Original article submitted June 24, 1961

It is known that ferrites are used extensively in technology. To increase the production of ferrites, the or~ ganization of special production departments is necessary. In these departments, working conditions must be created which satisfy present-day sanitary requirements.

With this purpose in view, investigations on the hygienic aspects of the production of nickel-zinc, man- ganese-zinc, and barium ferrites were conducted at some enterprises in 1958-1960. These investigations made it possible to detect individual shortcomings in the organization of production processes and, consequently, to devise in due t ime ways for eliminating these shortcomings.

The production of the first two kinds of ferrites mentioned above is based both on the treatment of metal sulfates and the treatment of metal oxides. In the production of barium ferrites, ferric oxide and barium car- bonate served as raw materials.

It is appropriate to mention that somewhat earlier attempts were aim made to use barium nitrate. How- ever, the thermal treatment of the charge, which was conducted in a chamber furnace, resulted in contamina- tion of the air with nitrogen oxides, notwithstanding the use of an exhaust ventilator installed at the location of the furnace. The concentration of nitrogen oxides in the vicinity of the furnace varied within the limits of 0,10 to 0.15 rag / l i t e r (the maximum permissible concentration is 0.005 rag/l i ter) . The very first attempt to apply the process under production-department conditions led to a poisoning of workers with nitrogen oxides. This circumstance was one of the reasons why the use of barium nitrate was abandoned and barium carbonate was used instead.

The production of ferrites involves disintegration of materials and then conversion of the resulting powders by different means, The majority of operations which are conducted are accompanied by the release of consider- able quantities of dust. The concentrations of dust are particularly high in connection with the preparation of the ferrite mixtures (mixing of powders, disintegration, sifting).

Thus, the connection with the production of n ickel-z inc and manganese-zinc ferrites from the sulfates of the metals, the concentration of dust at the locations where the workers were stationed, reached 352.0 r a g / m s during the knocking-out of the salts after dehydration and charging into the crucibles, and 208.0 r a g / m 3 during the servicing of vibration mills. In connection with the production of barium ferrites, the concentration of dust reached 623-1037 r a g / m s during the sifting of the powder through a sieve, 27.0-87.0 r a g / m 3 during the disinte- gration of the material on a crushing mill, and 28.0-61.0 r a g / m 3 in the servicing of vibration mills. In some places the high concentrations of dust occurred not only at the working stations: the whole production area was found to be contaminated with dust.

This dust cannot be regarded as nontoxic. It contains a harmful substance such as manganese which, on prolonged action on the organism of workers, may bring about chronic poisoning which is accompanied by an affliction of the central nervous system. At the t ime when individual operations involved in the production of manganese-zinc ferrites are carried out, the concentrations of manganese in the air reach rather high levels, For instance, during the knocking-out of the mixture from the tank after decrystallization, these concentrations reach 4.79 rag~ ma,when calculated on the basis of MnO2 (the maximum permissible concentration is 0.3 mg/mS). *

�9 Chemical analyses of the air samples were conducted by E. M. Stepanenko, Scientific Associate at the Institute.

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The dust also contains a number of substances (zinc, barium, etc.), which bring about definite changes in the respiratory organs of human beings.

In the production of barium ferrites, treatment of barium compounds may, in some cases, be accompanied by the release of dust in rather high concentrations, The concentration of dust is particularly high in connection with the sifting of powder through a sieve (24.8-57.3 mg/mS).

The concentration of dust in the air is considerably lower in connection with the production of finished products from the mixture (i,e., during pressing and sintering): the concentrations then amount to 1.0-9.0 mg per m s at the workers' stations, and 0.5-4.0 m g / m a in the room where the work is conducted.

One must also consider the process whereby ferrites are produced from the metal sulfates. Analysis of air samples taken above the furnaces in which the salts are calcined and the briquettes roasted showed that these fnrnaces generate an aerosol consisting of sulfuric acid, sulfur dioxide, and arsenice compounds (cf. table below).

Furna ce

For the calcining of salts For the roasting of briquettes

Quantity of substance involved Sulfuric acid Sulfur Arsenic aerosol, m g / m a dioxide, (arsenic trioxide),

rag/liter m g / m s

510.0-3590.0 0.91-2.81 Traces- 3.5 2 6 . 0 - 8 0 . 0 0.02 -

These substances enter into the air through the loading and charging ports of the furnaces and also through the openings through which the sllite rods pass. The chemically pure sulfates which are used may contain only very small quantities of arsenic. However, this]arsenic accumulates in rather high concentrations in the air above tbe furnace for the calcining of the salts.' It is most likely that it is evolved in the form of arsenic tri- oxide,

The furnaces for the thermal treatment of the salts and of the briquettes are equipped with exhaust venti- lators which are locally placed. The inlets of the exhausts above the furnaces are constructed in the form of cupola-shaped ('umbrella-shaped ") hoods which partially cover the top of the furnace, or hoods which have the shape of a visor. The velocity of the air entering the hoods varies within the limits of 0.65-2 m/sec. However, this equipment does not prevent completely contamination of the working zone of the rooms with the substances mentioned above. The concentration of sulfuric acid in the majority of cases exceeds constderably the maxi- mum permissible level of 1.0 m g / m s, reaching 8.0 mg/m s at the locations where the furnaces are serviced,and 3.0 rag /m s in the room. Sulfur dioxide was also found to be present both at the operators' stations and in the air of the rooms.

During the thermal treatment of the finished products, carbon monoxide and hydrocarbons may be re- leased into the air. These substances form, as a result of the incomplete combustion of organic substances (paraf- fin, polyvinyl alcohol) which have been introduced into the mixture. In the event that the products are treated with bakelite, benzene vapor may be evolved by reason of imperfect covering and ventilation.

One must note that unfavorable temperature conditions may arise at the locations where ferrites are pro- duced. For instance, the evolution of heat at one of the enterprises which was investigated exceeded 20 kcal per hr �9 m s. The temperature of the air in the building increases mainly because of the release of heat by the furnaces. In connection with sintering, the total electric energy which is used in this process is evolved in the form of heat, because the cooling of the manufactured products after sintering is usually conducted in the same room. The thermal gradients which arise in connection with the heat-treatment processes are so high that the parts of the plant in ivhich these processes are conducted must be considered overheated.

It can be seen from what has been said above that highly unsatisfactory working conditions exist at enter- prises where ferrites are produced from sulfates. In some parts of the production departments the salts are re- duced, so that the workers, in addition to being exposed to dust and heat, may be affected by the action of toxic substances such as sulfuric acid, sulfur dioxide, and arsenic. These substances have a harmful effect on the up- per respiratory tract, which has been confirmed by data obtained in the medical examination of the workers, in

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addi t ion to showing some other symptoms (it was found that the workers had bleeding from the nose, suffered

from chronic rhinitis, and exhibi ted a def ic ient sense of smell) .*

It follows from the information given above that technologica l processes which are based on the use of

meta l oxides as raw mater ia ls are preferable from the hygienic standpoint as far as the organizat ion of the pro- duction of manganese -z inc and n i cke l - z inc ferrites is concerned. The appl ica t ion of nitrates in connect ion with the production of bar ium ferrites is inadvisable.

In order to ensure that the production of ferrites complies with the fundamental requirements of labor hy- giene, al l operations involved in the conversion of the raw mate r ia l and the preparation of the powders should be mechan ized to the max imum extent. In connect ion with the mechaniza t ion of the flow of mater ia l s to the

units in which grinding, discharging, and separation take place , one may recommend a ver t ica l arrangement of the equipment combined with the instal la t ion of in termedia te capaci t ies .

Individual parts of the production line must be loca ted in isolated rooms arranged suitably under considera- tion of the operations which are to be carried out and the type of contaminat ion of the air which may take place. The workers who are employed in the preparat ion of the mixtures must have at their disposal a room for storage of the raw mate r ia l , another room for the preparat ion of the mixture, and sections where heat t rea tment is car- r ied out; the workers who produce finished ferri te ar t ic les must have isolated rooms for pressing, sintering, and mechan ica l t rea tment of the ar t icles , as well as rooms for control, bake l i t i za t ion , marking, and packaging. The sections where hea t t rea tment is carr ied out should be loca ted in places where a sufficient flow of air is pro- vided. It is r ecommended that the furnaces be arranged in such a manner that the operators ' stations are loca ted between a window and a furnace.

In rooms where dust is generated, adequate provisions for reducing the quantity of dust must be made from

the constructional standpoint. Furnaces of every type must be equipped with local exhausts (in the case of fur- naces equipped with sil i te rods, the air must be removed both from the charging ports and the openings through which the rods pass into the furnace). The air inlets and outlets instal led at furnaces for the ca lc in ing of salts must be constructed of acid-res is tant mater ia ls . The air which has been conducted away should be freed of sul- furic acid. The air being supplied into rooms where dust is generated should flow from the top to the bot tom and be distributed in a uniform manner, while the air being supplied into sections where heat is evolved should be blown into the parts of the rooms occupied by the workers. In the summer, the windows should be kept open.

C o n c l u s i o n s

It has been established that, in connect ion with the production of n i cke l -z inc , manganese-z inc , and bar i - um ferrites, conditions develop which are unfavorable from the standpoint of the heal th of the workers. This ap- plies par t icular ly to the preparat ion of mixtures from sulfates for the production of ferrites of the first two types ment ioned.

In connect ion with the select ion of the technologica l process for the production of ferrites, a preference between the two ava i lab le variants should be given from the hygienic standpoint to the one in which meta l oxides are used as raw mater ia l . The investigation which has been conducted made it possible to formulate the basic requirements to which the production of ferrites should conform.

*The med ica l examinat ion of the workers was carr ied out by I. I. Tsiryul 'nikova and A. A. Tatarskaya, Scien- t i f ic Associates at the Institute.

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