Stručni rad
MICROBIAL DEGRADATION OF EMULSIONS FOR COOLING AND LUBRICATION AT METALWORKING
Vedranka Bobić
Ljiljana Pedišić
Ivo Legiša
Sažetak
Abstract
Material degradation is a problem which has always been occupying the attention of experts, because, first of all, it leads to major economic losses. That is why the causes of deterioration of various materials have been the object of research for a number of years now. Organized groups of researchers, mostly in chemical industry, supported by governmental organizations, are engaged in analyses and research of this particular area.
The biggest role in degradation is that of biodeterioration, defined as any unwanted change of the material properties caused by the activities of living organisms. Biodegradation in the form of deterioration constitutes an unwanted process when it comes to the production and storage of materials, but is in turn a most desirable process when the material in question becomes waste, both of these processes usually involving often the same kinds of microorganisms.
Emulsions for cooling and lubrication at metalworking with a high water content of up to 98%, and are precisely for this reason most prone to microorganisms growth. The oil phase makes a good nutritional basis for microorganisms as a source of carbon. Because of the tiny drops dispersed in water, the contact interphase oil/water surface is very large, which is why the surface for microorganisms growth is sufficient as well, water being the essential medium for their development. Under the impact of the metabolism of microorganisms, the product changes both chemically and functionally, which is why the slimy microbial growths cause constant clogging of filters and devices.
Although the concentrates of emulsifying fluids from which working emulsions are made are usually sterile according also to the results of this paper, microorganisms, after blending with water, develop very soon. That is because neither the environment nor the water are sterile. Since there already are microorganisms in the containers, new emulsions are soon infected and the number of microorganisms grows very fast unless there is an antimicrobial agent present, respectively unless the devices and containers are properly maintained. As deterioration progresses, the foam and the mucilage become visible. Suspended growths on the surface point to infection by fungi, while the smell of ammonia and even more frequently that of sulphides also frequently appears. Emulsion changes colour, while pH progressively decreases, along with the corrosion protection property.
Our tests have shown that reservoirs for emulsions in two plants were quite infected with several kinds of microorganisms, which has been proven by cultivation on selective nutritive media, as well as through determination of species in authorized laboratories. The tests have furtherly shown that proper handling and maintenance of the plants and reservoirs considerably reduces emulsion deterioration, and hence also plant standstills, resulting in considerable financial savings.
Ključne riječi
metalworking oil emulsion; adverse biodegradability of material; prevention viewpoint; industrial microbial contamination and protection; microbiological screening and diagnostics; occupational hygiene
Hrčak ID:
7332
URI
Datum izdavanja:
27.2.2004.
Posjeta: 5.507 *