Επίλυση προβλημάτων στην βιομηχανία : μεθοδολογία και πειραματικός σχεδιασμός

Αγιαννίτης, Παναγιώτης

Master Thesis

Author

Αγιαννίτης, Παναγιώτης

Date

2016-06

Abstract

Water-cooling plays a major role in extracting heat from both the mold and solidifying metal during the Direct Chill Casting of Aluminum Alloys and is characterized by complex boiling phenomena. Heat extraction rates during water-cooling which have strong dependence on the metal surface temperature, can rapidly change with time as the ingot cools down. Consistent water quality is therefore a requirement in Aluminum casting if we mean to follow the procedure and deliver quality products with high performance. Consequently, uncontrolled cooling may cause fluctuations in the temperature gradients inside the solidifying shell and generate tensile thermal stresses at the solidification front that can ultimately lead to the appearance of hot tears or cracks in the final product. However, other materials used in DC Casting like lubricants -even been in small quantities- they are draining in the same tanks of the closed system with the water thus mixing with it. Moreover the most prominent water problems are deposits and corrosion and these are closely related to the instability of each specific water caused by the tendency of CaCo3 to dissolve or precipitate from it. Finally increased water temperatures play a key role in the growth of microorganisms and the development of biofilm. Biofilm development therefore impairs the efficiency of the system and can also lead to a number of other problems within a closed circuit such as; blockages of valves and pipework, under deposit corrosion and protection of bacteria present in the biofilm from any biocides in the system These parameters that can always be measured are influencing water’s quenchability. The escalation of the contaminants concentration leads to a continuous changing quality of the water which cannot sustain neither the demanding production process nor the hygiene issues when water is essential for cleaning. The definition of the critical water specifications and the effective control of them becomes to be a prerequisite of the process. We still have to decide whether we want to have immiscible lubricants that will eventually be extracted from the surface of the sump or soluble ones that will be controlled according specific factors following definite procedures always in respect to the environmental procedures and the quality standards. The tests to observe and ascertain the interactions in use of chemicals conducted live in Industrial environment. The chemicals concern scale and corrosion inhibitors, hardness stabilizer and biocide activator which affect the quenchability of the cooling water and forming altogether the cooling water triangle.

Postgraduate Studies Programme

Βιομηχανική Διοίκηση και Τεχνολογία

Department

Σχολή Ναυτιλίας και Βιομηχανίας. Tμήμα Βιομηχανικής Διοίκησης και Tεχνολογίας

Number of pages

Language

Greek

URI

https://dione.lib.unipi.gr/xmlui/handle/unipi/9305

Collections

Τμήμα Βιομηχανικής Διοίκησης και Τεχνολογίας

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