Title Utjecaj hlađenja hladnim komprimiranim zrakom na korozijsku otpornost pri obradi dijelova od nehrađajućeg čelika : doktorska disertacija
Title (english) Effect of cooling with cold compressed air on the corrosion resistance of machined parts made of stainless steel : doctoral thesis
Author Tihana Kostadin
Mentor Goran Cukor (mentor)
Committee member Zoran Jurković (predsjednik povjerenstva)
Committee member Dario Iljkić (član povjerenstva)
Committee member Dražen Bajić (član povjerenstva)
Granter University of Rijeka Faculty of Engineering Rijeka
Defense date and country 2019-10-18, Croatia
Scientific / art field, discipline and subdiscipline TECHNICAL SCIENCES Mechanical Engineering
Universal decimal classification (UDC ) 69 - Building (construction) trade. Building materials. Building practice and procedure
Abstract Kod strojne obrade nehrđajućih čelika rezanjem se redovito preporučuje uporaba specijalnih
tekućina za hlađenje i podmazivanje s visokim protokom. Međutim, konvencionalne tekućine
na osnovi mineralnih ulja imaju negativni učinak na okoliš, zdravlje radnika i troškove
proizvodnje. Alternativna tehnika hlađenja ohlađenim komprimiranim zrakom uporabom
Ranque-Hilschove vrtložne cijevi protusmjernog protoka u obradi martenzitnog nehrđajućeg
čelika X20Cr13 postupkom tokarenja je predmet ovog istraživanja. Cilj je bio utvrditi utjecaj
takvog hlađenja na korozijsku otpornost obrađene površine i njegovu tehnološku i ekonomsku
održivost u usporedbi s konvencionalnim hlađenjem emulzijom u svrhu postizanja ekološki
prihvatljive obrade. Zrak kao rashladni medij je potpuno prirodan pa je ova tehnika hlađenja
najčišća i ekološki najprihvatljivija. Budući da se korozija može pojaviti i u suhoj obradi,
korozijska otpornost je određena elektrokemijskim i gravimetrijskim mjerenjima. Kemijski
sastav i izgled površine prije i nakon ispitivanja korozijske otpornosti je utvrđen pretražnom
elektronskom mikroskopijom u kombinaciji s energijski razlučujućom rendgenskom
spektroskopijom. Od osobitog je značaja otkriće da se obrađena površina ispitnog materijala
tokarenog uz hlađenje vrtložnom cijevi dugoročno bolje odupire korozijskom djelovanju od
one dobivene tokarenjem uz hlađenje emulzijom. Također, potvrđeno je da minimalna
hrapavost obrađene površine osigurava maksimalnu korozijsku otpornost. Analiza uloge
hrapavosti obrađene površine u koroziji nehrđajućih čelika je osobito zanimljiva jer je to
parametar koji se može pratiti još u procesu obrade što je usvojeno u ovom istraživanju.
Analizom varijance eksperimentalnih rezultata dobivenih ispitivanjem obradivosti prema
okretljivom centralno kompozitnom planu pokusa je utvrđeno da različite tehnike hlađenja
(emulzijom odnosno vrtložnom cijevi) ne utječu značajno na hrapavost obrađene površine
ispitnog materijala i time na korozijsku otpornost. Izvornim proračunom jediničnog
proizvodnog troška je dokazano da hlađenje vrtložnom cijevi nudi ekonomično rješenje na
putu prema održivoj obradi. Zaključuje se da hlađenje ohlađenim komprimiranim zrakom
uporabom vrtložne cijevi pozitivno utječe na sva tri segmenta održivog razvoja – ekološki,
sociološki i ekonomski pa se za tokarenje martenzitnog nehrđajućeg čelika X20Cr13 umjesto
hlađenja emulzijom preporučuje ova tehnika hlađenja.
Abstract (english) It is recommended that cutting fluids with high flow rate are used when stainless steels are
machined. However, conventional mineral oil-based cutting fluids have a negative impact on
the environment, workers' health and production costs. Alternative cooling technique with
cooled compressed air using the Ranque-Hilsch's counter-flow vortex tube in machining of
martensitic stainless steel X20Cr13 by turning is the subject of this research. The aim was to
determine the effect of such cooling on the corrosion resistance of the machined surface and
its technological and economic viability compared to conventional emulsion cooling for the
purpose of achieving ecologically acceptable machining. The air as a cooling medium is
completely natural so this cooling technique is the cleanest and most environmentally
acceptable one. Since corrosion can also occur in dry machining, corrosion resistance was
determined by electrochemical and gravimetric measurements. The chemical composition and
appearance of the surface before and after the corrosion resistance test was determined by
scanning electron microscopy in combination with energy dispersive X-ray spectroscopy.
Particularly important is the discovery that the surface of the test material machined by the
turning operation with cooling by means of the vortex tube is more resistant to corrosion than
that obtained by the turning operation with cooling by means of the emulsion. Also, it has
been confirmed that the machined surface minimum roughness ensures maximum corrosion
resistance. The role analysis of the machined surface minimum roughness in the corrosion of
stainless steel is particularly interesting as this parameter can be traced yet in the machining
process, and this is adopted in this research. By the analysis of variance of the experimental
results obtained by the machinability testing according to the rotatable central composite
design of the experiments, it was found that various cooling techniques (emulsion or vortex
tube) did not significantly influence the machined surface roughness of test material, and
hence the corrosion resistance. By the original calculation of the unit production cost, it has
been proved that the cooling with the vortex tube offers an economical solution on the route
to sustainable machining. It is concluded that the cooling with cooled compressed air using
the vortex tube positively affects all three segments of sustainable development – ecologic,
sociologic and economic, so for the turning of martensitic stainless steel X20Cr13, instead of
conventional cooling by emulsion, the cooling with the vortex tube is recommended.
Keywords
tokarenje
martenzitni nehrđajući čelik X20Cr13
hlađenje ohlađenim komprimiranim zrakom
vrtložna cijev
korozijska otpornost
hrapavost površine
Keywords (english)
turning
martensitic stainless steel X20Cr13
cooling with cooled compressed air
vortex tube
corrosion resistance
surface roughness
Language croatian
URN:NBN urn:nbn:hr:190:018920
Promotion 2020
Study programme Title: Postgraduate university (doctoral) study Study programme type: university Study level: postgraduate Academic / professional title: doktor/doktorica znanosti, područje tehničkih znanosti (doktor/doktorica znanosti, područje tehničkih znanosti)
Type of resource Text
Extent V, 135 str. ; 31 cm
File origin Born digital
Access conditions Open access
Terms of use
Repository Repository of the University of Rijeka, Faculty of Engineering
Created on 2020-10-26 13:54:38