Trošenje dijelova pužnih preša za cijeđenje biljnog ulja

Marušić, Vlatko (1999) Trošenje dijelova pužnih preša za cijeđenje biljnog ulja. = Doctoral thesis , Sveučilište u Zagrebu, Fakultet strojarstva i brodogradnje, UNSPECIFIED. Mentor: Ivušić, Vinko.

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Abstract (Croatian)

Pužne preše za cjedenje ulja predstavljaju eklatantan primjer tribosustava s kojemu se, zbog abraziva (SiO2) sadržanog u uljnom sjemenju trošenje ne može izbjeći, ali se ispravnom tribološkom praksom gubici mogu smanjiti. U radu je ispitivana otpornost trošenju u uljarama najčešće korištenih cementiranih slojeva te novih postupaka zaštite: boriranje, vanadiranje, PVD slojevi CrN i višeslojni SiC+DLC i plazmatski naštrcani Al2O3 i Al2O3+P i naknadno fosfatiran). Zaštitni slojevi nanijeti su na noževe plašta košare, i ispitivani u tijeku kampanje preradbe suncokreta na dva tipa preša: preši za predprešanje tip VPI i preši za završno prešanje tip RD. U obje preše tlak postiže maksimalnu vrijednost u trećem radnom polju: u preši za predprešanje =250 bara i u preši za završno prešanje =450 bara. Međusobna usporedba zaštitnih slojeva izvršena je na temelju intenziteta trošenja izračunatog iz gubitka mase po jedinici prerađenog suncokreta. Analizom sastava mliva iz preša (u tijeku cijeđenja) utvrđeno je da se udio SiO2 smanjuje od ulaza prema izlazu. Konstatirano je da je to posljedica njegovog ispiranja iscjeđenim uljem. Zaštitni slojevi ispitani su i standardiziranom metodom za ispitivanje otvrđenja abrazijom po metodi suhi pijesak/gumeni kotac prema ASTM G65-94. \Nije utvrđena prihvatljivost ove metode za procjenu trošenja dijelova pužnih preša zaštićenih ispitivanim novim postupcima modificiranja površina. Analizom radnih površina noževa nakon ispitivanja u pužnim prešama konstatirano je da se kod zaštitnih slojeva koji su tvrdi od SiO2 trošenje u prvo vrijeme odvija po mehanizmu nulte abrazije, a potom uslijed umora površine. Utvrđen je značajan utjecaj kvalitete veze zaštitni sloj-osnovni materijal te strukture i tvrdoće osnovnog materijala neposredno ispod zaštitnog sloja. Kod cementiranih dijelova i na osnovnom materijalu nakon odnošenja zaštitnog sloja :utvrđen je abrazijski mehanizam trošenja karakterističan za uvjete u kojima je abraziv tvrđi od površine s kojom je u kontaktu. Utvrđeno je da intenzitet trošenja noževa raste od prvog do trećeg radnog polja u kojemu postiže maksimum, a da zatim prema izlazu iz preše opada. Pri tome je utvrđen intenzitet trošenja u preši za završno prešanje =5 puta veći nego u preši za predprešanje prvenstveno kao posljedica djelovanja tlaka koji je u preši za završno prešanje tip RD viši nego u preši za predprešanje tip VPI. Međusobnom usporedbom intenziteta trošenja noževa utvrđeno je da najmanju otpornost trošenju imaju boridni i CrN slojevi, zatim cementirani, pa Al203 i Al2O3+P, a da su najotporniji vanadirani i višeslojni SiC+DLC zaštitni slojevi.

Abstract

Worm presses for oil extraction represent a striking example of the tribosystem in which, due to the abrasive (SiO2) contained in oil seeds, wear cannot be avoided but losses can be reduced by proper tribological practices. The work gives the results of the investigations carried out to test the wear resistance of case hardened layers in standard use and variant procedures of protection: boriding, vanadium carbide layers, PVD layers of CrN and Multilayer SiC+DLC, then plasma sprayed AI2O3 and AI2O3+P (artificially aged by phosphating). The protection layers were applied to the vessel wall knives and tested on two types of presses in the course of the sunflower processing campaign: VPI-press for pre-pressing and RD-press for final pressing. In both presses the pressure reached its maximum value in working field III: 250 bars in VPI and 450 bars in RD-press. The protection layers were compared on the basis of the intensity of wear, calculated from the loss of mass per unit of the processed sunflower. By analyzing the composition of the grist from the press (during extraction) the proportion of SiO2 was found to be decreasing going from the inlet to the outlet. This was concluded to be the result of its being washed away by the extracted oil. The variant protection layers were also tested by the standard method for abrasion wear examination by applying dry sand/rubber wheel tests in accordance with the ASTM G65-94. This method did not prove to be acceptable to evaluate the wear of worm press parts protected by the variant procedures. Analysis of the specimens-knives' service surfaces following the testing in worm presses showed that the protection layers harder than SiO2 wore out first according to the mechanism of zero abrasion and then due to the fatigue of the surface. Quality of the link between protection layer and base material as well as the structure and hardness of the 'nse material immediately under the protection layer were found to be of great influence. With case hardened parts and on base material after removal of the protection layer the .i'Srasive mechanism of wear was found to have taken place. It is characteristic to take _ace in conditions in which the abrasive is harder than the surface with which it is in contact. The intensity of wear of the knives was found to increase from the working field I to the working field III in which it reached its maximum, decreasing after that towards the outlet of the press. At the same time the intensity of wear in the press for final pressing was 6etermined to be 5 times higher than in the press for pre-pressing. Mutual comparison of the intensity of wear of the variant protection layers showed that -. a least resistance to wear was found with boriding and CrN layers followed by the case .iardened ones and Al2O3 and Al2O3+P. The most resistant were found to be the vanadium amide and Multilayers SiC+DLC protection layers.

Item Type: Thesis (Doctoral thesis)
Uncontrolled Keywords: pužne preše; cijeđenje ulja; trošenje; zaštitni sloj
Divisions: 1000 Department of Materials
Date Deposited: 22 Sep 2014 18:00
Last Modified: 16 Oct 2015 13:20
URI: http://repozitorij.fsb.hr/id/eprint/57

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