Search

Predmet diplomskog rada bili su lean principi i njihova primjena u konkretnim procesima. Ukratko su teorijski objašnjeni pojmovi lean, OEE (Overall Equipment Effectivness), TEEP (Total Effective Equipment Performance), SMED (Single Minute Exchange of Dies) i TPM (Total Productive Maintenance). Detaljno su opisani promatrani procesi proizvodnje polistirenskih posuda termoformiranjem i izoliranje polistirenskih posuda poliuretanskom pjenom. Za svaki proces su izračunati OEE i TEEP. Napravljeno je mapiranje toka vrijednosti i gantogrami planirane proizvodnje. Prikazana je realizacija radnih naloga u vremenskom razdoblju od šest radnih dana. Također je napravljena usporedba između dva stroja za termoformiranje. The subject of this thesis were lean principles and their application in concrete processes. The terms lean, OEE (Overall Equipment Effectiveness), TEEP (Total Effective Equipment Performance), SMED (Single Minute Exchange of Dies) and TPM (Total Productive Maintenance) are briefly theoretically explained. Described in detail, are the observed processes of polystyrene containers production using thermoforming process and isolation of polystyrene containers with polyurethane foam. OEE and TEEP were calculated for each process. Value stream mapping and gantt charts of planned production were made. The realization of work orders in a time period of six working days was shown. A comparison was also made between the two thermoforming machines.

Kandžaste spojke mehanički elementi se već dugi niz godina upotrebljavaju u industriji za spajanje vratila, kompenzaciju aksijalnih pomaka, te ublažavanje vibracija i udara. U ovom radu konstruirana je kandžasta spojka s umetkom od poliuretana. Spojka svojim zubima preko umetka prenosi okretni moment, te poliuretanski umetak štiti pogonski stroj od utjecaja udara i vibracija. Okretni moment prenosi se s vratila na spojku preko pera te je spojka osigurana od aksijalnog pomicanja po vratilu s elastičnim zatikom. Potrebne momente koje spojka treba prenijeti izračunati su prema standardu DIN 740-2. Umetak od poliamida proračunali smo s obzirom na opterećenja na tlak. Kod metalnih prirubnica proračunali smo dali zubi konstruirane spojke mogu podnijeti opterećenje s obzirom na savijanje zuba te optrerećenje na smik. Kod ove spojke još smo odredili koji je najmanji promjer vratila koje može prenijeti okretni moment te smo za taj promjer odredili potrebnu dužinu pera. Za dodatnu provjeru dali spojka zadovoljava zadanim uvijetima provjerili smo najopterečeniji dio u programskom paketu Abaqus. Dog clutch is a mechanical element that have been used in the indsutry for shaft coupling, axial displacement compensation, vibration and shock mitigation. In this paper, a dog clutch with a polyurethane insert is desigened. The clutch transmits torque to its teeth via the insert, and polyurethane insert protects the drive machine from the effects od shock and vibration. The torque is transmitted from the shaft to the clutch via a parallel key and the coupling is securet against axial movement along the shaft with an elastic pin. The required torques to be transmitted bay the clutch are calculate according to DIN 740-2. The polyamide insert was calculated with respect to pressure load. In the case of metal flanges, we calculated whether the teeth of designed coupling can withstand the load with respect to the bending of the teeth and the shear load. With this clutch, we also determined the smallest diameter od the shaft that can transmit torque, and we determined the required length of the parallel key for this diameter. For additional verification of whether the coupling meets the specified conditions, we checked the most loaded part in the Abaqus software package.

U ovom radu istraživan je učinak dodatka višestjenih ugljikovih nanocjevčica (MWCNT) te MWCNT-a modificiranog skupinama COOH (MWCNT-COOH) u rasponu masenih udjela od 0 do 4 % na svojstva poliuretana. Uzorci nanokompozita pripravljani su dispergiranjem nanopunila u otopini poliuretana u acetonu te polaganim isparavanjem otapala pri sobnoj temperaturi. Utjecaj punila na mehanička svojstva kompozita ispitan je testom jednoosnog istezanja, a električna provodnost uzoraka određivana je metodom četiri kontakta. Toplinska postojanost istražena je termogravimetrijskom analizom (TGA). Obje vrste punila MWCNT povećavaju modul, ali snižavaju prekidnu čvrstoću i prekidno istezanje kompozita. Rezultati ispitivanja električne provodnosti pokazali su da se, u odnosu na čisti PU koji ima provodnost reda veličine 10–13 S cm–1, provodnost nanokompozita s masenim udjelom punila MWCNT 0,2 % znatno povećava na vrijednost reda veličine 10–6 S cm–1. Daljnjim povećanjem do masenog udjela obje vrste MWCNT-a 4 %, provodnost se dalje povećava do vrijednosti većih od 10–2 S cm–1. Taj učinak povećanja provodnosti neznatno je jače izražen u sustavima s MWCNT-COOH-om. Rezultati termogravimetrijske analize upućuju na to da se dodatkom obje vrste MWCNT-a znatno poboljšava toplinsku postojanost u istraživanom rasponu udjela nanopunila, pri čemu je ovaj učinak nešto izraženiji za sustave s punilom MWCNT. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna., In this paper, the influence of multiwalled carbon nanotubes (MWCNT) and carbon nanotubes modified with COOH groups (MWCNT-COOH) on the mechanical and electrical properties as well as on thermal stability of polyurethane (PU) were investigated. The samples of nanocomposite were prepared by dispersion of the nanofiller in a solution of polyurethane in acetone, followed by slow evaporation of the solvent at room temperature. The effect of the fillers on the mechanical properties of PU nanocomposites was examined by the uniaxial deformation test, and electrical properties of the samples were determined by the four probe method. Thermal stability was investigated by thermogravimetric analysis (TGA). The addition of both types of MWCNTs fillers increases modulus (Fig. 1), due to higher modulus of the nanofillers. Due to the better distribution in PU matrix and stronger interactions between COOH groups and carbonyl group in PU matrix, nanocomposites with MWCNT-COOH have higher modulus than nanocomposites with MWCNT filler. Most of the composites have lower strength and elongation at break than PU (Figs. 2 and 3). Smaller MWCNT-COOH aggregates and stronger interactions between this filler and the PU matrix cause less pronounced decreasing of strength at break. Compared to the pure PU, with conductivity of the order of 10–13 S cm–1, the conductivity of the nanocomposite with mass fraction of MWCNT nanofiller 0.2 % substantially increases up to the value of the order 10–6 S cm–1 (Fig. 4). A further increase up to 4 % for both types of MWCNTs, resulted in a further increase in conductivity up to values exceeding 10–2 S cm–1. Due to the better distribution in PU matrix and stronger interactions between COOH groups and carbonyl groups in PU matrix, the conductivity increase effect in systems with MWCNTs-COOH is slightly more pronounced. All investigated nanocomposites have potential applications as electric discharge materials and for electrostatic painting. The results of the thermogravimetric analysis indicate that the addition of both types of MWCNTs significantly improves the thermal stability (Figs. 6 and 7). The maximal degradation rate temperature of polyurethane increased by about 45 °C, thereby this effect is slightly more pronounced for systems with MWCNTs (Fig. 7). This work is licensed under a Creative Commons Attribution 4.0 International License.

U ovom radu istraživan je učinak dodatka višestjenih ugljikovih nanocjevčica (MWCNT) te MWCNT-a modificiranog skupinama COOH (MWCNT-COOH) u rasponu masenih udjela od 0 do 4 % na svojstva termoplastičnog poliuretana (PU). Uzorci nanokompozita pripravljani su postupkom polaganog sušenja iz smjese poliuretana i nanopunila u acetonu pri sobnoj temperaturi. Učinak dodatka nanopunila na sferolitnu morfologiju poliuretana te raspodijeljenost nanopunila u matrici PU analizirana je optičkom polarizacijskom mikroskopijom. Toplinska svojstva u neizotermnim i izotermnim uvjetima istraživana su diferencijalnom pretražnom kalorimetrijom (DSC). Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna., In this work, the influence of multiwalled carbon nanotubes (MWCNT) and carbon nanotubes modified with COOH groups (MWCNT-COOH) on the structure and properties of thermoplastic polyurethane (PU) were investigated. The samples of nanocomposite were prepared from a mixture of polyurethane and MWCNT in acetone by slow drying at room temperature. The effect of the addition of nanofillers on the spherulite structure of polyurethane and the distribution of the nanofillers in the PU matrix were analysed with optical polarization microscopy. Thermal properties in non-isothermal and isothermal conditions were investigated by differential scanning calorimetry (DSC). The results of contact angle measurement imply that modification of MWCNT surface with COOH groups changes its surface from hydrophobic to hydrophilic (Fig. 2 and Table 1). Optical polarization microscopy showed that the addition of both nanofillers disrupts the coarse spherulite morphology of the polyurethane matrix (Fig. 4 and Fig. 5). It was observed that, at the macro level, the modified MWCNT-COOH filler is better distributed in the PU matrix than is the MWCNT filler (Fig. 5). The DSC results showed that, in non-isothermal conditions, up to a certain amount, both nanofillers accelerate the crystallization of the soft segments of polyurethane. This effect is more pronounced in systems with MWCNT filler (Fig. 9). The results of the crystallization enthalpy during cooling showed that MWCNT filler, despite its worse distribution in the PU matrix, more significantly enhances crystallization of PU’s soft segment than does the MWCNT-COOH filler (Fig. 10). This conclusion can be ascribed to better compatibility between the nonpolar MWCNT filler and the nonpolar soft phase of the PU matrix, as well as to the previous scientific finding that functional groups at MWCNT surface decrease the nucleation effect of MWCNT. By analysing the melting peaks, it can be concluded that the PU systems with MWCNT compared to systems with MWCNT-COOH contain a higher proportion of less ordered crystalline soft phase (Fig. 11). In isothermal conditions, the MWCNT filler accelerates crystallization more significantly than does the MWCNT-COOH filler (Fig. 16). This work is licensed under a Creative Commons Attribution 4.0 International License.

U ovome radu prikazane su metode zaštite energetskih transformatorskih kućišta primjenom kombinacije epoksidnog i poliuretanskog premaza, prednosti i nedostaci i područje primjene. Diplomski rad se sastoji od teorijskog i eksperimentalnog dijela. U teorijskom dijelu je obrađeno oštećivanje materijala, klasifikacija korozija i metode zaštite od korozije premazima koje se danas koriste u zaštiti strojarskih konstrukcija i postrojenja. Posebno je obrađen odabir sustava zaštite transformatora, te epoksidni i poliuretanski premaz, jer se kombinacija tih premaza koristi u eksperimentalnom dijelu ovoga rada. U eksperimentalnom dijelu ispitan je sustav zaštite općih konstrukcijskih čelika od korozije kombinacijom epoksidnih i poliuteranskih premaza. Nizom ubrzanih ispitivanja kao što su slana i vlažna komora, mjerenje debljine premaza i prionjivosti, određeno je zaštitno djelovanje premaza. Priprema površine i nanošenje premaza provedeno je u tvrtki Komet d.o.o., dok su sva laboratorijska ispitivanja provedena na Katedri za zaštitu materijala, Fakulteta strojarstva i brodogradnje u Zagrebu. This thesis shows the methods of protection of power transformer casing using a combination of epoxy and polyurethane coatings, advantages and disadvantages and scope. The thesis consists of theoretical and experimental part. The theoretical part deals with corrosion, corrosion classification, methods of corrosion protection, coatings that are used in the protection of mechanical structures and facilities, as well as the selection of the paint system for the protection of transformers, epoxy and polyurethane coating, because the combination of this coatings is used in the experimental work. The experimental part deals with protection system of structural steel from corrosion by a combination of epoxy and polyurethane coatings. In a series of accelerated tests such as the salt fog and humidity chamber, the measurement of thickness and adhesion strength, the protective effect of the coating was determined. Surface preparation and coating application took place in the company Komet LLC, while all laboratory tests was carried out at the Chair of Materials Protection, Faculty of Mechanical Engineering and Naval Architecture in Zagreb.