Projektiranje i ispitivanje svojstava lokota za zaključavanje bicikla

master's thesis

• Title (english): Design and testing of bicycle lock properties
• Author: Stjepan Mandić
• Mentor: Darko Landek (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2025-03-27, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

Lokoti su naprave kojima se predmeti vežu i osiguravaju od provale. Najvažniji dijelovi lokota su brava koja se nalazi u kućištu lokota i zakrivljena šipka koja obuhvaća predmete. Kvaliteta i sigurnost lokota ovisi primarno o mehaničkim svojstvima materijala i konstrukcije mehanizma brave.. U radu su opisane brave s kombinacijom položaja cilindara i fizičkim ključem te njihovi mehanizmi rada. Zakrivljene šipke, lanci ili čelična užad koja obuhvaća predmete moraju biti otporni na udarce, velike sile savijanja, i rezanja u slučaju provale. Opisani su uvjeti za izbor materijala za izradu šipki lokota: čvrstoća, visoka površinska tvrdoća, korozijska postojanost, žilavost na sobnoj i niskim temperaturama, otpornost na abraziju i ostali. Prema ovim zahtjevima odabran je materijal i proizvedene su tri zakrivljene šipke od čelika za cementiranje 20MnCr5, kompatibilne sa tržišno dostupnom bravom lokota za zaključavanje bicikla. Na dvije komercijalno dostupe šipke i uzorcima cementiranih šipki provedena su ispitivanja tvrdoće i kemijskog sastava. Na metalografskom uzorku cementirane šipke provedena su ispitivanja mikrostrukture i određena je efektivna dubina cementiranja. Na temelju rezultata ispitivanja tvrdoće procijenjena je vlačna čvrstoća komercijalnih i u radu izrađenih šipki. Prema dobivenim rezultatima cementirana šipka lokota je boljih mehaničkih svojstava od tržišno dostupnih šipki..

Abstract (english)

Locks are devices with which objects are tied and secured against burglary. The most important parts of the lock (whole device) are the lock, which is located in the padlock housing, and the curved bar that encloses the items.. The quality and security of a padlock depends primarily on the mechanical properties of the material and the design of the lock mechanism. The paper describes locks with a combination of cylinder positions and a physical key and their operating mechanisms. Curved bars, chains or steel ropes that enclose objects must be resistant to impacts, high bending forces, shearing and cutting in the event of a burglary. The conditions for selecting materials for making lock rods are described: strength, high surface hardness, corrosion resistance, toughness at room and low temperatures, abrasion resistance and others. According to these requirements, the material was selected and three curved rods made of case-hardening steel 20MnCr5 were produced, compatible with a commercially available padlock for locking bicycles. Hardness and chemical composition tests were carried out on two commercially available rods and samples of case-hardened rods. Microstructure tests were performed on the metallographic sample of the cemented rod and the effective carburizing depth was determined. Based on the results of the hardness test, the tensile strength of the commercial and field-made bars was estimated. According to the obtained results, the cemented padlock bar has better mechanical properties than commercially available bars..

• Keywords: lokot; bicikl; izbor materijala; toplinska obrada; cementiranje; brava; 20MnCr5; metalografija
• Keywords (english): padlock; bicycle; material selection; heat treatment; case hardening; lock; 20MnCr5; metallography.
• Language: croatian
• URN:NBN: urn:nbn:hr:235:583717
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Embargoed access; Embargo expiration date: 2027-03-31
• Created on: 2025-03-24 23:07:56