Abstract | Polimerni materijali sve se više upotrebljavaju u proizvodnji kliznih ležaja koji u industriji imaju masovnu upotrebu. Prvenstveno zbog uštede u proizvodnji, ali i drugih pogodnih svojstava kao što su veća elastičnost i time izdržljivost, dobra kemijska otpornost, korozijska postojanost i mnoge druge. Polimeri su građeni od mera i izgledom mogu biti linearni, granati i umreženi. Prema ponašanju na povišenim temperaturama dijele se na duromere, elastomere, plastomere, te elastoplastomere. Deformacijska stanja u kojima se mogu pronaći ovisno o opterećenju su kapljasto, gumasto i staklasto stanje, a temperature pri kojima dolazi do prijelaza jednog stanja u dugo nazivamo staklište i tecište. Plastomeri su važni jer se mogu reciklirati i ponovno oblikovati, te se oni najviše koriste u proizvodnji. Najzastupljeniji plastomeri su polietilen, poliamidi, polipropilen, poli(vinil-klorid), polistiren, poli(etilen-tertaftalat) i poli(oksimetilen). U radu su prikazana svojstva i područja upotreba nekih važnijih polimera. POM primjerice odlikuju dobra klizna svojstva, otpornost na abraziju i adheziju, kemijska postojanost te dimenzijska stabilnost. PET odlikuju visoka žilavost, dobra klizna svojstva, kemijska otpornost i otpornost na kiseline, dimenzijska stabilnost, te dobra električna izolacija. Poliamidi imaju veliku sposobnost apsorpcije vlage i velike su čvrstoće. PEEK je slab na UV zračenje pa se pojačava staklenim i ugljičnim vlaknima. Koristi se u medicinskoj industriji. Svojstva su mu kemijska stabilnost, otpornost na gama zračenje, velika žilavost i niska sklonost puzanju. PVDF je vrlo otporan, oblikuje se ekstruzijom, kemijski je otporan, velike je toplinske ekspanzije, te je otporan na UV zrake. PEI ima visoku mehaničku čvrstoću i krutost, otpornost na puzanje pri velikim temperaturnim razlikama, veliku kemijsku otpornost, dimenzijsku stabilnost te je dobar električni izolator. PPSU i PSU su dobre čvrstoće i stabilnosti na visokoj temperaturi. PPSU ima visoku topljivost uz nisku apsorpciju vlage, postojanost na dezinfekcijska sredstva, otpornost na puzanje te dobra izolacijska svojstva. PPS odlikuju visoka čvrstoća i tvrdoća na visokim temperaturama, kemijska stabilnost, niska apsorpcija vode, dimenzijska stabilnost te dobra izolacijska svojstva. Polimerni klizni ležajevi znatno odstupaju od metalnih ležajeva bilo po masi, potrebi za podmazivanjem, te mehaničkim i toplinskim svojstvima. Stvaranje tankog filma od polimera na površini omogućava znatno bolja tribološka svojstva. Cilj je dobiti što manje trenje kako bi bio manji utrošak energije sustava. Kompoziti ojačani vlaknima s polimernom matricom puno su žilaviji, te drugačije utječu na trošenje ovisno o orijentaciji vlakana. Podmazivanje služi za smanjenje trenja, kraće vrijeme uhodavanja, hlađenje, te dulji vijek trajanja sustava. Ležaj koji podmazujemo mora biti kemijski postojan na mazivo. Prevlake koristimo kao površinski zaštitni sloj koji smanjuje trenje i osigurava postojanost oblika. Mehaničkim proračunom razmatramo površinske tlakove između ležaja i osovine, toplinskim proračunom pratimo kondukcijski, konvekcijski i zračenjem prenesenu toplinu između ležaja i osovine. Hidrauličkim proračunom utvrđujemo zračnost u ovisnosti o količini maziva. Polimerne klizne ležajeve upotrebljavamo u autoindustriji, industriji kućanskih aparata, brodograđevnoj industriji (ležaj osovine propelera), građevinskim strojevima, avioindustriji, za ležajeve turbinskih vratila hidroelektrane, te u mnoštvu drugih slučajeva gdje su njihova svojstva zadovoljavajuća. |
Abstract (english) | Polymeric materials are increasingly being used in the production of slide bearings, which are massively used in the industry. They are mainly used due to production savings, but also other features such as the great elasticity and the endurance, the good chemical resistance, the corrosion resistance and many others. Polymers are composed of mers and their structure can be linear, branched, and cross-linked. According to their behavior at the increased temperature they are divided into duromers, plastomers, elastomers and elastoplastomers. Deformation states depending on the load are airfoiled, rubbery and glassy, and temperatures at which a state transition occurs are called glass transition temperature and pour point. Plastomers are important because they can be recycled and re-formed, and they are most used in the production. The most used plastomers are polyethylene, polyamide, polypropylene, polyvinyl chloride, polystyrene, poly(ethylene-tertftalate), and poly(oxymethylene). This paper presents characteristics and areas of the use of the most important polymers. The POM, for example, has good sliding characteristics, the abrasion and adhesion resistance, the chemical stability and also the dimensional stability. The PET has the high toughness, good sliding characteristics, the chemical resistance, the resistance to the acid, the dimensional stability, and as well the good electrical insulation. Polyamides have the high ability to absorb the moisture and are very firm. The PEEK is weak on the UV radiation, so it is reinforced with glass or carbon fibers. It is used in the medical industry. Its characteristics are chemical stability, resistance to gamma radiation, high toughness and low tendency to slide. The PVDF is highly resistant, extruded, chemically resistant, resistant to UV rays and has a large thermal expansion. The PEI has high mechanical strength and stiffness, slide resistance at big temperature differences, good chemical resistance, dimensional stability and it is a good electrical insulator. The PPSU and the PSU are firm and stabile at high temperature. The PPSU has the high solubility with the low moisture absorption, the durability on disinfectants, the slide resistance and good insulating possibilities. The PPS is firm at high temperatures, and is characterized with the chemical stability, the low water absorption, the dimensional stability and good insulating characteristics. Polymer sliding bearings differ from metal bearings, either by weight, lubrication requirements, mechanical and thermal characteristics. Creating a thin film of polymer on the surface contributes to better tribological characteristics. The target is to lower the friction as much as possible to reduce the energy consumption of the system. Fiber-reinforced composites with a polymer matrix are much more rigid and have a different effect on consumption which is depending on the fiber orientation. The lubrication serves to reduce the friction, shorter the running-in time and cooling, and to prolong the structure life. The slide bearing must be chemically stabile on the lubricant. Coatings are used on the surface as the protective layer that reduces the friction and ensures the durability of the shape. The mechanical calculation studies the surface pressure between the bearing and the shaft and with the thermal calculation we follow the conductive, convective and radiated heat transfer between the bearing and the shaft. The hydraulic calculation determines the air volume depending on the amount of the lubricant. Polymer sliding bearings are used in automotive industry, household appliance industry, shipbuilding industry, construction machinery, aerospace industries, hydroelectric turbine shaft bearings, and many other cases where their characteristics are acceptable. |