Kumityyppi

Kumityyppi (rubber type) refers to the broad categories of elastomer materials used in engineering and manufacturing, defined by polymer composition and microstructure. The term is used to distinguish natural rubber from synthetic rubbers, and to categorize rubbers by their performance characteristics for different environments and applications.

Natural rubber (NR) is derived from rubber trees and consists mainly of polyisoprene. It offers excellent elasticity, high tensile strength, and good dynamic properties, but has limited resistance to heat, ozone, and many oils. Synthetic rubbers comprise several families, including styrene-butadiene rubber (SBR), polybutadiene rubber (BR), nitrile rubber (NBR), chloroprene rubber (CR, neoprene), ethylene-propylene-diene monomer rubber (EPDM), silicone rubber (VMQ), and fluororubbers (FKM). Each type is optimized for specific needs: SBR for general-purpose tires and mechanical goods; NBR for oil resistance; EPDM for weather and ozone resistance; silicone for extreme temperatures; FKM for high chemical resistance.

Properties that define kumityyppi include elasticity, hardness, temperature range, chemical resistance, aging behavior, and processability. These properties are tuned through formulation, including fillers, plasticizers, oils, and curing systems. Vulcanization, a crosslinking process, is commonly used to enhance elasticity and strength, with sulfur-based systems for many rubbers and peroxide systems for higher heat resistance.

Common applications are tires and belts (often NR or SBR), seals and gaskets (NBR and EPDM), hoses, medical items, and electrical insulation. Selection of a kumityyppi involves balancing elasticity, thermal and chemical resistance, durability, and cost for the intended operating conditions. Environmental considerations include recycling and devulcanization, making end-of-life handling an important factor in modern rubber design.