Common methods for calculating rubber hardness

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Preliminary calculation of formula hardness: Basic hardness of various rubbers – NR, low-temperature SBR, CIIR 40; oil-filled (25 phr) SBR: 31; high-temperature SBR: 37; oil-filled (37.5 phr) SBR: 26; IIR: 35. NBR, CR, CSM: 44. NBR with an acrylonitrile content of over 40%: 46. In the aforementioned base rubbers, for each additional portion of filler or softener used, the change in hardness is as follows: FEF, HAF, EPC: +0.5; ISAF: +2.5; SAF, vapor-phase silica: +2.5; SRF: +0.33; water-containing silica: +0.4; thermally cracked carbon black or hard clay: +0.25; calcium carbonate: +0.167; surface-treated calcium carbonate: +0.142; mineral rubber: –0.2; lipid-based plasticizers: –0.67; aliphatic oils or naphthenic oils: –0.5; aromatic oils: –0.588. Estimated hardness = basic hardness of the rubber + amount of filler (or softener) used × hardness change value