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Hardening - Types and resistances

Rolleri standard tools are induction hardened.

The most relevant characteristics the surface hardness, which can reach 60HRC and the penetration capacity of the treatment which can reach a depth of 4mm in the material. To guarantee a constant hardness on all the parts involved in the heat treatment, a double passage is necessary, therefore after the induction hardening phase, the tempering phase is carried out. Rolleri applies different tempering techniques in relation to the material used and the type of profile to be heat treated: it is possible to harden at "high frequency" and "low frequency". Thanks to the two techniques, the surface hardness is guaranteed but for profiles with narrow sections, we avoid risks of breakage or internal cracks. The following shows a comparison between heart hardening and Rolleri induction hardening.




During bending operations the tool is subjected to repeated loads and stresses, therefore Rolleri tools are designed and manufactured to withstand 1,000,000 work cycles. To achieve this goal, Rolleri chose the induction surface hardening, in fact tools with low surface hardness tend to deform in the working areas, becoming unusable and force the operator to replace the equipment or to grind worn parts.

Why surface induction hardening and not core hardening?

The induction surface hardening of ferrous materials is a selective treatment that allows the hardening of the working surfaces of the tools, improving their wear resistance properties. The hardened surfaces offer excellent resistance to damage, plastic deformation and contact load during operation. The treatment allows to harden multiple surfaces, even with different depths, so as to optimize the resistance characteristics of each region of the pieces. Induction hardening allows to combine the high hardness obtained on the surface (about 4 mm deep), 54-60 HRc (1980-2200 N / mm2), with the characteristics of mechanical strength and toughness (impact resistance) of the core ; in fact, the latter remain unchanged with respect to the preliminary state of the material, usually normalized for carbon-only steels (eg C45) and tempered for alloy steels (eg 42CrMo4). Compared to core hardening, which reaches 50 HRc, a higher surface hardness is obtained and the mechanical characteristics of the tool body remain unchanged. This translates into less wear and tear of the working areas and therefore a much longer tool life. The treatment consists of fast localized austenitizing heating, followed by an immediate cooling with water jets or polymer solutions conveyed directly to the heated area, the thermal cycle is completed by the finding of final relaxation. The treatment offers good control of distortions and deformations; it also has low risks of hardening failure.

Core hardening
Rolleri induction hardening

This graph shows that:

Rolleri induction hardening has a wear of 0.003 mm after 12600 strokes;

Core hardening has a wear of 0.014 mm after the same number of strokes.