Small gauge high carbon content steel wires are produced through successive drawing operations that reduce wire cross section up to 1000 times and more for instance from 5.5 to 0.18 mm). This very delicate process requires one or two intermediate heat treatments in order to re-form the original well proportioned microstructure of the wire, so enabling the material to withstand the final extreme grain elongation that is necessary to get the very high mechanical resistance required by the market to the final product (3.200 - 3.300 Mpa). The heat treatment consists in:
- phase a) heating up the wires up to +/- 1.000 C.
- phase b) abrupt cooling down of the wires up to 550-600 C. The very high working temperatures makes this process very critical in terms of energy consumption and efficiency.
The standard technology is actually based on "open fire furnaces" (phase a) and "lead baths" (phase b), pushing the industries to try different ways of process including the technology of "fluidized beds" for potenting (phase b) in view of the potential damages produced to the environment and to the operators by the use of big quantities of lead. Nevertheless, the fluidized bed technology cannot actually guarantee heat transfer coefficients as high as those obtained with the use of the lead and is not very well accepted.
HEATWIRE objectives and mains expected innovations are then related to: Objectives:
- reduction of energy consumption between 30% and 40%;
- increasing of efficiency in the use of energy up to 40%.;
- final removal of "lead bath" technology with consequent positive impacton the environmental and user's health with the new FIB technology; - constant heat transfer coefficients and constant values of process parameterswithin the equipment;
- increase of wire strength up to 10-20% with consequent reduction of tyresteel content. This should lead to a potential saving of car fuel andtoxic emissions.
- new compact high efficiency equipment with constant heat transfer coeffi cients. The new furnace will be based on an optimized fluidized bedtechnology;
- implementation of an integrated monitoring system capable of keeping theprocess under control;
- determination of the optimum thermic cycle relevant to the high carbon steels(0.7 and 0.8% C) being used;
- capability of reproducing (production level) a specified thermic cycle, sogetting mechanical characteristics of the final wire within very littletolerances.
The application of the new technology would lead to an expected energy saving of approximately 1.2 x 10 6 MJ only for the European lines. In addition, the increased resistance of the final product (steel cord), would lead to a lower tyre weight and a consequent reduction of toxic emissions. The new technology will allow to reduce production costs without reducing "labour" costs, and this is really going to have an important impact on European society, also in view of the quite little currency rate of the competitors of non European countries. The benefits of the research will be of general interest as they will be applicable to all high carbon steel wires industries, including production of cables, springs, steel cord and bead wire (automotive), hose wire, fasteners.
Funding SchemeCSC - Cost-sharing contracts