Within the pro­ject “PbFree­Pat”, the heat tre­at­ment of steel wire is inves­ti­ga­ted in depth. Steel wire is used in a varie­ty of dif­fe­rent pro­ducts. Appli­ca­ti­ons ran­ge from ropes or rope cores, tyre cord in tyres or pre-pro­ducts for the manu­fac­tu­ring of screws, pins and springs. During the pro­duc­tion of the pro­ducts, the dia­me­ter of the wire is con­ti­nuous­ly redu­ced from the rol­led wire to the final dimen­si­on through seve­ral dra­wing pro­ces­ses. In order to achie­ve lar­ge over­all dia­me­ter reduc­tions, a heat tre­at­ment is neces­sa­ry bet­ween the indi­vi­du­al dra­wing steps. This pro­cess stage is cal­led patenting and ensu­res a fine-pear­li­tic struc­tu­re in the wire. During this heat tre­at­ment, the wire is hea­ted to an aus­te­ni­ti­sa­ti­on tem­pe­ra­tu­re and then coo­led. In order for the pear­li­tic struc­tu­re in the wire to be com­ple­te­ly for­med, the coo­ling is fol­lo­wed by an iso­ther­mal hol­ding pha­se. In the cur­rent sta­te of the art, the coo­ling and the iso­ther­mal hol­ding pha­se are rea­li­sed with the help of mol­ten lead. In addi­ti­on to the coo­ling speed requi­red for the mate­ri­al and a uni­form hol­ding pha­se, liquid lead abo­ve all enables a simp­le pro­cess in which up to 30 wires of dif­fe­rent dia­me­ters can be trea­ted in par­al­lel. Howe­ver, the use of lead in indus­tri­al pro­ces­ses is under dis­cus­sion due to its toxicity.
The aim of the rese­arch pro­ject “PbFree­Pat” is the­r­e­fo­re the eva­lua­ti­on of pos­si­ble pro­cess alter­na­ti­ves for the sub­sti­tu­ti­on of lead in wire patenting, which is dis­ad­van­ta­ge­ous in terms of health as well as work and envi­ron­men­tal safety.

Insight into a fur­nace for hea­ting wires (Copy­right: H. KÜNNE GmbH & Co. KG)

Howe­ver, a solid eva­lua­ti­on is only pos­si­ble with a detail­ed under­stan­ding of the cur­rent refe­rence pro­cess. The­r­e­fo­re, the pro­ject includes the deve­lo­p­ment of a pro­cess model that ful­ly repres­ents the sta­te of the art in wire patenting. To ensu­re that the coo­ling in the lead bath is cor­rect­ly model­led, it is plan­ned to car­ry out a wide ran­ge of inves­ti­ga­ti­ons to deter­mi­ne the heat trans­fer coef­fi­ci­ent. For this pur­po­se, a test rig for wire samples will be deve­lo­ped, with which the inves­ti­ga­ti­ons can be car­ri­ed out direct­ly in the lead baths of indus­tri­al plants. In addi­ti­on, drag mea­su­re­ments at indus­tri­al plants are plan­ned in order to vali­da­te the pro­cess model.
Based on the deve­lo­ped pro­cess model, the key per­for­mance indi­ca­tors (KPI) of the pro­cess will be deter­mi­ned, which will then be used to eva­lua­te the pos­si­ble pro­cess alter­na­ti­ves. Once the alter­na­ti­ves have been iden­ti­fied, their key per­for­mance indi­ca­tors will be com­pared with each other and with the refe­rence pro­cess in order to iden­ti­fy the tech­ni­cal­ly and eco­no­mic­al­ly most sui­ta­ble lead-free alter­na­ti­ves. At the end of the pro­ject, the deve­lo­ped pro­cess model will be pro­vi­ded to the par­ti­ci­pa­ting indus­tri­al com­pa­nies in order to enable a more ener­gy-effi­ci­ent and resour­ce-con­ser­ving pro­cess manage­ment with the help of the know­ledge gained.