Development of novel resistance heating elements through innovative material and process combinations

In 2020, the demand for natu­ral gas as an ener­gy source in indus­try was 324 TWh, which cor­re­sponds to 31% of Germany’s total demand. With a plan­ned reduc­tion of 55% in green­house gas emis­si­ons in 2030 com­pared to 1990, the con­ver­si­on of gas-fired heat tre­at­ment plants to alter­na­ti­ve hea­ting methods is unavo­ida­ble in the long term. Added to this is the pres­su­re on indus­try resul­ting from increased pri­ma­ry ener­gy cos­ts and a pro­s­pec­ti­ve reduc­tion in depen­den­cy on the fos­sil fuel market.

Swit­ching to elec­tric hea­ting sys­tems with elec­tri­ci­ty from rene­wa­ble sources enables the grea­test pos­si­ble reduc­tion in CO2 emis­si­ons, even com­pared to hydro­gen hea­ting. In addi­ti­on, elec­tric hea­ting does not cau­se any direct CO2 emis­si­ons during pro­duc­tion, which saves com­pa­nies the cost of CO2 cer­ti­fi­ca­tes and impro­ves their com­pe­ti­ti­ve­ness in inter­na­tio­nal com­pe­ti­ti­on. The fle­xi­ble geo­me­tric cus­to­mi­sa­ti­on opti­ons of elec­tric hea­ting ele­ments are also advan­ta­ge­ous. Indus­tri­al fur­nace con­s­truc­tion com­pa­nies, ser­vice pro­vi­ders for auto­ma­ti­on and pro­cess model­ling as well as com­pa­nies out­side the metal­wor­king indus­try in par­ti­cu­lar would bene­fit from the con­ver­si­on of the hea­ting system.

In some fields of appli­ca­ti­on, such as vacu­um fur­naces in batch ope­ra­ti­on, elec­tri­cal hea­ting sys­tems with resis­tance hea­ting ele­ments are alre­a­dy estab­lished. In many sys­tems (e.g. rol­ler hearth fur­naces), howe­ver, resis­tance hea­ting ele­ments are not available or not yet estab­lished due to the requi­re­ments pla­ced on the sys­tems. The mecha­ni­cal stress on the hea­ting ele­ments is par­ti­cu­lar­ly problematic.

Sche­ma­tic struc­tu­re of a hea­ting lay­er system

The aim of the rese­arch pro­ject is the­r­e­fo­re to deve­lop a new type of hea­ting ele­ment that ful­fils the pro­cess requi­re­ment for mecha­ni­cal sta­bi­li­ty while at the same time pro­vi­ding suf­fi­ci­ent and uni­form heat input into the pro­cess. Ther­mal spray­ing (TS) is a pro­mi­sing method for manu­fac­tu­ring the­se hea­ting ele­ments. TS enables thin, flat lay­ers to be appli­ed to a metal­lic or cera­mic sub­stra­te. Over­all, the hea­ting ele­ment appli­ed by ther­mal spray­ing (see illus­tra­ti­on) is a laye­red sys­tem con­sis­ting of two insu­la­ting lay­ers and a con­duc­ti­ve lay­er in bet­ween. The lay­er that is expo­sed to the mecha­ni­cal load can be made of a che­mi­cal­ly and mecha­ni­cal­ly resistant mate­ri­al. Alt­hough the first suc­cessful appli­ca­ti­ons of TS alre­a­dy exist, e.g. in alu­mi­ni­um cas­ting, the use of TS hea­ting sys­tems in ther­mal pro­cess tech­no­lo­gy has not yet been car­ri­ed out or sci­en­ti­fi­cal­ly inves­ti­ga­ted. In par­ti­cu­lar, ques­ti­ons regar­ding the maxi­mum pos­si­ble heat input per sur­face, the elec­tri­cal cont­ac­ting for a hea­ting pro­fi­le that is as homo­ge­neous as pos­si­ble or the che­mi­cal and mecha­ni­cal resi­li­ence in the inten­ded area of appli­ca­ti­on are still open. This includes tem­pe­ra­tures up to 1150°C and dif­fe­rent atmo­sphe­res, which are deri­ved from the poten­ti­al appli­ca­ti­ons mentioned.