As part of the indus­tri­al pro­duc­tion of high-strength metal­lic mate­ri­als, they have to neces­s­a­ri­ly under­go a heat tre­at­ment to set the desi­red mecha­ni­cal pro­per­ties. In the case of flat pro­ducts, this heat tre­at­ment is usual­ly car­ri­ed out in con­ti­nuous plants which always include a coo­ling stage. During this pro­cess, the coo­ling rate has a decisi­ve influence on the resul­ting micros­truc­tu­re and thus on the mecha­ni­cal pro­per­ties. Espe­ci­al­ly in the field of high-strength mate­ri­als (e.g. age-har­denable 7XXX alu­mi­ni­um alloys), a par­ti­cu­lar­ly high coo­ling rate is requi­red, which can only be achie­ved by water coo­ling. For this pur­po­se, the water is disper­sed into dro­p­lets via spray nozz­les and appli­ed to the sur­face of the mate­ri­al. In con­ti­nuous plants, arrays of spray nozz­les are used for this pur­po­se, in which the spray are­as of the indi­vi­du­al nozz­les over­lap. As a result, com­plex flow phe­no­me­na (water moun­ta­ins, etc.) form on the sur­face, which influence the heat trans­fer and coo­ling rate. The­r­e­fo­re, the flow phe­no­me­na and their influence on the heat trans­fer are inves­ti­ga­ted in the pro­ject “Spray nozz­le fields in coo­ling sec­tions” in order to adjust the heat trans­fer on the sur­face in a defi­ned way after­wards. The flow phe­no­me­na are deter­mi­ned at the Depart­ment for Indus­tri­al Fur­nace and Heat Engi­nee­ring. The heat trans­fer coef­fi­ci­ents are deter­mi­ned at the Chair of Ther­mo­dy­na­mics and Com­bus­ti­on at Otto von Gue­ri­cke Uni­ver­si­ty Mag­de­burg. Sub­se­quent­ly, the results of the two pro­ject part­ners will be cor­re­la­ted in order to deter­mi­ne the influence of the rele­vant parameters.

To rea­li­se this objec­ti­ve, seve­ral test rigs have been set up at the Depart­ment for Indus­tri­al Fur­naces and Heat Engi­nee­ring as part of the pro­ject. With the first test rig, the flow on a sta­tio­na­ry hori­zon­tal sur­face below any given nozz­le field can be investigated.

In the cour­se of the pro­ject, a fur­nace model is being deve­lo­ped at the IOB that can cal­cu­la­te the pro­cess in the inno­va­ti­ve har­dening fur­nace inclu­ding the coo­ling unit. In addi­ti­on to describ­ing the strip tem­pe­ra­tures at each point in the pro­duc­tion pro­cess, the pro­cess model will also simu­la­te the mecha­ni­cal strip beha­viour in the plant. Based on expe­ri­men­tal coo­ling tests on a test rig at the IOB, a stu­dy will be car­ri­ed out to deve­lop a defor­ma­ti­on-opti­mi­sed coo­ling unit using simu­la­ti­ons.
Based on the inves­ti­ga­ti­ons, the coo­ling unit of the new plant will be desi­gned tog­e­ther with the pro­ject part­ners and sub­se­quent­ly used in the indus­tri­al anne­al­ing line.

Test rig for deter­mi­ning the flow in a nozz­le field on a sta­tio­na­ry hori­zon­tal surface

For this pur­po­se, dif­fe­rent mea­su­re­ment methods are used, some of which were deve­lo­ped within the scope of the pro­ject. For exam­p­le, the flow for­ma­ti­on can be opti­cal­ly quan­ti­fied with a came­ra. In addi­ti­on, an inves­ti­ga­ti­on with ultra­so­nic sen­sors or force sen­sors is pos­si­ble. The­se sen­sors can be used to deter­mi­ne both the cha­rac­te­ristics of the flow and the resul­ting impact momen­tum of the water dro­p­lets. The test rig has also been exten­ded to include the pos­si­bi­li­ty of mea­su­ring the impinge­ment den­si­ty of a nozz­le or a nozz­le field using a pat­ter­na­tor. The self-con­s­truc­ted pat­ter­na­tor con­sists of more than 1000 indi­vi­du­al mea­su­ring points, which are auto­ma­ti­cal­ly eva­lua­ted with the help of a respec­ti­ve set-up.

To ensu­re that the results obtai­ned can be trans­fer­red to indus­tri­al prac­ti­ce, the influence of the strip speed on the flow for­ma­ti­on is also inves­ti­ga­ted with ano­ther test rig. For this pur­po­se, a metal­lic strip is con­ti­nuous­ly run over two rol­lers at strip speeds simi­lar to tho­se used in indus­tri­al appli­ca­ti­ons. The strip width ran­ges up to one met­re. The same mea­su­ring methods for deter­mi­ning the flow are used on this test rig.

At the same time, a test rig at the Chair of Ther­mo­dy­na­mics and Com­bus­ti­on at the OvGU Mag­de­burg was modi­fied in order to enable the deter­mi­na­ti­on of the heat trans­fer coef­fi­ci­ent during the coo­ling of hori­zon­tal­ly moved samples. In both Aachen and Mag­de­burg, iden­ti­cal nozz­les and boun­da­ry con­di­ti­ons are used in all inves­ti­ga­ti­ons. In this way, a cor­re­la­ti­on of the obtai­ned results is possible.