Dishwashers made with recycled plastic components

Recy­cled plas­tic makes up seh many deter­gent bot­tles. As far as high­er-val­ue appli­ca­tions are con­cerned, recy­clates are still wait­ing to be wide­ly used. Researchers at the Fraun­hofer Insti­tute for Struc­tur­al Dura­bil­i­ty and Sys­tem Reli­a­bil­i­ty LBF, togeth­er with com­pa­nies, have shown that recy­cled plas­tic per­forms sim­i­lar­ly to vir­gin plas­tic — and is also suit­able as a mate­r­i­al for basic dish­wash­er supports.

Reusing plas­tics makes sense in the con­text of cli­mate and envi­ron­men­tal pro­tec­tion. While pack­ag­ing is already often made from recy­cled plas­tic on a pro rata basis, experts and com­pa­nies are still hes­i­tant when it comes to high­er-qual­i­ty prod­ucts. After all, prop­er­ties such as strength, odor or appear­ance of the for­mer waste dif­fer from new­ly pro­duced plas­tic due to batch fluc­tu­a­tions. How­ev­er, if recy­clates are pre­pared eco­nom­i­cal­ly, their prop­er­ties can be made to match those of vir­gin plastics.

“There is still a lack of con­fi­dence in the recy­cled material. ”

- Dominik Spanck­en, sci­en­tist at the Fraun­hofer LBF in Darm­stadt, Germany.

The researchers would like to strength­en this trust in the recy­cled mate­r­i­al. “We have there­fore joined forces with the com­pa­nies Bosch GmbH and Bosch-Siemens-Haus­geräte GmbH to inves­ti­gate what recy­cled plas­tic can real­ly do,” says Spanck­en. To this end, the Bosch com­pa­ny first opti­mized recy­clate from the hous­ing of car starter bat­ter­ies — for exam­ple, addi­tives were used to increase the strength and improve the opti­cal prop­er­ties. Is the opti­mized mate­r­i­al suit­able for the pro­duc­tion of dish­wash­er base carriers?

These com­po­nents, which weigh around two kilo­grams, form the basic struc­ture of the dish­wash­er, hold its side walls and accom­mo­date ancil­lary units such as the pump, sta­tus sen­sors and con­tain­ers for salts. If these basic sup­ports could be pro­duced from recy­clate, this would make a sig­nif­i­cant con­tri­bu­tion to sus­tain­able house­hold appli­ances: With an annu­al pro­duc­tion of three mil­lion dish­wash­ers, the low­er resource input of recy­clate would save around 2,500 met­ric tons of crude oil per year — rough­ly equiv­a­lent to the amount of oil that can be trans­port­ed by an inland water­way ship 110 meters long.

What can the recycled material do?

“At the Fraun­hofer LBF, we first inves­ti­gat­ed how the opti­mized recy­clate behaves under mechan­i­cal loads,” says Spanck­en. So the researchers pro­duced test spec­i­mens and pulled on them with a fixed force about 100,000 times — auto­mat­ed, of course. This fig­ure is based on the typ­i­cal appli­ca­tion and load spec­trum of large house­hold appli­ances. It spec­i­fies the loads that the mate­r­i­al must with­stand undam­aged. In accor­dance with these spec­i­fi­ca­tions, the experts from Fraun­hofer LBF, Bosch and BSH cre­at­ed para­me­ters for the design.

As for the 100,000 cycles, these are main­ly due to a fin­ger-thick pin on the dish­wash­er’s base sup­port. This is sub­ject­ed to mechan­i­cal stress every time the dish­wash­er door is opened and closed — and rep­re­sents the most demand­ing cycli­cal­ly loaded area on the dish­wash­er base carrier.

Assum­ing around 15 open­ings per day and a ser­vice life of the appli­ance of around 18 years, this works out at around 100,000 door open­ings per appli­ance life­time. Can a spig­ot made of recy­clate with­stand that? “Although the recy­clate has 15 per­cent less strength, it has sim­i­lar stiff­ness prop­er­ties to vir­gin plas­tic. Far more impor­tant, how­ev­er, is the plas­tic deforma­bil­i­ty, in which both mate­ri­als behave equal­ly. In sum­ma­ry, it can be said that the recy­clate can han­dle the same stress­es as vir­gin mate­r­i­al,” con­firms Spancken.

How resilient is the component made from recyclate?

To back up this result, the researchers test­ed not only the mate­r­i­al itself, but also the com­po­nent itself. “From the mate­r­i­al tests, we deter­mined mate­r­i­al char­ac­ter­is­tic val­ues. Using these char­ac­ter­is­tic val­ues, we then devel­oped a design method­ol­o­gy to check whether the jour­nal is oper­a­tional­ly sta­ble,” Spanck­en describes.

In oth­er words, the research team clamped the tenons from vir­gin base beams in a test rig and applied loads from use, such as those that occur when the machine is opened and closed. Since under­floor heat­ing and radi­ant heat from the dish­wash­er could heat the trun­nion to as much as 50 degrees, Spanck­en and his team tem­pered it to 50 degrees in the process. How much force must be applied before the cone breaks? How many times can it endure the open­ing process?

Using the exper­i­men­tal data, the researchers cre­at­ed a val­i­dat­ed cal­cu­la­tion and design method­ol­o­gy — and then “fed” this method­ol­o­gy with the mate­r­i­al char­ac­ter­is­tics of the recy­clate. “We were able to infer the behav­ior of a jour­nal made of recy­clate based on the tests on the vir­gin mate­r­i­al and the cal­cu­la­tion method­ol­o­gy,” Spanck­en says. The result is encour­ag­ing: the load-bear­ing capac­i­ty of tenons made of vir­gin mate­r­i­al and recy­clate dif­fers only in nuances. From the fea­si­bil­i­ty study, it can be con­clud­ed that the dish­wash­er base sup­port can be made of recy­clate and thus make an impor­tant con­tri­bu­tion to a sus­tain­able over­all appliance.