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Rub­ber spring ele­ments in the agri­cul­tur­al indus­try: a cau­tion­ary exam­ple from practice

15.12.2021   |  Lukas Grünig

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Mate­r­i­al exper­tise and prod­uct design that meets require­ments are basic pre­req­ui­sites for the suc­cess­ful use of rub­ber and plas­tic com­po­nents. In many engi­neer­ing devel­op­ment depart­ments, steel is the pre­dom­i­nant mate­r­i­al and there is a lack of expe­ri­ence in work­ing with poly­mer mate­ri­als. The lack of mate­ri­als exper­tise repeat­ed­ly leads to prob­lems with prod­ucts. What these dif­fi­cul­ties are based on and how com­pa­nies avoid them is illus­trat­ed by the exam­ple of rub­ber spring ele­ments in the agri­cul­tur­al industry. 

The ini­tial situation

Rub­ber spring ele­ments are used in agri­cul­tur­al engi­neer­ing, espe­cial­ly on machines for soil cul­ti­va­tion. In disc har­rows, they form the piv­ot joint between the rigid machine frame and the mov­able disc arm on which the met­al discs are pulled through the soil. Rub­ber spring ele­ments ensure that the hard shocks gen­er­at­ed by inho­mo­ge­neous soils (e.g. stones present in the field) are decou­pled from the machine frame. They also increase the soil con­tour track­ing capa­bil­i­ty of the indi­vid­ual discs. They are there­fore of high val­ue for the reli­a­bil­i­ty and life­time of an agri­cul­tur­al machine.

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Case Study: Spring ele­ments for agri­cul­tur­al technology

In our case study, you will learn how rub­ber spring ele­ments can be used to damp­en vibra­tions in agri­cul­tur­al machinery. 

Rub­ber spring ele­ments for disc har­rows are pro­duced all over the world by spe­cial­ized sup­pli­ers. Jäger Gum­mi und Kun­st­stoff, for exam­ple, has devel­oped spe­cial rub­ber spring ele­ments based on a high-per­for­mance elas­tomer com­pound togeth­er with sev­er­al Euro­pean OEMs of soil cul­ti­va­tion tech­nol­o­gy. These ele­ments have proven them­selves in the field for years and are per­ma­nent­ly being fur­ther developed.

Some time ago, a mechan­i­cal engi­neer­ing com­pa­ny approached the Jäger team in this regard. It was ini­tial­ly a loose inquiry in which the com­pa­ny pro­vid­ed rel­a­tive­ly lit­tle infor­ma­tion on the func­tion­al require­ments as well as the mate­r­i­al spec­i­fi­ca­tions rel­e­vant for its rub­ber spring ele­ments. In addi­tion, it spec­i­fied a low tar­get price, which — accord­ing to the first impres­sion — could not be real­ized with­out restric­tions regard­ing mate­r­i­al quality.

The cus­tomer pro­vid­ed a sam­ple of its pre­vi­ous com­po­nent for test­ing. Jäger exam­ined the com­po­nent both in the in-house test rig for rub­ber spring ele­ments and in the phys­i­cal-chem­i­cal lab­o­ra­to­ry. The focus was on func­tion­al­ly rel­e­vant phys­i­cal prop­er­ties such as rebound, com­pres­sion set and tear resis­tance. In a sec­ond step, Jäger test­ed the ful­ly assem­bled com­po­nents on a test rig that sim­u­lat­ed real-life field use over sev­er­al weeks.

What trap did the mechan­i­cal engi­neer­ing com­pa­ny fall into?

The lab­o­ra­to­ry and test rig results were unsat­is­fac­to­ry. The actu­al func­tion of the rub­ber spring ele­ments, which are arranged around a square tube to form the swiv­el joint and are sup­posed to return the deflect­ed disc arm after the appli­ca­tion of force (e.g. by a stone in the field), was not giv­en. The iden­ti­fied mal­func­tion of the rub­ber spring ele­ment was due to the poor phys­i­cal prop­er­ties of the elas­tomer mate­r­i­al. The per­ma­nent defor­ma­tions of the dis­as­sem­bled rub­ber spring ele­ment sug­gest­ed poor com­pres­sion set. Lab­o­ra­to­ry test­ing sub­stan­ti­at­ed this hypoth­e­sis. Among oth­er things, the com­po­nent con­tained a high pro­por­tion of fillers, which had a neg­a­tive effect on the mechan­i­cal prop­er­ties of the elas­tomer compound.


Despite these test results, the mechan­i­cal engi­neer­ing com­pa­ny con­tin­ued to work with the sup­pli­er of the sam­ple com­po­nent. This deci­sion, which sub­se­quent­ly caused major prob­lems, was ini­tial­ly quite obvi­ous from the company’s point of view. It was caused by the inter­play of var­i­ous fac­tors that occur again and again in the rub­ber and plas­tics sector:

What were the consequences?

Six months after the ini­tial inquiry, the agri­cul­tur­al machin­ery man­u­fac­tur­er con­tact­ed Jäger Gum­mi und Kun­st­stoff again. As feared, the rub­ber spring ele­ments installed in the agri­cul­tur­al machin­ery failed after a short time. This result­ed in numer­ous returns from the mar­ket world­wide, which not only caused the com­pa­ny immense costs, but also dam­aged its reputation.

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deformed rub­ber spring element 

Due to the exist­ing dam­age case, the agri­cul­tur­al machin­ery man­u­fac­tur­er decid­ed to resume the devel­op­ment of the rub­ber spring ele­ments. In close coor­di­na­tion with the mate­r­i­al experts from Jäger, the require­ments for the mate­r­i­al were pre­cise­ly defined and a high-qual­i­ty elas­tomer com­pound was adapt­ed to the func­tion­al needs of the com­po­nent. By means of an intel­li­gent tool­ing con­cept, pro­to­types could be pro­duced and exten­sive­ly test­ed at short notice.

This care paid off for the agri­cul­tur­al machin­ery man­u­fac­tur­er in the end. Togeth­er with Jäger, the man­u­fac­tur­er designed a spring ele­ment that is suit­able for the demand­ing work in the field and is still being installed in numer­ous oth­er agri­cul­tur­al machines today. The feed­back the com­pa­ny receives from the mar­ket is now pos­i­tive again.

Con­clu­sion

Exam­ples like this are not uncom­mon in mechan­i­cal engi­neer­ing. Due to the high time and cost pres­sures to which many com­pa­nies are sub­ject, they repeat­ed­ly make the wrong deci­sions when deal­ing with rub­ber and plas­tic com­po­nents. Espe­cial­ly since expe­ri­ence and know-how in this area are not avail­able in every devel­op­ment team. The sce­nario we have pre­sent­ed in this arti­cle can be effec­tive­ly avoid­ed if cus­tomers involve their sup­pli­ers in a devel­op­ment at an ear­ly stage and dis­cuss the spec­i­fi­ca­tions of the com­po­nent in detail. Expe­ri­ence has shown that if this hap­pens at the begin­ning of devel­op­ment projects, the best con­di­tions are cre­at­ed for mak­ing the best deci­sion with regard to the required func­tion­al­i­ty of the com­po­nent and the tar­get­ed price. 
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Author: Lukas Grünig

Lukas Grünig sup­ports OEMs from the agri­cul­tur­al machin­ery tech­nol­o­gy sec­tor in the devel­op­ment of com­po­nents made of rub­ber and plas­tic. Since 2020, the grad­u­at­ed mechan­i­cal engi­neer has been work­ing for Jäger as a cross-loca­tion indus­try man­ag­er in the field of agri­cul­tur­al technology.

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