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Rub­ber & Met­al in Con­struc­tion — Dif­fer­ences and Similarities

20.07.2022   | Andreas Fröhner

WHITEPAPER

Rub­ber and plas­tics in mod­ern agri­cul­tur­al technology 

Learn how agri­cul­tur­al engi­neer­ing can meet most of the cur­rent challenges

Rub­ber and met­al are among the mate­r­i­al groups found in almost all indus­tri­al prod­ucts. Know­ing their dif­fer­ences and sim­i­lar­i­ties is essen­tial for any man­u­fac­tur­ing com­pa­ny. How­ev­er, few orga­ni­za­tions can demon­strate com­pe­ten­cy in both areas.

Most design­ers come from the met­al world. That is where their core com­pe­ten­cies lie. They often have lit­tle expe­ri­ence with oth­er mate­ri­als. Yet it is well worth know­ing the dif­fer­ences and sim­i­lar­i­ties between elas­tomers and met­als so that they can be com­bined as effi­cient­ly as possible.

Rub­ber is flex­i­ble, met­al is precise

Rub­ber is an elas­tic mate­r­i­al that expands and con­tracts and reacts to exter­nal influ­ences. This is an advan­tage when it comes to seal­ing and damp­ing, because rub­ber can flex­i­bly adapt to dynam­ic forces. In con­struc­tion, on the oth­er hand, this prop­er­ty can pose a problem.

The elas­tic char­ac­ter­is­tics of rub­ber lim­it the pos­si­ble tol­er­ances in pro­duc­tion. Elas­tomers can­not be man­u­fac­tured as pre­cise­ly as met­als. The prop­er­ties of the mate­r­i­al do not allow this. In met­al con­struc­tion, for exam­ple, fil­i­gree geome­tries are pos­si­ble that are a frac­tion of a mil­lime­ter wide. Just think of knife blades. In elas­tomers, on the oth­er hand, a width of 0.5 mm is pos­si­ble with a great deal of effort.
Below that, the pro­duc­tion of rub­ber can no longer be car­ried out with process reliability.

Many design­ers are used to tol­er­ances in the hun­dredth or thou­sandth range and expect the same from rub­ber mold­ed parts. For this rea­son, pro­duc­ers often receive inquiries about geome­tries that can­not be real­ized. This leads to addi­tion­al tech­ni­cal arrange­ments and adjust­ments that can drag out the devel­op­ment project and often have a neg­a­tive impact on costs.

Anoth­er fac­tor con­cerns the vul­can­iza­tion process. Very fine geome­tries require opti­mum flow behav­ior in order to guide the raw rub­ber into all cor­ners of the mold. Even slight pre­ma­ture vul­can­iza­tion can mean that the raw rub­ber can no longer fill the fil­i­gree recess­es of the mold.

Under cer­tain cir­cum­stances, the tem­per­a­ture of the pre­heat­ed mold may already be suf­fi­cient to influ­ence the flow behav­ior of the raw rub­ber in such a way that the geom­e­try can no longer be real­ized. It would be pos­si­ble to allow the mold to cool down com­plete­ly, but this would have a neg­a­tive effect on cycle times and dri­ve up the price of the mold­ed arti­cles significantly.

Tip for designers: 

Be care­ful not to design too fil­i­gree geome­tries for rub­ber mold­ed parts. In many cas­es, these can­not be real­ized with an elas­tic mate­r­i­al. Expe­ri­ences from the met­al sec­tor can­not be trans­ferred 1:1 at this point. 

Rub­ber is less stan­dard­ized than metal

Com­pared with met­al com­po­nents, the require­ments analy­sis for rub­ber mold­ed parts is more com­plex and exten­sive. Elas­tomers are less stan­dard­ized than met­als. Their mate­r­i­al prop­er­ties depend to a large extent on the addi­tives that are mixed into the raw mate­r­i­al. Only in rare cas­es is it pos­si­ble to cov­er the desired prop­er­ties of a rub­ber com­po­nent with a stan­dard com­pound. Rub­ber is a flex­i­ble mate­r­i­al that must always be adapt­ed to the par­tic­u­lar application.

How­ev­er, this flex­i­bil­i­ty also offers room for error. There are many vari­ables to con­sid­er when select­ing an elas­tomer. If these are spec­i­fied incor­rect­ly, the end prod­uct may not have the desired prop­er­ties. This aspect dis­tin­guish­es elas­tomers from met­als, which inher­ent­ly have almost all of the key mate­r­i­al properties.

For this rea­son, require­ments analy­sis is a top pri­or­i­ty when spec­i­fy­ing a rub­ber mold­ed part. The pro­duc­tion part­ner must know, for example

These spec­i­fi­ca­tions are an impor­tant pre­req­ui­site for mate­r­i­al selec­tion, because they deter­mine the exact com­po­si­tion of the rub­ber compound.

Tip for designers: 

The require­ments analy­sis for elas­tomers is much more exten­sive than you are used to in the met­al sec­tor. Describe the intend­ed use of the mold­ed part as pre­cise­ly as pos­si­ble in your spec­i­fi­ca­tions and be pre­pared for queries. 

Met­al offers more design free­dom than rubber

In terms of pro­cess­ing, met­als offer more lee­way than elas­tomers. Rub­ber mold­ed parts are usu­al­ly pro­duced by injec­tion mold­ing in a mold. Sim­ple geome­tries can be cut or punched from sheets and pro­files extrud­ed. Sub­se­quent machin­ing is pos­si­ble only to a lim­it­ed extent. This is where elas­tomers dif­fer from met­als, which are main­ly machined.

Take, for exam­ple, a pipe that is to have a groove inside. With a met­al pipe, pro­duc­tion can sim­ply mill the groove into it. This is not pos­si­ble with a rub­ber pipe. Here, the groove must be tak­en into account dur­ing the design stage and the tool must be designed accord­ing­ly. The fin­er the groove is to be, the more dif­fi­cult this task is, because with very acute angles or fil­i­gree geome­tries, the mold­ed part can be dam­aged when it is removed from the mold. The design must also take this into account dur­ing prod­uct development.

Tip for designers: 

Keep the man­u­fac­tur­ing process in mind when design­ing a rub­ber mold­ed part. Elas­tomers can­not be machined in the same way as met­als. For very point­ed or fine geome­tries, it is advis­able to con­sult mate­r­i­al experts. 

Con­clu­sion

The dif­fer­ences between rub­ber and met­al pri­mar­i­ly con­cern the degree of stan­dard­iza­tion and flex­i­bil­i­ty in prod­uct devel­op­ment. Rub­ber is an elas­tic mate­r­i­al per­fect­ly suit­ed for damp­ing and seal­ing. This advan­tage comes at the price of a low­er degree of pre­ci­sion, which trans­lates into low­er tol­er­ances and dif­fi­cul­ties in real­iz­ing fil­i­gree geome­tries. At the same time, rub­ber must always be adapt­ed to its field of appli­ca­tion. This process requires a thor­ough analy­sis of requirements.

In prac­tice, these dif­fer­ences are main­ly rel­e­vant for design. Elas­tomers and met­als do not com­pete with each oth­er. They com­ple­ment each oth­er. Almost every indus­tri­al prod­uct con­tains a com­bi­na­tion of rub­ber and met­al. There­fore, the design should be famil­iar with both materials.

Whitepa­per:
Rub­ber and plas­tics in mod­ern agri­cul­tur­al technology 

Learn how agri­cul­tur­al engi­neer­ing can meet most of the cur­rent challenges

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Autor: Andreas Fröhner

Andreas Fröh­n­er has been a field sales rep­re­sen­ta­tive at Jäger’s Ham­burg loca­tion since 2001. The qual­i­fied tech­ni­cal busi­ness econ­o­mist orig­i­nal­ly comes from the auto­mo­tive sec­tor and has broad knowl­edge of the entire rub­ber and plas­tics range.

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