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Why seals should nev­er be under­es­ti­mat­ed
in devel­op­ment — three typ­i­cal problems

17.11.2021   |   Tim Eltze 
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Seals are designed to pre­vent unde­sir­able mass trans­fer with­in tech­ni­cal prod­ucts. Because they are rel­a­tive­ly inex­pen­sive com­po­nents, they are not usu­al­ly giv­en high pri­or­i­ty in design. This is why seals often cause prob­lems in devel­op­ment projects, because each appli­ca­tion has its own require­ments for a seal­ing ele­ment, which design­ers must be aware of.

In this arti­cle, we take a look at three typ­i­cal prob­lems that can arise due to neg­li­gent han­dling of seals in the devel­op­ment of machines and devices. We will also tell you how you can effec­tive­ly avoid the dif­fi­cul­ties described.

Prob­lem 1: The instal­la­tion space is unsuit­able for the intend­ed seal

Whether (and for how long) a seal can per­form the task assigned to it depends not least on its instal­la­tion envi­ron­ment. Even for sim­ple O‑rings suit­able grooves or recess­es, for exam­ple, must be planned in the design into which the seal can be fit­ted. The require­ments for sophis­ti­cat­ed ele­ments such as rotary or hydraulic seals are more com­plex and call for spe­cif­ic design expertise.

If the intend­ed instal­la­tion space for a seal is insuf­fi­cient, this can cause prob­lems. Typ­i­cal­ly, exist­ing design draw­ings need to be adjust­ed late in the prod­uct devel­op­ment process (PEP), requir­ing addi­tion­al devel­op­ment loops. To avoid this, some com­pa­nies opt for high­ly com­plex seal­ing ele­ments that have yet to be designed for the project — includ­ing cost­ly tool­ing con­cepts. In the worst case, a seal is installed defec­tive­ly so that it fails soon­er or lat­er in use. At one man­u­fac­tur­er of elec­tron­ic devices, for exam­ple, an improp­er­ly installed seal caused the elec­tron­ics to come into con­tact with dust and fail com­plete­ly after a short time.

Man­u­fac­tur­ing com­pa­nies that want to avoid delays, con­se­quen­tial costs and loss of rep­u­ta­tion must already suf­fi­cient­ly con­sid­er the require­ments of each seal­ing com­po­nent (instal­la­tion space, func­tion­al require­ments, etc.) in their design draw­ings. How­ev­er, this does not mean that design­ers should design their machines around the seal. A sim­ple cat­a­log of mea­sures list­ing all rel­e­vant require­ments and process­es can often nip the dif­fi­cul­ties described above in the bud.

Prob­lem 2: The seal mate­r­i­al does not match the gen­er­al con­di­tions of the machine

Seals are also some­times sub­ject to strict legal require­ments and qual­i­ty stan­dards. Design teams must be aware of these require­ments at the begin­ning of the devel­op­ment project in order to be able to design a seal cor­rect­ly. Oth­er­wise, this also leads to expen­sive delays and addi­tion­al devel­op­ment loops.

One exam­ple of this is the UL94 fire clas­si­fi­ca­tion. This is used when a plas­tic arti­cle is exposed to a cer­tain fire risk and must there­fore be flame-resis­tant. In some cas­es, com­pa­nies for­get that this prop­er­ty must affect the entire prod­uct, not just indi­vid­ual com­po­nents. They may use a UL94-rat­ed plas­tic for the enclo­sure, but not for the seal. As a result, the over­all prod­uct is not suf­fi­cient­ly flame resis­tant, which can affect fur­ther certifications.

Such prob­lems are not uncom­mon in the devel­op­ment of seal­ing com­po­nents. They can be cir­cum­vent­ed with con­sci­en­tious mate­r­i­al selec­tion. In doing so, com­pa­nies must ana­lyze in advance all rel­e­vant frame­work con­di­tions that are of impor­tance for the seal. In addi­tion to legal require­ments, these include:

The deci­sive fac­tors in mate­r­i­al selec­tion are care, expe­ri­ence and exper­tise. Per se, there is a suit­able mate­r­i­al for every seal. The chal­lenge is to iden­ti­fy the mix­ture from the mul­ti­tude of mate­ri­als that best meets the require­ments of the seal.

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Prob­lem 3: The geom­e­try of the com­po­nent is not designed to suit the seal

As a rule, design teams focus on met­al com­po­nents first. Rub­ber and plas­tic parts do not get their atten­tion until the prod­uct is large­ly designed. How­ev­er, this means that seal­ing require­ments receive lit­tle atten­tion for a large part of the design process. This presents a chal­lenge for sup­pli­ers of rub­ber and plas­tic com­po­nents, who are asked to deliv­er seals that either can­not be man­u­fac­tured in the intend­ed form or can only be man­u­fac­tured at great finan­cial expense. Both sce­nar­ios have a neg­a­tive impact on dead­lines and cost tar­gets in the prod­uct devel­op­ment process.

The geo­met­ric design of the com­po­nent in which the seal is to be installed is a par­tic­u­lar source of dif­fi­cul­ty. Point­ed cor­ners and edges, com­pli­cat­ed angles and unusu­al shapes can only be sealed with great effort, if at all. The same applies to com­po­nents in which there are height dif­fer­ences. These make it dif­fi­cult to apply a seal even­ly because the mate­r­i­al mix­ture can­not be com­pressed even­ly dur­ing pro­duc­tion. Con­se­quent­ly, seal man­u­fac­tur­ers have to resort to com­plex, cost­ly man­u­fac­tur­ing process­es to meet their cus­tomers’ requirements.

If seals are con­sid­ered too late in the design process, this often pre­vents the use of cost-effec­tive solu­tions that are eas­i­er to imple­ment in terms of man­u­fac­tur­ing tech­nol­o­gy. Stan­dard seals (e.g. O‑rings), which could sim­ply be bought in with­out a ded­i­cat­ed mold con­cept, can­not be used in com­plex geome­tries, for exam­ple. Poten­tial sav­ings — not only mon­e­tary, but also in terms of the company’s car­bon foot­print (mate­r­i­al scrap, ener­gy use, etc.) — remain unused in this way.

It makes much more sense for design­ers to take into account the pre­req­ui­sites that must be met for a seal as ear­ly as the plan­ning stage. Their first approach should be to use stan­dard com­po­nents as often as pos­si­ble. If this is out of the ques­tion, design teams should seek con­tact with mate­r­i­al experts at an ear­ly stage. Their know-how makes it eas­i­er to devel­op the best solu­tion with a view to mon­e­tary spec­i­fi­ca­tions and man­u­fac­tur­ing imple­men­ta­tion options.

Sum­ma­ry

Even minor neg­li­gence in seal­ing tech­nol­o­gy can result in dam­age claims, com­plex devel­op­ment loops and addi­tion­al costs. This makes it all the more impor­tant for design teams to take a detailed look at the gen­er­al con­di­tions to which their seals will be exposed right at the start of the project. This con­cerns, among oth­er things, the nec­es­sary instal­la­tion space, the mate­r­i­al to be used, and the geom­e­try of the com­po­nents in which the seals are to be installed.

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Author: Tim Eltze

Tim Eltze has been work­ing in the field of rub­ber and plas­tic prod­ucts for more than 20 years and has in-depth exper­tise in these areas. He is cur­rent­ly employed by Jäger as Region­al Man­ag­er North and Site Man­ag­er Hamburg. 

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