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Foamed seals in one component polyurethane CeraCon

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Foamed seals in one component polyurethane CeraCon Powered By Docstoc
					A. S. Kreissl, S. Hoof*




                                                                                                                      ters are carried out within very narrow tole-
             Foamed seals in                                                                                          rances. The technical requirements set upon
                                                                                                                      the plant for this are very complex and the
       one-component polyurethane                                                                                     process management problematic. Fluctua-
                                                                                                                      tions in the quality of the seals cannot be
                                                                                                                      excluded and are generally associated with
                                                                                                                      changes in ambient conditions (air humidity,
The Penguin foam system with the Foamply application technology produces foamed seals                                 temperature). Significant variations in the
in one-component elastomers directly onto the component to be sealed (FIPG sealing tech-                              chemical foam seal are common.
nology = form-in-place gaskets). Complex seal shapes can also be achieved. Foaming
takes place by ventilation of the liquid plastic with conventional compressed air. Curing                             In contrast, when foaming seals with the
time amounts to only a few minutes. The applied seal is characterised by closed cells with                            Penguin foam system, air and one-component
even pore distribution, resulting in a waterproof foam.                                                               polyurethane are homogenised and divided up
                                                                                                                      into fine bubbles. It is through this mechanical
                                                                                                                      foaming at room temperature that a closed
                                                                                                                      cell foam structure arises. The way in which
1. Introduction                                        nowned customers in Europe with foam                           it works can be described as follows (Fig. 2):
                                                       plants and the associated automation sys-                      after the introduction of a defined volume of
Elastomer seals are currently used in nume-            tems during the last 5 years. The one-com-                     air to liquid elastomer, a twin phase flow is
rous applications that require sealing against         ponent foams are based on polyurethane or                      stream is produced on a conveyor system.
dust or water. Conventional foam processes             silicone. Cold and hot curing versions of the                  This way, the gas is distributed evenly into the
often fail in sealing against water, as open           material are available.                                        liquid by shear force. Once ventilated, the
cell seals arise in the chemical foaming                                                                              process makes use of the specific flow pro-
process. Very high water absorption can be                                                                            perties of highly viscous polymers to finely
observed particularly when the seal’s skin is          2. Physical instead                                            distribute and homogenise the material. As
damaged. Single component physically fo-                  of chemical foaming                                         soon as the twin phase liquid relaxes again
amed seals are becoming increasingly ac-                                                                              under atmospheric pressure, the air expands
cepted for waterproof solutions. The Pengu-            Two basically different processes are possib-                  and it forms the desired foam. No curing re-
in foam process offers particular advantages           le for foaming of seals: chemical and mecha-                   action takes place in the plant, so that the
in this area. The system and its associated            nical foaming. The former produces a bubb-                     system never has to be rinsed or cleaned.
Foamply application technology has been                le structure by means of a chemical reaction,
developed by Sunstar in Japan and has been             in which two highly reactive components
used there successfully in the automotive              have to be precisely dosed and homogenous-                     3. The foam plant
and electronics industries for more than               ly mixed together. The high reactivity (chemi-
                 10 years (Fig. 1). The com-           cal curing reaction) in the materials mixing                   The material and the plant are developed in
                      pany CeraCon in Wei-             chamber requires that the process parame-                      harmony. A plant that is ready for production
                         kersheim, Germany,
                               has been supp-
                                                                                      Initial velocity ; 6.0 cm/sec                 Tubu diameter ; 10 mm, length ; 100 mm
                                     lying re-

                                                                                                          Bubble; φ 3.0 mm

Fig. 1:
Component with                                                                                                    Time = 0.001sec
foamed sealant bead




                                                                                                                  Time = 0.100 sec



* Andreas S. Kreissl
                                                                                  ▲




                                                       Fig. 2:
  Managing Director of CeraCon GmbH, Weikersheim
                                                       Diagram of distribution
  Stephan Hoof                                         of bubbles through shear                                   Time = 0.360 sec
  Technical Service Engineer at Sunstar, Weikersheim   force.




PU MAGAZINE – VOL. 2, NO. 2 – APRIL 2005                                                                                                                                     93
                                                                                                                          ten minutes, compared with several hours
                                                                                                                          with conventional two-component foams. As
                                                                                                                          only one component is dosed, very small
                                                                                                                          seals can also be reliably produced. The
                                                                                                                          hardness values of the seals in relation to the
                                                                                                                          degree of foaming are shown in Figure 5.
                                                                                                                          The interesting applications include the auto-
                                                                                                                          motive industry (door modules, lights, control
                                                                                                                          equipment), the household appliance industry
                                                                                                                          (washing and dishwashing machines, irons)




                                                                                                  ▲
                                                                                                      Fig. 3:
                                                                                                      Plant arrangement   and all types of housings (control cabinets,
                                                                                                                          fluorescent light fittings, electrical distributi-
consists of the Foamply application techno-                            It is also interesting that this technology can    on cabinets, filters).
logy with integrated control technology and                            operate reliably irrespective of component
a handling robot that applies the sealant                              temperature. This enables cold metal parts
bead to the component, followed by passage                             to be sealed without pre-heating, or warm          5. Conclusion
through an oven for a short period if a heat                           injection moulded parts without cooling. The
curing material version has been chosen.                               Foamply plant technology has been special-         The Foamply one-component foam technolo-
Figure 3 shows the arrangement of the                                  ly developed for Penguin foam materials, but       gy enables the application of waterproof
plant without the “Thermo” oven cure sys-                              it also operates in principle with other one-      elastomer seals with the highest degree of
                                                                       component thixotropic elastomers.                  reliability and plant availability, using simple
Fig. 4: Degree of foaming as a function of the                                                                            operation and minimum maintenance. Further
▼       ventilation pressure                                                                                              additional benefits are the very fast curing of
                                                                       4. Properties and                                  the seals, the environmentally beneficial
                          3,5
                                                                          application possibilities                       principle of elimination of rinsing cycles and
                                                                                                                          the insensitivity to fluctuations in room tem-
  Foaming Magnification




                          3,0
                                                                       The foam quality is entirely reproducible. This    perature and air humidity. Optimum harmo-
                          2,5                                          is a significant advantage, bearing in mind         nisation of plant technology and materials
                                                        #3150
                                                                       the usual certified quality assurance sys-          enables cost-effective and fast production of
                          2,0
                                                        #3160          tems. A further important aspect is the much       highest quality elastomer seals that are op-
                                                                       shorter curing times of the products. The hot      timally suited for the application.
                          1,5
                                                                       curing material version cures at 80 °C in just                                                   ■
                                                                       five minutes. The foamed components can
                          1,0
                             0,00   0,05     0,10      0,15     0,20   therefore be assembled already after five to
                                       Gas Pressure (MPa)

                                                                       Fig. 5: Shore A hardness as a function of the
                                                                       ▼       foaming ratio
tem. A feeding pump and a conventional
compressed air system (max. 6 bar) provide                                             80
material and air to the machine. The foam
                                                                                       70
                                                                                                                #3151
                                                                                                                #3160
                                                                                                                                       o
                                                                                                                               Want tllace ads?
volume can be varied very easily up to a
factor of 3.5:1 (Fig. 4). The essential advan-                                         60
                                                                                                                                     p a to contact:
tages of the process are:                                                              50
                                                                                                                             Don't hesitate
                                                                             Shore A




• Over 95 % plant availability (no rinsing                                             40

  agents, no special waste)                                                            30
• Stable running of the process, also under
                                                                                       20
  tough working conditions (wide tolerance
  to component temperature and ambient                                                 10
                                                                                                                                Phone: +49 (0) 2102 93 45-0
  conditions)
                                                                                       0
• Inline capability and direct modification                                                  1      2      2.5     3
                                                                                                                                 Fax: +49 (0) 2102 93 45-20
  after only several minutes (curing within                                                     Foaming ratio                  Email: ads@pu-magazine.com
  5 min. at 80 °C)



     94                                                                                                                            PU MAGAZINE – VOL. 2, NO. 2 – APRIL 2005

				
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