The quality of polyurethane (PU)foams depends on what happensduring their formation. It thereforemakes sense to record the forma-tion parameters by suitablemeans and to check these regul-arly on representative samples.Consistent product quality isensured by measuring the forma-tion parameters of samples ofstarting materials prior to the ac-tual foaming process and to com-pare them with specified stan-dards in the form of mastercurves. Many automotive systemssuppliers apply this method tovehicle-interior parts and mod-

ules. The furniture industry, alongwith the equipment insulation andconstruction industries, alsomeasures formation parametersfor the purposes of quality assur-ance. When foam systems withspecial properties are beingdeveloped, measuring the forma-tion parameters gives an insightinto how the reaction is proceed-ing and how foam formation canbe affected by additives, blowingagents, stabilizers and the mixingratio. The Foam Qualification Sys-tem FOAMAT® meets both strin-gent requirements on measuringaccuracy and versatility in ac-

Foam Qualification System FOAMAT®

Measuring Physical Parameters During Foam Formation

Figure 1. The foam qualification system FOAMAT with the ultrasonic fan sensor PFT, a thermocouple, and the pressure-measurement devices FPM 2 and FPM 150. The measurement sequence and the data processing are controlled by thesoftware ,,FOAM” (left).

®

commodating different samplecontainers.

Rise Height and Rise ProfileThe classic method for character-izing foams is to determine therise height or rise profile by meas-uring the change in height due tothe expansion of the foam samplein a cup, a cardboard box or acylindrical container. The starttime is generally accepted to bethe start of the reaction betweenthe mixed components A(polyol + additives) and B (iso-cyanate) after mixing. The risetime is the time which elapses

Product Information

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Figure 2. The experimental data for rise height, temperature, rise pressure, dielectric polarization, and loss of mass arerecorded simultaneously by the software FOAM and are displayed in a graph. The figure shows the curves for a semi rigidfoam measured with FOAMAT and FPM/CMD2.

until maximum expansion hasoccurred. The patented ultrasonicfan sensor PFT of the FOAMAT®

system (Figs. 1, 3) features anintegrated temperature sensor forspeed-of-sound compensationgiving high accuracy for all typesof foams, including rigid foamswith large heat release. The rise

profile is the fingerprint of a foam.During quality assurance testing,it is compared with given mastercurves. A master curve (Fig. 2) isa tolerance band showing themargins of the rise profile for a“good” foam sample. Rise heightmeasurement is still the standardtest in foam qualification. With the FOAMAT® system newmeasurement techniques havebecome available, revealing moredetailed information of the foamgeneration process.

Reaction TemperatureThe exothermal cross linkingreaction causes the temperatureincrease in the foam sample. Thinthermocouples are ideal formeasuring the temperature insidethe foam because they have alow heat capacity and are easy tohandle. They interfere little with

the foam formation and can beused repeatedly. The maximumcore temperature is measured byplacing the thermocouple in thelower third of the foam. The exactlocation of the thermocoupleabove the bottom of the cup canbe determined after the test byprojecting the temperature riseonto the rise height curve.

Rise PressurePressure builds up in the foamafter the components have set.Stable cell walls are formed thatprevent the foam from expandingfurther and to release blowingagents. Thus, wall elements, pan-els or sheet metal are stressed atright angles to the direction offoam flow if they are foam-backed for the purpose of provid-ing insulation or rigidity. As highpressure forces are generated,

Figure 3. The patented ultrasonic fansensor PFT ventilates the surface ofthe rising foam. It has an integratedtemperature sensor for speed ofsound compensation.

the production equipment has tobe reinforced or supported. Theforces are measured as the risepressure, so called because thelocal stress present inside thefoam after setting is criticallydependent on the foam riseheight. The rise pressure is meas-ured with the patented FPM(Foam Pressure Measurement)device into which the reactingfoam components are poured orinjected. The expanding foamloads the bottom of the expansioncontainer where the pressure

forces are measured. The expan-sion container is made of a card-board cylinder and a metal baseplate connected to a force sensor(Fig. 4,5). A PE film is used to pro-tect the base plate against con-tamination. The FPM replacesusual test cups.Whereas the rise curve reflectsthe dynamics of blowing agentgeneration, the rise pressure mir-rors the cell properties, which areaffected by the polymerizationreaction. Measuring the pressurecan yield important informationabout the effects of catalysts andstabilizers on the setting reaction.For production purposes, thepressure curve determines the gelpoint and the pressure decay,which indicates when to open themould. Since the foam is free toexpand upwardly while the pres-sure is being measured, the ultra-sonic fan sensor PFT canmeasure the rise height simul-taneously.

ViscosityA particular advantage of measur-ing the pressure at the bottom ofthe cylindrical expansion con-tainer of FPM is that it allows the

viscosity of the foam to be calcu-lated directly from the experimen-tal data provided by FOAMAT®.This is achieved by using theHagen-Poisseuille viscosity model(Fig. 5). The model starts on theassumption that the viscosity isdetermined by the force neces-sary to move a longitudinal ele-ment of foam at a specified speedthrough a tube, which is the card-board cylinder in this case. Thereaction force is obtained directlyfrom the rise pressure. The pres-sure data and the rise heightcurve measured in the cardboardcylinder are sufficient for calculat-ing the viscosity vs. time. For pro-ducers, the viscosity givesadditional information for optimiz-ing the process control inmoulded foam production.

Dielectric PolarizationDielectric polarization is a newmeasurement parameter thatgives insight into the electrochem-ical processes occurring duringfoam formation. Dielectricpolarization is essentially deter-mined by chain-like molecules

Figure 6. For measuring the loss ofmass, the test cup is placed on a labo-ratory balance with serial data interface.

Figure 4. The polarization sensor CMD which is integrated into the FPM devicemeasures the dielectric polarization of a foam sample simultaneously with therise pressure. Right: the foam specimen in the removed cardboard cylinder.

Figure 5. Physical model of Hagen-Poisseuille’s equation adapted to theFoam Pressure Measurement deviceFPM.

LABOMAT ESSOR - Representative for FRANCE37 boulevard Anatole France93287 Saint-Denis CedexPhone: +33 (0)1.48.09.66.11Fax: +33 (0)1.48.09.98.65E-mail: info@labomat.comwww.labomat.com

Patent No. 3621819 and 19730891® The Format logo and FOAMAT are registered trademarks of Format Messtechnik GmbH

tion shows the formation of inter-mediates like polyurea and dis-plays the final curing of the foamgiving a constant signal after thechemical reaction is completed.CMD is provided in combinationwith the pressure measurementdevice FPM. In order to simulatethe production conditions in amould, the CMD sensor can beheated with closed loop control.

Loss of MassTo obtain reproducible experimen-tal data, the reaction components

must be weighed out exactly.Despite the utmost care on thepart of the user remnants adher-ing to the mixer head and remain-ing in the mixing cup lead to dif-ferences in the tested foam mass.Integrating a laboratory balanceinto the FOAMAT® system (Fig. 6)provides automatically recordingthe mass of each component inthe batch documentation.Additionally, loss of mass dueto the release of blowing agentsand volatile components duringfoaming can be recorded con-tinually.Determining the foam densityfrom the mass of the finishedfoam sample and its final height isanother advantage of an inte-grated balance.

System ConfigurationThe complete Foam QualificationSystem FOAMAT® and its periph-ery is shown in Fig. 7. The mixeroperation is controlled by the soft-ware FOAM according to theuser’s input. Special adapters areavailable for 3-phase currentmixer motors.The controller unit and the bal-ance are connected to the PC viaserial interface.The foot switch (pedal) is used tostart a measurement cycle and tooperate the mixer off-line.

PC

SoftwareFOAM

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with a large dipole moment due totheir polar ends (OH, NCO). Chainformation precedes the cross-linking reaction that ultimatelysuppresses all dipole mobility dur-ing curing. The dielectric polariza-tion sensor CMD (Curing MonitorDevice) is located in the bottomsection of the FPM (Fig. 4).Because of the rise pressure, thefoam is pressed onto the surfaceof the CMD. The dielectric polar-ization is measured as an increasein capacity relative to the emptycontainer. The dielectric polariza-

Figure 7. System survey of the Foam Qualification System FOAMAT and itsperiphery.

Subject to change due to technical improvements

Product InformationFOAMAT®

Labomat Essor Labomat Essor37 Bld Anatole France Vlamingstraat 4F - 93287 Saint Denis Cedex B - 8560 WevelgemTel.: +33 1 48 09 66 11 Tel.: +32 56 43 28 13Fax: +33 1 48 09 98 65 Fax: +32 56 43 28 14E-mail : info@labomat.com E-mail : info@labomat.comwww.labomat.eu www.labomat.eu eeeee

L.E Solutions6 lmm B Résidence lbn Batoua Tel.: +212 52 22 41 714Place Prince Sidi Mohammed Fax: +212 52 22 42 751Belvedère younesbaou@menara.maMA - 20300 Casablanca www.labomat.eu

Labomat Essor Labomat Essor37 Bld Anatole France Vlamingstraat 4F - 93287 Saint Denis Cedex B - 8560 WevelgemTel.: +33 1 48 09 66 11 Tel.: +32 56 43 28 13Fax: +33 1 48 09 98 65 Fax: +32 56 43 28 14E-mail : info@labomat.com E-mail : info@labomat.comwww.labomat.eu www.labomat.eu eeeee

L.E Solutions6 lmm B Résidence lbn Batoua Tel.: +212 52 22 41 714Place Prince Sidi Mohammed Fax: +212 52 22 42 751Belvedère younesbaou@menara.maMA - 20300 Casablanca www.labomat.eu

Labomat Essor Labomat Essor37 Bld Anatole France Vlamingstraat 4F - 93287 Saint Denis Cedex B - 8560 WevelgemTel.: +33 1 48 09 66 11 Tel.: +32 56 43 28 13Fax: +33 1 48 09 98 65 Fax: +32 56 43 28 14E-mail : info@labomat.com E-mail : info@labomat.comwww.labomat.eu www.labomat.eu eeeee