TRUCK CABIN CORROSION RESISTANCE OBSERVATION IN ARTIFICIAL ATMOSPHERE

Transcription

1 ENGINEERING FOR RURAL DEVELOPMENT Jelgava,.-... TRUCK CABIN CORROSION RESISTANCE OBSERVATION IN ARTIFICIAL ATMOSPHERE Radek Pavelka, Milan Brozek Czec University of Life Sciences Prague Abstract. Tis article describes observation of corrosion resistance coating systems used on te cabin of a truck from te Czec truck producer Avia. On te quality of te coating systems for trucks are made very ig demands, for weatering, cemical and UV resistance and long-term corrosion resistance. Tese days optical criterions are not less important, wic are last days very close to te passenger veicle quality, because ig competitive environment puses truck producers to increase te truck quality in all fields, starting at engines and axles, electronics, safety elements and not finising wit painting systems, wic give te final look to every truck. And as it is known and valid more and more for trucks as well, design and look is selling. One of te most important quality criterions is corrosion resistance, wic was tested acc. EN ISO Corrosion tests wit artificial atmospere - Salt spray test, supplemented by observation and poto documentation during testing every,,,,,,,. Te main intention of tis testing is to evaluate all painting systems used on te cabin and find te most critical areas from te corrosion resistance view and observe te corrosion process at time intervals. Ten, from tis observation to find te weakest and strongest painting system of te cabin and propose corrective actions. Keywords: corrosion, truck cabin, cataporetic coating, painting. Introduction Protection against corrosion in automobiles is of great importance from te point of view of bot, te national economy and private car owners. Te automotive industry requires organic protective coating wit very ig resistance to degradation. Coating must protect te substrate against corrosion attack and keep it undamaged for long time wile at te same time offering persistently good aestetic properties, wic means a ig level of stability towards poto-oxidative degradation, mecanical abrasion and oter armful processes []. As well known, te automotive sector as contributed on a large scale to acieving compliance wit increasingly restrictive environmental legislation in te field of surface treatments, above all in anticorrosive coatings. Today, it can be stated tat te anticorrosive protection of almost all automotive bodywork includes a cataporetic primer []. Altoug electrodeposition was introduced in te automotive industry in te s, catodic electrodeposition rapidly replaced anodic electrodeposition in te s due to te greater anticorrosive protection tat it conferred and to oter film caracteristics, wic ad never been attained wit oter tecniques. At te beginning of te s, catodic systems were based on modified epoxy resins contained amino groups, systems wic were described by Pierce []. Tey were dispersed in water by neutralizing te amino groups wit organic acids. Te resins were cross-linked by blocked isocyanates. Pigmentation was based on titanium dioxide and extender pigments. Special lead-containing pigments, suc as silicates, were used as anticorrosive agents, altoug lead was also used to catalyse te curing reactions. Te first lead-free systems only came onto te market in te s, coinciding wit attempts to meet oter callenges suc as acieving reduction in te volatile organic solvent content and lowering te curing temperature [-]. Te electrodeposition process is controlled by many parameters, suc as mean applied voltage, anode-to-sample distance or temperature. All of tese ave an important effect on te final performance of te primer. For example, it is well known tat te ability of te cataporetic process to deposit a film of te paint in igly recessed areas increases te deposition voltage usually set by a penomenon called film rupture, wic causes blemises [-]. Nowadays, te anticorrosive protection of almost all-automobile bodywork includes a cataporetic primer ( % of cars are primed wit catodic electrocoat) []. In order to enance te adesion and te corrosion protection properties of te cataporetic coating, te metal substrate is usually subjected to a surface conversion pre-treatment []. Te automobile bodywork is composed of different metallic substrates suc as ot dip galvanized steel (HDG), electrogalvanized steel (EZ), steel and aluminium alloys. Tese metallic parts are assembled

2 ENGINEERING FOR RURAL DEVELOPMENT Jelgava,.-... before surface treatment. Te conversion treatment widely used is te trication pospatization wic is after activation compatible wit all tese substrates. Neverteless, tis treatment presents some environmental and economical drawbacks [; ]. Materials and metods As te cabin is a very complicated unit containing many molded parts welded togeter wit different welding tecnologies, it is very important to study all tese painting systems on te critical areas, wic are just tese welded connections tat mean ig temperature affected areas steel substrate. Te same like most truck producers Avia truck as well uses te most common welding tecnologies, spot welding, welding in protective atmospere CO, furter resistance welding is used to fix screws and nuts. Tis all is very interesting to compare to raw electrolytically zinc coated steel substrate witout temperature affection. So te sample panels were prepared:. Panels witout welding (temperature not affected).. Spot welded.. MAG welded in protective atmospere CO.,. Fixed screw and nuts by resistance welding. In tis article all painting systems used on te truck are described, i.e., in cabin interior cataporetic coating only or wit combination wit primer is used, in te blank space cataporetic coating + wax, on te cabin bottom cataporetic coating + plastosol + top coat and on te top of te cabin cataporetic coating + topcoat is used. On te base of tis fact te sample panels were prepared:. Only cataporetic primer (PPG Powercron ).. Cataporetic wax (WEDOLIT V -).. Cataporetic filler (PPG K waterborne topcoat).. Cataporetic plastisol ( Henkel Terotex M) + filler + topcoat.. Cataporetic preimer + filler + topcoat (PPG PUR K Waterborne topcoat). Testing was done in te corrosion cabinet acc. EN ISO - Corrosion tests wit artificial atmospere - Salt spray test by metod NNS, wic were extended by progressive observation and poto documentation every until. So every visually corrosion and blisters ave been assessed according to: EN ISO - General information and designation system; EN ISO - Assessment of degree of blistering; EN ISO - Assessment of degree of delamination and corrosion around a scribe; EN ISO - Assessment of degree of filiform corrosion. Measuring and observation as been done on all painted panels of eac sample and from tese measurements averages ave been calculated. Tested panels from electrolytically zinc coated steel DC+ZE acc. EN (according DIN St ZE), dimensions mm x mm x. mm were used. Te cemical composition of steel: C. %, P. %, S. %, Mn. %. Results and discussion For te purpose of tis article two metods of evaluation of all painting systems ave been selected, te first is assessment of te degree of blistering according to EN ISO - and te second is assessment of te degree of delamination and corrosion around a scribe according to EN ISO -. All panels were tested before and after testing for direct adesion according to ISO wit results GT. Dry film tickness (DFT) as been measured according to EN ISO (µm). Assessment of te degree of blistering according to EN ISO - (Table, ) allows evaluation of te size and volume of blisters. Tis metod was upgraded and improved for evaluation and potodocumentation in time intervals. From tis it was possible for all painting systems to express caracteristics for eac painting system. Te second metod is measuring, wic allows to measure in milimeters te degree of filiform corrosion. As well as in te first metod, measuring was done in time intervals and from te measured values it was possible to express caracteristics of eac painting system on panels welded by different welding tecnologies.

3 ENGINEERING FOR RURAL DEVELOPMENT Jelgava,.-... Table Dry film tickness and observation of assessment of degree of blistering acc. EN ISO - Painting system Cataporetic primer Cataporetic wax Cataporetic Filler Cataporetic Filler + Topcoat DFT, Observing time, Welding Nr µm tecnology Ø Vol./Size Not welded.. / / / / / / / / / MAG.. / / / / / / / / / spot welding.. / / / / / / / / / Fixed Nut.. / / / / / / / / / Fixed Screw.. / / / / / / / / / Not welded.. / / / / / / / / / MAG.. / / / / / / / / / spot welding.. / / / / / / / / / Fixed Nut.. / / / / / / / / / Fixed Screw.. / / / / / / / / / Not welded.. / / / / / / / / / MAG.. / / / / / / / / / spot welding.. / / / / / / / / / Fixed Nut.. / / / / / / / / / Fixed Screw.. / / / / / / / / / Not welded.. / / / / / / / / / MAG.. / / / / / / / / / spot welding.. / / / / / / / / / Fixed Nut.. / / / / / / / / / Fixed Screw.. / / / / / / / / / Not welded.. / / / / / / / / / MAG.. / / / / / / / / / spot welding.. / / / / / / / / / Fixed Nut.. / / / / / / / / / Cataporetic Plastisol+ Filler + Topcoat Fixed Screw.. / / / / / / / / / Observation of assessment of degree of blistering acc. EN ISO - Table Observing time, Painting system Welding tecnology Nr L/M, mm Not welded. / / / / / / / / / Cataporetic primer MAG. / / / / / / / / / spot welded. / / / / / / / / / Not welded. / / / / / / / / / Cataporetic wax MAG. / / / / / / / / / spot welded. / / / / / / / / / Not welded. / / / / / / / / / Cataporetic Filler MAG. / / / / / / / / / spot welded. / / / / / / / / / Not welded. / / / / / / / / / Cataporetic Filler MAG. / / / / / / / / / + Topcoat spot welded. / / / / / / / / / Cataporetic Not welded. / / / / / / / / / primer+plastisol+ MAG. / / / / / / / / / Filler+Topcoat spot welded. / / / / / / / / /. Spot welding Comparison of different painting systems on te panels welded by spot welding expressed by EN ISO - is sown in te graps in Fig.. From tis we can say tat on volume and size of blisters panels wit cataporetic primer ave te same caracteristics as well as panels wit cataporetic filler. Te second layer of filler as no affect to corrosion resistance. But te tird layer of

4 ENGINEERING FOR RURAL DEVELOPMENT Jelgava,.-... topcoat can be significantly affected by te blistering process. Tere you can see tat te final volume is lower and increasing later as tat of te previous two painting systems. Definitely best results witout any blisters and corrosion were on panels painted by cataporetic wax and on te painting system using on te bottom of te cabin included plastisol. Size Volume Fig.. Spot welding panels caracteristics from degree of blistering according EN ISO - Te second used metod of assessment of te degree of filiform corrosion EN ISO - allows to focus more detailed to te size of filiform corrosion respective blisters. It was possible to recognize average size L and maximal size M in millimeters. And as it is visible in Fig. evaluation of te same panels, tere are caracteristics more precise. Fig. sows corrosion progress on sample. M, mm L, mm Fig.. Spot welding panels caracteristics from degree of filiform corrosion - EN ISO - Fig.. Spot welding panels of Sample observation by,,. MAG welded in protective atmospere CO Observation of te panels welded by tecnology MAG in protective atmospere CO evaluated acc. EN ISO - sows analogous caracteristics as spot welded as it is visible in Fig.. But

5 ENGINEERING FOR RURAL DEVELOPMENT Jelgava,.-... evaluation of te size of blisters and filifrom corrosion on te same panels acc. EN ISO - sowed ow a more precise metod can elp. Size Volume Fig.. MAG welding panels caracteristics from degree of blistering according EN ISO - In Fig. it is visible, tat altoug caracteristics of spot and MAG welded panels evaluated according to te first metod are te same, evaluation acc. to EN ISO - as different progress. From tis we can say tat te tree layer system cataporetic filler + topcoat sows a smaller size level of blistering and corrosion. Fig. sows corrosion progress of sample. M, mm L, mm Fig.. MAG welding panels caracteristics from degree of filiform corrosion - EN ISO - Fig.. Spot welding panels of Sample observation by,,. Painting system (cataporetic Filler + Topcoat) on different welding tecnologies Comparison of te same paining system (cataporetic filler + Topcoat) on testing panels welded by different welding tecnologies is expressed in te figures below. In Fig. you can see caracteristics from observation according to EN ISO -. From tis you can see, tat blistering begins more earlier on spot and MAG welded panels after exposition, ten it as nearly te same

6 ENGINEERING FOR RURAL DEVELOPMENT Jelgava,.-... progress. On not welded panel te first blisters were found after, but after it was on te same level as for te welded panels. Ten to te end of exposition it stayed on te same level. Blistering on panels wit a fixed screw and nut was found after exposition, and it ad no oter progress and stayed on te same level to te end of exposition. Size Volume Fig.. One painting system on all panels caracteristics - according EN ISO - Evaluation of te size filiform corrosion acc. EN ISO - on te painting system cataporetic filler + topcoat can be seen in Fig., were tere is again more precise visible progress of te size of filiform corrosion. Fig. sows corrosion progress of sample. M, mm L, mm Fig.. One painting system on all panels caracteristics according EN ISO - Fig.. Spot welding panels of Sample observation by,, Conclusions On te base of te standards generally usable for evaluations and testing corrosion resistance was updated and new tecnics of progressive observation improved, wic can give us caracteristics of corrosion and te blistering process. From all tis measuring and observation it is possible to

7 ENGINEERING FOR RURAL DEVELOPMENT Jelgava,.-... understand te corrosion processes of different painting systems or same painting system on different testing panels welded wit different welding tecnologies in more detail. Generally, in tis case on panels simulated truck cabin from electrolytically zinc coated steel, wen we speak about corrosion, we mean wite corrosion from zinc layer. Neiter exposition tested panel ad corrosion from steel substrate. As te best painting systems were te painting systems used on te bottom of te truck cabin, were plastisol in ig film tickness is used, wic performs as a very good anticorrosion barrier. As well te painting system used in blank spaces, cataporetic + wax performs as a very good anticorrosion barrier, mainly due to te fact tat wax is permanent liquid and fulfills defects and scribes on te paint layer under. As weak points tere are welded joints, from tese results we can say, tat spot welding as a little bit iger volume of blisters and around spots areas were found bigger blisters tan on te panels welded by MAG - welded in protective atmospere CO. And tese areas can be improved by combination of painting systems wit plastisol on not visible connections or waxing in blank spaces. Tese facts sould be taken in consideration during cabin construction. References. García S.J, Suay J., Optimization of deposition voltage of cataporetic automotive primers assessed by EIS and AC/DC/AC, Progress in Organic Coatings, Elsevier,, pp. -.. García S.J, Rodríguez M.T., Izquierdo R., Suay J., Evaluation of cure temperature effects in cataporetic automotive primers by electrocemical tecniques, Progress in Organic Coatings, Elsevier, (November ), pp. -.. Pierce P.E., J. Coat. Tec.,, p.. Wernstal K.M., Carlsson B., J. Coat. Tec. (),, p.. Almeida E., Alves I., Brites C., Fedrizzi L., Prog. Org. Coat.,,.. Suay J.J., Rodriguez M.T, Izquierdo R., Kudama A.H.,. Coat.Tec. (),,.. Vatistas N., Prog. Org. Coat.,, p.. Brewer G.E.F., Hines R.F., J. Paint Tec.,, p.. Brown W.B., J. Paint Tec.,, p.. Suzuki Y.-I., Fukui H., Tsuciya K., Arita S., Ogata Y.H., J. Electrocem.Soc.,, p.. Oravitz J.J., Product Finising Online, February,,. Olivier M.-G., Poelman M., Demuynck M., Petitjean J.-P., Prog. Org. Coat.,, p.. van Ooij W.J., Zu D., Stacy M., Set A., Mugada T., Gandi J., Puomi P., Tsingua, Sci. Tecnol.,, p.. Bajat JB., Miskovic-Stankovic V.B., Kacarevic-Popovic Z., Corros. Sci.,, pp.