Influence of caused deformation during curing to final strength of adhesive bond

Proučevali smo vpliv deformacije med utrjevanjem lepila na končno trdnost lepilnega spoja. Uporabili smo fenol-formaldehidno (FF) lepilo za lepljenje vezanega lesa in bukov furnir (Fagus sylvatica L.). Debelina furnirja je bila 1,1 mm in nanos lepila je bil 200 g/m2. Preskušance smo testirali z univerzalnim testirnim strojem ZwickZ100 po prilagojeni metodi DGST "Dinamika Graditve Strižne Trdnosti", ki je prilagojena metoda ABES "Automated Bonding Evaluation System". Stroj je imel nameščeno manjšo vročo stiskalnico s posebnim ventilom, ki je pri povzročanju deformaciji znižal tlak stiskanja na 0 MPa, ne da bi se stiskalnica odprla. Preskušance smo lepili pri temperaturi stiskalnice 140 °C in tlaku 1,2 MPa. Med lepljenjem smo povzročali deformacije velikosti 0,5 mm, 0,75 mm in 1mm, pri različnih časih stiskanja (od 10 do 55 sekund po pričetku stiskanja). Rezultati raziskave so pokazali, da velikost deformacije ni bistveno vplivala na končno trdnost spoja, bolj je vplival čas pri katerem smo deformacijo povzročili. Deformacija povzročena po 10 sekundah stiskanja še ni imela vpliva na končno trdnost, pri 15 sekundah pa se je že opazil padec trdnosti in po 50 sekundah je bila končna trdnost spoja enaka 0 N/mm2. Številne nastale vezi v lepilu se namreč porušijo in se v tej fazi ne morejo več obnoviti.Influence of caused deformation during curing to final strength of adhesive bond was investigated. We used phenol-formaldehyde (PF) adhesive for plywood and beech veneer (Fagus sylvatica L.). The thickness of veneer was 1,1 mm and the coating of adhesive was 200 g/mm2. Test specimens were tested with universal testing machine Zwick Z100 by method similar DBSD "Dynamics of the Bond Strength Development" which is modified ABES "Automated Bonding Evaluation System" method. The machine had mounted a small hot press, with a special valve which reduced compression pressure to 0 MPa, when we caused deformation, without the press opening. The test specimens were glued at the temperature of 140 °C and 1,2 MPa pressure of the press. During curing we caused deformations in size of 0,5mm, 0,75 mm and 1mm at different times of the pressing (10 seconds to 55 seconds after beginning pressing). Results showed that the size of deformation does not significantly affect the final strength of adhesive bond, it was more affected by the time at which the deformation was caused. The deformation caused after 10 seconds of press did not have effect on final strength, at 15 seconds it was noticed the drop of strength, which has been decreasing, and after 50 seconds the final strength of adhesive bond is equal to 0 N/mm2. The adhesive bonds in the glue are destroyed and can no longer be restored