Analysis and Modeling of Curing Polyester Resin in Cylindrical Moulds Heated by Air

Abstract

Predložen je i izveden matematički model očvršćivanja poliesterskih smola u kalupima valjkastog oblika koji se griju zrakom. Model pretpostavlja konvektivni prijenos topline sa zraka na stijenku kalupa te vođenje topline kroz smolu. Temperatura unutar uzorka mijenja se tijekom očvršćivanja, što je posljedica egzotermnosti reakcije i procesa prijenosa topline. Dodatkom punila u smolu mijenjaju se toplinska svojstva smjese kao i iznos topline koja nastaje reakcijom u istom volumenu uzorka, što vodi do nižih temperaturnih maksimuma u centru simetrije valjkastog kalupa. Model je provjeren mnogobrojnim eksperimentima u kojima je mjerena temperatura uzorka smole unutar kalupa tijekom očvršćivanja. Nezavisnim eksperimentima u kojima je umjesto uzorka smole u kalupu bio glicerol te uz različite brzine strujanja zraka oko kalupa procijenjen je koeficijent prijenosa topline zrak - stijenka kalupa. Dobivene vrijednosti uspoređene su s poznatim korelacijama i dobiveno je dobro slaganje. Predloženim modelom vrlo dobro se može simulirati proces očvršćivanja u valjkastim kalupima te procijeniti utjecaje prijenosa topline i brzine reakcije na maksimalno moguće temperature unutar kalupa.The mathematical model of the cure of unsaturated polyester resin in cylindrical mould heated with warm air was suggested and derived. The model assumes convective heat transfer through air on the wall of the mould and conductive heat transfer through the resin. The temperature within the sample changes during the cure process, which is the result of the reaction being exothermal and the process of heat transfer. The addition of the filler changes the thermal properties of the mixture and reduces the amount of heat generated during the reaction in the sample of the same volume, which leads to lower temperature maximums in the center of the cylindrical mould. The model was tested with multiple experiments in which the temperature of the resin inside the mould during the cure process was measured. The heat transfer coefficients between the air and wall of the mould with different speeds of air flow were estimated using independent experiments where the glycerol was used instead of resin. Estimated values were compared with known correlations and good agreement was obtained. Using the suggested model, the cure process in the cylindrical mould can be simulated accurately and influents of the heat transfer and reaction rate on the temperature maximums can be studied