Curing thermosetting resins in plastics - comprises monitoring temp. throughout layout to indicate point when exothermic reaction finishes and heat supply can be cut-off

摘要

Thermosetting resins are cured under heat and pressure in a bonding process, where the energy used in the reaction is specific to the materials concerned. The amount of the energy used is monitored during the curing process so that the course and the end of the reaction are recorded for efficient utilisation. A conventional multi-daylight hot press is used, with its platens heated by suitable liquid. The temp. is measured at a number of points by thermocouples which are connected to a recorder with integral computer. The points are located at the heating oil feed and return, and various other places. The total heat supplied to the press equals the total heat lost. If the heat lost is greater or less than the heat supplied, the system must have an exothermic or endothermic reaction respectively. Monitoring the heat flow therefore can indicate whether the curing process is continuing or has already finished. In the first stages the temp. rises from room temp. and the exothermic reaction causes a steep rise. After a time the heat used drops off; this is a secure indicator that the cure reaction is nearly finished, and no further heating is required. ADVANTAGE - The mechanical strength of the prod. is appreciably higher than hitherto and its values lie within a strikingly narrow range. No energy is wasted. If the course of the reaction is not normal this is recognisable and can be interrupted. The measurements made do not come from direct connections to the material so that the set-up can be made a fixed layout.