Vliv kvality povrchu rozvodných kanálů na zatékavost elastomerní taveniny

Abstract

Tento článek podává výsledky studia vlivu jakosti povrchu rozvodných kanálů a vliv dalších technologických parametrů na tok polymerní taveniny. Výsledky experimentů provedených s vybranými druhy elastomerů prokázaly minimální vliv drsnosti povrchu tokových cest na tok polymerní taveniny. To především umožňuje odstoupit od dosavadních představ o vlivu drsnosti povrchu na tokové vlastnosti a vyloučit (pokud to podmínky dovolují) z technologického procesu velmi náročné a nákladné dokončovací operace. Využití výsledků měření může mít značný vliv na výrobu tvarových částí vstřikovacích forem zejména ve změně doposud používaných postupů a jejich nahrazením výrobními postupy méně nákladnými, např. se může při správném uplatnění projevit na zvýšení konkurenceschopnosti výrobce nástrojů a zkrácení doby od návrhu k realizaci výrobku.

The article deals with influence of surface roughness and other properties on fluidity of elastomers. Injection molding reduces the time required for curing eliminates the need to preform the rubber prior to molding reduces the amount of mold handling and scrap in comparison with compression molding. This paper shows influence of technological parameters on the flow length into mold cavity. The fluidity of elastomers is affected by many parameters (mold design, melt temperature, injection rate, pressure and curing process).

Polymer injection molding is the most used technology of polymer processing nowadays. It enables the manufacture of final products, which do not require any further operations. Injection molding reduces the time required for curing; eliminates the need to preform the rubber prior to molding; reduces the amount of mold handling and scrap in comparison with compression molding. The tools used for their production - the injecting molds - are very complicated machines that are made using several technologies. Working of shaping cavities is the major problem involving not only the cavity of the mold itself, giving the shape and dimensions of the future product, but also the flow pathway leading the polymer melt to the separate cavities. The flow pathway may be very complex and in most cases takes up to 40% volume of the product itself (shape cavity). In practice, high quality of flow pathway surface is still very often required. Hence surface polishing for perfect conditions for melt flow is demanded. The stated finishing operations are very time and money consuming leading to high costs of the tool production. This work gives the results of studying the influence of the quality of flow pathway surface and influences of other technological parameters on the polymer melt flow. Results of the experiments carried out with selected types of elastomers proved a minimal influence of surface roughness of the runners on the polymer melt flow. This considers excluding (if the conditions allow it) the very complex and expensive finishing operations from the technological process as the influence of the surface roughness on the flow characteristics does not seem to playas important role as was previously thought. Regressive models created on the basis of experiment results enable to predict the flow behaviour of the polymers quite precisely with regard to the surface quality and the parameters of the process injecting itself. Application of the measurement results may have significant influence on the production of shaping parts of the injecting moulds especially in changing the so far used processes and substituting them by less costly production processes which might increase the competitiveness of the tool producers and shorten the time between product plan and its implementation.