Vulcanization transfer moulding

A vulcanizing mould consists essentially of two or more plates that ean be brought together and separated by hydraulic pressure. The plates are usually heated by steam or eleetrieity. The rubber compounds are vulcanized in various moulds between the heated plates under pressure. The principal moulding processes for rubber are eompression moulding, transfer moulding and injection moulding. 

Fig. 10. Schematic diagram of the gas transfer mould (GTM). The left-hand section shows the rubber sample (black) being moulded and vulcanized under pressure. A standard profile is imposed on the rubber during the vulcanization stage not only for the purposes of reproducibility, but also because the final vulcanizate must complete the seal when the GTM operates in the gas transfer mode. The right-hand section shows how a head space is created to simulate mould opening, and through which a gas flow passes to effect the vapour transfer. (Reproduced by courtesy of Rapra Technology Ltd,...

Fig. 11. Direct analysis of vulcanization fume using the gas transfer mould operating on-line a Finnigan 1020 automated GC/MS. The mass spectrometer has the capability to provide diagnostic spectra on component quantities of ljug or less. These components are separated for analysis by the gas chromatograph which in tMs installation is a Perkin-Elmer Sigma 3 and is directly behind the GTM. (Reproduced by courtesy of Rapra Technology Ltd,...

Investigations of the species to be found in the vapours and mists from vulcanization have been mainly confined to the last ten years, and the current understanding can be attributed largely to laboratory studies. An essential ingredient of much of this work has been gas clu-omatog-raphy with on-line mass spectrometry (GC/MS) and the development of vulcanization techniques which can most effectively exploit this instrumentation has been described and reviewed.The gas transfer mould already described (Figs 10 and 11) represents the latest stage in the evolution of these techniques. ... 

The finished dry rubber and latex based rubber products can be vulcanized by several techniques depending on the type of rubber compound (dry rubber compound/latex compound), size of the finished product, and its shape and structure. Moulded rubber products are vulcanized by press curing using compression, transfer, or injection moulding presses. The vulcanization techniques other than moulding may be grouped into batch and continuous methods. The batch methods include the use of autoclaves, hot air/gas oven, and hot liquid/ water bath. Rubber products may be vulcanized at room temperature by cold curing either by immersion of rubber products in a carbon disulphide solution of sulphur chloride (SjCy, or by exposure to its vapour. 

Secondly, the mixture produced is thermoformed in a hot-plates press at 80 °C for 5 min using a pressure of 1 ton with the aim of obtaining circular samples. The thermoformed sample of activated NR was then introduced into a circular mould. The mould was also placed in the hot-plates press where the vulcanization and foaming process were performed simultaneously. The reason for choosing a hot-plates press instead of a conventional oven was that the heat transfer is faster in a press than in an oven, which consequently allows a reduction in the production time. Nevertheless, no pressure was applied to the material. The plates of the press were only in contact with the upper and lower surfaces of the mould. Temperature and time were set up respectively to 160 °C and 30 min. During this time, NR was crossUnked and expanded due to the decomposition of azodicarbonamide in gases, mainly N2 and CO, allowing NR to fill the mould completely. Finally, the mould was water cooled and the foam was removed from it. 

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