Continuously extruding silane crosslinked thermoplastics - using twin extruders with automatic degassing control, for prodn. of electric cable sleeving etc

Thermoplastics which are cross-linked by grafting a silane compound in the presence of moisture, such as olefin polymers or mixed polymers, elastomers, or thermoplastic rubbers, pref. for sleevings for e.g. electric cables, tubing etc. are produced continuously. The basic material and the silane or silane compound plus additives for grafting with/without cross-linking agents, e.g. peroxides, activators, etc. are mechanically mixed grafted, continuously degassed whilst hot, and moulded, these processes being performed under pressure monitoring. The material pressure during moulding over a period at least in the degassing area, during which the pressure is lower (pref. zero) ovr a time t1 and higher for a time t2, where t1+t2 = T, is used as a reference value. The value of t1/T is defined and determined by pressure measurement, this value is compared with an externally set nominal value and the process is regulated so as to equalise these two values. Control of the ratio of grafted yield:yield for moulding produces void-free material of high output rate.