| 摘要 |
<p>A method of forming a mineral insulated cable comprises: i) coating a particulate mineral insulant, for example silica, with not more than 5 % by weight of an uncured silicone oil; ii) subjecting the coated mineral insulant to a heat-treatment step in order at least partly to polymerise the silicone oil and to allow any hydrogen evolved during the polymerisation to be removed; iii) introducing the resulting mineral insulant into a metal tube that contains one or more elongate conductors that extend along the length thereof and are isolated from one another and from the tube, to form a cable preform; and iv) subjecting the cable preform to a number of drawing and annealing steps, whereby the preform is reduced in diameter, the annealing steps being such that the cable preform does not reach a temperature exceeding 450 °C. The method enables the intrinsic hydrophilic nature of the mineral insulant to be removed so that moisture ingress at the ends of the cable or in the event of damage to the sheath is prevented. This can be achieved without affecting the flowability of the mineral insulant powder to any signifiant extent, so that the cable can be manufactured by a dry-filling process such as the 'vertical-fill' or continuous process.</p> |
