GB966911A - Improvements in or relating to the manufacture of low pressure mercury vapour fluorescent electric discharge lamps - Google Patents

Abstract

<PICT:0966911/C4-C5/1> The manufacture of low-pressure mercury vapour fluorescent electric discharge lamps includes the steps of feeding the output of a hydro-cyclone separator 4, consisting of a water suspension of phosphor particles of sizes lying substantially wholly in a desired range, at a substantially constant rate to the container 13 of an envelope coating machine 14, coating the lamp envelopes 17, internally with the water suspension of phosphor particles from the container, and evaporating off the water, no intermediate drying of the phosphor taking place between the separator and the coating stage. The envelope coating machine 14 is a turret machine constructed in accordance with Specification 917,832. The output of the separator 4 can be fed first to an intermediate container 11 where additional water and a water-soluble binder, e.g. ammonium polymethacrylate (Vulcastab) are added in controlled amounts through the valves 20, 30 for increasing the viscosity of the suspension. The water suspension of phosphor particles, e.g. alkaline earth halophosphate in a concentration of about 1.25% by weight initially fed to the separator 4 from the reservoir 1 can contain, in addition to particles of sizes lying within said range-e.g. 5-25 microns, a proportion of sizes exceeding 25 microns and another proportion of sizes less than 5 microns, and the separator 4 consists of a two-stage separator, having a first cyclone 5, as described in Specification 927,354, which separates the phosphor suspension into two fractions, one containing particles of sizes exceeding 25 microns and the other containing particles of sizes 25 microns and less, the latter fraction being fed to a second cyclone 6 which separates the suspension into two further fractions, one containing particles of sizes less than 5 microns and the other containing particles of sizes between 5 and 25 microns, the latter fraction being fed to the container 11. The phosphor before being fed to the reservoir 1 can be milled in a rapidly vibrated milling vessel containing a multiplicity of generally cylindrical milling elements as described in Specification 966,832.