Continuous glass filaments are normally made in high speed filament forming operations. In these operations filaments can be drawn at linear speeds in the order of 5,000 to 15,000 feet-per-minute and faster.
In the usual glass filament forming operation filaments are withdrawn from streams flowing from a source of molten glass. The speeding filaments are gathered into a strand that is forwarded to a collection zone. And it is common practice to collect the strand into a wound package by a winder. Also, a rotary pulley device, such as a "pull wheel, " can advance the strand to a collection surface to form a mat.
The high linear velocities of the continuous filaments draw a considerable amount of air from the surrounding atmosphere in the direction of filament travel. In fact, the high processing speeds induce such a flow of air that the speeding filaments and strand might be considered an air pump.
The energy of the large quantities of air moving with the filaments in filament forming operations makes treatment of filaments with coating substances difficult.
Yet in processes producing glass strand it is a practice to apply a liquid sizing a individual glass filaments before they are combined into the strand. The sizing protects the glass filaments from abrasion by each other and unites the filaments into an integral bundle.
But prior liquid applying apparatus does not closely control the amount of sizing liquid applied to the filaments. Energy of air moving with the filaments plays a large part in nonuniform treatment of the filaments. To overcome nonuniform treatment difficulties prior methods normally apply excess liquid to avoid strand locations that might otherwise have insufficient liquid on them. Consequently, in filament forming processes collected glass strand normally has excess liquid unevenly applied alone its length.
Subsequent drying of excessively wet wound strand packages is a long process that causes migration of solids in the sizing or other liquid as liquid moves towards the periphery of packages for evaporation. Such movement of liquid tends to concentrate solids along the strand portions located near the periphery of packages. Hence, strands from these packages possess varying amounts of solids along their length; strand properties are not uniform. Accordingly, these strands are not wholly satisfactory.
Of course, increased processing speeds increases air flow with the filaments. Hence, in processes forming continuous glass filaments air flow has a significant effect on processing speeds. This is especially true for treatment of the filaments with special coating substances.