Abstract: In a process for preparing polybenzoxazole or polybenzothiazole filaments by extruding a polybenzoxazole or polybenzothiazole dope, drawing the dope filament across an air gap, and coagulating the dope filament; the number of filament breaks can be reduced by placing a stress isolation device after extruding but before coagulating the filament.

Abstract: A method of predicting final yarn package diameter (D) during winding of yarn onto the package. The yarn is to be wound onto the package for a known period of time (TD) to obtain the final yarn package diameter. The method comprises the steps of: measuring the time (TS) for the package to grow to a known diameter (DS); predicting yarn package diameter using the correlation:D=square root [k1+k2(TD/TS)]wherein k1 and k2 are empirically determined constants.

Abstract: A method of estimating yarn temperature comprises, measuring the temperature of a guide pin in contact with the yarn; measuring the tension of the yarn with a tensiometer; and estimating yarn temperature using the correlation:Tyarn=k1+k2.times.Tpin-k3.times.(F-k4)wherein Tyarn is the estimated temperature of the yarn:k1, k2, k3 and k4 are empirically determined constants; Tpin is the temperature of the guide pin; and F is yarn tension.

Abstract: A method of predicting changes in caterpillar length of yarn. The process is used in systems wherein yarn is passed through a set of hot rollers to bulk the fibre and is then contacted with an air jet to pull the yarn away from the rollers and impinge it upon a rotating drum. This drum comprises an endless textured screen forming a cylindrical outer surface of the drum and a frame to support the screen. A caterpillar is thereby formed on the screen. Air is then exhausted from the centre of said drum to draw air through the screen and cool the yarn. The yarn is then pulled off of the screen using take-up rollers. The process for predicting a change in yarn caterpillar length comprises a step of measuring during a given time period: the change in temperature of the exhaust air (dT1), the change in temperature of the yarn (dT2) after it is taken up from the drum and the change in tension of the yarn (dF) after it is taken up from the drum.