Method of stretching a tow

The method of stretching a tow of filaments selected from the group consisting of acrylic, modacrylic, nylon, polyester, rayon and polyvinyl chloride comprising:

• a. advancing the tow into a chamber at a first speed, said chamber having an opening at each end thereof for the passage of tow into and out of the chamber and for the passage of a heated liquid out of the chamber.
• b. forcing a stream of heated liquid into the chamber at a point between the openings in the chamber to fill the chamber with heated liquid and force said liquid through the tow from one side thereof to the other and, then transversely back through the tow and out of the chamber at said openings, said liquid being forced into the chamber at such a rate that the heated liquid flow rate outward through each of the openings is at least
• x = 3,000T .sqroot.(WN/h) (.mu./.rho.)
• where x is the flow rate through each openings in gallons per minute, T is the thickness in inches of the stream of heated liquid flowing through each opening, W is the width in inches of each liquid stream and the tow passing through the openings, h is the thickness in inches of the tow passing through said openings, N is the number of filaments in the tow, .mu. is the viscosity of the heated liquid in pounds per foot-second and .rho. is the density of the heated liquid in pounds per cubic foot, the dimensions W and h defining an area that the cross section of the tow is free to assume at the openings, the dimensions W and T defining an area WT which is the cross sectional area that the stream of liquid is free to assume at said openings, and
• c. withdrawing the tow from the chamber at a second speed greater than the first so that the filaments are stretched.