Process of making a laminated spinneret

In the production of a corrosion-resistant spinneret suitable for spinning filaments of poly(p-phenylene terephthalamide) from a viscous solution of the polymer in 98 to 100 percent sulfuric acid, the process steps which comprise

• a. machining a laminate, consisting of a plate of tantalum alloy or stainless steel clad on one face with a layer of commercially pure tantalum, to form a spinneret blank wherein the area of the blank which is to contain spinneret orifices has parallel flat faces, is of a thickness sufficient to prevent bulging of the spinneret face at spinning pressures, and has an exit face layer of tantalum about 0.025 to 0.04 inch thick,
• b. drilling a counterbore through the plate and partially into the tantalum layer at the location of each spinneret orifice,
• c. forming a conically tapering section at the bottom of each counterbore,
• d. wrapping the spinneret blank in tantalum metal foil and heat-treating the blank in vacuum at about 1,800.degree. to 2,000.degree. F to provide a soft-annealed tantalum layer,
• e. forming an axially aligned spinneret capillary, of about 3 to 12 square mils in cross-sectional area, from the tip of each conical taper through the tantalum layer to the exit face of the spinneret blank,
• f. polishing the exit face of the spinneret to remove protrusions formed by the capillary forming operations, and
• g. heat-treating the spinneret in nitrogen at about 1,600.degree. to 1,700.degree. F to harden the face.