Spiral Manifold History
Spiral manifold melt flow technology was brought about by
the need to eliminate the historic problem of knit lines (or weld lines) in the
walls of extruded tubular products made using conventional spider-style
extrusion dies. Spider-style extrusion dies require that polymer melt flow
around spider legs of different designs that hold the mandrel pin in the
melt flow channel.
Spiral manifold extrusion dies were first developed by
Egan Corporation (now a part of Davis-Standard) in the early 1960s.
Initially, they were a center-fed design with an arrangement of radial feedports
leading into spiral melt flow channels in the cylindrical die surface.
Egan Corporation adapted the new spiral design into blown film processes, as the
blown film process had come from experiments in inflating pipe performed during
the 1940s.
Soon after, the spiral manifold extrusion die became the
most widely used design for the blown film and pipe industry. Surprisingly, Egan Corporation never applied for a patent on the invention because Egan had thought in error that the invention fell under an earlier David-Standard patent for a wire-coating extrusion die that used a single spiral melt flow channel. Many competitors began manufacturing spiral manifold extrusion dies erasing the ability to acquire a patent.
During the 1960s and 1970s the blown film dies had only a
few spiral channels. An 8 or 12 inch die might have had 4 channels. Later, in
the 1980s, die designers began using melt flow analysis and learned that six channel
overlaps produced the best product quality and throughput.
In the 1990s the manifolds became shorter and more
streamlined in order to reduce polymer residence times. Die assembly and product
sizes became smaller, mainly driven by the medical device industry, where burst
pressure and product aesthetics became major design considerations.
In the 2000s, scaled down versions of the multi-spiral
melt flow manifolds were applied to smaller extrusion processes for medical
device and other small tube manufacturing processes where greater burst pressure
capability was needed.