초록 ▼

A plastic extrusion apparatus is provided which includes a gear pump for accurately metering the plastic through a die. The apparatus is adapted to process highly viscous plastic material under high temperature and pressure conditions, and the gear pump includes a non-leaking and substantially frict

A plastic extrusion apparatus is provided which includes a gear pump for accurately metering the plastic through a die. The apparatus is adapted to process highly viscous plastic material under high temperature and pressure conditions, and the gear pump includes a non-leaking and substantially frictionless seal for the drive shaft. The seal comprises a sleeve surrounding the shaft, and a shallow helical channel formed in the bore of the sleeve, with the helical channel being of a hand such that forward rotation of the shaft results in the plastic which enters the clearance between the shaft and sleeve to be effectively pumped back toward the interior of the housing.

대표청구항 ▼

In a method including extruding a melted plastic material and wherein the plastic is metered by passing through a gear pump, the improvement comprising: passing said plastic material through a gear pump having (a) an enclosed housing having inlet port means for receiving the melted plastic, and disc

In a method including extruding a melted plastic material and wherein the plastic is metered by passing through a gear pump, the improvement comprising: passing said plastic material through a gear pump having (a) an enclosed housing having inlet port means for receiving the melted plastic, and discharge port means for discharging the plastic therefrom, (b) gear means rotatably mounted within said housing and adapted upon forward rotation to convey the plastic from said inlet port means to said discharge port means, (c) a shaft extending through said housing and operatively connected to said gear means for transmitting rotational torque to the same, said shaft including a cylindrical outer surface portion, and (d) means for sealing said shaft to said housing to effectively preclude leakage of the melted plastic therebetween, said sealing means comprising a sleeve removably secured to said housing and having an internal cylindrical bore closely surrounding said cylindrical surface portion of said shaft, with said cylindrical bore having a shallow helical channel formed therein and extending along at least a substantial portion of the axial length thereof, said channel being of generally rectangular cross-sectional configuration and having a depth not exceeding the square root of 6(pi)DNuL/P tan Q wherein D is the diameter of said shaft, N is the rotational speed of the shaft in revolutions per second, u is the viscosity of the plastic, L is the length of the seal, P is the pressure of the plastic, and Q is the lead angle of the helical channel, with such variables being in consistent units, and with the helical channel being of a hand such that forward rotation of the shaft and gear means results in the plastic which enters the clearance between said shaft cylindrical bore to be effectively pumped back toward the interior of the housing, and including the steps of delivering the melted plastic to said inlet port means under pressure of at least about 600 psi, and rotating said gear means at said rotational speed and in a direction such as to forwardly convey the plastic, and including pumping substantially all of the plastic which enters the clearance between said shaft cylindrical surface portion and said cylindrical bore back toward the interior of said housing.