Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Using sonic – supersonic – or ultrasonic energy
Reexamination Certificate
1999-01-20
2001-03-20
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Using sonic, supersonic, or ultrasonic energy
C264S069000, C264S328170, C264S349000, C264S478000, C366S078000, C366S100000, C425S174200, C425S207000, C425S587000
Reexamination Certificate
active
06203747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an injection molding machine having an injection molding cylinder with a funnel-shaped material supply at a foot end of the injection molding cylinder and an injection nozzle corresponding to a mold at a head of the injection molding cylinder and a material conveyance unit attached to a drive and movable at least in the interior of the injection molding cylinder. The invention also relates to a process for guiding a melt through such an injection molding cylinder.
2. Description of the Related Art
German reference DE-Gbm 91 06 039 discloses a gum massage brush with a handle, wherein the final, finished shape of the brush is attained by folding a known plastic along two folding axes by local softening, for example, by ultrasound. Thus, according to the aforementioned document, the finished part is treated by ultrasound, but the plastic mass in the injection molding machine is not.
Usually, a plastic melt is mixed in the injection molding cylinder by a screw. This type of apparatus for mixing the plastic melt requires relatively high mechanical driving power and causes wear to both the screw and the cylinder.
To sufficiently mix the plastic melt and to achieve certain homogeneities of the melt, length/diameter ratios of the screw greater than 20 are necessary. This requirement substantially lengthens the structural form of the injection unit in question. In addition, no influence can be exerted on the coefficient of friction of the melt as it passes through the gate boring.
One negative consequence of high coefficients of friction in the injection mass, which lead to an increase in the melt temperature during the injection process, is partial combustion phenomena.
SUMMARY OF THE INVENTION
The object of the invention is to create a process and a corresponding device using a simply constructed injection molding unit for controlling the injection resistance of the melt Furthermore, homogenization of different melt components is to be achieved without mechanical means.
The object is attained by an injection molding machine with an injection molding cylinder with a funnel shaped material supply at a foot end of the cylinder and an injection nozzle corresponding to a mold at the head end of the cylinder and a material conveyance unit attached to a drive and movable in the interior of the cylinder. The injection molding machine further includes a vibration element attached to a frequency generator for producing movement between the injection molding cylinder and the material conveyance unit. The frequency generator is adjustable in a frequency range in which the portion of the injection molding machine connected to the vibration element can be placed into resonance vibration.
The object is also attained by a process for guiding the melt introduced via a material supply through an injection molding cylinder and a material conveyance unit attached to a drive including the steps of exerting forces that excite the flow on the melt for producing a tranverse relative movement between the injection molding cylinder and the material conveyance unit using vibration bodies in the ultrasound range.
According to the invention, forces that excite the melt to flow are exerted on the melt in that a periodic relative movement. These forces for exerting periodic movement are generated at a frequency in the ultrasound range between the melt injection cylinder and the material conveyance unit of the injection molding machine. For this purpose, the device of the invention has vibration elements attached to either the injection molding cylinder or the material conveyance unit. The vibration elements are connected to a frequency generator, which is adjustable in a frequency range wherein the part of the injection molding machine connected to the vibration element is placed into an advantageously harmonic resonance vibration.
The vibration element may, for example, be a piezovibrator which may, for example, include quartz or barium titanate. The generated vibrations are disseminated along the injection molding cylinder or the material conveyance unit. The ratio of the length of the material conveyance unit, which is also referred to as the screw length, to the wave length of the ultrasound must be adjusted to resonance to attain the necessary vibration amplitude at the screw peak.
Moreover, the piezovibrator must be kept under prestress. In an advantageous embodiment, tension screws are used to hold flanges for clamping the piezovibrator between the flanges.
The vibration element may be connected to the injection molding cylinder. In this case, the injection molding cylinder, including its injection nozzle, must be disconnected from the mold with respect to vibration. A sliding seal or a damping element may be used as the disconnection element.
In another advantageous embodiment, the vibration element is arranged between the material conveyance unit and the drive. If the material conveyance unit is embodied as a screw, loop contacts must be provided, because the screw, in addition to moving transversely, rotates for mixing the melt. However, the material conveyance unit may also comprise a smooth-walled piston connected via a driving rod to the drive. The piston may be tubular and the vibration element may be arranged in the part inclined toward the injection nozzle.
Smooth-walled pistons may be used because, according to the invention, the degree of homogenization of the melt caused by the ultrasound vibrations permits the elimination of the mixing function of a screw. As a result, a substantially simpler piston injection unit is constructed while retaining the same homogenization effect as in screw plastification.
Thus, in the proposed solution, the properties of the ultrasound vibrations are used to achieve a strong mixing effect on inhomogeneous melts. At the boundary regions (homogeneity boundary), forces produced by the ultrasound vibrations occur that produce currents in the melt that mix the melt. It does not matter whether grain boundaries of non-molten granulates or color pigments are involved. Furthermore, the invention uses a second property of the ultrasound, namely, that of reducing the internal molecular friction of substances exposed to the ultrasound field. Depending on the extent to which the internal friction is reduced, the design according to the invention makes it possible to decrease the required injection power or to increase the injection speed while maintaining the same power. Especially at high injection speeds, the pressure loss via the injection nozzle represents the greatest part of the total injection power.
The third property of ultrasound used by the invention is the heating of the granulate. The release of heat is carried out mainly at the homogeneity boundary points where a need for melting still exists.
In summary, the advantages of the present invention over the prior art are as follows:
the injection power may be reduced by reducing the internal molecular friction in the melt;
the requirement of expensive and complicated plastifying screws is eliminated;
the melt homogeneity is improved for problem materials;
when piston injection units are used, the injection unit length may be shortened;
the mixability of additives such as dyes and foreign components is improved;
the wear on moving parts is reduced;
the homogenization of the melt is improved, especially for optical applications.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
REFERENCES:
patent: 4994220 (1991-02-01), Gutjahr et al.
patent: 5017311 (1991-05-01), Furusawa et al.
patent: 5160466 (1992-11-01), Allan et al.
patent: 5202066 (1993-04-01), Furusawa et al.
patent
Cohen & Pontani, Lieberman & Pavane
Heitbrink Jill L.
Mannesmann AG
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