Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With means to heat or cool
Patent
1989-03-10
1990-09-04
Woo, Jay H.
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With means to heat or cool
26432815, 425568, 425570, B29C 4520
Patent
active
049540726
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electrically heated pinpoint gate nozzle.
A pinpoint gate for injection molds to produce plastic articles has the advantage that no further processing is required, there is no waste and energy is saved.
Since in principle the problem and the drawback is that the melt freezes too soon in the narrow, cool nozzle channel, and thus only incomplete dwell pressure can be exerted as a result of which the injection-molded parts can exhibit bad dimensional stability, it is known in principle to equip the pinpoint gate system with heating of the gate channel. For this purpose, the gate channel is generally permanently heated, and as the only variable, the temperature is adjusted as precisely as possible.
In the known heating system, for example according to DE-GM 85 35 572, the channel wall of the nozzle channel is heated by a heating coil surrounding it. In other systems, a heated torpedo jutting with the tip into the gate opening is used as mentioned, e.g., in the journal "PLASTverarbeiter, Vol. 33, 1982, pages 387 to 392." Because of the type of heating, for reasons of stability, the heating with the conventional torpedo constructions cannot be brought into the immediate vicinity of the thermally critical gate area. For this reason, the torpedo tips are often shaped over an extended length like pointed cones. The continuously decreasing, heat-conducting cross section necessarily leads to a larger temperature difference within the nozzle. The consequence is an increased risk of thermal damage to the melt flowing along the torpedo.
Heating a torpedo tip mounted in the nozzle channel by a separate control circuit has already been suggested and tried.
However, such a system is extremely wasteful and expensive and has not proved itself in practice.
Basically, a Japanese system in which the torpedo tip jutting into the gate opening is cyclically heated has also become known.
In the prior art initially cited, the heating of the hot well and of the pinpoint gate channel has the disadvantage that even when the injection molded part is demolded, the thermoplastic melt in the pinpoint gate still becomes hot and, therefore, plastic. This disrupts the demolding process, particularly with small parts.
In contrast to this, the prior art described in the second instance using heatable torpedoes can produce a so-called cosmetic gate since the outside of the sprue has cooled sufficiently during demolding and therefore breaks off cleanly. Nevertheless, this prior art has several other decisive disadvantages compared to the hot well heating. Thus, the fact that the heated tip juts into the gate opening even further increases the shear rate and thus the shear stress, which often reaches excessive values even in the case of the open nozzle. This can lead to mechanical damage of the material. A thicker melt boundary layer than that on the hot channel wall forms on the cold side of the nozzle chamber, thus further narrowing the free opening cross section, which should anyhow be as small as possible for a cosmetic gate. This also leads to a greater undesirable increase in the shear stress. In addition, the exact fitting-in of the torpedo tip into the nozzle opening requires a large technical expenditure, which is also reflected in the high cost of the system. Finally, if color or material are changed, a large number of the reject moldings occur because the complicated melt path only permits the new material to slowly displace the old.
It is the purpose of this invention to overcome the drawbacks according to the prior art and to produce a thermodynamic pinpoint gate nozzle with which a cosmetic gate can be achieved, using the largest possible flow opening to avoid viscous and shear stress.
In the pinpoint gate nozzle according to the invention, a low-mass inside nozzle is provided in the nozzle point which is heated there without the torpedo heating placed inside the nozzle channel. Thus, the inside nozzle can be extremely rapidly heated and just as rapidly cooled and the nozzle channel is kept hot only during
REFERENCES:
patent: 3970821 (1976-07-01), Crandell
Mold-Masters Pamphlet, Jun. 1988.
Patent Abstracts of Japan, vol. 8, No. 9 (M-268) (1446), Jan. 14, 1984, No. 58-171932 (Jiyuuou Shoji), Oct. 8, 1983.
"Wirtschalftliches Spritzgiessen mit kaltem Heisskanalsystem", Gunther, Kunststoofe-Plastics, Dec. 1981.
"Systeme des Angusslosen Spritzgiessens--Entscheidungschilfen zur Auswahl des geeigneten Systems" Hartmann, PLASTverarbeiter 33, Jahrgang 1982, No. 5.
"Systeme des Angusslosen Spritzgiessens--Entscheidungschilfen zur Auswahl des geeigneten Systems" Hartmann, PlASTverarbeiter 33, Jahrgang 1982, No. 4.
Heitbrink Timothy W.
Woo Jay H.
LandOfFree
Electrically heated pin-point gate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrically heated pin-point gate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrically heated pin-point gate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-438727