|Publication number||USRE40952 E1|
|Application number||US 11/847,881|
|Publication date||Nov 10, 2009|
|Filing date||Aug 30, 2007|
|Priority date||Jan 9, 2002|
|Also published as||CA2473112A1, CA2473112C, CN1638943A, CN100415485C, DE10392193T5, DE60316405D1, DE60316405T2, EP1463621A1, EP1463621B1, EP1862292A2, EP1862292A3, EP1862292B1, US6936199, US20030155674, WO2003059598A1|
|Publication number||11847881, 847881, US RE40952 E1, US RE40952E1, US-E1-RE40952, USRE40952 E1, USRE40952E1|
|Original Assignee||Mold-Masters (2007) Limited|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (47), Non-Patent Citations (5), Referenced by (2), Classifications (35), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of U.S. Provisional Application No. 60/346,279 filed on Jan. 9, 2002.
The present invention relates to an injection molding apparatus, in particular, a method and apparatus for measuring the temperature of molten material in a mold cavity.
Accurate control of temperature in an injection molding apparatus is fundamental to maintaining control of throughput rate and product quality in an injection molding process. Heaters are typically provided to heat the melt flowing through the manifold and nozzles and cooling channels are provided to cool the melt in the mold cavities. During injection, the melt must be maintained within a temperature range dictated by the melt material. Once the melt has been injected into the mold cavities, the melt is cooled at a predetermined rate to produce molded parts. The predetermined cooling rate is calculated based at least in part on the temperature of the melt as it enters the mold cavities.
In a multi-cavity injection molding apparatus, the temperature of the melt entering the mold cavities often varies from one mold cavity to the next. As such, the optimum cooling time for the plastic in each mold cavity may be slightly different. For injection molding applications in which semicrystalline resins are used, this temperature variation often results in the production of molded articles that are of insufficient quality.
A common application of semicrystalline resins is in the production of polyethylene terephthalate (PET) preforms. In order to produce high quality preforms, the semicrystalline resin must be cooled in the mold cavity for a sufficient period of time to allow the preform to solidify before being ejected, while avoiding the formation of crystalline portions. Crystalline portions typically form in the bottom portion of the preform adjacent the mold gate. The crystalline portions cause the preform to become brittle so that it may crack when it is blow molded.
There have been many attempts to optimize the cooling of PET preforms in order to produce high quality molded products efficiently. For example, U.S. Pat. No. 6,171,541 entitled “Preform Post-Mold Cooling Method and Apparatus” issued to Husky Injection Molding Systems Ltd. on Jan. 9, 2001, discloses a rapid injection molding process where the molded articles are ejected from the mold before the cooling step is complete.
U.S. Pat. No. 6,276,922 entitled “Core Fluid Velocity Inducer” issued to Husky Injection Molding Systems Ltd. on Aug. 21, 2001, discloses an inducer located at the outlet of a cooling supply tube for improving the circulation of the cooling supply throughout the core.
U.S. Pat. No. 6,176,700 entitled “Injection Molding Cooled Cavity Insert” issued to Jobst Gellert on Jan. 23, 2001, discloses an injection molding apparatus having a cavity insert with a cooling fluid flow channel extending between integral inner and outer portions thereof. The cavity insert attempts to improve the cooling process for molded articles. The nozzle includes a thermocouple that measures the temperature of the molten material as it leaves the nozzle.
Despite all of the attempts to improve the cooling process for molded articles, the method of measuring the temperature of the molten material in the mold cavity has not improved. It is desirable to obtain additional temperature measurements at the outlet of the nozzle because large temperature variations may occur in this area. It is therefore an object of the present invention to provide a method and apparatus for measuring the temperature of the molten material in the mold cavity.
In an embodiment of the present invention, an injection molding apparatus includes a manifold, a nozzle having a nozzle heater and a nozzle temperature sensor, a mold cavity having a mold core and a melt temperature sensor, and a controller. The controller is electrically coupled to the nozzle temperature sensor, the melt temperature sensor and the nozzle heater and adjusts the heater output depending on data from the temperature sensors.
In another embodiment of the present invention, an injection molding apparatus includes a manifold, a nozzle having a nozzle heater and a nozzle temperature sensor, a mold cavity having a core and a melt temperature sensor disposed in the mold core; and a controller. The controller is electrically coupled to the nozzle temperature sensor, the mold temperature sensor and the nozzle heater and adjusts the heater output depending on data from the temperature sensors.
In a further embodiment of the present invention, an injection molding apparatus includes a manifold, a plurality of nozzles each having a nozzle heater and a nozzle temperature sensor, at least one cavity having a melt temperature sensor disposed adjacent to the mold cavity; and a controller. The controller is electrically coupled to the nozzle temperature sensors, the melt temperature sensor and the nozzle heaters and adjusts the heater outputs depending on data from the temperature sensors.
Embodiments of the present invention will now be described more fully with reference to the accompanying drawings in which:
Referring now to
The mold cavity 20 is provided in a cavity plate 30 and is delimited by a first mold cavity surface 34 of a mold core 22 and a second, mold cavity surface 24 defined by a mold plate assembly 35. The first mold cavity surface 34 of the mold core 22 contacts an inner surface of the bottle preform and the second mold cavity surface 24 contacts an outer surface of the bottle preform. A central fluid cooling duct 26 extends through the mold core 22. Coolant flows through the central fluid cooling duct 26 to cool the molded bottle preform. The second mold cavity surface 24 of the mold cavity 20 is cooled via cooling lines 28, which extend through the cavity plate 30. Suitable coolants include water, oil or gas. The central fluid cooling duct 26 of the mold core 22 and the cooling lines 28 of the cavity plate 30 typically do not share the same coolant.
The injection molding apparatus 10 further includes a thermocouple 32, which extends through the mold core 22, along a portion of the length thereof. A hole is drilled in the mold core 22 for receiving the thermocouple 32. The thermocouple 32 measures the temperature of the molten material in the mold cavity 20.
In operation, the melt stream flows under pressure though the manifold channel 16 into the nozzle channels 18 of a plurality of nozzles 12 of the injection molding apparatus 10. The melt stream is then injected into the mold cavities 20. Upon completion of injection, each mold cavity 20 is cooled by the coolant, which flows through the respective central fluid cooling ducts 26. Once a predetermined cooling time has elapsed the molded preforms are ejected from the mold cavities 20.
The cooling rate of the molded preforms is dependent on the temperature of the coolant flowing through the central fluid cooling duct 26 and the temperature of the coolant flowing through the cooling lines 28 of the cavity plate 30. Because injection molding apparatus' having many mold cavities 20 typically circulate the same coolant through the central fluid cooling ducts 26 of each of the mold cavities 20, it is possible that the coolant may not be at the exact same temperature as it passes through each individual mold cavity 20. As such, the cooling rate of each mold cavity 20 will be different.
By obtaining two independent temperature measurements of the molten material near the mold gate 21 (i.e., in the mold cavity 20 and in the nozzle 12), the accuracy and reliability of the measurements is increased. Further, the thermocouple 32 on the mold core 22 allows the cause of crystallization in a preform to be more easily determined. It will be appreciated that temperatures may be measured by thermocouple 32 and nozzle thermocouple 19 sequentially or simultaneously.
Turning now to
In the injection molding apparatus of
A different type of cooling core is disclosed in U.S. Pat. No. 6,077,067 to Gellert, issued on Jun. 20, 2000, the contents of which are herein incorporated by reference. It will be appreciated by a person skilled in the art that at least one thermocouple can be coupled to the cooling core of the Gellert patent in a similar manner as has been described in relation to
The mold gate 121 is thermal gated and the mold gate 123 is valve gated. A valve pin 130 extends through the nozzle channel 118 to open and close the valve gate 123. This type of gating arrangement allows for the volume of melt flowing through the mold gate 123 to be adjusted. Valve pin gating systems are well known in the art and thus will not be described further herein.
Nozzle thermocouples 119 are coupled to the nozzles 112 to measure the temperature of the molten material as it is injected into the mold cavities 120.
Each mold cavity 120 is delimited by a first mold cavity surface 134 of a mold core 122 and a second mold cavity surface 124 of a mold plate 125. The first mold cavity surface 134 of the mold core 122 contacts an inner surface of the bottle preform and the second mold cavity surface 124 contacts an outer surface of the bottle preform. A central fluid cooling duct 126 extends through the mold core 122 to allow for cooling of the molded preform. A thermocouple 132 is provided in the mold core 122 of each mold cavity 120 to measure the temperature of the melt stream in the mold cavity 120. As shown, the thermocouple 132 is located at the tip of the mold core 122, however, it will be appreciated that the thermocouple 132 may be located at any other suitable point in the mold core 122.
A controller 140 is in communication with nozzle thermocouples 119 and mold cavity thermocouples 132 to receive temperature information therefrom. The controller 140 is also in communication with the heater controls 152 of the nozzle heaters 150 to allow the controller 140 to adjust the output of the nozzle heaters 150. The controller 140 is programmed to include at least predetermined target temperature data for melt in the mold cavity 120. The controller 140 includes a logic processor capable of comparing actual temperature measurements supplied by the thermocouples 132 to a predetermined target mold cavity temperature and calculating an input setting for the heater control 152 of each nozzle 118.
In operation, the melt stream flows under pressure though the manifold channel 116 into the nozzle channels 118 of a plurality of nozzles 112 of the injection molding apparatus 100. The melt stream is then injected into the mold cavities 120. As the injection process begins, temperature measurements are sent to the controller 140 from the nozzle thermocouple 119 and the mold cavity thermocouple 132. The controller 140 then compares the temperature of the mold cavity 120 with the target temperature. If the temperature of the mold cavity 120 is less than the target temperature, the controller 140 sends a signal to the heater control 152 to increase the heater output by a specified amount. Similarly, if the temperature of the mold cavity 120 is greater than the target temperature, the controller 140 sends a signal to the heater control 152 to decrease the heater output by a specified amount. The heater thermocouple 119 serves as a check to ensure that the nozzle heaters 150 are operating properly. The controller allows the temperature of the melt entering each mold cavity 120 to be independently adjusted in order ensure that the temperature of the melt is consistent for each mold cavity 120 in the injection molding apparatus 100.
Following injection, each mold cavity 120 is cooled by the coolant, which flows through the respective central fluid cooling ducts 126. Once a predetermined cooling time has elapsed the molded preforms are ejected from the mold cavities 120.
In the case of the mold gate 123 having a valve pin 130, the controller 140 may also control the stroke of the valve pin. This would allow the volume of melt entering the mold cavity to be adjusted in response to temperature information provided by the thermocouples 119, 132.
Turning now to
In the co-injection process, a first molten material is forced from a nozzle 58, through a mold gate 64, into the mold cavity 52, and then an interior molten barrier layer is forced into the first material via a second material dispenser 60. The finished product is a molded article having a barrier layer that is surrounded by a first material layer. During the co-injection process, the first molten material layer cools in the mold cavity 52 and becomes an insulator for the molten barrier layer. In order to ensure a high quality molded product, it is critical to measure the temperature of each molten material at the entrance to the mold cavity 52. The thermocouples located on the mold core 56 provide important information to an operator so that temperature can be optimized to produce high quality molded products.
The thermocouples 62 may alternatively be installed in a manner similar to thermocouples 32a and 32b, shown in FIG. 3.
In a large mold cavity, such as mold cavity 88 of
The co-injection molding apparatus 50 of FIG. 5 and the injection molding apparatus 80 of
It will be appreciated by a person skilled in the art that the thermocouples discussed in this application may be any type of thermocouple that is suitable for use in an injection molding apparatus. Alternatively, in addition, wire-wound resistance temperature detectors, thermistors and solid state sensors may be used. In a preferred embodiment, the thermocouples 119 and 132 are replaced with thin-film resistance temperature detectors manufactured by Minco Products Inc.
Although preferred embodiments of the present invention have been described, those of skill in the art will appreciate that variations and modifications may be made without departing from the spirit and scope thereof as defined by the appended claims. All patents and publications discussed herein are incorporated in their entirety by reference thereto.
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|U.S. Classification||264/40.6, 264/328.15, 425/547, 425/144, 425/549|
|International Classification||B29C45/28, B29C45/78, B29C45/73, B29C45/27|
|Cooperative Classification||B29C2045/2741, B29C2945/76755, B29C2945/76622, B29C2945/76785, B29C45/7337, B29C45/73, B29C2945/7604, B29C2945/76287, B29C45/2737, B29C2945/76943, B29C2045/274, B29C2045/2687, B29C45/2703, B29C2945/76545, B29C2945/76277, B29C2945/76531, B29C2945/76518, B29C2945/7621, B29K2105/253, B29C2945/76257, B29C45/78, B29C2945/76498, B29C45/2806|
|European Classification||B29C45/78, B29C45/27E, B29C45/73|
|Apr 3, 2008||AS||Assignment|
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