This invention relates generally to injection molding and more particularly to an injection molding nozzle having more than one heating element.
High reliability is critical in most injection molding applications. Failure of a component in an injection molding system results in lost output during the time it takes to detect what component has failed, replace the component and restart the molding process. Failure of the heating element for a hot runner injection molding nozzle during the molding operation can result in costly process interruptions.
There are generally two types of heaters for providing heat along the melt channel of a hot runner nozzle. The first type includes external heaters that are located outside of but in intimate contact with the outer surface of the nozzle body. External heaters typically can be removed from the injection molding system independently of the hot runner nozzle. Examples of external heaters can be seen in the following patents: U.S. Pat. No. 5,360,333 issued Nov. 1, 1994; U.S. Pat. No. 5,411,392 issued May 2, 1995; U.S. Pat. No. 6,409,497 issued Jun. 25, 2002; U.S. Pat. No. 4,940,870 issued Jul. 10, 1990; U.S. Pat. No. 6,163,016 issued Dec. 19, 2000; U.S. Pat. No. 4,268,241 issued May 19, 1981; and U.S. Pat. No. 6,043,466 issued Mar. 28, 2000 (the contents of all of which are incorporated herein by reference). Removable external heaters can typically be removed and replaced independently of the nozzle when a heater malfunctions. However, the use of a heater external to and removable from the nozzle can introduce heat transfer variables that can be difficult to predict and control, resulting in undesirable or unintended heat profiles along the nozzle body.
The second type of nozzle heaters includes embedded heaters that are embedded or at least partially embedded in the nozzle body. Embedded heaters include heaters that are internally embedded or cast in the nozzle body, examples of which can be seen in U.S. Pat. No. 4,238,671 issued Dec. 9, 1980; U.S. Pat. No. 4,386,262 issued May 31, 1983; U.S. Pat. No. 4,403,405 issued Sep. 13, 1983 and U.S. Pat. No. 6,394,784 issued May 28, 2002 (the contents of all of which are incorporated herein by reference). Embedded heaters also include heaters that are embedded or partially embedded in an outer surface of the nozzle body. Examples of surface embedded heaters can be seen in EP 1 252 998 A2 published Oct. 30, 2002 and U.S. Pat. No. 5,046,942 issued Sep. 10, 1991; U.S. Pat. No. 6,162,043 issued Dec. 19, 2000; U.S. Pat. No. 5,266,023 issued Nov. 30, 1993; U.S. Pat. No. 5,704,113 issued Jan. 6, 1998; U.S. Pat. No. 4,771,164 issued Sep. 13, 1998; 5,614,233 issued Mar. 25, 1997; U.S. Pat. No. 4,768,283 issued Sep. 6, 1988; U.S. Pat. No. 5,235,737 issued Aug. 17, 1993; U.S. Pat. No. 4,557,685 issued Dec. 10, 1985; U.S. Pat. No. 5,282,735 issued Feb. 1, 1994; and U.S. Pat. No. 5,046,942 issued Sep. 10, 1991 (the contents of all of which are incorporated herein by reference). Embedded heaters can often provide a better and more predictable heat transfer to the nozzle body than an external heater, but generally cannot be replaced independently of the nozzle. Some embedded heaters consist of elongate cartridges that are inserted into bores in the nozzle body that run parallel to the nozzle melt bore.
Attempts have been made at designs that permit a quick replacement of a nozzle heater by providing access to the nozzle from a mold side of the injection molding system. For example U.S. Pat. No. 6,162,043 issued Dec. 19, 2000 (the contents of which are incorporated herein by reference) discloses an injection molding apparatus in which a hot runner nozzle with an embedded heater has a threaded upper end such that it can be screwed in and out of the injection molding apparatus from a mold side thereof. U.S. Pat. No. 6,043,466 issued Mar. 28, 2000 shows an example of an externally mounted heater that can be accessed from the mold side. U.S. Pat. No. 6,309,207 issued Oct. 30, 2001 and U.S. Pat. No. 5,533,882 issued Jul. 9, 1996 (the contents of which are incorporated herein by reference) also show systems in which access from a mold side is provided to the nozzle heater.
In order to provide redundancy and avoid process interruptions due to heater failure, designs have been proposed in which two overlapping embedded heaters are provided along the heater nozzle, as shown for example, in the above mentioned U.S. Pat. No. 6,394,784 and EP patent application EP 1 252 998 A2. However, such solutions are limited by the size of the nozzle and do not provide the option of replacing the heater independent of the nozzle.
A common concern in hot runner nozzles is to provide a uniform heat profile along the length of the nozzle body, especially in areas of the nozzle body such as its tip and head that are close to heat losing contact points with the rest of the injection molding system.
Thus there is a need for a hot runner nozzle heating system which provides a high degree of reliability, predictable and efficient heat transfer, and which can be quickly repaired in the event of a failure. A heating system that can provide an efficient heat profile along the length of the hot runner nozzle is also desirable.
The present invention provides a hot runner nozzle that has at least two heaters, one of which is embedded or partially embedded in the nozzle body or in contact with the outer surface of the nozzle body, and the other of which is a replaceable heater that is located over the nozzle body. The replaceable heater may be configured so that it can be removed from the injection molding apparatus independently of the hot runner nozzle. The at least two heaters may be configured and calibrated to provide redundant heating functions and act as backup for each other, or to work in conjunction with each other. Each of the heaters could include more than one independent electrically resistive heating wires to provide further redundancy.
According to one aspect of the invention, there is provided an injection molding heated nozzle that includes a nozzle body defining a melt bore having an entry end and an exit end, a first heater carried by the nozzle body for heating the nozzle body along a length of the melt bore, and a second heater removably mounted to the nozzle body for heating the nozzle body, at least a portion of the second heater overlapping a portion of the first heater.
Other aspects and features of the present invention will become apparent to one of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying Figures.
Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:
As shown in
With reference to
According to embodiments of the invention, an external removable clamp heater 40 is provided over the steel body 12 of the nozzle 10, and clamped to its outer surface 24. The clamp heater 40 shown in
The embedded heater 20 and clamp heater 40 are both positioned to provide heat along the same portions of the nozzle body 12 surrounding the melt bore 14. Preferably, the clamp heater and embedded heater are pre-calibrated so that when operated independently they each provide an identical or similar heat profile along the melt bore. With reference to
In one mode of operation, the heating for the nozzle 10 is provided by embedded heater 20. In the event that feedback from thermocouple 28, when compared against a predetermined threshold value, indicates that embedded heater 20 has partially or completely failed, the controller 54 is configured to automatically switch power from embedded heater 20 to clamp heater 40, with minimal or no disturbance to the molding process. The controller 54 can monitor thermocouple 52 to track operation of the clamp heater 40. In the event that clamp heater 40 then fails, it can be removed from the nozzle 10 and replaced, without requiring the nozzle to be replaced, thereby reducing downtime. The nozzle 10 can subsequently be replaced with a nozzle having a working embedded heater during a scheduled maintenance downtime.
The use of an embedded heater in combination with a backup external removable heater can provide a design in which improved heat transfer characteristics of an embedded heater are normally realized. However, if the embedded heater fails, the backup clamp heater can take over without stopping the molding process.
In some embodiments, the embedded heater may act as the backup heater to the external clamp heater. In some embodiments, the embedded heater and the clamp heater may work simultaneously to improve the heat profile along the length of the nozzle melt bore and provide extra heating in areas of the nozzle where heat escapes faster, for example near the gate 110, and near the entry end 16.
Two thermocouples 28 and 52 are shown in the nozzle 10 of
The embedded heater configuration shown in
The first or embedded heater carried by nozzle 10 could take a number of forms other than that shown in
The embedded heater could also take other forms, for example, induction heating systems could be used a heat pipe could be used, and axial cartridge heaters could be used.
The external heater 40 can also take a number of different forms other than that shown in
In some embodiments, the nozzle may have two independent embedded heaters, in addition to the external heater, to provide additional backup redundancy. By way of example,
In some embodiments, an additional backup heater may also be used in clamp heater 40, and in this regard
The nozzles of the present invention are, in preferred embodiments used in injection molding systems that are configured to provide access to the clamp heater and nozzles from a mold side of the system, such as shown in U.S. Pat. Nos. 6,162,043; 6,043,466; 6,309,207 and 5,533,882. In some embodiments, the nozzle may be configured to be removed from the mold side, such as shown in U.S. Pat. No. 6,162,043.
The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those skilled in the art without departing from the scope of the invention, which is defined by the claims appended hereto.
The present application claims the benefit under 35 U.S.C. §119(e) of U.S. Application No. 60/431,242 filed Dec. 6, 2002. The disclosure of this referenced application is incorporated by reference herein in its entirety.
Number | Date | Country | |
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60431242 | Dec 2002 | US |