Patent Application
20090148550
The present invention generally relates to injection-molding systems, and more specifically, the present invention relates to hot-runner systems of injection-molding systems, and to hot-runner nozzle assemblies of hot-runner systems.
Known hot-runner nozzle assemblies include nozzle tips that have a copper alloy. Since the copper alloy wears out, these nozzle tips must be replaced from time to time, either: (i) preferably during preventive maintenance routines, or (ii) inadvertently during molding operations, in which replacement costs and repair costs tend to be even higher because the molding system remains idling while inadvertently failed nozzle tips are replaced, and this arrangement leads to lost efficiencies.
U.S. Pat. No. 6,164,954 (Inventor: MORTAZAVI et al.: Published: Dec. 26, 2000) discloses an injection nozzle apparatus that includes an inner body portion and an outer body portion. The inner body portion includes a melt channel. The outer body portion is made of a pressure resistant material. The ratio between the inner diameter of the outer body portion and the outer diameter of the inner body portion is selected so that a pre-load or a load is generated when assembling the outer body portion over the inner body portion. Preferably, the assembly of the two bodies is removably fastened to an injection nozzle body. Preferably the inner body portion includes a material having wear resistant characteristics to withstand abrasive or corrosive molten materials. The apparatus is particularly useful in molding machines and hot runner nozzles for high-pressure molding of materials at normal or elevated process temperatures.
U.S. Pat. No. 6,609,902 (Inventor: BLAIS et al.: Published: Aug. 26, 2003) discloses a nozzle for an injection molding runner system that includes: (i) a nozzle housing having a melt channel, (ii) a nozzle tip having a tip channel and at least one outlet aperture in communication with the tip channel, and (iii) a tip retainer that retains the nozzle tip against the nozzle housing such that the tip channel communicates with the melt channel. The tip retainer is significantly more thermally conductive than the nozzle tip. A nozzle seal: (i) is significantly less thermally conductive than the tip retainer, (ii) may be fused with the tip retainer, and (iii) may be annularly spaced from the nozzle tip.
U.S. Pat. No. 7,108,503 (Inventor: OLARU: Published: Sep. 19, 2006) discloses a nozzle for an injection molding apparatus. The injection molding apparatus has a mold component that defines a mold cavity and a gate leading into the mold cavity. The nozzle includes a nozzle body, a heater, a tip, a tip surrounding piece and a mold component contacting piece. The nozzle body defines a passage that is adapted to receive melt from a melt source. The heater is thermally connected to the nozzle body for heating melt in the nozzle body. The tip defines a tip melt passage that is located downstream from the melt passage. The tip is adapted to be upstream from the gate. The tip surrounding piece is removably connected with respect to said nozzle body. The mold component contacting piece is connected with respect to the nozzle body. The material of the mold component contacting piece has a thermal conductivity that is less than at least one of: (i) the thermal conductivity of the material of the tip, and (ii) the thermal conductivity of the material of the tip surrounding piece.
The inventor believes that in known nozzle tip assemblies, a highly heat conductive tip, which carries heat and melt to a mold gate, is retained by a surrounding piece that needs to possess a low-thermal conductivity to prevent heat loss upon contact (to seal) with the mold steel of the mold gate. Conventionally, (i) copper alloys with high thermal conductivity are used in nozzle tips, and (ii) tool steels (such as: an alloy of PH13-8, an alloy of H13, and/or titanium/nickel alloys, etc) are used in an insulating body that have relatively lower thermal conductivity. The inventor believes that the disadvantage with the prior art is that the steel alloys used in prior art nozzle assemblies possess different thermal expansion properties when compared to a copper alloy. The problem is evident when the nozzle tip is heated for molding and the two materials expand at varying rates of expansion, which leads to exertion of undesirable stress in the mating planes (between the materials) when the two pieces are joined by methods including (such as): welding, brazing, threading and/or interference fitting, etc.
According to a first aspect of the present invention, there is provided a hot-runner nozzle assembly, including: (i) a copper body having a copper alloy, and (ii) a reinforcement body being coupled with the copper body, the reinforcement body having a reinforcement alloy being configured to minimize thermal-expansion stress being induced between the copper alloy and the reinforcement alloy.
The technical effect of the reinforcement alloy is that the thermal properties of the reinforcement alloy (preferably, along with other attributes such as: high-temperature strength, corrosion resistance, oxidation resistance and/or wear resistance) make it suited for use in hot-runner nozzle assemblies. The reinforcement alloy may reduce significant amount of stresses in the hot-runner nozzle assembly, so that this arrangement may: (i) improve part life, (ii) prevent plastic leakage from critical seals, and/or (ii) increase customer run time. The aspects of the present invention permit improved service life of copper alloys in a hot-runner system.
A better understanding of the non-limiting embodiments of the present invention (including alternatives and/or variations thereof) may be obtained with reference to the detailed description of the non-limiting embodiments along with the following drawings, in which:
The copper body 104 has or includes, preferably, a copper alloy, such as (for example) a beryllium copper alloy (also known as “BeCu3”). The reinforcement body 106 has or includes a reinforcement alloy. The reinforcement alloy is configured so that any stress induced by thermal expansion of the copper alloy of the copper body 104 and of the reinforcement alloy is minimized. For example, the reinforcement alloy includes any one of: (i) an alloy A-286, (ii) an alloy of Inconel 718 (also known as IN718), and/or (iii) a high-strength 300 Series stainless steel alloy. The alloy of A-286 stainless steel possesses: (i) high thermal expansion property that is comparable to a copper alloy, and (ii) a low-thermal conductivity property that is comparable to an alloy of PH13-8. The alloy A-286 may be purchased from High Temp Metals, Incorporated (www.hightempmetals.com). The high-strength 300 Series stainless steel alloy may be purchased from Special Metals Corporation (www.specialmetals.com). The Inconel 718 may be purchased from Special Metals Corporation (www.specialmetals.com).
A thermal expansion coefficient of the reinforcement alloy is substantially similar to the thermal expansion coefficient of the copper alloy. The copper alloy and the reinforcement alloy may have a range of thermal expansion from between about 14×10−6 m/m/° C. (meter per meter per degree Centigrade) and about 18×10−6 m/m/° C. (meter per meter per degree Centigrade). A maximum difference in thermal expansion between the copper alloy and the reinforcement alloy may be about 4×10−6 m/m/° C. It will be appreciated that differences that are higher than 4×10−6 m/m/° C. may cause the mating planes 150 and 152 to experience higher mechanical stresses due to the thermal expansion between the reinforcement body 106 and the copper body 104, and thus separation between the reinforcement body 106 and the copper body 104 may be inadvertently and disadvantageously accelerated.
When heated, both the copper body 104 and the reinforcement body 106: (i) undergo substantial thermal expansion, and (ii) grow toward the direction of the nozzle tip 164. The segments of the reinforcement body 106 and the copper body 104 between the end stop 103 and the retention step 105 will expand according to the expansion property of the reinforcement alloy and the copper alloy associated with the reinforcement body 106 and the copper body 104, respectively. If the reinforcement body 106 expands considerably less than the copper body 104, then high stresses may occur on the copper body 104 near the retention step 105 since the growth of the copper body 104 will tend to be constrained in the axial direction. Selection of alloys where both alloys possess similar thermal expansion coefficients may greatly reduce the stresses caused by a differential in thermal expansion between the reinforcement alloy and the copper alloy.
According to a variant, the reinforcement body 106 includes (or is also known as) a “liner”. The reinforcement body 106 is configured to receive a stem 110, and the stem 110 is linearly axially movable along the reinforcement body 106. The reinforcement body 106 is coupled with the housing body 102 (via threads 161). The copper body 104 includes (or is also known as) a “sleeve”. The copper body 104 defines a copper-body bore that is configured to receive the reinforcement body 106. The second reinforcement body 108 includes (or is also known as) a “seal ring”. The second reinforcement body 108 defines a channel that extends through the second reinforcement body 108, and the channel is configured to receive the copper body 104.
The non-limiting embodiments described above reduces unwanted stresses in the mating planes 150, 151, 152 and 153 since the copper alloy and the reinforcement alloy (with comparable thermal expansion coefficients) expand at similar rates of expansion while providing desirable heat management with their differing thermal conductivities (that is, the reinforcement alloy tends to act as a heat insulator while the copper alloy tends to act as a thermal conductor). Additionally the reinforcement alloy has a tendency to resist thermal expansion under high temperature (relative to the copper alloy), while also having (advantageously) lower corrosion and lower oxidation attributes. By way of example: (i) the copper body 104 includes a nozzle-tip body 101, and (ii) the reinforcement body 106 includes an insulator, a liner, and/or a gate seal.
The description of the non-limiting embodiments provides non-limiting examples of the present invention; these non-limiting examples do not limit the scope of the claims of the present invention. The non-limiting embodiments described are within the scope of the claims of the present invention. The non-limiting embodiments described above may be: (i) adapted, modified and/or enhanced, as may be expected by persons skilled in the art, for specific conditions and/or functions, without departing from the scope of the claims herein, and/or (ii) further extended to a variety of other applications without departing from the scope of the claims herein. It is to be understood that the non-limiting embodiments illustrate the aspects of the present invention. Reference herein to details and description of the non-limiting embodiments is not intended to limit the scope of the claims of the present invention. Other non-limiting embodiments, which may not have been described above, may be within the scope of the appended claims. It is understood that: (i) the scope of the present invention is limited by the claims, (ii) the claims themselves recite those features regarded as essential to the present invention, and (ii) preferable embodiments of the present invention are the subject of dependent claims. Therefore, what is to be protected by way of letters patent are limited only by the scope of the following claims:
