WO2009084762A1

WO2009084762A1 - Apparatus for quick heating and cooling a injection mold and method of controlling temperature of the injection mold

Info

Publication number: WO2009084762A1
Application number: PCT/KR2008/000254
Authority: WO
Inventors: Nam Wuk Heo
Original assignee: Nam Wuk Heo
Priority date: 2007-12-28
Filing date: 2008-01-15
Publication date: 2009-07-09
Also published as: KR100975014B1; KR20090072901A

Abstract

The present invention relates to an apparatus for quickly heating or cooling an injection mold to the predetermined temperature. The apparatus comprises a plurality of heater-mounting holes (22), a plurality of electric heater cartridges (30) inserted into the heater-mounting hole (22), a fluid supply passage (40), and a heating/cooling fluid passage (50), in a mold block (20). According to the present invention, it is possible to prevent defects on the molded part due to temperature differential and to shorten a cycle time of the injection molding process.

Description

APPARATUS FOR QUICK HEATING AND COOLING A

INJECTION MOLD AND METHOD OF CONTROLLING

TEMPERATURE OF THE INJECTION MOLD

Technical Field

[1] The present invention relates to an apparatus for heating or cooling an injection mold, more particularly for quickly heating or cooling an injection mold to the predetermined temperature.

[2] Further, the present invention relates to method of controlling the temperature of an injection mold to minimize differential of the temperature around the whole cavity in the injection mold and further to shorten the cycle time of the injection molding process. Background Art

[3] A control of the temperature of the mold as well as the temperature of molten resin is very important in the injection molding process. When the temperature of the mold is not uniform, defects, such as 'weld-line' and 'flow-mark' occur on the surface of the moled product. When the temperature of the mold is excessively high, it is required to lower the temperature of the mold for ejecting the molded part from the mold and then to re -heat the mold for the following injection process. This makes a cycle time longer and thus causes low-productivity. Accordingly, it is required to control the temperature of the injection mold to be uniform within a predetermined range over the whole cavity for a good-quality of product and a high productivity.

[4] A conventional method of heating or cooling the injection mold is to provide electric heaters for heating the mold and passages of cooling fluid in the mold. For the conventional method, however, it is difficult to control the temperature of the mold uniformly over the whole mold because the mold is directly heated partially by the electric heaters. Particularly, the whole size of the mold becomes bigger because it requires additional space for the passage of the cooling or heating fluid.

[5] Another system is known to provide one kind of fluid passage in the mold, which allows the hot water and steam to flow therein for heating the mold and also cooling water to flow therein for cooling the mold. However, the system requires additional reservoir outside of the mold for generating hot fluid and storing the heated fluid. Therefore, the system becomes bigger in size and further is of low-efficiency of energy. Particularly, the productivity is low because it takes long to go through one cycle of the injection molding process, that is, a cycle time from heating the mold to cooling the mold for ejecting the molded part from the mold. Moreover, it is difficult to control the temperature of the mold uniformly. Disclosure of Invention Technical Problem

[6] It is an object to provide an apparatus for heating or cooling the temperature of an injection mold to shorten the cycle time and for controlling the temperature of an injection mold to minimize the temperature differential around the cavity.

[7] Further, it is another object to provide a method of heating or cooling the temperature of an injection mold to shorten the cycle time and controlling the temperature of an injection mold to minimize the temperature differential around the cavity. Technical Solution

[8] An apparatus according to the present invention comprises a mold block having a cavity for molten resin to be injected therein and a plurality of heater-mounting holes;

[9] a plurality of electric heater cartridges, each heater cartridge being inserted into the heater-mounting hole and having a heating element spaced with the inner wall of the heater-mounting hole to form an annular gap therebetween;

[10] a fluid supply passage formed in the mold block and being connected in parallel to inlets of the heater-mounting holes for supplying heating/cooling fluid into the heater- mounting holes; and

[11] a heating/cooling fluid passage formed in the mold block to be connected to outlets of the heater-mounting holes for allowing the heating/cooling fluid through the heater- mounting holes to circulate in the mold block,

[12] wherein the heating/cooling fluid passage allows the fluid heated by the heater cartridge in the heater-mounting hole to circulating in the mold block or allows the fluid to pass through the heater-mounting hole without being heated by the heater cartridge.

[13] The present invention further comprises a heat- transfer plate wound in a helix shape on the surface of the heating element and being contact with the inner wall of the heater-mounting hole to transfer heat of the heating element to the inner wall.

[14] The present invention further comprises a plurality of heat- transfer plates longitudinally mounted on the outer surface of the heating element, the heat-transfer plates being apart from each other along the circumference and being contact with the inner wall of the heater-mounting hole to transfer heat of the heating element thereto.

[15] The apparatus according to the present invention further comprises a heat- transfer tube fitted on the heat-transfer plate to transfer heat of the heating element to the inner wall of the heater-mounting hole.

[16] The apparatus according to the present invention further comprises a plurality of temperature sensors mounted around the cavity for detecting the local temperatures around the cavity in the mold block and thus transmitting the signal corresponding to the detected local temperature, and a temperature controller to selectively supply electric power to the electric heater cartridges according to the signals from the sensors. Advantageous Effects

[17] According to the present invention, the mold can be heated quickly up to the working temperature because the mold is directly heated by the electric heater cartridges and also is uniformly heated by the heating fluid. Further, the mold is also cooled quickly to the temperature for ejection because the cooling fluid through the heating/cooling fluid passage serves to cool the mold quickly. Thus, the present invention may increase the productivity of injection molding by shortening the cycle time of injection molding.

[18] Further, the present invention may prevent from the defect of quality derived from the temperature differential around the cavity, for example, "weld line" and "flow mark" because it can control the temperature of the mold uniformly.

[19] Moreover, the whole injection molding apparatus can be compact because the heater cartridges directly heat the fluid passing through the heater-mounting holes and thus additional equipments for heating the fluid, such as a boiler, the conduits and a tank for storing the fluid, are not required. Brief Description of Drawings

[20] Fig. 1 is a schematic plane elevation view of the apparatus for quick heating and cooling an injection mold according to the present invention.

[21] Fig. 2 is a cross sectional view taken along the line A-A of Fig. 1.

[22] Fig. 3 is a partially cross sectional view of another embodiment of the quick heating/ cooling device according to the present invention.

[23] Fig. 4 is a partially sectional view of another further embodiment of the quick heating/cooling device according to the present invention.

[24] Fig. 5 is a partially sectional view of another further embodiment of the quick heating/cooling device according to the present invention.

[25] Fig. 6 is a schematic diagram of a temperature control system for heating the injection mold according to the present invention.

[26] Fig. 7 is a schematic diagram of a temperature control system for cooling the injection mold according to the present invention. Best Mode for Carrying out the Invention

[27] Referring to Figs. 1 to 2, an apparatus for quickly heating or cooling an injection mold according to the present invention comprises a mold block (20) and a plurality of heater- mounting holes(22). [28] The mold block(20) has a cavity(24) where molten resin is injected and a plurality of heater-mounting holes(22) which are arranged laterally below the cavity(24) in such a manner that they are apart from each other. Each of the heater-mounting holes(22) has an inlet at the one end of the heater-mounting hole(22) and an outlet at the other end. A heater cartridge(30) is fitted into each heater-mounting hole(22) and thus serves to heat the mold block(20) selectively.

[29] In a heating mode for heating the mold("ON" mode), the heater cartridges(30) are supplied with electric powers and thus heated to radiate heat. In a cooling mode for cooling the mold("OFF" mode), the heater cartridges (30) are not supplied with the electric power.

[30] The electric heater cartridge(30) is detachably coupled into the heater-mounting hole(22) and has a heating element(32) spaced with the inner wall of the heater- mounting hole(22) to form a gap between its outer surface and the inner wall of the heater-mounting hole(22). The heating element(32) has outer diameter smaller than the diameter of heater-mounting hole(22). This leads to form a passage together with the heater-mounting hole(22) in order to allow the heating/cooling fluid to pass through.

[31] In the mold block(20), there is formed a fluid supply passage(40) which is connected in parallel to inlets of the heater-mounting holes(22) for supplying heating/cooling fluid into the heater-mounting holes (22).

[32] A heating/cooling fluid passage(50) is formed in such a manner that the passage(50) travels all around the cavity(24) in the mold. Further, the heating/cooling fluid passage(50) is connected in parallel to outlets of the heater-mounting holes(22) to lead the heating/cooling fluid through the heater-mounting holes(22) in areas around the cavity(24).

[33] On the heating mode, the fluid supplied into the heater-mounting holes(22) is heated by the electric heating element(32) of the electric heater cartridge(30) while it passes through the passage in the heater-mounting holes(22). In this way, the fluid is heated to be converted into saturated vapor. The saturated fluid enters into the heating/cooling fluid passage(50) and travels along the heating/cooling fluid passage(50) to heat the the mold block(20).

[34] On the cooling mode, the heater cartridges (30) are not supplied with the electric power and therefore are kept unheated. Thus, the fluid supplied into the heater- mounting holes(22) passes through the passage in the heater-mounting holes(22) as it is unheated and travels in the mold block along the heating/cooling fluid passage(50) to cool the mold block.

[35] It is preferable that the fluid is heated over 100⁰C and thus converted into saturated vapor at pressure of 6-9 bar and temperature of 160-190⁰C.

[36] [37] Further, the apparatus for quickly heating or cooling an injection mold according to the present invention comprises a plurality of temperature sensors (not shown) mounted around the cavity(24) for detecting the local temperatures around the cavity in the mold block and thus transmitting the signal corresponding to the detected local temperature, and a temperature controller(not shown) to selectively supply electric power to the electric heater cartridges according to the signals from the sensors.

[38]

[39] When the local temperature of the mold detected by the sensors is lower than the predetermined setting temperature, the temperature controller transmits a signal to a power supply to supply electric power to the electric heater cartridges according to the signals from the sensors. Thus, the electric heater cartridges(30) heat the fluid passing through the heater-mounting holes (22). The heated fluid is supplied through the heating/cooling fluid passage(50) in the mold block to heat the mold block.

[40] When the injection mold is required to be cooled for ejecting the molded part from the cavity or the local temperature of the mold detected by the sensors is over the predetermined setting temperature, the temperature controller transmits a signal to cut off electric power to the electric heater cartridges according to the signals from the sensors. Thus, the electric heater cartridges(30) is not heated. The fluid passes through the heater-mounting holes (22) without heating as it is supplied as it is entered into the heater- mounting holes(22). The unheated fluid is supplied through the heating/cooling fluid passage(50) in the mold block to cool the mold block. In this process, the mold temperature is kept uniform within the desired range.

[41] Moreover, a plurality of heat insulating holes (26) are formed around the heater- mounting holes(22) in order to prevent the heat of electric heater cartridges(30) from being transferred outside the mold. These heat insulating holes (26) reduce loss of heat and thus serve to keep the mold temperature uniform.

[42]

[43] Figs 3 through 5 show embodiments of the quick heating/cooling device according to the present invention.

[44] Fig. 3 shows another embodiment of the heater cartridge(30) fitted in the heater- mounting hole(22) of the mold block(20). The heater cartridge(30) comprises a plurality of heat- transfer plates(60) arranged in a helix shape on the outer surface of the heating element(32). The heat-transfer plates(60) are contact with the inner wall of the heater-mounting hole(22) to transfer heat of the heating element(32) to the inner wall. Further, the helix portions of the heat-transfer plates(60) form a helixed fluid passage between the helixed portions adjacent to each other.

[45] The fluid flowed in the heater-mounting hole(22) passes through the helixed fluid passage. While the fluid passes through the helixed fluid passage, the fluid is heated by the heating element(32) and then flows in the heating/cooling fluid passage(50).

[46] The heat-transfer plates(60) is of a thickness and a width and made of high thermal conductive material.

[47] The heat-transfer plates(60) serve to transfer heat from the heating element(32) to the inner wall of the heater-mounting hole(22) and thus serve to quickly accomplish the process of heating the injection mold .

[48] As shown in Fig. 4, a heat-transfer sleeve(70) may be put on the heat-transfer plate(60) in order to enhance efficiency of heat transfer between the heating element(32) and the inner wall of the heater-mounting hole(22). Preferably, the heat- transfer sleeve(70) is made of high thermal conductive material.

[49] Fig. 5 shows another further embodiment of the heat-transfer plates(60). The heat- transfer plates (60) according to this embodiment comprises a plurality of heat- transfer fins longitudinally formed on the outer surface of the heating element(32), the fins of the heat-transfer plates(60) are apart from each other along the circumference and contact with the inner wall of the heater-mounting hole(22) to transfer heat of the heating element(32) thereto. The function of the heat- transfer plates (60) according to this embodiment is the same as the others.

[50]

[51] Figs. 6 and 7 are schematic diagrams of a temperature control system for heating and cooling the injection mold according to the present invention.

[52] In a heating mode as shown in Fig. 6, a first valve(6a) and a third valve(6c) are kept opened, but a forth valve(6d), a fifth valve(6e) and a sixth valve(6f) are kept closed. In this state, fluid is supplied into a reservoir(2). The fluid in the reservoir(2) is supplied into the heating/cooling apparatus(l) according to the present invention through a hot fluid conduit(4) for by a pump(3). The fluid flowed in the eating/cooling apparatus(l) of the injection mold is heated by the heater cartridge(30) while it passes through the heater-mounting hole(22).

[53] While the fluid is heated, the fluid is converted into saturated vapors. The saturated fluid inflows in the heating/cooling apparatus(l) via the reservoir(2).

[54] In a cooling mode as shown in Fig. 7, on the contrary, the first valve(6a) and the third valve(6c) are kept closed, but the forth valve(6d), the fifth valve(6e) and the sixth valve(6f) are kept opened. In this mode, the cooling fluid is supplied directly into the heating/cooling apparatus(l) as it is unheated, and the pump is not operated. The cooling fluid passes through the heater-mounting hole(22) without being heated because the heater cartridge(30) is powered off in the cooling mode. While the cooling fluid passes through the heating/cooling passage(50), it drops the mold temperature to cool the injection mold.

[55] In the meanwhile, the heater cartridges(30) are kept being off in the cooling mode, but they may be powered on for reheating the mold. [56] The symbols '6b' and 7' indicate a valve for controlling the flow rate into the tank and a venting hole, respectively.

Industrial Applicability [57] The present invention is used in various injection molds for plastic part.

Claims

[1] An apparatus for heating and cooling an injection mold comprising: a mold block having a cavity for molten resin to be injected therein and a plurality of heater- mounting holes; a plurality of electric heater cartridges, each heater cartridge being inserted into the heater-mounting hole and having a heating element spaced with the inner wall of the heater-mounting hole to form an annular gap therebetween; a fluid supply passage formed in the mold block and being connected in parallel with inlets of the heater-mounting holes for supplying heating/cooling fluid into the heater- mounting holes; and a heating/cooling fluid passage formed in the mold block to be connected with the outlets of the heater-mounting holes for allowing the heating/cooling fluid through the heater-mounting holes to circulate in the mold block, wherein the heating/cooling fluid passage allows the fluid heated by the heater cartridge in the heater-mounting hole to circulating in the mold block or allows the fluid to pass through the heater-mounting hole without being heated by the heater cartridge.

[2] The apparatus according to claim 1, further comprising a heat-transfer plate wound in a helix shape on the surface of the heating element and being contact with the inner wall of the heater-mounting hole to transfer heat of the heating element thereto.

[3] The apparatus according to claim 1, further comprising a plurality of heat- transfer plates longitudinally mounted on the outer surface of the heating element, the heat-transfer plates being apart from each other along the circumference and being contact with the inner wall of the heater-mounting hole to transfer heat of the heating element thereto.

[4] The apparatus according to claims 2 or 3, further comprising a heat- transfer tube fitted on the heat-transfer plate to transfer heat of the heating element to the inner wall of the heater-mounting hole.

[5] The apparatus according to claim 1, further comprising a plurality of temperature sensors mounted around the cavity for detecting the local temperatures around the cavity in the mold block and thus transmitting the signal corresponding to the detected local temperature, and a temperature controller to selectively supply electric power to the electric heater cartridges according to the signals from the sensors.

[6] The apparatus according to claim 1 , further comprising a plurality of heat insulating holes formed around the heater-mounting holes for preventing loss of heat outside the mold.

[7] A method of controlling the temperature of the injection mold comprising a mold block having a cavity and a plurality of heater-mounting holes, a plurality of electric heater cartridges inserted into the heater-mounting hole, a plurality of temperature sensors mounted around the cavity for detecting the local temperatures around the cavity, a fluid supply passage for supplying heating/cooling fluid into the heater-mounting holes, and heating/cooling fluid passage for allowing the heating/cooling fluid through the heater-mounting holes to circulate in the mold block, which comprises the following steps: detecting the temperatures of locals around the cavity; supplying electric power to the electric heater cartridges and supplying fluid for heating into heater-mounting holes through fluid supply passage when the temperature detected by the sensor is lower than the predetermined setting temperature, thereby heating the fluid through the heater-mounting holes by the electric heater cartridges and then circulating the heated fluid in the heating/ cooling fluid passage; and cutting off electric power supplied to the electric heater cartridges and supplying fluid for cooling into heater-mounting holes through fluid supply passage when the temperature detected by the sensor is over the predetermined setting temperature, thereby circulating the cooling fluid through the heater-mounting holes without heating in the heating/cooling fluid passage.