GB2321959A

GB2321959A - Apparatus for controlling the temperature of a mould

Info

Publication number: GB2321959A
Application number: GB9801961A
Authority: GB
Inventors: Yukio Sugawara; Kaoru Muraoka
Original assignee: Mitsubishi Materials Techno Corp; Cleanup Corp
Current assignee: Mitsubishi Materials Techno Corp; Cleanup Corp
Priority date: 1997-02-10
Filing date: 1998-01-29
Publication date: 1998-08-12
Anticipated expiration: 2018-01-29
Also published as: GB9801961D0; GB2321959B; JP2957139B2; JPH10217251A; DE19805110B4; DE19805110A1

Abstract

Apparatus for controlling the temperature of a mould (6), the mould having a passage for a heat transfer liquid, usually water, comprises a circulation line (8) having a pump (7) for supplying the heat transfer liquid through the passage in the mould, a steam supply tube (5), a mixer (9) for introducing steam from the steam supply tube directly into the circulation line, and means (15,16,17) for detecting the temperature of the liquid in the circulation line and thereby controlling the amount of steam introduced into the circulation line through the steam supply tube. A pressure relief valve (12) is positioned at the outlet of the mould. A discharge pipe (11) is able to discharge water from the circulation line through discharge valves (14a,14b). In a mould cooling step, a pipe (10) is able to supply cooling water into the circulation line. The mixer (9) comprises a pipe line (21) in the circulation line (8) having a number of inclined nozzles (24) in the wall of the pipe line. Steam enters via an inlet (22). The inner chamber (20) of the mixer is filled with rectifier elements (23), such as metal flakes or spherical members.

Description

2321959 TEN2ERATURE CONTROLLING APPARATUS FOR A MOLD

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for controlling the temperature of various types of molds for plastics such as synthetic resins, which permits to control the temperature of the molds in accordance with programmed temperature patterns.

In a general and known method of forming various kinds of casings, parts, elements, etc. of synthetic resins, such as so-called injection molding and reaction molding, a cavity is formed between confronting surfaces of a pair of releasable mold halves, and melted synthetic resin is injected into the cavity until it is filled with the resin. After the melted resin is cooled to be set in the mold, the mold halves are released from each other and a resin product is taken out of the mold.

In the injection molding machine described above, it is necessary that the mold is pre-heated to keep a mobility of the resin to be employed before starting an operation of the injection molding, and after the injection of the resin is completed, the melted resin is heated and cooled in accordance with the programmed temperature patterns to set the resin. In order to comply with the requirement described above, an injection mold is provided with a channel for circulating therethrough a liquid such as water as a heat transfer medium, and a temperature controlling device is provided for controlling a temperature of each of the molds in accordance with the programmed temperature patterns by circulating the tempe raturecontrol led water to and through the channel of the mold.

In the conventional temperature controlling apparatus for the mold, a circulating line (or piping) is provided for supplying water as a heat transfer medium through the mold channel by means of a pump. The circulating line is provided with an electric heater for heatiikg the circulating water and also a heat exchanger for cooling the circulating water. Further, in the temperature controlling device, both an electric power supply of the electric heater and an amount of the cooling medium for the heat exchanger are controlled in accordance with a det.ected temperature of the circulating water so that temperature of the mold can be controlled to a predetermined temperature control pattern.

However, the conventional temperature controlling device for the mold provides a serious problem that an increased cost for operation is required because a heater requires expensive electric power.

Particularly, in case that a plurality of molds are used for injection molding and heat cycles of the molds are overlapped, it is likely to breach a demand contract of power with a power supply corporation, with the result that a productivity is decreased and, in some cases, additional device for complying with the demand contract is required, resulting in complexity of the controlling operation. Further, when an electric power is increased to cope smoothly with a peak current due to the simultaneous heating of the molds, it generally is necessary to amend a demand charge and, in some cases, additional installation of large scaled power receiving system is required, with the result that further increased costs for the installation and operation are required.

An attempt was made to provide a steam-type heat exchanger using a steam instead of the electric heater, but the steam-type heat exchanger provides less heating efficiency and, accordingly, an increased amount of steam is required and, moreover, a heat exchanger must be disposed. Therefore, an increased cost for the devices is required and periodical maintenance and cleaning of the devices such as heat exchanger tubes are needed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a new and improved temperature controlling apparatus for a mold which provides a higher heating efficiency.

Another object of the present invention is to provide an improved temperature controlling apparatus for a mold which has a simple structure and meets the requirements for decreasing an operational cost.

A further object of the present invention is to provide a temperature controlling apparatus for a mold which can easily meet with the requirements for temperature controlling of a plurality of molds.

According to a first aspect of the present invention, there is provided a temperature controlling apparatus comprising:

mold having a channel for a liquid as a heat transfer medium, circulation line having a pump for supplying the heat transfer liquid through the channel, a heating steam supply tube, having a mixer, for supplying steam directly into the circulation line through the mixer, a cooling means for cooling the liquid in the circulation line, a by-pass valve, fitted to the circulation line, for controlling an inner pressure of the circulation line to a predetermined value, and a controlling means for detecting a temperature of the liquid and controlling an amount of the steam provided by the heated steam supply tube.

The cooling means includes a system or device for providing a cooled liquid directly to the circulation line and a system or device for cooling the liquid by using a cooling water through a heat exchanger.

In a second aspect of the present invention, the heating steam supply tube is coupled to an inlet of the pump and the by-pass valve is coupled to an outlet of the mold.

In the third aspect of the present invention, the mixer has a pipe line for flowing therethrough the liquid and a plurality of nozzles for mixing the steam with the liquid in the pipe line - In the fourth aspect of the present invention in which a plurality of molds are disposed, an accumulator is provided to a steam outlet of a steam source for storing therein the steam, and each of the heating steam supply tubes is connected to, and directed by, the accumulator. The steam source may include a boiler of exclusive use for heating themolds only and/or any other suitable steam generators such as a furnace boiler.

In the present invention, for the purpose of heating the liquid as the heat transfer medium, the mixer is used to directly supplying the steam to the liquid and, therefore, both the latent heat and sensible heat of the steam can be entirely used for heating the liquid. Thus, an ef f icient heating with minimum heat loss can be obtained. Further, steam can be used much more economically relative to an electric power and it requires no heat exchanger and, accordingly, more economical heating of the liquid can be achieved with simpler facilities. The amount of steam supplied to the circulation is controlled by the difference between a pre- set temperature of the heating pattern and a detected temperature of liquid in the circulation line.

The steam directed to the liquid is condensed immediately by the mixer, but an inner pressure of the circulation line is increased due to introduction of steam and elevation of the liquid temperature. When the inner pressure of the circulation line is elevated up to a predetermined value, the by-pass valve (i.e., escape valve) is opened to permit a part of the liquid to discharge so that the inner pressure of the circulation line is held to a predetermined value.

In the second aspect of the invention, since the heating steam supply tube is coupled to the inlet of the pump and not to the outlet thereof, steam of lower pressure can effectively be supplied relative to a case that the heating steam supply tube is coupled to the outlet of the pump and, therefore, the pressure of supplied steam can be decreased. Thus, steam of wider range of pressure can be employed extensively. Further, the by-pass valve which is provided at the outlet of the mold, and not at the inlet of the same, permits the circulating water to be discharged after it is used for heating the mold, when the by-pass valve is actuated for maintaining the predetermined inner pressure of the circulation line. Thus, reduction of steam consumption can be achieved relative to a case in which the valve is coupled to the inlet of the mold.

A care must be taken that so-called "hammering" is generated to produce a large noise and/or vibration during the operation unless mixing and condensation of the steam to the liquid are carried out in a smooth manner when steam is directly supplied and introduced to the liquid. The hammering generates not only noises and vibrations as described but also, in the worse case, damage in the valve seats and leakage of water from the sealing portions.

The problems of hammering can be prevented completely by the structure of the third aspect of the invention described above since a plurality of nozzles are provided to eject the steam from these nozzles to the liquid in the pipe line such that the steam is readily and smoothly mixed with the liquid.

When a plurality of molds are used, a peak of steam consumption will be generated in a general case. In the fourth aspect of the present invention, however, the accumulator is provided to the outlet of the steam generator such as a boiler to store a desired amount of steam and, accordingly, the steam in the accumulator can effectively be used for a case of a maximum usage of the steam. Therefore, any counter-measurements against over-demand and/or peak current are not required while these counter-measurements are required in the conventional electric heating method.

In the present invention, a maximum consumption and minimum consumption of steam can be balanced or equalized by means of the accumulator and a capacity of the steam generator can be set to an average consumption value. This will permit small sizing of the steam generator.

If the second aspect and the fourth aspect of the invention described above are combined such that the heating steam supply tube is fitted to the outlet of the pump (second aspect) whereas the accumulator is fitted to the outlet of the steam generator (fourth aspect), a relatively maximum amount of the steam in the accumulator can be used and, therefore, small-sizing of a capacity of the steam generator can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram of a temperature controlling apparatus for a mold according to an embodiment of the invention; Fig. 2 is a sectional view of a mixer used in the temperature controlling apparatus shown in Fig. 1; Fig. 3 is a diagram of a whole system employing the temperature controlling apparatus of the present invention shown in Fig. 1; and Fig. 4 is a diagram of a conventional temperature controlling apparatus for a mold, showing an example of remodeling by modifications (addition and deletion) by phantom and solid lines.

PREFERRED EMBODIMENTS OF THE INVENTION A first embodiment of the present invention will now be described with reference to Figs. 1 to 3 in which a temperature controlling apparatus is applied to a plurality of molds for synthetic resins.

As shown in Fig. 3, a boiler 1 as a heat source (i.e., a steam generator) has at its steam outlet an accumulator 2 for storing therein a predetermined amount of steam, and the accumulator 2 has at its outlet a header 3. The header 3 is connected to each temperature controlling apparatus 4 through heating steam supply tubes 5 as illustrated in Fig. 3.

In Fig. 1 which shows one of the temperature controlling apparatuses 4 of Fig. 3, the temperature controlling apparatus 4 has a mold 6 composed of a pair of movable mold half and a fixed mold half and provided with a channel for water (liquid) as a heat transfer medium, circulation line 8 for supplying a circulation water to the channel of the mold 6 through a pump 7, and a mixer 9 fitted to an inlet portion of the pump 7 of the circulation line 8. The heating steam supply tube 5 is connected to the mixer 9. Further, the temperature controlling apparatus comprises a cooling means (cooling pipe) 10, a discharge pipe 11, fitted to an outlet portion of the mold 6 of the circulation line 8, for discharging a part of the circulation water, and a by-pass valve 12 fitted to the outlet portion of the mold 6. The by-pass valve 12 serves to protect the mold 6 and is set so that a pressure thereof is slightly lower than a minimum pressure of an available pressure range of steam based upon an inner pressure of the circulation line 8 at an introduction portion of the heating steam.

A check valve 13 is disposed between the discharge pipe 11 of the circulation line 8 and the cooling pipe 10, and the discharge pipe 11 has a discharge line 11a which has a discharge valve 14a for a large amount of flow and a discharge line 11b which has a discharge valve 14b for a small amount of flow, such that the discharge line 11a is in parallel with the discharge line l1b.

A temperature sensor 15 is disposed at an outlet portion of the pump 7 and at an inlet portion of the mold 6, and the detected signal from the temperature sensor 15 is converted into an air pressure by PID controller 16 so that a steam control valve 17 of a pneumatic type disposed to the heated steam supply tube 5 is in an open/close control. In the illustrated embodiment, reference numeral 18 designates a discharging line of the by-pass valve 12 and reference numeral 19 a pressure control valve of a mechanical type which is disposed to the cooling pipe 10.

In Fig. 2, the mixer 9 has, in its inner chamber 20, a passage or a pipe line 21 connected to the circulation line 8 so that circulation water flows therethrough, and the pipe line 21 has a reduced diameter portion at its inlet and is gradually enlarged in its diameter toward a downstream of the circulating water. The mixer 9 is connected with the heated steam supply tube 5 in an orthogonal direction relative to the pipe line 21, and provided with a hole 22 connected with the inner chamber 20 for introducing therethrough steam. The inner chamber 20 is filled with suitable rectifier elements 23 such as metal flakes or spherical members for rectifying the flow of steam. Inclined nozzles 24 are provided to the wall of the pipe line 21 along a longitudinal direction and a circumferential direction of the pipe line for ejecting steam from the inner chamber 20 to the interior of the pipe line 21 so that the steam is ejected toward the flowing direction of the circulation water. The rectifying elements are fixed by a cover member 25.

An operation of the temperature controlling apparatus 4 for the mold 6 will be described.

In the first place, the boiler 1 is driven to generate steam and store same in the accumulator 2 and a part of the stored steam is delivered from the heated steam supply tube 5 to the temperature controlling apparatus 4 through the header 3.

With reference to Fig. 1, water as a heat transfer medium is - circulated through the circulation line 8 by the'pump 7. For heating the the mold 6 in a molding method for synthetic resin, the steam control valve 17 is operated by the PID controlling device 16 in accordance with the detected signal from the temperature sensor 15 so that steam from the heated steam supply tube 5 is fed to the mixer 9. Then, the steam in the mixer 9 is rectified by the rectifying elements 23 and ejected, by a reducer effect, from the nozzles 24 to the circulation water and smoothly mixed therewith so that temperature of the circulation water is elevated to a predetermined temperature.

Due to introduction of steam, an inner pressure of the circulation line 8 is increased, and when the inner pressure is elevated higher than the predetermined value, the by-pass valve 12 is opened to permit the circulation water to partly be discharged from the discharging line 18 and, consequently, the inner pressure of the circulation line 8 is held to a predetermined range.

In the cooling step of the synthetic resin in the mold 6, the steam control valve 17 is closed and at least one of the discharge valves 14a, and 14b is opened to discharge the water of the circulation line 8. Thus, the inner pressure of the circulation line 8 is lowered and this is sensed by the mechanical type pressure control valve 19 of the cooling pipe 10. Consequently, the circulation water is supplied to the circulation line 8 to thereby lower the temperature of the circulation water.

Thus, in the temperature controlling apparatus 4 for the mold 6 described above, since steam is directly introduced to the circulation water via the mixer 9 when the circulation water is heated in order to heat the mold 6, a latent heat of the steam can entirely be used for heating of the liquid and, accordingly, an efficient heating with a minimum heat loss can be achieved. In addition, heat which is generated by a boiler 1 can be obtained with lower cost and without provision of a heat exchanger and, therefore, an economical effect in heating of the circulation water can be obtained with simple facilities.

Further, since an amount of the steam to be supplied to the circulation line 8 is controlled by operation of the steam control valve 17 by means of the PID controlling device 16, a desired response characteristic can be obtained with the result that a smooth control of the flow rate can be obtained. In addition, the pneumatic type steam controlling valve 17 is used as a steam controller, it will not be af f ected badly such as "burning" even by rapid and repeated open-close operations of the valve as conventionally experienced by a general electromagnetic valve which sometimes causes burning by heating. Further, the by-pass valve 12 is disposed at the outlet side of the mold 6. Therefore, when the by-pass valve 12 is actuated for the purposes of holding the inner pressure of the circulation line 8, the circulation water after it is used for heating the mold 6 is discharged and, therefore, a consumption of the steam can be greatly reduced relative to the case in which the by-pass valve is disposed to the inlet side of the mold 6.

In addition to the above, since the steam is ejected from the nozzles 24 to the liquid in the pipe line or passage 21 of the mixer 9, steam can be mixed with the circulation water in a smooth manner and, therefore, a generation of hammering which causes noises and/or vibrations can be prevented completely.

Further, the accumulator 2 which is disposed at the outlet portion of the boiler 1 in the present invention permits storage of a desired amount of steam and, therefore, the steam stored in the accumulator 2 can be easily used for the cases of maximum usage of steam. Thus, any countermeasurements, such as those for overdemand and/or peak current, which have been required in the conventional electric heating, will not be required in the present invention.

In addition, a maximum consumption of steam and a minimum consumption of same can be equalized and balanced to provide an average value, by the accumulator 2 and, therefore, the boiler 1 can be set to a value of an average consumption. Further, since the heated steam supply tube 5 is coupled to the inlet side of the pump 7, steam of lower pressure can also be supplied relative to a case in which the tube 5 is coupled to the outlet side of the pump 7. Thus, a supply pressure from the boiler 1 can be reduced so that a structure of the boiler 1 can be made simple.

The temperature controlling apparatus described above can be applied quite favorably and easily to the conventional electric heater type temperature controlling apparatus employing an electric heater when the conventional temperature controlling apparatus is remodeled. Fig. 4 shows an example of remodeling the conventional apparatus to the system of the present invention, in which the same reference numerals are used for the same or similar elements, parts and devices of the apparatus shown in Figs. 1 to 3 for the purposes of simplification and clarification only.

In Fig. 4, the parts and portions designated by phantom lines are those of the conventional temperature controlling apparatus 30 in which an electric heater 31 is provided to the circulation line 8 for heating the circulation water. The heating by the electric heater 31 is controlled by the PID controlling device 16 in accordance with signals detected by the temperature sensor 15 of the circulation water. Besides, the conventional temperature controlling apparatus 30 has a by-pass valve (in other words, escape valve) 12 at the inlet side of the mold 6 so as to keep the inner pressure of the circulation line 8 within a predetermined range.

In order to remodel the conventional temperature controlling apparatus to the system of the present invention, a steam resource or generator such as the boiler 1 is provided and, as shown by the solid lines in Fig. 4 of the drawing, a heating steam supply tube 5 is connected to the boiler 1 and a mixer 9 is disposed to the inlet side of the pump 7 of the circulation line 8 so that the mixer 9 is connected to the heated steam supply tube S. The by-pass valve 12 is moved to the outlet side of the mold 6. The electric heater 31, if desired, can be left as it is without displacing or omitting the same. Then, a steam controlling valve 17 is provided to the heating steam supply tube 5 so that the steam controlling valve 17 can be controlled by converting the controlled signal from the PID controlling device 16 into air pressure (or pneumatic value). Incidentally, unless the by-pass valve 12 is provided to the conventional apparatus 30, the by-pass valve 12 is provided to the outlet side of the mold 6. Thus, the conventional apparatus 30 can now be remodeled into the new system of the present invention.

As described above, according to the system of the present invention, the controlling means and devices as well as the cooling means and devices which have been fitted to the conventional electric heater type temperature controlling apparatus can be utilized and applied to remodel the same into the system of the present invention. Therefore, a relatively simple construction of expansion will be sufficient for the remodeling into the system of the present invention which uses steam in place of expensive electric power, without a great amount of investments for a power receiving system and the like. Thus, the present invention can provide a system which can be obtained simply remodeling the conventional electric heater type temperature controlling apparatus for a mold.

Although the present invention has been described with reference to its preferred embodiments for the mold for synthetic resins but it must be understood that the invention is not limited to these embodiments but can be applied to other molds which are used for rubbers and mixture of resins and metal powder. Further, the steam source or generator is not limited to a boiler as the boiler 1, but many other suitable steam generators such as a steam - is - generating furnace can be used.

Claims

WHAT IS CLAIMED IS:

A temperature controlling apparatus comprising:

a mold having a channel for a liquid as a heat transfer medium, a circulation line having a pump for supplying the heat transfer liquid through the channel, a heating steam supply tube, having a mixer, for supplying team directly into the circulation line through the mixer, cooling means for cooling the liquid in the circulation line, by-pass valve, fitted to the circulation line, for controlling an inner pressure of the circulation line to a predetermined value, and a controlling means for detecting a temperature of the liquid and controlling an amount of the steam provided by the heated steam supply tube.
2. A temperature controlling apparatus according to claim 1, wherein the heating steam supply tube is coupled to an inlet of the pump and the bypass valve is coupled to an outlet of the mold.
3. A temperature controlling apparatus according to claim 1 or 2, wherein the mixer has a pipe line for flowing therethrough the liquid and a plurality of nozzles for mixing the steam with the liquid in the pipe line.
4. A temperature controlling apparatus according to any one of preceding claims, wherein a plurality of molds are disposed, an accumulator is provided to a steam outlet of a steam source for storing therein the steam, and each of the heated steam supply tubes is connected to, and directed by, the accumulator.