Method And Apparatus For Heating And Cooling Presses And The Like

Abstract

A press or the like, to be heated and cooled alternately, is connected with circulatory system for supplying either heating or cooling fluid to the press. Heating fluid leaving the press, during a certain period of the heating of the press, is used for subsequent cooling of the press, while cooling fluid leaving the press, during a certain period of cooling of the press, is subsequently used for heating the press. The heating and cooling fluid preferably is a liquid, such as an oil. 17 Claims, No Drawings

Description

There are known forms of apparatus in which a press or the like is connected alternately to hot and cold liquid circuits. The hot liquid circuit comprises a storage vessel and a heating boiler, and the cold liquid circuit comprises a storage vessel and cooling means. Each circuit can be short-circuited while the press is connected with the other circuit, so that liquid in the circuit not then connected with the press can be heated or cooled. Such systems or apparatus constitute a substantial improvement over earlier systems in which heating takes place only during the heating part of the cycle and cooling takes place only during the cooling part of the cycle. However, known arrangements are not completely satisfactory inasmuch as their energy consumption is high during heating and during cooling, and consequently the heating means and the cooling means must be comparatively large.

This invention relates to a method and apparatus for alternately heating and cooling pressing means and, more particularly, to such a method and apparatus in which, for heating and cooling, hot and cold heat transfer liquid, respectively, and preferably oil, is circulated through the pressing means and is heated and cooled in two separate circuits.

The main field of application of the present invention is the heating and cooling of presses for plastic plates and for the production of board, such as chip board, in which the press is heated and then cooled for each charge. However, the invention is equally applicable to other processes, such as vulcanizing.

The present invention is directed to a method and apparatus of the type described above in which, in at least one stage, liquid emerging from the press is separately received during at least one part of the corresponding stage of the heating and/or cooling period and, without renewed heating and/or cooling, is passed through the press in a further stage of a later heating and/or cooling period. Thus, for example, a liquid emerging from the press in a first stage of a heating period is used to effect cooling in a first stage of the following cooling period before final cooling of the press is performed for a certain time in a second stage of the cooling period. Similarly, liquid emerging from the press in a first stage of the cooling period may be used for a first stage of the next following heating period.

The method of the invention can be performed in a relatively large number of stages. Since, however, with an increasing number of stages, not only is the amount of process equipment greater but also there is an increase in the amount of time required for heating and cooling, heating and cooling preferably are performed in two heating stages and two cooling stages.

In the simpliest case, the method can be performed in a manner such that liquid emerging from the press in the heating and/or cooling periods thereof is received in a common container, which then supplies liquid for the first stage of the heating and/or cooling periods. In this case, liquid is pumped as required from the common container through a heating device to a container for hot liquid, and through a cooling device to a container for cooling liquid. However, in an improvement over this simple form of the method in which the liquid has approximately the same temperature in both first stages, the method is performed in a manner such that the liquid in the first heating stage is hotter or warmer than the liquid in the first cooling stage. In this preferred embodiment of the method, the principle of the invention is exploited more advantageously.

In accordance with a preferred embodiment of the method of the invention, the steps are carried out in the following sequence. In a first stage of the heating period, liquid is caused to flow from a warm storage means through the press, and is returned, in a first part of this stage, to a tepid storage means and, in a second part of this stage, to a container for hot liquid. In a second stage of the heating period, liquid is caused to flow from a hot storage means through the press and, at least during the second part of this second stage, is returned into the hot storage means. In a first stage of the cooling period, liquid flows from the tepid storage means through the press and, in a first part of this first cooling period stage, is returned to the storage means for warm liquid while, in the second part of the same stage, it is returned to the container for tepid liquid. Finally, in a second stage of the cooling period, liquid passes from the cold liquid storage means through the press to the tepid storage means.

Heating and cooling apparatus embodying the invention comprises, on the one hand, a cooling circuit including a pump, a cooling means and a liquid storage means and, on the other hand, a heating circuit including a pump, a heating means and a liquid storage means. The apparatus further includes means for connecting the circuits selectively with the press, which is to be heated, for heating and cooling with respective cooling down and heating up of the liquid in the press.

In a preferred embodiment of the apparatus, there are four storage means for receiving, respectively, hot, warm, tepid and cold liquid. Discharge ducts leading from all these storage means can be connected at least with the supply ducts of the hot, warm and tepid storage means. The cooling means and the pump is connected between the tepid storage means and the cold storage means. The heating device can be provided with a pump connected with the hot storage means.

It should be noted that the terms hot, warm, tepid and cold, as used in the present specification and claims, are intended to be interpreted relatively with reference to the type of press to be used, and are chosen only for purposes of convenience. The hot storage means contains the hottest liquid, the warm storage means contains liquid which is somewhat cooler, and, in the tepid storage means, the liquid is still cooler, while the cold storage means contains the coolest liquid.

A discharge duct of the warm storage means can be connected through a pump with a supply duct of the hot storage means. This construction makes it possible to cause liquid to flow from the hot storage means to the press, then to the warm storage means, to the boiler, and finally to the hot storage means during heating up of the press.

In order to be able to even out the levels of liquid in the warm, tepid and cold storage means, and also to be able to set levels as required, the discharge ducts of these storage means can be connected together through ducts provided with valves which can be closed completely.

Preferably, there is a short circuit connection, provided with a closing valve, between the discharge duct of the hot storage means and the supply duct leading to the hot storage means. This enables the contents of the hot storage means to be heated with a circuit connection between the boiler and the hot storage means, the warm storage means being cut out of the circuit.

A particular advantage of the apparatus of the invention is that a space heating system can be connected with the discharge duct of the warm storage means, the return duct from the space heating system being preferably connected with the tepid storage means. Thereby, it is possible to make an additional use of the heat of the warm heat transfer liquid in the warm storage means, at least during cold periods of the year. In order to be able to regulate the temperature of the liquid supplied to the space heating system, the supply duct leading thereto additionally can be connected with the outlet duct of the tepid storage means. However, since this enables only the temperature to be reduced, while there may be a requirement for raising the temperature of the space heating system, an additional heating means can be provided and supplied, through a branch duct, from the hot storage means, the additional heating means being connected with a supply duct of the space heating system.

An object of the invention is to reduce the amount of energy used for heating and/or cooling pressing means or the like which are alternately heated and cooled.

Another object of the invention is to perform multistage heating with liquid which is at different temperatures, and/or to perform cooling with liquid which is at different temperatures.

A further object of the invention is to provide an improved method and apparatus for alternately heating and cooling pressing means or the like.

Another object of the invention is to provide such a method and apparatus in which heat of warm heat transfer liquid in a warm storage means can be used for space heating, at least during cold periods of the year.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a diagrammatic view of one simple form of apparatus embodying the invention; and

FIG. 2 is a diagrammatic view of a preferred form of apparatus embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings, the liquid flow ducts are illustrated by lines, with conventional illustration of valves therein, three triangles having their points touching denoting three-way valves which can be closed. Arrows indicate the direction of flow, and the storage means are denoted as "hot," "warm," "tepid" and "cold." The term press, as used hereinafter, is chosen by way of example of a unit which is to be alternately heated and cooled.

The heating device for the liquid which, in the example illustrated, is a heat transfer oil, preferably is a liquid tube boiler with gas or oil heating. The entire liquid system is vented to the atmosphere and operates at atmospheric pressure. Conventional means are provided for preventing oxidation of the heat transfer liquid. The cooler can be a simple water-cooled unit, as will be clear from FIG. 2.

Referring now to the embodiment of the invention shown in FIG. 1, it will be assumed that the four storage means hold liquid at 20, 70, 120 and 170.degree. C., respectively, by way of example. The press is charged with the material to be subjected to heating, and is to be heated. Pump PH conveys heat transfer oil from the hot storage means through duct 1 in a short circuit through the heating means, which may be a liquid tube boiler, and then back through duct 2 into the hot storage means. Pump PK pumps heat transfer oil from the tepid storage means through duct 3 to the cooler, from which it is returned through duct 4 to the cold storage means. These circulations are interrupted when level detecting or sensing means in the tepid storage means detects a minimum and/or when level sensing means in the cold storage means detects a maximum liquid level.

For the first stage of heating the press, valves V2 and V6 are opened so that heat transfer oil is drawn from the heat storage means by pump PP through duct 5 and valve V2 and delivered to the press through duct 6. The heat transfer oil is returned from the press through ducts 7 and 8 and valve V6 to the tepid storage means.

When the first heating stage has been completed, valves V2 and V6 are closed and valves V1 and V5 are opened. Pump PP now draws hot heat transfer oil from the hot storage means through duct 13 and valve V1 and delivers it to the press through duct 6. The hot heat transfer oil is returned through duct 7, valve V5 and duct 9 to the warm storage means until liquid transfer oil emerging from the press has a temperature of, for example, 150.degree.C. Valve V5 is then closed and valve V7 is opened so that the heat transfer oil is returned through valve V7 to the hot storage means. After the desired press temperature has been reached, valves V1 and V7 are closed and pump PP is deactivated.

During this time, pump PH has been heating heat transfer oil in the hot storage means in the mentioned short circuit. The hot storage means is provided with a temperature sensing device which switches off the burner of the heating means as soon as the temperature in the hot storage means has attained a certain level, and switches on the burner of the heating means or boiler as soon as the temperature in the hot storage means falls below a given temperature tolerance level.

If, after a certain elapsed time, the press is to be cooled again, valves V3 and V5 are opened and pump PP pumps heat transfer oil from the tepid storage means through duct 10, valve V3 and duct 6 to the press. The heat transfer oil is returned from the press through duct 7, valve V5 and duct 9 to the warm storage means. When the temperature of the heat transfer oil emerging from the press falls below a certain value, valve V5 is closed and valve V6 is opened, so that the heat transfer oil emerging from the press is returned into the tepid storage means.

For the second cooling stage, valve V3 is closed and valve V4 is opened, so that cooled heat transfer oil is delivered, by pump PP, through duct 11, valve V4 and duct 6 to the press. The oil emerging from the press is returned, through ducts 7 and 8 and valve V6 to the tepid storage means. When the press has been cooled sufficiently, the valves are closed again. During this cooling period, pump PK conveys heat transfer oil from the tepid storage means through the cooler into the cold storage means, the operation of pump PK being controlled by the level sensing means in the tepid storage means and the cold storage means.

It should be understood that the method can be performed in three stages instead of two, without changing the system. In the three-stage method, the press is supplied first with heat transfer oil from the tepid storage means, then from the warm storage means, and finally from the hot storage means. For cooling, the press is supplied first from the warm storage means, then from the tepid storage means and then finally from the cold storage means. However, in this case the temperature differences are comparatively small so that heating up the press and cooling the press down require longer times to complete.

A further modification, in operation, of the system shown in FIG. 1 is also possible. In this case, pump PW in duct 12 is operated so that the hot storage means is continuously supplied, through the heating means or boiler, with heat transfer oil from the warm storage means. In this modification, the procedure of heating up the press is carried out symmetrically with respect to the cooling procedure.

Referring now to the embodiment of the invention shown in FIG. 2, let it be assumed that the press is hot and is to be cooled down. In order to avoid thermal stresses, temperature differences of more than 100.degree. C., between the press temperature and the temperature of heat transfer oil, are to be avoided. Pump PK is operated, under the control of level sensing means, only to ensure that the level in the tepid storage means does not decrease below a certain minimum value and the level in the warm storage means does not exceed a particular value. In this embodiment, as in the embodiment of FIG. 1, the burner for the heating device or boiler is turned off only to avoid a certain maximum temperature in the hot storage means being exceeded, such turning off taking place automatically.

At the beginning of cooling of the press, pump PP draws heat transfer oil into the press from the tepid storage means through duct 20, switch over valve UV4, duct 21, switch over valve UV5, duct 22, switch over valve UV1 and duct 23. Returning from the press, heat transfer oil flows through duct 24, switch over valve UV2, duct 25, switch over valve UV3 and duct 26 into the warm storage means, until a temperature regulator at the switch over valve UV3 is actuated. If the temperature of the heat transfer oil falls to a value below a set value, switch over valve UV3 is so set that further removal of oil from the press is effected with the oil flowing through duct 27 into the tepid storage means.

When the press has been cooled sufficiently by heat transfer oil from the tepid storage means, heat transfer oil from the cold storage means is used to cool the press further. In this case, heat transfer oil flows through duct 29, switch over valve UV5, duct 22, switch over valve UV1, duct 23 and pump PP into the press, due to the suction effect of pump PP. Pump PP forces the heat transfer oil from the press through duct 24, switch over valve UV2, duct 25, switch over valve UV3 and duct 27 to the tepid storage means until the press has been cooled sufficiently. Pump PP is now deactivated, and the charge may be removed from the press and a new charge placed in the press. Under certain circumstances, heating of the press can be initiated during removal of the charge from the press or the placing of a new charge in the press, thus enabling a further shortening of the time required for operating the press.

For heating the press, switch over valve UV5 and UV4 are set to allow flow of liquid therethrough. For the initial heating stage, heat transfer oil from the tepid storage means is drawn by pump PP through duct 20, switch over valve UV4, duct 21, switch over valve UV5, duct 22 and switch over valve UV1, and is delivered to the press through duct 23. Heat transfer oil leaving the press flows through duct 24, switch over valve UV2, duct 25, switch over valve UV3, and duct 27 into the tepid storage means.

If the temperature regulator at valve UV3 is actuated responsive to a sufficiently high temperature of the heat transfer oil being attained, switch over valve UV3 is actuated and heat transfer oil now flows through duct 26 back into the warm storage means. When a suitable temperature has been reached, or when the warm storage means is empty, as indicated by a suitable level sensing means in the warm storage means, the warm storage means is disconnected from the press circuit and switch over valve UV1 is set for through flow so that heat transfer oil from the hot storage means is drawn by pump PP from the hot storage means through duct 30, regulating valve RV, duct 31, switch over valve UV1 and duct 23 for delivery into the press. Returning from the press, the heat transfer oil initially flows through duct 24, switch over valve UV2, duct 25, switch over valve UV3 and duct 26 into the warm storage means.

When a temperature sensing means at the inlet of the warm storage means indicates that a certain temperature has been exceeded, switch over valve UV2 is switched for through flow, and the heat transfer oil is directed through duct 32 back into the hot storage means until the necessary press temperature has been attained. It is now necessary for the final press temperature to be held precisely. This is effected by the regulating valve RV which allows only sufficient hot heat transfer oil to flow from the hot storage means into the duct 32 as is necessary to maintain the temperature. The oil circuit is then through ducts 30, 31, 23, 24 and 32.

The following points should be noted in connection with the operation of the apparatus embodying the invention. As the partition indicated in broken lines in the hot storage means indicates, a steady circulation of the heat transfer oil within the hot storage means can be assured by means of pump PH without the heat transfer oil being mixed, since pump PH has a suction side connected with the space to the right of the partition and the heat transfer oil from the heating device or boiler enters the space to the left of the partition. If the quantity of oil in the space to the left of the partition is too great, the oil flows over the upper edge of the partition.

As indicated in the drawing, the warm storage means, tepid storage means and cold storage means are so arranged that the tepid storage means is always filled to the highest level. The free spaces above the liquid level in these three storage means are connected, by means of ducts, and the spaces themselves are filled with nitrogen in order to avoid oxidation. Additionally, at the height of the designed level of the three storage means, balancing or compensation duct means are provided.

The tepid storage means is provided with a level sensing means or switch to ensure that it contains at least sufficient oil for performing the first part of the cooling stage of the press. The level switch and level sensing means controls the action of pump PK, which forces heat transfer oil from the tepid storage means through the cooler into the cold storage means.

Pump PP operates in all stages, and supplies the press either with warm or cold heat transfer oil. Pump PK operates until it is switched off by the level sensing means in the tepid storage means. As soon as the tepid storage means contains sufficient heat transfer oil, the oil is pumped by the pump through the cooler into the cold storage means, from which it is then withdrawn as required.

For better utilization of the heat energy, the system just described is connected with a space heating installation to which heat transfer oil is supplied from the warm storage means through duct 34, switch over valve UV6 and duct 35, under the effect of pump PR. The oil is returned from the space heating installation, which latter has not been shown, through duct 36 and back into the tepid storage means.

In order to be able to regulate the temperature of the heat transfer oil in the space heating installation, a duct 37 extends from the discharge of the tepid storage means to switch over valve UV6, and allows mixing of a suitable quantity of oil from the tepid storage means with oil flowing through the duct 34. This regulation provides for lowering the temperature of the oil in the space heating means.

In order to be able to raise the temperature of the oil flowing through the duct 35 to the space heating installation, this duct is provided with a heat exchanger W which is connected through ducts 38 and 39 with the hot storage means. A pump PR1 is provided in duct 39 for delivering oil from the hot storage means through the heat exchanger W. Pump PR1 is activated by means of a regulating element which is mounted in duct 35 downstream from heat exchanger W, and causes activation of pump PR1 when the temperature in duct 35 downstream from heat exchanger W, falls below a certain value.

Claims

1. In a method for alternate heating and cooling of a workpiece in a press means or the like in cyclically sequentially successive and alternating heating and cooling periods, and in which, during heating periods, heat transfer liquid warmer than the workpiece and, during cooling periods, heat transfer liquid colder than the workpiece, are circulated through the press means, with the heating liquid and the cooling liquid flowing, respectively, through heating means and cooling means externally of the press means: the improvement comprising the steps of, in at least one period of each cycle including a heating period and a cooling period, at least partly abstracting liquid emerging from the press means during a part of one period for return of the abstracted liquid to the press means during at least one later period of operation; bypassing the abstracted liquid relative to the heating and cooling means; initiating return of the abstracted liquid to the press means at a time when the difference between the instantaneous temperature of the workpiece and the final desired temperature of the workpiece at the end of the particular period is greater, in the same direction, than the difference between the instantaneous temperature of the abstracted liquid and such final desired temperature; and interrupting flow of the abstracted liquid when the temperature of the workpiece is not more substantially different from the

2. In a method for alternate heating and cooling of a workpiece in a press means or the like, the improvement claimed in claim 1, including storing the abstracted liquid in different storage means into each of which liquid

3. In a method for alternate heating and cooling of a workpiece in a press means or the like, the improvement claimed in claim 2, including the steps of dividing each heating period and each cooling period into respective first and second stages; supplying heat transfer liquid to the press means from the heating means in the second stage of each heating period; supplying heat transfer liquid to the press means from the cooling means in the second stage of each cooling period; and supplying such abstracted liquid to the press in the first stage of each heating period and in the

4. In a method for alternate heating and cooling of a workpiece in a press means or the like, the improvement claimed in claim 3, in which, during the first stage of each cooling period, liquid abstracted from the first stage of a preceding heating period is supplied to the press means and, in the first stage of each heating period, liquid abstracted in the first

5. In a method for alternate heating and cooling of a workpiece in a press means or the like, the improvement claimed in claim 3, in which in the first stage of each cooling period, liquid abstracted in the second stage of a preceding cooling period is supplied to the press means and, in the first stage of each heating period, liquid abstracted in the second stage

6. In a method for alternate heating and cooling of a workpiece in a press means or the like, the improvement claimed in claim 3, including the steps of, in a first stage of a heating period supplying liquid to the press means from a warm storage means; in a first part of such first stage returning liquid from the press means to a tepid storage means; and a second part of such first stage returning liquid from the press means to the warm storage means; in a second stage of the heating period supplying liquid to the press means from the hot storage means; at least during the latter part of such second stage, returning liquid from the press means to the hot storage means; in a first stage of the succeeding cooling period supplying liquid to the press means from the tepid storage means; in a first part of the first stage of the cooling period, returning liquid from the press means to the warm storage means; in the second part of this first stage of the cooling period, returning liquid from the press means to the tepid storage means; and, in a second stage of the cooling period, supplying liquid from a cold liquid storage means and returning the liquid

7. In a method for alternate heating and cooling of a workpiece in a press means or the like, the improvement claimed in claim 6, in which, in the first part of the second stage of the heating period, liquid supplied to

8. In a method for alternate heating and cooling of a workpiece in a press means or the like, the improvement claimed in claim 6, including the step of continuously circulating liquid from the tepid storage means through

9. In a method for alternate heating and cooling of a workpiece in a press means or the like, the improvement claimed in claim 6, including the step of continuously circulating liquid from one of the warm storage means and the hot storage means through the heating means and into the hot storage

10. In a method for alternate heating and cooling of a workpiece in a press means or the like, the improvement claimed in claim 1, including the step of continuously circulating liquid from the hot storage means through the

11. Apparatus for supplying heat to, and removing heat from, a press means or the like, comprising, in combination, a pump; a cool liquid circuit including said pump, a cooling means and liquid storage means; a hot liquid circuit including said pump, a heating means and liquid storage means; means selectively connecting said circuits with the press means or the like to provide for heating of the liquid during cooling of the press means or the like and cooling of the liquid during heating of the thermal load; said liquid storage means including hot, warm, tepid and cold liquid storage means in said circuits, and each having a discharge duct; means connecting the discharge ducts of said four storage means with the press means or the like; means connecting the press means or the like with at least the hot, warm and tepid storage means for transfer of liquid from the press means or the like to these three storage means; a pump connected in a circuit including said cooling means, said tepid storage means, and said cold storage means; and a pump connecting said heating means and said hot storage means for circulation of liquid between said heating means and

12. Apparatus, as claimed in claim 11, including a pump connecting the discharge duct of said warm storage means with said heating means to

13. Apparatus, as claimed in claim 11, comprising connections between the discharge ducts of said warm, tepid and cold storage means; and valve

14. Apparatus, as claimed in claim 11, comprising duct means providing a short circuit path leading from and to said hot storage means; and

15. Apparatus, as claimed in claim 11, comprising means connecting said warm storage means with a space heating installation for supply of liquid to the space heating installation; and return duct means connecting the

16. Apparatus, as claimed in claim 15, comprising means connecting said tepid storage means with the space heating installation for supplying liquid from said tepid storage means to the space heating installation.

17. Apparatus, as claimed in claim 15, comprising an additional heating device; a branch duct connected to said hot storage means to supply liquid from said hot storage means to said additional heating device; and means connecting said additional heating device to the space heating installation for supply of liquid from said additional heating device to the space heating installation.