JPH11156880A - Piping structure of foam molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To take a rapid measures to a case requiring the max. flow rate, improve the accuracy of pressure control in a small flow rate, and reduce piping cost by arranging control valves having the same capacity as the steam pipings branched to be connected to female and male molds. SOLUTION: A piping structure is constituted of a foam molding mold having a steam chamber 2, a steam piping 3 connected to the mold 1, a pressure detector 4 for detecting the pressure in the mold 1, a control valve 5 arranged at the steam piping 3 and a changeover valve 6. In this case, the steam piping 3 is branched to be connected to the mold 1 and control valves 5a, 5b... are arranged at the respective branched steam pipings 3a, 3b,... and changeover valves 6a, 6b... are constituted so as to open and close the branched steam pipings 3a, 3b... through contact valves 5a, 5b... or directly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a piping structure of a foam molding machine.

[0002]

2. Description of the Related Art In a series of heating steps in a foam molding machine, a flow heating step (for example, one-side heating, reverse one-side heating)
In the first half, the pre-expanded beads (35) filled in the mold (21) are not sufficiently expanded, and a large amount of steam is required. On the other hand, in the second half of the process such as the double-side heating process from the end of the flow process (for example, reverse one-side heating) in which the pre-expanded beads (35) have sufficiently foamed and the flow of steam has been reduced, Since the required flow rate of the steam is reduced, a small flow rate of the steam may be used. However, in order to accurately bake the foam, it is necessary to control the pressure accuracy severely and increase the pressure accuracy.

In one of the conventional examples shown in FIG. 3, a single steam pipe (23) is connected to both a male mold (21a) and a female mold (21b) of a mold (21), and one control pipe is connected to the steam pipe (23). Valve (25) was connected. In this case, the capacity of the control valve (25) is usually selected to have a large diameter corresponding to the maximum flow rate of the supplied steam. Therefore, although the above-mentioned flow-through process (one-side heating and the first half of reverse one-side heating) sufficiently exerts its ability, it is suitable for a large flow rate in the double-sided heating process from the end of the reverse one-side heating process, but a small flow rate is controlled. A large-diameter control valve (25), which is not suitable for, must control the pressure at a small flow rate, as shown in FIG. 5, as shown in FIG. Pressure control at this stage becomes extremely difficult, such as instability of the molded product, and various problems such as uneven baking and insufficient fusion of the surface portion of the foamed molded article. Was.

In another conventional example (not shown), a small-diameter control valve was used in some cases. In this case, excellent pressure is applied at the end of the reverse flow heating (that is, one-side heating when only one-side heating is not performed, one-side heating when only one-side heating is performed, and one-side heating when reverse-side heating is performed) or when heating both sides. Control is possible, but in the flow-through heating process that requires a large flow rate of steam, there is a problem in that the flow rate is insufficient and heating takes too much time, during which the steam flows out to the drain side and is wasted. Was.

Therefore, a technique as described in Japanese Patent Application Laid-Open No. 61-171326 has been proposed (not shown). That is, a steam pipe connected to the male and female molds is branched into two, a large-diameter control valve is connected to one of the branched steam pipes, and a small-diameter control valve for double-sided heating is installed in the other steam pipe. In order to solve the above-mentioned problems, the control valve is properly used according to the flow rate.

However, also in this case, a large-diameter control valve must be used in accordance with the maximum flow rate of steam, and a small-diameter control valve for double-sided heating must also be provided. However, there has been a problem that the piping cost is significantly increased.

[0007]

In the present invention, a control valve is installed in each of the steam pipes branched and connected to the male and female molds, so that a quick response when a maximum flow rate is required and a small flow rate can be achieved. The challenge is to solve the problems of improving the accuracy of pressure control and reducing piping costs at a glance.

[0008]

According to a first aspect of the present invention, there is provided a piping structure of a foam molding machine comprising: a foam molding die (1) having a steam chamber (2); Steam piping (3) and mold (1)
A pressure detection device (4) for detecting the internal pressure, a control valve (5) installed in a steam pipe (3), and a piping structure of a foam molding machine including a switching valve (6), A steam pipe (3) is branched and connected to a mold (1), and a control valve (5a) (5b) is provided for each of the branched steam pipes (3a) (3b).
Are installed, and the switching valves (6a) (6b) ... open and close the steam pipes (3a) (3b) ... which are branched through the control valves (5a) (5b) ... or directly. There is a feature.

According to this, at the time of flow heating which requires the maximum flow rate, especially the first half of the flow heating (that is, the first half of the one-side heating when the reverse one-side heating is not performed, and the one-side heating when the reverse one-side heating is performed). Switching valve (6a) (6b) ...
As will be described in detail later, all or most of the side-by-side control valves (5a), (5b) ... are opened, and the flow is heated (flow heating is performed if reverse heating is not performed. From the end stage of reverse one-side heating when performing reverse one-side heating) to double-sided heating, a part (usually one) is used to reduce the flow rate and perform accurate pressure control.

A second aspect of the present invention includes an example of a signal system of a piping structure of the foam molding machine according to the first aspect, wherein the signal system is connected to the control valves (5) based on output signals from a pressure detecting device (4). Controlling the switching valve (6) that is being operated. "
In this case, the switching valve is switched by an electric signal output from the pressure detector (4).
The control of (6) is performed electrically.

A third aspect of the present invention relates to another example of a control method.
The switching timing of the switching valve (6) connected to (5) is timer-controlled. " In this case, the switching valve (6) is controlled according to a preset sequence regardless of the mold pressure.

According to a fourth aspect of the present invention, in the piping structure of the foam molding machine according to any one of the first to third aspects, the "pressure detecting device (4)
From the drain hose (7) derived from the mold (1)
(8) connected to the pipe section (9) or the drain valve (8). According to this, the part to which the pressure detection device (4) is connected when performing mold replacement is the mold (1).
Since it is in a part separated from the mold, there is no need to disconnect the pipe of the pressure detecting device (4) every time the mold is replaced, and the mold replacement becomes very simple.

[0013] A fifth aspect of the present invention relates to a piping structure of a foam molding machine according to any one of the first to fourth aspects.
(5a) (5b) ... the capacity is the same ", so that the diameter of the control valve (5a) (5a) (5a) ( 5b) ... Therefore, a large-diameter control valve corresponding to the maximum flow rate is not required, and the cost can be reduced accordingly.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The piping structure of a foam molding machine according to the present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 shows a first embodiment, in which a mold (1) for foam molding is divided into a male mold (1a) and a female mold (1b), each of which is provided with a steam chamber (2a) (2b). Although not shown, a cooling pipe, a filler, and other necessary members are provided.

A steam pipe (3) extends from the steam source (10), and is further branched into a plurality (here, two) and connected to the male and female molds (1a) and (1b). The branched steam pipes (3a) (3b) have control valves (5a) (5
b) ... is installed. The control valves (5a) (5b)... May have the same capacity (that is, the diameter), but may select different ones. If the capacities are the same, the capacity of each control valve (5a) (5b) ...
｛= Maximum flow rate ÷ number ÷ If different, the sum of the capacities of the control valves (5a) (5b)... May be the maximum steam flow rate. In general, even if the abilities are different, those having similar abilities are used instead of using distant ones. (Of course, this does not deny the adoption of a device with a different capability.) In addition, if the capabilities of the control valves (5a), (5b) ... are the same, any one may be selected, but if they are different, The optimal combination is selected according to the situation in each process. These points can be said throughout the specification.

The control valves (5a) (5b)... Reduce the pressure of the steam discharged from the high-pressure steam source (10) to a required pressure and control the flow rate thereof to control the steam flow in the steam chambers (2a) (2b). The pressure is controlled so that the pressure is maintained at a predetermined pressure, and a pressure reducing valve is also a kind. In the first embodiment, the pressure reducing valve is used as the control valve (5). Further, the branched steam pipe (3a)
(3b) ... are male and female molds (1a) (1b) via steam side hose (14)
Is connected to the steam-side base (13) provided in the base.

Further, switching valves (6a) (6b), which are two-way valves, are provided upstream of the control valves (5a) (5b) of the branched steam pipes (3a) (3b). The opening and closing control of the branched steam pipes (3a) (3b) ... is directly performed.

On the drain side, a drain hose (7) is detachably connected to a drain base (12) extending from the bottom of the male and female molds (1a) and (1b). A drain valve (8) is connected to a pipe portion (9) provided on the downstream side.

One end of the pilot pipe (11) of the pressure detecting device (4) is connected to a pipe section (9) between the drain hose (7) and the drain valve (8) or the drain valve (8) itself. The other end is connected to a control valve (5a) (5b)..., And a pressure detecting device (4) is connected in the middle thereof. In addition, both pressure detectors
(4) The output of the pressure switch (4a) (4a) of (4) is input to the control circuit (17), and the output of the control circuit (17) is output to each of the switching valves (6a) (6b) and the drain valve (8a ) (8b). In addition, throughout the specification, when discussing each member separately with respect to the male and female molds (1a) (1b) or separately discussing the branched steam pipes (3a) (3b) ..., in order to distinguish the members. Was added with the lowercase letter of the alphabet next to the number as a branch symbol.

Next, an example of the heating step will be described. The pre-foamed beads (15) are filled into the cavity (16) of the closed male and female molds (1a) and (1b) through a filler (not shown), and a "bead filling step" is performed, followed by the male and female molds (1a). Open the drain valve (8) of (1b) and all (or most) of the switching valves (6a) (6b) ... to send steam at the maximum flow rate to the steam chamber (2a) of the male and female molds (1a) (1b) ( 2b) is passed, and the male and female molds (1a) and (1b) are heated. Thereby, the molds (1a) and (1b) are heated and the air and drain in the molds (1a) and (1b) are discharged (a mold heating step).

When the heating of the male and female molds (1a) and (1b) is completed, the process is switched to a heating step, in which the filling beads (15) are heated, and the air and drain between the beads (15) are discharged. To achieve uniform expansion. Here, the drain valve (8a) of the male type (1a) is opened, all the switching valves (6a) (6b) ... of the male type (1a) are closed, and the female type is opened.
When the drain valve (8b) of (1b) is closed and all (or most) switching valves (6a) (6b) ... of the female type (1b) are opened, the steam at the maximum flow rate is the female type (1b) steam. After heating the pre-expanded beads (15) in the cavity (16) from the chamber (2b) through the cavity (16), the male mold
It enters the steam chamber (2a) of (1a) and flows out of the male (1a) drain valve (8a). Of course, conversely, the flow may flow from the steam chamber (2a) of the male mold (1a) to the steam chamber (2b) of the female mold (1b). Is determined.

The change in the mold pressure in this step is as shown in FIG. 4. As shown in FIG. 4, the pre-expanded beads (15) gradually expand with the flow, the bead gap gradually narrows, and after the mold pressure once decreases, the mold pressure gradually decreases. Going up. This pressure increase is detected by the female (1b) pressure detecting device (4). When the detection value of the pressure detecting device (4) reaches a predetermined pressure (here, 0.5 kgf / cm ² ), the pressure switch (4a) of the female type (1b) pressure detecting device (4) switches. Then, this signal is input to the control circuit (17), and this step is completed, and the process is switched to the next step. 《One-side heating process》

On the other hand, when the heating step is completed, reverse one-side heating is performed as needed (in other words, reverse one-side heating may not be performed in some cases). In this step, the flow direction is reversed with respect to the flow direction of the one side heating, and the heating of the beads (15) and the discharge of air and drain between the beads (15) are performed as described above, and the further beads (15) are formed. Inflate. In this step, pre-foamed beads (1
5) is foamed to some extent and the gap between the beads is small and it is difficult to flow, so the amount of steam is reduced.
The drain valve (8a) of the male type (1a) is closed according to the signal of the control circuit (17), and the necessary switching valve (6a) of the entire switching valve (6a) (6b) ... of the male type (1a) In this case, open one｝, and female type (1b)
Open the drain valve (8b) of all female (1b) switching valves (6a) (6b) ...
When the is closed, the steam reduced to the required amount is supplied to the male (1a) steam chamber (2
After heating the pre-foamed beads (15) in the cavity (16) in the state of foaming from the a) through the cavity (16), the steam enters the steam chamber (2b) of the female mold (1b), and the female mold ( It flows out from the drain valve (8b) of 1b). (Of course, if the heating step flows from the opposite direction as described above, the situation is reversed.)

In the reverse one-side heating step, as shown in FIG. 4, the detected pressure rises rapidly, and in the final stage, almost no steam flows, and the detected pressure reaches the maximum pressure (0.75 kgf / cm ^{2 in} FIG. 4). Is shown. This mold pressure is detected by the male (1a) pressure detecting device (4). At this stage, a precise pressure control pressure is required. In the present invention, since a small number (one in this embodiment) of the control valve (5a) of a small flow rate is used in this step, a quick response is possible. A strong pressure rise can be avoided.

On the other hand, at the end of the heating step, the beads 15 in the cavity are sufficiently foamed to form a foamed molded product (S), and there is almost no steam flow. Then, the process is switched to the next double-sided heating step. The switching timing is based on the switching of the pressure switch (4a) of the pressure detector (4) of the male die (1a). In the double-sided heating step, the steam pressure is increased to increase the heating temperature, and mainly the fusion of the surface portion of the foamed molded product (S) is performed. Here, the drain valves (8
a) (8b) is closed and all the switching valves (6a) (6b) of the male and female molds (1a) (1b) ...
Open a part (here, one switching valve (6a) (6a)),
Control valve (5a) connected to the switching valve (6a) (6a)
(5a) is operated to supply steam to the steam chambers (2a) (2b) of the male and female molds (1a) (1b). In this case, the steam does not flow through the cavity (16), and the both sides of the foam molded body (S) are heated so that the beads (15) on the surface portion of the foam molded body (S) are sufficiently fused to each other. I do. Therefore, at this stage, as shown in FIG. 4, the pressure is accurately controlled so as to maintain the maximum pressure (0.75 kgf / cm ^{2 in} FIG. 4) and a constant pressure. Also in this case, since the control is performed by the small-diameter control valves (5a) and (5a), the pressure fluctuation and the rapid rise in the pressure as shown in FIG. 5 can be avoided.

When the double-sided heating is completed, the foam molded body in the cavity is cooled to a predetermined temperature by a suitable means such as vacuum cooling or water cooling << cooling step >>.

After that, the mold is opened and the foamed molded body is molded (1)
And the molding is completed. Such a cycle is repeated to mold the foam molded body,
The mold is changed before the lot is completed and the lot is changed to the next lot. At this time, the mold (1) and the piping system are hoses (14) (7)
The hoses (14) and (7) are disconnected at the bases (13) and (12) where they are connected. The input end of the pilot pipe (11) of the pressure detection device (4) is connected between the drain hose (7) and the drain valves (8a) (8b) or the drain valve (8a).
Since it is connected to (8b), it is not necessary to remove the pilot pipe (11) from the male and female molds (1a) and (1b) at the time of mold exchange, and mold exchange can be performed more easily.

Summarizing the above, a large flow rate of steam is required in the mold heating step and the one-side heating step, while a medium flow rate is required in the reverse one-side heating step and a small flow rate in the double-sided heating step. Enough. Therefore, the number of control valves (5a) (5b)... To be operated according to the flow rate is selected. Control valve
If the abilities (5a), (5b) ... are the same, any one may be selected, but if they are different, the optimal combination is selected depending on the situation. In the double-sided heating step, the mold pressure is an important factor. If the pressure is too high, the foamed product (S) will be overheated, and if it is too low, the burn will be insufficient. Since the mold pressure varies and causes uneven baking, stable mold pressure is indispensable for the production of a sound foamed product (S). For that purpose, a control valve (5) having a diameter corresponding to the flow rate is required, and this requirement can be achieved by arranging a plurality of control valves (5) having a small flow rate in parallel as in the present invention. Also,
By using the control valve (5) with a small flow rate, the responsiveness is improved as compared with a large-diameter valve for a large flow rate, and it is possible to respond quickly to a pressure change.

Next, a second embodiment of the present invention will be described. Since the technical concept of the second embodiment is the same as that of the first embodiment, parts having the same functions are denoted by the same reference numerals, and a description of parts having overlapping functions is omitted to avoid complexity. This will be mainly described. In this case, the steam pipe (3) is branched into three pipes, and control valves (5a), (5b), and (5c) are connected to the respective pipes. In this case, the control valve (5a) (5b) (5
c) is a normally-closed piston valve unlike the case of the first embodiment (pressure reducing valve), but has the same technical idea.

The switching valves (6a) (6b) (6c) are not directly connected to the branched steam pipes (3a) (3b) (3c) as in the first embodiment, but are control valves. (5a) (5b) (5c) is connected to the piston part, and the control valve (5a) (5b) (5
c) is opened and closed, but the control valve
The only difference is whether the steam pipes (3a), (3b) and (3c) branched via (5) are opened or closed or directly opened and closed. In this case as well, the functions in the technical idea are the same.

As in the first embodiment, the control valve (5
a) (5b) (5c) capabilities (ie caliber) may be the same,
A different one may be selected. If the capacities are the same, the capacities of the control valves (5a) (5b) ... may be 1 / maximum flow rate {number} of the maximum flow rate of the steam, and if different, each control valve (5a) (5b) It is sufficient that the sum of the capacities becomes the maximum steam flow rate. In general, even if the abilities are different, those having similar abilities are used instead of using distant ones. (Of course, it does not deny the adoption of one with a different ability.)
If the capabilities of the control valves (5a), (5b)... Are the same, any may be selected, but if they are different, the optimal combination is selected according to the situation in each process.

The pressure detecting device (4) of the second embodiment has a steam chamber
(2) Outputs the pressure inside as an electric signal,
The function of detecting the pressure in the steam chamber (2) is the same as that of the first embodiment. Therefore, the piping system is functionally the same as the first embodiment.

As in the first embodiment, a pilot pipe (11) connected to the pressure detecting device (4) is provided with a pipe section (9) between a drain hose (7) and a drain valve (8) or a drain valve. (8) Connected to itself. The output of the pressure detection device (4) is connected to a control circuit (17) such as a sequencer, and is output to a control valve driving unit (19). This control valve drive (1
9) is connected to a control valve driving air pressure source (18) for supplying pilot compressed air to the switching valves (6a) (6b) (6c), and the switching valves (6a) (6b) (6c ) Via control valve (5a)
(5b) It is connected to the piston part of (5c), and since this pipe functionally shows the same operation as the pilot pipe,
This is also shown in (11).

Next, the operation of the second embodiment will be described. As before, mold closing, bead filling, mold heating, and one-side heating are performed. In the mold heating step, all the control valves (5a) (5b) (5c) of the male and female molds (1a) (1b) may be fully opened and allowed to flow.
In some cases, one may open all control valves (5a) (5b) (5c) fully, the other may open most (5a) (5b), close some (5c), and adjust the flow rate . In that case, the control valve to be closed by the other control valve drive (19)
Close the pilot pipe (11) of (5c) and shut off the pneumatic source (18). As a result, compressed air is not supplied to the pin ton portion of the control valve (5c), so that the valve is closed by the action of the spring, and only the control valve (5c) is closed.
The pressure in the steam chambers (2a) and (2b) is
The information is monitored in (4) and input to the control circuit (17).

When the heating of the male and female molds (1a) and (1b) is completed, as in the first embodiment, the process is switched to the one-side heating step. In this step, the heating of the filled beads (15) and the air between the beads (15) are performed. And drain, and evenly expand the beads (15). Here, the male (1a) drain valve (8a) is opened, all the switching valves (6a) (6b) (6c) of the male (1a) are closed, and the female (1b) drain valve (8
b) is closed and all (or most) switching valves (6) of female type (1b) are closed.
a) When (6b) and (6c) are opened, steam flows from the steam chamber (2b) of the female mold (1b) through the cavity (16) at the maximum flow rate, and heats the pre-expanded beads (15) in the cavity (16). After that, the steam chamber of male type (1a) (2
Enters a) and flows out of the male (1a) drain valve (8a).
Of course, from the male (1a) steam chamber (2a) to the female (1b) steam chamber
The gas may flow through (2b), and the flowing direction is determined in consideration of the shape of the foamed molded product (S).

The mold pressure change in this step is also as shown in FIG. 4. The pre-expanded beads (15) gradually expand with the flow, the bead gap gradually narrows, and the mold pressure once decreases and then gradually increases. Go. This pressure increase is detected by the female (1b) pressure detecting device (4). When the detection value of the pressure detector (4) reaches a predetermined pressure (here, 0.5 kgf / cm ² ), a detection signal is sent from the female type (1b) pressure detector (4) to the control circuit (17). , The process is completed, and the process is switched to the next process << one-side heating process >>.

On the other hand, when the heating step is completed, reverse one-side heating is performed as necessary. In this step, as before, the prefoamed beads (15) are foamed to some extent and the gaps between the beads are reduced to make it difficult to flow, so that the amount of steam is reduced. Therefore, the switching valve (6a) or (6a) which operates by activating the control valve drive units (19) and (19) of the male and female molds (1a) and (1b).
(6b) and select the switching valve (6b) or (6b) (6c) to be stopped,
Activate the male (1a) control valve (5a) or (5a) (5b) with the same action as described above, and the female (1b) control valve (5b)
Or close (5b) and (5c). As a result, appropriate flow rate control and pressure control in this step are quickly performed.
As a result, it is possible to avoid a rapid pressure rise as shown in FIG. 4 observed at the end of the heating step.

On the other hand, when the one-side heating step is completed and the process is switched to the double-sided heating step, the flow rate is further reduced and the mold pressure is increased as described above. For this purpose, a switching valve (6a) that operates by operating the control valve drive units (19) (19) of the male and female molds (1a) (1b) and a switching valve (6b) (6c) that stops are selected. The control valve (5a) is operated by the same operation as described above, and the control valve (5b) (5
Close c). As a result, it is possible to avoid a rapid pressure rise and pressure fluctuation as shown in the conventional double-sided heating process as shown in FIG.

When the double-sided heating is completed, the mold is opened through the cooling step as described above, and the foam molded article (S) is taken out of the mold (1) to complete the molding.

Summarizing the above contents (an example of control),
It looks like the table below.Heating process Mold heating One-side heating Reverse one-side heating Double-side heating  One mold(5a) 〇 〇 × 〇 control (5b) 〇 〇 × × Open / close the valve (5c)) 〇 × × Of the other mold(5a) 〇 × 〇 〇 control (5b) 〇 × 〇 × Open / close the valve (5c)) × × × Here, 〇 is open and × is closed.

In the above two embodiments, the pressure detecting device is used.
Although the switching timing of the switching valve (6) was determined by the output of (4), the switching timing was input to the control circuit (17) in advance regardless of this, and the pressure detection device was
The switching of the switching valve (6) may be controlled by timer regardless of the output of (4).

[0042]

As described above, according to the present invention, by installing a control valve in each of the steam pipes branched and connected to the male and female molds, a quick response when a maximum flow rate is required and a small flow rate can be achieved. The problem of improving the accuracy of pressure control and reducing piping costs was solved at once. In addition, by devising the connection position of the portion to which the pressure detection device is connected with the mold, the mold exchange becomes very simple.

[Brief description of the drawings]

FIG. 1 is a piping system diagram of a first embodiment according to the present invention.

FIG. 2 is a piping system diagram of a second embodiment according to the present invention.

FIG. 3 is a piping diagram of a conventional example.

FIG. 4 is a graph of mold pressure change in each heating step obtained in the present invention.

FIG. 5 is a graph showing a change in mold pressure in each heating step of the conventional example.

[Explanation of symbols]

 (1)… Mold (1a)… Male (1b)… Female (2)… Steam chamber (2a)… Male steam chamber (2b)… Female steam chamber (3)… Steam piping (3a ) (3b) (3c)… Branch steam pipe (4)… Pressure detector (5a) (5b) (5c)… Control valve (6a) (6b) (6c)… Switching valve (7)… Drain hose (8a) (8b)… Drain valve (9)… Piping from drain hose to drain valve (10)… Steam source (11)… Pilot piping

Claims (5)

[Claims] 1. A mold for foam molding having a steam chamber, a steam pipe connected to the mold, a pressure detecting device for detecting a pressure in the mold, a switching valve, and a steam pipe. In the piping structure of a foam molding machine including a control valve, a steam pipe is branched and connected to a mold, and a control valve is installed in each of the branched steam pipes. A piping structure for a foam molding machine, wherein a steam piping branched off directly or via a control valve is opened and closed. 2. The foam molding machine according to claim 1, wherein the switching valves connected to the control valves are controlled based on an output signal from a pressure detecting device. Piping structure. 3. The piping structure of a foam molding machine according to claim 1, wherein a switching timing of a switching valve connected to each of the control valves is controlled by a timer. 4. The foam according to claim 1, wherein the pressure detecting device is connected to a pipe portion from a drain hose led out of a mold to a drain valve or to a drain valve. Piping structure of molding machine. 5. The piping structure of a foam molding machine according to claim 1, wherein the control valves have the same capacity.