GB2167706A - Hydraulic vulcanizing press - Google Patents

Abstract

In a hydraulic vulcanizing press having a hydraulic pressure generator device, for example including a pneumatic booster 10 (more particularly, a pneumatically operated hydraulic pressure booster), for supplying a desired hydraulic pressure to a hydraulic pressure cylinder 1 in a hydraulic circuit c on the pressure actuation side A of said cylinder, for the purpose of pressurizing and holding a pressure in the cylinder of the press, warning means are provided comprising a measurement instrument, such as a counter (33, Fig 3) for measuring the actual flow rate and issuing a signal (33a) to a setter (a pressure rising setter (34), or pressure holding setter (35). If the actual measurement signal (33a) exceeds the set signal (34a or 35a) this is detected by a comparator (36) which issues an alarm signal (36a) to actuate an alarm 37. <IMAGE>

Description

SPECIFICATION Hydraulic vulcanizing press The present invention relates to a hydraulic vulcanizing press in which pressurisation of a hydraulic pressure cylinder in the press is carried out and the pressurizing force is held by making use of a pneumatic booster which converts a pneumatic pressure to a hydraulic pressure according to an area ratio of a piston and which continuouslyfeeds the hydraulic pressure until the hydraulic pressure in the hydraulic cylinder balances with a load.

A pneumatic booster that is available in the aforementioned type of hydraulic vulcanizing press has a characteristic as illustrated in Figure, 1, where it will be noted that, in the case of setting a pressing force for the hydraulic cylinder by the intermediary of the fed pneumatic pressure, the delivered hydraulic pressure is proportional to the fed pneumatic pressure;; (1) if the fed pneumatic pressure is set at a pressure corresponding to a desired hydraulic pressure for pressing, it takes time until the hydraulic cylinder is pressurized up to the desired hydraulic pressure because the delivery rate of pressurized oil is reduced as the hydraulic pressure rises, and (2) if the fed pneumatic pressure is set higher than the pressure corresponding to the desired hydraulic pressure for pressing, the hydraulic pressure would eventually rise higher than the desired hydraulic pressure and hence a product or a machine would be adversely affected, although the time necessitated before attaining the desired hydraulic pressure is shortened.

On the other hand, if the fed pneumatic pressure is set higher than the pressure corresponding to the desired hydraulic pressure for pressing and the hydraulic pressure of a delivered pressurized oil is controlled by means of a pressure reducing valve, then the aforementioned shortcoming can be eliminated. However, the pressure reducing valve must always discharge drain oil for controlling the hydraulic pressure. Also, during the pressure holding period, even if there is no leakage from the pressure cylinder and/or other pipings, it is necessary to continue to supply pressurized oil. Hence, a correspondingly large capacity of pneumatic booster is necessitated. Moreover, a waste of energy results.

An object of the present invention is to provide a hydraulic vulcanizing press in which the hydraulic cylinder can be pressurized up to a desired hydraulic pressure within a short period of time and can hold the desired hydraulic pressure exactly, and in which there is no waste of energy.

According to one aspect of the present invention, there is provided a hydraulic vulcanizing press comprising a pneumatic boosterfor supplying hydraulic pressure to a hydraulic circuit on the pressure actuation side of a hydraulic pressure cylinder in said hydraulic vulcanizing press in orderto pressurize and hold the pressure in the cylinder, and a switching device for switching pressurized air fed to the pneumatic booster between high pressure air for boosting the hydraulic pressure to a desired pressure level and low pressure air for holding said desired hydraulic pressure after said desired level has been attained.

Another object of the present invention is to provide a hydraulic vulcanizing press in which a pressing force of the hydraulic pressure cylinder can be maintained at a predetermined pressure by supplying hydraulic pressure from a hydraulic pressure generator device, and abnormal lowering of the pressing force of the pressure hydraulic cylinder can be detected at an early time to generate an alarm so that the possibility of an accident can be preliminarily prevented.

According to another aspect of the present invention, there is provided a hydraulic vulcanizing press comprising a hydraulic pressure generator device for supplying hydraulic pressure to a hydraulic circuit on the pressure actuation side of a hydraulic pressure cylinder in the hydraulic vulcanizing press in order to pressurize and hold the pressure in the cylinder, and warning means consisting of a measurement instrument for measuring the flow rate of fluid having said hydraulic pressure and for issuing a measurement signal, a setter for issuing a set signal for said flow rate, a comparator for generating an alarm signal when the measurement signal exceeds the set signal, and an alarm acuated by said alarm signal.

The above-mentioned and other features and objects of the present invention will become more apparent by reference to the following description of one preferred embodiment of the invention, taken in conjunction with the accompanying drawings, and modifications thereof, wherein: Figure 1 is a diagram showing characteristics of a pneumatic booster, Figure 2 is a general system diagram showing said preferred embodiment of the present invention, Figure 3 is a longitudinal cross-section view of a hydraulic pressure generator device (a booster) shown in Figure 2, Figure 4 is a system diagram of warning means provided in Figure 2 and Figure 5 is a timing chart showing an operation sequence in the system shown in Figure 2.

Referring to Figure 2, a hydraulic pressure cylinder 1, for example, in a hydraulic press type tyre vulcanizing press (not shown), is adapted to clamp metallic moulds for vulcanizing a tyre, i.e. to apply a pressing force to said moulds. For this, the hydraulic chamber A on the pressure actuating side of the piston 1 a of the cylinder 1 is coupled to a hydraulic circuit (a), while the hydraulic chamber B on the other, piston rod side 1b of the cylinder (the cylinder return side), is coupled to a hydraulic circuit (b). Both hydraulic circuits (a) and (b) are coupled through a directional switching valve 2 to a low-pressure source 3 and a return tank 4. In addition, a pilot check valve 5 and a pressure switch 6 are provided.The aforementioned hydraulic circuit operates in such a manner that, if the directional switching valve 2 is shifted to a position 2a, then hydraulic pressure supplied from the low-pressure hydraulic pressure source 3 is introduced into the hydraulic chamber A via the circuit (a), and at the same time liquid within the hydraulic chamber B is discharged to the return tank 4 via the circuit b. Hence, due to hydraulic pressure within the hydraulic chamber A, the rod 1 b is projected by the intermediary of the piston 1 a, resulting in a pressing operation of the tyre vulcanizing press (not shown). Thereafter, if the directional switching valve 2 is shifted to position 2b, hydraulic pressure is introduced into the hydraulic chamber B, and at the same time the actuated liquid within the hydraulic chamber A is discharged.Hence, the rod 1 b and the piston 1 a are retracted to restore the hydraulic cylinder 1, and hence release pressure.

In addition, a hydraulic pressure supply circuit (c) having a check valve 6 is coupled to the abovementioned hydraulic circuit (a) on the pressure actuation side of the hydraulic cylinder. In this circuit (c), between a hydraulic pressure tank 8 and a check valve 7 is disposed a hydraulic pressure generator device 10 for boosting hydraulic pressure P1 on the side of the hydraulic pressure tank 8 up to a higher hydraulic pressure of P2 or P3 to supply such higher hydraulic pressure to the hydraulic cylinder 1. More particularly, a pneumatic booster 10 is provided which is pneumatically actuated to boost the original hydraulic pressure P1 to the higher hydraulic pressure P2 or P3 to be supplied to the hydraulic cylinder.

Referring to Figure 3, the pneumatically actuated booster 10 consists of a pneumatic cylinder 11 formed in a broad, transverse cross-section shape containing a piston 10a therein and having inlet/ outlet ports 11 a and 11 b for pneumatic pressure, and a hydraulic cylinder 12 formed in a narrow transverse cross-section shape having a plunger 10b advanced and retracted therethrough, which communicates with the cylinder 11 and is delimited by a pair of check valves 13 and 14, provided in the hydraulic pressure supply circuit (c).When the plunger lOb is projected into the cylinder 12 (downwardly as viewed in Figure 3) via the piston 1 0a by pressurized air flowing into the cylinder 11 through the inlet/outlet port 1 la (and flowing out of said cylinder through the inlet/outlet port 11 b), the hydraulic pressure P1 within the cylinder 12 is raised up to a higher pressure of P2 or P3, and then flows into the circuit (c) via the check valve 14 as shown by the arrow.On the other hand, when pressurized air is discharged through the inlet/outlet port 1 Ia and enters the cylinder 11 through the inlet/outlet port 11 b, the plunger lob is retracted (raised) via the piston 1 0a. Hence the volume within the cylinder 12 is increased, resulting in a negative pressure therein; thereby, liquid at pressure P1 on the side of the hydraulic pressure tank8 flows into the cylinder 12 through the check valve 13. Therefore, by repeating the aforementioned operations, liquid flow at a higher hydraulic pressure, P2 or P3 is generated in the circuit (c), and this hydraulic pressure flow is supplied to the hydraulic chamber A of the hydraulic cylinder 1 through the aforementioned hydraulic circuit (a).It is to be noted here that, since the transverse cross-section of the pneumatic cylinder 11 has a very large area ratio with respect to the transverse cross-section of the hydraulic cylinder, the higher hydraulic pressure P2 or F3 can be obtained with a relatively low pneumatic pressure.

The pneumatic circuit for the aforementioned booster 10 consists of a feed line (d) at a pressure A2 connected between a pneumatic pressure feed source 20 and the inlet/outlet port 11 a of the booster 11, and includes a pressure reducing valve 21, a directional switching valve 22 and a check valve 23.

A feed line (e) at pressure A3 is connected between the feed source 20 and the aforementioned inlet/ outlet port 11 a, and includes a pressure reducing valve 25 and a directional switching valve 24, as shown in Figure 2. Thus by manipulating the respective directional switching valves 22 and 24, a pneumatic pressure can be fed either from the pressure source 20 to the booster 11 through the inlet/outlet port 11 a, or discharged from said booster through said inlet/outlet port.

The pressure reducing valves 21 and 25 are provided for the purpose of reducing the feed from the source 20 which is at a pressure A1, the pneumatic pressure fed to the booster 10 being set at the pressure A2 by the reducing valve 25, and at the pressure A3 by the reducing valve 21. Here, it is assumed that A3 > A2 is fulfilled and, in the circuit of the illustrated embodiment, the set pressure in the reducing valve 25 is chosen at the higher pressure of the two set pressures.

The directional switching valves 22 and 24 serve to feed pressure atA2 and A3 respectively, fed through the pressure reducing valves 21 and 25 to the booster 10 or shut out pressure from the booster 10, and the check valve 23 serves as an inhibit valve for preventing the air at pressure A3 fed through the switching valve 24 from returning to the pneumatic pressure feed source 20 through the directional switching valve 22.

Furthermore, as shown in Figure 3, a rod 30 projecting from the pneumatic cylinder 11 of the booster 10 is provided on the upper surface of the piston 1 Oa so that a cam 31 mounted at the tip end portion of the rod may actuate a limit switch 32; also a counter 33 is provided for counting the number of actuations of the limit switch 32, as shown in Figure 4, to form a measurement instrument for measuring the flow rate of hydraulic fluid generated by the booster 10 (the flow rate through the hydraulic pressure supply circuit (c) on the basis of the count of the counter 33 and issuing a measurement signal 33a. In addition, there is provided a pressure rising period setter 34 for issuing a pressure rising period set signal 34a corresponding to the aforementioned measurement signal 33a, and a similar pressure holding period setter 35 for issuing a pressure holding period set signal 35a; thereby a pressure rising period set signal 34a corresponding to a number of necessary cycles of booster actuation, that is, corresponding to the aforementioned measurement signal 33a, under a normal condition during the period when the hydraulic pressure in the hydraulic chamber A of the hydraulic cylinder 1 rises from a no load condition up to a predetermined pressing force, and a pressure holding period set signal 35a corresponding to a number of necessary cycles per unit time of booster actuation, i.e. corresponding to the aforementioned measurement signal 33a, for supplementing a normal leakage rate of the hydraulic fluid to hold a predetermined pressing force during the period when the pressing force is held, can be preset. In the aforementioned respective processes, that is, in the pressure rising process and in the pressure holding process, the aforementioned measurement signal 33a is compared with the pressure rising period set signal 34a and the pressure holding period set signal 35a respectively, by means of a comparator 36, and there is provided warning means in which, when the abovementioned measurement signal 33a has exceeded the corresponding set signals 34a and 35a, an alarm signal 36a is generated. In response to the alarm signal 36a issued from the comparator 36, an alarm 37 such as a buzzer or the like may be automatically actuated.Furthermore, there is provided operation interruption means responsive to the abovementioned alarm signal 36a for stopping an automatic operation of the hydraulic vulcanizing press, or for controlling the hydraulic vulcanizing press, in the case of the pressing force is being held, not to enter the next cycle when the present cycle has been completed. This operation interruption means itself may possibly take many different forms of known control means depending upon the structure of the hydraulic vulcanizing press, and therefore, description of a more detailed structure of the operation interruption means will be omitted here.

Moreover, modification can be made such that the pressure rising period setter 34 and the pressure holding period setter 35 respectively can issue two steps of set signals 34a and 35a. Then control can be made such that, if the measurement signal 33a has exceeded the first step set signal, then only the alarm 37 is actuated, and if it has exceeded the second step set signal, then not only the alarm 37 is actuated, but also the hydraulic vulcanizing press is subjected to emergency interruption and the operation cycle is stopped.

It is to be noted that, while a booster having the structure shown in Figure 2 has been described as one example of the hydraulic pressure generator device in the above-described preferred embodiment, the hydraulic pressure generator device should not be limited to such a booster. Thus, the present invention is also applicable to the case of pressurizing by means of a pump. In addition, while description has been made of a measurement instrument which measures the flow rate of hydraulic liquid flow indirectly by measuring booster cycles with the aid of means mounted on a piston of the booster, the present invention should not be limited to this particular example. Thus, it is also possible to detect, for example, the inner pressure of the pneumatic circuit for actuating the booster or of the hydraulic cylinder of the booster by means of a pressure switch.Moreover, it is also possible to employ means for directly detecting the flow rate itself of the hydraulic fluid flow in the hydraulic pressure supply circuit.

In the following, in connection to a series of operations consisting of clamp, pressure-rise, pressure-hold and unclamp, the operation of the respective component parts will be explained.

Figure 5 shows variations in time of the operations of the respective switching valves and the inner pressure within the hydraulic chamber A. The levels 2a, neutral and 2b, the levels 24a and 24b and the levels 22a and 22b represent the respective positions ofthe directional switching valves 2,24 and 22 respectively, and the modes of change of the positions of the respective switching valves are indicated by thick solid lines. An inner pressure P1 within the hydraulic chamber A is a pressure that is necessary for driving the pressing cylinder 1, and this pressure is equal to the pressure of the lowpressure hydraulic pressure source 3. A pressure P2 is the pressure necessary for pressing, and this pressure is equal to the pressure obtained with the aid of the booster 10 by the pneumatic pressure A2 controlled through the pressure reducing valve 21.A pressure P3 is a pressure obtained with the aid of the booster 10 by the pneumatic pressure A3 controlled through the pressure reducing valve 25.

Upon pressing with the hydraulic vulcanizing press, at a moment the directional switching valves 2,24 and 22 are respectively switched to the positions 2a, 24a and 22a. Owing to the position 2a of the directional switching valve 2, the hydraulic pressure P1 is supplied to the cylinder 1 to drive said cylinder, and at a moment t2 the inner pressure within the hydraulic chamber A attains the pressure P,. Underthis condition, the hydraulic cylinder clamps the metallic moulds. After the moulds have been clamped, at a moments3, pressurized air at pressure A3 is fed to the pneumatic booster through the directional switching valve 24 and takes the position 24a.As a result, hydraulic fluid at pressure P3 is delivered from the pneumatic booster 10, and hence the inner pressure within the hydraulic chamber A would rise along the curve 16 shown in Figure 5. When the inner pressure within the hydraulic chamber A has reached the desired pressure P2, that is, at a moment t4, the directional switching valve 24 is switched from position 24a to position 24b and the directional switching valve 2 is switched from position 2a to the "neutral" position, so that feed of the air at pressure A3 to the pneumatic booster 10 is stopped, while the directional switching valve 22 retains its position 22a to feed the air at pressure A2 corresponding to the desired hydraulic pressure P2.

Therefore, the hydraulic chamber A is held at the hydraulic pressure P2, and thus the operation enters the pressure holding step.

During the pressure holding period, that is, during the period of 4 < t5, if the pressurized liquid within the hydraulic circuit leaks out and the pressure within the hydraulic chamber A is lowered, the pneumatic booster 10 would be automatically driven by the pneumatic pressure A2 fed through the directional switching valves 22 and the booster 10 supplies the pressurized liquid until the pressure within the hydraulic chamber A reaches the desired pressure P2.

During the pressure hold period, the directional switching valve 2 is kept at the "neutral" position and the directional switching valve 24 is kept at position 24b, but when the pressure hold period has elapsed, that is, when it has become a time t5, the directional switching valve 2 and 22 are switched to the positions 2b and 22b, respectively, to release the clamp. When the clamp is released, the inhibit of inverse flow through the check valve 5 is also released. Hence, the pressurized liquid within the hydraulic chamber A is discharged through the check valve 5 inversely.

It is to be noted that switching of the pneumatic circuit from the directional switching valve 24 to the directional switching valve 22 in the above description i.e. switching of the directional switching valve 24from position 24a to position 24b at the moment t, is carried out after the pressure switch 6 has been set at the pressure P2.

In connection to the above description, the curve 17 in Figure 5 represents the mode of increase of the hydraulic pressure in the hydraulic chamber A in the event that the pneumatic booster 10 is driven only by the pneumatic pressure A2 corresponding to the desired hydraulic pressure P2. Ity comparing curves 16 and 17, it will be readily seen that the pressure rise time can be greatly shortened according to the present invention.

In addition, with regard to the directional switching valve 2, modification could be made such that the neutral position of the valve 2 is omitted to make only two steps switching between the positions 2a and 2b; at the momentt5 it is switched from position 2a to position 2b and the state of position 2b is maintained from the moment t5 to the moment t7.

Alternatively, the directional switching valve 2 may be maintained at position 2a during the period t1 t3, it may be switched to the "neutral" position at the moments3, and it may be maintained at "neutral" during the period t3 -- t5.Furthermore, the directional switching valve 24 could be switched to the position 24a at the moment t3, then it could be maintained at the state of position 24a during the period t3 -- t4, and switched to position 24b at the moment t4, and it could be maintained at the state of position 24b during the period t4 - te (corresponding tot3). Still further, the directional switching valve 22 could be switched to position 22a at the momentt4, maintained at the state of position 22a, then switched to position 22b at the moment tS and maintained at the state of position 22b during the period t5 - tg (corresponding tot4).

In addition, it is to be noted that lowering of the pressing force of the hydraulic cylinder 1 caused by the conventional leakage of the hydraulic liquid can be prevented by supplying hydraulic liquid held at the higher pressure P2 with the aid of the hydraulic pressure generator device, that is the booster 10 to the hydraulic chamber A of the cylinder land thereby the pressing force produced by the cylinder 1 can be maintained at a predetermined value.

Furthermore, lowering of the pressing force produced by the cylinder 1 would result in increase of the flow rate of the hydraulic fluid (at the hydraulic presure P2) on the side of the hydraulic pressure supply circuit (c) with respect to the hydraulic chamber A of the cylinder 1, and also it is sensitively reflected as an increase of cycles of the booster 10.

Moreover, since the increase is virtually not influ ended from the side of the hydraulic vulcanizing press, by comparing the flow rate detected signal of the aforementioned hydraulic fluid flow detected either indirectly, or directly, with the corresponding set signal, abnormal lowering, i.e., lowering exceeding a predetermined value of the pressing force produced by the pressing hydraulic cylinder, can be detected appropriately at an early time to generate an alarm. If necessary, it is also possible to automatically stop the hydraulic vulcanizing press in such an abnormal case; hence, the present invention can greatly contribute to prevention of unacceptable products, prevention of dangers, etc., and it can remarkable enhance the working efficiency of a hydraulic vulcanizing press. Especially, upon holding a pressing force in the case of requiring a long vulcanizing period extending over several minutes to several hours, as is the case with a tyre vulcanizing press, the above-mentioned effects of the present invention are quite remarkable.

Claims (2)

1. A hydraulic vulcanizing press, characterised in that there is provided a hydraulic pressure generator device for supplying hydraulic pressure to a hydraulic circuit on the pressure actuation side of a hydraulic pressure cylinder in said hydraulic vulcanizing press in order to pressurize and hold the pressure in the cylinder, and warning means consisting of a measurement instrument for measuring the flow rate of fluid having said hydraulic pressure and for issuing a measurement signal, a setter for issuing a set signal for said flow rate, a comparator for generating an alarm signal when said measurement signal exceeds said set signal, and an alarm actuated by said alarm signal.

2. A hydraulic vulcanizing press constructed, arranged and adpated for use substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.