JPH0550978B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is characterized in that a split mold unit consisting of a pair of split molds that can be opened and closed moves once on a circular track by blowing air into the hollow part of the parison. The present invention relates to a mold clamping device in a rotary blow molding machine for producing hollow molded products, and a mold clamping control cam used in the device.

[Prior Art] A large number of split mold units each consisting of a pair of split molds that can be opened and closed in the horizontal axis direction are arranged at equal intervals around the outer periphery of a rotor that rotates around a horizontal axis. A rotary blow molding machine is known that extrudes a parison, then closes a split mold and blows air into the hollow part of the parison to form a hollow molded product.

In such a rotary blow molding machine,
The split mold must be clamped by a clamping force that overcomes the air pressure blown into it, and a clamping device for this purpose is shown in US Pat. No. 3,764,250.
In the mold clamping device shown therein, the split mold holder is clamped by a fixed cam via a slider crank mechanism and a compression spring.

[Problems to be Solved by the Invention] In the conventional mold clamping device described above, the cam follower that engages with the fixed cam must operate against the force of the compression spring, so the cam follower supported by the rotor cannot be driven. A large amount of force is required to do this, and the drive of the rotor fluctuates greatly due to the fluctuating load of the cam follower, which poses a problem in that the rotational speed of the rotor also fluctuates.

In addition, scraps such as defective molded products that occur in the early stages of blow molding are disposed of in the work space that exists between the split mold separation starting part and the molded product ejecting device (this work space is used for blow molding). (It is essential to the mechanism of the machine).

However, this work space is not necessary after the initial stage of molding and normal molding conditions have been reached, but the timing of closing and opening of the split molds is controlled by a single-shaped cam. In addition, even after normal molding conditions are reached, the split molds open at the same time as in the initial stage of molding, which shortens the blow molding period after normal molding conditions are achieved (split mold units in the closed state The problem was that the angle of rotation was reduced.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a mold clamping device for a rotary blow molding machine in which fluctuations in the load for driving the rotor are small.

Another object of the present invention is to provide a mold clamping device for a rotary blow molding machine in which the pressure applied to the cam used for mold clamping is small and the cam, cam follower, etc. are less likely to wear out.

Still another object of the present invention is to determine the rotation angle of the split mold unit in the closed state for blow molding (split mold open An object of the present invention is to provide a control cam for use in a mold clamping device in a rotary blow molding machine, which allows molded products of good quality to be obtained by varying the timing of release.

[Means for Solving the Problems] In order to solve the above problems, a mold clamping device for a rotary blow molding machine according to the present invention includes a pair of split mold holders for holding a pair of left and right split molds, respectively, mounted on the rotor. One split mold holder is slidably held on a guide rod, and one split mold holder is connected via a hydraulic cylinder unit to a slider that is slidably supported on the guide rod, and the other split mold holder is held in opposite directions to the slider. a cam follower movably coupled to the slider via a lever and engaging the slider with a clamping control cam disposed in the vicinity of the rotor; They are connected via a slider crank mechanism which can take two positions, and when the slider crank mechanism assumes the dead center position, mold clamping pressure is applied to the split mold holder by the hydraulic cylinder unit.

The mold clamping control cam is configured such that the closing control side of the split mold is a fixed cam and the split mold opening control side is a movable cam, so that the opening timing of the split mold can be made variable. The work space for handling scraps such as defective molded products generated during blow molding is not required during normal blow molding.

In addition, a fixed cam for mold clamping hydraulic pressure is attached to the fixed cam, a movable cam for mold clamping hydraulic pressure is attached to the movable cam,
The mold-clamping hydraulic movable cam is movable in synchronization with the mold-clamping movable cam, so that the period of hydraulic pressure supply to the hydraulic cylinder unit can be changed.

[Operation] No mold clamping force is applied to the slider crank mechanism that drives the split mold holder and the cam follower until the slider crank mechanism reaches its dead center position.
When the mold clamping force is applied by the hydraulic cylinder unit, the slider crank mechanism is at the dead center position, so the clamping force is received by the fulcrum of the slider crank mechanism, and no clamping force is applied to the cam follower. Therefore, no large force is applied to the cam follower held by the rotor, the load on the rotor is constant, and the rotor is driven at a constant speed.

In the early stages of blow molding, the movable cam is retracted to speed up the separation of the split molds, and a work space for scrapping defective molded products is created between the separation start part of the split molds and the molded product removal device. When blow molding is normal, the movable cam is extended so that the working space is used for the blow molding period, and the time for separating the split molds is extended.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of a rotary blow molding machine using the present invention. In the figure, 1, 1... are split type units, and the rotor 7 rotates around the rotating shaft 2.
(shown in Figure 2) are attached in large numbers at equal intervals on the outer periphery of the
When passing through the illustrated rotation range S, each split mold 1a, 1
a is closed, and the split molds 1a, 1 are opened in other rotation ranges.
a is opened. The opening/closing mechanism of the split unit 1 will be described later.

When the split molds 1a, 1a are closed, the plastic tube, that is, the parison, extruded from the extrusion die 3 between the left and right split molds 1a, 1a of each split mold unit 1 is sealed at both ends of the hollow part. Air is blown from a blow needle provided in the split molds, and the parison is pressed against the inner wall surfaces of the split molds 1a, 1a to form a container shape.

Thereafter, the molded plastic is cooled on the inner wall surfaces of the split molds 1a, 1a through which cooling water is passed, to form a molded product 8.

When the split molds 1a, 1a are opened, the scrap parison remaining between the split mold units 1 (interposed between the molded products) is blown with air into the scrap socket 6, and then the molded product 8 is replaced with the molded product. It is sucked and taken out by the take-out device 5, and sent onto a belt conveyor.

Thereafter, labels are placed on the left and right inner wall surfaces of the opened split molds 1a, 1a by the label placement device 4. The mechanism of the label placement device 4 will be described later. The labels placed on the walls of the split molds 1a, 1a are later fused and integrated with the molded product 8 when hot plastic is pressed against them. In this way, the molded product 8 with the label attached is manufactured during blow molding.

Next, the mechanism of the mold clamping device 37 will be explained with reference to FIGS. 2 and 3.

The rotation of the electric motor 9 is transmitted to the large gear 11 fixed to the rotating shaft 2 via the reducer 10, and the rotor 7 fixed to the rotating shaft 2 is driven to rotate at a constant speed.

On the right side of the rotor 7 is a mold clamping control cam (hereinafter referred to as
A cam (referred to as a cam) 26 is attached to the machine frame, and a cam follower 25 that engages with the cam 26 is pivoted to a slide block 24 that slides in the radial direction of the rotor 7 on a guide 23 that is fixed to the rotor 7. ing. In this way, slide block 2
4 reciprocates in the radial direction as the rotor 7 rotates.

The slide block 24 is further connected to the pin 1 on the rotor 7 via the pin 22, the link 20, and the pin 21.
The central portion of the lever 9 is connected to one end of a lever 18 which is pivotally supported, and causes the lever 18 to swing. The other end of the lever 18 is a pin 17, a link 15, and a pin 16.
It is coupled to the slider 14 via. The slider 14 is slidably supported by a guide rod 35 mounted on the outer periphery of the rotor 7, and together with the lever 18 and link 15 constitutes a slider crank mechanism. That is, as the lever 18 rotates, the slider 14 moves linearly on the guide rod 35.

Also, the slider 14 has a pin 27, a rod 28,
pin 29, lever 30, pin 32, link 33,
It is connected to one of the split holders 13 via a pin 34, and the central part of the lever 30 is connected to the rotor 7.
The slider 14 and the split mold holder 13 move in opposite directions since the lever 30 is pivotally supported by the upper pin 31 and changes the direction of its movement at both ends of the lever 30.

The other split mold holder 12 is connected to the slider 14 via a hydraulic cylinder unit 36 installed on the slider 14.
move in the same direction. That is, the split mold holders 12 and 13 are driven toward or away from each other. Split type holder 1 like this
The split molds 1a, 1a are attached to 2, 13. Clamping pressure is applied to the split molds 1a, 1a by the operation of a hydraulic cylinder unit 36.

The hydraulic cylinder unit 36 is of a type in which the piston rod is pushed out when oil is injected into the cylinder, and the piston rod is pulled into the cylinder by the action of a spring built into the cylinder when the pressure in the pipe leading to the cylinder decreases. . Oil is injected into or discharged from the hydraulic cylinder units 36 by three-way valves (not shown) arranged on the rotor 7 in the same number of sets as the split mold units 1. A supply pipe and a discharge pipe to the three-way valve are collected together, pass inside the rotating shaft 2, and are connected to a hydraulic pump and an oil tank via a rotary joint. The three-way valve is operated by an actuator located near the rotor 7.

And link 15 of the slider crank mechanism
When the lever 18 is aligned through the pins 16, 17, 19, and 21 as shown in the lower part of FIG. 2 (dead center position) and the split mold holders 12 and 13 approach, the three-way valve is activated by the actuator. Then, high pressure oil is injected into the hydraulic cylinder unit 36. At this time, the piston rod is pushed out and the split mold 1 is attached to the split mold holders 12 and 13.
Mold clamping pressure is applied to a and 1a. This mold clamping pressure is received by the pin 19 and the cam follower 25
I can't tell you.

Immediately before the split molds 1a, 1a are opened, the three-way valve is operated by the actuator, and when the inside of the hydraulic cylinder unit 36 communicates with the discharge pipe, the piston is pushed back by the spring inside the hydraulic cylinder unit 36, and the oil in the cylinder is discharged. At the same time, the piston rod is pulled in and the mold clamping pressure is released.
In this state, the split molds 1a, 1a are opened as shown in the upper part of FIG. 2 by the action of the cam 26 and the cam follower 25, but the contact pressure is small because the mold clamping pressure is not transmitted to the cam 26 and the cam follower 25.

Next, the structure of the cam 26 will be explained with reference to FIG. 4.

The cam 26 is for controlling the closing timing and opening timing of the split molds 1a, 1a as described above, and the fixed cam 26a is attached to the machine frame c and controls the closing timing, and the base part is attached to the machine frame c. The fixed cam 2 is operated by the cam driving hydraulic cylinder 112 which supports the
It consists of a movable cam 26b that rotates opposite to one side of the cam 6a and controls the timing of opening.

Further, a mold clamping hydraulic fixed cam 26c is attached to the fixed cam 26a, and the movable cam 26b
A mold clamping hydraulic movable cam 26d is attached to the movable cam 26d so as to move in synchronization with the movable cam 26b.

FIG. 5 is an explanatory diagram showing the state of the cam 26 at the initial stage of blow molding, in which the cam driving hydraulic cylinder 112 is inactive and the movable cam 26b and mold clamping hydraulic movable cam 26 are moved by retraction of the piston rod.
d rotates and is controlled by a fixed cam 26a
The rotation angle of the split mold unit 1 for blow molding from the closing completion time X of the split molds 1a, 1a to the separation start time Y of the split molds 1a, 1a controlled by the movable cam 26b is made small (for example, 175 Accordingly, the fixed cam 26c and the movable cam 26d control the hydraulic pressure valve 113 for hydraulic pressure supply to the cylinder unit 36 for mold clamping.

FIG. 6 shows the shape of the cam 26 at the initial stage of blow molding explained in FIG. 5.

FIG. 7 is an explanatory diagram showing the state of the cam 26 when the normal molding state has passed through the initial stage of blow molding.
The mold clamping hydraulic movable cam 26d rotates, and the split mold 1 controlled by the movable cam 26b starts from the closing completion time X of the split molds 1a, 1a controlled by the fixed cam 26a.
The rotation angle of the split mold unit 1 for blow molding up to the separation start time Y of a and 1a is increased,
(for example, 205 degrees), and as mentioned above, the work space for scrapping defective molded products in the early stage of blow molding is used during the blow molding period.

FIG. 8 shows the shape of the cam 26 during normal blow molding as explained in FIG. 7 above.

Next, the mechanism of the label placement device 4 will be explained with reference to FIGS. 9 to 11 and 15.

The label placement device 4 is attached to the opened split molds 1a, 1.
The label is placed on the inner wall of a, but the 9th
As shown in the figure, it is attached to the rotating shaft 40 and rotates together with the rotating shaft 40. The rotating shaft 40 is rotationally driven by a drive device shown in FIG.
Rubber cups 51, 51 arranged at the tip of the
...are the label take-out devices 80, 80, the split mold 1a,
Position facing the inner wall of 1a (position shown in Figure 9)
It rotates in one direction while repeating stopping at and rotating 180 degrees.

Incidentally, since four or three rubber cups 51 may be provided at equal intervals, the above-mentioned 180° includes 90° and 120°.

The shaft 74 of the drive device is driven so as to rotate once while the split mold unit 1 is being fed in pitch, and the rotation of this shaft 74 is controlled by the geneva stop mechanism 75.
When the shaft 74 rotates once, the shaft 73 is told to rotate 90 degrees and stop once. The rotation of shaft 73 is transmitted to rotary shaft 40 by gears 72 and 71 at a rotational speed ratio of 1:2.

That is, the rubber cups 51, 51... are attached to each split mold 1.
When a, 1a, .

As shown in FIG. 9, links 42, 49, lever holder 41 and dispensing head 5
0 are connected by pins 43, 43, . . . to form four parallelogram links. The lever holder 41 is fastened integrally with the rotating shaft 40.

The segment gear 44 fixed to the base end of the link 42 meshes with the rack 46 fixed to the slide block 45, and when the slide block 45 moves in the axial direction of the rotating shaft 40, the link 42 supported by the lever holder 41 swings around pin 43. The slide block 45 is the 10th
As shown in the figure, it is restrained in the rotational direction by a rotating shaft 40 and supported slidably in the axial direction.

The link 49 is biased toward the center by a tension spring 52, but the cam follower 47 provided on the slide block 45 is
When pushed by a cam 48 fixed to the slide block 45, the slide block 45 moves toward the center and swings the link 42 outward via the rack 46 and the segment gear 44. At this time, as will be described later, the label 67 adsorbed to the rubber cup 51 is attached to one of the split molds 1.
placed on the inner wall of a.

Air suction holes are opened in the inner walls of the pair of split molds 1a, 1a, and the arranged label 67 is held and welded to the plastic molded product 8. Rotating shaft 40
In the upper position, the parallelogram link is supported in position by the cam follower 47 engaging a cam 66 fixed to a bearing device that pivotally supports the rotary shaft 40, and the label 67 is removed from the label take-out device 80. Receive.

The dispensing head 50 transfers the label 67 by vacuum suction and by blowing compressed air. For this purpose, for example, the front label dispensing head 50 is provided with two rubber cups 51, 51 and an air jet nozzle 68, as shown in FIG. 55 and a rotary joint 64 to a vacuum pump, and the air jet nozzle 68 is connected to a compressed air tank via a flexible hose 62, a solenoid valve 56 and a rotary joint 65, respectively.

A dispensing head for the front label and a dispensing head for the back label are provided on the same side of the rotating shaft 40 in order to apply labels to the front and back sides of the molded product 8.These rubber cups are connected to the flexible hose 57, The air jet nozzle is connected to the solenoid valve 55 via a flexible hose 61 and to the solenoid valve 56 via a flexible hose 61. However, rotation axis 4
Another solenoid valve is connected to the dispensing head on the opposite side from zero.

These flexible hoses are fixed to the rotating shaft 40 via blocks 53 and 54, as shown in FIG. 11, and communicate with the solenoid valve through a hollow hole in the rotating shaft 40. These solenoid valves are opened and closed by the current flowing through the slip ring 63 (FIG. 9). The current flowing through the solenoid valves is controlled based on the signal from the rotation angle sensor of the rotor 7, and the dispensing head 50 is controlled based on the signal from the rotation angle sensor of the rotor 7. When receiving the label 67 from the label take-out device 80, the label 67 is sucked by the rubber cup 51, and then one of the split molds 1a
When the label 67 is placed on the inner wall of the label 67, air is blown onto the label 67 by an air jet nozzle 68.

Next, the label take-out device 80 will be explained with reference to FIGS. 12 to 14 and FIG. 16.

The frame 81 is supported by the shaft 82 and the drive shaft 83 and rotates intermittently by 180 degrees, and the shaft 96 is supported by the drive shaft 83.
It rotates back and forth once when it is stopped.

The operation of the label take-out device drive device 84 that drives the shaft 96 and the drive shaft 83 will be explained with reference to FIG. 16.

The shaft 85 is driven to rotate once while the split mold unit 1 is being fed in pitch, and the rotation of the shaft 85 is controlled by the geneva stop mechanism 86 and the gears 88, 89.
This tells the shaft 83 to rotate 180 degrees and once stop when the shaft 85 rotates once. Further, the rotation of the shaft 85 is transmitted by the Geneva stop mechanism 87 and gears 90, 91 so that when the shaft 85 rotates once, the shaft 92 rotates 360 degrees and once stops. Moreover, the shaft 92 rotates while the drive shaft 83 is stopped.

The stop position of the drive shaft 83 is such that the frame 81 fixed thereto is in the position shown in FIGS. Stop at a position. While the drive shaft 83 is stopped, the shaft 96
2 links 93, 94, 95 and pin 9
It rotates back and forth once through 8 and 99.

As shown in FIG. 14, a pair of opposing shafts 10
A lever 101 whose central portion is fixed to 0,100,
Both ends of 101 are connecting rods 102,1
02 to form a parallelogram link, and the shafts 100, 100 are connected to a frame 81 and guide rod stays 108, 108 as shown in FIG.
The lever 101,
101 are urged in the same direction by tension springs 103, 103.

As described above, when the shaft 96 reciprocates once, the lever 97 fixed thereto swings once between the position shown by the solid line in FIG. 14 and the position shown by the two-dot chain line. At this time, the lever 101 is pushed and swung, causing the shafts 100, 100 to rotate. Then, the lever 1 fixed to the shafts 100, 100
04, 104 swings, causing the cam followers 105, 105 engaged therewith to reciprocate.

The cam followers 105, 105 are supported by slide blocks 106, 106, and the slide blocks 106, 106 are further supported by guide rods 10 supported by guide rod stays 108, 108.
7, 107, the slide blocks 106, 106 are slidably supported by the levers 104, 107.
It reciprocates with the rocking of 104.

At this time, the rubber cups 109, 109 and air jet nozzles 110, 110 provided on the slide blocks 106, 106 are connected to the label magazine 11.
receives the label 67 from the label placement device 4;
The control of a solenoid valve (not shown) for this purpose is similar to that of the label placement device 4.

The rubber cup 109 that has received the label 67 from the label magazine 111 in this way is
When the frame 81 rotates 180 degrees in the direction of the arrow in the figure, it comes to a position facing the label placement device 4, and then when the slide block 106 reciprocates, it passes the label 67 to the label placement device 4.

[Effects of the Invention] As explained above, the mold clamping device in the rotary blow molding machine according to the present invention is composed of a slider crank mechanism and a hydraulic cylinder mechanism, and when the slider crank mechanism takes the dead center position, the hydraulic cylinder Since the mold clamping pressure is applied to the split mold holder by the unit, fluctuations in the load driving the rotor are small, preventing uneven rotational speed of the rotor, and the pressure acting on the cam is small, so that the cam, cam follower, etc. It is possible to obtain the effect of being less likely to wear out.

Furthermore, since the mold clamping control cam consists of a fixed cam (for controlling the closing timing of the split mold) and a movable cam (for controlling the opening timing of the split mold), it is possible to eliminate defective molded products that are required in the early stages of blow molding. The work space for scrapping can be used for the normal blow molding period, and by extending the cooling period during molding, the cooling effect can be increased and high quality molded products can be obtained.

In addition, when checking mold installation, mold alignment, scrap cutting, etc., if you work in the area of the movable cam, you can check without rotating the rotor to the mold clamping position, greatly improving work efficiency. Improvement can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a rotary blow molding machine using the present invention, Fig. 2 is a partially omitted front view of the machine,
Figure 3 is a partially omitted right side view of the same machine, Figure 4 is a front view of the mold clamping control cam of the same machine, Figure 5 is an explanatory diagram of the control cam in the early stage of blow molding, and Figure 6 is the same control cam as above. 7 is an explanatory diagram of the control cam during normal blow molding, FIG. 8 is a front view of the same control cam, and FIG. 9 is a front view showing a partial cross section of the label placement device of the same machine. Figure 10 is - in Figure 9.
11 is a sectional view taken along line XI-XI in FIG. 9, FIG. 12 is a sectional view taken along line XII-XII shown in FIG. , FIG. 14 is a view taken in the direction of the arrows in FIG. 12, FIG. 15 is a schematic diagram showing the drive mechanism of the label placement device used in the same machine, and FIG. 16 is a schematic diagram showing the drive mechanism of the label take-out device used in the same machine. It is. DESCRIPTION OF SYMBOLS 1... Split mold unit, 1a, 1a... Split mold, 2... Rotating shaft, 3... Extrusion die, 4... Label placement device,
5... Molded product removal device, 6... Scrap socket,
7... Rotor, 8... Molded product, 9... Electric motor, 10... Reducer, 11... Large gear, 12, 13... Split mold holder, 14... Slider, 15... Link, 16, 1
7... Pin, 18... Lever, 19... Pin, 20... Link, 21, 22... Pin, 23... Guide, 24...
Slide block, 25...Cam follower, 26
...Mold clamping control cam, 26a...Fixed cam, 26b...
Movable cam, 27... pin, 28... rod, 29... pin, 30... lever, 31, 32... pin, 33... lever, 34... pin, 35... guide rod, 36...
Hydraulic cylinder unit, 37... Mold clamping device, 4
0... Rotating shaft, 41... Lever holder, 42... Link, 43... Pin, 44... Segment gear, 45
...Slide block, 46...Rack, 47...Cam follower, 48...Cam, 49...Link, 50...
Dispensing head, 51...Rubber cup, 5
2...Tension spring, 53, 54...Block, 55,
56...Solenoid valve, 57, 58, 59, 60, 61,
62...Flexible hose, 63...Slip ring, 64, 65...Rotary joint, 66...Cam, 67...Label, 68...Air jet nozzle, 7
1, 72...Gear, 73, 74...Shaft, 75...Geneva stop mechanism, 80...Label take-out device, 81
... Frame, 82 ... Axis, 83 ... Drive shaft, 84 ... Label take-out device drive device, 85 ... Axis, 86, 8
7...Geneva stop mechanism, 88, 89, 90, 9
DESCRIPTION OF SYMBOLS 1...Gear, 92...Shaft, 93,94,95...Link, 96...Shaft, 97...Lever, 98,99...Pin, 100...Shaft, 101...Lever, 102...Connecting rod, 103...Tension spring, 104
...Lever, 105...Cam follower, 106...Slide block, 107...Guide rod, 108
...Guide rod stay, 109...Rubber cup, 1
10... Air jet nozzle, 111... Label magazine.

Claims (1)

[Claims] 1. A large number of split mold units consisting of a pair of split molds that can be opened and closed in the horizontal axis direction are arranged at equal intervals around the outer periphery of a rotor that rotates around a horizontal axis, and each of the split molds that is opened is In a rotary blow molding machine that extrudes a parison in between, then closes a split mold and blows air into the hollow part of the parison to form a hollow molded product, a pair of split mold holders that hold the pair of left and right split molds, respectively, One split mold holder is slidably supported by a guide rod mounted on the rotor, and one split mold holder is coupled via a hydraulic cylinder unit to a slider slidably supported by the guide rod, and the other split mold holder is The slider is coupled to the slider via a lever so as to move in opposite directions to the slider, and the slider moves in the radial direction of the rotor with a cam follower that engages with a mold clamping control cam installed near the rotor. The hydraulic cylinder unit is connected via a slider crank mechanism that can hold the mold and take the dead center position, and when the slider crank mechanism takes the dead center position, mold clamping pressure is applied to the split mold holder by the hydraulic cylinder unit. A mold clamping device for a rotary blow molding machine featuring: 2. The mold clamping control cam that the cam follower of the mold clamping device according to claim 1 engages is a fixed cam on the closing control side of the split mold and a movable cam on the opening control side, so that the opening timing of the split mold is variable. A control cam for a mold clamping device in a rotary blow molding machine. 3. A fixed cam is fixed to a machine frame of a rotary blow molding machine, and a movable cam is operated by a cam driving hydraulic cylinder whose base is pivotally supported on the machine frame.
Control cam for the mold clamping device described. 4 Attach the mold clamping hydraulic fixed cam to the fixed cam,
A mold-clamping hydraulic movable cam is attached to the movable cam, the mold-clamping hydraulic movable cam is movable in synchronization with the mold-clamping movable cam, and the hydraulic pressure supply period to the mold-clamping hydraulic cylinder unit is variable. 3. The control cam for a mold clamping device according to 3.