JPH0359813B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a hollow molded product of different diameters and an apparatus therefor.

Conventionally, when manufacturing products with locally varying diameters using the blow molding method, methods such as setting the parison wall thickness thicker according to the large diameter part and delaying the mold clamping time of the small diameter part are used to reduce the size of the small part. A method was adopted in which a part of the wall thickness was cut off by a mold to make the wall thickness of the molded product uniform. However, in the case of using the above method, the material that is cut into pieces is wasted, and it takes time and effort to deburr that part. or,
Ducts used in the intake system of automobile engines often have a bellows structure in their small diameter portions, and the generation of burrs in the above method causes a reduction in the elasticity of the bellows. Furthermore, although the cut-off portions are connected by the pressure of mold clamping, the strength of the portions is inevitably reduced to some extent.

In order to eliminate the above drawbacks, a method has been proposed in which the thickness of the parison 1 is selectively increased in accordance with the large diameter portion A of the shape to be formed, as shown in FIG. In this case, as shown in Fig. 2a, uniformity in the wall thickness of the small diameter part B of the molded product can be obtained, but in the large diameter part A, the enlargement ratio due to blowing is large, as shown in Fig. 2b. The thickness becomes uneven.

The present invention has been made in view of the above points, and provides a manufacturing method that allows blow molding of a hollow molded product with a uniform wall thickness without generating burrs even if the diameter is locally extremely different, and the manufacturing method thereof. The purpose is to provide equipment.

Hereinafter, the configuration of the present invention will be explained based on specific examples. First, one embodiment of a manufacturing apparatus in which the method of the present invention is implemented will be described based on the schematic diagram of FIG. In FIG. 3, a parison extruder 2 equipped with a screw 3 inside is provided with a nozzle 4 for dispensing the parison. The synthetic resin material is heated and melted and supplied to the nozzle 4 as the screw 3 rotates. The nozzle 4 includes a mandrel 4a provided in the center so as to be movable in the vertical direction, and an outer cylinder 4b surrounding the mandrel 4a. A space of a predetermined width is secured between the mandrel 4a and the outer cylinder 4b to form an annular channel 5 through which the molten material flows.
is formed, and this flow path 5 and the flow path 2a inside the extruder 2 are communicated with each other. The lower end of the mandrel 4a is formed into a tapered shape, and the diameter of the flow path 5 is gradually reduced along this, forming a spout E of the parison. By moving the mandrel 4a up and down, the flow path width at the spout E is changed, thereby controlling the amount of raw material spouted per hour. For example, in this example, mandrel 4
The lower end surface of a is the height of the lower end surface of the outer cylinder 4b.
The amount of material poured out is minimum in the state aligned with H ₀ , and increases from this state as the mandrel 4a is moved upward as shown by the two-dot chain line. An air hole 4c for injecting pressurized air into the parison is bored in the center of the mandrel 4a. The upper end of the mandrel 4a protruding from the nozzle 4 is connected to a hydraulic cylinder 5, which is communicated with a hydraulic pump 7 via a servo valve 6 connected to a computer 8. Therefore, the servo valve 6 is operated according to instructions from the computer 8, the supply of oil from the hydraulic pump 7 to the hydraulic cylinder 5 is adjusted, and the vertical movement of the mandrel 4a is controlled.

Thus, the air hole 4c is communicated with a pressurized gas source 10 via a pressure regulator 9. The pressure regulator 9 of this example is branched into four parallel flow paths, each branched flow path is provided with a pressure regulator 9a, and a pair of shut-off valves 9b, 9 are provided before and after the pressure regulator 9a.
b is arranged and configured. It is also possible to use only one of the shutoff valves 9b, but by providing one pair as in this example, it becomes possible to adjust the pressure more accurately and with good responsiveness. And each shutoff valve 9b
is connected to the computer 8 mentioned above. or,
A relief passage P is branched from a suitable position in the passage between the pressure regulator 9 and the air hole 4c, and a relief valve 11 connected to the computer 8 is interposed in this relief passage P, and its tip is open to the atmosphere. has been done.

An embodiment of the method of the present invention, which is carried out by the manufacturing apparatus configured as described above, will be described below. Before starting the pouring of the parison, the regulated pressure value of each pressure regulator 9a of the pressure regulating device 9 is set. For example, the adjusted pressure value of the pressure regulator 9a of the first branch channel B1 is set so that 1.2 kg/cm ² of pressurized air is supplied to the spout E when this channel is selectively opened. However, the pressure regulators 9a of the other second, third, and fourth branch channels B2, B3, and B4 are similarly set to 1.3, 1.4, and 1.5 Kg/cm ² , respectively. By setting different adjustment pressure values for each of the branch channels B in this way, only one of the four channels will be opened.
By selecting these, pressurized fluids with at least four different pressures can be supplied, and by appropriately combining the branch channels to be opened, pressurized air with even more different pressures can be supplied.

Pressurized gas of, for example, about 5 kg/cm ² is applied from the pressurized gas source 10 to the pressure regulating device 9, and the extruder 2 is also activated to make it possible to start pouring out the parison. At this time, all the shutoff valves 9b are closed and only the relief valve 11 is open.

The amount of raw material to be poured and the pre-discharge of pressurized air (pre-blow) are determined by the computer 8 based on a program created according to the shape of the product to be molded.
is appropriately controlled, and a parison with uniform wall thickness and locally varying diameters is poured out. Hereinafter, the control method will be explained in detail based on the time chart shown in FIG. First, the thickness p of the pressurized air is equal to the atmospheric pressure and the material is poured out, corresponding to the small diameter part G _A of the product to be molded (indicated by the shape of the cavity 12a of the mold 12) shown in FIG. The small diameter part g _A of the parison is formed under conditions where the quantity m is minimum and is fed into the corresponding cavity 12a. Therefore, the tip end surface of the mandrel 4a in this case is located at the lowermost portion _H0 , which coincides with the tip end surface of the outer cylinder 4b.

Next, in response to the first large diameter portion G _B of the product, the computer 8 selectively opens the pair of shutoff valves 9b in the first branch flow path B1, and operates the servo valve 6 to open the hydraulic cylinder 5. is activated to raise the mandrel 4a by a predetermined amount corresponding to the increase in the diameter of the product. In this case, the start timing of each operation is set so that the discharge of pressurized air is started with a delay of time Tα after the start of the increase in the material dispensing amount m. Furthermore, as shown in Fig. 4, since the rise of the material pouring amount m is not sharp and forms a unique slope, it is necessary to manipulate the rise of the air pressure p in the parison so that it follows this and forms a similar slope. However, in this example, this can be easily achieved by appropriately operating the pair of shut-off valves 9b. Shutoff valve 9b and servo valve 6 as shown above
By operating, the material pouring amount m increases by Δm and air pressurized to 1.2 kg/cm ² is pre-blown into the parison. Then, this operation state is changed to times T ₁ and T ₂ corresponding to the first large diameter portion shape G _B , respectively.
, and then returns to the initial state I corresponding to the next small diameter section G _A. That is, the relief valve 11 is opened by the support of the computer 8, and the branch flow path B1 is opened.
The shutoff valves 9b, 9b are closed as appropriate, and the servo valve 6 is operated to open the hydraulic cylinder 5.
The direction of the hydraulic pressure is switched and the mandrel 4a is lowered to the initial level _H0 .

In this case as well, it is necessary to reduce both the material pouring amount m and the pre-blow pressure p at substantially the same gradient as in the case of startup. However, regarding the point at which each valve starts to decrease, the pre-blow pressure p is set in advance, contrary to the rise time, and the operation specifications for each valve are set so that the drop in the pouring amount m is delayed by the time T〓. has been done. In this way, each operating factor m, p
The reason why there is a time difference between the start of the rise and the start of the decline is that, as shown in _{FIG .}
Q ₁ part, which expands rapidly in g _B , is inevitably prone to lack of material, so a large amount of material is poured into this Q ₁ part in advance to compensate for the lack of material and prevent the wall thickness from becoming thinner. It is. Further, in the opposite contraction part _Q2 , there is also a shortage of material, so in this case, the decrease in the amount of material poured out m is delayed from the decrease in the pre-blow pressure p.

Next, a second large diameter part _g'B of the parison is formed by _a similar operation corresponding to the second large diameter part G'B of the product.
In this case, since the diameter D' of the second large diameter part G' _B of the product is larger than the diameter D of the first large diameter part G _B , the pre-blow pressure p and material pouring amount m will be correspondingly high. is set to . That is, according to instructions from the computer 8, the mandrel 4a is raised higher than the previous time, and the second branch circuit B2 with a set pressure of 1.3 kg/cm ² is selectively opened. In this case as well, the time difference T' is set as in the previous pre-blow, and its length is ensured to be longer in accordance with the expanded portion of the second large diameter portion _G'B . Similarly, the duration of the high value state of each operating factor m, p
T' ₁ , T' ₂ and the time difference T' at the time of contraction are also set corresponding to the length L' and diameter D' of the second large diameter part G' _B of the product, and each valve is adjusted according to this. The operation is performed.

As described above, the setting specifications for each valve operation corresponding to the product shape are set in the computer 8 as a program, and the computer 8 controls the servo valve 6 and each shutoff valve 9 based on this program.
b and the relief valve 11 to locally form large diameter portions g _B , corresponding to the product shape as shown in FIG.
The parison g having a different diameter _g'B can be poured out with a uniform thickness and continuously supplied along the cavity 12a of the mold 12. After this, the mold is clamped and full-scale blow molding is carried out at a pressure higher than the pre-blow pressure p, so that even if the wall thickness is at the small diameter section G _A , it is still the same at each of the large diameter sections G _B and G' _B. Uniform hollow molded products with different diameters can be obtained even if

In the above embodiment, the pressure regulating device 9 for controlling the pre-blow pressure p was branched into four parallel channels B, but the number of branch channels is not limited to four and can be varied depending on the desired shape of the molded product. The optimum number of flow paths may be selected depending on the flow rate, and it is also possible to configure one variable flow rate control valve to be operated by a computer without branching. Furthermore, it is also possible to control the pre-blow pressure p by operating the valves using a sequence circuit combined with a timer or the like without using a computer.

As described in detail above, according to the present invention, when forming a parison, the amount of raw material poured out per hour and the gas pressure inside the parison are changed in accordance with the shape of the molded product, thereby achieving a uniform wall thickness. It becomes possible to form a parison of a desired shape. Therefore, by pouring the parison using this method, even molded products with different diameters where the diameter locally changes drastically,
Blow molding can be performed to a uniform wall thickness, and hollow molded products of different diameters with excellent strength can be easily obtained. It should be noted that the present invention should not be limited to the specific embodiments described above, and it goes without saying that various modifications can be made within the technical scope of the present invention.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a conventional manufacturing method of a hollow molded product of different diameters, Figs. 2a and 2b are sectional views showing the cross section of a product obtained by the conventional manufacturing method, The figure shows one of the manufacturing equipment that implements the method of the present invention.
FIG. 4 is a schematic diagram showing an example of the method of the present invention.
FIG. 5 is a time chart showing changes in material pouring amount m and pre-blow pressure p in an example, and FIG. 5 is an explanatory diagram showing an example of the present invention. (Explanation of symbols), 1: parison, 4a: mandrel, 6: servo valve, 8: computer,
9: Pressure regulator, 9a: Shut-off valve,
G _A : Small diameter part (product), g _A : Small diameter part (parison),
G _B : first large diameter section (product), g _B : first large diameter section (parison), G' _B : second large diameter section (product), g' _B : second large diameter section (parison).

Claims (1)

[Scope of Claims] 1. In a method for manufacturing a hollow molded product of different diameters whose diameter changes, when a molten raw material is poured out from a nozzle to form a parison, the raw material is A method for manufacturing a hollow molded product of different diameters, characterized in that a parison is formed by changing the pouring amount per hour and the gas pressure inside the parison, and the parison is housed in a mold and then blow molded. 2. In the above item 1, the gas pressure is increased in accordance with an increase in the amount of the raw material poured out, and is decreased in accordance with a decrease in the amount of poured out raw material, the hollow molded product having different diameters. manufacturing method. 3 In Paragraph 2 above, between the time when the gas pressure increases and the time when the amount of raw material poured out increases, and between the time when the gas pressure decreases and the time when the amount of poured out material decreases, A method for manufacturing a hollow molded product of different diameters, characterized in that a time difference is set in accordance with the shape of the product. 4. A nozzle equipped with a spout for pouring out molten raw material to form a parison, and a passage hole for blowing pressurized gas into the parison, and a pressurized gas source for supplying pressurized gas to the passage hole. , a pressure adjusting means interposed between the pressurized gas source and the communication hole to adjust the pressure of the pressurized gas, a pouring amount adjusting means to adjust the pouring amount of the raw material, and a product to be molded. A manufacturing apparatus for a hollow molded product of different diameters, comprising a control means for controlling the operation of the pressure adjustment means and the pouring amount adjustment means according to the shape.