JP4093672B2 - Rotational molding method and rotational molding machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rotational molding method and a rotational molding machine that rotate a mold while heating to mold a molded product. This rotational molding method and rotational molding machine are suitable for molding hollow molded products such as automobile equipment, streetlight shades, mannequins, etc., and more particularly suitable for molding transparent hollow molded products.
[0002]
[Prior art]
The following two types are known as conventional rotational molding methods and rotational molding machines.
(1) A rotary molding machine that rotates a mold around a single axis. For example, in the rotary molding machine shown in FIG. 8, the mold 101 is rotatably supported on the machine frame 103 by a shaft 102 and is driven to rotate by a motor 104. Since this type of rotary molding machine has a single axis of rotation, it is easy to supply a heat medium to the mold. Therefore, a heating pipe 105 is provided in contact with the mold body 108 of the mold 101 (line contact), and the heating pipe 105 is connected to the steam supply device 106. At the time of rotational molding, a powdery or gel-like thermoplastic resin material 107 is put into the mold 101, the mold 101 is rotated while being heated by supplying steam, and the resin material 107 is melted and adhered to the mold surface. A molded product is taken out after the mold 101 is cooled by spraying a water shower or the like.
[0003]
(2) A molding machine that rotates the mold around two orthogonal axes. Since this type of rotary molding machine has two rotation axes, it has not been possible to supply a heat medium to the mold. Therefore, the mold was heated from outside by a burner flame, radiant heat of an electric heater, or the like. The mold was cooled by spraying a water shower.
[0004]
[Problems to be solved by the invention]
According to the rotational molding machine of (1) above, since the mold 101 is rotated around a single axis, the resin material 107 is thickly attached to the mold surface around the rotational axis, and the mold surface is perpendicular to the rotational axis. There was a risk that the thickness of the molded product would be non-uniform, such as thin adhesion. Further, in the case of a molded product having a complicated shape, in order to attach the resin material 107 to each part of the mold surface with a predetermined thickness, it is necessary to rotate the mold 101 for a long time or to increase the heating temperature. There are problems that the molding efficiency is lowered, the color of the resin material 107 is discolored (often yellowing), and the physical properties are lowered. In addition to the rotation, attempts have been made to swing the mold 101, but these problems have not been solved.
[0005]
According to the rotary molding machine of (2) above, since the mold is heated from a remote location by a burner flame, radiant heat of an electric heater, etc., the accuracy of the mold heating temperature control is low and the mold temperature distribution is uniform. Since the property is low, there is a problem that the thickness of the molded product becomes uneven and the inner surface is wavy. In particular, in the case of a transparent hollow molded product, if waviness occurs on the inner surface, it appears to be distorted from the outside, so it is difficult to mold the transparent hollow molded product by rotational molding. It was virtually impossible to rotationally mold a large transparent resin molded product with a beautiful appearance.
[0006]
In addition, it takes a long time to heat the mold in the burner flame and the radiant heat of the electric heater, and it takes a long time to cool the mold in spraying a water shower. As a specific example, when a powdered polycarbonate resin material is used and the heating temperature of the mold is set to 280 ° C., it takes about 40 minutes to reach the heating temperature. Also, it took about 20 minutes from the same heating temperature to sufficiently cool the mold. Accordingly, the time required for one rotation molding is 60 minutes or more, and the molding efficiency is very low, and the resin material may be discolored and deteriorated in physical properties. Moreover, the precision of the control of the heating temperature is low, and the heating temperature is different each time it is heated.
[0007]
Therefore, the object of the present invention is to improve the temperature control accuracy of the mold and the uniformity of the temperature distribution, and a rotational molding method capable of efficiently rotationally molding a hollow resin molded product having a smooth inner surface in a short time. It is to provide a rotary molding machine.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the following measures were taken.
[A] A first shaft (5), a U-shaped swivel body (4) whose end is supported by the first shaft (5), and a first swivel member supported rotatably at the center of the swivel body (4). A rotary molding machine comprising a two-axis (11) and a mold (70) attached to the second axis (11), wherein the first axis (5) and the swivel body (4) rotate integrally. The second shaft (11) is configured to rotate and rotate independently of the first shaft (5) and the swivel body (4), and the mold (70) is a shell-shaped mold body having a molding surface on the surface. (74) and a temperature control pipe (76) surface-coupled to the back surface of the mold body (74), the second shaft (11) is formed in a hollow shape, The pipe (54) is inserted, and an oil passage (55) for sending oil to the temperature control pipe (76) is formed by a gap between the outer peripheral surface of the pipe (54) and the inner peripheral surface of the second shaft (11). The rotary molding machine is characterized in that the oil that has passed through the temperature control pipe (76) passes through the inside of the pipe (54).
[B] Using the rotary molding machine described in A above, heated oil is supplied to the temperature control pipe (76) to heat the mold body (74) rapidly and uniformly, and the first shaft (5) and the swivel body (4) and the second shaft (11) are swirled and rotated independently of the first shaft (5) and the swiveling body (4), and a powdery or gel-like thermoplastic resin material is obtained. After rotating and molding a hollow resin molded product by melting and adhering to the molding surface of the heated mold, a cooled oil is supplied to the temperature control pipe (76) to cool the mold body (74) rapidly and uniformly. The rotational molding method characterized by solidifying the rotationally molded resin molded product.
In these means, the following aspects can be taken.
(1) Oil heated from the outside of the mold to the temperature control tube using a mold including a shell-shaped mold body having a molding surface on the surface and a temperature control tube surface-bonded to the back surface of the mold body The mold body is heated rapidly and uniformly, the mold is rotated around two axes having different directions, and the powdery or gel-like thermoplastic resin material introduced into the mold body is applied to the molding surface. It is melt-adhered and rotationally molded, and the mold body is rapidly and uniformly cooled by supplying cooled oil to the temperature control tube from the outside of the mold, and the rotationally molded product is solidified and then the rotation is stopped. A rotational molding method characterized by the above.
[0009]
(2) Use of a mold including a shell-shaped mold body having a molding surface on the surface, an electric heater directly coupled to the back surface of the mold body, and a temperature control tube surface-coupled to the back surface of the mold body A powder-like or gel-like thermoplastic resin that is supplied to the electric heater, rapidly and uniformly heats the die body, rotates the die around two different axes, and is put into the die body The material is melt-adhered to the molding surface and rotationally molded. The cooled body is rapidly and uniformly cooled by supplying cooled oil to the temperature control tube from the outside of the mold, and the rotationally molded molded product is solidified. The rotation molding method is characterized in that the rotation is stopped.
[0010]
The rotational molding methods of (1) and (2) are not particularly limited in the type and color of the thermoplastic resin, but the inner surface is particularly visible because of the effect that the inner surface of the molded product is less likely to swell. In other words, it is optimal when the thermoplastic resin is a transparent resin and the molded product is a transparent resin molded product. Here, “transparent” means not only colorless and transparent, but also includes colored and translucent.
[0011]
The rotational molding methods of (1) and (2) are not particularly limited in the heating temperature of the mold body. However, the heating temperature of the mold body is 200 to 200, which is a high temperature range in which discoloration of the resin and deterioration of physical properties are problematic. It is optimal when it is 320 ° C. Since this method has the effect of heating and cooling the mold body rapidly and minimizing the amount of heat applied to the resin, it can prevent resin discoloration and physical properties from being lowered even in such a high temperature range. Because.
[0012]
In these rotational molding methods (1) and (2), the heating time of the mold body is preferably less than 30 minutes, and the cooling time of the mold body is preferably less than 15 minutes. This is to increase molding efficiency and to prevent discoloration and deterioration of physical properties of the resin.
[0013]
(3) A machine frame, a revolving body supported rotatably on the machine frame by a first axis, a means for rotationally driving the revolving body, and a second direction in which the first axis differs in the revolving body. A mold rotatably supported by a shaft, and means for rotationally driving the mold, the mold being surface-bonded to a shell-shaped mold body having a molding surface on the surface, and a back surface of the mold body An oil supply device provided outside the mold, and a piping mechanism for circulating oil between the oil supply device and the temperature control tube. A rotary molding machine including a first rotary joint provided on a second rotary joint provided on a second shaft.
[0014]
In the rotary molding machine of (3), the fact that the temperature control tube is surface-bonded to the back surface of the mold body means that the temperature control tube and the back surface of the mold body are not in line contact but joined via a surface having an area. It means that it has been. This is because the temperature of the temperature control tube is uniformly transmitted to the back surface of the mold body with high conductivity. The mode of surface bonding is not particularly limited, but the temperature control tube is disposed so as to contact the back surface of the mold body, and a thin body having a plurality of through holes and having conductivity on the surface is used as the temperature control tube. Covered from the back side and temporarily fixed to the mold body, an electroformed coating part is electroformed on the back surface of the mold body, the temperature control tube and the thin body, and the thin body and the electroformed coating part are interposed therebetween. Thus, it is preferable that the temperature control tube is surface-bonded to the back surface of the mold body.
[0015]
Moreover, it is preferable to arrange | position a 1st axis | shaft and a 2nd axis | shaft on two straight lines orthogonal at the approximate center of a type | mold so that a type | mold can be rotated with sufficient balance.
[0016]
Further, an oil heater and an oil cooler may be provided in the oil supply device so that the heating oil and the cooling oil can be selectively supplied to the mold body.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIGS. 1 to 4, the machine casing 1 of the rotary molding machine includes a base 2 and a pair of left and right stands 3. A U-shaped revolving body 4 is arranged between the stands 3, and a first shaft 5 is provided at the upper end of the stand 3, and the revolving body 4 can be rotated around the horizontal axis on the machine frame 1 by the first shaft 5. It is supported by. One stand 3 is provided with a motor 6, and its output shaft is connected to one first shaft 5 via gears 7 and 8, and the motor 6 constitutes a means for driving the revolving body 4 to rotate.
[0018]
A mold mounting member 10 is disposed inside the revolving body 4, a second shaft 11 is provided at a substantially central portion of the revolving body 4, and the mold mounting member 10 is connected to the revolving body 4 by the second shaft 11. Is supported so as to be rotatable about an axis perpendicular to the axis. A motor 12 is installed at the corner of the revolving body 4, and its output shaft is connected to the second shaft 11 through a chain wheel 13, a chain 14, and a chain wheel 15, and the motor 12 drives the mold mounting member 10 to rotate. Means. The power supply line 16 (see FIG. 2) of the motor 12 is wired through the first shaft 5.
[0019]
A die 70 is placed on the upper surface of the die attaching member 10 and attached by attaching means such as a bolt 18. As shown in FIG. 7, the mold 70 is a split mold composed of an upper mold 71 and a lower mold 72 that can be opened and closed. Both the upper mold 71 and the lower mold 72 are a box-shaped support frame 73 and a support frame. 73, a shell-shaped mold main body 74 supported on 73 and having a molding surface 75 on the surface, and a temperature control tube 76 surface-bonded to the back surface of the mold main body 74. The first shaft 5 and the second shaft 11 are arranged on two straight lines that are orthogonal to each other at the approximate center of the mold 70.
[0020]
The die body 74 of this embodiment is a nickel alloy shell produced by electroforming, and has a wall thickness of about 3 mm and a molding surface 75 having a spherical surface with a diameter of 260 mm. On the back surface of the mold main body 74, a continuous temperature adjusting tube 76 made of copper and having an outer diameter of 10 mm and a wall thickness of 1 mm is disposed so as to be in contact with each other. The pitch between the centers of the adjacent temperature adjusting tubes 76 is 30 to 100 mm. It is evenly arranged. A 14-mesh metal mesh 77 made of a stainless steel wire having a wire diameter of 0.3 mm is put on the temperature control tube 76 in a mountain shape from the back side, and the metal mesh 77 is temporarily fixed to the die body 74 by spot welding. . On the back surface of the mold main body 74, the temperature control tube 76 and the metal mesh 77, a copper electroformed coating portion 78 is electroformed. The mesh of the metal mesh 77 is closed with an electroformed coating portion 78. In addition, since the electroformed coating portion 78 is also attached between the wire mesh 77 and the back surface of the die main body 74 and between the wire mesh 77 and the temperature adjustment pipe 76 through a large number of meshes of the wire mesh 77, the temperature adjustment is performed. The tube 76 and the back surface of the mold body 74 are firmly bonded by surface bonding and are also firmly bonded thermally.
[0021]
An oil supply device 26 is installed at one end of the base 2. The oil supply device 26 includes an oil heater 27, an oil cooler 28, a pump 29, an outlet side valve 30, and an inlet side valve 31. By switching the valves 30 and 31, heating oil or cooling oil is provided. Can be selectively supplied to the internal piping of the mold 70.
[0022]
A piping mechanism 33 for circulating heating oil or cooling oil is provided between the oil supply device 26 and the mold 70. This piping mechanism 33 passes heating oil or cooling oil from the oil supply device 26 through a path of piping 34 → first rotary joint 35 → pipe 36 → second rotary joint 37 → lower branch pipe 38 → pipe 81. It is sent to the temperature control pipe 76 of the upper mold 71. The oil that has heated or cooled the mold main body 74 of the upper mold 71 through the temperature control pipe 76 is sent to the temperature control pipe 76 of the lower mold 72 through the communication pipe 83 in the mold 70. The oil that has heated or cooled the die main body 74 of the lower die 72 through the temperature control pipe 76 is a path of the pipe 82 → the upper branch pipe 39 → the second rotary joint 37 → the pipe 40 → the first rotary joint 35 → the pipe 41. It is configured to pass through and return to the oil supply device 26. The first rotary joint 35 is provided on the first shaft 5, and the second rotary joint 37 is provided on the second shaft 11.
[0023]
As shown in FIG. 5, the second shaft 11 is formed in a hollow shape and is rotatably supported by the revolving body 4 by a pair of upper and lower bushes 43 and 44. The chain wheel 15 is inserted into the middle portion of the second shaft 11 via a key 45, and a screw 46 is formed at the lower end portion of the second shaft 11. A nut 47 is fastened to the screw 46, and a rotating shaft 48 of the second rotary joint 37 is coupled to the nut 47 with a bolt 49.
[0024]
The upper end of the second shaft 11 is provided with a flange 50 fixed to the mold mounting member 10, an outlet 51 connected to the lower branch pipe 38, and an inlet 52 connected to the upper branch pipe 39. Yes. A pipe 54 is inserted inside the second shaft 11, and an oil passage 55 is formed by a gap between the pipe 54 and the second shaft 11. The upper end of the pipe 54 communicates with the inlet 52, and the upper end of the oil passage 55 communicates with the outlet 51.
[0025]
As shown in FIG. 6, the rotary shaft 48 is rotatably supported by a body 57 of the second rotary joint 37 by a pair of bearings 58 and 59, and a lower end portion of the pipe 54 is inserted therein. A gap between the pipe 54 and the rotary shaft 48 forms a passage 60, and the passage 60 is connected to an oil passage 55 on the second shaft 11 side. The body 57 is provided with an inlet 61 and an outlet 62, the inlet 61 communicates with the passage 60 through the hole 63 of the rotating shaft 48, and the outlet 62 communicates with the pipe 54.
[0026]
The body 57 is prevented from rotating by pipes 36 and 40 (see FIG. 2) connected to the inlet 61 and the outlet 62. The second rotary joint 37 includes a seal ring 64 that seals the gap between the body 57 and the rotary shaft 48, a spring 65 that presses the flange portion 48 a of the rotary shaft 48 against the seal ring 64, and a packing 66 that seals the lower end of the passage 60. Between the end surfaces of the second shaft 11 and the rotating shaft 48, a gasket 67 (see FIG. 5) for preventing oil leakage from the passages 55 and 60 is interposed. The first rotary joint 35 is configured in the same manner as the second rotary joint 37.
[0027]
In order to rotationally mold a molded product using the rotary molding machine having the above-described configuration, first, the oil heated by the oil heater 27 is supplied from the oil supply device 26 to the temperature control pipe 76, and the mold body 74 is quickly moved. And heat uniformly. At this time, the mold 70 may be stationary, but is preferably rotated as follows.
[0028]
The revolving body 4 is rotated around the first axis 5 by the motor 6 and the mold mounting member 10 is rotated around the second axis 11 by the motor 12, so that the mold 70 is moved between the two axes 5, 11 having different directions. The powder-like or gel-like thermoplastic resin material 80 charged in the mold body 74 is melted and adhered to the molding surface 75 and rotated.
[0029]
Thereafter, the valves 30 and 31 are switched, and the oil cooled by the oil cooler 28 is supplied from the oil supply device 26 to the temperature control pipe 76 to cool the mold body 74 rapidly and uniformly, and the rotationally molded spherical shell shape After the molded product is solidified, the rotation is stopped and the molded product is demolded.
[0030]
As one specific example, when a powdery transparent polycarbonate resin material is used and oil having a heating temperature of 300 ° C. is supplied to the temperature control tube 76, the heating temperature of the mold body 74 becomes 280 ° C. The time was rapid, about 12 minutes. In addition, the control of the heating temperature was highly accurate, and the heating temperature was accurate no matter how many times it was performed. Thereafter, a polycarbonate resin material was added, and rotation and heating were further continued for about 8 minutes for rotation molding. Therefore, the total heating time is about 20 minutes. Then, when oil with a cooling temperature of 30 ° C. was supplied to the temperature control tube 76, the cooling temperature of the mold body 74 became 50 ° C., and the cooling time until reaching the cooling temperature was about 8 minutes. Accordingly, the time required for one rotation molding is less than 30 minutes, the molding efficiency is very high, and the discoloration and physical property deterioration of the resin material can be prevented.
[0031]
The temperature control tube 76 and the back surface of the mold body 74 are surface-coupled via the wire mesh 77 and the electroformed coating portion 78, so that the thermal conductivity is high and the temperature of the temperature control tube 76 is wide in the mold body 74. Since it was transmitted to the area, temperature variation due to the portion of the mold body 74 could be prevented, and the mold body 74 could be heated uniformly. For this reason, the inner surface of the spherical shell-shaped transparent molded product is smooth without undulation, it does not appear to be distorted when viewed from the outside, and no voids are generated. Could get. Of course, various hollow shapes other than the spherical shell shape (for example, an elliptical spherical shell shape, a regular polyhedral shell shape, etc.) can be similarly rotationally molded. Such a high-quality hollow transparent molded product cannot be rotationally molded by our technology so far, and can be used as, for example, a streetlight shade, etc. You can also.
[0032]
In addition, this invention is not limited to the said embodiment, For example, as follows, it can also change suitably in the range which does not deviate from the meaning of invention, and can also be embodied.
(1) The rotating body is rotated around the vertical first axis, and the mold mounting member and the mold are rotated around the horizontal second axis.
(2) The first axis and the second axis are arranged on two straight lines that are orthogonal to each other at a position deviated from the center of the mold, or are arranged on two straight lines that intersect obliquely at a position deviated from the approximate center or center of the mold To do.
(3) Using a mold body having a large number of ventilation holes, reducing the pressure on the back surface of the mold body, and performing rotational molding while sucking the molding material onto the surface of the mold body.
(4) An electric heater is directly coupled to the back surface of the mold body, and the mold body is changed so as to be heated rapidly and uniformly by supplying power to the electric heater. Cooling is performed by the temperature control tube.
[0033]
【The invention's effect】
As described above in detail, according to the rotational molding method and the rotational molding machine of the present invention, the accuracy of temperature control of the mold and the uniformity of the temperature distribution are improved, and a smooth hollow resin molded product on the inner surface can be formed in a short time. It has an excellent effect that it can be efficiently rotationally molded.
[Brief description of the drawings]
FIG. 1 is a perspective view of a rotary molding machine according to an embodiment of the present invention.
FIG. 2 is a front view of the rotational molding machine.
FIG. 3 is a plan view of the rotational molding machine.
FIG. 4 is a side view of the rotational molding machine.
FIG. 5 is a cross-sectional view showing a support structure of a die attachment member in the same rotary molding machine.
FIG. 6 is a cross-sectional view showing the internal structure of a rotary joint in the same rotary molding machine.
FIG. 7 is a sectional view showing an internal structure of a mold in the rotary molding machine.
FIG. 8 is a schematic view showing a conventional rotary molding machine.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Machine frame 4 Revolving body 5 1st axis | shaft 6 Motor 10 type | mold mounting member 11 2nd axis | shaft 12 Motor 26 Oil supply apparatus 27 Oil heater 28 Oil cooler 33 Piping mechanism 35 1st rotation joint 37 2nd rotation joint 70 Type 74 Mold body 75 Molding surface 76 Temperature control tube 77 Wire mesh 78 Electroformed coating part

Claims (2)

A first shaft (5), a U-shaped swivel body (4) whose end is supported by the first shaft (5), and a second shaft (16) rotatably supported at the center of the swivel body (4). 11) and a mold (70) attached to the second shaft (11), wherein the first shaft (5) and the swivel body (4) rotate together to rotate, The shaft (11) is configured to rotate and rotate independently of the first shaft (5) and the swivel body (4), and the mold (70) is a shell-shaped mold body (74) having a molding surface on the surface. And a temperature control pipe (76) surface-coupled to the back surface of the mold body (74), the second shaft (11) is formed in a hollow shape, and a pipe (54) is formed inside the second shaft (11). ) Is inserted, and an oil passage (55) for sending oil to the temperature control pipe (76) is formed by a gap between the outer peripheral surface of the pipe (54) and the inner peripheral surface of the second shaft (11), Oil that has undergone degrees control pipe (76) is rotational molding machine, characterized in that it is configured to pass through the inside of the pipe (54). Using the rotary molding machine according to claim 1, heated oil is supplied to the temperature control pipe (76) to heat the mold body (74) rapidly and uniformly, and the first shaft (5) and the swivel body (4) ) And the second shaft (11) are swirled and rotated independently of the first shaft (5) and the swivel body (4) to heat the powder-like or gel-like thermoplastic resin material. After rotating and molding a hollow resin molded product by melting and adhering to the molding surface of the mold, a cooled oil is supplied to the temperature control pipe (76) to cool the mold body (74) rapidly and uniformly, A rotational molding method comprising solidifying a rotationally molded resin molded product.

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