JP6144088B2 - Tank manufacturing method - Google Patents

Description

The present invention relates to an improvement in a method of manufacturing a synthetic resin tank used for storing various chemicals and liquids such as water.

  Large tanks are used in factories to store liquids (contents) such as various chemicals and water. FIG. 3 shows a structure of a tank 1 having a conventional structure described in Patent Document 1. This tank 1 is made of a synthetic resin and has a cylindrical body 2, a bottom 3 that closes the lower opening of the body 2, and a top plate 4 that closes the upper opening of the body 2. Molded. In addition, a removable cap 5 is assembled to the opening formed in the top plate portion 4 of the tank 1. In addition, in this specification and a claim, a trunk | drum means the side wall part surrounding the circumference | surroundings of the content liquid stored inside a tank.

  In addition, as described in Non-Patent Document 1, for example, the above-described tank 1 has been conventionally manufactured by rotational molding of synthetic resin. In such rotational molding, a mold 6 as shown in FIG. 4A is used. The mold 6 includes a bottomed cylindrical mold body 7 that is open only at the top, and a lid 8 that closes the opening of the mold body 7. Further, such a mold 6 has an inner surface shape corresponding to the outer surface shape of the tank 1 to be molded in a state where the mold body 7 and the lid body 8 are assembled. The tank manufacturing method by rotational molding described in Non-Patent Document 1 will be briefly described below.

  In order to manufacture the tank 1 by rotational molding, first, as shown in FIG. 4A, powder (eg, polyethylene (PE), polypropylene (PP), polycarbonate ( PC) or other thermoplastic resin 9 (portion shown in FIG. 4). Next, as an example of the rotational molding method, as shown in FIG. 4B, the mold 6 in a state where the opening of the mold main body 7 is closed with the lid body 8 is placed in the rotational molding apparatus 10 as X. The heater 11 that constitutes the rotational molding apparatus 10 is disposed around the mold 6 while being assembled in a state that allows rotation around the axis and the Y axis.

  The heater 11 includes a radial gas burner 12, an upper gas burner 15, and a lower gas burner 17. Of these, the radial gas burner 12 has a length dimension substantially the same as the axial dimension of the mold body 7. The radial gas burner 12 is provided in a state of being spaced apart from the outer peripheral surface of the mold 6 by a predetermined distance. Such a radial gas burner 12 has radial nozzles 14 at a plurality of locations in the axial direction (vertical direction in FIG. 4). A flame can be emitted from each of the radial flame ports 14 toward the outer peripheral surface of the mold 6 (see arrow α in FIG. 4B).

The upper gas burner 15 has a length that is substantially half the outer diameter of the mold 6 and is provided at a predetermined distance from the upper surface of the mold 6 (lid 8). It has been. Such an upper gas burner 15 has upper flame holes 16 at a plurality of positions in the axial direction (left and right direction in FIG. 4), and flames are directed from the upper flame holes 16 toward the upper surface of the mold 6. {See arrow β in FIG. 4B}.
Further, the lower gas burner 17 has a length that is substantially half the outer diameter of the mold 6 and is spaced from the lower surface of the mold 6 (mold body 7) by a predetermined distance. Is provided. Such a lower gas burner 17 has lower flame ports 18 at a plurality of positions in the axial direction (left and right direction in FIG. 4), and the mold 6 (die body) is formed from each lower flame port 18. A flame can be emitted toward the lower surface of 7) {see arrow γ in FIG. 4B}.

  Each of the gas burners 12, 15, and 17 is provided so as to be able to rotate with the mold 6 with respect to the rotation of the mold 6 around the X axis. On the other hand, with respect to the rotation of the mold 6 around the Y axis, the mold 6 is provided in a state in which it cannot be rotated with the mold 6. In short, the gas burners 12, 15, and 17 rotate in synchronism with the mold 6 around the X axis, but do not rotate around the Y axis. In the above example, the mold is heated by the gas burners 12, 15, and 17, but another method is, for example, a so-called furnace method in which the mold is heated in a furnace. You can also do things.

  The mold 6 assembled in the rotational molding apparatus 10 in the state as described above is rotated around the X axis and the Y axis by the mold rotating means (not shown) of the rotational molding apparatus 10, and the The mold 6 is heated by the gas burners 12, 15, and 17 until the internal temperature becomes equal to or higher than the melting point of the thermoplastic resin 9. Then, the thermoplastic resin 9 inside the mold 6 is melted. The thermoplastic resin 9 thus melted has low fluidity and remains in place (melted position) by welding with another molten thermoplastic resin 9 existing on or near the inner surface of the mold 6. . On the other hand, the unmelted thermoplastic resin 9 moves inside the mold 6 as the mold 6 rotates. Thus, the operation of heating the mold 6 while rotating is continued until all the thermoplastic resins 9 are melted (welded).

Next, as shown in FIG. 4C, the mold 6 is cooled, and the thermoplastic resin 9 melted inside the mold 6 is solidified. As a cooling method, for example, in the state shown in FIG. 4 (b), only releasing the flames of the gas burners 12, 15, and 17 is stopped, and the mold 6 is rotated so as to naturally dissipate heat, or When it is desired to shorten the cooling time, a method of cooling with cooling water or the like can be employed.
Then, after the above-described cooling operation is completed, as shown in FIG. 4D, the lid body 8 is removed from the mold body 7 and the tank 1 is taken out.
The outer peripheral surface and the inner peripheral surface of the tank 1 formed as described above have a cylindrical surface shape in which the respective radial dimensions are constant over the entire axial length. Accordingly, the thickness and rigidity in the radial direction of the body 2 of the tank 1 are constant over the entire length in the axial direction.

  By the way, the above-mentioned tank is required to have rigidity to withstand the liquid pressure received from the liquid stored inside the tank in the state of use. Therefore, conventionally, the rigidity of the body of the tank has been secured by a method as shown in FIGS. In the structure shown in FIG. 5, the body 2 a of the synthetic resin tank 1 a formed by rotational molding is reinforced by a metal reinforcing frame 19 over the entire length in the axial direction. The reinforcing frame 19 is formed by bending and welding a steel plate made of, for example, a general structural rolled steel material (SS material) or a stainless steel material (SUS material) to form a cylindrical shape as a whole. And this reinforcement frame 19 is externally fitted by the outer peripheral surface of the trunk | drum 2a of the said tank 1a. In the case of the tank 1a having such a conventional structure, the rigidity of the trunk portion 2a of the tank 1a can be supplemented by the reinforcing frame 19. For this reason, the thickness dimension in the radial direction of the body portion 2a can be reduced to reduce the material cost of the thermoplastic resin and shorten the processing time of the tank 1a by rotational molding. However, the material cost and processing cost of the reinforcing frame 19 increase.

On the other hand, in the case of the structure shown in FIG. 6, only the synthetic resin tank 1b formed by rotational molding is used. Therefore, in order to ensure the rigidity of the body portion 2b of the tank 1b, and the thickness H _2b in the radial direction of the body portion 2b, the thickness in the radial direction of the body portion 2a of the tank 1a shown in FIG. 5 It is larger than H _2a (H _2b > H _2a ). In the case of the tank 1b having such a conventional structure, the cost for the reinforcing frame 19 can be reduced as compared with the structure in which the reinforcing frame 19 is provided. However, the material cost of the thermoplastic resin and the processing time by rotational molding become long, and the processing cost increases.

  Even in the tanks 1a and 1b having the above-described structure, a hydraulic pressure proportional to the depth is applied to the tanks 1a and 1b from the liquid stored inside the tanks 1a and 1b. Accordingly, the trunk portions 2a and 2b of the tanks 1a and 1b are required to have higher rigidity toward the lower side of the trunk portions 2a and 2b. In consideration of such circumstances, in the case of the tanks 1a and 1b having the conventional structure as described above, according to the rigidity required for the lower end portions of the body portions 2a and 2b, The thickness dimension (rigidity) in the radial direction is determined. For this reason, the rigidity of the upper end of each of the body parts 2a, 2b becomes excessive with respect to the rigidity necessary to withstand the hydraulic pressure applied to the parts. In this way, when determining the rigidity of each of the body parts 2a and 2b in accordance with the lower part of each of the body parts 2a and 2b, the rigidity of the parts other than the lower part becomes excessive, and the material cost is correspondingly increased. It becomes bulky.

JP 2004-196325 A

DAILIGHT Co., Ltd. website, “Technical information: Rotational molding”, [online], [Search on March 15, 2013], Internet <URL: http://www.dailite.co.jp/04_tex/01_seikei_kaiten.html >

  In view of the circumstances as described above, the present invention is configured such that the rigidity of each axial portion of the body portion of the tank formed by rotational molding is applied to the liquid pressure applied to each portion from the liquid inside the body portion. The invention was invented to realize a tank structure that can reduce the processing time without incurring extra material costs by designing it not to be excessive.

Among the tank manufacturing methods of the present invention, the tank that is the object of the tank manufacturing method according to claim 1 is a cylinder in which the outer peripheral surface of the hollow body is constant in outer diameter over the entire length in the axial direction. And the inner peripheral surface of the body portion is an inner diameter changing surface whose inner diameter dimension decreases linearly or curvilinearly from the upper end to the lower end, and the thickness of the body portion in the axial direction. The dimension increases continuously as it goes downward. The inner diameter changing surface includes any shape that decreases linearly or curvedly as the inner diameter dimension proceeds downward. In addition, the upper end portion of the body portion may be formed with a portion in which the inner diameter size and the thickness size do not change for convenience of design for ensuring a minimum thickness size. When the portion is formed, the inner diameter changing surface is formed below the portion.
In the case of the invention described in claim 1, the tank having the above-described configuration is heated while rotating the mold with the powdered thermoplastic resin inside the hollow mold. And it shape | molds by the rotational molding which welds the molten thermoplastic resin to the inner surface of the said metal mold | die. At this time, at the portion near the upper end of the inner peripheral surface of the mold, the amount of the thermoplastic resin to be melted is reduced, and the thermoplastic resin is melted as it proceeds downward from the upper end of the inner peripheral surface of the mold. Increase the amount to be gradually increased.

On the other hand, the tank which is the object of the method for manufacturing a tank according to claim 2 is such that the portion of the inner peripheral surface of the hollow body portion extending from the upper end to the intermediate portion in the axial direction is directed downward. The inner diameter change surface has a smaller inner diameter dimension, and the thickness dimension of the portion of the body portion that matches the inner diameter change surface portion increases toward the lower side.
Of the inner peripheral surface of the body portion, the inner diameter dimension of the remaining portion below the inner diameter changing surface portion is larger than the inner diameter size of the lower end portion of the inner diameter changing surface portion. The thickness dimension of the portion aligned with the remaining portion is smaller than the thickness dimension of the position aligned with the lower end portion of the inner diameter changing surface portion.
Furthermore, a hollow cylindrical reinforcing frame is externally fitted on the outer peripheral surface of the body portion at a position aligned with the remaining portion.

According to the present invention configured as described above, it is possible to reduce processing time by rotational molding without incurring extra material costs.
That is, in the case of the invention described in claim 1, the inner peripheral surface of the barrel portion of the target tank decreases in the inner diameter as it goes downward, and the thickness dimension of each axial portion of the barrel portion is It grows as you go down. Therefore, the rigidity of each part in the axial direction of the trunk portion increases as it goes downward. For this reason, the rigidity of each part in the axial direction of the body part can be appropriately set in relation to the magnitude of the hydraulic pressure that the part receives from the liquid. As a result, unlike the conventional structure described above, the rigidity of the upper end portion of the body portion does not become excessive with respect to the hydraulic pressure applied to the portion, and no extra material costs are incurred. Moreover, since the material used can be reduced, the processing time by rotational molding can be shortened.

Further, in the case of the invention described in claim 2, the thickness dimension of the portion near the lower end of the trunk portion of the target tank is made smaller than the thickness dimension of the upper portion of the portion. That is, as compared with the case of the tank that is the subject of the invention described in claim 1, the amount of material in the portion near the lower end of the body portion can be reduced. For this reason, it is possible to reduce the material cost and the processing time by rotational molding. In the case of the invention described in claim 2, such a reinforcement frame is provided outside the portion in order to supplement the rigidity of the portion near the lower end of the trunk portion constituting the target tank. Although the cost of the frame is required separately, the total cost for manufacturing can be kept lower than the manufacturing cost of the tank having the conventional structure described above.

Sectional drawing of a tank which shows the 1st example of embodiment of this invention. Sectional drawing of the tank which shows the 2nd example of embodiment of this invention. The side view which shows the structure of the tank of a conventional structure. The schematic diagram for demonstrating the process of shape | molding a tank by rotational molding. Sectional drawing of the tank which shows an example of the structure for ensuring the rigidity of the tank of a conventional structure. Similarly, sectional drawing of the tank which shows another example.

[First example of embodiment]
FIG. 1 shows a first example of an embodiment of the present invention corresponding to claim 1. The tank 1c of this example is made of a thermoplastic resin such as polyethylene (PE), polypropylene (PP), polycarbonate (PC), etc., and is cylindrical like the tanks 1, 1a, 1b of the conventional structure described above. A body 2c, a disk-shaped bottom 3a that closes the lower opening of the body 2c, and a disk-shaped top 4a that also closes the upper opening are integrally formed by rotational molding. Become. Note that an opening (not shown) for assembling the cap 5 (see FIG. 5) is formed in the top plate portion 4a.

By the way, in the state of use of the tank 1c, the magnitude of the liquid pressure received from the liquid existing inside the body part 2c is determined by the depth of the part (distance from the liquid surface of the liquid). ). Accordingly, this hydraulic pressure is greatest at the lower end of the inner surface (inclined surface 20) of the body portion 2c. Therefore, in the case of this example, the thickness dimension H _2c (rigidity) in the radial direction of each part in the axial direction of the body portion 2c is set based on the hydraulic pressure applied to the portion in use.

Specifically, at the tank 1c of the present embodiment, the outer peripheral surface of the body portion 2c, the outer diameter D _2c is an axial constant cylindrical surface over the entire length of (the vertical direction in FIG. 1) . On the other hand, the inner circumferential surface of the body portion 2c, the inner diameter d _2c is inclined linearly (or curved) to decrease direction toward the lower, corresponding to the inner diameters of surfaces as set forth in the appended claims The inclined surface 20 is used. In this manner, the thickness dimension _H2c in the radial direction of each part in the axial direction of the body portion 2c is increased toward the lower side.

  Next, the manufacturing method of the tank 1c of this example as described above will be briefly described. The tank 1c of this example is formed by the rotational molding shown in FIG. However, in the case of this example, the process of FIG. 4B, that is, the mold 6 is rotated around the X axis and the Y axis by the mold rotating means of the rotary molding apparatus, and each gas burner 12, 15, 17 is rotated. The process of heating with is devised.

  Specifically, when the thermoplastic resin melts, it fuses with another already melted thermoplastic resin existing on or near the inner surface of the mold 6 and uses the property that it stays in place (melted position). And the tank 1c of this example is shape | molded. That is, by controlling the processing conditions of the mold rotating means or the gas burners 12, 15, 17, etc., for example, in the portion near the upper end of the inner peripheral surface of the mold 6, the amount by which the thermoplastic resin is melted And the amount of the thermoplastic resin to be melted in each portion is gradually increased as it proceeds downward from the upper end of the inner peripheral surface of the mold 6. Then, due to the above-described properties, the thermoplastic resin remains welded at the melted position, so that the thickness dimension in the radial direction becomes larger as the thermoplastic resin is melted more. In this way, after all the thermoplastic resin is melted (welded), the mold 6 is cooled and melted inside the mold 6 in the same manner as the conventional manufacturing method described above. The thermoplastic resin is solidified. Then, after this cooling operation is completed, as shown in FIG. 4D, the lid body 8 is removed from the mold body 7 and the tank 1c is taken out.

According to the tank 1c of the present example configured as described above, it is possible to reduce processing time by rotational molding without incurring extra material costs.
That is, in the case of this example, the inner diameter of the barrel 2c of the tank 1c decreases as it goes downward, and the thickness of each axial portion of the barrel 2c decreases downward. growing. Accordingly, the rigidity of each part in the axial direction of the trunk portion 2c increases as it goes downward. For this reason, the rigidity of each part in the axial direction of the body 2c can be appropriately designed in relation to the magnitude of the hydraulic pressure received by the part from the liquid. As a result, like the tanks 1, 1a, 1b of the conventional structure described above, the rigidity of the upper ends of the body parts 2, 2a, 2b does not become excessive with respect to the hydraulic pressure applied to the parts, There is no extra material cost.
In the case of the tank 1c of this example, the mass of the tank (conventional amount of the material to be used) of the tank having the conventional structure made under the same usage conditions (for example, specific gravity of the liquid content) The amount of thermoplastic resin to be reduced). As a result, the processing time by rotational molding can be shortened.

[Second Example of Embodiment]
FIG. 2 shows a second example of an embodiment of the present invention corresponding to claim 2. In the case of the tank 1d of this example, the outer diameter surface D2d of the outer peripheral surface of the body _2d is axially (in the vertical direction of FIG. 2) similar to the body 2c of the tank 1c of the first example of the above-described embodiment. (Direction) is a constant cylindrical surface over the entire length. On the other hand, the inner peripheral surface of the body portion 2d is composed of an inclined surface 20a, a cylindrical surface 21 provided below the inclined surface 20a, and a continuous surface 22 that connects these both surfaces 20a and 21. . The inclined surface 20 corresponds to the inner diameter changing surface described in the claims, and the cylindrical surface 21 and the continuous surface 22 are portions corresponding to the remaining portion.

Of these, the inclined surface 20a is formed so as to extend from the upper end of the inner peripheral surface of the body portion 2d to the intermediate portion in the axial direction (position of about 2/3 of the entire length), and its inner diameter increases downward. It is inclined linearly in the direction in which the dimension _d20a decreases. Also, the thickness H _20a of the portion matching the inclined surface 20a of the body portion 2d increases as downward. In addition, the axial position of the lower end of such an inclined surface 20a is not limited to the case of this example. Based on the thermoplastic resin to be used, the type of the reinforcing frame 19a described later, and the like, a position that can be manufactured at the lowest cost is appropriately determined by design.
The cylindrical surface 21 is formed so as to hang from the axially intermediate portion (position of about 2/3 of the entire length) to the lower end portion of the inner peripheral surface of the body portion 2d. Further, the inner diameter d _{21 of} the cylindrical surface 21 and the thickness dimension H ₂₁ in the radial direction of the position matching the cylindrical surface 21 of the body portion 2d are constant over the entire length. Is substantially the same as the inner diameter and thickness at the upper end of the body 2d. Note that the axial position of the upper end of the cylindrical surface 21 is not limited to this example. Based on the thermoplastic resin to be used, the type of the reinforcing frame 19a described later, and the like, a position that can be manufactured at the lowest cost is appropriately determined by design.
Further, the continuous surface 22, and the lower end of the inclined surface 20a, and an inclined surface continuous to the upper end of the cylindrical surface 21, the inner diameter d ₂₂ is greater toward the bottom. Also, the thickness H ₂₂ in the radial direction of the position aligned with the continuous surface 22 of the body portion 2c is reduced toward the lower side.

Furthermore, in the case of the tank 1d of this example, a cylindrical reinforcing frame 19a made of metal is externally fitted on the outer peripheral surface of the barrel portion 2d at a position aligned with the cylindrical surface 21 and the continuous surface 22. Yes. The reinforcing frame 19a has both a cylindrical surface on the inner peripheral surface and an outer peripheral surface, and has a constant radial thickness over the entire length in the axial direction. The reinforcing frame 19a is formed by bending and welding, for example, a plate-shaped rolled steel material for general structure (SS material) or stainless steel material (SUS material), as in the conventional structure described above. The whole is cylindrical.
In the case of the tank 1d of the present example configured as described above, the rigidity of the body portion 2d of the tank 1d (the thickness dimension of each portion of the body portion 2d in the axial direction) is set, and the portion closer to the lower end of the body portion 2d In a state reinforced by 19a, an appropriate size is set in relation to the hydraulic pressure applied to each axial portion of the body portion 2c.

As described above, in the case of the tank 1d of this example, as compared with the tank 1c of the first example of the above-described embodiment, a portion closer to the lower end of the trunk portion 2d (a portion aligned with the continuous surface 22 and the cylindrical surface 21). The thickness dimension is small. For this reason, compared with the tank 1c of the 1st example of above-mentioned embodiment, the quantity of the thermoplastic resin which comprises the said trunk | drum 2d can be decreased. Thus, according to the structure of the tank 1d of this example, it is possible to reduce the material cost and the processing time. In the case of a tank 1d of the present embodiment, in order to compensate for the rigidity of the lower end portion near the body portion 2d, because it provided the reinforcing frame 19a on the outer peripheral surface of the part, it is required separately cost of the reinforcing frame 19a It becomes. However, the total cost for manufacturing can be suppressed more than the manufacturing cost of the tank having the conventional structure described above. Such a tank 1d of this example is suitable for the case where it is desired to shorten the processing time by rotational molding even if the cost of the reinforcing frame 19a is increased.

  The method for manufacturing the tank 1d of this example is the same as the method for manufacturing the tank 1c of the first example of the above-described embodiment, and the mold rotating means of the rotational molding apparatus or each gas burner 12, 15, 17 (FIG. 4) and other processing conditions are controlled. Specifically, for example, when the inclined surface 20a is molded, the amount of the thermoplastic resin to be melted is gradually increased from the upper end of the inner peripheral surface of the mold 6 downward. Further, when the continuous surface 22 is molded, the amount of the thermoplastic resin to be melted is gradually reduced from the portion corresponding to the upper end of the continuous surface 22 toward the lower side. Further, when the cylindrical surface 21 is formed, the amount of the thermoplastic resin to be melted is made constant over the entire length of the cylindrical portion 21. Other manufacturing methods are the same as those in the first example of the embodiment described above.

When implementing this invention, the shape of the outer peripheral surface of the trunk | drum which comprises the tank used as object is not limited to a cylindrical surface. Further, the shape of the inner peripheral surface of the body portion of the structure of the first example of the embodiment described above and the inclined surface (the axial length, the inclination angle, etc.) of the body portion of the second example of the embodiment. Is determined appropriately in design in consideration of use conditions, processing conditions, and the like.

DESCRIPTION OF SYMBOLS 1, 1a, 1b, 1c, 1d Tank 2, 2a, 2b, 2c, 2d Trunk part 3, 3a Bottom part 4, 4a Top plate part 5 Cap 6 Mold 7 Mold main body 8 Lid body 9 Thermoplastic resin 10 Rotation molding Device 11 Heater 12 Radial Gas Burner 13 Upper Gas Burner 14 Radial Flame Port 15 Upper Gas Burner 16 Upper Flame Port 17 Lower Gas Burner 18 Lower Flame Port 19, 19a Reinforcement Frame 20, 20a Inclined Surface 21 Cylindrical Surface 22 Continuous Surface

Claims (2)

The outer peripheral surface of the hollow body is a cylindrical surface whose outer diameter is constant over the entire length in the axial direction, and the inner diameter of the inner surface of this body is linear as it goes from the upper end to the lower end. Alternatively, it is a method of manufacturing a tank that is an inner diameter changing surface that is curvilinearly reduced, and the thickness dimension in the radial direction of the body portion continuously increases toward the lower side,
With the powdered thermoplastic resin inside the hollow mold, the mold is rotated and heated, and molded by rotational molding in which the molten thermoplastic resin is welded to the inner surface of the mold. At this time, in the portion near the upper end of the inner peripheral surface of the mold, the amount of the thermoplastic resin to be melted is reduced, and the thermoplastic resin is melted as it proceeds downward from the upper end of the inner peripheral surface of the mold. A tank manufacturing method characterized by gradually increasing the volume . Of the inner peripheral surface of the hollow body portion, the portion from the upper end to the intermediate portion in the axial direction is an inner diameter changing surface whose inner diameter dimension decreases as it goes downward, and of the body portion, The thickness dimension of the portion aligned with the inner diameter changing surface portion is increased toward the lower side,
Of the inner peripheral surface of the body portion, the inner diameter dimension of the remaining portion that is the lower part of the inner diameter changing surface is larger than the inner diameter dimension of the lower end portion of the inner diameter changing surface portion,
Of the body portion, the thickness dimension of the portion that matches the remaining portion is smaller than the thickness dimension of the position that matches the lower end portion of the inner diameter changing surface portion,
A manufacturing method of a tank comprising a hollow reinforcing frame fitted on an outer peripheral surface of the body portion at a position aligned with the remaining portion,
The body is rotated by rotating the mold and heating it with the thermoplastic resin inside the hollow mold to weld the molten thermoplastic resin to the inner surface of the mold. A method of manufacturing a tank characterized by molding.

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