Rotational molding system and method for large-volume inner container

Abstract

The invention discloses a rotational molding system for a large-volume inner container, which comprises a rotational molding mold used for performing rotational molding on raw materials to form the large-volume inner container; electric heating wires are uniformly arranged on the rotational molding mold; vent holes are formed in the front end and the rear end of the rotational molding mold; the power device is used for rotating the rotational molding mold; the power device is used for supplying power to the heating wire; and the ventilation device is used for ventilating the ventilation holes, so that materials in the rotational molding mold are cooled. According to the invention, the electric heating rotational molding machine is adopted, and the uniform temperature field of the large-volume mold can be realized through the special arrangement of the resistance wires on the mold, so that the heating and cooling time is shortened, and the production efficiency is improved. And in addition, a mode of simultaneously cooling inside and outside is adopted, so that the cooling time is greatly shortened, the production efficiency is improved, the cooling effect is better than that of a traditional natural cooling mode, and the product quality is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of rotational molding, and in particular to a rotational molding system and method for a large-volume liner. Background Art

[0002] In the field of plastic processing technology, rotational molding is a common plastic processing method, especially suitable for the manufacture of large hollow products. Rotomolding is a process in which thermoplastic plastic powder is heated and melted in a mold, and then the plastic is evenly attached to the inner surface of the mold under the action of gravity or centrifugal force. After cooling, the hollow product is demolded. The advantage of this method is that it can produce products with complex shapes, and it has high production efficiency and low cost. However, for large-volume plastic liners, such as Type IV bottle liners with a volume greater than 1000L, the traditional rotational molding process has certain challenges.

[0003] The existing large-volume IV-type bottle plastic liner molding is usually carried out using an oven-type rotational molding machine. This method is to put plastic powder into a mold, and then put the mold into an oven to heat it, so that the plastic powder is heated and melted in the mold, and adheres to the inner surface of the mold under the action of gravity or centrifugal force. Finally, the mold is taken out, cooled and demolded to obtain a plastic liner.

[0004] The existing oven-type rotational molding machine has some problems when molding large-volume plastic liners: First, due to the large size of the mold, the heating and cooling time is long, resulting in low production efficiency. Secondly, due to the uneven temperature distribution inside the mold, the thickness of the plastic liner may be uneven, affecting product quality. In addition, during the cooling process of traditional rotational molding machines, natural cooling is usually used, which not only takes a long time, but also has an unsatisfactory cooling effect, which also affects production efficiency. Summary of the invention

[0005] In order to improve the rotomolding efficiency and quality of a large-volume liner, the present invention proposes a rotomolding system and method for a large-volume liner. The above-mentioned purpose can be achieved by implementing the following technical solutions:

[0006] A rotational molding system for a large-volume liner, comprising:

[0007] A rotational molding mold is used to rotationally mold the raw material to form the large-volume inner container; the rotational molding mold is evenly provided with electric heating wires; the front end and the rear end of the rotational molding mold are both provided with ventilation holes;

[0008] A power device for rotating the rotational molding mold;

[0009] An electric device for supplying power to the heating wire;

[0010] The ventilation device is used for ventilating the vent holes to cool the material in the rotational molding mold.

[0011] Optionally, the rotational molding mold includes a sealing head and a barrel, and an opening mechanism is provided between the sealing head and the barrel;

[0012] The barrel is cylindrical, and the central axis of the barrel is horizontally arranged; the sealing head is hemispherical; the sealing head is connected to the bottom surface of the barrel. Optionally, the front end and the rear end of the barrel are both connected to the sealing head; the vent hole is arranged on the sealing head.

[0013] Optionally, the power device includes a power cabinet, and the power cabinet is connected to the rotational molding mold via a transmission shaft;

[0014] Optionally, the transmission shaft includes a main shaft and a secondary shaft; the main shaft is used to rotate the rotational molding mold around the central axis, the secondary shaft is connected to the rotational molding mold through a chassis, and the chassis is used to rotate the rotational molding mold in a horizontal direction.

[0015] Optionally, the power device includes a power cabinet, and the power cabinet is connected to the heating wire through a power slip ring.

[0016] Optionally, the heating wires are arranged in a mesh-like staggered manner, spirally arranged around the rotational molding mold, or equidistantly and parallelly arranged.

[0017] Optionally, the heating wire is arranged in a straight line or in a wavy shape.

[0018] Optionally, the diameter of the heating wire is 0.2-4 mm, and the distance between adjacent heating wires is 1 cm-40 cm.

[0019] Optionally, the heating wire is at least one of nickel-chromium alloy, iron-chromium-aluminum alloy, carbon fiber bundle, and tungsten alloy.

[0020] Optionally, the mold has a length of 500 to 3000 mm, a diameter of 300 to 1200 mm, and a volume of 32 L to 3100 L.

[0021] A rotational molding method for a large-volume liner comprises the following steps:

[0022] S1. Install the rotomolding mold on the chassis and fix the rotomolding mold to the spindle; insert the metal insert into the rotomolding mold;

[0023] S2, set the ratio of chassis speed to rotation speed of the rotational mold around the central axis to 1:10-2:1, and energize the heating wire;

[0024] S3, adding raw materials to the rotational molding mold;

[0025] S4, heating the rotomolding mold, the temperature of the heating wire is 150℃~170℃, and it lasts for 10~40min;

[0026] S5, the rotational mold is melted at a temperature of 170°C to 250°C for 15 to 40 minutes;

[0027] S6, cooling the rotomolding mold, the temperature inside the rotomolding mold drops to 190-150°C; cooling air is blown into the mold through the vent holes, and the temperature inside the rotomolding mold drops to 80-40°C;

[0028] S7. Open the rotational molding mold to obtain the inner liner.

[0029] Optionally, the raw material is at least one of polyethylene, nylon, polypropylene, polyvinyl chloride, and polycarbonate.

[0030] Optionally, the cooling air temperature is -20 to 40°C and the flow rate is 2 to 20 m 3 / min.

[0031] The technical solution of the present invention has the following advantages:

[0032] The present invention adopts an electric heating rotomolding machine, which can achieve a uniform temperature field in a large-volume mold through the resistance wire on the mold, thereby shortening the heating and cooling time and improving production efficiency. Compared with the traditional oven-type rotomolding machine, the single production time is compressed from 2 hours to 1 hour. The production efficiency of the present invention is greatly improved. Since the present invention adopts an electric heating rotomolding machine, a uniform temperature field can be achieved in a large-volume mold. Therefore, the thickness of the plastic liner can be guaranteed to be uniform, thereby improving the quality of the product. Compared with the traditional rotomolding machine, the product quality of the present invention is significantly improved. The present invention adopts a method of simultaneous internal and external cooling, which not only greatly shortens the cooling time and improves production efficiency, but also has a better cooling effect than the traditional natural cooling method, further improving the quality of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 It is a schematic diagram of the system of the present invention;

[0035] Figure 2 It is a schematic diagram of mold rotation;

[0036] Figure 3 It is a schematic diagram of the arrangement of the heating wires;

[0037] Figure 4 It is a schematic diagram of cooling air;

[0038] Figure 5 It is a schematic diagram of the mold opening structure. DETAILED DESCRIPTION

[0039] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0040] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0041] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0042] like Figure 1 and Figure 5 A rotational molding system of a large volume liner is shown, comprising:

[0043] The rotational molding mold 1 is used to rotationally mold the raw material to form the large volume inner container; the rotational molding mold is evenly provided with electric heating wires 14; the front end and the rear end of the rotational molding mold are both provided with vent holes 4 (the arrangement of the vent holes 4 is as shown in FIG. Figure 4 As shown, the arrow direction in the figure indicates cooling airflow);

[0044] A power device for rotating the rotational molding mold;

[0045] An electric device for supplying power to the heating wire;

[0046] The ventilation device is used to ventilate the vent holes to cool the material in the rotational mold. A fan or other device may be used.

[0047] The power cabinet is driven by a motor and can provide a speed output of 0.1 to 20 rpm. The transmission shaft 2 can be an L-arm, a straight arm, or a frame, which distributes the input rotational power to the main shaft and the secondary shaft according to a speed ratio of 1:20 to 20:1, and can be driven and distributed through chains and gears. The mold is installed on the transmission shaft. Figure 2 As shown, the transmission shaft includes a main shaft and a secondary shaft; the main shaft is used to rotate the rotational molding mold around the central axis of the rotational molding mold, and the secondary shaft is connected to the rotational molding mold through a chassis, and the chassis is used to rotate the rotational molding mold in the horizontal direction ( Figure 2The arrow in the figure shows the direction of rotation). During the rotational molding process, a specific speed setting is used, wherein the main shaft speed is 2 to 20 rpm / min, and the main shaft and auxiliary shaft speed ratio is 0.5:1 to 1:20.

[0048] The power cabinet provides 10-200kw power output. The power slip ring 3 transmits power to the resistance wire through the brush while rotating. The resistance wire converts electrical energy into heat energy. The resistance wire is arranged on the outer surface of the mold. The diameter of the resistance wire is 0.2-4mm, and the material is nickel-chromium alloy, iron-chromium-aluminum, carbon fiber tow, and tungsten alloy. The arrangement of the heating carrier is not limited to Figure 1 The grid is shown as Figure 3 As shown, it can also be spiral, wavy, or equidistant, with a spacing of 1 cm to 40 cm.

[0049] like Figure 4 As shown, the ventilation device blows cooling air into the mold through the vent holes on the mold. The temperature of the cooling air is -20℃~40℃ and the flow rate is 2~20m 3 / min. Through the simultaneous cooling of the inside and outside, a large volume plastic liner is formed.

[0050] like Figure 5 As shown, the mold includes a head 13 and a barrel 11. The mold uses the junction of the head and the barrel as a parting surface, and is provided with an opening mechanism 12. The opening mechanism 12 can separate the head part from the barrel part, and can be a buckle, a bolt, etc., so as to remove the inner liner that has completed the rotational molding process from the mold. The barrel is cylindrical, and the central axis of the barrel is horizontally arranged; the head is hemispherical; the head is connected to the bottom surface of the barrel. The front end and the rear end of the barrel are both connected to the head; the vent is arranged on the head.

[0051] This embodiment also discloses a rotational molding method of a large-volume liner using the above system, comprising the following steps:

[0052] S1. Install the rotomolding mold on the chassis and fix the rotomolding mold to the spindle; insert the metal insert into the rotomolding mold;

[0053] S2. Set the ratio of chassis speed to mold rotation speed to between 1:10 and 2:1. Turn on the heating carrier on the mold surface;

[0054] S3, adding raw materials into the rotational molding mold; the raw materials are at least one of polyethylene, nylon, polypropylene, polyvinyl chloride, and polycarbonate.

[0055] S4, heating the rotomolding mold, the temperature of the heating wire is 150℃~170℃, and it lasts for 10~40min;

[0056] S5, the rotational molding mold is melted, the temperature of the electric heating wire is 170℃~250℃, and the duration is 25~40min;

[0057] S6, cooling the rotomolding mold, the temperature inside the rotomolding mold drops to 190-150°C; the ventilation device blows cooling air into the mold through the vents, the cooling air temperature is -20-40°C, the flow rate is 2-20m 3 / min. The temperature inside the rotational mold drops to 80-40°C;

[0058] S7, open the rotational molding mold, plastic liner.

[0059] Example 2

[0060] This embodiment discloses a rotational molding method of a large-volume liner using the system of embodiment 1, comprising the following steps:

[0061] S1. Install the rotomolding mold on the chassis and fix the rotomolding mold to the spindle; insert the metal insert into the rotomolding mold;

[0062] S2. Set the chassis speed to 4.3rpm / min, and the ratio of chassis speed to mold rotation speed to 4.3:10. Turn on the heating carrier on the mold surface;

[0063] S3. Add polyethylene raw material into the rotational molding mold.

[0064] S4, heating the rotomolding mold, the temperature of the heating wire is 160°C, and the duration is 30 minutes;

[0065] S5, melting the rotomolding mold, the heating wire temperature is 220°C, and the duration is 15 minutes;

[0066] S6, cooling the rotomolding mold, the temperature inside the rotomolding mold drops to 150°C; the ventilation device blows cooling air into the mold through the vent holes, the cooling air temperature is 24°C, and the flow rate is 4m 3 / min. The temperature dropped to 68°C;

[0067] S7, open the rotational molding mold, plastic liner.

[0068] The thickness of the inner liner obtained was 4.5 mm, and the uniformity of the thickness was tested, and the result was: 4.5±0.2 mm.

[0069] Example 2

[0070] This embodiment discloses a rotational molding method of a large-volume liner using the system of embodiment 1, comprising the following steps:

[0071] S1. Install the rotomolding mold on the chassis and fix the rotomolding mold to the spindle; insert the metal insert into the rotomolding mold;

[0072] S2. Set the chassis speed to 6 rpm / min, and the ratio of chassis speed to mold rotation speed is 2:1. Turn on the heating carrier on the mold surface;

[0073] S3. Add polypropylene raw material into the rotational molding mold.

[0074] S4, heating the rotomolding mold, the temperature of the heating wire is 170°C, and the duration is 30 minutes;

[0075] S5, the rotational molding mold is melted, the heating wire temperature is 250°C, and the duration is 15 minutes;

[0076] S6, cooling the rotomolding mold, the temperature inside the rotomolding mold drops to 160°C; cooling air is blown into the mold through the vent holes, the cooling air temperature is -10°C, and the flow rate is 5m 3 / min. The temperature dropped to 40℃;

[0077] S7, open the rotational molding mold, plastic liner.

[0078] The thickness of the inner liner obtained was 4.2 mm, and the uniformity of the thickness was tested, with the result being: 4.2±0.2 mm.

[0079] Example 3

[0080] This embodiment discloses a rotational molding method of a large-volume liner using the system of embodiment 1, comprising the following steps:

[0081] S1. Install the rotomolding mold on the chassis and fix the rotomolding mold to the spindle; insert the metal insert into the rotomolding mold;

[0082] S2, set the chassis speed to 2rpm / min, and the chassis speed to the mold rotation speed is 1:10. And turn on the heating carrier on the mold surface;

[0083] S3. Add polyethylene raw material into the rotational molding mold.

[0084] S4, heating the rotomolding mold, the temperature of the heating wire is 150°C, and the duration is 40 minutes;

[0085] S5, melting the rotomolding mold, the heating wire temperature is 170°C, and the duration is 15 minutes;

[0086] S6, cooling the rotomolding mold, the temperature inside the rotomolding mold drops to 150°C; cooling air is blown into the mold through the vent holes, the cooling air temperature is 0°C, and the flow rate is 2m3 / min. The temperature dropped to 48°C;

[0087] S7, open the rotational molding mold, plastic liner.

[0088] The thickness of the inner liner obtained was 4 mm, and the uniformity of the thickness was tested, with the result being: 4±0.2 mm.

[0089] Comparative Example

[0090] The traditional process of preparing the inner liner was carried out using an oven-type rotational molding machine. It took a total of 2.5 hours to obtain an inner liner with a thickness of 3.5 mm. The uniformity of the thickness was tested and the result was: 3.5±0.5 mm.

[0091] The rotomolding system and rotomolding method of the present invention can be widely used in application fields such as plastic processing, rotomolding equipment manufacturing, and type IV bottle manufacturing. First, the present invention adopts an electric heating rotomolding machine, and through the special arrangement of the resistance wire on the mold, a uniform temperature field in a large-volume mold is achieved, which will greatly improve the molding quality of the plastic liner and reduce the problem of uneven thickness, thereby improving the market competitiveness of the product. Secondly, the present invention greatly shortens the cooling time and improves production efficiency by cooling both inside and outside at the same time, meeting the market demand for high-efficiency and high-quality production. In addition, the rotomolding machine of the present invention can also be used for the manufacture of other large hollow products, and has great market potential.

[0092] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A rotational molding system for a large volume liner, characterized in that: include: A rotational molding mold is used to rotationally mold the raw material to form the large-volume liner; the rotational molding mold is evenly provided with electric heating wires; the front end and the rear end of the rotational molding mold are both provided with ventilation holes; A power device for rotating the rotational molding mold; An electric device for supplying power to the heating wire; The ventilation device is used for ventilating the vent holes to cool the material in the rotational molding mold.

2. A rotational molding system for a large volume liner according to claim 1, characterized in that: The rotational molding mold comprises a sealing head and a barrel, and an opening mechanism is arranged between the sealing head and the barrel; Preferably, the barrel is a hollow cylinder, and the central axis of the barrel is horizontally arranged; the sealing head is hemispherical; and the sealing head is connected to the end of the barrel; Preferably, the front end and the rear end of the barrel are both connected to a head; and the vent hole is arranged on the head.

3. A rotational molding system for a large volume liner according to claim 1, characterized in that: The power device comprises a power cabinet, and the power cabinet is connected to the rotational molding mold through a transmission shaft; Preferably, the transmission shaft includes a main shaft and a secondary shaft; the main shaft is used to make the rotational molding mold rotate around the central axis, the secondary shaft is connected to the rotational molding mold through a chassis, and the chassis is used to make the rotational molding mold rotate in the horizontal direction.

4. A rotational molding system for a large volume liner according to claim 1, characterized in that: The electric device comprises an electric cabinet, and the electric cabinet is connected to the heating wire through an electric slip ring.

5. A rotational molding system for a large volume liner according to claim 1, characterized in that: The heating wires are arranged in a mesh-like staggered manner, spirally arranged around the rotational molding mold, or equidistantly and parallelly arranged.

6. A rotational molding system for a large volume liner according to claim 1, characterized in that: The heating wire is arranged in a straight line or in a wavy shape; Preferably, the diameter of the heating wire is 0.2 to 4 mm, and the distance between adjacent heating wires is 1 cm to 40 cm; Preferably, the heating wire is at least one of nickel-chromium alloy, iron-chromium-aluminum alloy, carbon fiber tow, and tungsten alloy.

7. A rotational molding system for a large volume liner according to claim 1, characterized in that: The mold has a length of 500 to 3000 mm, a diameter of 300 to 1200 mm, and a volume of 32L to 3100L.

8. A method for rotational molding of a large volume liner, characterized in that: The rotational molding system of the large volume liner according to any one of claims 1 to 7 comprises the following steps: S1. Install the rotomolding mold on the chassis and fix the rotomolding mold to the spindle; insert the metal insert into the rotomolding mold; S2, set the ratio of chassis speed to rotation speed of the rotational mold around the central axis to 1:10-2:1, and energize the heating wire; S3, adding raw materials to the rotational molding mold; S4, heating the rotomolding mold, the temperature of the heating wire is 150℃~170℃, and it lasts for 10~40min; S5, the rotational mold is melted at a temperature of 170°C to 250°C for 15 to 40 minutes; S6, cooling the rotomolding mold, the temperature inside the rotomolding mold drops to 190-150°C; cooling air is blown into the mold through the vent holes, and the temperature inside the rotomolding mold drops to 80-40°C; S7. Open the rotational molding mold to obtain the inner liner.

9. A rotational molding method for a large-volume liner according to claim 8, characterized in that: The raw material is at least one of polyethylene, nylon, polypropylene, polyvinyl chloride and polycarbonate.

10. A rotational molding method for a large volume liner according to claim 8, characterized in that: The cooling air temperature is -20 to 40°C, and the flow rate is 2 to 20 m 3 / min.

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