Rotary forming equipment and method

Abstract

The invention provides rotary forming equipment and method. The rotary forming equipment comprises a rotational molding barrel, a transparent part, a heating assembly, a cantilever shaft, a rotational molding rack, a ventilation pipe, a gas assembly and a driving assembly. The rotational molding cylinder is a hollow cylinder with two through ends, and the axis is parallel to the horizontal plane; two ends of the rotational molding cylinder are respectively connected with the front end cover and the rear end cover; the diameter of the transparent part is greater than the inner diameter of the rotational molding cylinder body; the transparent part is arranged between the front end cover and the rotational molding cylinder body; the heating assembly is connected with the peripheral surface of the rotational molding barrel; one end of the cantilever shaft is fixedly connected with the rear end cover, and the other end is rotationally connected with the rotational molding rack; the cantilever shaft is connected with the driving assembly; one end of the breather pipe is arranged on the rotational molding barrel, and the other end of the breather pipe is rotationally connected with the gas assembly; the breather pipe is connected with the rear end cover. According to the rotational molding equipment, materials are fused in the metal rotational molding barrel, it is guaranteed that the materials are heated, and the transparent part is arranged at the front end of the rotational molding barrel so that real-time observation can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic processing, and in particular relates to a rotational molding device and a method. Background Art

[0002] There are many types of plastic molding methods, such as extrusion molding, blow molding, injection molding, calendering molding, etc. Compared with these molding methods, rotational molding has significant characteristics and advantages. Rotational molding, also known as rotational molding, is an important thermoplastic molding method, mainly suitable for various types of hollow products, especially products designed with special structures and uses, such as water tanks, oil tanks, rafts, etc., which can achieve one-piece molding or molding defects that cannot be solved by other molding methods such as injection molding, extrusion blow molding, etc. The method is to first add one or more thermoplastic plastics and their additives (generally solid powder or liquid) into the mold, and then heat the mold (oven heating or electric heating). The mold rotates continuously along the vertical and horizontal axes at a specific speed. The material in the mold is gradually melted after being heated, and is evenly coated and adhered to the inner surface of the mold under the action of gravity, and then cooled and shaped to form a product. This method is suitable for the processing and molding of various thermoplastic materials, such as PP (polypropylene), PE (polyethylene), PA (polyamide), etc. Rotational molding can achieve one-piece molding of materials, which can avoid molding defects, especially "flash" defects. The rotational molding mold rotates continuously during the preparation process to ensure the uniformity of the material. The rotational molded products have a wide range of applicability in size, and the mold can be selected according to different needs.

[0003] However, most of the existing rotational molding equipment has some shortcomings in structural design. Most of the rotational molding equipment has a complex structure, high manufacturing and maintenance costs, insufficient power, low rotation rate, low molding efficiency, poor uniformity of molten material adhering to the mold cavity surface, and low yield rate. The existing rotational molding technology generally adjusts the product performance by controlling parameters such as heating rate, heating temperature and rotation speed. The control factors are single, and the material properties of the rotational molding materials cannot be effectively controlled. The raw materials used for rotational molding are mostly thermoplastic materials. This type of material is easily oxidized during long-term heating, resulting in different degrees of performance degradation (such as PA materials, the performance degradation may exceed 50%), which greatly affects the performance of the product. In addition, the rotational molding cycle is relatively long. There are obvious differences in the coating, melting and curing processes of different materials during the rotational molding process. Especially for newly developed materials, a large number of experiments are required to improve the product performance in the process of application. This undoubtedly increases the development cost of materials and products, and may even fail to achieve the formulation of the optimal process plan. Finally, some products with high performance requirements also require raw materials with special properties, and such materials often require more stringent molding conditions, such as sufficient inert gas protection, drying, pressure regulation and other special links, which are far from being achieved by current equipment, resulting in the products being unable to meet the expected requirements.

[0004] With the continuous development of rotational molding technology and the continuous enrichment of application scenarios, the demand for various special application scenarios has increased accordingly, and the requirements for the uniformity and reliability of molded products have become more stringent. For example, high-pressure gas containers need to meet very strict safety performance requirements, which requires the simultaneous improvement of raw materials, processes and equipment, especially the coordinated cooperation of these three. How to more effectively control the factors of rotational molding, especially considering material factors, how to clearly observe the coating, melting and curing processes during the rotational molding process, so as to improve the efficiency of the research and development of rotational molding technology, improve the performance of rotational molded products and expand product applications, have become research hotspots in this field. Among them, the traditional rotational molding technology only provides an air environment in the rotational molding cavity. This air can easily cause the rotational molded products to be heated and oxidized, seriously affecting the appearance and performance of the rotational molded products. In addition, the traditional rotational molding molds are all closed, and the rotational molding process cannot be clearly and intuitively observed. The operator cannot observe the melting of the material inside the mold, and the process cannot be efficiently and accurately controlled.

[0005] Therefore, how to prevent the rotationally molded products from being oxidized by the air in the mold cavity of the rotational molding equipment and how to observe the melting of the material inside the mold of the rotational molding equipment in real time, thereby improving the appearance and mechanical properties of the rotationally molded products, has become an urgent problem to be solved by technical personnel in this field. Summary of the invention

[0006] The purpose of the present invention is to solve the above-mentioned problems existing in the prior art and provide a rotational molding device and method.

[0007] One of the inventive objectives of the present invention is to provide a rotational molding device, including a roto-molding cylinder, a transparent part, a heating component, a cantilever shaft, a roto-molding frame, a vent pipe, a gas component, and a driving component; the roto-molding cylinder is a hollow cylinder with two ends passing through, and its axis is parallel to the horizontal plane; the two ends of the roto-molding cylinder are respectively connected to the front cover and the rear cover; the transparent part is circular, and its diameter is larger than the inner diameter of the roto-molding cylinder; the transparent part is arranged between the front cover and the roto-molding cylinder; the heating component is connected to the outer circumferential surface of the roto-molding cylinder; one end of the cantilever shaft is fixedly connected to the rear cover, and the other end is rotatably connected to the roto-molding frame; the cantilever shaft is connected to the driving component; the vent pipe is passed through the cantilever shaft, one end of which is arranged on the roto-molding cylinder, and the other end is rotatably connected to the gas component; the vent pipe is connected to the rear cover.

[0008] In a preferred embodiment of the present invention,

[0009] The rotomolding cylinder is made of metal material; and / or,

[0010] The roto-molding cylinder is detachably connected to the front end cover; and / or,

[0011] The rotationally molded cylinder is detachably connected to the rear end cover.

[0012] In a preferred embodiment of the present invention,

[0013] The rotational molding device further comprises a front sealing ring, which is arranged between the rotational molding cylinder and the transparent member; and / or,

[0014] The rotational molding device further includes a protective pad disposed between the transparent member and the front end cover; and / or,

[0015] The rotational molding device also includes a rear sealing ring, which is arranged between the transparent member and the rear end cover.

[0016] In a preferred embodiment of the present invention,

[0017] The rotational molding device further comprises a pressure gauge, which is arranged outside the rotational molding cylinder and connected to the transparent member; and / or,

[0018] The rotational molding device further comprises a temperature sensor connected to the peripheral surface of the rotational molding cylinder; the sensitive element of the temperature sensor is arranged in the rotational molding cylinder; and / or,

[0019] The rotational molding device also includes a rotation speed sensor, which is connected to the circumferential surface of the rotational molding cylinder.

[0020] In a preferred embodiment of the present invention,

[0021] The driving assembly includes a rotating motor, a driving chain and a sprocket; one end of the driving chain and the sprocket is connected to the cantilever shaft, and the other end is connected to the rotating motor;

[0022] Preferably, the rotary motor is arranged below the rotational molding frame and connected to the rotational molding frame.

[0023] In a preferred embodiment of the present invention,

[0024] The cantilever shaft is tubular and is coaxially arranged with the rotomolding cylinder; and / or,

[0025] The vent pipe is coaxially arranged with the cantilever shaft, and the vent pipe is coaxially arranged with the rotational molding cylinder.

[0026] In a preferred embodiment of the present invention,

[0027] The gas assembly comprises a gas ball valve, and the gas ball valve is rotatably connected to the vent pipe via a rotary joint; and / or,

[0028] A joint is provided between the gas component and the ventilation pipe.

[0029] In a preferred embodiment of the present invention,

[0030] The heating component is annular; the inner diameter of the heating component is the same as the outer diameter of the rotomolding cylinder; the length of the heating component is the same as the length of the rotomolding cylinder.

[0031] In a preferred embodiment of the present invention,

[0032] The rotational molding equipment also includes a control system, which is communicatively connected with the temperature sensor, the barometer, and the rotation speed sensor.

[0033] The second object of the present invention is to provide a rotational molding method, which is performed using the rotational molding device described in one of the objects of the present invention, and comprises the following steps:

[0034] S1: Place the rotomolding material in the rotomolding cylinder; fix the transparent part and the front cover; start the drive assembly;

[0035] S2: Connect the gas component to the vacuum pump and turn on the gas component to pump the air pressure inside the rotational molding cylinder to a preset negative pressure, and then turn off the gas component;

[0036] S3: Turn on the heating component, and the rotomolding material in the rotomolding cylinder is heated and melted;

[0037] S4: After observing through the transparent part that the material inside the rotomolding cylinder is completely melted and flows evenly, connect the gas assembly to the inert gas storage device and open the gas assembly, introduce inert gas into the rotomolding cylinder to a preset pressure, and close the gas assembly;

[0038] S5: Turn off the heating component, and the rotomolding material in the rotomolding cylinder is cooled and formed;

[0039] Preferably,

[0040] In step S2, the negative pressure is preset to be -0.1 to 0 MPa, more preferably -0.08 to -0.04 MPa; and / or,

[0041] In step S3, the heating time is 0 to 1 hour, more preferably 20 to 40 minutes; and / or,

[0042] In step S4, the preset pressure is 0-0.5 MPa, preferably 0.04-0.1 MPa;

[0043] More preferably, the rotational molding method further comprises:

[0044] S6: After the rotomolded product inside the rotomolding cylinder is completely cooled, the gas component is turned on to restore the normal pressure inside the rotomolding cylinder; the drive component is turned off;

[0045] S7: Remove the front end cover and the transparent part, and take out the rotomolded product in the rotomolding cylinder.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. In the rotational molding equipment of the present invention, the material is melted in the metal rotational molding cylinder, the heat transfer time is short, the heating efficiency is high, and a transparent part is arranged at the front end of the rotational molding cylinder, which can not only ensure that the heating mode of the material is not changed, but also can be observed all the time under the actual working conditions closer to the material.

[0048] 2. The rotational molding equipment of the present invention has a visualized working window that allows the operator to monitor the whole process changes such as the melting, flow and solidification of the material during the rotational molding process in real time, providing a true and reliable basis for adjusting the process plan, which is conducive to the operator to dynamically adjust the rotational molding process in real time, and to personalize the settings and adjustments of various parameters in the molding process, thereby simplifying the molding process, improving the efficiency of rotational molding, ensuring the optimization cost and effect of the molding process, achieving the best molding effect and product performance, and efficiently and quickly preparing high-performance rotational molded products. Specifically, when using the rotational molding equipment of the present invention, parameters such as rotation speed, molding pressure, and molding temperature can be adjusted according to factors such as the type, melting point, and key special characteristics of the material to meet various special requirements for material molding, achieve the best molding effect, and realize the rotational molding of truly high-quality products.

[0049] 3. In the rotational molding equipment of the present invention, the heating component is an annular heating sleeve, and its inner diameter is the same as the outer diameter of the rotational molding cylinder. The annular electric heating sleeve is directly connected to the outer peripheral surface of the rotational molding cylinder, and has fast heating efficiency, low energy loss during heating, short working time, and easy temperature control, which can ensure the heating efficiency and precise temperature control of the rotational molding cylinder. In addition, the length of the heating component is the same as the length of the rotational molding cylinder 7, which can achieve a more uniform heating effect.

[0050] 4. The rotational molding equipment of the present invention is provided with a gas component and a vent pipe connected to the inside of the rotational molding cylinder, and has a high degree of sealing. After filling the rotational molding material, vacuuming and heating the rotational molding material to complete melting, inert gases such as nitrogen and argon can be used to pressurize the inside of the rotational molding cylinder, which not only helps to discharge the gas in the melt, so that the melt can be fully filled on the inner wall of the rotational molding cylinder, but also can protect the rotational molding material from oxidation damage to a great extent, thereby improving the performance of the product.

[0051] 5. The rotational molding equipment of the present invention is equipped with sensors and a control system to achieve real-time monitoring and control during the rotational molding process. These sensors can monitor and record various key parameters in the molding process, such as rotation speed, molding pressure, molding temperature, etc., so that operators can promptly discover and correct problems, ensure the stability of the molding process, and reduce the generation of waste. At the same time, the present invention uses an advanced control system to control the temperature, rotation speed, pressure, and time during the rotational molding process, and accurately adjust and control various parameters in the molding process; the control system can automatically adjust the working state and working parameters of the rotational molding equipment according to the preset parameter values, realizing true automation and high efficiency.

[0052] 6. The rotational molding equipment of the present invention has a simple and compact structure and low manufacturing and maintenance costs. It can be widely used in the field of rotational molding processing technology and is easy to be modified on commercial rotational molding equipment.

[0053] 7. The rotational molding method of the present invention is to fill nitrogen into the rotational molding cylinder after the rotational molding cylinder is evacuated and the rotational molding material is heated to complete melting. Under the dual effects of negative pressure and heating to a complete melting state (good fluidity), it is helpful to discharge the gas in the melt, so that the melt can be fully filled on the inner wall of the rotational molding cylinder, improving the appearance performance of the rotational molding product. At the same time, the rotational molding method of the present invention also significantly improves the mechanical properties of the rotational molding product, especially the elongation at break; the molding efficiency and yield rate of the rotational molding product are high. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The rotary molding device of the present invention;

[0055] Figure 2 The surface morphology of the rotomoulded products of Example 1, Comparative Example 1 and Comparative Example 2;

[0056] In the figure, 1-pressure gauge; 2-front end cover; 3-first bolt; 4-protection pad; 5-transparent part; 6-front sealing ring; 7-roto-molded cylinder; 8-temperature sensor; 9-rear sealing ring; 10-second bolt; 11-cantilever shaft; 12-ventilation pipe; 13-bearing; 14-drive chain and sprocket; 15-joint; 16-rotating joint; 17-ball valve; 18-frame; 19-rotating motor; 20-control system. DETAILED DESCRIPTION

[0057] In the present invention, the rotomolding material used in the examples and comparative examples is polyamide 6 (PA6), which is a conventional commercially available product.

[0058] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0059] like Figure 1As shown, the present invention provides a rotational molding device, including a roto-molding cylinder 7, a heating component, a transparent part 5, a cantilever shaft 11, a vent pipe 12, a roto-molding frame 18, a gas component and a drive component. The roto-molding cylinder 7, the heating component, the transparent part 5, the cantilever shaft 11, the vent pipe 12, the gas component and the drive component are introduced in detail below. The roto-molding cylinder 7 is a hollow cylinder with two ends through, and its axis is parallel to the horizontal plane, which is used for molding roto-molded products. Observing from the side of the roto-molding cylinder 7, it is annular; in other words, the inner circle of the roto-molding cylinder 7 is coaxially arranged with the outer circle of the roto-molding cylinder 7. Preferably, the roto-molding cylinder 7 is made of metal material. One end of the roto-molding cylinder 7 is connected to the front end cover 2, and the other end is connected to the rear end cover. The transparent part 5 is circular, and its diameter is larger than the inner diameter of the roto-molding cylinder 7. The front end cover 2 is in the shape of a circular ring, and its diameter is larger than the diameter of the transparent member 5 and smaller than the outer diameter of the rotomolding cylinder 7. Therefore, the front end cover 2 is connected to one of the side surfaces of the rotomolding cylinder 7, and the transparent member 5 is arranged between the front end cover 2 and the rotomolding cylinder 7. It should be noted that, since the front end cover 2 is in the shape of a circular ring, it will not block the staff from observing the situation inside the rotomolding cylinder 7 through the transparent member 5. The diameter of the rear end cover is also smaller than the inner diameter of the rotomolding cylinder 7, and therefore, the rear end cover is connected to the other side surface of the rotomolding cylinder 7. Preferably, the rotomolding cylinder 7 is detachably connected to the front end cover 2. For example, the two can be connected by at least two first bolts 3, preferably by eight first bolts 3, that is, the eight first bolts 3 are distributed on the outermost circle of the front end face 2. The transparent member 5 is sandwiched between the front end cover 2 and the rotomolding cylinder 7 and does not contact the first bolts 3, which not only realizes the fixing effect of the transparent member 5, but also does not cause damage to the transparent member 5 and affect the sealing effect. Similarly, the rotomolding cylinder 7 is detachably connected to the rear end cover, and illustratively, the two can be connected by at least two second bolts 10, preferably by eight second bolts 10. The rotomolding cylinder 7 is fixedly connected to the rotomolding frame 18.

[0060] The transparent part 5 is a visual working window of the rotational molding equipment, which is convenient for the operator to monitor the whole process changes of the melting, flow and solidification of the material during the rotational molding process in real time, and provide a true and reliable basis for adjusting the process plan. Exemplarily, the transparent part 5 can be made of tempered glass. In the present invention, the material is melted in the metal rotational molding cylinder 7, the heat transfer time is short, the heating efficiency is high, and the transparent part 5 is arranged at the front end of the rotational molding cylinder 7, which can not only ensure that the heating method of the material is not changed, but also can be observed at all times under the actual working conditions closer to the material.

[0061] In a preferred embodiment of the present invention, the rotational molding device further includes a front sealing ring 6, which is disposed between the rotomolding cylinder 7 and the transparent member 5 to achieve sealing inside the rotomolding cylinder 7. The front sealing ring 6 is in a circular shape, and its inner diameter is larger than the inner diameter of the rotomolding cylinder 7 and not larger than the diameter of the transparent member 5, so that it can be sandwiched between the rotomolding cylinder 7 and the transparent member 5 to play a sealing role, and will not block the staff from observing the situation inside the rotomolding cylinder 7 through the transparent member 5.

[0062] In a preferred embodiment of the present invention, the rotational molding device further includes a protective pad 4, which is arranged between the transparent member 5 and the front end cover 2, so that the transparent member 5 does not directly contact the front end cover 2, further preventing the transparent member 5 from being damaged. The protective pad 4 is in a circular shape, and its inner diameter is larger than the inner diameter of the rotational molding cylinder 7 and not larger than the diameter of the transparent member 5, so that it can be sandwiched between the front end cover 2 and the transparent member 5 to play a protective role, and will not block the staff from observing the situation inside the rotational molding cylinder 7 through the transparent member 5.

[0063] In a preferred embodiment of the present invention, the rotational molding device further includes a rear sealing ring 9, which is disposed between the rotomolding cylinder 7 and the rear end cover to achieve sealing inside the rotomolding cylinder 7. The rear sealing ring 9 is circular, and its diameter is larger than the inner diameter of the rotomolding cylinder 7, so that it can be clamped between the rotomolding cylinder 7 and the rear end cover. It should be emphasized that the rear end cover is circular rather than annular, because the rear end of the rotomolding cylinder 7 does not need to be installed with a transparent member 5 to observe the situation inside the rotomolding cylinder 7.

[0064] In a preferred embodiment of the present invention, the rotational molding device further includes a barometer 1, which is arranged outside the rotational molding cylinder 7 and connected to the transparent member 5, preferably connected to the middle of the transparent member 5, to monitor the pressure inside the rotational molding cylinder 7. Preferably, the rotational molding device further includes a temperature sensor 8, which is connected to the circumference of the rotational molding cylinder 7. The sensitive element of the temperature sensor 8 is arranged in the rotational molding cylinder 7, preferably at the center of the rotational molding cylinder 7, for real-time monitoring of the temperature inside the rotational molding cylinder 7. More preferably, the rotational molding device further includes a rotation speed sensor (not shown in the figure), which is connected to the circumference of the rotational molding cylinder 7 to monitor the rotation speed of the rotational molding cylinder 7.

[0065] The heating component is connected to the outer peripheral surface of the rotomolding cylinder 7, and is used to heat the rotomolding material in the rotomolding cylinder 7 so that the material in the rotomolding cylinder 7 reaches a molten state. Preferably, the heating component is an annular electric heating sleeve, and its inner diameter is the same as the outer diameter of the rotomolding cylinder 7. The annular electric heating sleeve is directly connected to the outer peripheral surface of the rotomolding cylinder 7, has a fast heating efficiency, low energy loss during heating, short working time, and easy temperature control, which can ensure the heating efficiency and precise temperature control of the rotomolding cylinder 7. In addition, the length of the heating component is the same as the length of the rotomolding cylinder 7 to achieve a more uniform heating effect.

[0066] One end of the cantilever shaft 11 is fixedly connected to the rear end cover, and the other end is rotatably connected to the roto-molding frame 18 to fix the position of the cantilever shaft 11. The cantilever shaft 11 is also connected to the driving assembly to realize the roto-molding of the material in the roto-molding cylinder 7. Exemplarily, the cantilever shaft 11 is provided with a bearing 13, and the cantilever shaft 11 is fixedly connected to the inner ring of the bearing 13 so that the cantilever shaft 11 rotates under the drive of the driving assembly and then drives the roto-molding cylinder 7 to rotate, and the roto-molding frame 18 is fixedly connected to the outer ring of the bearing 13 so that the roto-molding frame 18 does not rotate with the rotation of the cantilever shaft 11. Preferably, the cantilever shaft 11 is tubular and is coaxially arranged with the roto-molding cylinder 7. Preferably, the driving assembly includes a rotary motor 19, a driving chain and a sprocket 14. One end of the driving chain and the sprocket 14 is connected to the cantilever shaft 11, and the other end is connected to the output shaft of the rotary motor 19. The output shaft of the rotary motor 19 transmits the rotary power to the drive chain and sprocket 14, and then drives the cantilever shaft 11 to rotate through the drive chain and sprocket 14, thereby driving the rotation of the roto-molding cylinder 7. More preferably, the rotary motor 19 is arranged below the roto-molding frame 18 and connected to the roto-molding frame 18.

[0067] The vent pipe 12 is passed through the cantilever shaft 11, one end of which is arranged on the roto-molding cylinder 7, and the other end is rotatably connected to the gas assembly; it should be noted that the gas assembly is arranged outside the cantilever shaft 11. The vent pipe 12 is fixedly connected to the rear end cover to achieve the fixation of the position of the vent pipe 12, one end of the vent pipe 12 is arranged in the roto-molding cylinder 7 for the introduction of protective gas, and the other end of the vent pipe 12 is rotatably connected to the gas assembly to achieve the introduction of protective gas and prevent the gas assembly from rotating with the rotation of the vent pipe 12. Preferably, the vent pipe 12 is coaxially arranged with the cantilever shaft 11, and the vent pipe 12 is coaxially arranged with the roto-molding cylinder 7. More preferably, the gas assembly includes a gas ball valve 17, and the gas ball valve 17 is rotatably connected to the vent pipe 12 through a rotary joint 16. One of the functions of the gas ball valve 17 is to allow the protective gas to be introduced into the roto-molding cylinder 7 through the vent pipe 12, and the second function of the gas ball valve 17 is to regulate the amount of the protective gas introduced. The function of the rotary joint 16 is to prevent the gas component from rotating with the rotation of the vent pipe 12. Most preferably, a joint 15 is provided between the gas component and the vent pipe 12 to better connect the gas path; specifically in this embodiment, one end of the joint 15 is fixedly connected to the vent pipe 12, and the other end is rotatably connected to the rotary joint 16.

[0068] In a preferred embodiment of the present invention, the rotational molding device also includes a control system 20 which is connected to the temperature sensor 8, the barometer 1, and the rotation speed sensor in communication, so as to accurately adjust and control various parameters in the molding process according to preset parameter values, so as to achieve true automation and high efficiency. Exemplarily, the temperature, pressure, and spindle rotation speed in the rotational molding cylinder 7 can be adjusted according to the material conditions. The working mode of the control system 20 is described below. The preset parameters are input into the control system 20, and the rotational molding device can control the temperature, rotation speed, and pressure of each stage of rotational molding according to the heating time. During the rotational molding process, the staff can observe the situation of the material in the rotational molding cylinder 7 through the transparent part 5 at any time, and can adjust the parameters in the control system 20 at any time, so as to achieve precise adjustment and control. The preset parameters include but are not limited to rotation speed, pressure, temperature, and heating time.

[0069] The present invention provides a rotational molding method, which is performed using the above-mentioned rotational molding device and specifically comprises the following steps:

[0070] S1: Remove the first bolt 3, the front cover 2, the transparent member 5, the pressure gauge 1, the protective pad 4, and the front sealing ring 6; quantitatively place the rotomolding material in the rotomolding cylinder 7; fix the transparent member 5, the front sealing ring 6, the pressure gauge 1, the protective pad 4, and the front cover 2 to one end of the rotomolding cylinder 7 through the first bolt 3. Start the driving assembly, and the rotomolding cylinder 7, the cantilever shaft 11, and the vent pipe 12 rotate along the axis of the rotomolding cylinder 7.

[0071] S2: Connect the gas assembly to the vacuum pump and turn on the gas assembly to pump the air pressure inside the rotomolding cylinder 7 to a preset negative pressure; when the barometer 1 reaches the preset negative pressure, turn off the gas assembly. Preferably, the preset negative pressure is -0.1 to 0 MPa, more preferably -0.08 to -0.04 MPa.

[0072] S3: Turn on the heating component, and the material inside the rotational molding cylinder 7 begins to melt due to the heat. Preferably, the heating time is 0 to 1 hour, more preferably 20 to 40 minutes. It should be noted that the heating time can be adjusted accordingly according to the different materials.

[0073] S4: The material inside the rotomolding cylinder 7 is observed through the transparent member 5. After the material is completely melted and flows evenly, the gas assembly is connected to the inert gas storage device and the gas assembly is turned on, and the inert gas is introduced into the rotomolding cylinder 7 to a preset pressure, and the gas assembly is turned off, and the heating assembly is turned off. Preferably, the preset pressure is 0 to 0.5 MPa, preferably 0.04 to 0.1 MPa.

[0074] S5: The rotomolding material inside the rotomolding cylinder 7 is cooled and formed. During the cooling and forming process of the rotomolding material, a fan can be used to blow to cool the outer peripheral surface of the rotomolding cylinder 7. Since the rotomolding cylinder 7 is always in a rotating state, the entire peripheral surface is cooled evenly during the cooling process using the fan.

[0075] S6: After the rotomoulding product inside the rotomoulding cylinder 7 is completely cooled, the gas component is turned on to restore the pressure inside the rotomoulding cylinder 7 to normal pressure; and the driving component is turned off.

[0076] S7: Remove the first bolt 3, the front end cover 2, the transparent part 5, the pressure gauge 1, the protective pad 4, and the front sealing ring 6, and take out the rotationally molded product in the rotationally molded cylinder 7.

[0077] Example 1

[0078] S1: Open the front end cover 2, the transparent member 5 and the barometer 1 through the first bolt 3, quantitatively place the rotomolding material in the rotomolding cylinder 7, and then fix the front end cover 2, the transparent member 5 and the barometer 1 through the first bolt 3. Start the rotary motor 19, and the rotomolding cylinder 7, the cantilever shaft 11 and the vent pipe 12 rotate along the axis of the rotomolding cylinder 7.

[0079] S2: Connect the air pump through the gas ball valve 17 to pump the internal air pressure of the rotomolding cylinder 7 to a negative pressure of -0.08MPa, and observe that the pressure gauge 1 shows that the internal air pressure of the rotomolding cylinder 7 is constant. If the air pressure is not constant, check the sealing condition of the rotomolding cylinder 7 and make up for the air leakage. After confirming that the pressure gauge 1 shows that the internal air pressure of the rotomolding cylinder 7 is constant, maintain it for 5 minutes. Then close the gas ball valve 17.

[0080] S3: The material inside the rotomolding cylinder 7 is heated to melt by the heating component on the outer layer of the rotomolding cylinder 7, and the state of the material inside the rotomolding cylinder 7 is observed at any time through the transparent part 5, and the heating process is controlled at any time to adjust the rotomolding process in time.

[0081] S4: After observing through the transparent member 5 that the material inside the rotomolding cylinder 7 is completely melted and flows evenly, nitrogen is added to the rotomolding cylinder 7 to 0.1 MPa through the gas ball valve 17 connected to the nitrogen bottle, and the gas ball valve 17 is closed.

[0082] S5: Turn off the heating assembly of the outer layer of the rotomolding cylinder 7, and use a fan to blow outside the rotomolding cylinder 7 to cool the rotomolding cylinder 7.

[0083] S6: After the rotomolded product inside the rotomolding cylinder 7 is completely cooled, the gas ball valve 17 is opened to restore the gas pressure inside the rotomolding cylinder 7 to normal pressure.

[0084] S7: Open the front end cover 2, the transparent part 5 and the pressure gauge 1 through the first bolt 3 to take out the rotationally molded product.

[0085] Comparative Example 1

[0086] S1: Open the front end cover 2, the transparent member 5 and the barometer 1 through the first bolt 3, quantitatively place the rotomolding material in the rotomolding cylinder 7, and then fix the front end cover 2, the transparent member 5 and the barometer 1 through the first bolt 3. Start the rotary motor 19, and the rotomolding cylinder 7, the cantilever shaft 11 and the vent pipe 12 rotate along the axis of the rotomolding cylinder 7.

[0087] S2: Connect the air pump through the gas ball valve 17 to pump the internal air pressure of the rotomolding cylinder 7 to a negative pressure of -0.08MPa, and observe that the pressure gauge 1 shows that the internal air pressure of the rotomolding cylinder 7 is constant. If the air pressure is not constant, check the sealing condition of the rotomolding cylinder 7 and make up for the air leakage. After confirming that the pressure gauge 1 shows that the internal air pressure of the rotomolding cylinder 7 is constant, maintain it for 5 minutes. Then close the gas ball valve 17.

[0088] S3: Connect the nitrogen bottle through the gas ball valve 17 to add nitrogen into the rotational molding cylinder 7 to 0.1 MPa, and close the gas ball valve 17.

[0089] S4: The material inside the rotomolding cylinder 7 is heated to melt by the heating component on the outer layer of the rotomolding cylinder 7, and the state of the material inside the rotomolding cylinder 7 is observed at any time through the transparent part 5, and the heating process is controlled at any time to adjust the rotomolding process in time.

[0090] S5: After observing through the transparent member 5 that the material inside the rotomolding cylinder 7 is completely melted and flows evenly, the heating component of the outer layer of the rotomolding cylinder 7 is turned off.

[0091] S6: Use a fan to blow outside the rotomolding cylinder 7 to cool the rotomolding cylinder 7.

[0092] S7: After the rotomolded product inside the rotomolding cylinder 7 is completely cooled, the front end cover 2, the transparent member 5 and the pressure gauge 1 are opened by the first bolt 3 to take out the rotomolded product.

[0093] Comparative Example 2

[0094] S1: Open the front end cover 2, the transparent member 5 and the barometer 1 through the first bolt 3, quantitatively place the rotomolding material in the rotomolding cylinder 7, and then fix the front end cover 2, the transparent member 5 and the barometer 1 through the first bolt 3. Start the rotary motor 19, and the rotomolding cylinder 7, the cantilever shaft 11 and the vent pipe 12 rotate along the axis of the rotomolding cylinder 7.

[0095] S2: The material inside the rotomolding cylinder 7 is heated to melt by the heating component on the outer layer of the rotomolding cylinder 7, and the state of the material inside the rotomolding cylinder 7 is observed at any time through the transparent part 5, and the heating process is controlled at any time to adjust the rotomolding process in time.

[0096] S3: After observing through the transparent member 5 that the material inside the rotomolding cylinder 7 is completely melted and flows evenly, the heating component of the outer layer of the rotomolding cylinder 7 is turned off.

[0097] S4: Use a fan to blow outside the rotomolding cylinder 7 to cool the rotomolding cylinder 7.

[0098] S5: After the rotomolded product inside the rotomolding cylinder 7 is completely cooled, the front end cover 2, the transparent member 5 and the pressure gauge 1 are opened by the first bolt 3 to take out the rotomolded product.

[0099] The rotomolded products obtained in Example 1 and Comparative Examples 1 to 2 were magnified and photographed using a microscope. The results are as follows: Figure 2As shown. According to the national standard "GB / T 1040.1-2018", the rotomolded products obtained in Example 1 and Comparative Examples 1 to 2 were measured to obtain the tensile strength and elongation at break of the three rotomolded products (as shown in Table 1). According to the national standard "GB / T 1043.1-2008", the rotomolded products obtained in Example 1 and Comparative Examples 1 to 2 were measured to obtain the impact strength of the three rotomolded products (as shown in Table 1).

[0100] Table 1 Tensile strength, elongation at break and impact strength of the rotomoulded products in Example 1 and Comparative Examples 1-2

[0101]

[0102] analyze Figure 2 It can be seen that the cross section and outer surface of the rotomolded product of Comparative Example 2 show a large number of large bubbles, which are caused by the absorption of water in the air by the rotomolding material during the rotational molding process, greatly affecting the performance of the product. In addition, the inner surface of the rotomolded product of Comparative Example 2 can be seen to be oxidized and yellowed. In the rotomolded product of Comparative Example 1, nitrogen was filled into the rotomolding cylinder 7 before heating the rotomolding material. It was observed that there were almost no large bubbles and only a small number of tiny bubbles in the cross section and outer surface of the rotomolded product obtained. This is because the air inside the rotomolding cylinder 7 was removed and replaced with nitrogen during the rotational molding process, which is conducive to suppressing the generation of bubbles. In addition, the oxidation and yellowing phenomenon of the inner surface of the rotomolded product of Comparative Example 1 was also greatly improved. The rotomolded product of Example 1 is filled with nitrogen after the rotomolding cylinder 6 is evacuated and the rotomolding material is heated to complete melting. Under the dual effects of negative pressure and heating to a complete melting state (good fluidity), it helps to discharge the gas in the melt, so that the melt can be fully filled on the inner wall of the rotomolding cylinder 7. Therefore, fewer bubbles are observed on the cross-section and outer surface of the obtained rotomolded product. In addition, there is almost no oxidation and yellowing on the inner surface of the rotomolded product of Example 1. Analysis of the data in Table 1 shows that compared with Comparative Examples 1 and 2, the elongation at break and impact strength of Example 1 are greatly improved. It should be noted that when the elongation at break test is performed, the rotomolded products of Comparative Examples 1 and 2 are very easy to break, and bubbles can be observed to be torn at the break position.

[0103] In summary, the rotational molded product obtained by the rotational molding method of Example 1 of the present invention has significantly improved appearance and performance.

[0104] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0105] In the description of the present invention, unless otherwise specified, the terms "upper", "lower", "left", "right", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

[0106] The above technical solution is only one implementation mode of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the principles disclosed in the present invention, and it is not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the above description is only preferred and does not have a restrictive meaning.

Claims

1. A rotational molding device, characterized in that: It includes a roto-molding cylinder, a transparent part, a heating component, a cantilever shaft, a roto-molding frame, a vent pipe, a gas component, and a driving component; the roto-molding cylinder is a hollow cylinder with two ends penetrating, and its axis is parallel to the horizontal plane; the two ends of the roto-molding cylinder are respectively connected to the front cover and the rear cover; the transparent part is circular, and its diameter is larger than the inner diameter of the roto-molding cylinder; the transparent part is arranged between the front cover and the roto-molding cylinder; the heating component is connected to the outer circumferential surface of the roto-molding cylinder; one end of the cantilever shaft is fixedly connected to the rear cover, and the other end is rotatably connected to the roto-molding frame; the cantilever shaft is connected to the driving component; the vent pipe is passed through the cantilever shaft, one end of which is arranged on the roto-molding cylinder, and the other end is rotatably connected to the gas component; the vent pipe is connected to the rear cover.

2. The rotational molding device according to claim 1, characterized in that: The rotomolding cylinder is made of metal material; and / or, The roto-molding cylinder is detachably connected to the front end cover; and / or, The rotationally molded cylinder is detachably connected to the rear end cover.

3. The rotational molding device according to claim 1, characterized in that: The rotational molding device further comprises a front sealing ring, which is arranged between the rotational molding cylinder and the transparent member; and / or, The rotational molding device further includes a protective pad disposed between the transparent member and the front end cover; and / or, The rotational molding device also includes a rear sealing ring, which is arranged between the transparent member and the rear end cover.

4. The rotational molding device according to claim 1, characterized in that: The rotational molding device further comprises a pressure gauge, which is arranged outside the rotational molding cylinder and connected to the transparent member; and / or, The rotational molding device further comprises a temperature sensor connected to the peripheral surface of the rotational molding cylinder; the sensitive element of the temperature sensor is arranged in the rotational molding cylinder; and / or, The rotational molding device also includes a rotation speed sensor, which is connected to the circumferential surface of the rotational molding cylinder.

5. The rotational molding device according to claim 1, characterized in that: The driving assembly includes a rotating motor, a driving chain and a sprocket; one end of the driving chain and the sprocket is connected to the cantilever shaft, and the other end is connected to the rotating motor; Preferably, the rotary motor is arranged below the rotational molding frame and connected to the rotational molding frame.

6. The rotational molding device according to claim 1, characterized in that: The cantilever shaft is tubular and is coaxially arranged with the rotomolding cylinder; and / or, The vent pipe is coaxially arranged with the cantilever shaft, and the vent pipe is coaxially arranged with the rotational molding cylinder.

7. The rotational molding device according to claim 1, characterized in that: The gas assembly comprises a gas ball valve, and the gas ball valve is rotatably connected to the vent pipe via a rotary joint; and / or, A joint is provided between the gas component and the ventilation pipe.

8. The rotational molding equipment according to any one of claims 1 to 7, characterized in that: The heating component is annular; the inner diameter of the heating component is the same as the outer diameter of the rotomolding cylinder; the length of the heating component is the same as the length of the rotomolding cylinder.

9. The rotational molding device according to claim 4, characterized in that: The rotational molding equipment also includes a control system, which is communicatively connected with the temperature sensor, the barometer, and the rotation speed sensor.

10. A rotational molding method, carried out using the rotational molding device according to any one of claims 1 to 9, characterized in that: The steps include: S1: Place the rotomolding material in the rotomolding cylinder; fix the transparent part and the front cover; start the driving assembly; S2: Connect the gas component to the vacuum pump and turn on the gas component to pump the air pressure inside the rotational molding cylinder to a preset negative pressure, and then turn off the gas component; S3: Turn on the heating component, and the rotomolding material in the rotomolding cylinder is heated and melted; S4: After observing through the transparent part that the material inside the rotomolding cylinder is completely melted and flows evenly, connect the gas assembly to the inert gas storage device and open the gas assembly, introduce inert gas into the rotomolding cylinder to a preset pressure, and close the gas assembly; S5: Turn off the heating component, and the rotomolding material in the rotomolding cylinder is cooled and formed; Preferably, In step S2, the negative pressure is preset to be -0.1 to 0 MPa, more preferably -0.08 to -0.04 MPa; and / or, In step S3, the heating time is 0 to 1 hour, more preferably 20 to 40 minutes; and / or, In step S4, the preset pressure is 0-0.5 MPa, preferably 0.04-0.1 MPa; More preferably, the rotational molding method further comprises: S6: After the rotomolded product inside the rotomolding cylinder is completely cooled, the gas component is turned on to restore the normal pressure inside the rotomolding cylinder; the drive component is turned off; S7: Remove the front end cover and the transparent part, and take out the rotomolded product in the rotomolding cylinder.

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