Lower screw sealing leak-proof structure of double screw injection molding machine

Abstract

The application provides a lower screw sealing leak-proof structure of a double-screw injection molding machine, and relates to the field of injection molding machines.The lower screw sealing leak-proof structure comprises an upper injection assembly, a lower injection assembly, a first material port and a second material port.The upper injection assembly comprises a feeding cylinder and an upper screw.The lower injection assembly comprises a lower feeding cylinder and a lower screw.The lower screw comprises a light rod section and a screw section.The side wall of the lower feeding cylinder is provided with the first material port and the second material port.The first material port is located on the movement path of the screw section and is in communication with the discharge port of the upper injection assembly.The second material port is located on the movement path of the light rod section and is used for releasing leaked material or gas between the outer wall of the light rod section and the inner wall of the lower feeding cylinder when the lower screw pushes the material.The second hopper is in communication with the second material port and is used for containing the material released from the second material port or providing a release space for the discharged gas.The lower screw sealing leak-proof structure of the double-screw injection molding machine has a simple and compact structure, can effectively block the path of material or gas leakage to the rear end, and is safe and reliable to use.

Description

Technical Field

[0001] This invention relates to the field of injection molding machines, and in particular to a sealing and leak-proof structure for the lower screw of a twin-screw injection molding machine. Background Technology

[0002] Injection molding is one of the most commonly used molding methods in the plastics processing industry. Its principle involves heating and plasticizing plastic granules in a barrel until they become molten. The molten plastic is then injected into a mold cavity by a screw, and after cooling, the desired shape is obtained. Traditional injection molding machines typically use a single-screw structure, meaning one screw performs both plasticizing and injection functions. During the plasticizing stage, the rotating screw conveys and melts the plastic, accumulating at the screw tip. During the injection stage, the screw stops rotating and acts as a plunger, injecting the molten material into the mold.

[0003] However, single-screw injection molding machines have significant efficiency bottlenecks. Because the plasticizing and injection processes are completed by the same screw, they are sequential in time. The screw cannot plasticize during the injection phase, and injection cannot be performed during the plasticizing phase. This mechanism means that during the injection phase, the screw must wait for the molten material to be replenished before it can perform the next injection, resulting in non-productive waiting time. As injection-molded products become larger and more precise, the limitations of single-screw injection molding machines in terms of efficiency and capacity become increasingly prominent, making it difficult to meet the demands of high-efficiency production.

[0004] To overcome the aforementioned shortcomings, our technical staff proposed a twin-screw (twin-barrel) injection molding machine solution. This solution employs two independent screw systems: the upper screw (feed screw) is dedicated to plasticizing, melting and plasticizing the plastic granules; the lower screw (injection screw) is used to temporarily store the molten material and complete the injection process. After plasticizing, the upper screw transports the molten material through the feed channel to the storage space at the front end of the lower screw for temporary storage, and then the lower screw injects the molten material into the mold. This twin-screw structure enables parallel operation of plasticizing and injection—while the lower screw is injecting, the upper screw can simultaneously perform plasticizing for the next cycle, thereby effectively shortening the molding cycle and improving production efficiency.

[0005] However, twin-screw injection molding machines have revealed new technical challenges in practical applications. Specifically, during the injection process, due to the large stroke of the lower screw, the molten plastic is prone to leaking to the rear end through the unavoidable gap between the outer wall of the lower screw and the inner wall of the barrel under high pressure. The fit gap between the screw and the barrel, which is maintained to meet the relative motion requirements, becomes a leakage channel under the high pressure of the molten material. This is especially prominent in the rear end area of ​​the lower screw, where there is a lack of effective sealing structure design due to its proximity to the screw drive end. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a simple and compact lower screw sealing and leak-proof structure for a twin-screw injection molding machine that effectively blocks the leakage path of molten material to the rear end along the fit gap between the two while ensuring normal relative movement between the lower screw and the barrel.

[0007] This invention provides a leak-proof sealing structure for the lower screw of a twin-screw injection molding machine, comprising: The upper injection assembly includes a feed cylinder and an upper screw disposed inside the feed cylinder, wherein a first hopper is provided on the feed cylinder; The lower injection assembly includes a feed cylinder and a lower screw disposed within the feed cylinder and capable of circumferential rotation and axial movement. The lower screw includes a smooth section and a screw section located at the front end of the smooth section. The side wall of the feed cylinder is provided with a first feed port and a second feed port. The first feed port is located on the movement path of the screw section and communicates with the discharge port of the upper injection assembly. The second feed port is located on the movement path of the smooth section and is used to release leaked material or gas between the outer wall of the smooth section and the inner wall of the feed cylinder when the lower screw pushes the material.

[0008] Furthermore, it also includes a second hopper, which is connected to the second feed port and is used to contain the material released from the second feed port or to provide a release space for the discharged gas.

[0009] Furthermore, the second hopper includes a hopper body and a connecting pipe located at the lower end of the hopper body. The connecting pipe is coaxial with and communicates with the second feed port. The connecting pipe is provided with a spiral blade, which is used to reverse the flow of material from the second feed port and / or the connecting pipe into the second hopper.

[0010] Furthermore, a heating ring is provided on the side wall of the second feed port, which can keep the material at the bottom of the second feed port in a molten state and form a molten material layer.

[0011] Furthermore, the inner wall of the feeding cylinder is provided with one or more annular grooves communicating with the second feed port, and an annular release space is formed between the annular grooves and the outer wall of the polished rod section; when pushing material, leaked material or gas from front to back can be released to the second feed port through the annular release space.

[0012] Furthermore, the axis of the annular groove is parallel to the axis of the feed cylinder, and the plane containing the annular groove passes through the second feed inlet.

[0013] Furthermore, the feeding cylinder is provided with an annular mounting groove, which is located at the rear end of the second feed port; the annular mounting groove is provided with a sealing assembly, which includes an outer sealing ring coaxially arranged and an inner sealing ring located inside the outer sealing ring. The outer sealing ring is made of elastic sealing material, and the two ends of the inner sealing ring are staggered and have multiple strip grooves evenly distributed around the circumference, giving the inner sealing ring radial elastic deformation capability, thereby enabling the inner wall of the inner sealing ring to tightly fit against the outer wall of the smooth rod section and achieve a seal; the annular mounting groove is provided with a limiting structure for radially limiting the inner sealing ring.

[0014] Furthermore, at least one end of the annular mounting groove is provided with a limiting ring, and the end of the limiting ring is circumferentially distributed with limiting protrusions. The limiting protrusions face the inner sealing ring and can be axially inserted into the strip groove, thereby restricting the circumferential rotation of the inner sealing ring.

[0015] Furthermore, the inner wall of the inner sealing ring forms a first sealing surface and can fit and seal against the outer wall of the smooth rod section; the outer wall of the inner sealing ring forms a second sealing surface and can fit and seal against the inner wall of the outer sealing ring; and the two ends of the inner sealing ring form stop portions and can contact the two ends of the annular mounting groove to achieve axial positioning.

[0016] Furthermore, the rear end of the feeding cylinder is provided with an installation cavity, which is a stepped hole with a first hole and a second hole. A pressure ring is installed in the second hole, and the end of the pressure ring forms the annular installation groove with the first hole. A limit ring is fixed to the end of the pressure ring. The limit ring has mounting holes, a first pin hole, and a limit protrusion evenly distributed around its circumference. The mounting holes are used to fix the pressure ring with bolts. A pin is installed in the first pin hole and is used to withstand radial force. The limit protrusion can be axially inserted into the strip groove and circumferentially limit the inner sealing ring.

[0017] Furthermore, the inner sealing ring is made of engineering plastic or metal.

[0018] The lower screw sealing and leak-proof structure of this twin-screw injection molding machine features a second material inlet at the rear end of the barrel, specifically along the movement path of the smooth screw section. This inlet is designed to release any leaked material or gas, reducing the impact of high-pressure molten material on the rear structure. Even minor leaks can be promptly discharged, preventing pressure buildup that could lead to larger-scale spraying or leakage. It also prevents molten material from seeping into the rear drive mechanism and causing equipment jamming, thus improving operational safety. This lower screw sealing and leak-proof structure is simple and compact. While ensuring normal relative movement between the lower screw and the barrel, it effectively blocks the path of material or gas leaking to the rear end along the gap between them, ensuring safe and reliable operation. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 2 This is a schematic diagram of the installation of the lower injection assembly of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 3 This is a cross-sectional view of the lower injection assembly of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 4 This is a schematic diagram of the lower screw of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 5 This is a cross-sectional view of the feed cylinder of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 6 This is a schematic diagram of the annular groove in the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 7 This is a schematic diagram of the installation of the sealing assembly of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 8 This is a schematic diagram of the mounting cavity of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 9 This is an exploded structural diagram of the sealing assembly of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention. Figure 10 This is a schematic diagram of the outer sealing ring of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 11 This is a schematic diagram of the inner sealing ring of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 12 This is a schematic diagram of the limiting ring of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; Figure 13 This is a schematic diagram of the pressure ring structure of the lower screw sealing and leak-proof structure of the twin-screw injection molding machine of the present invention; In the diagram: 1. Frame; 11. Front base; 110. Material inlet; 12. Slide; 13. Drive unit; 132. Pulley; 14. Push-pull cylinder; 141. Output shaft; 21. Upper cylinder; 31. Lower cylinder; 310. Center hole; 311. First material inlet; 312. Second material inlet; 3101. Annular groove; 3102. First bore; 3103. Second bore; 32. Lower screw; 321. Polished section; 322. Screw section; 323. 4. Connector, inner sealing ring, 4a. first sealing surface, 4b. second sealing surface, 4c. stop part, 410. strip groove, 5. outer sealing ring, 51. annular protrusion, 6. limiting ring, 62. limiting protrusion, 610. mounting hole, 611. first pin hole, 63. pin, 7. pressure ring, 71. pressure ring body, 710. mounting groove, 7101. screw hole, 7102. second pin hole, 72. flange part, 91. first hopper, 92. second hopper. Detailed Implementation

[0020] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0021] See Figures 1-13 The present invention provides a lower screw sealing and leak-proof structure for a twin-screw injection molding machine, which includes a frame 1, on which an upper injection assembly and a lower injection assembly are provided.

[0022] The upper injection assembly includes a feed cylinder 21 and an upper screw disposed inside the feed cylinder 21. A first hopper 91 is provided on the feed cylinder 21 for feeding materials.

[0023] The injection assembly includes a feed cylinder 31 and a lower screw 32 disposed within the feed cylinder 31. The lower screw 32 can rotate circumferentially and move axially. Specifically, a slide block 12 is slidably mounted on the frame 1, and the sliding direction of the slide block 12 is parallel to the axis of the feed cylinder 31. The rear end of the lower screw 32 is rotatably connected to the slide block 12. At the same time, a drive device 13 is mounted on the slide block 12. The drive device 13 is an electric motor or a hydraulic motor, and its output end is connected to the pulley 132 at the rear end of the lower screw 32 via a synchronous belt, thereby driving the lower screw 32 to rotate circumferentially. A push-pull cylinder 14 is provided at the rear end of the frame 1. The output shaft 141 of the push-pull cylinder 14 is connected to the slide block 12 and is used to drive the slide block to slide axially, thereby driving the lower screw to move axially.

[0024] The lower screw 32 includes a smooth rod section 321 and a screw section 322. The screw section 322 is coaxial with the smooth rod section 321 and is located at the front end of the smooth rod section 321. The smooth rod section 321 is a smooth rod structure with a circular cross-section and an overall round rod structure. The side wall of the screw section is provided with a spiral structure. A connector 323 is provided at the rear end of the smooth rod section 321. A keyway is provided on the side wall of the connector 323, which is connected to the rotating mechanism on the slide block 12 through a key.

[0025] The length of the polished rod section 321 is greater than the length of the screw section 322. The rear end of the polished rod section 321 passes through the rear end of the feed cylinder 31 and extends to the outside of the feed cylinder 31, where it connects with the slide block 12.

[0026] A first feed port 311 and a second feed port 312 are provided on the side wall of the feed cylinder 31. The first feed port 311 is located in the middle of the feed cylinder 31, facing upwards, and is located on the movement path of the screw section 322. The first feed port 311 is connected to the outlet of the upper injection assembly and is used to receive the molten material output by the upper injection assembly. When feeding, the front end of the lower screw moves backward to a position close to the first feed port 311.

[0027] The second feed port 312 is located at the rear end of the feed cylinder and is located on the movement path of the polished rod section 321. The screw section 322 will not move to the second feed port 312. The second feed port 312 is used to release leaked material or gas between the outer wall of the polished rod section 321 and the inner wall of the feed cylinder 31 when the lower screw 32 pushes the material.

[0028] This application provides a second feed port at the rear end of the feed cylinder, specifically on the movement path of the smooth rod section, which is dedicated to releasing leaked materials or gas. This reduces the impact of high-pressure molten material on the rear structure. Even if there is a small amount of leakage, it can be discharged in time, avoiding pressure buildup that could lead to larger-scale spraying or leakage. It also prevents molten material from seeping into the rear drive mechanism and causing the equipment to jam, while improving the safety of use.

[0029] The first feed port is located in the middle and receives the high-pressure molten material output by the upper screw. The second feed port is located at the rear end and can release the high-pressure molten material that the rear end originally had to withstand through the second feed port. This allows the sealing part of the bare rod section extending out of the barrel wall to only withstand atmospheric pressure or low-pressure gas, which greatly improves the installation difficulty and reliability of the sealing part at this point.

[0030] In this application, the screw section is responsible for conveying and ejecting the plasticized material, while the smooth section, as a smooth cylinder, is responsible for transmission and axial displacement. Since the second feed port is located on the movement path of the smooth section, and the screw section will not move backward to that position, it ensures that when depressurizing, the pressure relief port faces the smooth cylindrical surface, rather than the screw section with helical edges.

[0031] In this embodiment, a second hopper 92 is also included. The second hopper 92 is connected to the second feed port 312 and is used to contain the material released from the second feed port 312 or to provide a release space for the discharged gas.

[0032] In injection molding workshops, leaks of high-temperature molten plastic can generate fumes, volatiles, or carbonized impurities, which not only pollute the environment but may also affect the health of operators. This application provides a dedicated buffer container for leaked trace amounts of molten material or high-pressure gas by setting up a second hopper, which changes the problem of leaked material flowing along the outer wall of the barrel or spraying onto the machine frame and the ground, thus achieving closed-loop depressurization and collection. Furthermore, the second hopper can temporarily store these waste materials, which can be centrally recycled and crushed after cooling for use as secondary materials, thereby reducing raw material loss costs.

[0033] Meanwhile, an exhaust port can be set on the second hopper. This exhaust port is connected to a vacuum pump or waste gas treatment device to actively extract harmful gases from the rear end of the barrel and keep the interior of the rear end of the barrel under a slight negative pressure. This actively adsorbs and removes volatile components from the molten material, improves the smoothness of the screw operation, and avoids the volatiles from affecting the workshop environment.

[0034] In this embodiment, the second hopper 92 includes a hopper body and a connecting pipe located at the lower end of the hopper body. A cover plate is provided at the open end of the upper part of the hopper body. The connecting pipe is coaxial with and communicates with the second material outlet 312. A spiral blade is provided inside the connecting pipe. The spiral blade includes a main shaft and a spiral blade body provided on the side wall of the main shaft. The main shaft is connected to a motor or handle. The spiral blade can be driven to rotate electrically or manually, and it can achieve forward and reverse rotation. The spiral blade is used to transport the material in the second material outlet 312 and the connecting pipe in the opposite direction to the second hopper 92. Preferably, the edge of the spiral blade is provided with a blade. The second material outlet is located on the side wall of the discharge cylinder. The leaked material or gas is outward. If the leaked material has high viscosity or cools quickly, it is easy to accumulate and solidify in the connecting pipe, blocking the pressure relief channel. The spiral blade rotates under the drive of the motor or handle, pushing the material in the connecting pipe and the second material outlet back to the hopper body in the opposite direction. It can forcibly clean the connecting pipe and ensure that the pressure relief channel is unobstructed for a long time.

[0035] In this embodiment, a heating ring is provided on the side wall of the second feed port 312. The heating ring can keep the material at the bottom of the second feed port 312 in a molten state. The heating ring heats the second feed port, keeping the material in a molten state, maintaining good fluidity, avoiding solidification that could block the pressure relief channel, and ensuring the reliability of the release port.

[0036] The heating coil creates a layer of molten material inside the second feed port, forming a buffer zone. On one hand, it acts as a pressure buffer layer, utilizing the viscous damping effect of the molten material to transform the impact pressure of leaking material into stable discharge, eliminating the risk of splashing. On the other hand, it acts as a thermal buffer layer, isolating the direct heat exchange between the external cold zone and the internal hot zone, preventing the cold material from solidifying and blocking the pressure relief channel. Furthermore, it reduces the escape velocity of volatile gases and traps entrained solid particles, providing stable operating conditions for subsequent negative pressure pumping and material recovery. At the same time, the heating coil melts the material, reducing the torque load when the spiral blades shear and push the material, extending the motor's service life, and making manual operation easier and less labor-intensive, facilitating the cleaning of internal materials.

[0037] In this application, one or more annular grooves 3101 are provided on the inner wall of the feed cylinder 31. These annular grooves 3101 communicate with the second feed inlet 312. Specifically, the axis of the annular groove 3101 is parallel to the axis of the feed cylinder 31, preferably coaxial, and the plane containing the annular groove 3101 passes through the second feed inlet 312. (See reference...) Figure 6 The annular groove 3101 and the outer wall of the smooth rod section 321 form an annular release space; when pushing material, the leaked material or gas from front to back can be released to the second material port 312 through the annular release space; the edge of the annular groove is provided with rounded corners or bevels.

[0038] Because the gap between the polished rod section and the inner wall of the barrel is extremely small, when molten material or gas leaks towards the rear end along this gap, only a small portion directly opposite the second feed port can be quickly discharged, while a high-pressure retention zone is formed at the position far from the second feed port. In this embodiment, by setting an annular groove, the pressure relief space is expanded. When molten material leaks from the front end of the screw to this section, the material in the entire circumferential direction can enter the annular groove and flow along the annular channel to the second feed port for discharge. This allows the leakage pressure at any position of this section to be released in time, avoiding single-point spraying or uneven wear of the inner wall of the barrel due to excessive local pressure. The annular groove is equivalent to setting a flow interception area in the middle position. When the molten material or gas moving towards the rear end along the gap reaches the position of the annular groove, it will be intercepted by the annular space and discharged towards the second feed port, forming an effective sealing and blocking structure in the axial direction, which greatly reduces the pressure on the rear sealing element.

[0039] In this embodiment, the width of the annular groove is 2-10mm, the depth is 1-5mm, and the cross-sectional shape of the annular groove is any one of rectangle, trapezoid or arc. The side wall of the annular groove facing the second feed port is provided with a guide slope. The guide slope is used to smoothly guide the material or gas in the annular groove to the second feed port to reduce flow resistance.

[0040] When the inner wall of the feed cylinder is provided with multiple annular grooves, each annular groove is distributed at intervals along the axial direction of the feed cylinder, and each annular groove is connected to the second feed port, forming a multi-stage pressure relief structure.

[0041] In this embodiment, an annular mounting groove is also provided inside the feeding cylinder 31. This annular mounting groove is located at the rear end of the second feed port 312, specifically at the end of the feeding cylinder 31. The annular mounting groove is coaxial with the feeding cylinder 31. A sealing assembly is provided inside the annular mounting groove. The sealing assembly includes an outer sealing ring 5 and an inner sealing ring 4, which are coaxially arranged. The inner sealing ring 4 is located inside the outer sealing ring 5, and the two are on the same radial plane. The outer sealing ring 5 is made of an elastic sealing material, which in this embodiment is made of high-temperature resistant rubber or silicone. The inner sealing ring 4 is circular in shape and has a rectangular cross-section. The inner wall diameter of the inner sealing ring 4 is the same as the outer wall diameter of the polished rod section. The two ends of the inner sealing ring 4 are staggered and evenly distributed circumferentially. Multiple strip grooves 410 are provided at both ends of the inner sealing ring. The length of the strip groove 410 is greater than 50% of the width of the inner sealing ring. The number of strip grooves at both ends is the same and they are evenly distributed circumferentially. The strip grooves at both ends are staggered, which makes the surface of the entire inner sealing ring 4 form a wave-shaped structure, giving the inner sealing ring 4 radial elastic deformation capability. This allows the inner wall of the inner sealing ring 4 to fit tightly against the outer wall of the smooth rod section 321 and achieve a seal. The outer sealing ring is interference-fitted between the outer side of the inner sealing ring and the inner wall of the annular mounting groove. At the same time, a limiting structure is provided in the annular mounting groove to radially limit the inner sealing ring and prevent it from wearing the outer sealing ring due to circumferential rotation with the smooth rod section.

[0042] Because the polished rod section itself undergoes circumferential rotation and axial movement, and generates temperature, conventional rubber or silicone seals are prone to frictional heating and tearing failure when in direct contact with the rotating or moving polished rod section. This application addresses this by setting an inner and outer sealing ring structure. The outer sealing ring is made of an elastomer and provides radial preload, while the inner sealing ring directly contacts the polished rod section. The two seals combine to form a sealing assembly, ensuring sealing performance under high pressure and significantly extending the service life of the seal.

[0043] The strip groove divides the complete circular ring into multiple interconnected S-shaped elastic arms. When the inner sealing ring is radially compressed by the outer sealing ring, the strip groove can close or open, causing the inner ring as a whole to radially contract like a spring, thereby actively conforming to the outer diameter of the polished rod section. This elastic deformation capability ensures that the inner wall of the inner sealing ring is always tightly fitted to the outer wall of the polished rod section, achieving a seal.

[0044] Meanwhile, by setting a limiting structure, the inner sealing ring is circumferentially fixed, so that it can only produce radial elastic deformation and cannot rotate circumferentially. This keeps the sealing assembly in a static sealing state relative to the smooth rod section, avoiding rotation and wear on the outer sealing ring, thus improving service life and sealing reliability.

[0045] In this embodiment, the outer sealing ring 5 is generally annular with a rectangular cross-section. Multiple annular protrusions 51 are provided on the outer wall of the outer sealing ring 5 to form sealing lips. These annular protrusions 51 are equidistantly arranged along the axial direction of the outer sealing ring, forming multiple sealing lips, thereby enhancing the sealing effect between the outer sealing ring and the inner wall of the annular mounting groove. A first sealing surface 4a is formed on the inner wall of the inner sealing ring 4, which can fit against the outer wall of the smooth rod section 321 and achieve a seal. A second sealing surface 4b is formed on the outer wall of the inner sealing ring 4, which can fit against the inner wall of the outer sealing ring 5 and achieve a seal. Stop portions 4c are formed at both ends of the inner sealing ring 4, which can contact both ends of the annular mounting groove to achieve axial limiting.

[0046] In this embodiment, the inner sealing ring is made of engineering plastic or metal. Preferably, it is made of engineering plastic or metal with self-lubricating properties. In this embodiment, the inner sealing ring is preferably made of self-lubricating engineering plastic or self-lubricating metal matrix composite material, which has high strength, low coefficient of friction, reduces wear, and extends service life.

[0047] At least one end of the annular mounting groove is provided with a limiting ring 6, i.e. the aforementioned limiting structure. The end of the limiting ring 6 is circumferentially distributed with limiting protrusions 62. The limiting protrusions 62 face the inner sealing ring 4 and can be axially inserted into the strip groove 410, thereby restricting the circumferential rotation of the inner sealing ring 4. The width of the limiting protrusion is smaller than the width of the strip groove, so it will not affect its deformation capacity. Preferably, the number of limiting protrusions is the same as the number of strip grooves on one side.

[0048] In this embodiment, an installation cavity is provided at the rear end of the feeding cylinder 31. This cavity is coaxial with and communicates with the central hole 310 inside the feeding cylinder 31. The installation cavity is a stepped hole with a smaller front end and a larger rear end, and has a first hole 3102 and a second hole 3103. The first hole 3102 is located at the front end and has a relatively smaller diameter, while the second hole is located at the rear end and has a relatively larger diameter, forming a stepped surface between them. A pressure ring 7 is installed inside the second hole 3103. An annular installation groove is formed between the end of the pressure ring 7 and the first hole 3102 for installing a sealing assembly. The inner sealing ring 6 is fixed with mounting holes 610, first pin holes 611, and limiting protrusions 62 evenly distributed circumferentially. The mounting holes 610 are used to fix the inner sealing ring 7 with bolts. The mounting holes are countersunk holes for installing hexagonal socket head cap screws, and the bolt heads are not exposed after installation. The first pin holes 611 are fitted with pins 63 and are used to bear radial force and provide radial positioning. The limiting protrusions 62 can be axially inserted into the strip groove 410 to circumferentially limit the inner sealing ring. The inner sealing ring adopts a split structure, which facilitates the processing, assembly, and maintenance of the parts.

[0049] Specifically, the pressure ring 7 includes a cylindrical pressure ring body 71. The end face of the first end of the pressure ring body is concave to form a mounting groove 710, which can just accommodate the limiting ring 6. Screw holes 7101 and second pin holes 7102 are evenly distributed circumferentially on the end face of the mounting groove 710, which correspond to the mounting holes and first pin holes on the limiting ring, and are used to install bolts and pins respectively. The second end of the pressure ring body 71 extends radially outward to form a flange portion 72. Holes are evenly distributed circumferentially on the flange portion for fixing to the feed cylinder by bolts to achieve fixing and tightening.

[0050] In this embodiment, the rear end of the feeding cylinder 31 is fixed on the front base 11 of the frame 1. A material hole 110 is provided on the front base 11, which is connected to the second material port on the feeding cylinder 31, and the second hopper is fixed on the front base 11.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A leak-proof sealing structure for the lower screw of a twin-screw injection molding machine, characterized in that, include: The upper injection assembly includes a feed cylinder and an upper screw disposed inside the feed cylinder, wherein a first hopper is provided on the feed cylinder; The lower injection assembly includes a feed cylinder and a lower screw disposed within the feed cylinder and capable of circumferential rotation and axial movement. The lower screw includes a smooth section and a screw section located at the front end of the smooth section. The side wall of the feed cylinder is provided with a first feed port and a second feed port. The first feed port is located on the movement path of the screw section and communicates with the discharge port of the upper injection assembly. The second feed port is located on the movement path of the smooth section and is used to release leaked material or gas between the outer wall of the smooth section and the inner wall of the feed cylinder when the lower screw pushes the material. The second hopper, connected to the second feed port, is used to contain the material released from the second feed port or to provide a release space for the discharged gas.

2. The leak-proof sealing structure for the lower screw of a twin-screw injection molding machine as described in claim 1, characterized in that: The second hopper includes a hopper body and a connecting pipe located at the lower end of the hopper body. The connecting pipe is coaxial with and communicates with the second feed port. The connecting pipe is provided with a spiral blade, which is used to reverse the flow of material from the second feed port and / or the connecting pipe into the second hopper.

3. The leak-proof sealing structure for the lower screw of a twin-screw injection molding machine as described in claim 1, characterized in that: The side wall of the second feed port is provided with a heating ring, which can keep the material at the bottom of the second feed port in a molten state and form a molten material layer.

4. The leak-proof sealing structure for the lower screw of a twin-screw injection molding machine as described in claim 1, characterized in that: The inner wall of the feeding cylinder is provided with one or more annular grooves communicating with the second feed port, and an annular release space is formed between the annular grooves and the outer wall of the smooth rod section; when pushing material, the leaked material or gas from front to back can be released to the second feed port through the annular release space.

5. The lower screw sealing and leak-proof structure of the twin-screw injection molding machine as described in claim 4, characterized in that: The axis of the annular groove is parallel to the axis of the feed cylinder, and the plane containing the annular groove passes through the second feed inlet.

6. The leak-proof sealing structure for the lower screw of a twin-screw injection molding machine as described in claim 1, characterized in that: The feeding cylinder is provided with an annular mounting groove, which is located at the rear end of the second feed port. A sealing assembly is provided in the annular mounting groove. The sealing assembly includes an outer sealing ring arranged coaxially and an inner sealing ring located inside the outer sealing ring. The outer sealing ring is made of elastic sealing material. The two ends of the inner sealing ring are staggered and have multiple strip grooves evenly distributed around its circumference, giving the inner sealing ring radial elastic deformation capability. This allows the inner wall of the inner sealing ring to tightly fit against the outer wall of the smooth rod section and achieve a seal. A limiting structure is provided in the annular mounting groove for radially limiting the inner sealing ring.

7. The lower screw sealing and leak-proof structure of the twin-screw injection molding machine as described in claim 6, characterized in that: At least one end of the annular mounting groove is provided with a limiting ring, and the end of the limiting ring is circumferentially distributed with limiting protrusions. The limiting protrusions face the inner sealing ring and can be axially inserted into the strip groove, thereby restricting the circumferential rotation of the inner sealing ring.

8. The leak-proof sealing structure for the lower screw of a twin-screw injection molding machine as described in claim 6, characterized in that: The inner wall of the inner sealing ring forms a first sealing surface and can fit and seal against the outer wall of the smooth rod section. The outer wall of the inner sealing ring forms a second sealing surface and can fit and seal against the inner wall of the outer sealing ring. The two ends of the inner sealing ring form stop portions and can contact the two ends of the annular mounting groove to achieve axial positioning.

9. The lower screw sealing and leak-proof structure of the twin-screw injection molding machine as described in claim 6, characterized in that: The rear end of the feed cylinder has an installation cavity, which is a stepped hole with a first hole and a second hole. A pressure ring is installed in the second hole, and an annular installation groove is formed between the end of the pressure ring and the first hole. A limit ring is fixed to the end of the pressure ring. The limit ring has mounting holes, a first pin hole, and a limit protrusion evenly distributed around its circumference. The mounting holes are used to fix the pressure ring with bolts. A pin is installed in the first pin hole and is used to withstand radial force. The limit protrusion can be axially inserted into the strip groove and circumferentially limit the inner sealing ring.

10. The leak-proof sealing structure for the lower screw of a twin-screw injection molding machine as described in claim 6, characterized in that: The inner sealing ring is made of engineering plastic or metal.

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