Double action ring oil cylinder for large plastic pipe joint die pressing production

Abstract

The application discloses a double-acting annular oil cylinder for large plastic pipe joint die molding production and belongs to the technical field of high-end hydraulic equipment. The oil cylinder comprises a cylinder body and coaxially distributed first and second piston groups, and the cylinder body is provided with double oil inlet / outlet ports controlled independently. During operation, the first piston group is first actuated to drive the male die to move downward and keep pressure, and the second piston group is second actuated to drive the pressure head to apply pressure. Through double-oil-port pressure linkage adjustment, the first oil inlet pressure and the second oil inlet pressure are dynamically matched during the die molding pressure keeping stage, the upward reverse force generated in the male die step area is absorbed and offset in real time by using the hydraulic flexible balance characteristics, and the traditional mechanical locking structure is replaced. In conclusion, the application completely solves the male die floating problem during large pipe joint die molding, and has the advantages of simplified structure, low equipment cost, self-adaptive pressure adjustment, high die molding precision, significant improvement of the yield and the like.

Description

Technical Field

[0001] This invention relates to the field of high-end hydraulic equipment and intelligent molding equipment technology, and in particular to a double-acting annular cylinder for the molding production of large thick-walled plastic pipes. Background Technology

[0002] PVC socket fittings are one of the most common connection methods in the plastic pipe industry. For large, thick-walled pipe fittings with a diameter of 500 mm or more, due to limitations in injection molding equipment, compression molding is now the most common production method.

[0003] In the molding process, the punch first descends to the mold-closing position, and then molten plastic is injected into the cavity formed between the punch and the die. A circular pressure head (also called a pressure ring) applies pressure to the molten plastic inside the die, molding the plastic. However, because pipe fittings of different diameters need to be connected at both ends, a transition step area is provided at the bottom of the punch. During the pressure application process, the molten plastic generates a huge upward counterforce on the punch step area, forcing the punch to move upwards. This causes the molding process to fail, resulting in defects such as flash and insufficient material in the product.

[0004] To address the aforementioned problems, existing technologies typically employ a mechanical locking structure to fix the position of the punch. For example, Chinese invention patent CN103879007B discloses a double-acting hydraulic press, which uses separately arranged inner and outer hydraulic cylinders. The inner piston drives the inner forming die to move first, and the outer piston drives the outer forming die to move subsequently, achieving sequential extrusion molding. However, this technical solution has the following shortcomings: Relying on mechanical bearing reaction force: Although sequential actions are achieved, the reaction force generated during the molding process still needs to be borne by the frame and mechanical locking structure, which places extremely high demands on the rigidity of the equipment and the strength of the mold locking mechanism; Complex structure and high cost: It requires the arrangement of complex mechanical locking mechanisms (such as limit pins, locking blocks, servo locking cylinders, etc.) and the use of expensive multi-functional hydraulic presses, resulting in a significant increase in equipment investment and operation and maintenance costs; Weak impact resistance: Mechanical rigid clamping molds are prone to fatigue fracture when subjected to transient high pressure reaction forces, which affects the service life of equipment and product yield. The split layout occupies a large space: the internal and external hydraulic cylinders are arranged separately, the overall size of the equipment is huge, the space utilization rate is low, and it is not conducive to the integrated design of large molds.

[0005] Therefore, there is an urgent need for a dual-action ring cylinder that can reliably offset molding reaction force with a simplified structure, avoid mechanical mold clamping failure, and significantly reduce production costs. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a technical solution that can solve the above problems.

[0007] This invention provides a double-acting annular hydraulic cylinder for the molding production of large plastic pipe fittings, comprising: Cylinder block; A first piston group and a second piston group are coaxially disposed in the cylinder body, and the first piston group and the second piston group are arranged in an inner and outer ring along the radial direction; The cylinder body is provided with a first oil inlet and a first oil outlet that connect the working chamber of the first piston assembly, and a second oil inlet and a second oil outlet that connect the working chamber of the second piston assembly. The first oil inlet and the second oil inlet are configured to independently control the input timing of the pressure oil, so that the first piston group moves first to drive the punch downward and maintain pressure, and the second piston group moves later to drive the pressure head to apply pressure to the molten plastic, so as to apply and maintain hydraulic force on the punch during the molding process.

[0008] Furthermore: the working hydraulic pressure P2 of the second oil inlet is adjustable according to the molding process parameters; the working hydraulic pressure P1 of the first oil inlet is configured to be adjusted in conjunction with the change of P2, so that during the molding and holding stage, P1 and P2 always meet the hydraulic flexible balance condition, so as to dynamically absorb and offset the upward displacement trend of the punch step area caused by the reaction force of molten plastic.

[0009] Furthermore, the hydraulic flexible balance condition includes: when P2≤P1, the downward holding force generated by the first piston group is greater than or equal to the upward reverse force generated by the punch step area; when P2 increases with process requirements, P1 increases synchronously and maintains the pressure relationship of P2≤P1 to maintain the hydraulic flexible balance.

[0010] Furthermore, the hydraulic flexible balance condition includes: when P2 > P1, P1 and P2 satisfy the following relationship in real time: P1≥P2×(As / A1)×k×cosθ; Where: As is the horizontal projected area of ​​the punch step area; A1 is the effective pressure-bearing area of ​​the first piston group; θ is the inclination angle of the punch step area relative to the horizontal molding plane, with a value range of 0°~90°; k is the plastic melt flow and friction correction coefficient, with a value range of 0.6~0.9; When P2 is adjusted according to process requirements, P1 is adjusted accordingly according to the above relationship, so that the inequality continues to hold during the molding and holding pressure stage.

[0011] Furthermore, the hydraulic pressure matching between the first oil inlet and the second oil inlet is achieved through one of the following methods: Method 1: The first oil inlet and the second oil inlet are respectively connected to the first hydraulic power unit and the second hydraulic power unit. The first hydraulic power unit and the second hydraulic power unit are respectively equipped with pressure detection elements and pressure control elements to form a pressure linkage control loop. Method 2: The first oil inlet and the second oil inlet are connected to the same hydraulic power unit and connected through a flow distribution valve group, so that the working pressure of the first oil inlet and the second oil inlet is kept equal or distributed according to a preset ratio.

[0012] Further: In the first method, the first hydraulic power unit and the second hydraulic power unit respectively include a hydraulic pump, a relief valve and a pressure sensor. The output end of the pressure sensor is electrically connected to the controller. The controller adjusts the set pressure of the relief valve of the second hydraulic power unit or the output flow of the hydraulic pump according to the pressure signal of the first oil inlet, so that the working hydraulic pressure P2 of the second oil inlet and the working hydraulic pressure P1 of the first oil inlet satisfy the relationship described in claim 3 or claim 4, thereby realizing dynamic tracking and matching.

[0013] Further: In the second method, the flow distribution valve group is one of a flow divider / combiner valve, a proportional flow divider valve, or a series speed control valve; the pipelines of the first oil inlet and the second oil inlet are respectively provided with a one-way sequence valve or a hydraulically controlled one-way valve, which is used to maintain the pressure stability of the first oil inlet after the first piston group acts to maintain pressure, so that when P2 is adjusted according to the process, P1 can respond synchronously according to a preset ratio or an independent set value to maintain the hydraulic flexible balance condition.

[0014] Furthermore: Both the first piston group and the second piston group include a piston body and multiple piston push rods evenly distributed along the circumference; one end of each of the multiple piston push rods is detachably connected to the piston body, and the other end constitutes a drive output end.

[0015] Furthermore, it also includes an annular load distribution ring, wherein the drive output ends of the multiple piston push rods are respectively fixedly connected to one side end face of the annular load distribution ring, and the other side end face of the annular load distribution ring is used to connect to the punch or pressure head; The annular load distribution ring rigidly connects the multiple piston push rods into an integral force-bearing ring, transmitting the driving force of the piston assembly evenly and synchronously to the punch or pressure head.

[0016] Further: The cylinder body includes a cylinder top cover and a cylinder base that respectively form the two ends of the cylinder body, as well as a central column, a first cylinder and a second cylinder coaxially assembled between the cylinder top cover and the cylinder base; The spindle is fixedly installed at the center of the cylinder, and the first cylinder is coaxially sleeved on the outside of the spindle, and the two cooperate to form the first working chamber of the first piston assembly. The second cylinder is coaxially sleeved on the outside of the first cylinder, and the first cylinder and the second cylinder cooperate to form the second working chamber of the second piston assembly.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. Replacing mechanical rigid mold clamping with hydraulic flexible balancing completely solves the problem of punch floating. This invention employs a coaxially arranged first and second piston assembly, along with an independently controllable dual-inlet system. The first piston assembly moves first, driving the punch downwards and maintaining pressure, while the second piston assembly moves subsequently, driving the pressure head to apply pressure. During the molding and pressure-holding stage, the first inlet maintains hydraulic pressure, creating a "hydraulic flexible constraint" on the punch. When the punch step area experiences an upward counterforce from the molten plastic, this counterforce is transmitted through the punch to the pressure-bearing surface of the first piston assembly, forming a dynamic torque balance with the circuit hydraulic pressure. This completely counteracts the punch's upward tendency, eliminating the need for traditional mechanical locking structures.

[0018] 2. Dynamic pressure matching control to adapt to different materials and process requirements. In this invention, the working hydraulic pressure P2 of the second oil inlet can be dynamically adjusted according to the plastic material (such as PVC-U, PVC-M), pipe wall thickness, and product grade requirements. The pressure P1 of the first oil inlet is configured to adjust in conjunction with changes in P2, maintaining a pressure relationship of P2≤P1 under the condition of P2≤P1, and satisfying the formula P1≥P2×(As / A1)×k×cosθ in real time under the condition of P2>P1. This dynamic matching mechanism ensures that the hydraulic flexible balance condition is always maintained under various molding process conditions, the punch displacement is controlled within 0.05mm, and there are no flash or missing material at the product steps.

[0019] 3. Flexible configuration of isobaric or dual-pump linkage, balancing cost and accuracy. This invention provides two pressure matching methods: Method 1 uses independent pressure supply from dual hydraulic power units + pressure linkage control circuit, suitable for high-precision molding conditions; Method 2 uses homogeneous pressure supply from a single hydraulic power unit + flow distribution valve group, suitable for normal molding conditions. Users can flexibly choose according to product grade and budget. Method 2 can save more than 30% of hydraulic system costs while meeting the balance requirements under P2≤P1 conditions.

[0020] 4. The split multi-rod structure with annular load distribution ring significantly improves the reliability of large hydraulic cylinders. For large hydraulic cylinders with a diameter of 500mm or more, this invention replaces the traditional one-piece heavy-duty piston rod with multiple split piston push rods evenly distributed circumferentially (e.g., 16 on the outer ring and 8 on the inner ring), and rigidly connects the multiple push rods into a single load-bearing ring through an annular load distribution ring. This design has the following advantages: Reduce the equivalent weight of moving parts and decrease inertial impact; Discretized hydraulic thrust avoids single-point overload and localized stress concentration; The annular load distribution ring achieves secondary load equalization, ensuring uniform circumferential pressure transmission; When a single push rod is damaged, it can be quickly replaced, significantly reducing maintenance costs and downtime.

[0021] 5. Modular assembly cylinder block structure, breaking through the bottleneck of large hydraulic cylinder manufacturing. This invention disassembles the cylinder body into independent components such as the cylinder top cover, cylinder base, shaft column, first cylinder, and second cylinder, which are then assembled using high-strength bolts. This facilitates the segmented precision machining and heat treatment of large-size cylinder bodies, reduces the difficulty of overall casting / forging, enables rapid partial disassembly and maintenance, and facilitates transportation and on-site assembly, thus solving the logistical challenges of ultra-large hydraulic cylinders.

[0022] 6. Significant overall economic benefits Compared with the existing "complex mechanical clamping mechanism + multi-functional hydraulic press" solution, this invention achieves a comprehensive reduction in equipment cost, operation and maintenance cost and production cost through multiple technologies such as hydraulic flexible balance to replace mechanical rigid clamping, modular assembly to reduce manufacturing difficulty, and split structure to improve maintenance convenience. At the same time, it significantly improves product yield and equipment lifespan, bringing considerable economic benefits to large plastic pipe fitting manufacturers.

[0023] Therefore, in the field of high-end equipment manufacturing, this invention can significantly reduce equipment energy consumption and maintenance costs by replacing traditional rigid mechanical clamping with hydraulic flexible balancing, which is in line with the green and intelligent upgrading direction and development trend of the manufacturing industry.

[0024] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a front view of the present invention; Figure 3 This is a cross-sectional schematic diagram of the present invention from a frontal viewing angle; Figure 4 This is a schematic diagram of the structure of the central column, the first cylinder, and the second cylinder of the present invention; Figure 5 This is a schematic diagram of the structure of the cylinder base and the docking hook of the present invention; Figure 6 This is a schematic diagram of the structure of the first piston assembly of the present invention; Figure 7 This is a schematic diagram of the structure of the second piston assembly of the present invention; Figure 8 This is a cross-sectional schematic diagram of the die, punch, and pressure head of the present invention in the molding state; Figure 9 This is a structural schematic diagram of the punch and step area of ​​the present invention.

[0027] The reference numerals and names in the figure are as follows: 10 Cylinder block; 11 Cylinder top cover; 12 Load-bearing lifting ring; 13 Cylinder base; 14 Connecting hook; 15 Shaft column; 16 First cylinder; 17 Second cylinder; 20 Piston sealing ring; 21 End sealing ring; 30 Piston body; 31 Piston push rod; 32 Annular load distribution ring; 40 First piston assembly; 41 First oil inlet; 42 First oil outlet; 43 Second piston assembly; 44 Second oil inlet; 45 Second oil outlet; 51 Die; 52 Punch; 53 Stepped area; 54 Pressure head; 55 Pipe joint. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: Overall Structure of a Double-Action Ring Cylinder like Figures 1 to 3 As shown, this embodiment provides a double-acting annular hydraulic cylinder for the molding production of large plastic pipe fittings, including a cylinder body 10, a first piston group 40, and a second piston group 43.

[0030] The cylinder body 10 includes a cylinder top cover 11, a cylinder base 13, a spindle 15, a first cylinder 16, and a second cylinder 17. The spindle 15 is fixedly disposed at the axial center of the cylinder body 10. The first cylinder 16 is coaxially sleeved on the outside of the spindle 15, and the two cooperate to form the first working chamber of the first piston assembly 40. The second cylinder 17 is coaxially sleeved on the outside of the first cylinder 16, and the first cylinder 16 and the second cylinder 17 cooperate to form the second working chamber of the second piston assembly 43.

[0031] The first piston assembly 40 and the second piston assembly 43 are coaxially disposed within the cylinder body 10 and are arranged in an inner and outer ring along the radial direction. The cylinder body 10 is provided with a first oil inlet 41 and a first oil outlet 42 that connect the working chamber of the first piston assembly 40, and a second oil inlet 44 and a second oil outlet 45 that connect the working chamber of the second piston assembly 43.

[0032] like Figure 8 and Figure 9 As shown, during the molding process, the first oil inlet 41 and the second oil inlet 44 are configured to independently control the input timing of the pressurized oil. During operation, the first piston assembly 40 first drives the punch 52 downwards and maintains pressure, followed by the second piston assembly 43 driving the pressure head 54 to apply pressure to the molten plastic inside the die 51, molding the plastic into a pipe fitting 55. During the molding process, the first piston assembly 40 applies and maintains a hydraulic force on the punch 52 to counteract the upward reverse force generated by the punch step area 53.

[0033] This embodiment achieves a balance between sequential action and hydraulic flexibility by setting up a coaxially arranged double piston group and an independently controllable dual oil circuit system, thus completely solving the technical problem of punch floating during the molding process of large pipe joints.

[0034] II. Example 2: Hydraulic Flexible Balance Control under P2≤P1 Condition like Figure 3 , Figure 8 and Figure 9 As shown, this embodiment, based on embodiment 1, further illustrates the hydraulic flexible balance control method when the working hydraulic pressure P2 of the second oil inlet 44 is less than or equal to the working hydraulic pressure P1 of the first oil inlet 41.

[0035] In actual molding production, since the punch step area 53 is a sloping structure, the upward reverse force F_up it experiences is always less than the molding pressure F2 applied by the second piston group 43. Therefore, when P2≤P1, the downward holding force F1 generated by the first piston group 40 is naturally greater than the upward reverse force F_up, and hydraulic flexible balance can be achieved without complex calculations.

[0036] The specific control process is as follows: Step 1: Pressurized oil is input into the first oil inlet 41, and the first piston assembly 40 drives the punch 52 to move down to the mold closing position and maintains pressure P1; Step 2: Pressurized oil is input into the second oil inlet 44, and the second piston assembly 43 drives the pressure head 54 to apply downward pressure, with a pressure of P2 and P2≤P1; Step 3: During the molding and holding stage, the first oil inlet 41 continuously maintains pressure P1, forming a hydraulic flexible constraint on the punch 52. Step 4: When the punch step area 53 is subjected to an upward reverse force from the molten plastic, the reverse force is transmitted through the punch 52 to the bearing surface of the first piston group 40, forming a dynamic balance with the circuit hydraulic pressure P1, thus counteracting the upward floating trend of the punch.

[0037] This embodiment employs a single hydraulic power unit with a common pressure supply method. A flow distribution valve group maintains the working pressure of the first oil inlet 41 and the second oil inlet 44 at a relationship of P2 ≤ P1. This operating condition is suitable for normal pressure-controlled production, and features a simple structure, low cost, and convenient control.

[0038] III. Example 3: Dynamic pressure matching control under the P2>P1 condition like Figure 3 , Figure 8 and Figure 9 As shown, this embodiment, based on embodiment 1, further illustrates the dynamic pressure matching control method when the working hydraulic pressure P2 of the second oil inlet 44 is greater than the working hydraulic pressure P1 of the first oil inlet 41.

[0039] In certain high-precision molding processes, higher molding pressure P2 is required to ensure product density. In this case, the following relationship must be satisfied: P1≥P2×(As / A1)×k×cosθ in: As is the horizontal projected area of ​​the punch step region 53; A1 is the effective pressure-bearing area of ​​the first piston assembly 40; θ is the inclination angle of the punch step area 53 relative to the horizontal molding plane, and its value ranges from 0° to 90°. k is the plastic melt flow and friction correction coefficient, with a value ranging from 0.6 to 0.9.

[0040] Explanation of mechanical principles: During the molding process, the molten plastic generates molding pressure P2 under the drive of the second piston assembly 43. This pressure acts perpendicularly on the surface of the punch step region 53. Due to the inclination angle θ of the step region, the resulting upward counterforce F_up consists only of the perpendicular component of the pressure. According to the hydrostatic projection theorem, F_up = P2 × As × k × cosθ.

[0041] The downward holding force provided by the first piston assembly 40 is F1 = P1 × A1.

[0042] To achieve hydraulic flexible balance, F1 ≥ F_up must be satisfied, that is: P1 × A1 ≥ P2 × As × k × cosθ Simplifying, we get: P1≥P2×(As / A1)×k×cosθ Dynamic control process: When P2 is adjusted according to process requirements, P1 is adjusted accordingly based on the aforementioned relationship, ensuring that the inequality remains valid throughout the molding and holding pressure stages. For example, when the process requires an increase in molding pressure P2, the control system automatically calculates the required target value of P1 and adjusts the output pressure of the first hydraulic power unit to ensure that the hydraulic flexible balance condition is always met.

[0043] This embodiment is applicable to high-pressure precision molding conditions. Through precise pressure matching calculation and dynamic tracking control, it ensures product quality while avoiding energy waste caused by excessively high P1.

[0044] IV. Example 4: Dual Hydraulic Power Unit Independent Pressure Supply System like Figure 3 As shown, this embodiment further illustrates the implementation method of using dual hydraulic power units for independent pressure supply, based on embodiment 2 or 3.

[0045] The first oil inlet 41 and the second oil inlet 44 are respectively connected to the first hydraulic power unit and the second hydraulic power unit. The first hydraulic power unit and the second hydraulic power unit are respectively equipped with a hydraulic pump, a relief valve and a pressure sensor, forming a pressure linkage control loop.

[0046] The output of the pressure sensor is electrically connected to the controller (such as a PLC controller). The controller adjusts the set pressure of the relief valve of the second hydraulic power unit or the output flow of the hydraulic pump according to the pressure signal of the first oil inlet 41, so that the working hydraulic pressure P2 of the second oil inlet 44 and the working hydraulic pressure P1 of the first oil inlet 41 satisfy the relationship described in Embodiment 2 or Embodiment 3, thereby realizing dynamic tracking and matching.

[0047] Control logic: 1. The first hydraulic power unit starts, the first oil inlet 41 establishes pressure P1, and the first piston group 40 drives the punch 52 to move down to the position; 2. The pressure sensor collects the P1 value in real time and transmits it to the controller; 3. The controller calculates the target value of P2 based on the process parameters (P2≤P1 or P1≥P2×(As / A1)×k×cosθ); 4. The controller adjusts the set pressure of the relief valve of the second hydraulic power unit to make P2 reach the target value; 5. Pressure P2 is established at the second oil inlet 44, and the second piston assembly 43 drives the pressure head 54 to apply pressure; 6. During the molding and holding pressure stage, the controller continuously monitors P1 and P2 and dynamically adjusts them to maintain a balanced relationship.

[0048] This embodiment adopts a dual-pump independent pressure supply + electronic control linkage method, which has high pressure control accuracy and fast response speed, and is suitable for the production of high-end products with high molding quality requirements.

[0049] V. Example 5: Single Hydraulic Power Unit Homogeneous Pressure Supply System like Figure 3 As shown, this embodiment further illustrates the implementation method of using a single hydraulic power unit with the same source of pressure, based on embodiment 2.

[0050] The first oil inlet 41 and the second oil inlet 44 are connected to the same hydraulic power unit (such as a hydraulic pump) and are connected through a flow distribution valve group. The flow distribution valve group is one of a flow divider / combiner valve, a proportional flow divider valve, or a series speed control valve.

[0051] The pipelines of the first oil inlet 41 and the second oil inlet 44 are respectively equipped with a one-way sequence valve or a hydraulic one-way valve, which is used to maintain the pressure of the first oil inlet 41 after the first piston group 40 first acts to maintain pressure, so that when P2 is adjusted with the process, P1 can respond synchronously according to a preset ratio or an independent set value to maintain the hydraulic flexible balance condition.

[0052] Working principle: 1. When the hydraulic pump starts, the pressurized oil first enters the first oil inlet 41 through the one-way sequence valve, and the first piston group 40 drives the punch 52 to move downward. 2. After the first piston group 40 is in position, the one-way sequence valve closes and maintains pressure to keep P1 stable; 3. The hydraulic pump continues to supply oil, and the pressurized oil is proportionally distributed to the second oil inlet 44 through the flow distribution valve group; 4. The second piston group 43 drives the pressure head 54 to apply pressure. At this time, the system pressure is uniformly limited by the relief valve, P1=P2 or distributed according to the preset ratio. 5. During the molding and pressure holding stage, the hydraulic control check valve maintains the pressure at the first oil inlet 41 to prevent backflow of pressurized oil.

[0053] This embodiment adopts a single pump with the same source of pressure supply, which is simple in structure, low in cost and highly reliable. It is suitable for normal pressure conditions where P2≤P1, and can save more than 30% of the hydraulic system cost.

[0054] VI. Example 6: Split Multi-Rod Piston Assembly Structure like Figure 4 , Figure 6 and Figure 7 As shown, this embodiment further illustrates the split multi-rod structure design of the first piston group 40 and the second piston group 43 based on embodiment 1.

[0055] For molding large, thick-walled pipe fittings with diameters exceeding 500 mm, traditional one-piece heavy-duty piston rods suffer from drawbacks such as high weight, uneven thermal expansion, localized stress concentration, and difficulty in maintenance and replacement. Therefore, both the first piston assembly 40 and the second piston assembly 43 include a piston body 30 and multiple piston push rods 31 evenly distributed circumferentially.

[0056] One end of each of the multiple piston push rods 31 is detachably connected to the piston body 30 via high-strength bolts, and the other end forms a drive output end, replacing the traditional one-piece piston rod. In a preferred embodiment, the second piston group 43 can be configured with 12-20 piston push rods 31 (16 in the example shown), and the first piston group 40 can be configured with 6-12 piston push rods 31 (8 in the example shown). The specific number can be increased or decreased as needed based on the cylinder diameter and rated tonnage.

[0057] like Figure 5 , Figure 6 and Figure 7 As shown, it also includes an annular load distribution ring 32. The drive output ends of the multiple piston push rods 31 are respectively fixedly connected to one side end face of the annular load distribution ring 32 by high-strength bolts. The other side end face of the annular load distribution ring 32 is used to connect to the punch 52 or the pressure head 54.

[0058] The annular load distribution ring 32 is integrally formed from forged steel or ductile iron, which rigidly connects the multiple piston push rods 31 into an integral force-bearing ring, and transmits the annular driving force of the piston assembly to the punch 52 or pressure head 54 evenly and synchronously.

[0059] Technical effects: 1. Reduced weight of moving parts: The split multi-rod design significantly reduces the equivalent moment of inertia and overall weight of moving parts, reducing inertial impact; 2. Avoid single-point overload: The hydraulic thrust is discretized along the circumference to avoid single-point overload and local stress concentration; 3. Uniform load transfer: The annular load distribution ring 32 realizes secondary load equalization, ensuring uniform 360° circumferential pressure transfer and small flatness deviation at the output end; 4. Easy to maintain and replace: When a single piston push rod 31 is damaged, it can be quickly replaced without the need for complete disassembly, which significantly reduces maintenance costs and downtime. 5. Suppressing off-center load moment: The ring-shaped rigid coupling structure effectively suppresses the off-center load moment caused by the molding reaction force, prevents the punch 52 from tilting and jamming, and ensures the long-term stability of the hydraulic sealing system.

[0060] VII. Example 7: Modular Assembly Cylinder Block Structure like Figure 3 , Figure 4 and Figure 5As shown, this embodiment further illustrates the modular assembly structure design of the cylinder block 10 based on embodiment 1.

[0061] For the large-size hydraulic cylinders required for the molding production of large pipe fittings, in order to overcome the manufacturing process bottleneck of large integral cast and forged cylinder bodies and reduce machining difficulty and transportation costs, this embodiment adopts a modular assembly design.

[0062] The cylinder body 10 includes a cylinder top cover 11 and a cylinder base 13 that form the two ends of the cylinder body, and a central column 15, a first cylinder 16, and a second cylinder 17 coaxially assembled between the cylinder top cover 11 and the cylinder base 13. After each component is processed and formed, they are assembled and connected by high-strength fastening bolts and locating pins evenly distributed along the circumference to form a high-rigidity integral cylinder body structure.

[0063] Assembly process: 1. The spindle 15 is rigidly fixed to the center position of the cylinder base 13 by the bottom flange and bolt group, thus establishing the core reference spindle of the whole machine; 2. The first cylinder 16 is coaxially sleeved and assembled with the spindle 15 as the inner guide reference, and the annular space between its inner wall and the outer wall of the spindle 15 constitutes the first working chamber of the first piston assembly 40. 3. The second cylinder 17 is coaxially sleeved and assembled with the first cylinder 16 as the inner guide reference, and the annular space between its inner wall and the outer wall of the first cylinder 16 constitutes the second working chamber of the second piston assembly 43. 4. The cylinder top cover 11 is fastened to the cylinder base 13 by high-strength bolts, and the shaft column 15, the first cylinder 16 and the second cylinder 17 are encapsulated inside the cylinder body 10.

[0064] The coaxial assembly process of "layer-by-layer nesting and step-by-step guidance" effectively ensures the extremely high coaxiality of the inner and outer working chambers, providing strict geometric accuracy guarantee for the smooth reciprocating motion of the first piston group 40 and the second piston group 43 under high pressure conditions.

[0065] Sealing system: like Figure 3 As shown, to ensure the sealing reliability of the high-pressure molding oil circuit, this embodiment is equipped with a graded sealing structure: 1. Dynamic seal: Piston sealing rings 20 are respectively embedded on the inner and outer walls of the piston body 30 of the first piston group 40 and the second piston group 43 to achieve sliding seal between the piston and the side wall of the shaft column 15, the first cylinder 16 or the second cylinder 17. 2. Static sealing: End sealing rings 21 are precisely inlaid at the axial end mating surfaces of the shaft column 15, the first cylinder 16 and the second cylinder 17. These rings are used to form a reliable static sealing band when the cylinder top cover 11, the cylinder base 13 and the inner cylinder are mated and pressed together, completely blocking the path of high-pressure oil leakage from the assembly joint.

[0066] Auxiliary structure: like Figures 1 to 5 As shown, this is to adapt to the lifting operations and molding machine docking requirements of large mold workshops: 1. The top of the cylinder top cover 11 is symmetrically provided with load-bearing lifting rings 12, which facilitates the hoisting and positioning of the whole machine and its flow on the production line; 2. An L-shaped hook 14 is provided on the outer edge of the bottom of the cylinder base 13 for mechanical engagement with the base guide rail or fixed platform of the molding equipment and for locking with high-strength bolts. This anchoring structure rigidly fixes the cylinder body 10 to the molding host, effectively resisting the overturning moment and vibration displacement generated by the molding reaction force, and ensuring that the downward pressing force of the first piston group 40 and the second piston group 43 on the punch 52 and the pressure head 54 is transmitted more stably and accurately.

[0067] Technical effects: 1. Facilitates segmented precision machining and heat treatment of large-size cylinder blocks, significantly improving machining accuracy; 2. Reduces the overall casting / forging difficulty, significantly lowering manufacturing costs; 3. Enables rapid partial disassembly and repair, significantly reducing maintenance downtime; 4. Facilitates transportation and on-site assembly, solving the logistics challenges of oversized hydraulic cylinders.

[0068] 8. Example 8: Complete Molding Process Flow Combination Figure 3 , Figure 8 and Figure 9 This embodiment illustrates the complete process flow for molding large plastic pipe joints using the aforementioned double-acting annular hydraulic cylinder.

[0069] Step 1: Mold installation and oil circuit connection The punch 52 is fixedly connected to the annular load distribution ring 32 of the first piston assembly 40, and the pressure head 54 is fixedly connected to the annular load distribution ring 32 of the second piston assembly 43. The die 51 is installed on the worktable of the molding equipment. The first oil inlet 41, the first oil outlet 42, the second oil inlet 44, and the second oil outlet 45 are connected to the hydraulic power unit.

[0070] Step 2: The first piston assembly moves first. Pressurized oil is introduced through the first oil inlet 41, and the first piston assembly 40 drives the punch 52 downward to the mold-closing position inside the die 51. The outer wall of the punch 52 mates with the inner wall of the die 51 to form the forming cavity of the main body of the pipe connector 55. The stepped area 53 at the lower part of the punch 52 mates with the corresponding area of ​​the die 51 to form the forming cavity of the transition section between the two ends of the pipe connector 55 with different diameters. The first oil inlet 41 maintains a pressure P1, forming a hydraulic flexible constraint on the punch 52.

[0071] Step 3: Fill with molten plastic Preheated PVC plastic material is filled into the cavity 51.

[0072] Step 4: Pressurizing and molding the second piston assembly Pressurized oil is introduced through the second oil inlet 44, and the second piston assembly 43 drives the pressure head 54 to move downward, applying molding pressure P2 to the molten plastic in the die 51. Under pressure, the molten plastic fills the cavity and is formed into a pipe fitting 55.

[0073] Step 5: Hydraulic Flexible Balancing During the molding and holding stage, while the pressure head 54 applies pressure to the molten plastic, the molten plastic also generates an upward reverse force on the punch step area 53. Since the first oil inlet 41 maintains pressure P1, the downward holding force generated by the first piston assembly 40 and the upward reverse force form a dynamic balance, and the punch 52 maintains a stable position without upward displacement.

[0074] According to process requirements, one of the following balancing methods shall be adopted: When P2≤P1, the downward holding force of the first piston assembly 40 is naturally greater than the upward counterforce; When P2>P1, P1 and P2 satisfy the relationship: P1≥P2×(As / A1)×k×cosθ.

[0075] Step 6: Pressure Holding and Cooling Maintain pressure for a period of time to allow the plastic to fully solidify and set.

[0076] Step 7: Depressurization and Mold Opening Oil returns from the first oil outlet 42 and the second oil outlet 45. The first piston assembly 40 and the second piston assembly 43 move upward to reset, and the formed pipe joint 55 is removed.

[0077] This embodiment completely solves the technical problem of punch floating during the molding process of large pipe joints by using hydraulic flexible balancing technology. It eliminates the need for complicated mechanical mold locking mechanisms, significantly reduces equipment and production costs, and improves product yield.

[0078] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A double-acting annular hydraulic cylinder for the molding production of large plastic pipe fittings, characterized in that, include: Cylinder block (10); A first piston group (40) and a second piston group (43) are coaxially arranged in the cylinder (10), and the first piston group (40) and the second piston group (43) are arranged in an inner and outer ring along the radial direction; The cylinder body (10) is provided with a first oil inlet (41) and a first oil outlet (42) that connect the working chamber of the first piston group (40), and a second oil inlet (44) and a second oil outlet (45) that connect the working chamber of the second piston group (43). The first oil inlet (41) and the second oil inlet (44) are configured to independently control the input timing of the pressure oil, so that the first piston assembly (40) first drives the punch (52) to move downward and hold pressure, and the second piston assembly (43) then drives the pressure head (54) to apply pressure to the molten plastic, so as to apply and maintain hydraulic force on the punch (52) during the molding process.

2. The double-acting annular hydraulic cylinder according to claim 1, characterized in that, The working hydraulic pressure P2 of the second oil inlet (44) is adjustable according to the molding process parameters; the working hydraulic pressure P1 of the first oil inlet (41) is configured to be adjusted in conjunction with the change of P2, so that P1 and P2 always meet the hydraulic flexible balance condition during the molding and holding stage, so as to dynamically absorb and offset the upward displacement trend of the punch (52) step area (53) caused by the reaction force of molten plastic.

3. The double-acting annular hydraulic cylinder according to claim 2, characterized in that, The hydraulic flexible balance conditions include: when P2≤P1, the downward holding force generated by the first piston group (40) is greater than or equal to the upward reverse force generated by the step area (53) of the punch (52); when P2 increases with process requirements, P1 increases synchronously and maintains the pressure relationship of P2≤P1 to maintain the hydraulic flexible balance.

4. The double-acting annular hydraulic cylinder according to claim 2, characterized in that, The hydraulic flexible balance condition includes: when P2 > P1, P1 and P2 satisfy the following relationship in real time: P1≥P2×(As / A1)×k×cosθ; Where: As is the horizontal projected area of ​​the step area (53) of the punch (52); A1 is the effective bearing area of ​​the first piston group (40); θ is the inclination angle of the step area (53) of the punch (52) relative to the horizontal molding plane, with a value range of 0°~90°; k is the plastic melt flow and friction correction coefficient, with a value range of 0.6~0.9; When P2 is adjusted according to process requirements, P1 is adjusted accordingly according to the above relationship, so that the inequality continues to hold during the molding and holding pressure stage.

5. The double-acting annular hydraulic cylinder according to claim 2, characterized in that, The hydraulic pressure matching between the first oil inlet (41) and the second oil inlet (44) is achieved through one of the following methods: Method 1: The first oil inlet (41) and the second oil inlet (44) are respectively connected to the first hydraulic power unit and the second hydraulic power unit. The first hydraulic power unit and the second hydraulic power unit are respectively equipped with pressure detection elements and pressure control elements to form a pressure linkage control loop. Method 2: The first oil inlet (41) and the second oil inlet (44) are connected to the same hydraulic power unit and connected through a flow distribution valve group, so that the working pressure of the first oil inlet (41) and the second oil inlet (44) are kept equal or distributed according to a preset ratio.

6. The double-acting annular hydraulic cylinder according to claim 5, characterized in that, In the first method, the first hydraulic power unit and the second hydraulic power unit respectively include a hydraulic pump, an overflow valve and a pressure sensor. The output end of the pressure sensor is electrically connected to the controller. The controller adjusts the set pressure of the overflow valve of the second hydraulic power unit or the output flow of the hydraulic pump according to the pressure signal of the first oil inlet (41), so that the working hydraulic pressure P2 of the second oil inlet (44) and the working hydraulic pressure P1 of the first oil inlet (41) satisfy the relationship described in claim 3 or claim 4, thereby realizing dynamic tracking and matching.

7. The double-acting annular hydraulic cylinder according to claim 5, characterized in that, In the second method, the flow distribution valve group is one of the following: a flow divider valve, a proportional flow divider valve, or a series speed control valve; a one-way sequence valve or a hydraulic control one-way valve is respectively installed in the pipelines of the first oil inlet (41) and the second oil inlet (44) to maintain the pressure stability of the first oil inlet (41) after the first piston group (40) first acts to maintain pressure, so that when P2 is adjusted with the process, P1 can respond synchronously according to the preset ratio or independent set value to maintain the hydraulic flexible balance condition.

8. The double-acting annular hydraulic cylinder according to claim 1, characterized in that, Both the first piston group (40) and the second piston group (43) include a piston body (30) and multiple piston push rods (31) evenly distributed along the circumference; one end of each piston push rod (31) is detachably connected to the piston body (30), and the other end constitutes a drive output end.

9. The double-acting annular hydraulic cylinder according to claim 8, characterized in that, It also includes an annular load distribution ring (32), the drive output ends of the multiple piston push rods (31) are respectively fixedly connected to one side end face of the annular load distribution ring (32), and the other side end face of the annular load distribution ring (32) is used to connect to the punch (52) or the pressure head (54). The annular load distribution ring (32) rigidly connects the multiple piston push rods (31) into an integral force-bearing ring, and transmits the driving force of the piston group to the punch (52) or the pressure head (54) evenly and synchronously.

10. The double-acting annular hydraulic cylinder according to claim 1, characterized in that, The cylinder body (10) includes a cylinder top cover (11) and a cylinder base (13) that respectively form the two ends of the cylinder body (10), as well as a spindle (15), a first cylinder (16) and a second cylinder (17) coaxially assembled between the cylinder top cover (11) and the cylinder base (13). The spindle (15) is fixedly installed at the axial position of the cylinder (10), and the first cylinder (16) is coaxially sleeved on the outside of the spindle (15). The two cooperate to form the first working chamber of the first piston assembly (40). The second cylinder (17) is coaxially sleeved on the outside of the first cylinder (16), and the first cylinder (16) and the second cylinder (17) cooperate to form the second working chamber of the second piston assembly (43).

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