Forming device and forming method of polytetrafluoroethylene uniform wall thickness expansion joint

Abstract

The present invention provides a molding device and a molding method for a polytetrafluoroethylene uniform wall thickness expansion joint, belonging to the technical field of molding devices. The present invention comprises: a workbench, a pushing device, a heating device, a central axis, a fixing device, a central axis positioning plate and a push-pull device; the present invention uses a pushing device to push and shape the uniformly heated molding pipe to an equal pitch to obtain a finished product with uniform wall thickness, which has high precision, effectively controls the uniformity of the wall thickness of the product, and can produce a uniform and high-quality finished product.

Description

Technical Field

[0001] The invention relates to the technical field of molding devices, in particular to a molding device and a molding method for a polytetrafluoroethylene uniform wall thickness expansion joint. Background Art

[0002] Existing technology:

[0003] In addition to some PTFE expansion joint products that are processed by turning rods or by filling powder and then molding, most of them are made of PTFE semi-finished pipes through secondary molding to produce the required shape and size. This is partly because turning still has restrictions on the specifications of rods, and the processing is more difficult; while filling molding has high costs, complicated processes, and low efficiency.

[0004] The above-mentioned secondary shaping technology is mostly realized through heating, pressure, mold fixtures, ovens, etc. For example:

[0005] Cold pressing: After sealing both ends of the pipe, fill it with water, and then use a hydraulic device to compress the liquid in the pipe. A mold fixture is applied to the outside of the pipe for support. After the cold pressing shaping, it is passed through an oven to fix the shape.

[0006] Hot blow molding: Use a heated mold with a machined inner groove to seal the pipe and insert it into the heated mold. Then inject air pressure to expand the pipe to the inner groove of the hot mold, achieve blow molding, and then cool and shape.

[0007] Problems and shortcomings of existing technologies:

[0008] The problem with cold press forming is that the pressure is difficult to control accurately, which may cause over-pressure rupture or uneven wall thickness of the finished product. Uneven adjustment of the forming mold and fixture may also cause inconsistent shapes. It is difficult to control the final size after cold pressing.

[0009] The disadvantages of cold forming are that the process is complicated, the quality of the finished product is easily affected by operating conditions, and there may even be product defects caused by stress concentration.

[0010] The problem with hot blow molding is that the hot mold heating often causes uneven heating of the tube, which may cause uneven wall thickness of the finished product during the blowing process, and gas pressure blowing has size limitations.

[0011] The disadvantages of hot blow molding are that it is limited to small sizes and the size is difficult to control. The irregular molding often hides quality defects in the molding material, making the finished product have poor pressure resistance.

[0012] The most common defects in the existing technology are: uneven wall thickness or irregular ripples caused by pressure molding, dents or hems caused by molding jigs, and stress whitening defects caused by external pressure molding. These problems that cause defects are not allowed to exist in the application fields of petroleum, chemical industry, electronic appliances, medical treatment, machinery, etc., because the industrial losses and safety hazards they cause are huge. Figure 1 Schematic comparison of defective corrugation shown with ideal corrugation. Summary of the invention

[0013] In view of this, in order to solve the technical problems in the prior art that the heating uniformity of the polytetrafluoroethylene pipe is insufficient, the molding process is complicated or lacks humanization, the wall thickness of the finished product is uneven, the waveform of the finished product is irregular, and the finished product has residual stress in the memory, on the one hand, the present invention provides a molding device for a polytetrafluoroethylene uniform wall thickness expansion joint, which utilizes a pushing device in the molding device to push and shape the uniformly heated molded pipe to an equal pitch to obtain a finished product with uniform wall thickness.

[0014] To achieve the above object, the present invention provides the following technical solutions:

[0015] The molding device of polytetrafluoroethylene uniform wall thickness expansion joint comprises:

[0016] workbench;

[0017] A pushing device, which is arranged on the workbench and is used to apply pressure to the formed pipe;

[0018] A heating device, which is arranged at the lower end of the workbench and is used to heat the formed pipe;

[0019] A central shaft, one end of which is located in the heating device and is used to sleeve the formed tube on the central shaft;

[0020] A fixing device, which is arranged at the lower end of the heating device and is used to fix the other end of the central axis and the formed pipe;

[0021] A central axis positioning plate, which is arranged at the bottom end of the central axis and the fixing device, and is used to provide support for the central axis and the fixing device, and ensure that the central axis and the heating device are in a concentric position;

[0022] A push-pull device, one end of which is connected to the central axis positioning plate, and the other end of which is connected to the workbench, and is used to drive the central axis to rise or fall;

[0023] The fixing device has spaces for accommodating the waveforms on both sides.

[0024] Preferably, the fixing device comprises an upper clamping ring and a lower clamping ring;

[0025] The upper clamping ring and the lower clamping ring are connected via a buffer rod.

[0026] Preferably, a buffer spring is sleeved on the outer end of the connection between the lower clamping ring and the buffer rod.

[0027] Preferably, a pressure sensor is provided at the connection between the buffer rod and the upper clamping ring.

[0028] Preferably, the heating device comprises a heating mold for accommodating the formed pipe and a heating sleeve arranged around the outer circumference of the heating mold.

[0029] Preferably, the pushing device comprises a pushing cylinder and a pushing die;

[0030] The pushing cylinder is used to control the pushing die to apply pressure to the formed pipe.

[0031] Preferably, the pushing die is a tubular metal die, which will not damage the heating device and the central axis during the pushing process.

[0032] Preferably, the push-pull device is a push-pull cylinder.

[0033] Preferably, the pushing device, the heating device and the push-pull device are controlled by a programmable program.

[0034] On the other hand, the present invention also provides a molding method using the molding device of the polytetrafluoroethylene uniform wall thickness expansion joint, comprising the following steps:

[0035] Step 1: Sleeve the formed pipe on the central axis and place it in the space formed by the central axis and the heating device, fix the formed pipe to the central axis with a fixing device, and position the plate close to the central axis;

[0036] Step 2: Push the push-pull device upward to bury the formed pipe in the heating device, and the heating device starts to heat the formed pipe to a plastic temperature;

[0037] Step 3: Push the push-pull device downward to position the formed pipe at the fixing device, and start the pushing device to push the formed pipe to complete the shaping.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention provides a forming device for a polytetrafluoroethylene expansion joint with uniform wall thickness, which uses a pushing device in the forming device to push and shape the uniformly heated formed pipe to a uniform pitch to obtain a finished product with uniform wall thickness, and effectively solves the technical problems of the existing process such as insufficient heating uniformity of the polytetrafluoroethylene pipe, complicated or lack of humanization in the forming process, uneven wall thickness of the obtained finished product, irregular waveform of the obtained finished product, residual stress in the obtained finished product, etc.

[0040] The molding device and molding method of the polytetrafluoroethylene uniform wall thickness expansion joint provided by the present invention can make the operation process of the same specification and cost simple and smooth, and can improve the productivity;

[0041] The uniformity of the material's absorption of heat energy helps improve product quality and reduce production errors;

[0042] The molding device has high precision and effectively controls the uniformity of the product's wall thickness;

[0043] The molding device has high operating safety and can avoid explosion or environmental pollution caused by pressure molding;

[0044] By utilizing the expansion characteristics of polytetrafluoroethylene and the molding temperature range, uniform and high-quality finished products can be produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of defective ripples and ideal ripples;

[0046] Figure 2 It is a structural schematic diagram of a molding device;

[0047] Figure 3 It is a schematic diagram of molding;

[0048] Figure 4 This is the application diagram of the finished product;

[0049] In the figure, 1. forming pipe, 2. workbench, 3. heating mold, 4. heating sleeve, 5. center axis, 6. center axis positioning plate, 7. push-pull cylinder, 8. push mold, 9. push cylinder, 10. clamping ring, 101. upper clamping ring, 102. lower clamping ring, 11. buffer rod, 12. pressure sensor. DETAILED DESCRIPTION

[0050] like Figure 2-4 As shown, the present invention provides a molding device for a polytetrafluoroethylene uniform wall thickness expansion joint, comprising:

[0051] A workbench 2, preferably a vertical workbench;

[0052] A pushing device, which is arranged on the workbench 2 and is used to apply pressure to the formed pipe 1;

[0053] A heating device is provided at the lower end of the workbench 2 and is used to heat the formed pipe 1. The temperature control is preferably achieved by using a programmable control meter with a thermocouple to ensure a temperature difference of + / - 2°C;

[0054] A central shaft 5, one end of which is located in the heating device and is used to sleeve the formed tube 1 on the central shaft 5;

[0055] A fixing device, which is arranged at the lower end of the heating device and is used to fix the other end of the central axis 5 and the formed pipe 1;

[0056] A central axis positioning plate 6 is arranged at the bottom end of the central axis 5 and the fixing device, and is used to provide support for the central axis 5 and the fixing device, and ensure that the central axis 5 and the heating device are in a concentric position. The central axis positioning plate 6 is arranged to ensure that the central axis 5 and the heating device are in a concentric position on the one hand, and to provide support for the central axis 5 and the fixing device on the other hand;

[0057] A push-pull device, one end of which is connected to the central axis positioning plate 6, and the other end is connected to the workbench 2, and is used to drive the central axis 5 to rise or fall. When rising, it is convenient to install the formed pipe 1 and move the formed pipe 1 to the heating device to evenly heat the formed pipe 1;

[0058] The fixing device has spaces for accommodating the waveforms on both sides, so that the pushing device can push the uniformly heated shaped pipe 1 to accommodate the waveforms with uniform wall thickness.

[0059] In the present invention, the fixing device comprises an upper clamping ring 101 and a lower clamping ring 102, which are preferably two halves of the workpiece;

[0060] The upper clamping ring 101 and the lower clamping ring 102 are connected by the buffer rod 11, and the upper clamping ring 101 and the lower clamping ring 102 constitute the clamping ring 10. In order to avoid touching the buffer rod 11 when stacking the finished products, the space for the clamping ring to accommodate the waveform can be set according to 1.1 times the outermost diameter of the waveform after compaction of the finished product with the largest specification, and there should be space to accommodate the waveform.

[0061] In the present invention, a buffer spring is sleeved on the outer end of the connection between the lower clamping ring 102 and the buffer rod 11 to provide a buffering effect.

[0062] In the present invention, a pressure sensor 12 is provided at the connection between the buffer rod 11 and the upper clamping ring 101 for detecting the range of the pushing force and transmitting the detected pressure signal to the control device, which controls the pushing device to adjust the speed according to the pressure.

[0063] In the present invention, the heating device comprises a heating mold 3 for accommodating the shaped tube 1 and a heating sleeve 4 arranged around the outer periphery of the heating mold 3. Such a heating device can ensure uniform heating of the shaped tube 1, so that after the volume of the shaped tube 1 expands, the inside and outside of the shaped tube 1 fully contact the inner wall of the cavity of the heating mold 3 and the outer wall of the central axis 5 (described above and Figure 2-3 It can be seen that the central axis 5 is inside the heating mold 3, the molding tube 1 is sleeved on the central axis 5, and is located in the mold cavity of the heating mold 3, forming the mold cavity of the heating mold 3-molding tube 1-central axis 5).

[0064] In the present invention, the pushing device comprises a pushing cylinder 9 and a pushing die 8;

[0065] The pushing cylinder 9 is used to control the pushing die 8 to apply pressure to the formed pipe 1 .

[0066] In the present invention, the pushing die 8 is a tubular metal die, which will not damage the heating device and the central axis 5 during the pushing process. Its inner and outer diameters usually correspond to the sizes of the heating die 3 and the central axis 5, and the deviation must be 0.1 mm.

[0067] In the present invention, the push-pull device is a push-pull cylinder 7, one end of which is connected to the central axis positioning plate 6 and the other end is connected to both sides of the workbench 2.

[0068] In the present invention, the pushing device, the heating device and the push-pull device are controlled by programmable control, that is, the formed pipe 1 is heated by the programmable control heating device, and the pressure sensor 12 is used to transmit the detected pushing force to the control device, and the control device adjusts the pushing speed of the pushing device according to the pressure signal.

[0069] In the present invention, the formed pipe 1 is preferably a round pipe of equal wall thickness for making expansion joints. After measuring the cutting working length in advance, the formed pipe 1 is placed in the heating mold 3. The heating mold 3 is connected to the bottom end of the workbench 2, and a heating sleeve 4 is provided on the outside to provide a resistance heating function. The temperature is controlled by a programmable control head with a thermocouple to ensure a temperature difference of + / -2°C. The heating mold 3 has a central axis 5 inside. This central axis 5 is assembled in a concentric position in the heating mold 3 through a central axis positioning plate 6, so that the formed pipe 1 is not affected by interference when placed in.

[0070] The central axis positioning plate 6 is connected to both sides of the workbench 2 through a push-pull cylinder 7. The function of the push-pull cylinder 7 is to pull down the central axis positioning plate 6 and the central axis 5 at the same time when the molding is completed to facilitate the removal of the finished product.

[0071] The workbench 2 preferably adopts a vertical structure, with a pushing die 8 at the upper end, and performs up and down pushing actions through a pushing cylinder 9. The pushing die 8 is a tubular metal die, and its inner and outer diameters usually correspond to the dimensions of the heating die 3 and the center axis 5. The deviation must be 0.1mm to ensure that the pushing process of the pushing die 8 will not damage the heating die 3 and the center axis 5, and the concentricity must be guaranteed to be good.

[0072] The pushing cylinder 9 is controlled by a programmable program to ensure that the speed and distance of each push are consistent.

[0073] After the formed tube 1 is placed between the heating mold 3 and the center axis 5, the lower end is clamped and fixed to the formed tube 1 and the center axis 5 by a clamping ring 10. The clamping ring 10 is preferably a workpiece split into two halves, which is close to the center axis positioning plate 6 and can be moved by a push-pull cylinder 7.

[0074] Preferably, one end of the buffer rod 11 is connected to the flange below the heating mold 3 together with the pressure sensor 12, and the other end passes through the through hole on the clamping ring 10 and is fixed after being covered with a buffer spring.

[0075] On the other hand, the present invention also provides a molding method using the molding device of the polytetrafluoroethylene uniform wall thickness expansion joint, and the specific working process is as follows:

[0076] The formed tube 1 of polytetrafluoroethylene of equal wall thickness for making expansion joint is measured and cut to the working length in advance, and then placed from top to bottom in the space of the workbench 2 into the space surrounded by the heating mold 3 and the central axis 5. The upper clamping ring 101 and the lower clamping ring 102 of the clamping ring 10 are used to clamp and fix the formed tube 1 and the central axis 5 at the lower end, and close to the central axis positioning plate 6. The formed tube 1 is pulled up by the push-pull cylinder 7 to bury it in the heating mold 3. After the heating sleeve 4 starts to heat the polytetrafluoroethylene tube to expand its volume, the inside and outside of the formed tube 1 are fully in contact with each other. To the inner wall of the mold cavity of the heating mold 3 and the outer wall of the central axis 5, the heat energy is evenly absorbed to the plastic temperature, and then the push-pull cylinder 7 is pushed down to the processing position (the area where the fixing device is located). At this time, the push cylinder 9 is started to push the push die 8 down to the position set to contact the formed pipe 1, and the first shaping is performed at an equidistant distance. After the first tube material to be shaped is naturally cooled and formed, the push cylinder 9 is started again to push the push die 8 down to perform the second shaping at an equidistant distance..., and the shaping and cooling of the formed pipe 1 are repeated until the number of waveforms of the finished expansion joint is completed. Finally, the push-pull cylinder 7 is started again to pull down the central axis positioning plate 6 and the central axis 5 at the same time to take out the finished product.

[0077] It should be noted that the above working process pays special attention to the pushing die 8 under the pushing cylinder 9 to cause the expanded molded pipe 1 to be pushed out of the heating die 3. Since the central axis 5 provides support, the molded pipe 1 will naturally expand outward and stack on each other. At this time, the buffer spring at the lower end of the buffer rod 11 will avoid excessive compression spacing and correspond to the range of pushing force of the pressure sensor 12. Excessive or insufficient pushing force will be transmitted to the control device through a signal, and the control device will adjust the speed of the pushing cylinder 9. In this way, each forming force is stabilized to produce a polytetrafluoroethylene expansion joint with uniform wall thickness.

[0078] In summary, the working principle of the present invention is as follows:

[0079] 1) The molding method of the polytetrafluoroethylene uniform wall thickness expansion joint is based on the principle that when the polytetrafluoroethylene molding pipe 1 is uniformly heated to a suitable molding temperature range, the material has the characteristics of expanding while maintaining the plastic softening rigidity.

[0080] 2) After the polytetrafluoroethylene molded tube 1 reaches the molding temperature range, it must be used with the molding device of the present invention to push and mold the polytetrafluoroethylene molded tube 1 into an expansion joint product with equal pitch and uniform wall thickness at a constant speed and equal distance using a pushing die 8 under programmable control.

[0081] 3) The above-mentioned constant speed and equal distance mechanical device is also capable of placing the polytetrafluoroethylene molded tube 1 between the mold cavity of the heating mold 3 and the central axis 5 and heating the polytetrafluoroethylene molded tube 1 through the heating sleeve 4 until the volume of the polytetrafluoroethylene molded tube 1 expands, so that the inner and outer walls of the molded tube 1 can fully contact the inner wall of the mold cavity of the heating mold 3 and the outer wall of the central axis 5 to achieve uniform absorption of heat energy, and then use the pushing mold 8 to push and mold the number of expansion joint shapes in sequence.

[0082] 4) The polytetrafluoroethylene tube material is expanded by high-temperature heating and closely adheres to the gap between the mold cavity of the heating mold 3 and the central axis 5, basically achieving the effect of uniform wall thickness shaping, and each pitch is naturally softened and formed under an extremely uniform temperature state. Because there is no forced effect of external pressure, and a buffer spring and a pressure sensor 12 are added in the natural forming pushing process to monitor the compression force of the material at any time during forming, the polytetrafluoroethylene expansion joint with uniform wall thickness can be manufactured by stabilizing the forming force each time.

[0083] The molding device and molding method provided by the present invention are based on the above principle, which can make the operation process of the same specification and cost simple and smooth, and can improve the productivity;

[0084] The uniformity of the material's absorption of heat energy helps improve product quality and reduce production errors;

[0085] The mechanical device has high precision and effectively controls the uniformity of the product's wall thickness;

[0086] The device has high operating safety, which can avoid explosion or environmental pollution caused by pressure molding;

[0087] By utilizing the expansion characteristics of polytetrafluoroethylene and the molding temperature range, uniform and high-quality finished products can be produced.

[0088] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0089] Take 2-inch specification as an example to illustrate, the details are as follows:

[0090] The formed polytetrafluoroethylene tube 1 of equal wall thickness for making expansion joints is cut to a working length of about 24 cm and then placed from top to bottom in the space of the workbench 2 into the space surrounded by the heating mold 3 and the center axis 5. The lower end is clamped and fixed by a clamping ring 10, and is close to the center axis positioning plate 6. The formed tube 1 is pulled up by the push-pull cylinder 7 to allow the formed tube 1 to be completely buried in the mold cavity of the heating mold 3, and the heating sleeve 4 located on the outer periphery of the heating mold 3 is started. Set 330℃ to start heating for about 30 minutes. After the mold temperature reaches the set temperature as measured by the thermocouple buried in the heating mold 3, the heating is timed for another 20 minutes. At this time, the volume of the polytetrafluoroethylene molded tube 1 expands by 20%, and it has fully contacted the inner wall of the mold cavity of the heating mold 3 and the outer wall of the central axis 5, achieving uniform absorption of heat energy. Then, the push-pull cylinder 7 is pushed down 5cm to the processing position (fixed device area), and the push cylinder 9 is started to push the push mold 8 down to the set contact position of the molded tube 1, and then push down 25mm at an equal distance for the first shaping. It can be seen that when the expanded molded tube 1 is pushed out of the heating mold 3, due to the central axis 5 The formed pipe 1 will naturally expand outward and stack on each other. The buffer spring at the lower end of the buffer rod 11 will prevent the compression spacing from being too large, and the corresponding pushing force of the pressure sensor 12 is measured to be in the range of 0.3-1kgf, which is a natural forming force. After cooling for about 5 minutes, the pushing cylinder 9 is started again to push the pushing die 8 down for the second shaping at an equal distance of 25mm. The shaping and cooling of the formed pipe 1 are repeated for the third time until the expansion joint is completed. The number of three waveforms is completed, and finally the push-pull cylinder 7 is started again to pull down the center axis positioning plate 6 and the center axis 5 at the same time, and the finished product is taken out and stretched. After the three-layer stacked formed pipe 1 is pushed (such as Figure 3 As shown), a relatively stable expansion joint shape can be obtained, and after the outer side of the flange is flanging, the ideal product of the device of the present invention is successfully completed, such as Figure 4 shown.

[0091] After the cross-section wall thickness of the polytetrafluoroethylene expansion joint produced by this molding method is measured, the thickness deviation between the trough and the peak is between 0.1-0.15mm. Based on the standard wall thickness of 3.5mm, it is in line with the shrinkage ratio of fluoroplastic materials and is much better than the thickness deviation of traditional molding processes.

[0092] The above are only preferred specific embodiments of the present invention; however, the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and improved concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A forming device for a polytetrafluoroethylene uniform wall thickness expansion joint, characterized in that: include: workbench; A pushing device, which is arranged on the workbench and is used to apply pressure to the formed pipe; A heating device, which is arranged at the lower end of the workbench and is used to heat the formed pipe; A central shaft, one end of which is located in the heating device and is used to sleeve the formed tube on the central shaft; A fixing device, which is arranged at the lower end of the heating device and is used to fix the other end of the central axis and the formed pipe; A central axis positioning plate, which is arranged at the bottom end of the central axis and the fixing device, and is used to provide support for the central axis and the fixing device, and ensure that the central axis and the heating device are in a concentric position; A push-pull device, one end of which is connected to the central axis positioning plate, and the other end of which is connected to the workbench, and is used to drive the central axis to rise or fall; The fixing device has spaces for accommodating waveforms on both sides; The fixing device comprises an upper clamping ring and a lower clamping ring; The upper clamping ring and the lower clamping ring are connected via a buffer rod; A buffer spring is sleeved on the outer end of the connection between the lower clamping ring and the buffer rod.

2. The molding device for polytetrafluoroethylene uniform wall thickness expansion joint according to claim 1, characterized in that: A pressure sensor is provided at the connection between the buffer rod and the upper clamping ring.

3. The molding device of polytetrafluoroethylene uniform wall thickness expansion joint according to claim 1, characterized in that: The heating device comprises a heating mold for accommodating the formed pipe and a heating sleeve arranged around the outer periphery of the heating mold.

4. The molding device of polytetrafluoroethylene uniform wall thickness expansion joint according to claim 1, characterized in that: The pushing device comprises a pushing cylinder and a pushing die; The pushing cylinder is used to control the pushing die to apply pressure to the formed pipe.

5. The molding device for polytetrafluoroethylene uniform wall thickness expansion joint according to claim 4, characterized in that: The pushing die is a tubular metal die, and the heating device and the central axis will not be damaged during the pushing process.

6. The molding device of polytetrafluoroethylene uniform wall thickness expansion joint according to claim 1, characterized in that: The push-pull device is a push-pull cylinder.

7. The molding device for a polytetrafluoroethylene uniform wall thickness expansion joint according to any one of claims 1 to 6, characterized in that: The pushing device, the heating device and the pushing and pulling device are controlled by programmable programming.

8. A molding method of a molding device for a polytetrafluoroethylene uniform wall thickness expansion joint according to any one of claims 1 to 7, characterized in that: The steps include: Step 1: Sleeve the formed pipe on the central axis and place it in the space formed by the central axis and the heating device, fix the formed pipe to the central axis with a fixing device, and position the plate close to the central axis; Step 2: Push the push-pull device upward to bury the formed pipe in the heating device, and the heating device starts to heat the formed pipe to a plastic temperature; Step 3: Push the push-pull device downward to position the formed pipe at the fixing device, and start the pushing device to push the formed pipe to complete the shaping.

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