High-speed extrusion die for non-equal-diameter thermoplastic pipes

Abstract

The invention discloses a non-equal-diameter thermoplastic pipe high-speed extrusion die, which comprises a mouth die and a core die arranged in the mouth die, a gap used as a melting runner during pipe extrusion is arranged between the mouth die and the core die, and the non-equal-diameter thermoplastic pipe high-speed extrusion die is characterized in that a flowing cavity is of a non-equal-diameter structure which is gradually enlarged from inside to outside. The machine neck section of the mold is designed into the two-section structure with the inner diameter difference, so that the internal stress of a molten material is released in advance through the diameter difference structure before demolding, the problem that a pipe blank is sharply expanded due to sudden disappearance of pressure during demolding is solved, and finally the purpose of reducing the longitudinal retraction rate of a pipe is achieved.

Description

Technical Field

[0001] The invention relates to the field of pipe manufacturing, in particular to a high-speed extrusion die for non-uniform diameter thermoplastic pipes. Background Art

[0002] Figure 2 The figure shows an existing thermoplastic pipe extrusion die, which includes a mouth die 10 and a core die 20 arranged at the center of the mouth die 10. The molten material flows in the flow cavity 30, is diverted by the diversion section 31, extruded and formed by the compression section 32, and finally extruded from the die through the neck extrusion section 33. The neck extrusion section 33 is straight, and the gap between the core die 20 and the mouth die 10 is kept consistent and equal.

[0003] For common extrusion equipment, such as the commonly used SJZ-65 conical twin-screw extruder, the die inner diameter is designed to be greater than or equal to the outer diameter dn of the produced pipe ( Figure 1 ), and the outer diameter of the core die d is slightly smaller than dn-en. When the unit output is low, the die expansion during the extrusion process is small and will not have a significant impact on the longitudinal shrinkage rate index of the pipe.

[0004] However, with the application of high-speed extrusion lines, screw speeds have increased from 25-30 rpm to 40-60 rpm, and unit output has increased from 250-450 kg / h to 600-800 kg / h, and even to over 900 kg / h. This increased production rate significantly increases the compressive stress between the molecules of the molten material, which in turn changes the die expansion rate. Small changes in die expansion can be compensated by changing the pulling and stretching speed, but if the die expansion changes too much, the longitudinal shrinkage rate of the pipe will become uncontrollable. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the purpose of the present invention is to provide a high-speed extrusion die for non-uniform diameter thermoplastic pipes, so as to improve the unqualified longitudinal shrinkage rate of the thermoplastic pipes while increasing the extrusion speed of the die.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: A high-speed extrusion die for non-uniform thermoplastic pipes comprises a mouth die and a core die arranged inside the mouth die. A gap is provided between the mouth die and the core die, which serves as a melting flow channel during pipe extrusion. The flow channel presents a non-uniform structure that gradually expands from the inside to the outside.

[0007] In a preferred embodiment of the present invention, the non-uniform diameter structure is composed of segment A and segment B, and the mold cavity gap at segment B is larger than that at segment A.

[0008] In a preferred embodiment of the present invention, the inner diameters of the die at the segment A and the segment B are consistent.

[0009] In a preferred embodiment of the present invention, the outer diameter of the core mold at the segment B is larger than that of the segment A.

[0010] In a preferred embodiment of the present invention, the gap ratio between the segment B and the segment A is 1:1.05.

[0011] In a preferred embodiment of the present invention, the inner diameter of the die is smaller than the outer diameter of the tube.

[0012] In a preferred embodiment of the present invention, the inner diameter of the die is D, the outer diameter of the tube is dn, and the calculation relationship between the inner diameter of the die and the outer diameter of the tube is D=K*dn, where K is a constant less than 1.

[0013] In a preferred embodiment of the present invention, the value range of K is [0.98, 0.99].

[0014] In a preferred embodiment of the present invention, the outer diameter of the core mold is d, and the calculation relationship between the outer diameter of the core mold and the inner diameter of the die is d=D-2*en*k, where k is a constant less than 1, and the value range of k is [0.85,0.95].

[0015] In a preferred embodiment of the present invention, the pipe is a PVC pipe.

[0016] The beneficial effects of the present invention are: The present invention provides a high-speed extrusion die for non-uniform-diameter thermoplastic pipes. By designing the die neck section into a two-section structure with an inner diameter difference, the internal stress of the molten material is pre-released through the diameter difference structure before demolding, thereby alleviating the problem of rapid expansion of the tube embryo caused by the sudden loss of pressure during demolding, and ultimately achieving the purpose of reducing the longitudinal shrinkage rate of the pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0018] Figure 1 The present invention is a schematic diagram of the cross-sectional structure of a pipe.

[0019] Figure 2 It is a schematic diagram of the cross-sectional structure of a mold in the prior art.

[0020] Figure 3 It is a schematic diagram of the cross-sectional structure of the present invention.

[0021] Figure 4 yes Figure 3 Enlarged view of section E of the mold. DETAILED DESCRIPTION

[0022] In the description of the present invention, it should be noted that the terms "up", "down", "left", "right", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. The above description is simplified for the convenience of describing the present invention, and does not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, it should not be understood as a limitation on the present invention.

[0023] As used in this specification, the singular forms "a," "an," "said," and "the" include the plural forms unless otherwise expressly stated. The terms "include," "comprise," and "contain" as used in this specification indicate the presence of the claimed features, but do not exclude the presence of one or more additional features. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0024] In the specification, when an element is referred to as being “on,” “fixed” to, “connected to,” or “engaged to,” etc., another element, the element may be directly on, fixed to, connected to, engaged to, or in contact with the other element, or intervening elements may be present. In the specification, when a feature is arranged “adjacent” to another feature, it may mean that the feature has a portion overlapping with the adjacent feature or a portion located above or below the adjacent feature.

[0025] It will be understood that although the terms "first," "second," etc. may be used herein to describe different elements, these elements should not be limited by these terms. These terms are merely used to distinguish one element from another. Thus, a first element may be referred to as a second element without departing from the teachings of the present invention.

[0026] The following describes exemplary embodiments of the present application with reference to the accompanying drawings. However, it should be understood that the present application can be presented in many different ways and is not limited to the embodiments described below. It should also be understood that the embodiments disclosed herein can be combined in various ways to provide many additional embodiments. In all figures, the same reference numerals represent the same elements or elements with the same function.

[0027] refer to Figure 3 and Figure 4A high-speed extrusion die for non-uniform thermoplastic pipes is demonstrated. The die neck extrusion section 33 is designed as a two-stage non-uniform cavity structure with sections A and B. The cavity gap between the core die 20 and the die 10 at section B is larger than that at section A, and section B is located at the end of the flow channel relative to section A. This allows the die to achieve maximum compression when the molten material enters the cavity of section A through the compression section 32. As the molten material enters the cavity of section B along the extrusion direction, the cross-section of the flow channel 30 increases, and the cavity volume also increases. This reduces the internal pressure of the melt, allowing some molecular chains to elastically retract, reducing intermolecular forces. This mitigates the problem of rapid expansion of the tube embryo caused by the sudden loss of pressure upon demolding, ultimately reducing the longitudinal shrinkage rate of the pipe.

[0028] Furthermore, the inner diameter (d) of the die 10 at segments A and B remains constant, while the outer diameter db of the corresponding core die 20 decreases from segment A to segment B, achieving the aforementioned non-uniform diameter structure with a gradually increasing inter-die gap C. The difference in inter-die gap C between segments A and B is 5%, meaning the ratio of the inter-die gap between segment Cb and segment Ca is 1:1.05.

[0029] The die inner diameter D and the core outer diameter d are calculated using the following relationship: die inner diameter D = K*dn, where K = [0.98, 0.99]; core outer diameter d = D-2*en*k, where k is a commonly used coefficient, k = [0.85, 0.95]. The die inner diameter D is designed to be smaller than usual, pre-scaling to control die expansion. The range of K and k values ​​needs to be explained based on experimental data.

[0030] In some embodiments, the thermoplastic pipe mold is a PVC pipe mold.

[0031] In some embodiments, the PVC pipe is a PVC-U pipe.

[0032] Example 1: The pipe DN50mm*EN2.0mm was produced at a production rate of 600-650Kg / h to form sample 4. The inner diameter of the die D4 = 49mm, the outer diameter of the core die d4a = 45.4mm, d4b = 45.6, the die was subjected to an extrusion pressure of 18-20MPa, and the pulling speed was 10m±1.5m / min*2 (one out of two) Example 2: The pipe dn75mm*en2.3mm is produced at a production capacity of 700-750Kg / h to form sample 5, the inner diameter of the die D5=73.6, the outer diameter of the core die d5a=69.4mm, d5b=69.6mm, the die is subjected to an extrusion pressure of 18-20MPa, and the pulling speed is 7m±1.0m / min*2 (one out of two).

[0033] Example 3: The produced pipe dn110mm*en3.2mm pipe is produced at an output of 800-850Kg / h to form sample 6, the inner diameter of the die D6=108.2, the outer diameter of the core die d6a=102.4, d6b=102.7, the die is subjected to an extrusion pressure of 18-20MPa, and the pulling speed is 4m±1.0m / min*2 (one out of two).

[0034] By setting up a control experiment according to the "Determination of Longitudinal Shrinkage of Thermoplastic Pipes" standard (GB / T 6671-2001), the longitudinal shrinkage of samples 4, 5, and 6 in the above three groups of examples and samples 1, 2, and 3 produced according to the prior art were measured.

[0035] 1. Test instrument: The oven should be thermostatically controlled at the temperature specified in Appendix A. TR and ensure that after the sample is placed, the temperature in the oven should return to the test temperature range within 15 minutes.

[0036] The marker ensures that the distance between the two marking lines is 100 mm Thermometer accuracy is 0.5℃ 2. Sampling requirements: Take three samples from a pipe, the sampling length is 200±20mm 3. Dry test steps: The sample is placed at (23±2)°C for at least 2h Measuring line spacing , accurate to 0.25mm Place the specimen in the oven so that it does not touch the bottom or walls. If the specimen is suspended, the hanging point should be at the end farthest from the marking line. If the specimen is laid flat, it should be placed on a flat plate padded with talcum powder. When slicing the specimen, place it with the convex surface facing downward.

[0037] Place the sample in the oven and keep it for the time specified in Appendix A. This time should be counted from the time when the oven temperature returns to the specified temperature. Take the sample out of the oven and place it flat on a smooth surface. When it is completely cooled to (23±2)°C, measure the maximum or minimum distance between the markings along the generatrix on the surface of the sample. , accurate to 0.25 mm 4. Calculation results: Calculate the longitudinal shrinkage of each sample Expressed as a percentage.

[0038] Calculate three samples The arithmetic mean of the longitudinal shrinkage rate of the pipe is

[0039]

[0040] Remark: The production process parameters of samples 1-3 and 4-6, such as extrusion pressure and output, are consistent, and the only difference is the mold structure.

[0041] The longitudinal shrinkage rate of PVC pipes is required to be ≤5%.

Claims

1. A high-speed extrusion die for thermoplastic pipes of non-uniform diameters, comprising a die and a core die disposed within the die, wherein a gap is provided between the die and the core die for a melt flow path during pipe extrusion, characterized in that: The flow cavity presents a gradually enlarged non-uniform diameter structure from the inside to the outside, and the non-uniform diameter structure is composed of segment A and segment B. The mold cavity gap at segment B is larger than that at segment A. The outer diameter of the core mold at segment B is larger than that at segment A. The outer diameter of the core mold is d. The calculation relationship between the outer diameter of the core mold and the inner diameter of the die is d=D-2*en*k. The pipe is a PVC-U pipe.

2. A high-speed extrusion die for non-uniform diameter thermoplastic pipes according to claim 1, characterized in that: The inner diameters of the die at the sections A and B are consistent.

3. The high-speed extrusion die for non-uniform diameter thermoplastic pipes according to claim 1, characterized in that: The gap ratio between the segment B and the segment A is 1:1.

05.

4. The high-speed extrusion die for non-uniform diameter thermoplastic pipes according to claim 2, characterized in that: The inner diameter of the die is smaller than the outer diameter of the pipe.

5. The high-speed extrusion die for non-uniform diameter thermoplastic pipes according to claim 4, characterized in that: The inner diameter of the die is D, the outer diameter of the tube is dn, and the calculation relationship between the inner diameter of the die and the outer diameter of the tube is D=K*dn, where K is a constant less than 1.

6. The high-speed extrusion die for non-uniform diameter thermoplastic pipes according to claim 5, characterized in that: The value range of K is [0.98, 0.99].

7. The high-speed extrusion die for non-uniform diameter thermoplastic pipes according to claim 5, characterized in that: Wherein k is a constant less than 1, and the value range of k is [0.85, 0.95].

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