Lightweight polyvinyl chloride pipe and preparation method thereof

Abstract

The application discloses a light-weight polyvinyl chloride pipe and a preparation method thereof. The light-weight polyvinyl chloride pipe comprises an inner layer and an outer layer, the inner layer and the outer layer are produced by double-layer co-extrusion, the inner layer is a polyvinyl chloride layer, and the outer layer is a light-weight polyvinyl chloride layer. A certain amount of hollow glass microbeads is mixed into the light-weight polyvinyl chloride layer, so that the pipe density can be reduced, and the pipe as a whole can be lightened.

Description

Technical Field

[0001] This invention relates to the field of pipe technology, and more specifically, to a method for preparing lightweight polyvinyl chloride (PVC) pipes, and also to a lightweight PVC pipe. Background Technology

[0002] PVC pipes, with their excellent corrosion resistance, insulation, and ease of processing, are widely used in various industries such as construction, agriculture, and power. However, traditional PVC pipes are relatively heavy, which significantly increases logistics costs during transportation and requires more manpower and time during installation, severely impacting construction efficiency. To achieve lightweighting of PVC pipes, lightweight materials are usually incorporated into the pipe material, thereby reducing the overall density and achieving weight reduction. This invention proposes a new solution to address this problem. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a lightweight polyvinyl chloride pipe and its preparation method.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing lightweight polyvinyl chloride pipe, wherein the lightweight polyvinyl chloride pipe comprises an inner layer and an outer layer, the inner layer and the outer layer are produced by double-layer co-extrusion, the inner layer is a polyvinyl chloride layer, and the outer layer is a lightweight polyvinyl chloride layer.

[0005] The present invention is further configured such that the lightweight polyvinyl chloride layer comprises polyvinyl chloride material, hollow glass microspheres and coupling agent, wherein the mass ratio of the hollow glass microspheres is 2%-5.8% and the mass ratio of the coupling agent is 1%-2%.

[0006] The present invention is further configured such that the density of the polyvinyl chloride layer is ρ1, the density of the lightweight polyvinyl chloride layer is ρ2, ρ1>ρ2; and the overall density of the lightweight polyvinyl chloride pipe is ρ(i), ρ1>ρ(i)>ρ2.

[0007] The present invention is further configured such that the inner layer material is fed to the co-extrusion die from one direction of the extruder, and the outer layer material is fed to the co-extrusion die from the other direction of the extruder, and a double-layered tube structure is formed by passing through the co-extrusion die.

[0008] The present invention is further configured such that the preparation method includes the following steps:

[0009] Step 1: Obtain the coefficients k1 and k2 of the rotational speed and base speed of the inner and outer layer materials during the basic processes of extruder 1 and extruder 2, respectively;

[0010] Step 2: Obtain the density values ​​of the inner and outer layer materials after extrusion, ρ1 and ρ2, respectively;

[0011] Step 3: Obtain the theoretical value of the overall density required for pipe production, ρ_theoretical, and the theoretical value of the extrusion speed, Q_theoretical;

[0012] Step 4: Based on ρ theory and Q theory, calculate the theoretical speed requirements of extruder 1 and extruder 2, and obtain the initial speeds n1 and n2 of extruder 1 and extruder 2;

[0013] Step 5: Extrude the pipe and record the serial number of the pipe as i. Adjust the speed of extruder one and extruder two according to the extrusion speed and density during the extrusion process.

[0014] Step 6: Define the extrusion speed deviation value as ΔQ and the density deviation value as Δρ during the production process;

[0015] Step 7: Adjust the rotation speeds of extruder one and extruder two according to the relationship between Δρ(i) and the density deviation threshold;

[0016] During the adjustment process, the speed of extruder one is kept constant, n1(i+1)=n1(i), and the speed of extruder two is adjusted separately. The adjustment coefficient is set to p(i), and the speed of extruder two is: n2(i+1)=(1+p(i))·n2(i).

[0017] The present invention is further configured such that the preparation method includes the following steps:

[0018] Step 8: After adjustment, continue to test the pipe and repeat steps 6-8 several times until Δρ(i) is not greater than the density deviation threshold in three consecutive tests.

[0019] Step 9: Adjust the rotational speeds of extruder one and extruder two according to the relationship between ΔQ(i) and the speed deviation threshold;

[0020] Step 10: After adjustment, the pipe is inspected, and the rotation speeds of extruder one and extruder two are adjusted accordingly based on the relationship between Δρ(i) and the density deviation threshold.

[0021] Step 11: After adjustment, continue to test the pipe and repeat steps 10 and 11 several times until ΔQ(i) and Δρ(i) are not greater than the density deviation threshold in three consecutive tests.

[0022] The present invention is further configured such that step 1 includes the following steps:

[0023] Step 1.1: Extruder 1 runs alone at a speed of n1, while extruder 2 is paused. The extrusion speed of extruder 1 is Q1. Calculate the initial value of the coefficient k1 between the speed of extruder 1 and the extrusion speed: Q1 = k1·n1, k1 = Q1 / n1.

[0024] Step 1.2:

[0025] Extruder 2 runs independently at a speed of n2. Extruder 2 is paused, and the extrusion speed of extruder 2 is Q2. Calculate the initial value of the coefficient k2 between the speed of extruder 2 and the extrusion speed: Q2 = k2·n2, k2 = Q2 / n2.

[0026] The present invention is further configured such that step 2 includes the following steps:

[0027] Step 2.1: Detect the weight of the extruded tube in Step 1.1, and deduce the volume of the tube based on the length and cross-sectional area of ​​the extruded tube, so as to obtain the density ρ1 of material 1 in extruder 1 after extrusion.

[0028] Step 2.2: Detect the weight of the extruded tube in Step 1.2, and deduce the volume of the tube based on its length and cross-sectional area, thus obtaining the density ρ2 of material 2 in extruder 2 after extrusion.

[0029] The present invention is further configured such that, in step 4, the relationship between ρ_theory and Q_theory and the initial rotational speeds n1 and n2 is as follows:

[0030] Q_theory = Q1 + Q2 = k1·n1 + k2·n2,

[0031] ρ_theory·Q_theory = Q1·ρ1 + Q2·ρ2 = k1·n1·ρ1 + k2·n2·ρ2,

[0032] ρ_theory = (k1·ρ1 / Q_theory)·n1 + (k2·ρ2 / Q_theory)·n2,

[0033] The initial rotational speeds n1 and n2 can be obtained through calculation;

[0034] The present invention is further configured such that, in step 5,

[0035] n1(i) is the value of extruder 1 when extruding the i-th pipe;

[0036] n2(i) is the value of extruder 2 when extruding the i-th pipe;

[0037] Q(i) is the extrusion speed of the i-th pipe;

[0038] ρ(i) represents the overall density of the i-th pipe.

[0039] The present invention is further configured such that, in step 9, the rotational speeds of extruder one and extruder two are adjusted simultaneously, with an adjustment coefficient set as w(i), and the rotational speeds of extruder one and extruder two being:

[0040] n1(i+1)=(1+w(i)-λ(i,j))·n1(i);

[0041] n2(i+1)=(1+w(i)+λ(i,j))·n2(i);

[0042] λ(i,j) is the comprehensive adjustment coefficient, j is the number of adjustments, j=j+1 for each adjustment, and the initial value is λ(0)=0;

[0043] When ΔQ(i) is not greater than the speed deviation threshold, w(i) is set to 0;

[0044] In step 9, when ΔQ(i) is greater than the speed deviation threshold, Q_theoretical = Q(i)·(1+w(i)), w(i) = Q_theoretical / Q(i)-1.

[0045] In step 10, when Δρ(i) is not greater than the density deviation threshold, the current rotation speed is maintained; when Δρ(i) is greater than the density deviation threshold, comprehensive compensation adjustment is performed according to the comprehensive adjustment coefficient λ(i,j), where λ(i,j) = Δρ(i) / ρ(i).

[0046] The present invention also provides a lightweight polyvinyl chloride pipe, which is produced by the preparation method described above, and lightweight polyvinyl chloride pipe material can be obtained.

[0047] In summary, the present invention has the following beneficial effects:

[0048] The inner layer is a polyvinyl chloride (PVC) layer; the outer layer is a lightweight PVC layer. A certain amount of hollow glass microspheres are mixed into the lightweight PVC layer, which can reduce its density, thereby enabling the pipe to be lightweight as a whole.

[0049] By placing a lightweight PVC layer containing hollow glass microspheres on the outer layer, it is possible to prevent some of the hollow glass microspheres from separating into the medium being transported inside the pipe, thereby preventing contamination of the medium being transported inside the pipe.

[0050] In this scheme, each section of pipe is weighed during the production process. The comprehensive density of the pipe material, ρ, is calculated by combining the weight G with the pipe size. The ratio of the inner and outer layers can be obtained from the comprehensive density ρ, and thus the corresponding thickness of the inner and outer layers can be obtained. Therefore, the thickness of the inner and outer layers can be represented by the comprehensive density. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the cross-section of a lightweight polyvinyl chloride pipe in this embodiment;

[0052] Figure 2 This is a schematic diagram of the co-extrusion die in this embodiment, to illustrate the flow channel for the co-extrusion of the two materials;

[0053] Reference numerals: Inner layer 1; Outer layer 2; Co-extrusion die 3; Inner layer flow channel 31; Outer layer flow channel 32; Co-extrusion flow channel 33. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0055] This embodiment discloses a method for preparing lightweight polyvinyl chloride pipes, referring to... Figure 1 , Figure 1 As shown, the lightweight polyvinyl chloride pipe includes an inner layer and an outer layer, which are produced by double-layer co-extrusion. Specifically, the inner layer material is fed to the co-extrusion die from one direction of the extruder, and the outer layer material is fed to the co-extrusion die from the other direction of the extruder. After passing through the co-extrusion die, a double-layer pipe structure is formed.

[0056] The inner layer is made of polyvinyl chloride (PVC) and the outer layer is made of lightweight PVC. The lightweight PVC layer contains a certain amount of hollow glass microspheres, which can reduce its density and thus make the pipe as a whole lightweight.

[0057] Specifically, the lightweight PVC layer consists of PVC material, hollow glass microspheres, and coupling agent, wherein the mass ratio of hollow glass microspheres is 2%-5.8%, and the mass ratio of coupling agent is 1%-2%.

[0058] The specific particle size of hollow glass microspheres can be selected according to the actual lightweight requirements of the pipe; the coupling agent can be a silane coupling agent or a titanate coupling agent, etc.

[0059] Since the density of the PVC layer is ρ1 and the density of the lightweight PVC layer is ρ2, ρ1>ρ2; therefore, the overall density of the final lightweight PVC pipe is ρ(i), where ρ1>ρ(i)>ρ2. The density range of ρ(i) lies between the two and is specifically set according to the ratio of the two materials.

[0060] Since the inner layer 1 of the pipe is in direct contact with the medium being transported inside, by setting a lightweight polyvinyl chloride layer mixed with hollow glass microspheres on the outer layer, it is possible to prevent some of the hollow glass microspheres from separating into the medium being transported inside the pipe, thereby preventing contamination of the medium being transported inside the pipe.

[0061] Furthermore, due to the co-extrusion process, the current method for determining the proportion of the two materials in a pipe is typically to cut and measure the inner wall of the pipe. Before testing, a sample of the pipe needs to be cut to expose the cross-section, and then the proportions of the two materials in the cross-section are measured to determine whether it meets the pipe's production design requirements. However, in actual measurement, the two substrates of the inner and outer layers may be similar in color, and there may not be a clear transition surface at the interface, leading to significant errors in the testing of the inner and outer layers of the pipe.

[0062] In this embodiment, PVC pipes with an outer diameter of D are produced. The pipe consists of two layers: an inner layer with a thickness of a1 and a density of ρ1; and an outer layer with a thickness of a2 and a density of ρ2. During production, each pipe segment is produced to a length of L. Each segment is weighed, and the overall density ρ of the pipe is calculated using the weight G and the pipe dimensions. The overall density ρ gives the proportion of the inner and outer layers, allowing us to determine their corresponding thicknesses. Therefore, the overall density can be used to represent the thickness of the inner and outer layers.

[0063] During the production process, the two materials are fed by two screw extruders respectively. The inner layer material is fed by extruder one at a speed of n1; the outer layer material is fed by extruder two at a speed of n2. Theoretically, the above-mentioned pipe can be produced according to the speeds of n1 and n2, and the extrusion speed of the pipe is Q.

[0064] However, in actual production, the extrusion speed of the pipe and the thickness of the inner and outer layers will deviate to some extent according to the rotation speeds of n1 and n2. By adjusting the rotation speeds of n1 and n2, the parameters of the basic speed of pipe production and the thickness of the inner and outer layers can be corrected.

[0065] The method for preparing lightweight polyvinyl chloride pipes in this embodiment includes the following steps:

[0066] Step 1:

[0067] Obtain the coefficients k1 and k2 of the rotational speed and base speed of the inner layer material and the outer layer material during the basic processes of extruder 1 and extruder 2, respectively;

[0068] Specifically, step 1 includes the following steps:

[0069] Step 1.1: Extruder 1 runs alone at a speed of n1, while extruder 2 is paused. The extrusion speed of extruder 1 is Q1. Calculate the initial value of the coefficient k1 between the speed of extruder 1 and the extrusion speed: Q1 = k1·n1, k1 = Q1 / n1.

[0070] Step 1.2:

[0071] Extruder 2 operates independently at a speed of n2. When extruder 2 is paused, the extrusion speed of extruder 2 is Q2. The initial value of the coefficient k2 between the speed of extruder 2 and the extrusion speed is calculated: Q2 = k2·n2, k2 = Q2 / n2.

[0072] Step 2:

[0073] Obtain the density values ​​of the inner and outer layer materials after extrusion, ρ1 and ρ2, respectively;

[0074] Specifically, step 2 includes the following steps:

[0075] Step 2.1: Detect the weight of the extruded tube in Step 1.1, and deduce the volume of the tube based on the length and cross-sectional area of ​​the extruded tube, so as to obtain the density ρ1 of material 1 in extruder 1 after extrusion.

[0076] Step 2.2: Detect the weight of the extruded tube in Step 1.2, and deduce the volume of the tube based on its length and cross-sectional area, thus obtaining the density ρ2 of material 2 in extruder 2 after extrusion.

[0077] Step 3:

[0078] Obtain the theoretical value of the overall density required for pipe production, ρ (theoretical), and the theoretical value of the extrusion speed, Q (theoretical).

[0079] The values ​​of ρ_theory and Q_theory are determined based on parameters in the production design. These parameters are known before production and are specifically determined according to the design of each different type of pipe.

[0080] Step 4:

[0081] Based on ρ theory and Q theory, the theoretical speed requirements of extruder 1 and extruder 2 are calculated, and the initial speeds n1 and n2 of extruder 1 and extruder 2 are obtained.

[0082] In this embodiment, since the mold used is fixed, the cross-sectional value of the pipe is fixed during the foundation process. In addition, according to the law of conservation of fluid flow, the foundation amount of the two materials is determined by the extrusion speed during the foundation process.

[0083] In step 4, the relationship between the ρ theory and the Q theory and the initial rotational speeds n1 and n2 is as follows:

[0084] Q_theory = Q1 + Q2 = k1·n1 + k2·n2,

[0085] ρ_theory·Q_theory = Q1·ρ1 + Q2·ρ2 = k1·n1·ρ1 + k2·n2·ρ2,

[0086] ρ_theory = (k1·ρ1 / Q_theory)·n1 + (k2·ρ2 / Q_theory)·n2,

[0087] Based on the above calculations, the initial rotational speeds n1 and n2 can be calculated. In the initial stage of production, extruder one and extruder two operate at initial speeds n1 and n2, respectively.

[0088] Step 5:

[0089] The pipe is produced by extrusion. The serial number of the pipe is recorded as i. The relationship between each parameter and the serial number i is established.

[0090] n1(i) is the value of extruder 1 when extruding the i-th pipe;

[0091] n2(i) is the value of extruder 2 when extruding the i-th pipe;

[0092] Q(i) is the extrusion speed of the i-th pipe;

[0093] ρ(i) is the comprehensive density of the i-th pipe;

[0094] The rotational speeds of extruder one and extruder two are adjusted based on the extrusion speed and density during the extrusion process.

[0095] For example, when the first tube is extruded, i=1. Substituting the initial rotation speed mentioned above, we get the initial n1(1) and n2(1);

[0096] The extrusion speed of the first pipe was measured to obtain Q(1);

[0097] The density of the first pipe is measured to obtain ρ(1); in each subsequent pipe test, i=i+1.

[0098] Step 6:

[0099] Define the deviations of ρ_theory and Q_theory from ρ(i) and Q(i) during the production process;

[0100] Extrusion speed deviation ΔQ and density deviation Δρ;

[0101] ΔQ(i) = Q(i) - Q(i-1), Q(0) = Q_theory, that is, the initial value of Q(i) is Q_theory;

[0102] Δρ(i) = ρ(i) - ρ(i-1), ρ(0) = ρ_theory, that is, the initial value of ρ(i) is ρ_theory;

[0103] Step 7:

[0104] Based on the relationship between Δρ(i) and the density deviation threshold, the rotational speeds of extruder one and extruder two are adjusted;

[0105] During the adjustment process, the speed of extruder one is kept constant, n1(i+1)=n1(i), and the speed of extruder two is adjusted separately. The adjustment coefficient is set to p(i), and the speed of extruder two is: n2(i+1)=(1+p(i))·n2(i);

[0106] By adjusting the speed of one of the extruders, namely extruder two, the extrusion ratio of the two materials can be adjusted, thereby controlling the overall density of the final extruded pipe within a preset threshold range. The theoretical threshold range of ρ is usually around ±5%. By controlling the overall density of the pipe within an appropriate range, it can be ensured that the thickness of the inner and outer layers can meet the corresponding production design requirements.

[0107] In the specific adjustments in step 7,

[0108] When Δρ(i) is not greater than the density deviation threshold, it indicates that the overall density of the extruded pipe meets the production design requirements, that is, the speed of the second extruder is not adjusted, and p(i)=0; n1(i+1)=n1(i), n2(i+1)=n2(i);

[0109] When Δρ(i) is greater than the density deviation threshold, it is adjusted by the adjustment coefficient p(i). The correlation of the adjustment coefficient p(i) is as follows:

[0110] Q(i+1)=Q1(i+1)+Q2(i+1)=k1·n1(i+1)+k2·n2(i+1),

[0111] Substituting n1(i+1)=n1(i) and n2(i+1)=(1+p(i))·n2(i) into the above equation, we get:

[0112] Q(i+1)=k1·n1(i)+k2·(1+p(i))·n2(i)

[0113] Additionally, ρ_theory·Q(i+1)=k1·n1(i)·ρ1+k2·(1+p(i))·n2(i)·ρ2,

[0114] Substituting Q(i+1) into the above equation, we get:

[0115] ρ_theory·[k1·n1(i)+k2·(1+p(i))·n2(i)]=k1·n1(i)·ρ1+k2·(1+p(i))·n2(i)·ρ2;

[0116] Expand and rearrange the equation:

[0117] ρ_theory·k1·n1(i)+ρ_theory·k2·(1+p(i))·n2(i)=k1·n1(i)·ρ1+k2·(1+p(i))·n2(i)·ρ2;

[0118] Rearrange and group:

[0119] ρ_theory·k1·n1(i)-k1·n1(i)·ρ1+ρ_theory·k2·n2(i)·(1+p(i))-k2·n2(i)·ρ2·(1+p(i))=0;

[0120] Extract common factors:

[0121] k1·n1(i)·(ρ_theory-ρ1)+·k2·n2(i)·(ρ_theory-ρ2)·(1+p(i)=0;

[0122] The value of the adjustment coefficient p(i) is obtained:

[0123]

[0124] Substituting the adjustment coefficient p(i) into the speed of extruder two, we obtain the adjusted speed of extruder two.

[0125] Step 8:

[0126] After adjustment, continue to test the pipe and repeat steps 6-8 several times.

[0127] Until three consecutive tests, Δρ(i) is not greater than the density deviation threshold; through multiple adjustments, the overall density of the pipe can meet the final adjustment requirements, and the overall density can meet the production design requirements of the pipe.

[0128] At this point, the adjustment of the overall density of the pipe is complete, and the subsequent adjustment begins on the extrusion speed. If the extrusion speed is too high, it may easily lead to surface defects in the pipe, while if the extrusion speed is too low, it will affect the production efficiency. Therefore, the extrusion speed needs to be controlled within a threshold range. The threshold range for extrusion speed is generally about ±8% of the theoretical design value.

[0129] Step 9:

[0130] ΔQ(i) = Q(i) - Q(i-1), and the rotational speeds of extruder one and extruder two are adjusted according to the relationship between ΔQ(i) and the speed deviation threshold.

[0131] During the adjustment process, the speeds of extruder one and extruder two are adjusted simultaneously, with the adjustment coefficient set to w(i). The speeds of extruder one and extruder two are as follows:

[0132] n1(i+1)=(1+w(i)-λ(i,j))·n1(i);

[0133] n2(i+1)=(1+w(i)+λ(i,j))·n2(i);

[0134] Where λ(i,j) is the comprehensive adjustment coefficient, i follows the number of pipes inspected, j is the number of adjustments, j=j+1 for each adjustment, and the initial value is λ(0)=0;

[0135] During the adjustment process, when ΔQ(i) is not greater than the speed deviation threshold, it indicates that the extrusion speed of the extruded pipe meets the production design requirements, that is, the speed of extruder 1 and extruder 2 is not adjusted, and w(i) is set to 0.

[0136] When ΔQ(i) is greater than the speed deviation threshold, it indicates that the extrusion speed of the extruded pipe does not meet the production design requirements, and the rotation speeds of extruder one and extruder two need to be adjusted. The relationship between w(i) and Q(i) is as follows:

[0137] Q_theory = Q(i)·(1+w(i))

[0138] The calculation yields w(i) for this adjustment, w(i) = Q_theoretical / Q(i)-1;

[0139] Step 10:

[0140] After adjustment, due to the slight difference in the rotational speeds of extruder 1 and extruder 2, the flow state of the two materials in the co-extrusion die 3 will also change, which may slightly change the proportion of the two materials in the base.

[0141] Therefore, the pipe is inspected, and the rotation speeds of extruder 1 and extruder 2 are adjusted according to the relationship between Δρ(i) and density deviation threshold, so that the adjusted Δρ(i) can meet the density deviation threshold and ensure that it meets the production requirements.

[0142] Specifically, in step 10, when Δρ(i) is not greater than the density deviation threshold, it indicates that the overall density of the extruded pipe meets the production design requirements, and there is no need to adjust the speed of extruder 1 and extruder 2; the current speed can be maintained.

[0143] When Δρ(i) is greater than the density deviation threshold, it indicates that the overall density of the extruded pipe does not meet the production design requirements, that is, the speed of extruder 1 and extruder 2 needs to be compensated and adjusted.

[0144] During the adjustment process, comprehensive compensation adjustment is carried out based on the comprehensive adjustment coefficient λ(i,j), where j=j+1;

[0145] λ(i,j)=Δρ(i) / ρ(i)

[0146] Substituting λ(i,j) into the equation, we can calculate the rotational speeds of extruder one and extruder two as follows:

[0147] n1(i+1)=(1+w(i)-λ(i,j))·n1(i);

[0148] n2(i+1)=(1+w(i)+λ(i,j))·n2(i);

[0149] When the density of ρ(i) is greater than the preset density, it indicates that the material of the inner layer 1 is excessive. In this case, the speed n1 of the extruder 1 needs to be reduced appropriately so that the combined density of the supply and output of both can meet the requirements. At the same time, the speed n2 of the extruder 2 should be increased appropriately to compensate for the total amount of material output by co-extrusion and maintain the basic speed.

[0150] Conversely, if the density of ρ(i) is less than the preset density, it means that the material of inner layer 1 is too little. In this case, the speed n1 of extruder 1 needs to be increased appropriately so that the combined density of the two supplies and outputs can meet the requirements. At the same time, the speed n2 of extruder 2 should be reduced appropriately to compensate for the total amount of material output by co-extrusion and maintain the basic speed.

[0151] By introducing a comprehensive adjustment coefficient λ(i,j) during the adjustment process, the comprehensive adjustment coefficient λ(i,j) can automatically change with the number of adjustments. Moreover, after each adjustment, the difference between the comprehensive density of the pipe and the theoretical density value of the pipe will be further reduced, which will also reduce the value of Δρ(i), thereby reducing the comprehensive adjustment coefficient and reducing the adjustment range, thus enabling the final value to reach a stable state in the region.

[0152] Step 11:

[0153] After adjustment, continue to test the pipe and repeat steps 10 and 11 several times, generally at least 5-8 times. During the cycle, continuously re-compensate the comprehensive adjustment coefficient and continuously correct the operating parameters of extruder one and extruder two.

[0154] If ΔQ(i) and Δρ(i) are not greater than the density deviation threshold after three consecutive tests, it indicates that the operating parameters of extruder 1 and extruder 2 meet the production design requirements and can produce the required pipe at the designed basic speed.

[0155] This embodiment also discloses a lightweight polyvinyl chloride pipe, which can be prepared and produced using the above-described preparation method, resulting in a lightweight polyvinyl chloride pipe.

[0156] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing lightweight polyvinyl chloride pipes, characterized in that, The lightweight polyvinyl chloride pipe includes an inner layer and an outer layer, which are produced by double-layer co-extrusion. The inner layer is a polyvinyl chloride layer, and the outer layer is a lightweight polyvinyl chloride layer. The preparation method includes the following steps: Step 1: Obtain the coefficients k1 and k2 of the rotational speed and extrusion speed of the inner layer material and the outer layer material during the extrusion process of extruder 1 and extruder 2, respectively; Step 2: Obtain the density values ​​of the inner and outer layer materials after extrusion, ρ1 and ρ2, respectively; Step 3: Obtain the theoretical value of the overall density required for pipe production, ρ_theoretical, and the theoretical value of the extrusion speed, Q_theoretical; Step 4: Based on ρ theory and Q theory, calculate the theoretical speed requirements of extruder 1 and extruder 2, and obtain the initial speeds n1 and n2 of extruder 1 and extruder 2; Step 5: Extrude the pipe and record the serial number of the pipe as i. Adjust the speed of extruder one and extruder two according to the extrusion speed and density during the extrusion process. Step 6: Define the extrusion speed deviation value as ΔQ and the density deviation value as Δρ during the production process; Step 7: Adjust the rotation speeds of extruder one and extruder two according to the relationship between Δρ(i) and the density deviation threshold; During the adjustment process, the speed of extruder one is kept constant, n1(i+1)=n1(i), and the speed of extruder two is adjusted separately. The adjustment coefficient is set to p(i), and the speed of extruder two is: n2(i+1)=(1+p(i))·n2(i); The preparation method further includes the following steps: Step 8: After adjustment, continue to test the pipe and repeat steps 6-8 several times until Δρ(i) is not greater than the density deviation threshold in three consecutive tests. Step 9: Adjust the rotational speeds of extruder one and extruder two according to the relationship between ΔQ(i) and the speed deviation threshold; Step 10: After adjustment, the pipe is inspected, and the rotation speeds of extruder one and extruder two are adjusted accordingly based on the relationship between Δρ(i) and the density deviation threshold. Step 11: After adjustment, continue to test the pipe and repeat steps 10 and 11 several times until ΔQ(i) and Δρ(i) are not greater than the density deviation threshold in three consecutive tests. Step 1 includes the following steps: Step 1.1: Extruder 1 runs alone at a speed of n1, while extruder 2 is paused. The extrusion speed of extruder 1 is Q1. Calculate the initial value of the coefficient k1 between the speed of extruder 1 and the extrusion speed: Q1 = k1·n1, k1 = Q1 / n1. Step 1.2: Extruder 2 runs independently at a speed of n2. Extruder 2 is paused and its extrusion speed is Q2. Calculate the initial value of the coefficient k2 between the speed of extruder 2 and the extrusion speed: Q2 = k2·n2, k2 = Q2 / n2. Step 2 includes the following steps: Step 2.1: Detect the weight of the extruded tube in Step 1.1, and deduce the volume of the tube based on the length and cross-sectional area of ​​the extruded tube, so as to obtain the density ρ1 of material 1 in extruder 1 after extrusion. Step 2.2: Detect the weight of the extruded tube in Step 1.2, and deduce the volume of the tube based on the length and cross-sectional area of ​​the extruded tube, thus obtaining the density ρ2 of material 2 in extruder 2 after extrusion. In step 4, the relationship between ρ_theory and Q_theory and the initial rotational speeds n1 and n2 is as follows: Q_theory = Q1 + Q2 = k1·n1 + k2·n2, ρ_theory·Q_theory = Q1·ρ1 + Q2·ρ2 = k1·n1·ρ1 + k2·n2·ρ2, ρ_theory = (k1·ρ1 / Q_theory)·n1 + (k2·ρ2 / Q_theory)·n2, The initial rotational speeds n1 and n2 can be obtained through calculation.

2. The method for preparing lightweight polyvinyl chloride pipes according to claim 1, characterized in that, The lightweight polyvinyl chloride layer comprises polyvinyl chloride material, hollow glass microspheres, and a coupling agent, wherein the mass ratio of the hollow glass microspheres is 2%-5.8%, and the mass ratio of the coupling agent is 1%-2%.

3. The method for preparing lightweight polyvinyl chloride pipes according to claim 1, characterized in that, The density of the polyvinyl chloride layer is ρ1, the density of the lightweight polyvinyl chloride layer is ρ2, and ρ1>ρ2; the overall density of the lightweight polyvinyl chloride pipe is ρ(i), and ρ1>ρ(i)>ρ2.

4. The method for preparing lightweight polyvinyl chloride pipes according to claim 1, characterized in that, The inner layer is fed to the co-extrusion die from one direction of the extruder, and the outer layer material is fed to the co-extrusion die from the other direction of the extruder. After passing through the co-extrusion die, a double-layered tubular structure is formed.

5. The method for preparing lightweight polyvinyl chloride pipes according to claim 1, characterized in that, In step 9, the rotational speeds of extruder one and extruder two are adjusted simultaneously, with the adjustment coefficient set to w(i). The rotational speeds of extruder one and extruder two are as follows: n1(i+1)=(1+w(i)-λ(i,j))·n1(i); n2(i+1)=(1+w(i)+λ(i,j))·n2(i); λ(i,j) is the comprehensive adjustment coefficient, j is the number of adjustments, j=j+1 for each adjustment, and the initial value is λ(0)=0; When ΔQ(i) is not greater than the speed deviation threshold, w(i) is set to 0; In step 9, when ΔQ(i) is greater than the speed deviation threshold, Q_theoretical = Q(i)·(1+w(i)), w(i) = Q_theoretical / Q(i)-1; In step 10, when Δρ(i) is not greater than the density deviation threshold, the current rotation speed is maintained; when Δρ(i) is greater than the density deviation threshold, comprehensive compensation adjustment is performed according to the comprehensive adjustment coefficient λ(i,j), where λ(i,j) = Δρ(i) / ρ(i).

6. A lightweight polyvinyl chloride pipe, characterized in that, The product is manufactured using the preparation method described in any one of claims 1-5.

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