A method for preparing a test sample of a halogen-free and low-smoke cable sheath raw material for mining

Abstract

The present invention discloses a method for preparing a sample of halogen-free, low-smoke cable sheath material for mining. The sample is made by cutting a sheet into a dumbbell shape using a single-screw extruder with a horizontal rectangular discharge die. The extruder screw has a constant pitch and constant groove depth. The sheet is prepared according to the following steps: 1) preheating, which involves preheating the extruder and starting it; 2) feeding, which involves feeding halogen-free, low-smoke sheathing granules into the extruder; 3) extrusion, which involves melting the halogen-free, low-smoke sheathing granules within the extruder and extruding them through the die to produce a sheet with a rectangular cross-section; and 4) receiving, which involves receiving the sheet using a horizontal belt and allowing the sheet to naturally cool and harden on the belt. This method overcomes the drawbacks of unstable test data and inaccurate results associated with existing sample preparation methods. The sample prepared using this method can truly reflect the tensile properties of cable sheaths made from the halogen-free, low-smoke cable sheathing raw materials.

Description

Technical Field

[0001] The present invention relates to the technical field of cable sheath raw material inspection, and in particular to a method for preparing a halogen-free and low-smoke cable sheath raw material inspection sample. Background Art

[0002] The current GB / T32129-2015 standard for "Halogen-free, Low-smoke, Flame-retardant Cable Materials for Wires and Cables" requires that the elongation at break of halogen-free, low-smoke, flame-retardant cable materials be greater than or equal to 160%. In order to ensure the safety of coal mine production, the "General Safety Technical Requirements for Halogen-free, Low-smoke Cables for Coal Mines" stipulates that the sheath performance of fixed-laying halogen-free, low-smoke cables such as power cables, control cables, and communication cables used in coal mines must be based on the requirements of Appendix B of G / T19666-2005, and the tensile strength before aging must be increased to 10N / mm 2 , elongation at break increased to 200%, and other technical indicators should meet the requirements of the MT818 series of standards. Existing technical standards do not specifically address the preparation of test specimens for halogen-free, low-smoke cable sheathing materials used in coal mines. The industry typically adopts the sample preparation method specified in GB / T8115-2008, "Soft Polyvinyl Chloride Plastics for Wires and Cables." This involves using plasticizers to plasticize halogen-free, low-smoke, flame-retardant cable sheathing raw material pellets, pressing them into sheets, and then cutting them into dumbbell-shaped specimens for tensile performance testing. Alternatively, the industry typically adopts the GB / T1040.3-2006 method, which involves directly placing halogen-free, low-smoke, flame-retardant cable sheathing raw material pellets into molds, subjecting them to high temperature and high pressure to form sheets, which are then cut into dumbbell-shaped specimens for tensile performance testing.

[0003] Because halogen-free, low-smoke sheathing materials contain a large amount of inorganic flame retardants, their melt strength, elongation, and viscosity differ significantly from those of other cable materials. The mechanical properties of halogen-free, low-smoke sheathing materials are lower than those of conventional cable materials, with an elongation ratio of only approximately 2.5 to 3.2. Consequently, samples prepared using the plasticizer-based pelletizing method do not fully mix the halogen-free, low-smoke sheathing material, resulting in unstable tensile test data. The tensile test results of multiple samples cut from the same pellet, as well as those of samples made from different pellets from the same batch of sheathing pellets, vary significantly from the mean. The test results also differ significantly from those of samples prepared from cable sheath chips. Qualified halogen-free, low-smoke sheathing materials often fail elongation at break tests, leading to misjudgments and unwarranted product returns. If halogen-free, low-smoke sheathing materials are directly put into production without elongation testing, failing the elongation at break will result in substandard finished cables, resulting in significant waste. Furthermore, cable fires caused by these substandard materials can cause significant casualties and property damage. Therefore, the samples made by using a plasticizer to press the plastic into sheets and the samples made by using a mold at high temperature and high pressure cannot truly reflect the tensile properties of the halogen-free, low-smoke, flame-retardant cable sheath raw materials, and cannot meet the requirements for inspecting the halogen-free, low-smoke, flame-retardant cable sheath raw materials before the production of halogen-free, low-smoke cables for coal mines. Summary of the Invention

[0004] The technical problem to be solved by the invention is to provide a method for preparing inspection samples of halogen-free and low-smoke cable sheath raw materials for mining. This method can overcome the disadvantages of unstable inspection data and inaccurate results of existing sample preparation methods. The samples made by this method can truly reflect the tensile properties of cable sheaths made from halogen-free and low-smoke cable sheath raw materials.

[0005] The technical solution adopted to solve the technical problem is: a method for preparing a sample of a halogen-free and low-smoke cable sheath material for mining. The sample is made by cutting a sheet into a dumbbell shape. The sheet is made by using a single-screw extruder with a horizontal rectangular discharge die head. The extruder screw is an extrusion screw with a constant pitch and constant groove depth. The sheet is prepared according to the following steps:

[0006] 1) Preheating: Preheat the extruder and start it;

[0007] 2) Feeding the halogen-free and low-smoke sheath granules into the extruder;

[0008] 3) Extrusion: The halogen-free low-smoke sheath granular material is melted in the extruder, and the molten material is stirred, sheared and homogenized before being conveyed to the die head. After being extruded by the die head, a rectangular cross-section sheet is output. The ratio of the cross-sectional area of ​​the die head's feed port to the cross-sectional area of ​​the horizontal rectangular discharge port is not less than 50;

[0009] 4) Receiving: When the sheet output from the die outlet is continuous without breakage, uniform in texture, and flat on the surface without defects, a horizontal belt with the same extrusion direction, the same output speed as the sheet, and the same height as the bottom edge of the horizontal rectangular outlet is used to receive the sheet. The sheet is naturally cooled and hardened on the horizontal belt to obtain the sheet.

[0010] As a further improvement of the present invention: the sample is cut into a dumbbell shape by punching the sheet using a die, the sheet is placed on a press, and the dumbbell-shaped die is used to punch the sheet into a dumbbell-shaped sample along the thickness direction of the sheet.

[0011] As a further improvement of the present invention: in step 3, the temperature of the extruder feeding section is 125°C, the conveying section is 133°C, the melting section is 145°C, and the die head is 155°C.

[0012] As a further improvement of the present invention, the thickness of the sheet is 2-4 mm greater than the thickness of the sample. Before pressing and cutting, the sheet is planed from both sides to the thickness of the sample.

[0013] As a further improvement of the present invention: the width of the sheet is equal to the width of both ends of the sample.

[0014] As a further improvement of the present invention: a funnel-shaped extrusion zone is provided between the feed port and the discharge port of the die head, and the cone angle of the funnel-shaped extrusion zone is 45 degrees.

[0015] Beneficial effects: The method for preparing the test sample of the raw material of the halogen-free and low-smoke cable sheath for mining use of the present invention adopts an extruder to make the sheet and then cut it into dumbbell-shaped samples. The halogen-free and low-smoke sheath granular material is melted in the extruder. The material is fully mixed and the air is discharged under the stirring, shearing and homogenizing action of the screw in the molten state. The material is then extruded by the die head at a force of not less than 50 times, thereby avoiding the formation of defects such as cavities, slag inclusions, and cracks on the surface and inside of the sample that affect the test results. As a result, the prepared sample can truly reflect the tensile properties of the halogen-free and low-smoke cable sheath material for mining use. Since a belt is used to receive the sheet, the sheet is naturally cooled on the belt. Therefore, the factors that affect the performance of the sample, such as the stretching or distortion of the sheet when the sheet is made by the extruder, can be overcome, so that the test results of the sample prepared by the method of the present invention are more accurate. Due to the rationally defined temperatures of each section in the extruder and the presence of a funnel-shaped extrusion zone between the die's feed and discharge ports, the tensile properties of samples produced using a small extruder with four-stage heating can reach those of cable sheaths produced using an eight-stage heating cable sheath extruder. Because the thickness of the sheet is 2-4mm greater than the sample thickness, the sheet is planed from both sides to the sample thickness before cutting. This allows samples made from the core of the sheet to overcome surface defects that may form during the cooling process, ensuring that the resulting sample more accurately reflects the true performance of the raw material for halogen-free, low-smoke cable sheaths used in mining applications. The sheet width is equal to the width of the sample at both ends, reducing the amount of surface area required for subsequent cutting, preventing mechanical damage to the sample that could affect the accuracy of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the structure of an extruder for implementing the method of the present invention;

[0017] Figure 2 An axial view of a die head for an extruder for implementing the method of the present invention;

[0018] Figure 3 It is an enlarged axial cross-sectional view of a special die head for an extruder for implementing the method of the present invention. Implementation Method

[0019] A method for preparing a sample of a halogen-free, low-smoke cable sheath material for mining use, wherein the sample is prepared by cutting a sheet into a dumbbell shape. The sheet is prepared using a single-screw extruder with a horizontal rectangular discharge die head, wherein the extruder screw has a constant pitch and constant groove depth. The sheet is prepared according to the following steps:

[0020] 1) Preheating: Preheat the extruder and start it;

[0021] 2) Feeding the halogen-free and low-smoke sheath granules into the extruder;

[0022] 3) Extrusion: The halogen-free low-smoke sheath granular material is melted in the extruder, and the molten material is stirred, sheared and homogenized before being conveyed to the die head. After being extruded through the die head, a rectangular cross-section sheet is output;

[0023] 4) Receiving: When the sheet output from the die outlet is continuous without breakage, uniform in texture, and flat on the surface without defects, a horizontal belt with the same extrusion direction, the same output speed as the sheet, and the same height as the bottom edge of the horizontal rectangular outlet is used to receive the sheet. The sheet is naturally cooled and hardened on the horizontal belt to obtain the sheet.

[0024] Preferably, the sample is cut into a dumbbell shape by punching a sheet using a die cutter, the sheet is placed on a press, and the dumbbell-shaped die cuts the sheet into a dumbbell-shaped sample along the thickness direction of the sheet.

[0025] Preferably, in step 3, the extruder feeding section is 125°C, the conveying section is 133°C, the melting section is 145°C, and the die head is 155°C.

[0026] Preferably, the thickness of the sheet is 2-4 mm greater than the thickness of the sample. Before pressing and cutting, the sheet is planed from both sides to the thickness of the sample. The width of the sheet is equal to the width of the two ends of the sample.

[0027] like Figure 2 、 3 As shown, the ratio of the cross-sectional area of ​​the die feed port 8 to the cross-sectional area of ​​the horizontal rectangular discharge port 2 is not less than 50, and a funnel-shaped extrusion zone 7 is provided between the die feed port and the discharge port, and the cone angle R of the funnel-shaped extrusion zone is 45 degrees.

[0028] like Figure 1 As shown, the extruder for implementing the method of the present invention includes an extrusion barrel 4. An extrusion screw with equal pitch and equal groove depth is provided in the extrusion barrel. A hopper 5 is installed on the barrel wall at one end of the extrusion barrel and an extrusion die 6 is installed at the other end. Four groups of induction heating coils 3 are provided outside the extrusion barrel corresponding to the feeding section, conveying section, melting section and die head. A horizontal belt 1 is provided in front of the extrusion die. The inner diameter of the extruder barrel is 30 mm and the length of the extrusion barrel is 500 mm.

[0029] The following is the elongation at break (%) test data for the same batch of halogen-free, low-smoke cable sheathing raw material pellets for mining applications, obtained using GB / T1040.3-2006, GB / T8115-2008, finished cable sheath chips, and test specimens prepared using the present invention. Each method was used in five passes to produce five slugs, A, B, C, D, and E. Each slug was then cut into pieces 1, 2, 3, 4, and 5, for a total of five specimens.

[0030] Table 1 shows the test specimens required by GB / T1040.3 standard;

[0031] Table 2 shows the samples made using GB / T8115-2008 standard;

[0032] Table 3 shows the samples made from finished cable sheath chips;

[0033] Table 4 shows the samples prepared by the method of the present invention.

[0034]

[0035] A comparison of the data in Tables 1-4 indicates that the test data for the halogen-free, low-smoke cable sheathing raw material for mining produced using the present method is substantially consistent with the test data for cable sheathing samples produced using this raw material, effectively reflecting the tensile properties of the halogen-free, low-smoke cable sheathing raw material for mining. Furthermore, the implementation of this method requires minimal operator proficiency and technical expertise, and the required extrusion equipment is compact and inexpensive. This method overcomes the shortcomings of current standards and allows for convenient and accurate determination of compliance of halogen-free, low-smoke cable sheathing raw material for mining.

Claims

1. A method for preparing a sample of a halogen-free, low-smoke cable sheath material for mining use, wherein the sample is made by cutting a sheet of material into a dumbbell shape, and wherein: The tablet is made by a single-screw extruder with a horizontal rectangular discharge die. The extruder screw has a constant pitch and constant groove depth. A funnel-shaped extrusion zone is provided between the feed port and the discharge port of the die. The cone angle of the funnel-shaped extrusion zone is 45 degrees. The tablet is prepared according to the following steps: 1) Preheating: Preheat the extruder and start it; 2) Feeding the halogen-free and low-smoke sheath granules into the extruder; 3) Extrusion: The halogen-free low-smoke sheath granular material is melted in the extruder, and the molten material is stirred, sheared and homogenized before being conveyed to the die head. After being extruded by the die head, a rectangular cross-section sheet is output. The ratio of the cross-sectional area of ​​the die head's feed port to the cross-sectional area of ​​the horizontal rectangular discharge port is not less than 50; 4) Receiving: When the sheet output from the die outlet is continuous without breakage, uniform in texture, and flat on the surface without defects, a horizontal belt with the same extrusion direction, the same output speed as the sheet, and the same height as the bottom edge of the horizontal rectangular outlet is used to receive the sheet. The sheet is naturally cooled and hardened on the horizontal belt to obtain the sheet.

2. The method for preparing a sample of a halogen-free and low-smoke cable sheath material for mining use according to claim 1, wherein: The sample is cut into a dumbbell shape by punching a sheet using a die cutter. The sheet is placed on a press and the dumbbell-shaped die cuts the sheet into a dumbbell-shaped sample along the thickness direction of the sheet.

3. The method for preparing a sample of a halogen-free and low-smoke cable sheath material for mining use according to claim 2, wherein: In step 3, the extruder feeding section is 125°C, the conveying section is 133°C, the melting section is 145°C, and the die head is 155°C.

4. The method for preparing a sample of a halogen-free and low-smoke cable sheath material for mining use according to claim 3, wherein: The thickness of the sheet is 2-4 mm greater than the thickness of the sample. Before pressing and cutting, the sheet is planed from both sides to the thickness of the sample.

5. The method for preparing a sample of a halogen-free and low-smoke cable sheath material for mining use according to claim 4, wherein: The width of the sheet is equal to the width of the specimen at both ends.

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