Extrusion molding process for mpp seven-hole pipe

Abstract

The invention relates to the field of pipeline processing and production, and discloses an mpp seven-hole pipe extrusion molding process which comprises the following steps: S1, raw material pretreatment and mixing: raw materials are put into a high-speed mixer to form a basic mixture, and the mixed basic material is poured into a twin-screw extruder; s2, a melting plasticizing and extruding process: firstly heating the base material by using a double-screw extruder, and finally injecting the material into a seven-hole clothes hanger die head; s3, multi-cavity die head dynamic forming is conducted, specifically, the melt enters a seven-hole clothes hanger type die head and then enters a gradient cooling water tank; and S4, graded cooling and shaping are conducted, specifically, the pipe blank sequentially passes through three sections of temperature control water tanks, is pulled out at a constant speed through a synchronous closed-loop control traction machine, and finally is wound or cut after being fed back and adjusted through a laser diameter measuring instrument. Through the synergistic effect of maleic anhydride grafted polypropylene and silicone master batch, the melt viscosity difference is reduced, and through combination with a seven-hole die head dynamic compensation technology, the hole wall thickness uniformity is better, and the ovality of a finished product is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of pipe processing and production, and specifically to an extrusion molding process for MPP seven-hole pipes. Background Art

[0002] As the mainstream choice for communication and power threading pipes, MPP (modified polypropylene) seven-hole pipes need to meet core requirements such as high ring stiffness, multi-cavity high-precision molding, and long-term weather resistance, and are commonly used in municipal engineering and 5G network construction.

[0003] During the processing of MPP seven-hole pipes, an extruder is usually used in combination with a multi-hole die head. After pouring the mixed raw materials into the extruder, the extruder forms the raw materials gradually through heating and extrusion.

[0004] During the extrusion of MPP seven-hole pipes, due to the characteristics of the seven holes, when co-extruding the seven holes, there is a large difference in the flow rate of the melt flowing through the multi-cavity die head, resulting in uneven wall thickness of the holes. This not only affects the quality standard of the MPP seven-hole pipe finished product, but also easily leads to a large number of MPP seven-hole pipe finished products that do not meet the production requirements during the extrusion process, affecting the cost of the manufacturer. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides an extrusion molding process for MPP seven-hole pipes, which solves the problem of uneven wall thickness caused by the difference in melt flow rate during the multi-cavity co-extrusion of MPP seven-hole pipes, resulting in unqualified finished product quality and increased scrap rate, and significantly increasing production costs.

[0006] To achieve the above objectives, the present invention is realized through the following technical solutions: An MPP seven-hole pipe includes 63-67% polypropylene, 6-8% toughening modifier, 8-10% calcium carbonate, 2.8-3.2% compound lubricant, 0.6-0.8% antioxidant, 0.5-1% flow promoter, 0.3-0.4% light stabilizer, and 2%-3% color masterbatch.

[0007] Preferably, the toughening modifier is specifically polyolefin elastomer.

[0008] Preferably, the compound lubricant includes 1.2-1.5% calcium stearate and 1.6-1.7% silicone masterbatch.

[0009] Preferably, the antioxidant is specifically phosphite.

[0010] Preferably, the flow promoter is specifically maleic anhydride grafted polypropylene.

[0011] Preferably, the light stabilizer is specifically benzotriazole.

[0012] An extrusion molding process for MPP seven-hole pipes, comprising the following steps: S1. Raw material pretreatment and mixing: Put PP, calcium carbonate, calcium stearate, and antioxidant into a high-speed mixer to form a basic mixture, then add a flow promoter and masterbatch to improve compatibility, and pour the mixed base material into a twin-screw extruder; S2. Melting, plasticizing and extrusion process: Use a twin-screw extruder to heat the base material first, which is divided into three stages, and finally inject the material into a seven-hole hanger die head, and dynamically inject an antistatic agent through a synchronous side-feed pump to complete in-line blending; S3. Dynamic forming of multi-cavity die head: The melt enters the seven-hole hanger die head, adjust the opening of the die lips of each flow channel, and the infrared thickness gauge monitors the wall thickness of the initially shaped pipe blank in real time. The formed pipe blank with a V1-level finish is adsorbed and shrunk by a negative pressure -0.1MPa vacuum sizing sleeve, and then enters a gradient cooling water tank; S4. Gradient cooling and shaping: The pipe blank passes through three sections of temperature-controlled water tanks in sequence, and the traction machine is pulled out at a constant speed by synchronous closed-loop control. Finally, it is wound or cut after feedback adjustment by a laser diameter gauge.

[0013] Preferably, the three stages in step S2 include: the feeding section uses 170°C for preliminary melting, the plasticizing section uses 185°C for continuous heating, and the homogenizing section uses 200°C for high-temperature heating.

[0014] The present invention provides an extrusion molding process for MPP seven-hole pipes. It has the following beneficial effects: 1. Through the synergistic effect of maleic anhydride grafted polypropylene and silicone masterbatch, the present invention reduces the melt viscosity difference (Δη≤15%). Combining with the dynamic compensation technology of the seven-hole die head, the wall thickness uniformity of the holes is optimized from ±0.3mm to ±0.1mm, and the ovality of the finished product is reduced by 40%. It solves the problem that in the traditional extrusion molding process of MPP seven-hole pipes, the flow rate difference of the melt flowing through the multi-cavity die head is large, resulting in uneven wall thickness of the holes.

[0015] 2. By setting Example 2 and Example 3, when facing different situations, such as when the production volume is large, the formula and method of Example 2 are used for processing to improve production efficiency. When used outdoors, the formula and method of Example 3 are used for processing to further improve the high-temperature resistance effect of the finished product. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] Embodiment 1: Please refer to the attached Figure 1 , the embodiment of the present invention provides an MPP seven-hole pipe, which comprises 63-67% of polypropylene, 6-8% of toughening modifier, 8-10% of calcium carbonate, 2.8-3.2% of composite lubricant, 0.6-0.8% of antioxidant, 0.5-1% of flow promoter, 0.3-0.4% of light stabilizer, and 2%-3% of masterbatch; The toughening modifier is specifically a polyolefin elastomer; The composite lubricant comprises 1.2-1.5% of calcium stearate and 1.6-1.7% of silicone masterbatch; The antioxidant is specifically a phosphite; The flow promoter is specifically maleic anhydride grafted polypropylene; The light stabilizer is specifically benzotriazole; An extrusion molding process for an MPP seven-hole pipe comprises the following steps: S1. Pretreatment and mixing of raw materials: Put PP, calcium carbonate, calcium stearate, and antioxidant into a high-speed mixer, with a mixing speed of 1200 rpm and a mixing time of 15 minutes to form a basic mixture. Then add a flow promoter (PP-g-MAH) and masterbatch, and adjust the mixing speed to 600 rpm and the mixing time to 5 minutes to improve compatibility. Pour the mixed base material into a twin-screw extruder; S2. Melting, plasticizing, and extrusion process: Use a twin-screw extruder to heat the base material first, which is divided into three stages. The three stages include: the feeding section uses 170°C for preliminary melting, the plasticizing section uses 185°C for continuous heating, and the homogenizing section uses 200°C for high-temperature heating. The screw speed throughout the process is 150 rpm, the torque load is 80%, and the negative pressure in the vacuum exhaust section is -0.08 MPa to remove volatiles. Finally, keep the temperature at 195°C and inject the material into a seven-hole hanger die head, and dynamically inject an antistatic agent (1.2%) through a side feeding pump to complete online blending; S3. Dynamic forming of multi-cavity die head: The melt enters the seven-hole hanger die head (hard chromium-plated runner, Ra ≤ 0.05 μm) at a flow rate of 60 kg / h, is temperature-controlled at 195 ± 2 °C through PID zoning, and the die lip openings of each runner are adjusted (differential compensation accuracy of 0.1 mm) to control the pressure fluctuation within ≤ 0.3 MPa. The wall thickness of the initially formed tube blank is monitored in real time by an infrared thickness gauge (tolerance of ± 0.1 mm). The formed tube blank with V1-level finish is adsorbed and shrunk by a vacuum sizing sleeve with a negative pressure of -0.1 MPa (cooling water at 25 °C ± 1 °C), and the outer diameter is accurately controlled to Φ32 ± 0.2 mm, and then enters the gradient cooling water tank; S4. Gradient cooling and shaping: The tube blank passes through three temperature-controlled water tanks in sequence (the first section is rapidly cooled and shaped at 40 °C, the second section relieves stress at 30 °C, and the third section balances crystallization at 20 °C). The traction machine is synchronously and closed-loop controlled (driven by a servo motor, with a tension fluctuation of ≤ 2%) and pulled out at a speed of 6 m / min. The ovality of the pipe is ≤ 0.5%, and the straightness error is < 1 mm / m. Finally, it is wound or cut after feedback adjustment by a laser diameter gauge, and the moisture content of the finished product is ≤ 0.05%.

[0019] Beneficial effects of Example 1: Through the synergistic effect of maleic anhydride grafted polypropylene and silicone masterbatch, the difference in melt viscosity is reduced (Δη ≤ 15%). Combining with the dynamic compensation technology of the seven-hole die head, the wall thickness uniformity of the hole wall is optimized from ± 0.3 mm to ± 0.1 mm, and the ovality of the finished product is reduced by 40%. It solves the problem of large flow rate differences of the melt flowing through the multi-cavity die head during the extrusion molding of traditional mpp seven-hole pipes, resulting in uneven wall thickness of the hole wall.

[0020] Example 2: An mpp seven-hole pipe, comprising 62 - 65% of polypropylene, 5 - 7% of toughening modifier, 7 - 9% of calcium carbonate, 2.8 - 3.3% of compound lubricant, 0.6 - 0.8% of antioxidant, 1.2 - 1.5% of flow promoter, 0.3 - 0.4% of light stabilizer, 2 - 3% of color masterbatch, and 0.8 - 1.2% of β-crystal nucleating agent; The toughening modifier is specifically a polyolefin elastomer; The compound lubricant includes 2.2 - 2.5% of silicone masterbatch and 0.6 - 0.8% of zinc stearate; The antioxidant is specifically a thioester compound antioxidant; The flow promoter is specifically maleic anhydride grafted polypropylene; The light stabilizer is specifically benzotriazole; On the basis of Example 1, the process steps are adjusted as follows: During the extrusion process, the screw speed is increased to 200 rpm, and the temperature of the forming section is increased to 205 - 210 °C; During the vacuum sizing process, the water temperature is reduced to 18 - 20 °C, and the traction speed reaches 8 m / min.

[0021] Beneficial effects of Example 2: On the basis of Example 1, a β-crystalline nucleating agent is newly added, and the composite lubricant is adjusted to silicone masterbatch 2.2 - 2.5% + zinc stearate 0.6 - 0.8%. The antioxidant is replaced with a thioester composite antioxidant (0.6 - 0.8%), making the molding faster and the output higher during the processing and production of this type of MPP seven-hole pipe, and it is more suitable for large-batch production requirements.

[0022] Example 3: An MPP seven-hole pipe, comprising 60 - 64% polypropylene, 8 - 10% toughening modifier, 10 - 12% wollastonite powder, 2.8 - 3.2% composite lubricant, 0.6 - 0.8% antioxidant, 0.5 - 1% flow promoter, 0.5 - 0.6% light stabilizer, 2 - 3% color masterbatch, 5 - 8% chopped glass fiber; The toughening modifier is specifically POE-g-MAH (maleic anhydride grafted polyolefin elastomer); The composite lubricant includes 2.0 - 2.2% calcium stearate and 0.8 - 1.0% polyethylene wax; The antioxidant is specifically phosphite; The flow promoter is specifically maleic anhydride grafted polypropylene; The light stabilizer is specifically a hindered amine-benzotriazole compound system; On the basis of Example 1, the process steps are adjusted, specifically: During the extrusion process, the temperature of the die head section is precisely controlled at 200 ± 2 °C, and the process of oriented orientation of chopped glass fiber is added; During the vacuum sizing process, an infrared annealing process (temperature 110 °C, time 30 seconds) is added in the latter section to eliminate the internal stress of the pipe.

[0023] Beneficial effects of Example 3: On the basis of Example 1, by replacing the toughening modifier with POE-g-MAH, calcium carbonate with wollastonite powder and adding chopped glass fiber, the composite lubricant is adjusted to 2.0 - 2.2% calcium stearate and 0.8 - 1.0% polyethylene wax, and the light stabilizer is upgraded to a hindered amine-benzotriazole compound system, combined with the infrared annealing process, the ring stiffness of this type of MPP seven-hole pipe is increased to 20 kN / m² (160% higher than that of Example 1), and the tensile strength retention rate is > 90% after high-temperature aging at 85 °C for 1000 hours, especially suitable for high-temperature, high-pressure and harsh outdoor environments.

[0024] Comparative experiment: I. Experimental objects and grouping Experimental group: Example 1 (standard optimized type) Example 2 (Short-cycle high-efficiency forming type) Example 3 (High weather resistance and compressive resistance type) Control group: Traditional MPP seven-hole pipe (commercial common formula: PP 65%, calcium carbonate 12%, calcium stearate 1.0%, general antioxidant 0.5%, without using dynamic die compensation technology or enhanced process).

[0025] II. Experimental steps and parameter settings (1) Sample preparation Raw materials and equipment: Strictly according to the formula ratios of each example and the control group, use the same batch of raw materials (such as Sinopec PP T30S), the same brand of twin-screw extruder (L / D = 36:1), and seven-hole hanger die head.

[0026] Process parameters: Example 1: Execute according to steps S1 - S4, screw speed 150 rpm, gradient cooling temperature 40°C → 30°C → 20°C.

[0027] Example 2: Screw speed 200 rpm, forming section temperature 205 - 210°C, vacuum sizing water temperature 18 - 20°C, traction speed 8 m / min.

[0028] Example 3: Die head section temperature 200 ± 2°C (glass fiber orientation process), infrared annealing after vacuum sizing (110°C / 30 s).

[0029] Control group: According to the conventional process (screw speed 150 rpm, three-section temperature 175°C → 190°C → 195°C, without die head compensation or enhancement treatment).

[0030] (2) Test items and parameters III. Comparison and analysis of experimental results IV. Conclusion Example 1 significantly optimized the wall thickness uniformity (σ = ±0.08 mm, 77% higher than the control group) and roundness (decreased by 81%), verifying the effectiveness of the die head dynamic compensation technology.

[0031] Example 2 shortened the forming cycle by 30% and reduced the energy consumption by 31% (vs the control group) through β-crystalline nucleating agent and high-speed process, and the daily production capacity can reach 1200 kg (800 kg for the control group).

[0032] Example 3 integrated the ring stiffness (20 kN / m²) and the strength retention rate after high-temperature aging (92%), meeting the requirements of extreme environments and becoming an upgraded alternative to traditional pipes.

[0033] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An mpp seven-hole pipe, characterized in that: It includes 63-67% polypropylene, 6-8% toughening modifier, 8-10% calcium carbonate, 2.8-3.2% composite lubricant, 0.6-0.8% antioxidant, 0.5-1% flow promoter, 0.3-0.4% light stabilizer and 2%-3% masterbatch.

2. The mpp seven-hole pipe according to claim 1, characterized in that: The toughening modifier is a polyolefin elastomer.

3. The mpp seven-hole pipe according to claim 1, characterized in that: The composite lubricant comprises 1.2-1.5% of calcium stearate and 1.6-1.7% of silicone masterbatch.

4. The mpp seven-hole pipe according to claim 1, characterized in that: The antioxidant is phosphite.

5. The mpp seven-hole pipe according to claim 1, characterized in that: The flow promoter is maleic anhydride grafted polypropylene.

6. The mpp seven-hole pipe according to claim 1, characterized in that: The light stabilizer is specifically benzotriazole.

7. An MPP seven-hole pipe extrusion molding process, characterized in that: The following steps are involved: S1. Raw material pretreatment and mixing: PP, calcium carbonate, calcium stearate and antioxidant are put into a high-speed mixer to form a basic mixture, and then a flow promoter and a masterbatch are added to improve compatibility, and the mixed base material is poured into a twin-screw extruder; S2. Melt plasticization and extrusion process: The base material is first heated using a twin-screw extruder and divided into three stages. Finally, the material is injected into a seven-hole hanger die head, and the antistatic agent is dynamically injected into the synchronous side feed pump to complete the online blending; S3. Dynamic molding with multi-cavity die: The melt enters the seven-hole hanger die, and the opening of each channel die lip is adjusted. The infrared thickness gauge monitors the wall thickness of the initial tube in real time. The formed V1 grade smooth tube is adsorbed and shrunk by the negative pressure -0.1MPa vacuum sizing sleeve, and then enters the gradient cooling water tank; S4. Gradual cooling and shaping: The tube billet passes through three temperature-controlled water tanks in sequence, and is pulled out at a uniform speed by a synchronous closed-loop controlled traction machine. Finally, it is rolled or cut after feedback adjustment by a laser diameter gauge.

8. The MPP seven-hole pipe extrusion molding process according to claim 7 is characterized in that: The three stages in step S2 include: initial melting at 170° C. in the feeding stage, continuous heating at 185° C. in the plasticizing stage, and high-temperature heating at 200° C. in the homogenizing stage.

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