Research of Calcium Carbonate in PVC-U Pipe application.
Compared with traditional metal pipe, cement pipe and glass fiber reinforced plastic pipe, it has light weight, corrosion resistance, small water flow resistance, good mechanical strength, environmental protection, convenient construction and high cost performance. The advantages of long service life have been widely used in many fields such as urban water supply and drainage, human drinking engineering, building water supply and drainage, agricultural water saving irrigation, aquaculture, greening, golf course engineering and so on.
However, there are few technical documents on the production and processing of low-pressure (≤0.6MPa) hard PVC pipes for water irrigation (especially drip irrigation systems, forest belt irrigation, farmland water-saving irrigation, etc.), resulting in PVC for low-pressure water irrigation. - U pipe quality is uneven, which has greatly affected the benign development of the industry. In view of this, in order to further reduce production costs and improve product quality,
This paper studies the development of high-filled (nano-scale active calcium carbonate) PVC-U pipe based on the national standard GB/T13664-2006. It can not only improve product quality, but also save raw materials, reduce production costs and create economic benefits for enterprises. . Therefore, this paper takes all aspects of factors into consideration, analysis and objective evaluation, and then optimizes to get the lowest cost and best performance products. We chose to carry out the experiment on the D90mm, L/D= 22:1 parallel twin-screw extruder, and produced PVC-U pipe for low-pressure water-flooding irrigation with l60×3.2m m and PN0.32Mpa specifications. the result of.
1, PVC - U pipe experimental part
1.1 Main raw materials
PVC (SG-5) Resin Powder, Xinjiang Tianye (Group) Tianneng Chemical Co., Ltd. Composite Stabilizer (1904 7T), Dalian Kaimisen Chemical Products Co., Ltd.; External Lubricant (PE Wax) Chengdu Shengteng Plastic Additives Co., Ltd.; semi-refined paraffin Liaoning Fushun Petrochemical Company; anti-medium processing modifier CPE-l 35A Shandong Rioke Rubber & Plastic Technology Co., Ltd., processing modifier (HLn-401) Shandong Rioke Chemical Co., Ltd.; Active) CaCO Shanxi Orchid Huaming Nano Materials Co., Ltd.; coloring agent carbon black N330 Xinjiang Fukang Hongtai Chemical Co., Ltd. are all commercially available.
1.2 Experimental equipment
D90mm, L/D= 22:1 parallel twin-screw extruder, extrusion die, sizing sleeve, flaring die, etc., Hangzhou Shuanglin Extrusion Equipment Manufacturing Co., Ltd.: high and low mixing unit, Zhangjiagang Lianguan Co., Ltd. .
1.3 Experimental methods
PVC (SG ~ 5 type) resin powder, composite stabilizer, external lubricant, anti-medium processing modifier, nano-sized (active) calcium carbonate, carbon black N330, etc. are mixed in a high proportion in a high-mixing machine. After cold mixing, the tube was extruded on a D90 parallel twin screw extruder. Appropriately adjust process parameters such as process temperature, main engine speed, feed speed, main engine vacuum, traction speed, vacuum tank vacuum, etc., to produce PVC-u pipes with low cost and high filling low-pressure water supply irrigation that meet the requirements of national standards.
2. Analysis of PV C-U pipe production factors
2.1 Equipment and mould
The design parameters of the extruder screw directly affect the back pressure and plasticization degree of the material plasticization. However, for the general-purpose extruder that has been popularized, the most concern is the gap between the screw and the barrel. If the gap is too large, it will easily cause the leakage of the material, which will inevitably affect the plasticization. Mold (head) design, feed volume data and compression ratio data are critical. For high-filled PVC pipes, it is necessary to have a larger supply amount and a larger compression ratio, which is beneficial to the stability of the feed and the tightness of the pipe, ensuring uniform plasticization, and the design of the mandrel bracket should be as small and smooth as possible. The surface of the mold should be hard chrome-plated, so that the effect of the seam line on the performance of the tube is as small as possible. For high-fill PVC-U pipe production, it is necessary to use a machine head, die, mandrel, sizing sleeve and flared mold made by a professional manufacturer.
2.2 Ingredients and Mixtures
This is a factor that is easy to ignore. Generally speaking, the mixing process is considered to control the mixing temperature under the premise of accurate metering. In fact, the most important thing is to mix the ingredients and mix, and the material is evenly dispersed, and the volatiles are completely evaporated. The material is not evenly dispersed. When the extrusion is produced, the product performance is unstable. Volatile volatiles are not completely evaporated. Extrusion of high-filled PVC-U pipes is more likely to cause bubbles and turning, which affects product performance. It is generally recommended that the mixing temperature be controlled at 11 5 to 1 35 degrees. The high mixing temperature in Xinjiang should be slightly higher in winter, the mixing time is 8 to 10 minutes, and the apparent density of dry mixing is controlled at 0.60 to 0.65 g/ml. The feed amount of the high stirrer should be controlled at 50 to 70% of the empty volume of the high mixing chamber (for example, a high stirrer with a high mixing chamber volume of 800L, the feeding amount should be controlled between 200KG and 280KG and it is recommended to be above 240KG). . When the non-uniformly dispersed mixture enters the barrel screw, the material that has been shear-engaged exhibits a different gelation state in the machine head, forming an uneven elastomer. In addition, the temperature of the mixture discharged through the low-speed mixer is also critical, generally 40 to 50 degrees. This can not only increase the extrusion speed but also ensure that the wall thickness of the high-filled PVC-u pipe does not fluctuate. In addition, when the volatile matter volatilizes, it is easy to condense on the inside of the top of the high stirrer. When the amount of condensation is large, droplets and PVC resin powder, nano-sized (active) calcium carbonate, carbon black and other materials are formed into particles. These granules are prone to plasticized "crystal spots" during extrusion production, which affects the performance of the pipe. It is easy to produce deformed trachoma water during hydraulic testing. Therefore, the raw materials should be strictly controlled before the raw materials are put into use. The high stirrer cover is open to prevent the occurrence of "crystal point", and the high-mixed material is cold-mixed to a discharge of 50 degrees or less, and the dry-mixed material is passed through a vibrating screen (20 to 40 mesh). ) is a very necessary process to ensure the quality of high-filled PVC-U pipes.
2.3 Raw and auxiliary materials and formulas
Since the detection of raw and auxiliary materials is only a sampling test, and the evaluation of the performance of raw and auxiliary materials according to the test indicators has certain limitations, experienced formulators, in addition to the test results of the original and auxiliary materials, also carry out some additional empirical tests. Or on the machine test, according to the test results of the test pipe, further determine the performance of the raw and auxiliary materials. For the formulation design of PVC-U pipe for low-pressure water-flooding irrigation, in addition to considering the processing performance like conventional products, special attention must be paid to the pressure resistance of pipes. According to the force analysis of the plastic pipe under the action of hydrostatic P, the relationship between the hoop stress (tensile strength) and the outer diameter and wall thickness of the wall thickness can be obtained.
\In the case of a certain outer diameter and wall thickness of the pipe, the instantaneous breaking pressure is proportional to the instantaneous tensile strength, that is, the higher the tensile strength, the stronger the water pressure resistance. In addition to the type and quantity of the formulation materials such as the anti-modification agent and the processing modifier in the formulation, the tensile strength is closely related to the main load of the pipe (host current value/main motor current during machine processing). Therefore, a reasonable formula is designed, and a reasonable formulation process adjustment is made to ensure that the load of the high-filled PVC-u pipe main body is controlled at 60% to 75% in order to obtain good product performance. At the same time, the tensile strength of the pipe is inversely proportional to the temperature of the environment and the fluid. Therefore, in the case of a certain outer diameter and wall thickness of the pipe, the instantaneous breaking pressure also decreases as the environment and fluid temperature increase.
When the ambient temperature and the water delivery temperature are different, the working pressure shall be corrected according to the pressure reduction factor (ft) at different temperatures given in Table 2 (see GB/T10002.1). Multiply the nominal pressure by the reduction factor to obtain the maximum allowable working pressure. Therefore, in order to prevent the instantaneous pressure from damaging the pipe, it is necessary to prevent brittle failure below 0 degrees, and it is also considered that the maximum use temperature of the PVC-u pipe cannot exceed 45 degrees.
2.3.1 PVC resin powder
PVC resin powder is tested according to GB/T5761—2006 national standard. The extrusion rate of high-filled PVC-U pipe has a great relationship with the performance of the resin. The shape is regular, the internal pores are uniform, and the apparent density is high.
The grease generally has a good processing rheological behavior and a high extrusion rate. These properties of the resin are very advantageous for the pipe processing enterprise to increase the productivity of the extruder and reduce the cost of the product. Therefore, the resin for pipe should have the characteristics of high form factor (regular shape), high apparent density, high porosity (high plasticizer absorption).
It has been proved that the PVC (U-5) resin with an apparent density of 0.64 g/m] can produce PVC-U pipe, which can increase the extrusion rate by 15 to 25%, and the other properties of the pipe are good. According to the experience of the water supply pipe production for more than ten years and the test results of the pipe, if the technical index of PVC (SG-5 type) resin is 118ml/g ≥ viscosity number ≥ 113mI / g, apparent density ≥ 0.54g / ml, The remaining indicators can reach the national standard. This resin is used to produce PVC-u pipe, the hydraulic pressure is guaranteed from the source, and the extrusion rate is stable.
2.3.2 Stabilizer and lubricant system
This is the most demanding and difficult to quantify factor. of course. The produced pipe has good thermal stability, no stickiness, no discoloration, smooth inner and outer walls, no joint line is the basic requirement; good plasticizing performance (passing methylene chloride impregnation), stable processing, high requirements; rheological properties Well, the process can be adjusted in a wide range, suitable for rapid extrusion, which is a higher requirement. Stabilizers are added to inhibit discoloration, decomposition, and deterioration of properties of PVC resins during processing. At present, most domestic manufacturers use calcium-zinc composite stabilizers, organotin stabilizers, etc. Calcium-zinc composite stabilizers and organotin stabilizers are mainly used in the production of water supply and drainage pipes. Under normal circumstances, when the content of nano-sized (active) calcium carbonate is less than 20 parts, the internal lubricant is not used, and the amount of external lubricant necessary for processing is preferably small, and it is recommended that it be added within 0.1 part or not.
2.3.3 nanoscale (active) calcium carbonate
Nano-sized (active) calcium carbonate, the surface of the active nano-calcium carbonate is specially treated with a special activator, which has good compatibility with the resin, can effectively improve the fluidity, smoothness and bending strength of the material; lower the melt index and system viscosity, and improve the processing. Performance; improve the rheological properties, dimensional stability, heat and aging resistance of the product; maintain its toughness while reinforcing the material, and partially replace the expensive titanium dioxide, fluorescent whitening agent, meteorological white carbon, etc. Materials and additives, to greatly reduce the amount of PVC resin and PVC anti-process processing modifier, reduce production costs and improve market competitiveness. (The surface-specific activator stearic acid HST is added in an amount of 3-5%).
2.3.4 Resistance Medium processing modification system
For PVC-U pipe production, it is recommended to add 0.5-1 part ACR processing modifier, which promotes the plasticization of PVC, improves the uniformity of melt plasticization, lowers the plasticizing temperature, and minimizes heat stability. The loss of the agent in the processing, the ability to improve the aging resistance in the later period can improve the strength of the product, and is an important control point in the formulation of PVC-u pipe. After more than 20 tests before and after the production machine, it lasted for more than 6 months, and it is preferred to formulate the formula for mass production.
2.4 Extrusion process
The main effect of the adjustment process is to adjust the host load. In the case of reasonable formula, adjust the process temperature, screw speed, feed speed and other process parameters. Specifically, the screw speed is controlled at 60 to 75% of the maximum speed. If the maximum speed is 40 rpm, the actual production speed is about 24 to 30 rpm. At the same time, the feeding speed is matched to ensure that the host torque is about 40~60%. The matching between the screw speed and the feeding speed corresponds to the rheological property of the formulation, otherwise the plasticization will be affected. Pay special attention to the vacuum exhaust device of the extruder to work normally, and ensure the vacuum degree ≥0.05MPa to prevent the occurrence of bubbles in the cross section of PVC-U pipe products caused by volatile substances in the mixture, which will affect the physical and mechanical properties of the product.
After the machine head is evenly discharged, it is also necessary to pay attention to whether the water tank bracket, the sizing sleeve, the tractor track and the pipe surface are in the same plane, whether the temperature of the sizing sleeve is consistent, etc. If there is any problem, adjust it in time, especially before driving. Be fully prepared to produce qualified products with quality and quantity.
1) Nano-scale (active) CaC03 can effectively improve the compatibility of PVC pipe formulation system, and can bridge the interface between inorganic materials and polymer materials to form an interpenetrating network structure and increase polymer materials and inorganic materials. The mutual bonding force is such that the melt interface bond strength after melting is improved. The performance of the produced nano-scale PVC pipe is improved.
2) Nano-scale (active) CaC03 has a toughening and strengthening effect on PVC pipes.
3) Compared with the original production formula, the nano-scale (active) CaC03 added to the PVC formula in the normal production process can replace the light calcium to make the material have stronger plasticizing ability and superior processing flow performance. At the same time, the material forming process is stable, the extrusion speed is improved, the traction speed is increased, thereby increasing the output and reducing the production cost.
4) Strengthening the process recipe control of high-filled PVC pipes, not only can improve product quality, but also save raw materials and reduce costs. Take D160 × 4.0mm pipe produced by a PVC pipe manufacturer as an example. The formula cost per ton of nano-grade PVC pipe is reduced by about RMB 200/ton (there are differences in caliber). If 10,000 tons of pipe is produced per year, The company has saved a lot of PVC resin, and its economic benefits are considerable.