PVC-U core layer foam pipe

日期:2022/5/25 8:39:41 / 阅读: / 来源:本站

PVC-U core layer foam pipe
1. Material selection and formula design
(1) G4g-5sg-6 resin is commonly used for PV grease VC layer foam pipe.
SG-4:P=1000~1080  K=68~70
SG-5:P=850-980 K=65-68
SG-6:P=730~830 K=62.5-65
P - average degree of polymerization; K=r/D; R - shear force; D - shear rate.
PVC is an amorphous polymer with a crystallinity of only 5% ~ 10%, no fixed melting point, and the melting temperature range is 175 ~ 190 ℃. The K value reflects the difficulty of PVC processing. The degree of polymerization P is low, the K value is low, the fluidity is good, and the melting temperature Tg is low, which is easy to process; High P, high product strength and good performance; The narrower the p distribution, the more stable the plasticizing quality. Single layer and multilayer coextrusion casting film production line www.handern.com com
(2) Stabilizer
1) Lead salts. Mainly tribasic lead sulfate (3PbO · PbSO4 · H2O), white powder, relative molecular weight 991, lead content 22.6% ~ 84%, moisture ≤ 0.4%, easy to absorb moisture, relative density 7.1, fineness 200 mesh. It is an excellent stabilizer for PVC and can activate foaming agent AC.
2) Metal soaps. Including lead stearate (PBST), calcium stearate (CAST), barium stearate (BST), etc. It is generally white powder, which is easy to absorb moisture in the air and has the function of internal lubricant. Excessive dosage will affect plasticization.
3) Close and stable. German bear brand lead based composite stabilizer (SMS 305) is recommended. It is white flake with 35% lead content. It has good activation effect on foaming agent and contains internal and external lubricants. There is no need to add additional lubricants in the formula. It has low toxicity, low dosage and low cost. Single layer and multilayer coextrusion casting film production line www.handern.com com
(3) Toughening agents, toughening agents and processing aids are commonly used, such as acrmbsabs, CPE, etc.
Common varieties of ACR (acrylate): zb530 acr201 acr401. Zb530 has the best effect. It can improve the impact resistance; Used for outdoor products to improve weather resistance; Improve the processability, reduce the melting temperature of PVC, reduce the melt fracture phenomenon, and be conducive to uniform foaming; Improve the apparent quality of products.
(4) Foaming agent AC (Azodicarbonamide), orange powder, with relative molecular weight of 116, relative density of 1.65, fineness of 200 mesh, decomposition temperature of 190 ~ 205 ℃, non flammable, gas generation of 200 ~ 300ml / g, and stable storage at room temperature. This product is a high-efficiency foaming agent, which decomposes to produce nitrogen and is non-toxic.
The quality and dosage of AC are very important. The AC produced by Shanghai Xiangyang Chemical Plant is available, and the dosage is between 0.20 ~ 0.35 phr. It is closely related to the product density, formula and process conditions, and is the key to the quality of foam pipe. The effect of composite foaming agent is better than that of single foaming agent. Single layer and multilayer coextrusion casting film production line www.handern.com com
2. Main equipment
(1) Process unit the process unit mainly consists of 200L / 500L mixing unit sjsz65 / 132 conical twin screw, two sjsz35 / 77 conical twin screw Φ 50- Φ 160mm three-layer composite pipe head Φ 50- Φ 160mm vacuum sizing box, cooling water tank, four claw traction Φ 50- Φ 160mm rotary cutting machine, stacking rack, etc.
Sjsz65 / 132 and jsz35 / 77 conical twin-screw extruders are equipped with quantitative feeding device; It is equipped with melt pressure sensor, measuring force gate and computer to centrally control each unit, which is convenient for refining operation. 6m fixed box and 6m box ensure high-speed production of the unit; The clamping force of the four claw tractor is uniform to ensure the roundness of the pipe; Cutter type rotary cutting machine, with flat incision and smooth chamfer; The flat push unloading rack is flexible, stable and reliable.
(2) Design of three-layer composite pipe die the three-layer composite pipe die adopts the latest patented die, which is fed by three extruders to the inner and middle three-layer flow channels respectively, the middle foaming layer is fed by sjsz65 shaped twin-screw extruder, and the inner and outer layers are fed by two sjsz35 conical twin-screw extruders respectively.
The main design points and principles of the machine head are as follows:
1) The middle foaming layer is fed by sjsz65 / 132 conical twin-screw extruder, accounting for about 70% of the total material consumption. In order to maximize the output, the middle layer channel is designed as straight through type, with large cross-sectional area and low resistance;
2) The inner and outer layers are not provided with shunt support, and the spiral flow channel is adopted. The materials are supplied by two sjsz357 conical twin-screw extruders at a certain angle with the center of the production line, which is exactly equal to the spiral rise angle of the spiral flow channel. It is conducive to the uniform advance of the melt to the die, the uniform discharge around the die, the complete elimination of the internal and external wall clamping line, and the flat and smooth appearance of the pipe; Single layer and multilayer coextrusion casting film production line www.handern.com com
3) There are three groups of extrusion machines for BC and BC, which can process three layers of composite pipes for different purposes. Arbitrarily adjust the thickness of the inner and outer layers to meet the requirements of three different ring stiffness of s0s1s2 (according to the purpose of the pipe, the ring stiffness of the pipe is divided into three levels according to the new national standard, which are sos1s2 Level 3, which is only applicable to indoor drainage, while S1S2 can be used for buried drainage).
3. Preparation process
The forming process of PVC-U core layer foamed pipe is a popular process in the 1990s. The forming steps are to add the prepared inner, outer and intermediate materials into the mixer respectively, and then plasticize the materials through three conical double screw extruders and squeeze them into the composite pipe head; After forming the machine head, enter the vacuum setting box for sizing and cooling; The last four claws are used for traction, fixed length rotary cutting and stacking.
Compared with two extruders, three extruders are used to feed each layer, the thickness of each layer can be adjusted separately, and different formulas can be used for the inner and outer layers according to needs. The formula has low cost and strong adaptability. At the same time, the production efficiency has been improved accordingly, which is an ideal molding process for core foam pipe.
(2) The process characteristics must know the accurate feeding amount of each revolution of each quantitative feeding device, and set the feeding speed and host speed of each layer of extruder according to the feeding amount, so as to extrude products with different requirements. When increasing the speed, the speed must be increased at the same time according to strict proportion, which can be better solved by computer centralized control; The extruder of each layer must work in the under saturated state (the melt in the screw groove of the exhaust section is between full and not full); The extruder and head must be kept warm for more than half an hour after heating to the set temperature, and when starting up, the inner and outer extruders must be opened for 5 ~ 10min, and then the middle extruder must be opened to ensure the head pressure balance. Single layer and multilayer coextrusion casting film production line www.handern.com com
(3) Process quality control: ensure the correct process and operation in the molding process of core foam pipe; Accurate measurement of temperature and pressure parameters; Calculate the material consumption of each layer of the pipe with different ring stiffness requirements, and control the output of the extruder to meet the requirements. Products must avoid defects such as obvious clamping line and bubbles in the inner and outer layers. These defects not only affect the appearance, but also affect its mechanical properties. Avoidance methods are:
1) When mixing materials, the inner and outer materials must be separated from the foaming materials in the middle layer to avoid foaming due to the mixing of foaming agent in the inner and outer materials.
2) The melt pressure of the transition body of the intermediate layer sjsz65 / 132 conical twin-screw extruder is controlled at 15 ~ 25MPa to ensure no foaming in the head; The melt pressure of the transition body of the inner and outer sjsz35 / 77 conical twin-screw extruder shall not be less than 15MPa to avoid uneven thickness of the inner and outer layers.
3) The distance between the die and the sizing sleeve of the vacuum sizing box should be controlled between 5 ~ 10cm to allow enough time for foaming after the pipe blank is exported to the die, so as to make the foaming of the intermediate layer more uniform.

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