Weekly topic: 8 Wealth points for those who answer correctly, 2 Wealth points for participation； Question 123

Selection of raw materials, temperature control, screw speed, and mold shape. ------Factors affecting the blow molding process: inflation pressure, blowing speed, inflation ratio, and blow molding mold temperature.

Factors affecting the blow molding process: The preform, which has been heated to the stretching temperature, is placed in a blow molding mold. It is longitudinally stretched using a stretching rod, while lateral expansion is achieved by inflating compressed air, thereby producing a biaxially stretched blow molded bottle. 　　①Stretching temperature. The optimal stretching temperature varies for different plastics. The drawing temperature of typical crystalline plastics is slightly lower than their melting point ； Amorphous plastics and those in which crystal formation is prevented by rapid cooling require a slightly higher stretching temperature. For example, the stretching temperature of PET is 95 to 110℃ ； The stretching temperature for PVC is 90–120°C, while the stretching temperature for PP is approximately 150°C. The drawing temperature for parisons with thicker walls is slightly higher, while that for parisons with thinner walls is slightly lower. The stretching temperature is too high, resulting in insufficient orientation ； Conversely, it affects the transparency of the product. 　　②Stretch ratio. The stretch ratio is equal to the ratio of the bottle diameter to the preform diameter. The stretch ratio directly affects the properties of hollow products. The higher the draw ratio, the greater the tensile strength of the hollow product, and its gas barrier properties also improve. 　　③Stretching speed. During parison stretch blow molding, a certain stretch strain rate should be maintained to prevent the relaxation of the molecular orientation induced by stretching. But it also can’t be too large, otherwise it will damage the polymer structure and cause defects such as tiny cracks in the bottle.

What are the influencing factors in the blow molding process? The factors affecting the molding process mainly include inflation pressure, inflation speed, inflation ratio, and blow molding mold temperature

What are the influencing factors in the blow molding process? Answer: There are aspects related to the molding of parisons and the factors that influence it, such as blowing pressure and inflation speed. Mold temperature, cooling time, and molding cycle are also important. The requirements for parisons are high transparency, uniform wall thickness, no internal stresses, and no defects in appearance

Factors affecting the blow molding process: 1. Par temperature 2. Blowing pressure and inflation speed 3. Expansion ratio 4. Mold temperature and cooling time 5. Molding cycle

Rubber content, rubber particle size, and SAN molecular weight

Answer: 1 Par temperature, 2 Blowing pressure and inflation speed, 3 Inflation ratio, 4 Mold temperature and cooling time, 5 Molding cycle

I’ve never worked with this process before, but wind speed or air pressure must have some impact on it

This post was last edited by ljtjbx on 2015-7-29 14:06: The main influencing factors and control methods in the parison manufacturing process. Extrusion blow molding begins with the production of parisons, whose quality has a significant impact on the performance and appearance of the final product. The influencing factors and control methods in the parison manufacturing process are as follows. 　　①Selection of raw materials. In blow molding, the selection of raw materials is very important. Firstly, the properties of the raw materials must meet the requirements for the use of the final product; secondly, their processability must satisfy the requirements of the blow molding process, and hollow-grade resins are generally chosen for this purpose. For example, in HDPE blow-molded products, the melt flow rate (MFR) is generally in the range of 0.01 to 1.0 ∙10⁻³ g/10 min. Resins with a low MFR help prevent the parison from sagging, allowing for parisons with uniform wall thicknesses to be obtained. However, as the screw speed increases, the surface of the melt with low MFR tends to become rough. Therefore, for the range of MFR values suitable for blow molding, medium and large-sized blow-molded products should have a relatively lower value in order to prevent sagging ； Small blow-molded products should be taller. 　　②Temperature control. During the extrusion of parisons, temperature control of the extruder is very important. The selection of the extrusion temperature depends mainly on the properties of the resin. The extrusion temperature is too low, resulting in a rough surface on the parison ； Excessively high extrusion temperature reduces melt strength, resulting in uneven wall thickness of the product. For example, the extrusion temperature of PC blow-molded bottles is controlled within ±3°C. For PVC thermosensitive plastics, it is even more important to control the temperature to prevent thermal decomposition. 　　③Screw speed. The screw speed is another important factor affecting the quality of the extruded parison. 　　High extrusion speeds can increase production and reduce parison sagging, but the surface quality of the parisons deteriorates; especially when the shear rate is too high, it may cause melt fracture in certain plastics such as HDPE. Increasing the screw speed easily generates a large amount of frictional heat, posing a risk of thermal decomposition for heat-sensitive plastics such as PVC. For general blow molding, a larger extruder is used, with the screw speed kept below 70 r/min. 　　④The size and quality of the die. The die is the main device that determines the size and shape of the parison; therefore, its inner surface must be smooth with a low surface roughness to facilitate the production of parisons with a smooth surface. The length of the die setting section is generally chosen to be 8 times the gap distance between the die and the mandrel. 　　(2) Main influencing factors and control methods during the blow molding process. During the blow molding of parisons, the factors that affect the molding process mainly include inflation pressure, gas injection speed, inflation ratio, and the temperature of the blow molding mold. 　　①Inflation pressure. During the blow molding process, compressed air is used for two purposes: first, it uses its pressure to expand the semi-molten tube blank so that it adheres tightly to the walls of the mold cavity, thereby taking on the desired shape ； Second, it serves to cool blow-molded products. The air pressure depends on the type of plastic and the parison temperature, and is generally controlled between 0.2 and 1.0 MPa. For plastics with low melt viscosity and high deformability (such as PA, HDPE), a lower value should be used ； For plastics with high melt viscosity (such as PC), a higher value should be used, and the parison wall thickness should also be set at a higher value. The inflation pressure is also related to the volume of the product; products with a larger volume require a higher inflation pressure, while those with a smaller volume need a lower one. The optimal inflation pressure should be such that the shape and patterns of the product remain clear after molding. 　　②Blowing speed. To reduce the blowing time and enable the product to achieve a more uniform thickness and better appearance, it is necessary to inject a large volume of air at a low airflow velocity, so as to ensure that the parison expands evenly and rapidly within the mold cavity, thereby shortening the cooling time there and improving the product’s properties. A low gas flow rate can also prevent the Venturi effect from occurring within the parison, which could lead to the formation of a local vacuum and thus cause the parison to collapse. This can be ensured by using a larger blowing tube. 　　③Inflation ratio. The blow-up ratio refers to the ratio of the maximum diameter of the plastic part to the diameter of the parison. When the size and mass of the parison remain constant, the larger the size of the final product, the greater the blow-up ratio of the parison, but the thinner the thickness of the product. The blow-up ratio is usually determined based on the type and properties of the plastic, the shape and size of the product, as well as the size of the parison. As the inflation ratio increases, the thickness of the product decreases, its strength and stiffness decline, and molding also becomes more difficult. Generally, the inflation ratio is controlled at 1:（2—4）。 　　④Blow molding mold temperature. The temperature of the blow molding mold has a significant impact on the quality of the product (especially its appearance). Generally, the temperature distribution within the mold should be even, in order to allow the product to cool uniformly as much as possible. The temperature of the mold is related to the type of plastic, as well as the thickness and size of the product. For different types of plastics, the mold temperature for a few plastics (such as blow-molded PC bottles) should be controlled in stages.

Correct answer: Temperature, pressure, time, etc