Back pressure or voltage multiplication? ? ?

It’s back pressure! ～ Back pressure is actually referred to as the exhaust pressure at the turbine outlet; it is commonly called back pressure. It denotes steam that still possesses a certain pressure and temperature after performing work. In power plants, this steam is converted into water in a condenser and then fed back into the boiler. In other factories and mines, it is used as steam for production processes or for heating water for daily use. Therefore, it is necessary to maintain a certain pressure and temperature, usually between 0.5MP and 1MP, with a temperature of over 200 degrees Celsius; such steam does not return to the boiler. Back pressure is a pressure that arises in hydraulic systems due to downstream resistance or changes in the impedance ratio at the inlet and outlet of components. Explanation of back pressure related to injection molding I. Formation of back pressure During the melting and plasticizing of plastics, the molten material continuously moves toward the front end of the barrel (the metering chamber), in increasing amounts, gradually generating a pressure that pushes the screw backward. To prevent the screw from moving backward too quickly and to ensure even compaction of the molten material, it is necessary to apply a pressure in the opposite direction to the screw. This pressure that prevents the screw from moving backward is known as back pressure. Back pressure, also known as plasticizing pressure, is controlled by adjusting the return oil throttle valve of the injection cylinder. The rear part of the injection cylinder in pre-plasticizing screw injection molding machines is equipped with a back pressure valve, which regulates the speed at which oil is released from the injection cylinder as the screw rotates backward, thereby maintaining a certain pressure in the cylinder (as shown in the figure below) ； The rearward movement speed (resistance) of the screw driven by the motor is controlled by an AC servo valve. II. Benefits of properly adjusting the back pressure 1. It can compress the molten material inside the barrel, increasing its density and thereby enhancing the amount of plastic injected, as well as the stability of the product’s weight and dimensions. 2. It can \"expel\" the gases within the molten material, reducing gas bubbles on the surface of the product and internal bubbles, as well as improving the uniformity of the gloss. Reduce the speed at which the screw retracts, so that the melt in the barrel can be fully plasticized; this improves the uniformity of mixing between the color powder, color masterbatch, and the melt, thereby preventing color mixing in the finished products. 3. Slow down the retraction speed of the screw to ensure thorough plasticization of the melt in the barrel, thereby improving the uniformity of mixing between the color powder/color masterbatch and the melt, and preventing color mixing in the finished products. 4. Increasing the back pressure appropriately can improve surface shrinkage of the product as well as the wettability around it. 5. It can raise the temperature of the molten material, improving its plasticization quality and enhancing its flowability during filling of the mold, resulting in a product surface free from cold shrink marks. III. When the back pressure is too low, the following problems are likely to occur: 1. With too low back pressure, the screw retracts too quickly; the density of the melt flowing into the front end of the barrel is low (it is looser), and more air gets trapped within it. 2. It leads to poor plasticizing quality, unstable injection volume, and large variations in product weight and dimensions. 3. Defects such as shrinkage, air bubbles, cold flow marks, and uneven gloss may appear on the surface of the product. 4. Bubbles are likely to form inside the product, and the areas around the product as well as the bone-shaped parts may not be fully coated with adhesive. IV. Excessively high back pressure can lead to the following problems: 1. The pressure of the molten material at the front end of the barrel is too high; the material temperature is elevated and its viscosity decreases. This results in backflow of the molten material within the screw channels, as well as increased leakage through the gaps between the barrel and the screw, thereby reducing the plasticization efficiency (the amount of material that can be plasticized per unit time). 2. For plastics with poor thermal stability (such as PVC, POM, etc.) or colorants, the increase in molten material temperature and the longer heating time in the barrel can cause thermal decomposition, or the colorants may change color, leading to a deterioration in the surface color and gloss of the finished products. 3. Excessively high back pressure causes the screw to move backward slowly, resulting in a longer pre-plasticization time; this increases the cycle time and leads to a decrease in production efficiency. 4. High back pressure and high melt pressure can cause the nozzle to experience melt dripping after injection; during the next injection, cold material in the gate channel may block the gate, or cold spots may appear in the finished product. 5. During the plastic injection process, excessive back pressure often causes leakage at the nozzle, resulting in waste of raw material and damage to the heating element located near the nozzle. 6. Mechanical wear of the pre-plasticizing mechanism and screw barrel increases. V. Adjustment of back pressure: The adjustment of the injection back pressure should be determined based on the properties of the raw material, its level of drying, the product’s structure, and its quality. The back pressure is generally set between 3–15 kg/cm3. When there is slight bubbling, color mixing, shrinkage on the product surface, or significant variations in the product’s size and weight, the back pressure can be increased appropriately. When the nozzle shows glue leakage, dripping, excessive heat-induced decomposition of the melt, product discoloration, or slow material return, considering a suitable reduction in back pressure may be appropriate. Back pressure is one of the important parameters in the injection molding process for controlling the quality of the molten material and the final product. An appropriate back pressure plays a crucial role in improving product quality, and it cannot be ignored!

Back pressure refers to the outlet pressure. The steam outlet pressure of a turbine is generally referred to as back pressure. There are many other places as well that can be referred to as back pressure. Hehe, that’s exactly what I mean.

Back pressure: the back-to-back design cancels out the axial thrust!

What is referred to on the first floor is likely the back pressure. Some medium-frequency converters have an inner seal; during normal operation, the pressure on the concave side of this inner seal should be higher than that on the convex side. This situation represents positive pressure. If the operation of such a medium-frequency converter is not proper, the pressure on the concave side of the inner seal can end up being lower than that on the convex side, which is what is known as back pressure on the inner seal. This can easily lead to instability and deformation of the inner seal.