Raw material control
Selection of PVC resin
The densities of PVC resins with different degrees of polymerization vary, which can affect the weight of baseball. When purchasing raw materials, it is necessary to strictly control the specifications of PVC resin to ensure that the density of PVC resin used for producing baseball shells in the same batch or different batches fluctuates within a small range. For instance, by signing quality agreements with suppliers, the density index range of PVC resin is clearly stipulated, and sampling tests are conducted each time the goods are purchased. Raw materials that do not meet the requirements are resolutely rejected.
Additive ratio
Plasticizers, stabilizers, fillers, etc. are often added in the production of PVC baseball. Plasticizers can lower the glass transition temperature of PVC and increase its flexibility. However, excessive addition will make the baseball shell softer and increase its weight. Stabilizers are used to prevent the decomposition of PVC during processing and use. Their types and addition amounts also affect the weight of the product. Fillers such as calcium carbonate can reduce costs, but changes in the amount added will directly alter the weight of the baseball. Therefore, based on the product performance requirements and weight standards, the addition ratios of various additives should be precisely calculated and strictly controlled. For instance, high-precision metering equipment is adopted to control the addition error of additives within an extremely small range, such as within ±0.1%.
Mold design
Mold dimensional accuracy
The dimensional accuracy of the mold directly determines the size of the PVC baseball shell, which in turn affects the weight. During the mold manufacturing process, high-precision processing equipment and techniques should be adopted to ensure that the cavity dimensions of the mold are highly consistent with the designed dimensions. For instance, when using a CNC machining center for mold processing, the dimensional tolerance of the mold should be controlled within ±0.05mm. Meanwhile, during the use of the mold, regular maintenance and care should be carried out. The wear of the mold should be inspected, and severely worn mold components should be repaired or replaced in a timely manner to ensure the dimensional stability of the mold.
Mold structure optimization
A reasonable mold structure helps to evenly fill the PVC material in the mold, reducing the weight difference caused by uneven filling. For instance, designing a reasonable gate position and size enables the PVC melt to flow smoothly and evenly into the mold cavity, avoiding situations where local filling is insufficient or too thick. In addition, exhaust grooves can be set up inside the mold to promptly discharge the gas inside the mold, preventing problems such as bubbles and material shortage caused by gas residue in the product, thereby ensuring the uniformity of the baseball’s weight.
Injection molding process parameter control
Injection pressure
The magnitude of the injection pressure will affect the filling situation of the PVC melt in the mold cavity. If the pressure is too low and the melt filling is insufficient, it will cause the baseball shell to be too light in weight. If the pressure is too high, it may cause the melt to overflow the mold, resulting in flash. At the same time, it will also increase the weight of the baseball. Therefore, the injection pressure should be precisely adjusted according to the structure of the mold and the characteristics of the PVC material. For example, through multiple mold trials, the optimal injection pressure value that can ensure the melt fully fills the mold cavity without generating flash is found and remains stable during the production process.
Injection speed
The injection speed also has an important influence on the fluidity and filling effect of the PVC melt. An appropriate injection speed can ensure that the melt flows uniformly within the mold, avoiding defects such as flow marks and weld marks, and also helps control the weight of the baseball. Generally speaking, the injection speed should be adjusted according to the size and wall thickness of the baseball. For baseball shells with thinner walls, the injection speed can be appropriately increased to ensure that the melt can quickly fill the cavity. For baseball shells with thicker walls, the injection speed should be appropriately reduced to prevent the melt from overheating and decomposing in the cavity.
Holding pressure time and pressure
The holding time and pressure are designed to compensate for the shrinkage of the PVC material during the cooling process, ensuring the dimensional accuracy and weight stability of the baseball shell. If the holding pressure time is too short or the pressure is insufficient, the baseball shell will shrink and dent, and its weight will decrease. If the holding time is too long or the pressure is too high, it may cause internal stress in the baseball shell, affecting the product quality and also increasing the weight of the baseball. Therefore, the holding time and pressure should be reasonably determined based on the shrinkage rate of the PVC material and the structure of the mold. For instance, the optimal holding time and pressure combination are determined through experiments, and operations are strictly carried out in accordance with these parameters during the production process.
Cooling time and temperature
The cooling time and temperature will affect the crystallinity and shrinkage rate of PVC material, and thereby influence the weight of the baseball. If the cooling time is too short and the PVC material fails to crystallize and cool sufficiently, it will cause the baseball shell to continue to shrink and lose weight after demolding. If the cooling time is too long, it will reduce production efficiency. If the cooling temperature is too high, the cooling rate of PVC material will slow down and the shrinkage rate will increase. If the cooling temperature is too low, it may cause internal stress in the baseball shell. Therefore, the cooling time and temperature should be reasonably controlled based on the characteristics of the PVC material and the structure of the mold. For instance, a segmented cooling approach is adopted, with different cooling temperatures set at different stages to ensure the cooling effect and weight stability of the baseball shell.
Online detection and adjustment
Weight detection equipment
Install high-precision weight detection equipment on the production line to conduct real-time weight detection on each PVC baseball. For instance, by adopting a dynamic weighing system, when a baseball passes through the production line, its weight can be measured quickly and accurately, and the data can be transmitted to the control system.
Feedback adjustment mechanism
When the weight detection equipment detects that the weight of the baseball exceeds the specified range, the control system should immediately send a signal to automatically adjust the injection molding process parameters. For example, if the weight of the baseball is detected to be too light, the control system can automatically increase the injection pressure or the holding time. If the weight of the baseball is detected to be too heavy, the injection pressure or holding time can be automatically reduced. Through this feedback adjustment mechanism, weight deviations during the production process can be corrected in a timely manner to ensure that the weight of each PVC baseball meets the standard requirements.