Recently, a batch of plastic hand pumps worth over 20,000 U.S. dollars exported to Egypt by a sprayer company in Yuyao were easily detached due to pressing parts, and they were returned to the country for rework.
The Ningbo Yuyao Inspection and Quarantine Bureau immediately followed the requirements of the import and return goods repairing process and investigated the situation of the goods. The on-site investigation found that the specific reason for the return was that the enterprise did not carefully consider the shrinkage rate of the plastic material in the injection molding process for manufacturing the plastic hand pump, resulting in inconsistent product component sizes, and the upper and lower parts of the product bounced apart, affecting product use.
The shrinkage rate of plastic refers to the percentage of the dimensional difference between the size of the plastic part at the molding temperature and the temperature after it is removed from the mold and cooled to room temperature. It reflects the degree of size reduction after the plastic parts are removed from the mold and cooled. Any plastic product has a certain size requirement, and there are plastic products that meet the requirements in use or installation, and their dimensional accuracy is higher. The difference between the plastic shrinkage and the actual shrinkage rate estimated by the design mold and the fluctuation value of the shrinkage when producing the product will all affect the dimensional accuracy of the plastic product. Secondly, the shrinkage rate of plastics is also closely related to the shape of plastic parts, the complexity of internal structures, and the presence of inserts. In addition, the mold cavity wears out during use, so that the same mold has different sizes when it is new or old. The variation in the mounting dimensions and the fit clearance of the mold forming parts will affect the tolerances of the plastic parts.
To this end, it is recommended that the relevant exporting companies: If it is extrusion or injection molding products shrinkage, it should increase the corresponding margin from the mold; if the raw material shrinkage is large, you can use fiberglass modification to reduce the raw materials The problem of large shrinkage; if the uneven shrinkage of the product affects the appearance, it should be considered in the thickness distribution structure of the product. In the mold design must take measures to control the temperature of the mold heating or cooling, and in order to minimize the temperature difference between the mold cavity, and must pay attention to the temperature control to the cooling circuit design.
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