What problems may be encountered during the production of polyurethane casting products?

The production process of polyurethane casting products may encounter the following problems in raw materials, processes, equipment and other aspects:
Raw materials
Unstable quality of raw materials: the quality of polyurethane raw materials is affected by factors such as manufacturer and batch. If the indexes of hydroxyl value, acid value and moisture content of polyol fluctuate, and the purity and functionality of isocyanate are unstable, it will lead to differences in reactivity and product performance and affect the consistency of product quality.
Raw material storage problems: polyols are easy to absorb water, isocyanate is sensitive to moisture, if the storage conditions are not appropriate, such as high environmental humidity, poor sealing of the storage container, the raw material absorbs water will occur after the side reaction, the production of carbon dioxide gas, resulting in the emergence of bubbles, holes and other defects in the product, and will also affect the mechanical properties of the product.
Compatibility of raw materials: In order to improve the performance of polyurethane, often add a variety of additives, such as catalysts, chain expanders, fillers and so on. However, there may be poor compatibility between certain additives and polyurethane raw materials, which may lead to phase separation, surface stickiness, decreased mechanical properties and other problems.
Process
Improper control of reaction temperature: the polymerization reaction of polyurethane is sensitive to temperature, too high a temperature and too fast reaction speed may lead to the system burst polymerization, the product appears burnt, discoloration and other problems, and at the same time will make the molecular chain structure of the product is irregular, which will affect the performance; too low a temperature and a slow reaction speed may lead to an incomplete reaction, and the product's strength, hardness and other properties can not meet the requirements.
Inaccurate reaction time: if the reaction time is too short, the raw materials are not fully reacted, and the performance of the products can not reach the best state, such as insufficient hardness, low tensile strength, etc.; if the reaction time is too long, the products may be overly crosslinked, which will lead to brittleness and decrease in toughness of the products.
Uneven mixing: In the process of mixing raw materials, if the mixing speed and time are not appropriate, it will lead to uneven mixing of polyol, isocyanate and various additives, which will make the reaction locally excessive or insufficient, and the product performance will be uneven, such as the hardness and elasticity have obvious differences in different parts.
Demolding problem: If the mold design is unreasonable, improper selection of mold release agent or incorrect use, it will lead to product demolding difficulties, which may scratch and deform the surface of the product, or even damage the product, affecting the appearance and dimensional accuracy of the product.
Equipment
Accuracy of metering equipment: The accuracy of metering equipment such as metering pumps, flow meters, etc. directly affects the accuracy of raw material proportioning. If there is any error in the metering equipment, resulting in the ratio of polyol and isocyanate deviating from the design value, it will make the performance of the product change greatly, such as hardness, elasticity, heat resistance, etc. can not meet the requirements.
Mold problem: The processing precision, surface quality and structural design of the mold are crucial to product quality. Insufficient precision of the mold will lead to large deviation of product size; mold surface is not smooth will make the product surface rough, burrs; mold structure is unreasonable, such as improper runner design, will lead to uneven flow of raw materials, resulting in filling the mold is not full, bubbles and other defects.
Equipment maintenance is not in place: production equipment after a long period of operation, if not timely maintenance, equipment failure may occur, such as mixer failure will affect the mixing effect of raw materials, heating system failure will lead to inaccurate temperature control, these will affect the stability of the production process and product quality.