During actual use, cars will face various extreme temperature environments. As an important part of cars, the performance of plastic parts will change significantly under extreme temperatures. These changes not only affect the performance of cars, but also affect driving safety and service life. Therefore, it is important to have a deep understanding of their changing patterns.
In high temperature environments, plastic products, automotive plastic parts will first soften and deform. Most plastic materials have a certain glass transition temperature and melting point. When the ambient temperature exceeds their tolerance range, the activity of the plastic molecular chain increases, and the stiffness and strength of the material decrease. For example, automotive interior plastic parts made of polyvinyl chloride (PVC) are prone to softening and warping under high temperature exposure. The originally fitted instrument panel decorative panel may deform, affecting the beauty of the interior, and may even get stuck to nearby mechanical parts due to deformation, affecting functional use. At the same time, high temperature will accelerate the aging process of plastic parts, causing their surface to fade and crack, and reduce the mechanical properties and service life of the material.
High temperature environment will also affect the chemical stability of plastic products, automotive plastic parts. Additives in plastics, such as antioxidants and plasticizers, may volatilize or migrate at high temperatures. The volatilization of plasticizers will cause plastics to become hard and brittle, and lose their original flexibility; the reduction of antioxidants will make plastics more susceptible to oxidation and accelerate aging. For example, some automobile intake manifolds made of polypropylene (PP) materials may cause material performance to decline in the long-term high-temperature engine compartment environment due to changes in internal additives, which will in turn affect the sealing and reliability of the intake system and have an adverse effect on the engine's power performance.
In low-temperature environments, the main problem faced by plastic products and automotive plastic parts is embrittlement cracking. Low temperatures will reduce the activity of plastic molecular chains, making their toughness and ductility worse. When impacted by external forces, plastic parts that originally had a certain degree of toughness become easy to break. For example, car bumpers are mostly made of modified polypropylene materials. In extremely cold weather, their impact resistance will drop significantly, and a slight collision may cause the bumper to break. In addition, low temperatures will also affect the connection performance between plastic parts and other material components, such as plastic and metal connectors. Due to the different thermal expansion coefficients of the two, they may become loose at low temperatures, affecting the stability and reliability of the components.
Frequent changes in extreme temperatures can also cause damage to plastic products and automotive plastic parts. As the temperature rises and falls repeatedly, plastic parts will continue to experience thermal expansion and contraction, which will cause fatigue stress inside the material. Over time, these stress concentration areas may crack, even engineering plastics with good temperature resistance are difficult to avoid. For example, the plastic water pipes in the cooling system of a car engine are prone to cracks at joints or weak points during the engine start and stop process, resulting in coolant leakage and affecting the normal cooling of the engine.
Different types of plastic products and automotive plastic parts have different degrees of performance changes in extreme temperature environments. Generally speaking, general-purpose plastics such as polyethylene (PE) and polystyrene (PS) have relatively poor temperature resistance and are more likely to experience performance degradation under extreme temperatures; while engineering plastics such as polycarbonate (PC) and polyamide (PA) have good heat resistance and cold resistance, but their performance will also be affected under long-term extreme temperature conditions. In addition, plastic materials that have undergone special modification can improve temperature resistance to a certain extent, but they cannot completely eliminate the effects of extreme temperatures.
To cope with the impact of extreme temperatures on the performance of plastic products and automotive plastic parts, automakers have taken a variety of measures. In terms of material selection, priority is given to engineering plastics with better temperature resistance, and the materials are modified, such as adding reinforcing fibers and anti-aging agents, to improve the overall performance of the materials. In terms of design, the structure of parts is optimized, reinforcing ribs and buffer structures are added, and the deformation and impact resistance of parts are improved. At the same time, in the whole vehicle testing phase, the car will be tested in extreme environments such as high and low temperatures to simulate various usage scenarios to ensure that plastic parts can work normally under extreme temperatures and ensure the safety and reliability of the car.
