Research On The Structure And Material Of Ring Shaped Plastic Bonnet And Its Molding Process

Injection molding is the manufacturing method commonly used for the plastic bonnet with the integration of function and structure in transportation station heat pump heating or cooling equipment. To adapt to the changes of outdoor temperature, the bonnet mostly adopts the ring structure and the material is generally automobile plastics.The gating system of injection molding generally relies on design by experience. In order to improve the efficiency of heat transfer, material properties, forming quality and reduce the production cost, the paper made researches on the structural design and material modification of ring shaped plastic bonnet and its injection process.First of all, the paper studied the influences of the heat-exchange hole size and shape of the ring shaped plastic bonnet through CFD simulation technology, established the structure design numerical calculation simplified model of the ring shaped bonnet of heat pump water heater and put forward the analysis and evaluation method of ventilation heat exchange efficiency of plastic bonnet. The research shows that round holes were better than bar holes: with the increase of hole diameter, the heat exchange efficiency presented the trend of increasing first and then decreasing; when the ring wall was opened with 40 groups circular holes with alternated sizes, the heat exchange efficiency could rise 34%.Secondly, with SAN as matrix, using the melting method to add POE and rubber to increase toughness, introducing active group through branches in macromolecules, the chemical key would play role when it’s mixed physically, leading to block modification and better effect of increasing toughness. A SAN toughening formula by polyolefin elastomer is put forward, the test results shows that if the ratio of the polycarbonate(PC), polyethylene (PE) and maleic anhydride (MAH) copolymer (PE-g-MAH) of 1.8%grafting ratio and SAN was 40:5:55.,the notched impact strength reached 5.41 kJ/m2,which is 4.3 times of pure SAN resin. A SAN toughening formula by rubber is put forward and the toughening mechanism is shear yielding. If the ratio of chlorinated polyethylene (CPE), methacrylic butadiene styrene copolymer (MBS) and SAN is 20:20:60, the impact strength reaches 16.77 kJ/m2, which is 13.3 times of pure SAN resin.For the gating system design of ring shaped plastic bonnet, this paper researches the method of the shortest shunt layout design for the gating system in the case when the feeding quantity n was more than 3, the shortest runner layout design and method was proposed. On the basis. Moldflow commercial software was further used to study on the relationship between the efficiency and quantity of ring shaped plastic parts injection molding and the radius of ring structure, the height of ring and the feeding quantity n. If given any of the two variables, the range of the third variables according to the relation can be got. Comparing to the existing wheel layout method, in the case of n=12, injection molding could reduce the proportion of feeding system in total injection volume from 35% to 15%～20%.The paper centered on the research achievements obtained from the problems of heat exchange efficiency analysis and material modification of ring shaped heat exchange plastic bonnet, and its injection process, which could provide theoretical guidance for the structure design, material selection and gating system design, and it has important engineering reference value for the engineering application and promotion of heat pump water heater.