| The shell process has played an important role in the production of castings, and will be popular continuously in the near future. As far as homemade novolac resins for the shell process are concerned, however, there are problems such as longer cure time under adequate softening point, lower cold-tensile strength, higher free phenol content and sticking together when stored in summer compared to those made in developed countries. To solve the problems above-mentioned and make domestic novolac resins more competitive, systemic researches on complex catalysis, modification, and determination of novolac resins are carried out. Based on determination for novolac resins at the present time, the influence of the rate of rise of temperature and media on softening point are fully conducted, and (5±0.5)℃/min is recommended. Experiments show that novolac resin with softening point less than 95℃can be determined in the bath of pure water or distilled water instead of glycerin. Reasonable process for novolac resins made by 2# catalyst under strong acid conditions is obtained: the molar ratio of formaldehyde to phenol is 0.86~0.88, pH is 0.5~1.5, reaction time is 3.0h~4.5h, and dehydrated temperature is 150℃~180℃. Though fast curing and high-ortho structural novolac resins are made by the use of 1# catalyst under weak acid conditions, they can't be in a batch production because of high free phenol content and reaction time as long as 11h. Complex catalysis is put forward in order to produce high-ortho novolac resins and shorten reaction time. It is easy to prepare novolac resins with softening point 80℃~90℃, cure time 20s~30s and more cold tensile strength under complex catalysis conditions. IR shows that fast curing novolac resins made by complex catalysis are mainly ortho-oriented whereas novolac resins made under strong acid conditions are para-oriented. Such are the conditions for fast curing and high-ortho novolac resins: pH is 4.5~5.5, the molar ratio of formaldehyde to phenol is about 0.85, the ratio of formaldehyde in the first and second stage is 2.0, 2# catalyst is 0.57% based on phenol weight, the total reaction time is 7h, and dehydrated temperature is 170℃. When it comes to modification of novolac resins, cure time becomes remarkably fast and cold-tensile strength is enhanced by the use of 4# modifier; cold-tensile strength of novolac resins modified by 8# modifier is as 1.7 times as that of traditional novolac resins; 2.4% free phenol content can be achieved using 10# modifier; 12# modifier, which can prevents novolac resins sticking together when stored in summer, has been developed. Novolac resins with cure time less than 45s, 2.4% free phenol, cold-tensile strength more than 1.7MPa when 10g novolac resin added in 1000g sand, and softening point less than 80℃and not sticking to each other in summer are prepared by the use of 10# modifier added in the fist stage, 8# modifier and 12# modifier both added after water being dehydrated under complex catalysis conditions. Additive A added can enhance tensile strength of resin-coated sand distinctly, and its reasonable amount is 5% based on novolac resins weight. SEM shows that additive A makes zone of fracture of the resin coated sand sample transfer from interfacial rupture to cohesive rupture. IR demonstrates that some function groups of additive A still exist and have become indiscerptible parts of molecular structure of novolac resins. Through system design, database design and programming, Management Information System of Novolac resins (NMIS) for the shell process is developed using C++ Builder 6 and SQL Server 2000 in Client/Server mode. The function of NMIS is safety management and backup of database, code management, information management including query, modification and calculation. Some information is expressed by code for convenience. The information above is referred to the data related to synthesis and determination of novolac resins.
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