It is the largest automobile tire mold plaster casting applications, the tire molding mold made of aluminum alloy, with a plaster casting can correctly reproduce the complex structure of the tire. Since tires are high-volume and variety of products, so you want a short, low-cost manufacture the tire mold. Plaster casting prototype technology combined with RT tire mold for casting, cast metal having a low surface roughness, high dimensional accuracy and deformation characteristics, can significantly shorten the manufacturing cycle, reduce costs and achieve complex type Near net shape cavity mold. Simply use the ɑ- hemihydrate plaster casting can not be performed because the hemihydrate gypsum dewatering phase transition occurs in the drying process: at 150 ~ 200 ℃ dehydration contraction; a sharp increase over 400 ℃, linear shrinkage, cracking tends to increase ; 700 ℃ when ɑ- Hemihydrate linear shrinkage rate of more than 10%. Therefore, only by adding some pure gypsum upon heating to produce a phase change material that expands to make plaster molding has a certain strength, permeability resistance, expansion and contraction of the smooth surface, to meet a variety of mechanical mold, physics and technology Performance requirements. Based on the mix of different types of plaster and thermal expansion characteristics, strength, resistance to cracking and other properties tendentious research experiments, the effect of fillers and additives to the plaster mix performance tire developed into a plaster mold casting and successfully applied in Qingdao MESNAC Ltd. aluminum production mold production. 2, the tire of the technical requirements of the casting plaster mold casting plaster 2.1 tire mold casting process of a tire mold gypsum plaster molds used, after the tire is stirred for casting gypsum slurry (preferably vacuum mixing) pre-processed cast silicon rubber mold, molding removed after hardening of the reaction of silicon rubber mold, plaster mold and then dried, the aluminum or other metal smelting good pouring into the plaster mold after solidification clean out plaster, precision castings on tires complete. 2.2 tire casting plaster powder mainly tire performance requirements different from ordinary mold plaster mold casting, casting plaster powder tire performance have special requirements, mainly in the setting time, expansion coefficient, strength, high temperature and so on. 2.2.1 setting time casting plaster mold powder tire setting time is mainly reflected in the initial setting aspect, when compressed air is blown if the initial setting time is too short, since the vacuum mixing gypsum slurry inadequate, prone to bubbles and large through hole, mold Since outlet uneven body is likely to cause a release uneven, bad blank form; but the initial setting time is too long, will result in lower labor efficiency and cause electricity waste of resources, affect the production of the mold. According to the actual situation, the initial setting time is about 10-15 minutes as well. 2.2.2 intensity in the use of the tire mold casting plaster products, gypsum slurry is cast in a rubber mold, in order to facilitate mold release, patches, stitching, thus the silicone rubber tire plaster mold must have a high strength, anti-two hours Fold strength should be around 2.0Mpa. 2.2.3 The coefficient of expansion in the use of silicon tire casting plaster mold production, because the product of the size requirements more stringent, and therefore must be reasonable control tire casting plaster mold powder expansion coefficient, coefficient of expansion should be controlled at about 0.16%. 2.2.4 tire temperature casting plaster mold drying at high temperatures due to the need of more than 220 ℃ and 660 ℃ pouring temperature of molten aluminum, and therefore high temperature no crack, no crack, no chemical reaction with other substances to generate liquid aluminum mold become successful key. Study tire casting plaster mold powder 3.1 Effect of gypsum plaster mold 3.1.1 polymorph tire casting plaster mold plaster powder used is one of the most important factors shaping mold plaster using silicone rubber tire, but the effects of gypsum The main factor is the different properties of gypsum powder crystal forms. Hemihydrate two crystal: α type and β type (see Figure 1). α gypsum is water vapor pressure in the gypsum (CaSO4 · 2H2O), heating the resulting hemihydrate gypsum, β-type (crystal Figure 1) Gypsum is made of gypsum (CaSO4 · 2H2O) in the air heating hemihydrate obtained. α-type crystal is usually dense, full of coarse primary particles, cylindrical or needle-like crystals, the main difference is that one is a wet process (crystal see Figure 2), a massive process of autoclaved (crystal Fig. 3) , such crystal particles specific surface area is small, a small amount of water; β-type crystal mostly flakes, irregular crystals, the tiny individual grains of secondary particles, large surface area, large quantities of water. Foreign use of α-type of gypsum plaster as casting, general domestic use α-type, β-type mixing plaster. Tire molds for casting plaster technical requirements, the ratio of building materials produced using Xiangfu high purity α gypsum powder purity natural gypsum plaster 3.1.2 often mixed with clay, sand, calcium carbonate, pyrite and other impurities. These impurities reduce the content of dihydrate gypsum, hemihydrate gypsum in the coagulation process, these impurities act as filler. In the molding process due to the presence of these impurities, tire mold casting plaster work surface is easy to precipitate appears, prone to chemical reaction at high temperature aluminum pouring, the work surface will appear uneven phenomenon. This has seriously affected the mold surface finish. Moreover, the presence of impurities in itself reduces the gypsum purity, resulting in a lower strength gypsum powder. Therefore, the silicone rubber tire must have a high gypsum powder purity should normally be about 95%. In order to achieve the purpose of improving the purity of the gypsum ore, by crushing, sorting, washing and other ways to purify the ore to reduce the influence of impurities on silicon rubber tires plaster mold. 3.1.3 gypsum plaster powder fineness fineness same silicon rubber tires for plaster mold has an important impact. Gypsum powder is too rough, uneven surface of the mold, so that the surface roughness body, affect the finished appearance; but too small particles (specific surface area> 1500cm2 / g), since the crystals have a greater stress, strength decreases, resulting in the same mold strength. The proportion using a 300 mesh sieve is less than 3% of high-purity gypsum powder, not only to the inner surface of the mold has a good feel, and a higher strength. 3.2 Effects of adding auxiliary materials for die casting plaster mold needs due to the tire pouring molten aluminum at high temperatures, so the temperature does not become an important indicator of tire cracking plaster mold. Because pure plaster mold at different temperatures dehydration converted back to different substances, crystal phase transition.