Jewelry Making Procedure: Plaster Mold

As one of the very important part in jewelry making procedure, plaster mold is relative complicated. But gets to know something about it would be helpful for our comprehension of how a finished item is produced.1. Fusion welding. It means to weld the wax mold one by one for the convenience of massive production by taking advantage of the cavity space of the mold. We call the welded mold wax tree vividly, and the channels for liquids to flow out and metal casting nozzle which connect the wax molds like a trunk in layers on the top. The nozzle should be thick enough, without acute angle and bending, the welding part where wax mold, branches and main stems are connected smoothly. The wax mold with more complicated shape should be set with more nozzle and supporting nozzle. The branch nozzles should be short enough to less than 15mm, and the main one should be regularly more than 7mm, location of the nozzles are related with the methods of casting. According to different shapes, sizes, and categories of wax molds, different waxes should be distributed on the branches in balance. The welded wax mold should not be too closed to each other in case that the plaster mold made in the next step would be broken due to the thick mold cavity. Impurity and grease on the surface of the finished welding wax tree should be cleansed by using of organic solvent such as carbon tetrachloride. Weight of the tree should be recorded to provide effective data for counting corresponding metal weights.2. Mastering the palter mold. Preparation for mastering a plaster mold is to put the wax tree with steel tube. The basic categories of steel tubes are centrifuge casting cylindrical tube without holes, vacuum machine casting cylinder with shoulder pads and holes. The powder which is used to produce plaster mold is not completely composed with gypsum powder, expect of 25% to 30% calcined gypsum powder, other materials such as quartz sand, calcite, solidification additives and reducing agent and so on. The plasters that can be purchased in market are Romen- Vest, Kerr Scurin, Last R&R, Ulter- Vest and some other categories. Data shows that the ratio of powder and water is that the weight of water is 40% by the weight of gypsum. The modulated slurry should be conducted in the room temperature between 21 ° C to -26 ° C. It would regularly cost 9 minutes to stir the water and powder mixing into slurry state, period among the time is called operating time in which the cylinder can only be allowed to stand.3. Pulping and filling the cylinder. Machines and tools in the procedure concluded are glass or plaster graduated cylinder and platform scale, mixing spoons and bowls used for stirring, pulping vacuum pumping for vacuuming.Dewaxing and mould drying. The powder cylinder can be used for casting only by getting through steps of dewaxing and drying. Electric stream by which the temperature is under control is proved. When outing down the plaster mold into the machine, the nozzle should be downward. In the drying procedure, temperature of the electric up to 900 should be adjustable, while the actual temperature should be less than 760. The temperature should be rises gradually in the process and about 3 hours insulation is needed once the highest temperature is reached to make sure that temperatures of all plaster molds can be down to their optimal temperature in the oven after reaching reach a consistent state together. Here is the simple introduction of the plaster molding making, the following step is to casting and cleaning. We will introduce some of them in the following articles.