It is absolutely impossible to obtain high-quality lost foam castings without high-quality patterns. STMMA is an expandable copolymer resin bead specially used for the pattern material of lost foam casting. Pentane is mainly used as the foaming agent, and the content of pentane directly affects the quality of the mold. The main process of pentane control: pre-expansion – bead curing – die drying In the process of pre-expansion, on the one hand, it is the process of expanding and foaming the beads, and on the other hand, it is the main process of pentane loss. Pentane is the basis for pre-expanding and molding, but after the molding is completed, it is hoped that the pentane can be completely and completely dissipated. Copolymerized beads with less than 9.5% of the original bead pentane can shorten the heating time during pre-expanding, and it is recommended to control it at about 40s; Control it around 60s. The structure of the beads is damaged if the pre-expansion time is long, and too much foaming agent is consumed; thus affecting the quality of the secondary molding. STMMA storage method: low temperature storage ≤ 10 degrees. When it is not used up after opening, remember to re-tighten the bag, and keep the barrel covered at low temperature to prevent the loss of pentane. Bead aging The newly foamed beads have negative pressure inside and are easy to collapse. They must be put into the aging warehouse for aging treatment, allowing air to enter the interior of the beads to achieve internal and external balance. Aging is a process for the pre-released beads to reach stability. During the stabilization process, the beads change: most of the water evaporates, the beads recover a certain degree of elasticity, and the content of pentane decreases. When the pentane content is less than 9.5%, the curing time of the pre-haired beads is generally controlled to be 12-48 hours. When the content of pentane is greater than 9.5%, the curing time of the pre-haired beads is generally controlled at 3-4 days. In this curing process, the pentane content is controlled at 7%-8% to reduce the possibility of expansion bubbles in the later stage after bead molding. At this time, the mold is filled evenly, easy to form, the surface of the mold is high, strong, and the beads are fused with each other. Die shrinkage is stable and consistent. When the pentane content of the beads is less than 5% after bead curing, it is very difficult to form a die, the surface collapses, shrinks, and the uneven surface is not smooth.
Molds are produced when the pentane content is less than 5%
Die made with pentane content of 7%-8%The higher the die drying temperature, the faster the pentane volatilizes. The die pieces are placed in the air for natural aging, and the pentane and water content evaporate slowly. According to my many years of production experience: under normal circumstances, after one day of curing, the dies are sent to the drying room at a temperature controlled between 45-50 degrees, and sent to the pentane content after drying for 4-5 days. If the pentane content is greater than 5%, it can continue to be cured at high temperature, and it can be used when it is less than 5%. When the pentane content of the pattern is greater than 5%, the dip-coated pattern is wrapped by the coating, even if the high-temperature drying gas is difficult to volatilize. During the pouring process, the amount of gas is too large, which causes the imbalance of internal and external air pressure to cause reverse spray and collapse of the box. Castings produce porosity, air separation, and incompleteness lead to castings being scrapped.