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Lost mode white mold EPS raw material ripening process

2019-05-17

The pre-expansion and ripening of EPS raw materials are two important steps in the production of the lost foam white mold. The pre-foaming process of EPS raw materials has been introduced in the previous process document. Here we will focus on the ripening of EPS raw materials in the lost foam white area. The process flow of the link. The EPS raw material is matured by injecting the pre-expanded beads into a pre-designed mold to continue foaming to obtain a shape and density that meets the requirements.

The pre-expansion reduces the density gradient during molding and allows for uniform expansion molding. The freshly prepared EPS pre-beads are partially vacuumed after cooling. The presence of partial vacuum will affect the fusion between the particles during forming and cause the shrinkage of the part. In order to eliminate the partial vacuum in the beads, the newly prepared beads should be placed in a certain environment for a certain period of time to make the environment The gas penetrates into the cells of the pre-expanded beads to achieve internal and external pressure balance, a process called ripening or maturation.

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After the freshly discharged beads are cooled, the blowing agent and the water vapor in the cells are cooled and liquefied to form a vacuum in the cells. During the ripening process, the air penetrates into the cells, so that the pressure in the cells in the beads tends to balance. The best curing temperature of the beads is 23-25 ° C, and the ripening time is related to the moisture and density of the beads and the temperature and humidity of the environment. Pre-expanded beads ripening time: EPS is usually 4-24 hours, and StMMA is usually 12-48 hours. Curing is the main process of producing a qualified appearance.

The pre-expanded beads are stored in a silo for ripening--referred to as a ripening bin; the general capacity is 1 to 5 cubic meters, and is made of anti-static cloth or stainless steel mesh, in order to prevent the static electricity generated by the transport beads from causing the beads to escape, Alkane combustion, generally using metal pipe transport, the curing warehouse should be placed under good ventilation conditions, all pipes, silos, etc. should be well grounded to reduce the static electricity of the mature beads.

Mature warehouse

The environmental requirements for EPS raw material ripening are as follows: the matured warehouse should be placed under good ventilation conditions; the optimum ripening temperature of the beads: 23~25 °C; humidity <30%; ripening time -12--48 hours.

The requirements for the ripening warehouse when the EPS raw material is matured are as follows: the volume of the matured warehouse is not too large (preferably about 1 cubic meter); the matured warehouse net is not too fine (less than the diameter of the minimum pre-fabricated beads); Anti-static material.

Judging of qualified beads: Throughout the curing process, it can be seen by the naked eye whether the beads are normal pre-fabric: good beads generally have a glossy surface, rounded, and have good resilience by hand; If the hair is not good, the surface will foam, some will be elliptical, have no elasticity, and the volatiles will run relatively fast.

Matured bead comparison

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In addition, commonly used curing processes include normal temperature and pressure, atmospheric pressure - high pressure, high pressure and high temperature, as follows:

Normal temperature and normal pressure method: The pre-formed beads are placed in a curing chamber made of cotton cloth or mesh, and placed at 20-26 ° C for 18-24 hours. This method is suitable for large production, mature pre-beads can be made. A foamed article having an apparent density of 0.016 to U.020 g/cm was obtained.

Atmospheric pressure-high pressure method: fresh pre-expanded beads are first matured under normal simmer for 2 hours, then the pressure in the chamber is raised to 200-600 kPa, and then matured at a certain time, and the pre-formed beads matured by this method can be obtained. A foam block having a density of 0.007 to 0.008 g/cm 3 and a molded article having an apparent density of 0.012 to 0.016 g/cm.

High-pressure method: the pre-expanded beads flow into the mature warehouse, and the air, carbon dioxide or nitrogen is passed to maintain the pressure in the warehouse at 35-100 kPa and the temperature is 15-25 °C. The ripening time is 0.5-3h. This method is ripe for a short time.

High-temperature method: pre-formed beads with apparent density of 0.016-0.032g/cm by continuous steam pre-fabrication technology, separated from the necker and transported by air at 90°C, and removed by a cyclone And then sent to a porous reservoir for use.

After processing the ripening link of EPS raw materials, it is basically able to produce absolutely high-quality blank mold blank products; it lays a solid foundation for the production of high quality lost foam castings.

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