- Feb 25, 2016 -
The particles of the appropriate particle size are selected to be placed in the eps pre expander machine, which is steamed or other medium, at a certain temperature, for a period of time to expand to the top rated density. This process is called pre-foaming, and the resulting beads are called polystyrene pre-beads. Pre-foaming process according to the different heating methods are steam, hot water, hot air, infrared and vacuum method: which steam method is divided into two kinds of continuous steam and intermittent steam method.
1) continuous steam method
A continuous steam eps pre expander machine with stirring is used. Steam and expandable polystyrene beads are fed continuously from the bottom of the pre-evaporator, the vapor pressure is 0.05-0.1 MPa, the foaming temperature is from 9u to 105C, the pre-discharged beads are continuously discharged from the upper outlet, Fall into the receiver, and then use the wind transport device into the mature storage device. Adjust the export height, control the apparent density of the pre-beads: the law can be obtained from the minimum apparent density of c.012 a u.016g + C1TI, the pre-beads, high yield, but uniformity difficult to control.
2) Intermittent steam method
The intermittent pre-dispenser with agitation is used. Steam from the bottom for the people, EPS beads from the top to join, pre-release beads from the bottom of the discharge, intermittent operation. Steam pressure 0.055 a 0.1MPa, foaming temperature 98-100 ℃, holding time 20 a 30min. Adjust the steam pressure and holding time, can be obtained with the lowest apparent density of 0.012 a 0.016g / cm of the pre-beads, the apparent density is easy to control, but also more uniform.
3) hot water method
The EPS beads were placed in 85-99 ~ C water and kept for a certain time to obtain the pre-particles with apparent density higher than o and 08g / cm. This method can precisely control the apparent density, but only for a small amount of EPS pre-hair, low production efficiency.
4) hot air method
Using a preheater similar to the continuous steam method, with hot air injection system, EPS pre-hair, apparent density can be higher than 0.04g, cm :. The resulting pre-beads can be used for molding without maturation. But this method is 4 times longer than the steam method, and the apparent density is difficult to control precisely.
5) vacuum method using vacuum preheater:
When the top, the jacket through the steam, heated to 9-104 ℃, to maintain a certain time, and then evacuated to 50 a 66kPa, the introduction of a certain amount of water to generate 71-82 ℃ low temperature steam, so that the foam beads Cooled and solidified when the surface of the beads does not shrink. Finally, the control to eliminate the vacuum, people compressed air, the pre-beads through the lower discharge port blowing. This method produces preformed beads having an apparent density of 0.0064 g / cm. Mature time is short, density distribution uniform;
Just pre-made good EPS pre-emblem after cooling was local vacuum state. The presence of local vacuum will affect the fusion between the particles during molding and the shrinkage of the part. To eliminate the local vacuum in the beads, the beads that are pre-made are placed in a given environment for a certain period of time Of the gas into the pre-foam beads in the cells, to balance the internal and external pressure, the process known as ripening or mature. The most commonly used curing process for normal temperature and pressure method. In addition, there are high-pressure method, atmospheric pressure - high pressure method and high temperature method, different curing process of the pre-beads can be different density foam pieces.
1) At room temperature and atmospheric pressure method will be pre-beads placed in cotton or sieve made of the aging of the warehouse, placed at 20 to 26 ℃ for 18-24h, this method is suitable for large production, A foamed article having an apparent density of 0.016 to 1 U.020 g / cm was prepared.
2) high pressure method will advance the beads into the people into the curing warehouse, through the air, carbon dioxide or nitrogen, so that the pressure in the warehouse to maintain the 35-100kPa (gauge pressure), the temperature is 15-25 ℃. Aging time is 0.5-3h. The aging time of this method is short;
3) Atmospheric pressure - high pressure method will be fresh pre-beads in the ordinary box under the aging 2h, and then the pressure inside the warehouse rose to 200-600kPa (gauge pressure, and then a certain period of time, with this method of aging beads A foam mass having an apparent density of 0.007 to 0.008 g / cmn3 and a molded article having an apparent density of 0.012 to 0.016 g / cm can be obtained.
4) high temperature method by the continuous steam pre-process to obtain the apparent density of 0.016 a 0.032g / cm; pre-hair beads, left the hair dryer after 90 ℃ or so air transport, through a cyclone, the water Removed, and then into the porous receptacle. This method can be made both dry and fully ripened pre-beads, Chen mature time is short.
Molding is the maturing pre-beads placed in the mold, and then steam heating, so that it re-expansion and melt bonding into one, the cooling stereotypes into a certain shape of the foam products, the main process of steam cylinder and molding machine law.
1) steam cylinder method will be cooked with a good pre-loaded beads with a number of small holes in the mold, the mold will be placed in the mold after the mold, and then to the cylinder through the steam, in c.05-0.25MPa Under the pressure of heating: a 3min, and finally open the steamer out of the mold, after cooling to get off the parts.
This method is suitable for the manufacture of small, complex shape of small products, the apparent density of u.020 - (:). 030g / cm ,: Although this method is simple to use, easy to operate, but the labor intensity. Difficult to achieve mechanization and automated production.
Steam cylinder method can also be used secondary molding process, that is, after a molding, placed for some time, then the foam into the mold in the secondary molding. The mold and process conditions used are the same as the primary molding process. Steam cylinder secondary molding process can be made of wall thickness of 3-4mm, density o.016g / cm, the size of the shape of the complex foam foam.
2) molding machine molding machine method, also known as gas chamber method: the method used for the mold with two air-conditioned mold, by the steam room, mold frame and mold core composition. In the mold frame and mold core plane every 20 to 30mm drill diameter of 7.5mm ventilated larvae L (or gas tank). The two pieces of the mold are fixed on the two press plates of the press respectively. According to the different parts - as a package molding machine and sheet metal forming machine, the form of horizontal and vertical two.
Molding, the first mold, the gas chamber into the 0.1-0.2MPa steam, the mold preheated to 100 ~ C or higher, while removing the remaining condensate, and then use the compressed air will be sent to the beads People in the mold. After the cavity is filled with top beads, close the outlet. When feeding the mold parting surface must be open a small gap, the size of the gap to the workpiece without flash prevailing, after feeding, to the gas chamber through the o.1 a o.2MPa steam, heating l 2min (packaging products For 30s), mold cavity material temperature up to 110 ~ C. Then, immediately close the parting surface, quickly boost to the appropriate value. Hold - set time: the last. Close the steam valve, water cooling stereotypes, stripping that was foam plastic products. The cooling setting time depends on the size and wall thickness of the product.
This method is intermittent production, widely used. Suitable for forming foam and simple thick-walled foam.
3) continuous chamber method This method of the cavity by the four endless steel belt composition, the upper and lower with two holes, the pre-beads into the mold cavity, the mold continued to move forward, followed by Steam heating zone and cooling zone? Through the heating zone, the steam through the upper and lower holes into the beads into the middle of their melting together. Into the cooling zone with forced ventilation cooling.