Rotational Molding
Rotational Molding:
And "secondary material" process is different, "a feed" method of two different materials into the mold of polyethylene, a polyethylene for the powder, while the other is mixed with a small spherical polyethylene foam. Powdered polyethylene adhesive die first and continued circulation of small spherical polyethylene and continue to heat, and then formed plastic shell followed by foam skin reaction. Take a look at this different from the traditional "secondary material" in rotational molding process where a new
To improve the traditional "secondary material" rotational molding process highlights limitations, Polivinil Rotomachinery has developed "a feed" Rotational new process for the production of polyethylene structural foam panels. This area of research interest is the point of junction in between the plates can be filled with a kind of improved the performance of sheet material, the performance of chemistry? Physical properties (such as insulation, density, buoyancy, etc.) or mechanical properties (such as vibration resistance, structural strength, etc.). In addition to the structure are made of polyethylene foam products, their interest is another reason to consider using recycled materials.
Traditional "secondary material" process will begin in a certain amount of materials necessary for molding plastic parts into the outer ("skin shell"), once the material within the melt in the furnace will remove mold from the oven and add foaming agent (such as: a pre-mixed in polyethylene in powder additives), and immediately re-inserted within the furnace to complete the molding cycle (second melting, cooling, etc.). There are security issues in this process, because the manual operation of the high-temperature mold to molding cycle is extended by the length of time in direct proportion with the mold, but also in the skin and shell materials suitable for freezing before dropping down to interrupt operation (die the greater the more serious this phenomenon).
And "secondary material" process is different, "a feed" method of two different materials into the mold of polyethylene, a polyethylene for the powder, while the other is mixed with a small spherical polyethylene foam. Powdered polyethylene foam decomposition temperature than the melting point is low, and the particle size is different, for forming the outer surface of plastic parts. (Polyethylene powder particle size of 500 to 1000 microns, small ball (a mixture of foam) polyethylene particle size of 3 ~ 4 mm). Powdered polyethylene adhesive die first and continued circulation of small spherical polyethylene and continue to heat, and then formed plastic shell followed by foam skin reaction.
Material at 210 ℃ under the first stage of melting, starting powder material adheres to the mold, only the surface of the formation of a plastic shell only to the temperature of 265 ℃ to promote the second phase of melting, softening point of polyethylene formed Sphere. As the foaming agent decomposition caused by internal pressure, the process continued until the internal pressure equilibrium with atmospheric pressure until the exhaust port. Followed by small spherical particles of polyethylene foam up big, and finally fill the entire cavity, solidification by cooling after the polyethylene. The ideal result is two kinds of materials technology in the molding stage of complete separation of foam control by adjusting the processing temperature, melting and cooling time, rotation speed and the exhaust port location. Further, must be avoided in the epidermis with small spherical shell in the bonding of polyethylene particles, in normal conditions, due to the decomposition of blowing agent pressure, uniform heating of small spherical particle softening, foam. Therefore, if the shell does not melt plastic parts surface, unless the ball completely wrapped, small spherical polyethylene particles may sink (almost inevitable), heating and small spherical particles make contact with shell reaches its softening point but it did not happen expansion foam ball only contacts with the Office shell decomposition (here after the yield point), in the plastic surface to leave visible traces.
Foaming process is a continuous process, when the small spherical polyethylene foam mold temperature is higher than the decomposition temperature, mold pressure is not high there is room to allow mold material was expanded, this time beginning to foam, the material expansion of the mold air from the exhaust discharge. Process-related issues with the foam blowing agent in the cell wall may rupture, to collapse and bubble increases. Too thin foam plastic and mold causing harmful closed flange stripping difficulties.
Foam produced in the exhaust port and are growing up near the bubble wall can break and tear squeezed, reducing the processed products of mechanical robustness, thus forming a large bubble area (hole big bubble unpopular). Foam long-term stay at a high temperature expansion process to increase the duration of the cell produces the danger of growing up. Foam from the foaming agent right right to impose the thrust cell wall will cause the collapse of the cell, resulting in the cell aggregation of the merger, so that the cell becomes more and more, the cell growth in the size of the molten phase and the second time proportional, but also with the thickness of foam sheet is proportional to (high temperature in the core plate was isothermal blowing the Department of decomposition reaction heat control becomes more difficult).
In order to avoid the occurrence of all these circumstances, we must maximize the cooling rate, that alone is not enough practice, but also reduce the duration of the second molten phase. This expansion process can be regarded as macro-particles of polyethylene ball sports growing up, the ball shell from the surface to the low pressure area (outlet area) grew up in uniform if the cell growth and (or) is not normal, will produce big balloon area undesirable, inconsistent distribution of polyethylene pellets, increasing the cell block and (or) the lack of obstruction or vent can lead to this phenomenon. Polyethylene ball distribution is inconsistent with some of the regional distribution of the insufficient number of small ball, it is not full of mold cavity (even if fully foam), so rotate to make adjustments. If the mold growth in the memory foam in the hamper movement of obstacles, the foam material can not be full of mold cavity, especially in the high temperature molten phase and the second time, especially over short time. Moreover, when the cell may be evenly distributed, but just the air vent plug size too small and confined to a certain extent, the air pressure under the bubble internal pressure within the foam rather hinder further grow. Therefore, the exhaust port must have the correct size or number sufficient to enable the smooth discharge of gas. When the expansion material outlet plug, the mold pressure will increase, in some cases, materials will be out through the closed mold flange overflow, the result apart from dirty flange (leading to production must be interrupted), also caused by mold damage.
Completed experiments show that the temperature of the first melting phase must be as low as possible in order to protect the beads began to soften when the hole full. Logica PRM 3000 8C machines in use in the minimum temperature of 215 ℃. Unless there are special aesthetic requirements, the shell thickness skin foam sheet generally 2 ~ 3 mm. To avoid the ball emitting surface shell thickness could be increased to 3 ~ 4 mm, and has more than strengthen the tendons of the complexity of convex shape. The thicker the foam board is the longer second stage of melting, because the dense surface shell heat transfer bad. Rotational speed must be higher to reduce the hole in each shell beads and skin contact time. As at the design stage, with "a feeding method," the structure of foam production should be such a board, and air holes remain in the board itself, to ensure the flow of air from a hole to a neighboring hole, air can be easily discharged. On the other hand, have to die on a certain amount of exhaust design, the time when the foam material can guarantee the smooth discharge. On the contrary, in the molding process, the melting temperature of the formation of surface shell must only consider adding solid material to the mold only in the process to set the temperature (no foam beads). By setting the temperature of 200 ~ 230 ℃ to reduce the molding time is not desirable. Must be based on the desired surface with the shell thickness to determine the time of the first stage of melting. Mold in the molten phase into the material for the production of skin and foam shell with small spherical when the duration of the mold to increase by 10% as calories absorbed by the foam ball. In this case it is necessary to calculate the theoretical material and the amount of foaming agent to consider no surface shell theory when the cavity size and foam density. Best results are the first products to use materials with lower foam production, foam ball around with 20% ~ 25%. Relative to the theoretical amount, this amount is insufficient, but when it was observed in the foam material properties of foam. Finally, the product can be close to key office closed mold flange cut in order to observe the section of the structure. These key Department also exhaust the mouth, the air bubble region and a large foam tearing region.
Rotational Molding Company in China.
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[ Author: admin] [ Date: 6/7/2010 ] [ Hits: ]
