Molding Technology of High-Gloss Plastic Parts
High-gloss molding technology is the process of producing high-gloss molded parts by injecting molten thermoplastic into a mold. Though it could be seen as a complex process, the sole aim is to produce plastic parts with high surface quality. Today it is commonly used to production of flat panel TVs, computer LCD monitors, air conditioners, optical Instruments and medical exterior parts without melt marks, no flow marks, no flow lines, no shrink marks.
What should we consider by making high-gloss molded parts?
High-gloss molded parts are fine shiny surface molded parts manufactured when a combination of molten plastic resin and glass fibre as injected into a mold at high temperature. The higher the molding temperature, the longer the injection molding cycle. Therefore, the use of high-performance material like wollastonite filler as a supplement for glass fibre can reduce the cooling time by at least 40% and thus reducing the injection mold temperature.
Mold design consideration
Before commencing a high-gloss plastic parts production, there are some things of mold design requirements to be considered for effectiveness. These requirements are there to make sure a quality high-gloss molded part is achieved finally. Below are some mold design considerations:
High-gloss injection molds are supposed to be either electric rod or steam heated. However, it is better to employ the electric rod heating method for high-gloss production because of its efficiency, high energy saving capacity and high utility rate.
Working principle of both steam and electric rod heating method:
Electric rod heating: This type of heating method makes using of electricity as its fundamental energy source and is cooled by a coolant (Water) after every molding process.
Steam heating: For this heating method, hot water is injected into the injection mold through a temperature control system as the molding process is on, to generate heat energy as the primary power source, and is cooled with the help of a coolant (Water).
Higher temperature in injection molding process
One significant consideration for a high-gloss mold model is high temperature. Mold process requires a very high temperature of between 75℃ and 130℃, this is to make sure deformation and defects, flow marks and weld marks are completely expelled for the surface of the system. During operation, molds are supposed to be treated with heat, to reduce heat loss.
More hot nozzles on the hot runner system
To ensure that there are no weld marks on the surface of the mold part, each heat nozzle has their various warm air passages, which has separate sealing valves and a relay to determine the feed time for each nozzle.
Very bright steel cavity image surface
A highly glossy cavity surface for a, at least a mold with mirror level II, this is because high-gloss molded parts will be used/assembled straight from the mold, with no further treatment of the surface area. So for this reason, high-quality materials and mold steel must be employed.
Tooling steel material for high-gloss plastic parts
For high light requirements, mold steel materials like CEANA1 and S136H, are recommended NK80 serves almost all high-gloss mold steel surface purpose, however, the CPM40 and GEST80 are also nice options too. Therefore, the NK80 is the best mold steel material choice, as it is easy to modify molded parts, as well as enhances further processing if need be. Unlike some materials like S13H, NK80 does need treatment to be quenched.
Plastic material for high-gloss plastic parts
The following are commonly used injection molding material for the manufacturing of high-gloss plastic parts:
• Combination of Acryl Butadiene Styrene and Polymethylmethacrylate(ABS+PMMA)
• Combination of Acryl Butadiene Styrene and Polycarbonate (ABS+PC)
During over mold, Acryl Butadiene Styrene can readily be used in conjunction with polycarbonate as casing material, to produce molded parts with excellent impact resistance and yet high-gloss surface and toughness. However, the combination of these high-performance materials is to meet the desired need for a particular condition.
If the high-gloss plastic part is being molded for toughness and stress resistance, then it is combined with Polymethymethacrylate.
If it is being designed to suit a specific weather condition, then the Acrylonitrile Styrene Acrylate is a choice for using.
Maintenance of high-gloss mold
First, the surface of the mold workpiece must have a high-grade rust inhibitor or seal with a plastic wrap to prevent direct contact with the air and cause damage. Second, it is forbidden to contact any cavity or hand directly with the cavity surface. Third, clean the mirror surface workpiece, should use high-density paper towel spray with cleaning agent from top to bottom, gently scrub, and cannot scrub back and forth; cannot use medical cotton wool and cloth strip; cannot use air gun directly on the workpiece, because the gas in the tube water vapor can cause damage to the working surface. Finally, after each production or trial out, the cooling water in the mold water channel must be blown off with an air gun to prevent the injection mold from rusting which can affect the mold life.
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