Silver lines are produced from a variety of silver filament from the front of the volatile emissions.
For example, the degradation of silver is partially degraded after the thermoplastic is heated, and small bubbles are formed on the surface of the plastic when the gas decomposes. The traces of these small bubbles on the surface of the plastic are generally arranged in a 'V' shape. V The tip of the word is back to the center of the gate.
Another example is the main reason for the water vapor silver wire is the raw material moisture content is too high, the water vapor generated when bubbles lead to the surface of plastic parts of silver, especially polyamide and polyacid superabsorbent polymer, if the melt Moisture generated when the gas can not be completely discharged, it will form a plastic surface water gas silver wire.
Plastic in the mold filling process by the gas interference often appear in the product surface silver markings or tiny bubbles or the formation of bubbles in the thick wall products.These gases are mainly raw materials containing water or volatile substances or excessive lubricant may also It is expected that the plastic will be degraded if the plastic is heated for a long time or degraded due to poor exhaust.
First, the equipment
Nozzle hole is too small, the material drooling or drawing in the nozzle, barrel or nozzle has obstacles, high-speed flow friction heat generated when the material decomposition.
Second, the mold:
Due to design flaws
Such as: the poor location of the gate, the gate is too small, multi-gate parts gate arrangement asymmetry, small flow channel, the mold cooling system unreasonable so that the mold temperature difference is too large and other causes the melt flow in the cavity Continuous, blocked the air channel.
Mold parting surface
Lack of necessary venting or insufficient venting, clogged, poor placement, and lack of machining gaps such as inserts and thimbles to vent the air in the pocket at the same time as the plastic enters.
Poor mold surface roughness
So the surface friction resistance, resulting in local hot spots, so that through the plastic decomposition.
Third, the process
temperature
Material temperature is too high, causing decomposition. Barrel temperature is too high or heating imbalance, the cylinder temperature should be reduced paragraph by paragraph. The feeding section temperature is too high, so that part of the plastic melt prematurely filled with screw slot, the air can not discharge from the feeding port.
speed
Injection speed is too fast, so that the molten plastic by a large shear effect and decomposition, resulting in decomposition gas; injection speed is too slow, can not be filled in time due to the cavity surface density caused by lack of silver lines.
Use multi-stage injection to reduce the silver pattern: medium-speed injection filling flow channel → slow filling gate → rapid injection → slow low-pressure mode filling, so that the mold gas can be removed in time in all sections clean.
Pre-plastic
Lack of material, feeding cushion is too large, the material temperature is too low or too low mold temperature will affect the melt flow and molding pressure, resulting in bubbles.
Back pressure
Screw pre-plastic back pressure is too low, the speed is too high, so that the screw back too fast, easy to push the air along with the material to the front barrel. Molten plastic poor. If the melt less heated in the barrel, poor plasticization, Particles that have not completely melted form speckles when exposed to the surface of the part.
This shaped mica flaky dark spots, each piece of dark spots close to the size of a grain size in the transmission light observation can be seen at the markings of the poor transparency, and sometimes can be clearly distinguished not Through the raw material particles.
Runner
According to the reasons for the formation of dark spots, when eliminating this failure, the temperature of the barrel should be increased and the molding cycle should be lengthened appropriately, as far as possible, the inner heating inlet should be used or the cold material hole should be lengthened and the longer flowing channel should be enlarged. , But also for the larger cylinder diameter injection molding machine, plastic melt to enhance the plastic.
Fourth, raw materials
Raw materials mixed with different kinds of plastics or pellets mixed with a large amount of powder, easy to entrain the air melt, and sometimes appear silver grain. Raw materials contaminated or contain harmful raw materials vulnerable to decomposition of raw materials.
Loose particle structure of recycled materials, micropores stored in the large amount of air; Regeneration of the regeneration of the number of times too much or with the new material is too high (generally less than 20%)
The raw materials contain volatile solvents or liquid additives in the raw materials such as bleaching aid white oil, lubricant silicone oil, plasticizer dibutyl ester, and stabilizers, antistatic agents, such as excessive use or uneven mixing to the accumulation state Into the cavity, the formation of silver lines.
Plastic without drying or moisture absorption from the atmosphere should be fully dried raw materials and the use of dry hopper.
Some grades of plastic itself can not withstand higher temperatures or longer heating time, especially with traces of moisture, catalytic cracking reactions may occur.