Silver streaks (material flowers). All kinds of silver threads are produced from volatiles ejected from front end of flow material. For example, degraded silver wire is a part of degradation of thermoplastics after heating, when gas is decomposed, small bubbles are formed and distributed on the surface of plastic parts. Traces left by these small bubbles on the surface of plastic parts are generally arranged in a "V" shape, with tip of "V" facing away from center of gate.
Another example is that main reason for production of water vapor silver wire is that moisture content in raw material is too high. Bubbles generated when water volatilizes lead to production of silver wires on the surface of plastic parts, especially super absorbent resins such as polyamide and polyester. When gas generated by volatilization of water cannot be completely discharged, water vapor silver wire will be formed on the surface of plastic part.

 

Plastics are disturbed by gas during filling process, often silver stripes or tiny bubbles appear on the surface of product, or bubbles are formed in thick wall of product. Sources of these gases are mainly moisture or volatile substances or excessive lubricants in raw materials. It may also be caused by degradation of material due to high temperature of plastic or poor exhaust due to long heating time.

Nozzle hole is too small, material is drooling or drawing at nozzle, barrel or nozzle is obstructed, high-speed material flow generates frictional heat to decompose material.

Due to design defects, such as: poor gate position, too small gate, asymmetric gate arrangement of multi-gate parts, small runners, unreasonable mold cooling system, so that mold temperature difference is too large, melt flow in mold cavity is discontinuous, and air passage is blocked.
Mold parting surface lacks necessary vents or vents are insufficient, blocked, poorly positioned, there is no processing gap such as inserts and thimble to vent, so that air in cavity cannot leave at the same time when plastic enters.
Surface roughness of mold is poor, frictional resistance is large, causing local hot spots and decomposing passing plastic.

Material temperature is too high, causing decomposition. If barrel temperature is too high or heating is out of adjustment, barrel temperature should be reduced step by step.
Temperature in feeding section is too high, so that a part of plastic melts and fills screw groove prematurely, air cannot be discharged from feeding port.
If injection speed is too fast, molten plastic will be decomposed by a large shearing action, resulting in decomposition gas; if injection speed is too slow, cavity cannot be filled in time, resulting in insufficient surface density of product, resulting in silver streaks. Use multi-stage injection to reduce silver streak: medium-speed injection fills runner → slow-speed fills gate → fast injection → low-pressure and slow-speed injection to fill mold, so that gas in mold can be removed in time in each section.
Insufficient amount of material, too large feeding cushion, too low material temperature or too low mold temperature will affect flow and molding pressure of melt, and generate bubbles.
When screw is pre-molded, back pressure is too low and rotation speed is too high, so that screw returns too fast, air is easily pushed to front end of barrel along with material, and melt is not plasticized. If molten material is not heated enough in barrel and plasticization is not good, markings will be formed when incompletely molten material is exposed on the surface of plastic part. This dark spot is shaped like a mica flake, and area of each dark spot is close to size of a pellet.
Observed under transmitted light, it can be seen that transparency at spots is poor, and sometimes convex unmelted raw material particles can be clearly distinguished. According to cause of dark spots, when troubleshooting this fault, barrel temperature should be appropriately increased and molding cycle should be extended, internal heating type injection port should be used as much as possible or cold material cavity should be enlarged, runner should be lengthened. In the case of possible conditions, an injection molding machine with a relatively large barrel length can also be used to enhance plasticization of melt.

When raw materials are mixed with dissimilar plastics or granules are mixed with a large amount of powder, it is easy to entrain air when melting, sometimes silver streaks may appear. When raw material is contaminated or contains harmful scraps, raw material is easily decomposed by heat.
Granular structure of recycled material is loose, amount of air stored in micropores is large; number of regenerations of recycled material is too much or ratio with new material is too high (generally less than 20%)
Raw materials contain volatile solvents or liquid additives in raw materials such as white oil, lubricant silicone oil, plasticizer dibutyl ester, stabilizer, antistatic agent, etc., are excessively used or mixed unevenly, enter cavity in an accumulated state to form silver streaks.
Plastic does not dry or absorb moisture from atmosphere. Raw materials should be fully dried and a drying hopper should be used.
Some brands of plastic cannot withstand higher temperature or longer heating time. Especially when a trace amount of water is contained, a catalytic cracking reaction may occur. For this type of plastic, it is necessary to consider adding external lubricants such as stearic acid and its salts (up to 50g per 10kg of material) to minimize its processing temperature.

Wall thickness is too thick, cooling rate is different between surface and inside. Size of main runner, runner and gate should be appropriately enlarged during mold manufacturing.