First of all, let's first understand the definition of flower material: silver grain, also known as flower flower, water flower, is a blister-like line produced on the surface of injection molded parts, mostly in the shape of a shear head, and the cutting head points to the rubber mouth.
Figure 1 Silver streak typical defect picture
Figure 2 Silver streak typical defect picture
The cause of a flower
Equipment aspect
The nozzle hole is too small, the material flows or draws at the nozzle, the barrel or the nozzle has an obstacle, and the high-speed material passes through the friction heat to decompose the material;
The barrel, the screw wears or the rubber head and the apron have a dead angle of the material, and are decomposed by heat for a long time;
If the heating system is out of control, the temperature will be too high and decompose. Check whether there are any problems with the heating elements such as thermocouples and heating coils. Improper screw design, resulting in decomposition or easy to bring in air.
2. Mold aspect
Due to design defects, such as: poor gate position, too small gate, asymmetrical gate layout, small flow path, unreasonable mold cooling system, too much difference in mold temperature, etc. The flow in the cavity is discontinuous, blocking the passage of the air.
The corner is too sharp, and the cut is too large when the flow passes, causing the appearance of silver streaks;
The mold parting surface lacks the necessary venting holes or insufficient venting holes, blockage, poor position, and no machining gaps such as inserts and thimbles, so that the air in the cavity cannot be left at the same time as the plastic enters. .
The surface roughness of the mold is poor, and the frictional resistance is large, causing local hot spots to decompose the passing plastic.
The mold leaks oil, leaks, and leaks into the mold cavity, which is easy to cause the workpiece to show silver streaks.
3. Process aspects
The material temperature is too high, causing decomposition. If the barrel temperature is too high or the heating is out of adjustment, the barrel temperature should be reduced step by step. The temperature of the feed section is too high, so that a part of the plastic melts prematurely and fills the groove, and the air cannot be discharged from the feed port.
The injection speed is too fast, so that the molten plastic is decomposed by large shearing action to generate decomposition gas; the injection speed is too slow, and the cavity cannot be filled in time to cause the surface density of the product to be insufficient to produce silver streaks.
Insufficient material, too large a feed cushion, too low a material temperature or too low a mold temperature will affect the flow of the melt and the molding pressure, resulting in bubbles.
When the screw is pre-molded, the back pressure is too low and the rotation speed is too high, so that the screw is retracted too fast, and the air is easily pushed to the front end of the barrel together with the material.
4. Raw materials
The raw materials are mixed with impurities or pellets, and a large amount of dust is mixed therein. When melted, it is easy to entrain air, and sometimes silver streaks appear. When the raw materials are contaminated or the dust is excessive, the raw materials are easily decomposed by heat.
The nozzle material (recycled material) is added too much, and the number of regenerations of the nozzle material is too high or the ratio with the new material is too high (generally less than 20%).
The auxiliaries in the material decompose to form silver streaks.
Excessive moisture in the material does not dry sufficiently, resulting in a silver streak.
The moisture content of the material is too high or the material has a bee hole, which causes the silver grain of the workpiece.
Second site troubleshooting steps
1. Whether the material is damp
The materials inspected have no obvious water and moisture. It can be visually observed that the outer packaging is filled with no water and moisture. The material is unpacked and the material is sensitive to moisture. The material that has been wetted by water is difficult to dry.
2. Feeding link
Check the feeding link to ensure that the barrel and feeding process are clean to avoid mixing of the foreign materials, and check whether the material particles have obvious bees;
3. Drying equipment inspection
Check the drying equipment to see if the heating temperature of the drying equipment is normal (there is a temperature gauge at the bottom of the cylinder). If the air blows in and out, it will be smooth, and you can feel the obvious air outlet feeling by hand.
Figure 3 shows the actual temperature of the air inlet of the drying cylinder should match the set temperature.
Figure 4 shows the air outlet to be smooth
4. Does the shot block have foaming?
Exit the shooting table to see if there is any foaming phenomenon in the rubber block. The normal production material should not have foaming phenomenon. If there is foaming, there is gas. Continue to dry or reduce the temperature of the cylinder;
Figure 5: The bubble is obvious, the material is overheated or not dried.
Figure 6: The rubber block is smooth and round and well dried.
5. Check the nozzle electric heating ring and barrel
Check whether the nozzle electric heating coil and barrel heating are normal, the strip can be tested on the nozzle, the strip is melted normally, the temperature is not normal when the strip is not reacted; the temperature of the barrel can be viewed, it can not be compared The value deviation exceeds 20 degrees;
6. Injection molding process
Check the key conditions affecting the silver streaks in the injection molding process, the loosening position is reduced as much as possible, the back pressure can be appropriately increased, the injection speed is increased and the two-way verification is reduced;
7. Mold problem check
Check the mold for oil leakage, air leakage, and water leakage;
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