Original|Meite Polymer Nova
The defects of ordinary injection molded parts mainly include appearance, size, and skills. Appearance is closely related to injection molding conditions, size is related to mold design and material shrinkage, and skills are mainly related to resin type. This article mainly deals with appearance defects and suggests measures to improve the injection molding process.1. There is a dark area near material head.
This means that there is a clear ring around head of material. If a center flap is used, this will be center circle and side flap will be a concentric circle. This phenomenon mainly occurs when processing materials with high viscosity. such as PC, PMMA and ABS. If injection speed is too high, flow rate of molten material is too high and viscosity is high, and material on surface layer near die is easily dislodged and penetrated. And these dislocations will appear in outer layer in form of a halo.
1. If flow rate is too high, multi-stage injection is required, such as slow-fast-fast; 2. The temperature of melting material is too low, and barrel treatment temperature should be 3. The mold temperature is insufficient or mold is not set Warm up machine, set it, and increase mold temperature to set temperature.2. There are dark areas in material flow area with sharp edges.
The surface of product is clean, down to sharp edges. However, after a sharp edge, dark areas appear on surface and they are rough. The main reason is that injection rate is too high and flow rate is too high, especially for highly viscous melts. The surface layer is easily displaced and infiltrated behind bevel and sharp edge, resulting in dark areas and roughness.
The main reason is that liquid front velocity is too high and a multi-stage injection, such as fast-slow injection, can be applied to reduce injection speed before liquid front reaches a sharp edge.Three, uneven surface gloss
This means that under a uniform mold surface material, surface of product is dull and uneven. The surface of injection molded product is usually a copy of surface of mold, and surface roughness of product depends on viscosity of thermoplastic resin and setting of injection molding process. Therefore, due to roughness of surface of mold, surface of product will appear dull, dark or smooth.
1. The holding pressure is insufficient and holding pressure must be increased; 2. The holding time is not enough, and holding time needs to be increased; 3. The mold temperature is too low or not, and mold temperature should be increased 4. The melt temperature is too low, barrel temperature must be increased accordingly.Fourth, break
There are round or oblong bubbles inside product, which are usually found in products with thicker walls. This is usually because air in mold is surrounded by molten material flowing into cavity and exists in a thicker wall.
1. The holding pressure is too low, which must be increased accordingly; 2. The holding time is insufficient and timei excerpts must be increased accordingly; 3. The mold temperature is too low, and mold temperature should be increased accordingly 4. The melt temperature is too high, barrel temperature must be reduced accordingly.Five, bubbles
There are many bubbles on surface and inside product, which differ from voids (only in thickest part of product). Bubbles mainly occur in heat-sensitive materials that must be processed at high temperatures. If molding temperature is too high, molecular splitting will cause material to decompose, and melt will undergo thermal decomposition, resulting in bubbles.
1. The temperature of molten material is too high, so it is necessary to reduce temperature of barrel and speed of screw; 2. The material stays in drum too long, so a smaller diameter drum should be used.Six white dots
There are unmelted particles near tip. Due to short production cycle and injection molding of thin-walled products, injection machine must perform plasticizing at a high screw speed, so that residence time of molten material in screw is very short, and for plasticizing and generally injection molding of polyethylene and polypropylene is easy to produce.
1. The melting material temperature is too low, and barrel temperature must be increased accordingly; 2. The screw speed is too high, and material is plasticized and melted too late, so screw speed must be reduced accordingly; 3. The auger back pressure is too low, so increase auger back pressure; 4. The cycle time is too short, material remains in cylinder for insufficient time, and melting is not enough, so cycle time must be increased accordingly.Seven, gray and black markings
This usually occurs next to gate, in middle of track and in part away from gate, and can only be seen in transparent products commonly seen in PMMA, polycarbonate and polystyrene. If dosing process starts too early, air trapped in pellets in feed area of the screw does not exit feed port, air will be forced into melt, and pressure in feed area is too low to move screw. air at back, air squeezed into molten material in barrel will cause gray and black spots on product.
1. The auger back pressure is too low, increase auger back pressure accordingly; 2. The set temperature in supply zone is too high and reduce it accordingly; 3. The auger speed is too high and auger speed should be reduced accordingly.Eight, there are gray and black spots near material head.
Silver or black marks appear on surface of product at center of gate or nearby point. This is another veeand air bubbles that are squeezed out and compressed. When pressure drop of screw is too high and speed is too high, melt in front of screw head will be released too much, which will create a negative pressure in melt. and when temperature is too high. In this case, air bubbles form in melt, and these air bubbles will be compressed again at a later injection stage, resulting in formation of lines.
1. The pressure drop of auger is too high and needs to be adjusted accordingly 2. The depressurization rate of auger is too high and should be reduced accordingly 3. The melt temperature is too high, and barrel temperature, auger backpressure and auger speed need to be reduced.Nine, polar pattern
Referring to sprue injection, dark gray melt jet is immediately covered by subsequently injected molten material after lightly touching mold wall and partially or completely hidden within product.
1. The injection speed is too high, so reduce it accordingly; 2. The injection speed is single-stage, use multi-stage injection, such as slow-fast; 3. Melt temperature too low, increase cylinder temperature. 4. Mold temperature at gate area. If it is too low, increase it accordingly.Ten, cool head
This means that a piece of cold material has stuck or stuck to surface near head of material. The main reason is that temperature control around nozzle of machine or hot runner is impractical, which results in melt being cooled in nozzle before injection and finally injected into cavity.
1. Nozzle temperature is too low, increase it accordingly and reduce nozzle contact area to prevent temperature loss 2. Hot runner temperature is too low, increase it accordingly.Eleven, write down pattern
Deep grooves are visible throughout direction of material flow and even at end of flow channel. The most common products are made of PC and ABS. Under conditions of low injection speed, melt in contact with mold surface solidifies too quickly and resistance is too high, which will cause distortion at liquid front, and solidified material of outer layer will not fully contact mold cavity, but will form waves.
1. The injection speed is too low, increase it accordingly; 2. The temperature of material is too low, increase temperature of cylinder and corresponding screw back pressure; 3. The mold temperature is too low, increase it accordingly; 4. The holding pressure is not enough, increase it accordingly.Twelve, seam
Also called a weld line, when front ends of fluids meet, intersection line. It is impossible to completely avoid debugging a process at all, which is possibleAbout to do is to reduce brightness or move it to an inconspicuous place.
1. If injection speed is too low, increase it accordingly; 2. If temperature of mold is insufficient, increase it accordingly; 3. If temperature of material is insufficient, increase cylinder temperature accordingly; pressure is insufficient, increase it appropriately and switch the holding pressure as soon as possible.Thirteen, watermarks
There are very long silver threads on surface of product, and direction of hole coincides with direction of material flow. PA, ABS, PMMA, SAN and PBT, which are easy to absorb water, easy to absorb water. When particles are melted, moisture on surface of particles turns into vapor to form bubbles. texture.
The moisture content of material is too high and needs to be dried.Fourteen, overflow edge
A thin burr appears on parting line or sealing surface of mold. The main reason is that clamping force of machine is insufficient during injection process and pressure holding, mold cannot be locked and sealed, and molten material will overflow.
1. Insufficient mold clamping force, increase it accordingly 2. Injection speed is too high, reduce it accordingly, and use multi-stage injection: fast-slow 3. Holding pressure switching is late, and it should be earlier accordingly; 4. The melt temperature is too high, reduce cylinder temperature accordingly; 5. If mold temperature is too high, reduce it accordingly; 6. If holding pressure is too high, reduce it accordingly.
Recommended Reading: Causes and Solutions for Flash in TPE Injection Molding15. Warping
Product rotates or curls for a while after demolding or cooling. During demoulding, depending on shape of product, stresses will cause different degrees of deformation. like polyethylene, polypropylene, and polyoxymethylene are more prone to shrinkage and deformation than non-crystalline materials such as polystyrene, ABS, PMMA, and polycarbonate.
1. The mold pressure is too high, reduce holding pressure accordingly and switch holding pressure in advance; 2. The mold temperature is too low, increase it accordingly; 3. Injection speed is too low. increase it accordingly 4. The melt temperature is too low, increase barrel temperature properly and increase screw back pressure.
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