Injection Molding Defects And Solutions

Injection Molding Defects and Solutions -- Whitening 2025-10-20

Whitening (Stress Whitening): During demolding, excessive ejection force is applied to the surface areas around ejector pins or grooves. Due to forced demolding, high internal stress develops in these regions, sometimes causing deformation. Whitening is a sign of stress cracking. Materials such as ABS and HIPS are particularly prone to this phenomenon.

Injection Molding Defects and Solutions -- Stains 2025-10-20

Stains, Impurities, and Foreign Substances The plastic material is impure or contaminated. 23.1 Causes 23.2 Solutions 23.1.1 Raw materials, pellets, or pigments are impure. 23.2.1 Replace the raw materials, dyes, or pigments. 23.1.2 The plastic has decomposed or deteriorated. 23.2.2 Adjust the processing conditions to prevent material decomposition. 23.1.3 The barrel and hopper are not clean. 23.2...

Injection Molding Defects and Solutions -- Poor Transparency 2025-10-20

Poor Transparency: Due to poor contact between the molten material and the mold surface, tiny pits appear on the surface of the molded part, causing light scattering. Alternatively, the mold surface may not be sufficiently polished, resulting in decreased or uneven transparency in transparent products. 22.1 Causes 22.2 Solutions 22.1.1 Low mold temperature or low material temperature, causing poor...

Injection Molding Defects and Solutions -- Dull Surface 2025-10-20

Dull Surface (Lack of Gloss): Due to poor mold surface finish, inadequate contact between the molten material and the mold surface, or improper material and mold temperatures, the molded product fails to exhibit the natural gloss of the resin. Instead, the surface appears whitish, cloudy, or dull. 21.1 Causes 21.2 Solutions 21.1.1 Poor mold surface finish; presence of scratches, moisture, or oil c...

Injection Molding Defects and Solutions -- Unmelted Lumps 2025-10-20

Cold Slugs / Unmelted Lumps: Unmelted or insufficiently plasticized material enters the mold cavity along with the melt flow, causing hard plastic lumps to become embedded inside or on the surface of the molded part. 20.1 Causes 20.2 Solutions 20.1.1 Material temperature, mold temperature, and nozzle temperature are too low, or injection speed is too slow. 20.2.1 Properly increase the material, mo...

Injection Molding Defects and Solutions -- Gate Sticking 2025-10-20

Gate Sticking: The gate sticks in the gate sleeve due to mechanical resistance inside the sleeve, insufficient cooling, or a malfunction of the pull pin. 19.1 Causes 19.2 Solutions 19.1.1 Insufficient runner draft angle, no mold release agent used. 19.2.1 Increase the runner draft angle and apply mold release agent appropriately. 19.1.2 Cooling time too short, nozzle and fixed mold temperatures to...

Injection Molding Defects and Solutions -- Plastic Brittleness 2025-10-20

Plastic Brittleness: Due to poor plastic properties, obvious orientation, high internal stress, and poor structural design of the plastic part, the strength decreases, making it prone to cracking (especially along the flow direction of the material). 18.1 Causes 18.2 Solutions 18.1.1 Material degradation, depolymerization, hydrolysis, or poor-quality pigment (e.g. deterioration). 18.2.1 Replace ra...

Injection Molding Defects and Solutions -- Uneven Color or Discoloration 2025-10-17

Uneven Color or Discoloration: Uneven color on the surface of a plastic part may result from poor dispersion of pigments or fillers, or from discoloration of the plastic or pigments. If the entire plastic part shows uneven color, it is usually caused by poor thermal stability of the plastic. When the color is uneven at weld lines, it is related to the nature of the pigment. Causes Solutions ...

Injection Molding Defects and Solutions -- Ejection Defects 2025-10-17

Poor Demolding / Ejection Defects: Poor demolding occurs when the mold structure is unreasonable, manufacturing precision is insufficient, or overfilling makes it difficult to eject the part. It can also cause the part to be scratched, stretched, or deformed after ejection. 16.1 Causes 16.2 Solutions 16.1.1 Mold surface not smooth. 16.2.1 Polish the mold to meet surface finish requirements; reduce...

Injection Molding Defects and Solutions -- Cracks 2025-10-17

Cracks: Cracks occur when poor part design or inferior plastic material properties cause high internal stress, uneven cooling, poor demolding, or other defects. These stresses lead to cracks forming at stress concentration points or near the gate. Under overload or the influence of solvents, these cracks may propagate, resulting in part failure. No. Causes Solutions 15.1.1 Low material temperature...

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