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What Causes Flow Lines in Plastic Injection Molding?

By Jackie | November 22, 2019

Definition of Flow Lines:                                                Flow lines, also known as flow marks Linear marks on the surface of a molded product, which indicates the flow direction of the molten plastic. Injection Molding process 1.Insufficient Pressure / Holding Pressure                                                The injection pressure and the holding pressure are not high enough to press the solidified layer against the mold surface, thus leaving flow lines along the melt flow direction. Increase the injection pressure and the holding pressure, to press … Read more

What causes silver streaks or marks during injection molding?

By Jackie | November 21, 2019

Definition of silver Streaks: Silver streaks are also referred to as silver marks, which appear like burst blisters on the surface of injection molded parts, mostly in the shape arrows pointing to the gate. Causes of Silver Streaks: I. Equipment 1. The nozzle hole is too small, the material leaks or draws at the nozzle, or the barrel or the nozzle is obstructed, and the material decomposes due to the frictional heat caused by high-speed melt flow; 2. The barrel and the screw wear, or melt flow dead ends exist in the screw cap and collar, which are decomposed due to long-time heating. 3. The heating system is out of control, causing the temperature to be too high and resulting … Read more

What causes air bubbles or voids in injection molding?

By Jackie | November 20, 2019

According to the cause of air bubbles or vacuum voids , the solutions to the defects are described as below: (1) When the wall thickness of the product is large, the outer surface is cooled down faster than the center portion. Therefore, as the cooling progresses, the resin at the center portion is expanded toward the surface while shrinking, so that the center portion is insufficiently filled. This situation is referred to as air bubbles, to which the main solutions are: a) Determine the proper gate and runner size based on wall thickness. Generally, the height of the gate should be 50%-60% of the product wall thickness. b) A certain amount of supplementary injection material is retained until the gate … Read more

PC/ABS injection molding defects and solutions

By Jackie | November 18, 2019

Seven Common Defects and Solutions for PC/ABS injection molding Products Flow Lines The flow lines are caused due to the poor fluidity of the material. Unlike silver streaks, it is not caused by moisture or material decomposition, thus resulting in a different look. Solution: The flow lines can be eliminated by raising the material temperature so as to improve the fluidity. Appropriate increase of mold temperature and decrease of injection speed can also solve the problem.    Pitting The shrinkage cavities are caused by short shot in the mold cavity. Solution: Increase mold temperature and material temperature appropriately to improve material fluidity; extend the injection / pressure holding time, and raise the injection speed to improve the mold filling, or increase … Read more

How to Control the Dimensions Tolerance of Injection Molding Products

By Jackie | November 16, 2019

Due to the greatly varied market demands for molds and molded products, there are many kinds of changes and thus high requirements for us in such aspects as shape, size, material, structure and more, causing us many problems and difficulties in the production process of molds and products. How to effectively control the geometric dimensions of the mold and the product is just one of them. For different types of molds and products, there are different control techniques and methods for dimensions control. Personally, I usually start from the following aspects. Mold Design Control Firstly, we have to fully understand the technical requirements for the mold structure, material, hardness, and precision, etc., including whether the shrinkage rate of the plastic … Read more

PVC injection molding plastic resin

By Jackie | November 13, 2019

PVC plastic is a heat-sensitive material that features a poor injection moldability, for which the reason is that an excessively high melt temperature or an excessively long heating time easily causes PVC decomposition. Therefore, the key to molding the PVC products lies in the control of the melting temperature. The heat sources for melting the raw PVC material are usually from two aspects, i.e., the shear heating generated by screw motion and the resistance wire heating provided by the outer wall of the barrel, among which, the former is the main source, while the latter is mostly provided during machine operation. Due to the unsatisfactory heat transfer property of the PVC material, although the outer portion is heated, the inner … Read more

Mold steels P20,718 and H13 comparison

By Jackie | November 12, 2019

P20 Mold steel Overview The P20 Steel is a type of mold welding consumable, and the earliest is P20, followed by P20H and P20Ni. The P20 Steel is applicable to the production of molds for plastic materials, as well as those for diecasting low melting point metals. This steel material features great machinability, as well as mirror polishing properties.   Chemical composition: Element C Si Mn Mo Cr Ni (%) 0.28~0.40 0.20~0.80 0.60~1.00 0.30~0.55 1.40~2.00 0.80~1.20   How to Use: The P20 Steel is pre-hardened to 285-330HB (30-36HRC), which is equivalent to 618 of Sweden and GS-2311 of Germany. It can be directly used for molding, and boasts a great dimensional stability. Pre-hardened steel is able to meet the requirements … Read more

High impact polystyrene(HIPS)plastic injection molding resin material

By Jackie | November 11, 2019

HIPS(High impact polystyrene) is an impact-resistant polystyrene product created by adding butyl rubber particles to polystyrene. This polystyrene product is added with micron-sized rubber particles, and links the polystyrene and the rubber particles together by means of grafting. When subject to an impact, the tip end stress of the crack propagation is released by the relatively soft rubber particles. Therefore, the crack propagation is hindered and the impact resistance is improved.   HIPS Engineering Plastic Milky white opaque pellets, with a density of 1.05g/cm3, a melting temperature of 150-180°C, and a thermal decomposition temperature of 300°C. HIPS is one of the cheapest engineering plastics. When compared with ABS, PC/ABS and PC, the glossiness of the material is relatively poor, and … Read more

Steel hardness test method and conversion table

By Jackie | November 8, 2019

Steel hardness describes the properties of steels that resist deformation, indentation, penetration, and scratching. steel hardness is important because the inherent resistance of the surface to withstand friction or erosion by oil, steam, and water from injection molding process,there are several harness test method as below: 1.Brinell Hardness (HB) Press a hardened steel ball of a certain size (usually 10mm in diameter) against the surface of the material with a certain load (usually 3,000kg) for a period of time. After the load is removed, the ratio of the load to the area of indentation is referred to as the Brinell hardness (HB), measured in kg/mm2 (N/mm2).   2.Vickers Hardness (HV) Use a diamond square cone presser to penetrate into the surface of … Read more

TPE,TPR,TPU and TPV injection molding

By Jackie | November 6, 2019

Thermoplastic Elastomer (TPE) Domestically in China, it is usually known as “TPE”, basically referring to the styrene-based thermoplastic elastomer. The styrene-based TPE (known as TPS in foreign markets) is a copolymer of butadiene or isoprene and styrene block, so its performance is similar to that of SBR. Strengths: High elasticity of rubber and plastic injection moldability; environmentally friendly, non-toxic and safe; excellent coloring, smooth touch, weatherability, fatigue / temperature resistance, excellent processability, no need for vulcanization, and able to be recycled for cost reduction. It can be co-molded with such base materials as PP, PE, PC, PS and ABS, or molded separately. Weaknesses: The biggest problem with SBS and SIS is their low heat resistance – the temperature should not … Read more