pom成型不良及其对策.doc1.doc

pom成型不良及其对策 表8-1 成型不良的原因及其对策不良现象原因对策1 流痕1. 表面残留树脂通过浇口部分时发生的喷射纹。 最初的对策：防止产生喷射纹。 1. 降低初期的浇口通过速度。 2. 扩大浇口断面尺寸。 3. 改用流动性好的品级。 4. 提高树脂温度。 进一步的对策：即使发生喷射纹，也使之不留下痕迹。 5. 提高模具温度。提高保压力。 6. 改变浇口位置（缩短通过浇口后的直进距离）。 a. 将浇口改在树脂流与模芯碰撞的位置。 b. 将浇口改在厚度薄的部位。 c. 使用护耳式浇口。 2. 树脂通过拐角部位或厚度过渡部位时产生流速变化，因此而产生的流动纹路残留在表面。 1. 在拐角部位设置圆弧。 2. 在厚度变换部位设置平缓坡度或圆弧。 3. 气体排出不良 1. 强化排气口。 麻点、波纹1. 模腔内压不足，造成树脂对模腔密接不良。 1. 提高保压力，延长保压时间。 2. 加大流道和浇口的尺寸。 3. 提高模具温度，提高树脂温度。 4. 提高注射速度。 2. 排气不良 1. 强化排气口的沟槽。 2. 不过分提高树脂温度。 3. 充分干燥材料。 熔合纹1. 流动前端融合不良 1. 提高模具温度（在熔合纹部位埋设内装式加热器）。 2. 提高注射速度。 3. 改为流动性好的品级。 4. 强化熔合纹部位的排气口沟槽。 5. 设置熔合纹逃逸。 6. 修正部分厚度，改变向熔合纹部位流动的方式。 银纹1. 水分、分解气体等挥发成分或塑化时卷入的空气。 2. 由于模腔内的流动不平衡，造成气泡。 1. 充分干燥材料（100以上）。 2. 不过分提高树脂温度。 3. 提高螺杆背压。 4. 强化排气口沟槽。 5. 从流道排气。 3. PE、PP等异种材料的混入。 1. 对料筒进行充分清扫。 凹痕1. 由于壁厚部位或加强筋部位冷却不足、模腔内压不足，表面随着内部收缩而凹陷。 1. 降低模具温度。 2. 加大直浇口、流道和浇口的断面尺寸。 3. 提高保压力，延长保压时间。 4. 使缓冲量一直留到浇口封闭为止。 5. 将加强筋厚度与基体厚度之比改为1/3左右。 6. 去除厚度厚的部分。 表面剥离1. PE、PP等异种材料。 1. 对料筒进行充分清扫。 2. 剪切剥离。 1. 提高模具温度。 2. 降低注射速度。 3. 加大浇口的断面尺寸。 3. 含油型材料的油分离。 1. 降低初期的浇口通过速度。 2. 防止因塑化不良而卷入空气（料筒温度的控制）。 表面粗糙1. 模垢。 1. 模垢对策 a. 充分干燥材料（100以上）。 b. 不过分提高树脂温度。 c. 强化排气口沟槽。 d. 提高模具温度。 2. 模腔的清洗 a. 将模具镶块放入溶剂中进行超声波清洗。 2. 与模腔的密接不良。 1. 提高模具温度，提高注射速度。 2. 提高保压力，延长保压时间。 3. 加大直浇口、流道和浇口的尺寸。 4. 强化排气口沟槽。 真空空洞1. 当厚成型品表面固化快时，中心部位的树脂随着冷却、收缩而在表面产生凹陷，从而，造成中心部位充填不足。 1. 将浇口位置设在成型品最厚部位。 2. 加大浇口、流道、直浇口及喷嘴的断面面积，使之与成型品厚度协调一致。改浇口厚度为成型品厚度的5060%。 3. 提高保压力，延长保压时间。使缓冲量一直剩留到浇口封闭为止。 4. 确保逆止阀的功能，以免保压时发生倒流。 5. 降低注射速度。 6. 改用高粘度品级。 8Measures for Preventing Molding Defects Table 8-1 Causes of and measures against molding defects (1) Defect phenomenonCausesMeasures(1) Flow mark(1)Residual jetting pattern on the surface generated when the resin passes through the gate Primary measure : Prevent jetting.(1)Make initial running rate at the gate slow.(2)Enlarge the gate.(3)Change the resin to a higher flow grade.(4)Elevate resin temperature.Secondary measure : Prevent jetting pattern if jetting is generated.(5)Elevate the mold temperature. Increase holding pressure. (6)After the gate position (Make straight length short after resin passes through the gate).a)After the gate position to the section where flow comes in contact with the core.b)Move the gate position to a thin wall section.c)Use a tub gate.(2)Residual flow pattern on the surface due to flow rate change, generated when the resin passes corner sections or sections of nonuniform wall thickness (this wall thick wall) (1)Make comers rounded.(2)Make sections where wall thickness changes gently inclined and rounded.(3)Insufficient degassing (1)Enlarge the gas vent. (2)Pit marks,wrinkles (1)Insufficient adhesion of resin to cavity due to lack of inner pressure in cavity. (1)Increase the holding pressure and hold time.(2)Enlarge runners and gates.(3)Raise mold temperature. Raise material temperature.(4)Increase injection speed.(2)Insufficient degassing (1)Enlarge the gas vent.(2)Do not elevate resin temperature too high.(3)Dry the material sufficiently.(3) Weld mark(1)Insufficient melting adhesion of flow front (1)Raise the mold temperature (buried cartridge heaters in weld sections).(2)Increase injection speed.(3)Change the resin to a higher flow grade.(4)Enlarge the gas vent in welds.(5)Provide weld escape.(6)Change flow pattern into welds by adjustment of thickness.(4) Silver mark(1)Volatile components such as moisture and decomposed gas and air entrapped in plasticization.(2)Air pocket occurrence by unbalanced flow in cavity.(1)Dry the material sufficiently (100 or higher)(2)Do not raise the resin temperature to high.(3)Increase screw back pressure.(4)Enlarge gas vent.(5)Degas from runners.(3)Contamination of foreign materials such as PE,PP. (1)Purge sufficiently from the cylinder. Table 8-1 Causes of and measures against molding defects (2) Defect phenomenonCausesMeasures(5) Sink mark(1)Surface sink with shrinkage of inner part due to insufficient cooling of thick wall and rib section and insufficient inner pressure in the cavity.(1)Lower the mold temperature.(2)Enlarge sprue, runners, and gates.(3)Raise holding pressure. Prolong holding time. (4)Keep cushion amount of material until gate seal. (5)Minimize the rib thickness to approximately one-third of the base thickness.(6)Decrease the thickness of thick wall sections.(6)Surface delamination (1)Contamination of foreign materials such as PE,PP.(1)Sufficiently purge the material from the cylinder. (2)Shear delamination(1)Raise the mold temperature.(2)Lower the injection speed.(3)Enlarge gates.(3)Separation of oil from oil filled grades(1)Decrease initial gate passing speed.(2)Prevent air trapping by poor feeding through screw during plasticization (control of cylinder temperature)(7)Surface roughness (1)Mold deposit(1)Measures against mold deposita)Sufficiently dry the material (100 or higher).b)Do not raise material temperature too high.c)Enlarge gas vent.d)Raise mold temperature.(2)Cleaning cavitiesa)Ultrasonic cleaning of core in a solvent.(2)Insufficient adhesion to cavity(1)Raise mold temperature. Increase injection speed. (2)Increase holding pressure. Extend holding time. (3)Enlarge sprue, gates, runners.(4)Enlarge gas vent grooves.(8) Vacuum void(1)Inner molten resin is pulled to surface due to fast solidification of surface layer, then voids are occurred in inner section.(1)Locate the gate at the thickest section of molding.(2)Enlarge gate, runner, sprue, and nozzle in an accordance with thickness of molding.Increase gate thickness to