塑膠材料的種類 塑膠在模具內的流動模式 流動性質的影響 溫度性質的影響

Presentation on theme: "塑膠材料的種類 塑膠在模具內的流動模式 流動性質的影響 溫度性質的影響"— Presentation transcript:

1 塑膠材料的種類 塑膠在模具內的流動模式 流動性質的影響 溫度性質的影響
Lesson 3. 材料的選擇對製程的影響 塑膠材料的種類 塑膠在模具內的流動模式 流動性質的影響 溫度性質的影響

2 塑膠材料的種類 非結晶性 Amorphous 在成型過程中分子鏈的結構不變 半結晶性 Semi-crystalline
冷卻時分子鏈結構會壓縮，加熱後變成非結晶性

3 塑膠的流動模式 熔融塑膠 噴泉流區域 Fountain Flow Region 凝固層 Frozen Layer 模具 Mold Wall
If you fill the mold too slowly, the mass of the plastic is no longer a major factor, but it freezes more during filling, thereby lowering the viscosity and restricting the flow due to a thicker frozen layer at each mold wall surface.

4 塑膠的黏度 黏度模型 Viscosity Models Newtonian Power Law Cross WLF     . 4

5 塑膠的黏度 定義: 流動時的抵抗力 黏度會隨著剪切率或是溫度的提高而降低 Increasing temperature High
Shear Rate (1/s) Viscosity (Pa-s) Low resistance to flow High Material Viscosity Water 10 Polymer 10,000 Glass Polymer Viscosity Polymer viscosity is the driving factor for polymer flow simulation. Definition Viscosity is the polymer’s resistance to flow. It is the ratio of the shear stress to the shear rate. It has the units of Pa.s (pascal.seconds) or poise. It is measured using a capillary rheometer. The data is fit to form scientific equations which represent the flow characteristics. Material Comparisons Let me give you an idea of how the polymer flows compared with other materials. Water has a viscosity of 10 poise and molten glass has a viscosity of 1E20 poise. Polymers fall in between these materials. They range from 2 to 3000 poise. 8

6 熔融指數 在等溫及等剪切率下進行 不同的塑膠材料會採用不同的試驗條件 Higher Pressure Low MFR Material
High MFR Material Lower W Flow properties such as melt flow rate (MFR) and viscosity fall into this category. Can someone briefly explain how the MFR is determined? (get feedback from audience and then explain if necessary) The plastic is heated to a certain temperature inside a capillary die with a specific weight placed on top of the molten plastic. However much plastic flows through the die in a ten minute period (weighed in grams) is the melt flow rate. What if I have a low MFR vs. a high MFR; how does this influence pressure? Can you compare two materials such as ABS and PP based on MFR? Why or why not? (MFR test settings are different based on what resin you are testing; for example, the temperature and possibly the weight would be different for ABS than for PP.)

7 壓力與黏度的關係 黏度會隨著壓力升高而增大 黏度與溫度及剪接率也有關 黏度與薄殼（Thin-Wall）產品的應用息息相關 還有…
Polymer Viscosity Polymer viscosity is the driving factor for polymer flow simulation. Definition Viscosity is the polymer’s resistance to flow. It is the ratio of the shear stress to the shear rate. It has the units of Pa.s (pascal.seconds) or poise. It is measured using a capillary rheometer. The data is fit to form scientific equations which represent the flow characteristics. Material Comparisons Let me give you an idea of how the polymer flows compared with other materials. Water has a viscosity of 10 poise and molten glass has a viscosity of 1E20 poise. Polymers fall in between these materials. They range from 2 to 3000 poise. 8

8 材料對射出壓力及鎖模力的影響 不同的材料需要不同的射出壓力 不同的材料在黏度上的差異極大 PMMA
Hi Viscosity PP Low Viscosity Fill Time (sec) Inj. Pressure and Clamp Force Low MFR 不同的材料需要不同的射出壓力 不同的材料在黏度上的差異極大 Material and Injection Pressure The type of material used can have a tremendous affect on the required injection pressure. Some materials flow quite easily while others are very hard to process. This graph shows the required injection pressure to mold a specific part. The two curves represent two different materials and the required pressure to mold the same geometry. The PP requires less pressure than the PMMA material and has a larger window for appropriate fill times. 14

9 塑膠的溫度特性 Cp - specific heat capacity 吸熱的能力 k - thermal conductivity
傳熱的能力 8

10 材料對冷卻時間的影響 冷卻時間與熱傳導係數、密度及比熱有關 這些性質總和就是材料的熱擴散係數 “thermal diffusivity”
還有… Density (p) Specific Heat (Cp) Thermal Conductivity (k) Cooling Time Change

11 PVT特性 p – 壓力; v – 比容; T – 溫度 描述塑膠如何隨著壓力及溫度的變化而發生體積上的變化 Pressure
在充填及保壓的階段，塑膠隨著壓力的增加而膨脹 在冷卻的階段，塑膠隨著溫度的降低而收縮 Pressure Increases Specific Volume Temperature