塑胶模具排气系统设计Venting System Design

排氣系統設計Venting System Design

徐昌煜

Charles Hsu

2003. 8. 25.

排氣系統的合理化

蔡毓斌

•注射的過程中，模穴(型腔)的空氣必須順利排出，塑料才能順利充填。

•排氣不良時，產品(制件)表面會有困氣造成的氣泡、甚至是焦痕。

•澆注系統的設計不當時，排氣易生問題。•產品(制件)造型設計不當時，排氣問題難解。

排氣設計檢查點

蔡毓斌

•檢查模穴(型腔)充填末端是否能夠順利排氣（可以CAE模擬預測最後充填位置）

•可利用澆口位置或/和尺寸的變更，調整最後充填位置。

排氣位置

•在充填末端要加排氣(充填末端可用CAE模擬預測)

•排氣位置可藉產品(制件)設計和澆口/流道設計而改變

滑雪靴扣件設計

焦痕

組立圖

3D 充填模式

Y-Z 剖面

造型對排氣的影響

原始設計修正設計

材料：透明PC

3D 充填模式

利用澆口尺寸控制排氣位置

3D Model

分析軟體：Moldflow MPI 4.0

LCD TV

喇叭飾板的設計

排氣

Vent

為何排氣仍然還是一個問題？

Why venting is still a problem ?

因為降低射速，讓積風(氣穴)有較多的時間逃氣，是一件太容易的事。但是…

Because it is too easy to slow down the injection speed and give the trapped air more time to escape. But ...

排氣

Vent

射速一降，熔膠溫度很快降低，射壓必須提高，殘餘應力隨之提高，翹曲的可能性增加。如果想藉提高料溫，以降低射壓，料溫必須升得很高，這樣又會引起塑料劣解(降解)。

When injection speed is lower, melt temperature goes down very fast, injection pressure has to be increased, residual stress is increased and the possibility getting warppage becomes higher. If one would like to increase barrel temperature to reduce the required injection pressure, the barrel temperature has to be increased to a quite high level and polymer degradation would be induced.

排氣

Vent

高料溫和高射壓都說明充填系統有了流動的問題Both high barrel temperature and high injection pressure are indications of flow problem in the filling system.

排氣

Vent

我們常發現: 射速提高時，塑料表現得更為出色。

It is quite common that material performs better when it is injected faster.

最適化螺桿速度充分運用摩擦熱，將塑流保持在最佳狀態。許多充填和翹曲的問題也就迎刃而解。

An optimized ram speed profile fully uses the friction heat to keep the best flow characteristics, which corrects many of the fill and warpage problems.

排氣

Vent

有了適當的排氣，射速可以提高，充填和保壓可達良好狀態，不須過度增加料管和噴嘴的溫度。

With proper venting, the injection speed could be increased to achieve good fill and pack conditions, without having to raise the barrel and nozzle heats, improperly.

排氣系統

Venting System

高射速使得排氣更為重要，以防氣困引燃。典型的分模面(分型面)排氣是0.01~0.04mm深、5mm寬，甚至沿分模面(分型面)全周長排氣。在型心銷、頂出銷(推杆)、肋和螺柱處排氣也是很有用的。流道末端的充分排氣以及對模穴(型腔)抽真空都可以減輕模穴(型腔)排氣的負荷。Faster injection rates will make gas venting even more critical to prevent gas-entrapment burning. Vent dimensions are typically 0.01~0.04 mm deep by 5 mm wide (or even wider to be a perimeter vent). It is useful to vent core pins, as well as ejector pins, ribs and bosses. Vent at end of each runner and vacuum evacuation of the cavities are able to reduce the cavity-vent-loading.