注塑气辅技术指南

- Reduced secondary operations

-

减少二次操作

Dimensional Stability

尺寸稳定性

?

Uniform Packing from Within the Cavity Can Result in:

?

型腔内保压一致可：

- Reduced stress within part

-

降低产品的内应力

- Reduced part warpage

-

减少产品的翘曲

- Reduced sink marks Enhance

-

减少凹痕

Enhance Flow/Tool Design

提高流 动

/

工装设计

?

Tool Design Freedom Can Be Obtained by:

?

以下方法可提高工装设计自由度：

- Replacement of external hot and cold runners with interior gas channels

-

将外部的冷热流道替换为内部的气道

Several variations of gas assist molding are used by the plastics industry. They are differentiated by the

method and location of the gas injection into the polymer melt. The gas can be injected through the

machine nozzle, runner system, sprue, or directly into the mold cavity under a constant pressure or a

constant

volume.

Some

gas

injection

methods

are

covered

by

one

or

more

process

patents.

An

appropriate licensing agreement must be obtained prior to utilizing a specific type of gas assist molding

process.

目前，在塑料业使用着几种不同的气辅成型 。它们的不同之处是由不同的气体注入方法和位置

产生的。气体可通过机器喷嘴、流道系 统、浇口、或通过恒定压力和体积直接注入模具型腔

中。一些气体注射法有一种或更多的 专利保护。在使用一种明确的气辅成型工艺前应获得一份

合适的许可证。

气体辅助技术使采用

CY COLOY

树脂制成的

C&A

塑料注塑 成型成汽车上刹车块的操作变得更简

易，同时还增加了零件的坚固度。

< br>

Process Mechanics

过程机制

Stages of Gas Assist Molding

Gas

assist

molding

can

be

divided

into

three

stages:

resin

injection,

primary

gas

penetration,

and

secondary gas penetration (See Figure 1).

气辅成型的步骤

气辅成型可分为

3

个阶段：树脂注入，初始气体穿透和二次气体穿透（见图

1

）。

Stage 1: Resin Injection

–

The polymer is injected into the mold as a short shot or partially packed cavity.

步骤

1

：

树脂注入

-

聚合物作为

“

短射

”

被注入到模腔中。

Stage 2: Primary Gas Penetration

–

Gas

is

introduced

into

the

molten

core

forming

a

bubble.

The

gas

bubble

displaces

some

of

the

molten core, pushing it into the unfilled cavity and completing the mold filling

步骤

2

：初步气体穿透

—

气体被注入到熔芯中形成气泡。气泡占据了熔芯的一部 分，并将树脂推入到未填充的型腔中

从而完成型腔的填充。

Stage 3: Secondary Gas Penetration

–

Secondary gas penetration begins at the end of the filling stage when the polymer has reached the end

of the mold.

The gas bubble extends as the part cools and the material shrinks. The extra cavity volume created as

the material shrinks is taken up by the gas bubble. The pressure in the bubble also provides packing of

the part during secondary gas penetration.

步骤二：

—

在聚合物到达模具末端完成填充时，二次气体穿透过程随之开始。当零件冷却和材料 收缩

时，气泡将扩张。当材料收缩被气泡占据时，额外的型腔空间就会随之产生。在二次 气体穿透

期间，气泡中的压力提供了产品的保压。

Stage:

阶段，

melt:

熔体

, short shot:

短射，

melt front:

熔体前端，

solid layer

：固化层，

primary gas

penetration

：初始气体穿透，

defo rming

melt:

未成型熔体，

molten

layer

：熔体层，

gas

front

：气

体前端，

hollow core:

气核，

secondary gas penetration:

二次气体穿透

图

1

：

气辅成型的步骤

气体进入阻力最小的路径

The gas bubble propagates within the molten core along the path of least resistance through the cavity.

This

path

is

determined

by

lower

pressures

and

higher

temperatures.

Lower

pressure

areas

are

determined

by

melt

front

location,

cross-sectional

area,

and

position

of

the

polymer

injection

gate.

Higher temperature areas occur in centers of thick sections, high- shear regions, and as a result of mold

temperature variations.

Higher temperatures also result in lower melt viscosities. During primary gas

penetr

ation, the gas bubble can only penetrate into areas of the part, where displaced polymer can flow

easily to unfilled sections of the mold. The melt pressure variation within the cavity usually dominates

the bubble propagation during primary gas penetration.

气泡在熔核内沿着阻力最小的路径通过型腔不断扩 张。这个阻力最小的路径取决于低气压高温

度。低气压区域取决于熔体前沿位置，

截面区域和聚合物注入浇口的位置。高温区域发生在厚

截面

h

和高剪切速率区以及模温变化的结果。高温也 可导致熔体低粘度。在初始气体穿透过程

中，气泡仅能穿透零件的一些部位，在这些部位 聚合物可容易地流到模具的未填充部位。

Packing Via Gas Assist

通过气辅保压

During

the

packing/hold

phase

of

processing

there

will

be

some

additional

gas

penetration

resulting

from shrinkage as well as compression of the molten polymer.

在保压过程中，会出现额外的气体穿透，这是由收缩和熔融的聚合物压缩导致的。

The method of packing by gas

assist molding offers some intrinsic advantages over

that of injection

molding:

?

More uniform packing from within the cavity via the gas bubble

?

Longer duration of packing (not limited by gate freeze-off)

通过气辅成型保压的方法比传统的注塑成型 保压方法有着本质上的优点：

?

保压一致性更高

?

保压时间更长

The pressure during the packing stage in gas assist molding is provided by the gas bubble and not by

the

machine

screw

as

in

traditional

injection

molding.

The

pressure

is

uniform

through-out

the

gas

bubble, and the bubble is distributed throughout the cavity. This means that the cavity is maintained at

a nearly uniform pressure during solidification. In traditional injection molding, non-uniform stresses

result because the pressure cannot

be distributed uniformly throughout

the high viscosity resin.

This

point is illustrated in Figure 2.

气辅成型中保压阶段的气压是由 气泡提供的，而是向传统注塑成型那样由注塑机提供的。通过

气泡，这个气压是均匀的而 且这个气泡是充填整个型腔的。这就意味着在熔体凝固过程中，型

腔维持着一个几乎一致 的气压。在传统的注塑成型中，由于通过高粘性的树脂，气压不能均匀

的被分布从而导致 不一致的应力。

有关这点的说明，见图

2

Injection molding:

注塑成型，

pressure:

压力，

flow length:

流道长度，

gas assisted mo lding

：气辅

成型，

nozzle :

喷嘴

图

2.

Packing internally with gas assist also increases the allowable effective hold time during solidification.

Packing

via

conventional

techniques

is

susceptible

to

gate

while

gas

pressures

may

be

maintained throughout the cooling time.

气辅保压也增加了凝固过程中的有效保压时间。

Process Methods

工艺方法

Process Sequence

工艺顺序

The gas assist molding sequence is similar to standard injection molding with the addition of the gas

injection stages:

1. Mold closes and reaches clamp tonnage.

2. Resin is injected into the mold cavity as a short shot or with reduced packing (no cushion).

3. Gas is introduced into the hot melt.

4. Gas pressure is maintained during the cooling cycle.

5. Gas pressure is released.

6. Mold opens and part ejects.

气辅成型顺序与标准注塑成型相似，只是外加了一个气体注入阶段：< /p>

1.

合模并达到锁模力

2.

通过短射将树脂注入到模腔中。

3.

将气体注入到熔体中

4.

在冷却周期中气体保压

5.

释放气压

6.

开模，零件被顶出

This

sequence

will

not

typically

add

cycle

time

to

the

process

since

the

added

steps

occur

simultaneously during the cooling cycle. Step four replaces, or is coupled with, the packing phase of

standard injection molding.

这个顺序不会增加工艺的周期时间，因为增加的步骤在冷却中同时发生。

Gas Injection Location

气体注入位置

Gas assist methods vary in the location along the melt stream in which the gas is introduced. Gas may

be introduced to the melt at the machine nozzle, the runner, and/or directly into the mold cavity.

气辅方法的不同处在于气体注入的位置。气体可能 通过机器喷嘴、流道和

/

或直接注入模腔中。

< br>

Machine Nozzle

机器喷嘴

Gas introduced via a special shut-

off nozzle attached to the barrel of the press is known as “through

-

nozzle” gas assist molding (See Figure 3).

通过一个安装在料筒上的截流式喷嘴将气体注入。（见图

3

）

Part

：零件，

N2 IN:

氮气进气，

N2 out via recovery:

氮气排出，通过恢复，

N2 out at sprue break:

氮气排出，通过浇口

Figure 3. Gas Injection Through the Machine Nozzle.

图

3

：经过机器喷嘴注入气体

In this method, all gas channels must be connected to the sprue or gate since the gas originates from

one point. Hot manifold systems are not suggested for this process because polymer in the manifold

will be displaced by the gas, possibly resulting in inconsistent shot sizes and splay. In some cases, hot

manifolds

may

be

eliminated

from

the

tool

design

by

designing

flow

runners

in

the

part

and

then

hollowing them out to create gas channels. A shut-off portion of the nozzle is suggested to help prevent

gas from penetrating into the barrel.

在这种方法中，

所有的气道必须与浇 口或注入口相连接，因为气体是从一个点注入的。对于这

种方法不建议使用热流道系统， 因为在流道中的聚合物将被气体代替，可能导致不一致的射入

尺寸和扩张。在一些情况中 ，通过在零件中设计流道，排除工装设计中的热流道，然后将他们

掏空产生气道。截流式 喷嘴有助于防止气体进入料筒。

Resin Delivery System

树脂运送系统

Gas introduced into the runner system or the sprue bushing via gas pins is kno

wn as “in

-

runner” gas

assist molding (See Figure 4). If the part is direct-sprue gated, the channels must all originate from the

sprue.

This

method

results

in

hollow

runners

and/or

sprue

which

can

help

to

reduce

the

amount

of

regrind. Hot manifold systems

are not suggested for this process either, because the polymer will be

displaced by the gas in the manifold, possibly resulting in inconsistent shot sizes and splay. A shut-off

nozzle is suggested to help prevent gas from penetrating into the machine barrel.

通过气针将气体注入流道系统或浇口（见图