Runners and Gates

8/8/2019 Runners and Gates

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RUNNERS AND

Information contained in this presentation is to be used by Seneca College Students while

registered at the College Only and can not be reproduced.


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All injection mould (plastic and die-cast)

have Runners.

A runner is a channel which connects the

gate(s) of a mould to the sprue.

gate(s) of a mould to the sprue.


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When ever possible runners should be:

1. as short as possible

2. have the same length for multi-runner

Branch runners are employed when it is

impossible to generate a ideal runner

leading from the sprue.


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http://www.injectionplasticmold.com/wp-content/uploads/2009/01/naturally_balanced_runner6.gif


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Runners must always be polished.

Why is polishing important on the runnerif the runner (cold) is always trimmed off.

Runners must be large enough to carry

sufficient material to the cavity of the

mould.

Runner should always be as small aspossible. Why?


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The two most frequently used runner

shapes are:

1. trapezoidal

2. round

http://www.injectionplasticmold.com/wp-content/uploads/2009/01/cross_sectional_runner_p1_6.gif


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Trapezoidal:

+ve. Easy to machine

-ve. Increased surface friction

Round:+ve. Reduced surface friction

Increased volume

-ve. Difficult to machine into both sides

of the mould


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Gate:

The narrow and shallow portion of the

runner as it enters the cavity.


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It is important that gates be located

where they are easily trimmed and not

easily seen on the finished product.

Gates should be located so that theflowing material hits what?

The opposing surface as soon as possible

after entry into the cavity.


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Note, material entering into: thick

section, ribs, parallel wall sections or anyopen area will result in visible shrinkage

marks on the finished product.

Gates are made as small as possible.

piece part from the runner and sprue.


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Small gates also promote proper flow of

molten material prevent strains and weld

marks.

Weld marks normally result from poor

gating and venting. What is a weld mark?


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http://www.injectionplasticmold.com/wp-content/uploads/2009/01/cross_sectional_runner_p1_6.gif


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For asymmetrical mould gravities designers

cannot rely on radially spaced runners and

gate.

Desi ners must make chan es to the ates

to allow the cavities to fill uniformly.

How do you think this is achieved?


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Cold Slug Well

When material is injected into the mould

the leading of the injected material issomewhat cooler.

Why is this a problem?

Cold Slug well is located opposite the sprue

to trap this cooler material allowing the

hotter material to fill the cavity of the

mould.


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Cold Slug wells are also found at the end ofbranch runners.


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Sprue Puller

An undercut is normally machined into

either the cold slug well or the ejector pinimmediately under the cold slug.

What is the purpose of this undercut?

This undercut will pull the sprue out of the

sprue bushing, thus allowing the mould to

cycle again.


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http://www.globalspec.com/reference/50137/203279/Chapter-17-Runner-and-Gate-Design


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Fan gate:

A fan gate is used with acrylic material. This

type of gate improves the flow of acrylicmaterial by spreading the material into the

cavit .

http://2.bp.blogspot.com/_oF_1Qcfku_w/SAjITuV5_AI/AAAAAAAAAeQ/VzC1438MwW8/s400/faN%2BGA

T3%2Bcopy.jpg


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Ring gate:

This type of gate is used to feed material

into long cylindrical parts with thin wallsection.

http://www.injectionplasticmold.com/wp-content/uploads/2008/12/internal_ring_gate6.gif


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Disc gate:

The disc gate is

used to fill a cavityfrom a hold

located inside the

part. The materialfrom the sprue

spreads out evenly

and all sections of

the cavity are filled

simultaneously.

http://2.bp.blogspot.com/_oF_1Qcfku_w/SDBDRVUq8YI/AAAAAAAAAfQ/ZnqIINQzXdI/s400/disc-gate.jpg


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Direct gate:

This gate allows the injected material to flow

from the sprue directly into the cavity.


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Tab gate:

This type of gate

generates a betterflow pattern by

havin the tab take

up any strains andimperfections in the

flowing material.

http://4.bp.blogspot.com/_oF_1Qcfku_w/R--s2bvduCI/AAAAAAAAAcw/SiRdaYQC-jc/s400/tab-gate3.jpg


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Tunnel or Submarine gate:

There are many advantages to using the tunnel

gate. The gate is sheared off as the piece isejected from the mould. The gate does not have

possible to gate on boss/deep sections of themould. Venting is often not a problem because

the cavity fills from the bottom up-thus allowing

the cavity to vent at the parting-line.


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Tunnel or Submarine gate contd

Tunnel gates very in diameter from .020-.050

and have a land approximately .040.

http://www.rtpcompany.com/info/molding/design/graphics/tunnelgate.gif


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Overflow well

If the part design causes problems of weld lines,

.

is generally located opposite the gate.


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Venting:

All plastic mould must be vented. Venting is

achieved by machining vent grooves into thecavity at the parting line which will carry the

gases out the side of the mould. These vent

grooves are approximately .005 deep and 1/8to 1/4 wide and are located opposite the gate.


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Venting contd

Injection mould are vented to get rid of any air

that might be trapped in the cavity by the

flowing material. In addition to vents, air in

injection mould escapes around ejector pins,

oa e nser s, an a e par ng ne.

A properly vented mould will prevent

incomplete piece parts, burn spots on the part,and will produce excellent weld.


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Slides:

Slides are used

to produce

undercuts onmoulded

parts.


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SIDE OPEN POSITION SLIDE IN CLOSED POSITION


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HORN PINS/LOCKING PINS

Horn pins are used to move a slide backwards andforward and to also lock the slide in position when

material is injected in to the mould cavity. If a slide

moves backwards; this movement is called blowback.


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Wear Plates

What is a wear plate?

Where is a wear plate located?

It is always important to use as hard a steel as

possible when designing a wear plate.

When ever possible a wear plate

should always be designed with

lubrication in mind. Grease grooves

The fit of a wear plate is also

The designer must never use the same

hardness on both members rubbing against

each other.

Also the alloys used might also affect how the

mold functions.

Size of the wear plate The ride-height of the wear plate

The surface of the wear plate is

also very important

The attachment method used

Surface finish of the wear plate

Runners and Gates

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