RUNNERS AND
GATES
GATES
Information contained in this presentation is to be used by Seneca College Students while registered at the College Only and can not be reproduced.
A runner is a channel which connects the 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.
A runner is a channel which connects the gate(s) of a mould to the sprue.
Runners should always be radially spaced 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
Runners should always be radially spaced leading from the sprue.
Runners must always be polished.
Why is polishing important on the runner if 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 as possible. Why?
The two most frequently used runner shapes are:
1. trapezoidal 2. round
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
Gate:
The narrow and shallow portion of the runner as it enters the cavity.
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 the flowing material hits what?
The opposing surface as soon as possible after entry into the cavity.
Note, material entering into: thick
section, ribs, parallel wall sections or any open area will result in visible shrinkage marks on the finished product.
Gates are made as small as possible.
Small gates facilitate the removal of the Small gates facilitate the removal of the piece part from the runner and sprue.
Small gates also promote proper flow of molten material prevent strains and weld marks.
Weld marks normally result from poor
For asymmetrical mould gravities designers cannot rely on radially spaced runners and gate.
Designers must make changes to the gates Designers must make changes to the gates to allow the cavities to fill uniformly.
Cold Slug Well
When material is injected into the mould the leading of the injected material is
somewhat 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.
Cold Slug wells are also found at the end of branch runners.
Sprue Puller
An undercut is normally machined into
either the cold slug well or the ejector pin immediately 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.
Fan gate:
A fan gate is used with acrylic material. This type of gate improves the flow of acrylic
material by spreading the material into the cavity.
cavity.
http://2.bp.blogspot.com/_oF_1Qcfku_w/SAjITuV5_AI/AAAAAAAAAeQ/VzC1438MwW8/s400/faN%2BGA T3%2Bcopy.jpg
Ring gate:
This type of gate is used to feed material into long cylindrical parts with thin wall section.
Disc gate:
The disc gate is
used to fill a cavity from a hold
located inside the located inside the part. The material from the sprue
spreads out evenly and all sections of the cavity are filled simultaneously.
Direct gate:
This gate allows the injected material to flow from the sprue directly into the cavity.
Tab gate:
This type of gate generates a better flow pattern by
having the tab take having the tab take up any strains and imperfections in the flowing material.
Pin point gate:
The pin point
gate is generally used in three plate mould plate mould construction with multiple cavities and having trapezoidal runner. http://4.bp.blogspot.com/_oF_1Qcfku_w/RuVaduEmQgI/AAAAAAAAAHY/RuJ1kQH7wPc/s400/mold.gif
Tunnel or Submarine gate:
There are many advantages to using the tunnel gate. The gate is sheared off as the piece is
ejected from the mould. The gate does not have to be located on the parting line and it is
to be located on the parting line and it is
possible to gate on boss/deep sections of the mould. Venting is often not a problem because the cavity fills from the bottom up-thus allowing the cavity to vent at the parting-line.
Tunnel or Submarine gate cont’d
Tunnel gates very in diameter from .020”-.050” and have a land approximately .040”.
Overflow well
If the part design causes problems of weld lines, an overflow will is provided. The overflow well an overflow will is provided. The overflow well is generally located opposite the gate.
Venting:
All plastic mould must be vented. Venting is achieved by machining vent grooves into the cavity at the parting line which will carry the gases out the side of the mould. These vent
grooves are approximately .005” deep and 1/8” grooves are approximately .005” deep and 1/8” to 1/4” wide and are located opposite the gate.
Venting cont’d
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, loaded inserts, and at the parting line.
loaded inserts, and at the parting line.
A properly vented mould will prevent
incomplete piece parts, burn spots on the part, and will produce excellent weld.
Slides:
Slides are used to produce
undercuts on undercuts on moulded
HORN PINS/LOCKING PINS
Horn pins are used to move a slide backwards and forward 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.
Slide Movement
Which method of moving a slide do you think is cheapest to incorporate
in your mold design?
Regardless of the movement method used all slides and core-pull must be
designed with a housing.
• There are two components
which make up a slide housing.
• Back plate • Side plates
• Slides must also have carriers.
• The carrier allows for attachment of the
designed with a housing.
What is a housing? And what is its purpose?
• The carrier allows for attachment of the slide insert.
• The carrier must have guide pin bushing and dowel pins to allow for proper
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
critical to the function of a mold
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.
critical to the function of a mold
– 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
