7.2 Gating System Design

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7.2 Gating System Design
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High-performance Mold
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Plastic Mold Casting System
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Injection Molding Parts
Projected area
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7.2.1 Concept of gating system
Gating systemflow channel from the nozzle of
injection machine to the cavity Effectsmooth and
orderly filling of plastic fluid, fully pass
injection pressure to the various part during
filling and solidification process, get density
plastic part Classification Common gating
systemCold runner runnerless gating
systemHot runner, insulated runner
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7.2.2 Gating System and their effects
Sprue
Runner
gate
Main runner
Branch runner
runner
Branch runner
Cavity
runner system has a direct impact on the
appearance, physical properties and of
dimensional accuracy and cycle time of molded
product
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7.2.3 Gating System Design Principles
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7.2.3 Gating System Design Principles

1. guarantee the quality of plastic parts

Gate Placed on the Thickest part of Product

• From the thickest pouring provide better filling
  and packing effects
• If there are underpacking, the thinner areas will
  solidify faster than thick regions
• Avoid gate on the region with sudden change of
  wall thickness, prevent hysteresis or short shot

Sink mark
Un-cure
Under packing
gate
Sink mark
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7.2.3 Gating System Design Principles
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Weld lines/Meld Lines

• Weld from different directions, the front part of
  the molten resin is cooled in the junction can
  not fully integrated. Under normal circumstances,
  affect the appearance, impact on the coating,
  electroplating. Severe impact on the product
  strength (especially fiber reinforced resin)

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Weld Line
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7.2.3 Gating System Design Principles

1. guarantee the quality of plastic parts

sink
overpacking
rib
poor gating system design or improper operating
conditions, make the melt pressure in the cavity
takes too long or too high overpacking will make
the product density, to increase the internal
stress, or even flash
underpacking
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7.2.3 Gating System Design Principles

1. guarantee the quality of plastic parts

flow disorderly make poor workpiece strength and
surface flow
Simple
Complex
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Consider Molecules orientation

• If the product is long and narrow shape, provides
  a single direction from a unilateral into the
  pouring uniform plastic flow
• Although the volume shrinkage of products at the
  different ends is different, there is no warpage
• Molecular distribution in a different direction
  often leads to warping

gate
Uniform
Uneven
Uniform
Non-uniform molecular orientation and warpage
deformation and large
Uniform
Runner
uniform molecular orientation and warpage
deformation and large
Uniform
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7.2.3 Gating System Design Principles
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Filling in the Central

• Gate placed in the central of the product are
  available for same flow length
• Long flow length will affect the required
  injection pressure
• Central pouring makes all directions holding
  pressure evenly to avoid uneven volume shrinkage

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Symmetry of Gates

• Symmetry gates can avoid product warpage
• Asymmetric flow will lead to filling first in
  certain areas, even before solidification may
  cause uneven product of the volume shrinkage,
  which will cause warpage

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7.2.4 Sprue Design and Manufacture
Sectional shape, taper, length, spherical R,
fillet r
Nozzle diameter
spheric radius
shape and size of sprue
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7.2.4 Sprue Design and Manufacture
Sprue bushing through two plate should be a
ladder-like, or using gate sets
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7.2.4 Sprue Design and Manufacture
Straight sprue and inclined sprue
sprue
sprue
runner
runner
Cold slug
Cold slug
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7.2.4 Sprue Design and Manufacture
relationship between locating ring and sprue
bushing
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7.2.4 Sprue Design and Manufacture
Often using standard component for sprue bushing,
45 steel, machining after assembly
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7.2.5 Runner Design and Manufacture
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7.2.5 Runner Design and Manufacture
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7.2.5 Runner Design and Manufacture
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7.2.5 Runner Design and Manufacture
1. Runner section shape
Rectangular cross section
The efficiency of flow channel is nearly equal to
Circular section, 27 area more than that of
Circular, increase injection waste and demolding
force
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7.2.5 Runner Design and Manufacture
1. Runner section shape
Trapezoidal cross section
39 more area than that of circular, and more
waste, while with simple making method
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7.2.5 Runner Design and Manufacture
1. Runner section shape
U shaped
Also known as the modified trapezoidal flow
channel, combined with the round and trapezoid
advantages, 14 area more than that of circular
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7.2.5 Runner Design and Manufacture
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7.2.5 Runner Design and Manufacture
2. Runner design points
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7.2.5 Runner Design and Manufacture
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7.2.5 Runner Design and Manufacture
3. Runner size design
DgtProduct most wall thickness1.5mm B1.25D
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7.2.5 Runner Design and Manufacture
3. Runner size design
Flow channel diameter is too large not only a
waste of materials, and the cooling time
increased, the molding cycle also grows,
resulting in waste costs. Flow channel
diameter is too small the flow resistance of the
material, could easily lead to the filling or
injection pressure must be increased in order to
fill. Runner diameter should be suitable for
the weight of the product or the projected area
Diameter of the flow channel(mm) Product weight(g)
4 95
6 95
6 375
8 375
8 More than 375
10 More than 375
12 Large-scale
Diameter of the flow channel(mm) Projected area(cm2)
4 Less than 10
6 200
8 500
10 1200
12 Large-scale
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7.2.5 Runner Design and Manufacture
2. Runner size design
The length of the flow channel can be calculated
by the following empirical formula
D
DRunner diameter mm W - product weight g L -
stream channel length (mm)
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7.2.5 Runner Design and Manufacture
4. Runner Road layout

• principle of flow channel array

• same distance for molten plastic from sprue to
  different gate
•  The cavity center of pressure coincide with the
  center of injection molding machine

• The layout of the flow channel

Natural balance Artificial balance
Unbalanced
Natural balance
Artificial balance
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Flow Balance

• Naturally balanced runner systemThe same
  distance from nozzle and to different cavity,
  filling all cavities in the same time under the
  same pressure
• Artificially balanced runner systemResizing flow
  channel to complete filling of all cavities in
  the same time under the same pressure

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Artificially Balanced Runner System

• filling order for different cavity is extremely
  complex, not only with the section size and
  length of the Runner, and the plastic melt
  temperature, pressure, viscosity, mold
  temperature and viscosity on pressure drop and
  temperaturelowering the degree of sensitivity.
  Gate size of the balance of each cavity can be
  fixed after the test mold or mold flow analysis

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7.2.5 Runner Design and Manufacture
4. Runner Road layout
balance of Runner arrangement
unbalance of Runner arrangement
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7.2.5 Runner Design and Manufacture
5.Runner manufacturing points
Connection of Runner and the gate
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7.2.5 Runner Design and Manufacture
5. Runner manufacturing points
Circular milling, to ensure positional accuracy
Crossed, milling, grinding(Ra1.6µm)
Crossed, milling, grinding(Ra1.6µm)
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7.2.6 Cold slug and the Pulling Rod
The flow
Settings of the cold slug
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7.2.6 Cold slug and the Pulling Rod
1. Hook-shaped pull cold material of the feed rod
hole
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7.2.6 Cold slug and the Pulling Rod
2.Cold slug of Ball head pulling rod
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7.2.6 Cold slug and the Pulling Rod
3. cold slug of pulling rod
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7.2.6 Cold slug and the Pulling Rod
4. Technical requirements of pulling rod
Pulling rod Material T8A or T10AHeat treatment
the head of HRC 50 55With  Pulling rod and
push pieces of board H9/f9 (gap should be less
than plastic flash value)fixed part of the
pulling rod H7/m6Surface roughness  With the
part Ra0.8
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7.2.7 Design and Manufacture of Gate
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7.2.7 Design and Manufacture of Gate

• Adjust flow speed
• Adjust feed time
• Prevent back flow

Gate dimension often determined by experience,
take low value first, then revised by trying.
generally, the gate area size is about 3-9 of
that of runner, with short length about 1-1.5mm,
often using rectangle or round section
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7.2.7 Design and Manufacture of Gate
Non restrict gate(sprue gate)
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7.2.7 Design and Manufacture of Gate
1.role of gate
Dimension reduced
too small gate
swell
too big Gate
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
Direct gate(sprue gate)
Direct gate is widely used in single-cavity
moldDisadvantages difficult removal of gate,
leave marks on surface of molding
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
side gate
Generally opened in the parting surface, suitable
for multi-cavity mold, convenient gate removal
but the pressure loss, shell-shaped venting
inconvenience, easy to produce the weld.
typical size thickness of 0.4 to 6.4mm, width
from 1.6 to 12.7mm.
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
overlap gate
Overlapping gate and side gate is similar, there
is overlap between gate and the finished wall or
finished surfaces
typical gate size thickness 0.4 to 6.4mm, width
from 1.6 to 12.7mm.
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
fan gate
Typical gate size thickness 0.25-1.6mm, width of
6.4 to 25 of the length of the cavity sidewall.
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
disk gate or dish gate
Disc gate is often used for forming the inside of
the opening of the cylinder or round
productsThis type of gate for concentric,
demanding strict dimension, and not allow Weld
line
Typical gate thickness 0.25 to 1.27mm
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
ring gate
melt flow freely along the center part of ring
gate, and then melt down to filling the
moldTypical gate thickness 0.25 to 1.6mm.
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
spoke gate
Spoke gate, also known as 4-point gate or cross
gate. Mostly for tubular plastic products, and
gate removing easy and material
savingDisadvantages may produce weld line , not
possible to create perfect roundnessTypical
gate thickness 0.8 to 4.8mm, width from 1.6 to
6.4mm.
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
film gate
Similar to ring gate, with straight edge of the
plastic partsApplies to flat and large area,
warping reducingTypical thickness 0.25 to
0.63mm, with short length, approximately 0.63mm
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
tab gate
Normally used in tablet-shaped and thin moldings,
in order to reduce the shear stress
Gate around high shear stress is limited to the
secondary tabs, tabs will be removedConvex
tablets gate is widely applied to the PC, SAN,
and ABS resin molding
Tabs on the minimum width of 6.4mm, the minimum
thickness for 75 of the cavity depth.
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
pin point gate
Suitable for multi-cavity, three boards and two
open mold, the mold point gate off automatically.
Small Gate with high pressure loss, which need
higher injection pressure
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
submarine gate
Gate open on one side of the core, the gate
automatically cut off from the mold
Submarine gate mold
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7.2.7 Design and Manufacture of Gate
2. type and characteristics of gate
Banana gate
Gate in core side, cut off during ejection,
LgtL1L2, and L1 could not too short
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7.2.7 Design and Manufacture of Gate
4. Gate design principles
A good gate can make fast, uniform and better
single-directional flow, and suitable gate
solidification time
?To prevent the gate at the jet phenomenon in the
filling process, the traces of the corrugated.To
prevent the approach increase the gate size or
impact-type gate.
Non-impact gate
Core
impact gate
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Spray pattern
Overlapping gate, avoid jet stream
fan gate, avoid the jet stream
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7.2.7 Design and Manufacture of Gate
Set up multiple gates to reduce the deformation
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7.2.7 Design and Manufacture of Gate
4. Gate design principles
?Prevent direct impact on slender core or insert
Change the location of the gate to prevent the
deformation of core
Change the location of the gate to prevent the
deformation of core
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7.2.7 Design and Manufacture of Gate
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7.2.7 Design and Manufacture of Gate
4. Gate design principles
?not enough flow ratio, using more gate
?gate location avoiding weld line, or avoid them
in functional area, load area, or appearance part
cooling tank
Gate
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7.2.8 Venting System Design
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7.2.8 Venting System Design
1. Venting system design
?Mold parting surface and with the clearance of
natural venting  venting clearance does not
produce excess material is limited, usually
0.03-0.05mm
?Use of sintered metal block venting vent
diameter D should not be too much.
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7.2.8 venting System Design
1. Venting system design
?venting groove, venting Suitable for large
volumes of gas generated in the larger plastic
parts molding process
Parting surface
Venting groove shall be open parts of the final
filling of the cavityventing groove should not
face operating workers
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7.2.8 venting System Design
1. venting system design
?ejector pin venting
Side view
Reduce friction
Top View
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7.2.8 venting System Design
2. Lead the design of the gas system
Large deep shell shaped bag tight core to form a
vacuum, difficult to demolding, air valve device?
air valve venting
Splicing venting
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Gate Location Options
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Gate Location Options
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Gate Location Options
Location of the gate
Reasonable location of the gate
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Gate location example