INJECTION MOULD DESIGN: MARPLEX MATERIALS

INJECTION MOULD DESIGN: MARPLEX MATERIALS

Mould Types

Two-plate, three-plate, hot runner, or runner less moulds can be used with the majority of Engineering
Thermoplastic.
Two-Plate Mould: The two plate mould is simple in design, yet versatile. It consists of a front and
stationary half. The cavity or core can be mounted on either half, depending upon the part design and
the location of the location of the knock-out pins. This mould is easily adapted for different designs and
all part ejection methods.
Three-Plate Mould: This type of mould is used primarily to centre gate or submarine gate parts in
multiple cavities. It consists of the standard two-plate design with the third movable between the two.
Automatic degating is possible with three-plate moulds, but runner scrap is increased.

INJECTION MOULD DESIGN: MARPLEX MATERIALS

Hot-Manifold Mould: The hot manifold mould is similar to the three-plate mould in design. The runner
system, however, is confined in a block and heated by cartridge heaters. This system will eliminate large
quantities of runner scrap and improve automatic cycling. If heated torpedos are used, they should be
made from a good grade stainless steel. Beryllium copper is not recommended.
To obtain optimum results, the hot manifold system should be balanced properly, insulated from other
parts of the mould to minimise heat loss or heat transfer to the mould plate, and provide uniform
distribution of heat throughout the manifold.
Insulated Runner Mould: This system utilises the hot manifold concept without the cartridge heaters.
The insulated runner system depends entirely on heat generation in plasticising cylinder and insulation
around the runner to maintain proper melt temperature. This system is not usually recommended for
Marplex materials.

INJECTION MOULD DESIGN: MARPLEX MATERIALS

Venting

Moulds must be well vented to eliminate any possibility of gas or air being trapped as the part is moulded.
The entire circumference of each cavity should have venting to prevent gas or air burns at the parting
lines. In some instances a minimum of 40% venting is recommended for intricately designed parts.
Vents should normally be 0.05mm deep. If internal vents are necessary, ejector pins, sleeves and core
pins may be utilised if they are located where the trapped gas and/ or air occur. Ejector pins and sleeves
are preferred because the movement of ejection in the moulding cycles automatically cleans the vents.

Sprue Bushes

Sprue bushes may be categorised as either cold (standard) sprues or heated sprues. The cold sprue
bush is low in cost, easy to install and requires very little maintenance. This type of system however,
generates more material that must be reground and reprocessed than the heated sprue.
Should the cavity depth require a long sprue bush to accommodate the runner system, the heated sprue
bush should be considered. Since the sprue is not ejected with the part, the sprue trimming and scrap
are eliminated and moulding time can be reduced by the amount of time normally allowed for cooling the
sprue.

INJECTION MOULD DESIGN: MARPLEX MATERIALS

The internal surface of the bushing should taper from a diameter of 16-19mm at the nozzle end to a
diameter of 9.5mm at the cavity end, and should be perfectly smooth and polished. A 450 chamfer is
desirable for nozzle seal-off and seating. The orifice (gate) should be a minimum of 3.2mm and a land
length can be minimized by sinking 1.5mm to 2.3mm from cavity end. Counter sinking removes the gate
land from the immediate vicinity of the cavity, thus preventing damage to the orifice and reducing the risk
of freezing off.

The diameters of the outer surface of the bush should slip fit into the mould plate when both the bush and
mould or cold. There should be a shoulder not more than 40mm from the cavity to prevent expansion of
the bush into the cavity when heat is applied. For bushes more than 200mm long, a second shoulder,
situated 75mm to 100mm from the cavity end, is recommended. The remainder of the outer surface of the
bush should be machined to provide an insulated air gap which will minimize heat transfer to the mould
plate and cavity, and also provide areas for mounting the heated bands. Two 125watt heater bands are
usually satisfactory. Before the bush is installed in the mould, it should be heated to the operating
temperature range of 1750-2050C, followed by tightening of the heater bands.

INJECTION MOULD DESIGN: MARPLEX MATERIALS

There are two methods of heating the hot sprue bush. The one most commonly used is the installation of
heater bands around the outside diameter of the bush. The other method of heating the sprue is by
installing heater cartridges within the wall of the sprue bush or directly in the melt flow chamber. Heated
sprue bushes should be made from a good grade of steel, and be oil or air-hardened after machining.

INJECTION MOULD DESIGN: MARPLEX MATERIALS

Runners

For most normal injection moulding, runners with a circular (full round) section provide maximum flow.
Main runners should have a cross sectional diameter of 6mm to 12.7mm. Secondary runners should
have a cross sectional diameter of 4.8mm to 8mm. Normally all main runners to a given mould should be
equal in diameter, and all secondary runners in the mould should be equal in diameter, but they need not
be equal in length. When the runner system is cut into only one mould face, trapezoidal runners are
preferred to half-round runners of the same depth.
It is advisable to locate a cold slug well opposite the sprue, and to extend the main runners beyond each
intersection with the secondary runners so that the extensions also act as cold slug wells.
To help reduce friction and material hang-up, a highly polished chrome plated runner system may be
used. The diameter should be a minimum of 8mm for small parts and 9.5mm to 11mm for larger parts.
Hot runner moulds require runners of 12mm to 19mm diameter.

INJECTION MOULD DESIGN: MARPLEX MATERIALS

3 Plate Mould Pin Point Gate Direct Sprue
Pin Gate Orifice
Orifice Land Length 3.0mm
Advantages: 4.50-6.40mm min
The design is useful when multiple gates per cavity are needed to mPP 1.2mm 2-3mm 3.80-6.40mm min
assure symmetric filling or where long flow paths must be reduced to ABS 4.75mm min
assure packing to all areas of the part. Runners are torn from the part POM 1.27mm min 0mm 4.50-6.40mm min
during ejection due to the reverse taper drops of a pin point gate. PMMA 4.75mm min
ABS-PC 1.27mm 1-2mm 4.8-6.4mm min
Disadvantages: PC 5.60mm min
Gate vestige can cause problems, this can be rectified with the use of mPPE Not recommended except very small parts
a sunken contour to keep the vestige below the design surface. The PET/PBT 4.50-6.40mm min
gate could also be placed in a non visible area. Pneumatic nozzles Not recommended except very small parts Not recommended except very
can also be used for automatic ejection of a runner with a pin point PA small parts
gate. TPE Not recommended except very small parts
Pin point gates should not be used with highly viscous polymers, or
those which are heat sensitive. Not recommended except very small parts

Direct Sprue 1.25-2.3mm 0mm
1.5-2.5mm GF 0mm
Advantages:
A direct sprue is commonly used for single cavity moulds, where the Not recommended except very small parts
sprue feeds material directly into the cavity rapidly with minimum
pressure drop. This design can also be used in thick walled parts or 0.80mm 3-5mm
for gentle processing of high viscosity material.

Disadvantages:
The sprue must be removed after part ejection takes place. This
design can leave a gate mark on the part surface after the sprue or
runner has been removed. The part shrinkage near the sprue gate
will be low, shrinkage in the sprue will be high, the result is high
tensile stresses near the gate.

INJECTION MOULD DESIGN: MARPLEX MATERIALS

Fan Gate mPP Suitability
POM YES
A fan gate is a wide edge gate with PMMA YES
variable thickness. ABS YES
Advantages: ABS-PC YES
It permits rapid filling of large parts or PC YES
fragile mould sections through a mPPE YES
large entry area. It can be used to PET/PBT YES
create a uniform flow front into wide PA YES
parts, where warpage and TPE YES
dimensional stability are concerns. NO
Used to eliminate jetting. mPP
Disadvantages: ABS Orifice Land Length
Requires removal of sprue and POM 50-60% wall thickness
runner. PMMA 70-85% wall thickness 0.51-0.76mm Short as possible
ABS-PC 50% wall thickness
Edge Gate PC 75-90% wall thickness 0.51-0.76mm Short as possible
mPPE 85-100% wall thickness
Advantages: PET/PBT 75-100% wall thickness 0.51-0.76mm Short as possible
An edge gate is located on the PA 70-85% wall thickness
parting line of the mould and typically TPE 70-85% wall thickness 0.51-0.76mm Short as possible
fills the part from the side, top and 50% wall thickness
bottom Not recommended except very small 0.51-0.76mm Short as possible
parts
Disadvantages: 0.51-0.76mm Short as possible
Jetting can occur. Trimming
operation required.

0-0.76mm Short as possible

0.38-0.51mm Short as possible

0mm Short as possible

INJECTION MOULD DESIGN: MARPLEX MATERIALS

S Runner Orifice Diameter Land Length
0.51-0.76mm
Advantages: mPP 1.27mm min 0.51-0.76mm
Slows the flow of polymer ABS 0.51-0.76mm
entering the part giving good POM 1.27mm min 0.51-0.76mm
surface appearance. PMMA 0.51-0.76mm
ABS-PC 1.27mm 0.51-0.76mm
Disadvantages: PC 1.0mm max
More material is used in the mPPE 1.27mm 0.38-0.51mm
runner. This design is best done PET/PBT
with a full round runner. Surface 1.27mm Not recommended except very
appearance is only better if PA small parts
material does not shear too 1.27mm Not recommended except very
much through gate. TPE small parts
1.14-2.54mm
Jump Gate mPP
POM 1.25-2.3mm 0mm
Advantages: PMMA 1.5-2.5mm GF 0mm
Gate into wall has no visible ABS
marks on the appearance of ABS-PC Not recommended except very
surface or interference with PC small parts
fitment. mPPE
PET/PBT Not recommended except very
Disadvantages: PA small parts
Prone to jetting if the gate was TPE
not wide enough, still possible if Land Length
gate is wide. Difficult to trim 0.51-0.76mm
gate off part and keep a clean 0.51-0.76mm
square edge. 0.51-0.76mm
0.76mm
0.51-0.76mm
0.51-0.76mm
1.0mm
0.38-0.51mm
0-0.80mm
Not recommended except very
small parts

INJECTION MOULD DESIGN: MARPLEX MATERIALS

Direct Center Sprue mPP Orifice Land Length
POM 3.0mm 0.51-0.76mm
Advantages: PMMA 3.80-6.40mm min 0.51-0.76mm
A direct sprue is commonly used for ABS 4.75mm min 0.51-0.76mm
single cavity moulds, where the sprue ABS-PC 4.50-6.40mm min 0.76mm
feeds material directly into the cavity PC 4.50-6.40mm min 0.51-0.76mm
rapidly with minimum pressure drop. mPPE 4.75mm min 0.51-0.76mm
This design can also be used in thick PET/PBT 5.10mm min 1.0mm
walled parts or for gentle processing PA 5.60mm min 0.38-0.51mm
of high viscosity material. TPE 4.50-6.40mm min 0-0.80mm
0.8mm
Disadvantages: mPP
The sprue must be removed after part POM Thickness of Gate
ejection takes place. This design can PMMA 1.0mm min
leave a gate mark on the part surface ABS 1.0mm min
after the sprue or runner has been ABS-PC 1.0mm min
removed. The part shrinkage near PC 1.0mm min
the sprue gate will be low, shrinkage mPPE 1.0mm min
in the sprue will be high, the result is PET/PBT 1.0mm min
high tensile stresses near the gate. PA 1.0mm min
TPE 1.0mm min
Diaphragm Gate 1.0mm min
Not recommended
A diaphragm gate is often used for
gating cylindrical or round parts that
have an open inside diameter.
Advantages:
It is used when concentricity is an
important dimensional requirement
and the presence of a weld line is
objectionable. Uniform flow to all
parts of the gate is easy to maintain.
Disadvantages:
Sprue must be removed after
moulded

INJECTION MOULD DESIGN: MARPLEX MATERIALS

Sub Gate mPP Orifice Land Length Taper from Part
POM 1.5-2.3mm 2-3mm 50mm
A submarine gate is used in two- PMMA 1.27-2.4mm 0mm 50mm
plate mould construction. An ABS 1.5-2.3mm 0mm 50mm
angled, tapered tunnel is ABS-PC 1.5-.2.3mm 0mm 50mm
machined from the end of the PC 1.27mm min 0mm 50mm
runner cavity, just below the part mPPE <50mm
line. PET/PBT 1.27mm 0.51-0.76mm 50mm
Advantages: 1.52mm 0mm 50mm
As the parts and runners are PA 1.27-2.3mm
ejected, the gate is sheared at TPE 1.5-2.5mm GF 0.38-0.51mm 50mm
the part line. A full round runner 2.4mm
should be used. mPP Not recommended except 0-0.80mm Taper from Part
Disadvantages: POM very small parts 50mm
Poor results in reinforced PMMA 50mm
materials. Premature gate ABS Orifice Land Length 50mm
freeze can be a problem. ABS-PC 1.5-2.3mm 2-3mm 50mm
PC 1.27-2.4mm 0mm 50mm
Sub Gate with mPPE 1.5-2.3mm 0mm <50mm
Knockout Pin PET/PBT 1.5-2.3mm 0mm 50mm
1.0mm min 0mm 50mm
If a larger diameter pin is added PA
to a non-functional area of the 1.27mm 0.51-0.76mm 50mm
part, the submarine gate can be TPE 1.52mm 0mm
built into a pin. Not recommended
Advantages: except very small parts 0.38-0.51mm
This avoids the need for a 1.27-2.2mm
vertical surface for the gate to be 1.5-2.4mm GF 0-0.80mm
placed. If the pin surface is Not recommended
hidden, it does not have to be except very small parts
removed.
Disadvantages:
Poor results in reinforced
materials. Premature gate
freeze can be a problem.

INJECTION MOULD DESIGN: MARPLEX MATERIALS

Chisel Gate mPP Orifice Land Length
POM 3.0mm 2-3mm
Advantages: PMMA 4.50-6.40mm min
Similar to applications which require a ABS 3.80-6.40mm min
fan gate. Good for reinforced ABS-PC 4.75mm min
materials. PC 4.50-6.40mm min
mPPE 4.75mm min
Disadvantages: PET/PBT 4.8-6.4mm min
A disadvantage with chisel gates is PA 5.60mm min
the large blemish which occurs on TPE 4.50-6.40mm min
removal of the sprue/runner. Very Not recommended
hard to trim vestige. mPP
POM Orifice Diameter
Curved Tunnel Gate PMMA 1.2mm
ABS
Advantages: ABS-PC Not recommended Not recommended
Best gate design for TPE. Leaves PC Not recommended
non visible vestige on part. mPPE Not recommended Not recommended
PET/PBT Not recommended
Disadvantages: Not recommended Not recommended
Not easily used on many other PA 0.38-0.51mm
materials due to the shear which the TPE Not recommended
material will incur through the gate. Small as possible.
3-5mm
Not recommended

1.25-2.3mm 0mm
1.5-2.5mm GF 0mm

Not in GF. Small parts only.

0.8mm

INJECTION MOULD DESIGN: MARPLEX MATERIALS

The content of this report is based on test methods and results we believe reliable, but any
results or recommendations contained should not be construed as a guarantee of final product
performance by Marplex Australia Pty Ltd.