Tool N Die for Marplex Polymers

8/22/2019 Tool N Die for Marplex Polymers

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INJECTION MOULD DESIGN: MARPLEX MATERIALS

Mould Types

Two-plate, three-plate, hot runner, or runner less moulds can be used with the majority of EngineeringThermoplastic.

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 andthe location of the location of the knock-out pins. This mould is easily adapted for different designs andall part ejection methods.

Three-Plate Mould: This type of mould is used primarily to centre gate or submarine gate parts inmultiple 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.


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Hot-Manifold Mould: The hot manifold mould is similar to the three-plate mould in design. The runnersystem, however, is confined in a block and heated by cartridge heaters. This system will eliminate largequantities of runner scrap and improve automatic cycling. If heated torpedos are used, they should bemade 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 otherparts 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 insulationaround the runner to maintain proper melt temperature. This system is not usually recommended forMarplex materials.


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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 partinglines. 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 corepins may be utilised if they are located where the trapped gas and/ or air occur. Ejector pins and sleevesare 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 spruebush 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 spruebush should be considered. Since the sprue is not ejected with the part, the sprue trimming and scrapare eliminated and moulding time can be reduced by the amount of time normally allowed for cooling the

sprue.


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The internal surface of the bushing should taper from a diameter of 16-19mm at the nozzle end to adiameter of 9.5mm at the cavity end, and should be perfectly smooth and polished. A 450 chamfer isdesirable for nozzle seal-off and seating. The orifice (gate) should be a minimum of 3.2mm and a landlength 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 riskof freezing off.

The diameters of the outer surface of the bush should slip fit into the mould plate when both the bush andmould or cold. There should be a shoulder not more than 40mm from the cavity to prevent expansion ofthe 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 thebush should be machined to provide an insulated air gap which will minimize heat transfer to the mouldplate and cavity, and also provide areas for mounting the heated bands. Two 125watt heater bands areusually satisfactory. Before the bush is installed in the mould, it should be heated to the operatingtemperature range of 1750-2050C, followed by tightening of the heater bands.


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


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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 shouldhave a cross sectional diameter of 4.8mm to 8mm. Normally all main runners to a given mould should beequal in diameter, and all secondary runners in the mould should be equal in diameter, but they need notbe equal in length. When the runner system is cut into only one mould face, trapezoidal runners arepreferred 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 eachintersection 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 beused. 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.


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3 Plate Mould

Pin GateAdvantages:

The design is useful when multiple gates per cavity are needed toassure symmetric filling or where long flow paths must be reduced to

assure packing to all areas of the part. Runners are torn from the part

during ejection due to the reverse taper drops of a pin point gate.

Disadvantages:

Gate vestige can cause problems, this can be rectified with the use of

a sunken contour to keep the vestige below the design surface. Thegate could also be placed in a non visible area. Pneumatic nozzles

can also be used for automatic ejection of a runner with a pin pointgate.

Pin point gates should not be used with highly viscous polymers, or

those which are heat sensitive.

Direct SprueAdvantages:

A direct sprue is commonly used for single cavity moulds, where thesprue feeds material directly into the cavity rapidly with minimumpressure drop. This design can also be used in thick walled parts or

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 orrunner has been removed. The part shrinkage near the sprue gate

will be low, shrinkage in the sprue will be high, the result is hightensile stresses near the gate.

3.80-6.40mm min1.27mm 1-2mmPOM

4.75mm minNot recommended except very small partsPMMA

Not recommended except verysmall parts

0.80mm 3-5mmTPE

4.50-6.40mm minNot recommended except very small partsPA

5.60mm min1.25-2.3mm 0mm

1.5-2.5mm GF 0mm

PET/PBT

4.8-6.4mm minNot recommended except very small partsmPPE

4.75mm minNot recommended except very small partsPC

4.50-6.40mm minNot recommended except very small partsABS-PC

4.50-6.40mm min1.27mm min 0mmABS

3.0mm1.2mm 2-3mmmPP

Direct Sprue

Orifice

Pin Point Gate

Orifice Land Length


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Fan Gate

A fan gate is a wide edge gate withvariable thickness.

Advantages:It permits rapid filling of large parts orfragile mould sections through alarge entry area. It can be used to

create a uniform flow front into wideparts, where warpage anddimensional stability are concerns.Used to eliminate jetting.

Disadvantages:Requires removal of sprue andrunner.

Edge Gate

Advantages:An edge gate is located on theparting line of the mould and typicallyfills the part from the side, top andbottom

Disadvantages:Jetting can occur. Trimming

operation required.

YESPOM

YESPMMA

NOTPE

YESPA

YESPET/PBT

YESmPPE

YESPC

YESABS-PC

YESABS

YESmPP

Suitability

0.51-0.76mm Short as possible50% wall thicknessPOM

0.51-0.76mm Short as possible75-90% wall thicknessPMMA

Not recommended except very smallparts

TPE

0mm Short as possible50% wall thicknessPA

0.38-0.51mm Short as possible70-85% wall thicknessPET/PBT

0-0.76mm Short as possible70-85% wall thicknessmPPE

0.51-0.76mm Short as possible75-100% wall thicknessPC

0.51-0.76mm Short as possible85-100% wall thicknessABS-PC

0.51-0.76mm Short as possible70-85% wall thicknessABS

0.51-0.76mm Short as possible50-60% wall thicknessmPP

Land LengthOrifice


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S RunnerAdvantages:

Slows the flow of polymer

entering the part giving goodsurface appearance.

Disadvantages:

More material is used in therunner. This design is best donewith a full round runner. Surface

appearance is only better ifmaterial does not shear toomuch through gate.

Jump GateAdvantages:

Gate into wall has no visible

marks on the appearance ofsurface or interference with

fitment.

Disadvantages:

Prone to jetting if the gate wasnot wide enough, still possible ifgate is wide. Difficult to trimgate off part and keep a clean

square edge.

0.51-0.76mm1.27mmPOM

0.51-0.76mm1.27mmPMMA



TPE



PA

0.38-0.51mm1.25-2.3mm 0mm

1.5-2.5mm GF 0mm

PET/PBT

1.0mm max1.14-2.54mmmPPE

0.51-0.76mm1.27mmPC

0.51-0.76mm1.27mmABS-PC

0.51-0.76mm1.27mm minABS

0.51-0.76mm1.27mm minmPP

Land LengthOrifice Diameter

0.51-0.76mmPOM

0.51-0.76mmPMMA


TPE

0-0.80mmPA

0.38-0.51mmPET/PBT

1.0mmmPPE

0.51-0.76mmPC

0.51-0.76mmABS-PC

0.76mmABS

0.51-0.76mmmPP

Land Length


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Direct Center SprueAdvantages:

A direct sprue is commonly used forsingle cavity moulds, where the spruefeeds material directly into the cavityrapidly with minimum pressure drop.This design can also be used in thickwalled parts or for gentle processing

of high viscosity material.Disadvantages:

The sprue must be removed after partejection takes place. This design canleave a gate mark on the part surfaceafter the sprue or runner has beenremoved. The part shrinkage nearthe sprue gate will be low, shrinkagein the sprue will be high, the result ishigh tensile stresses near the gate.

Diaphragm GateA diaphragm gate is often used forgating cylindrical or round parts thathave an open inside diameter.

Advantages:

It is used when concentricity is animportant dimensional requirementand the presence of a weld line isobjectionable. Uniform flow to all

parts of the gate is easy to maintain.Disadvantages:

Sprue must be removed aftermoulded

0.51-0.76mm1.0mm minPOM

0.51-0.76mm1.0mm minPMMA

Not recommendedTPE

0-0.80mm1.0mm minPA

0.38-0.51mm1.0mm minPET/PBT

1.0mm1.0mm minmPPE

0.51-0.76mm1.0mm minPC

0.51-0.76mm1.0mm minABS-PC

0.76mm1.0mm minABS

0.51-0.76mm1.0mm minmPP

Land LengthThickness of Gate

4.75mm minPMMA

3.80-6.40mm minPOM

0.8mmTPE

4.50-6.40mm minPA

5.60mm minPET/PBT

5.10mm minmPPE

4.75mm minPC

4.50-6.40mm minABS-PC

4.50-6.40mm minABS

3.0mmmPP

Orifice


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Sub GateA submarine gate is used in two-plate mould construction. Anangled, tapered tunnel ismachined from the end of therunner cavity, just below the partline.

Advantages:

As the parts and runners areejected, the gate is sheared atthe part line. A full round runnershould be used.

Disadvantages:

Poor results in reinforcedmaterials. Premature gatefreeze can be a problem.

Sub Gate with

Knockout PinIf a larger diameter pin is addedto a non-functional area of thepart, the submarine gate can bebuilt into a pin.

Advantages:

This avoids the need for avertical surface for the gate to beplaced. If the pin surface ishidden, it does not have to beremoved.

Disadvantages:

Poor results in reinforcedmaterials. Premature gatefreeze can be a problem.

50mm0mm1.27-2.4mmPOM

50mm0mm1.5-2.3mmPMMA

0-0.80mm

0.38-0.51mm

0mm

0.51-0.76mm

0mm

0mm

2-3mm

Land Length

Not recommended exceptvery small parts

TPE

50mm2.4mmPA

50mm1.27-2.3mm

1.5-2.5mm GF

PET/PBT

50mm1.52mmmPPE


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Chisel GateAdvantages:

Similar to applications which require a

fan gate. Good for reinforcedmaterials.

Disadvantages:

A disadvantage with chisel gates isthe large blemish which occurs onremoval of the sprue/runner. Very

hard to trim vestige.

Curved Tunnel GateAdvantages:

Best gate design for TPE. Leaves

non visible vestige on part.

Disadvantages:

Not easily used on many othermaterials due to the shear which the

material will incur through the gate.

4.50-6.40mm minPOM

3.80-6.40mm minPMMA

Not recommendedTPE

4.50-6.40mm minPA

5.60mm minPET/PBT

4.8-6.4mm minmPPE

4.75mm minPC

4.50-6.40mm minABS-PC

4.75mm minABS

3.0mmmPP

Orifice

POM

Not recommendedNot recommendedPMMA

3-5mm0.8mmTPE

Small as possible.Not in GF. Small parts only.PA

0.38-0.51mm1.25-2.3mm 0mm

1.5-2.5mm GF 0mm

PET/PBT

Not recommendedNot recommendedmPPE

Not recommendedNot recommendedPC

Not recommendedNot recommendedABS-PC

Not recommendedNot recommendedABS

2-3mm1.2mmmPP

Land LengthOrifice Diameter


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

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Tool N Die for Marplex Polymers