Document16

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No.: 32/292

Title:

Runner and Gating System Rev.: A

Created by: **** Approved by: **** Last Modified: 3.25.05

1.The runner system used for guiding molten resin injecting from the nozzle of

injection molding machine into mold cavity . This system consists of sprue, main

runner, sub runner and gate. The runner & gate system have substantial effects on

quality, precision, appearance and molding cycle.

2.Sprue is the filling port of molten resin, usually has a 2° ~ 4° taper in order to

detach from the machine nozzle.

3.Main runner and branch runner is the passage between sprue and gate,where the

most heat & pressure loss occured.

4.Gate is the entrance of molten resin enters mold cavity. gate is of one the main

reason of part defects.

5.The cross section of runner preferred:

Kwik-Mold Inc. Moldmaking Guide

Cold Well

Primary Runner

Sprue

Part

Gate Second Runner

Notes P: perimeter

R=A/P


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Title:



6.How to decide runner diameter:


1.1 1.2 1.3 1.4 1.5

250

200

150

50

100

300


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Title:



7.Cold slug well.

7.1Used for receiving the cold material first emerging from the nozzle.

7.2 Cold slug needed at the end of runner whenever possible and should be vented also.


Venting


Sprue Sprue

Sprue Sprue

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Title:



8.Gate

8.1 The following items must be kept in mind when designing gate: 1.easely removed and Min. vestige left; 2.multi-caviies mold can be balanced; 3. Large parts that require multiple gates should include gates that are positioned close enough together to reduce pressure loss. This will help provide good weld line strength by minimizing cooling where the leading edges of resin flow come together. Gating dimensions should provide resin fill at reasonable pressures and fill speeds. 4.Gate land lengths should be kept as short as possible. 5.An impinging gate will help ensure that the incoming flow is directed against the cavity wall or core to avoid jetting. 6.To avoid trapped gas, the resin flow from the gates should direct air toward the vents. 7.Gates should be located to provide flow from thick to thin sections; to minimize weld lines; and away from impact or other stressed areas. 8.To minimize jetting, splay and gate blush, the gates should be located at right angles to the runner; 9.Direct gating to a cosmetic surface may cause surface imperfections. 10. Other items:

1. Rheological Properties 2.normal wall thickness 3.partweight 4.mekting temperature 5.mold temperature



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Title:



8.2 Gate design



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Title:



8.2.1 The Sprue Gate

Ben

efits

1.Good fluidity 2.Simple construction 3.Wide range of resin applicable 4.Good filling ability of material 5.Little retraction denting on surface of molded products. 6.Eliminated the processing at runner. 7.Less pressure loss 8.Can mold large or greater depth molded products.

Shor

tcom

ings

1.Only one product per mold. 2.Gate residue exists and could affect appearance and adding the post processing. 3.For flat, shallow products, it tends to cause distortion and twisting. 4.Need to determine the gate circulation 5.Gate nearby has high residual stress and likely to cause crack or deformation.

App

licat

ion

Suitable for container type large part. Suitable plastics: Polyvinyl Chloride, PVC Polyethylene, PE Polypropylene, PP Polycarbonate, PC Polystyrene, PS Polyamide, PA Polyacetal, Polyoxy Methylene, POM Acrylonitrile-Butadene, AS Acrylonitrile-Butadene-Styrene, ABS Acrylic Resin, PMMA


1.5o(Min.)

d2<1.5t


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Title:



8.2.2 Edge Gate

W=Width of gate,

h=Depth of Gate,

L=Land Length,

t=Part Wall thickness,

n =coeffcient

Ben

efits Low residual stress.

Correct gate size (rectangular cut) Easy to separate gate from molded products. Can prevent the reverse flow of material. Friction heat at the gate can raise the material temperature to promote the filling.

Shor

tcom

ings

Large fluidity resistance High pressure loss Likely to have insufficient filling or solidifying midway for material of poor fluidity. Flat or large area molded products is easy to have bubbles or flow mark, due to narrow gate.

App

licat

ion

Suitable plastics :Polyvinyl Chloride, PVC, Polyethylene, PE, Polypropylene, PP, Polycarbonate, PC, Polyamide, PA, Polyacetal, Polyoxy Methylene, POM, Acrylonitrile-Butadiene, AS, Acrylonitrile-Styrene-Styrene, ABS, Acrylic Resin, PMMA, short fiber plastics Often used in multi-mold cavity mold.

Resin n PE,PS 0.6

POM,PC,PP 0.7 CA,PMMA,PA 0.8

PVC 0.9


h = nt W= 2h


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Title:



The automatic degate design:


W

<0.01” <2/3W Part

E.J. Pin

Undercut

E.J. Retainer plate

E.J. Retainer Plate

Sprue Puller

Delay Pin


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Title:



8.2.3 Overlap Gate

W=Width of gate,

h=Depth of Gate,

L2=Land Length,


n =coefficient

Benefits

Can prevent reverse flow of material Friction heat can raise material temperature to enhance filling Can prevent jetting Can prevent twisting and cracking at gate nearby due residual stress

Shortcomings High pressure loss. difficulty in cutting off gate

Application Don’t use it for PVC

Resin n PE,PS 0.6


PVC 0.9


W=(n√A)/30;

h = nt;

L2 = h+W/2


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Title:



8.2.4 Fan Gate

W=Width of gate,

H1=Depth 1 of Gate,

H2=Depth 2 of Gate,

L=Land Length,1.3-2mm


A=Area of cavity surface

n =coefficient

Benefits

Good fluidity Can fill evenly and prevent deformation of molded product. Low Gate orientation Product appearance good, almost free of defects.

Shortcomings Time consuming in gate processing difficult to cut out gate part.

Application Especially suitable for composite material with strong orientation Large Part with a thin wall Especially suitable for PMMA plate

Resin n PE,PS 0.6


PVC 0.9


W=n*√A/30 H1 = nt;(But W*h1<0.25*π*D2) H2 = W*H1/D

Chamfering can decrease the turbulence flow


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Title:



8.2.5 Diaphragm Gate

h=Depth of Gate,

L=Land Length,


n =coefficient

Benefits

Good fluidity. High precision in round molding product Can prevent occurrence of flow mark Saved runner processing Has the function of direct gate, low-pressure loss.

Shortcomings

Time consuming in gate post -processing. difficult in gate cutting off. Used in single cavity mold. Product hole center needs be aligned with runner

Application Suitable for disk, cylindrical product (gear or deep small cylinder)

Resin n PE,PS 0.6


PVC 0.9

L=0.75-1.0mm

H = 0.7nt



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Title:



8.2.6 Ring Gate

h=Depth of Gate,

L=Land Length,


n =coefficient

Benefits Can prevent occurrence of flow mark and tilt of core pins. Can evenly fill cylindrical product and avoid the forming of soldering line or deformation, eccentric due regional over filling

Shortcomings Time consuming in gate post -processing. difficult in gate cutting off.

Application Suitable for disk, cylindrical product (gear or deep small cylinder)

Resin n PE,PS 0.6


PVC 0.9

L=0.75-1.0mm

H = 0.7nt



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Title:



8.2.7 Film Gate

h=Depth of Gate,

L=Land Length,


n =coefficient

Benefits

Good fluidity. High precision in round molding product. Can fill evenly and prevent deformation of product. Can produce good appearance product, almost free of defective piece.

Shortcomings Time consuming in post processing of gate. difficult in cutting out gate portion.

Application Disk, cylinder (gears, etc) or large think wall part

L=1.00-1.30mm

h = 0.7t



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Title:



8.2.8 Tab Gate

Benefits

Has remolding capacity: before entering molding space, the flow is held to reheat the resin to compensating runner cooling and improve fluidity. Low residual stress: Slow down regional stress concentration at gate and eliminate strain from excessive filling. Can eliminate the denting at gate nearby Can eliminate the strain due excessive filling and generation of flow mark. Can ease the stress concentration at gate nearby. Friction heat generated at gate can raise material temperature again. Holding flow before entering molding space to re-heat resin to compensate the runner cooling and improve fluidity.

Shortcomings

Rather higher in flow resistance High-pressure loss It is a little difficult in cutting off gate. Troublesome in post- processing.

Application

This kind of gate is often used when it is desired to set at the side face or central space of molded product, or prevent gas burning or strain, for poor fluidity resin shall set large gate. Use for improvement in products easy to form jetting or burn. Especially suitable for PMMA part


W = D D=Runner Dia. h1= 0.9 t t=Normal wall thickness h2= 0.7 t L1>1.5mm L2>1.5 D


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Title:



8.2.9 Pin-Point Gate

Resin n PE,PS 0.6


PVC 0.9

D=n*t

Benefits

Has plastering capacity Auto cut-off of gate Little gate trace, free of post-processing Free choice of gate location Gate can be filled in from several points, low stress and strain. Suitable for multiple piece molding. Has the benefit of restricted gate.

Shortcomings

High flow resistance Easy to be overheating Complicate mold construction Resin / Product ration low. Some resins are not suitable. High pressure loss>

Application For large piece, multi-gate application, one shot molding, one time multi-molding



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Title:



8.2.10 Submarine Gate

d = Gate Dia.(Min. t/2) A = Area of Cavity surface t =normal wall thickness(inch) c = 1.03√t Ød = nc (4√A) (inch)

Resin n PE,PS 0.6


PVC 0.9

T 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 C 0.178 0.206 0.230 0.242 0.272 0.294 0.309 0.326

Benefits

Has plastering ability. Gate automatically cut off, free of post processing. Small gate trace. Can freely set gate at outer or inner sides of product.

Shortcomings High f low resistance Difficult to work on the finishing side. High pressure loss

Application Needs no post-processing. Applicable for feeding system automatic separation



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Title:



Crystalline - Round Gate Amorphous - Conical Gate

Nylon,PA PBT PET POM PPS

ABS, PMMA, SAN,PET ASA, PPO, SB

CAB, PSU, TPU PC, PVC

PEI, PVCP PES, PVC

Semi-Crystalline PP(COPOLYHER/HOMO

POLYMER) PE Benefits:

- slow the gate frozen -suitablie the round area

- good break

Benefits: - fast cool and short cycle

- easily machined



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Title:



Gating from pin


>0.15”

D>3/16”


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Title:



Runner insert:used for flat part


Part

Runner Insert


(Max.)

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Title:



8.2.11 Hook Gate

Used when gate vestige on part appearance is not permited and submarine can’t work.



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Title:



The balance ejection of hook gate:

The making of hook gate insert:



A

A

1 2 3 4 5 6 7 8 9

10

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Title:



8.3 runner scale

Used for the easy adjustment of molding parameter with multi-cavity mold or

precision mold.


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