Dimensional Molding Shrinkages

High Performance Thermoplastics 1

Dimensional molding shrinkage of athermoplastic part is a typical phenomenonrelated to the injection molding process,caused by the volumetric shrinkage, duringand after molding cycle.For this reason, cavities, from which part ismolded, have to be measured consideringthis important aspect, so that the part initself has its desired measures.However, the shrinkage entity is difficult tobe evaluated because it is linked to manyconcomitant factors such as materialfeatures, part geometry and transformationconditions.Purpose of this experimentation is toanalyze the interact ion betweenproduct-process variables and moldingshrinkage property.After introducing terms and definitions(in tabular form), the first section concernsthe material typology (chemical structureand filling process); the second oneanalyses the influence of part geometry,underlining, above all, the part thickness;the third section, concerns transformationconditions.Among transformation conditions, it isoften important to analyze some parametersjointly. Injection molding is, in fact, atechnology based on the combination ofdifferent physical properties such astemperature, speed, pressure and time.Tests have been performed, in mostcases, on semi-crystalline resins(prevalently PA66). These are very sensitiveto shrinkage phenomena and to allconnected parameters, unlike amorphousresins.The exposition is supplemented, dependingon the circumstances, with schedules, graphsor explanation diagrams. Otherwise curveshave been obtained keeping constanttransformation parameters.Different typologies of test specimens havebeen used (specified from time to time); forthe study of transformation parameters,PLATE ISO 294-3 D2 TYPE is prevalentlyused. It is provided with cavity transducer,which allows important studies abouteffective pressure load.Using different size and thicknesses testspecimens, the obtained results underlinesimilar trends; however these trends can havesensitively different values. IN

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2

RM Medium molding shrinkage(RL+ RT)/2

[%]It defines in percentage the medium shrinkage entity:

RMmin; RMmed; RMmax

RD Differential shrinkageRT-RL

[%]

It defines the difference between RT and RL; theobtained value is inversely proportional to the partplanarity:

RDmin; RDmed; RDmax

WL Side warpage parallel to theinjection flow

((Ln-Lm min)/Tn)*10

[10- 2

mm/cm]

It defines the side warpage entity parallel to the flow,which is how many hundredths of millimeters ofbending are obtained for each centimeter of platelength.The obtained value is inversely proportional to thepart planarity

WT Side warpage orthogonal to theinjection flow

((Tn-Tm min)/Ln)*10

[10- 2

mm/cm]

It defines the side warpage entity orthogonal to theflow, which is how many hundredths of millimeters ofbending are obtained for each centimeter of platelength.The obtained value is inversely proportional to thepart planarity

S Planarity index

Proportional calculus asfunction of RD e W (100for RD and W= 0,0 forRD=1 and W= 4)

Data Definition Calculus Practical meaning

Ln Part nominal length parallel to theinjection flow

Tn Part nominal length orthogonal tothe injection flow

Lm Real part measure parallel to theinjection flow

Tm Real part measure orthogonal to theinjection flow

RL Molding shrinkage parallel to theinjection flow

((Ln-Lm)/Ln)*100

[%]

It defines in percentage shrinkage entity parallel tothe injection flow:

RLmin; RLmed; RLmax

RT Molding shrinkage orthogonal to theinjection flow

((Tn-Tm)/Tn)*100

[%]

It defines in percentage the shrinkage entity orthogo-nal to the injection flow:

RTmin; RTmed; RTmax

DATA

RD, differential shrinkage

VALUE

-0.20÷0.20

0.20÷0.40

0.40÷0.60

0.60÷0.80

PLANARITY

EXCELLENT

GOOD

MIDDLE

SCARCE

WARPAGE

>1.00 VERY BAD

WL, WT, side warpage

0÷1

1÷2

2÷3

3÷4

VERY LOW

LOW

MIDDLE

HIGH

>4 VERY HIGH

S, dimensional stability

00÷30

30÷50

50÷70

70÷90

90÷100

DIMENSIONALSTABILITY

VERY BAD

SCARCE

MIDDLE

GOOD

EXCELLENT

[A] Used terms and definitions

[B] Practical meaning of differential shrinkage and Side warpage

It defines a significant value of a part dimensional sta-bility considering RD, WL and WT


At room temperature, parts, molded withthermoplastic resins, may have some areas inwhich macromolecules tend to arrangethemselves in parallel one to each other(ordered), alternated in region, in which arearranged disorderly. The first one percentage(crystalline), in comparison with the secondone (amorphous) determines the crystallinepolymer degree. In practice, there are amorphousresins (up to 0%) and semi-crystalline resins(up to 70%).This condition is extremely important for theshrinkage phenomenon. In fact, among semi-crystalline resins, over glass-transition temperature,macromolecules, arranged in the ordered

areas, start untying themselves from theirstructure, obtaining a higher and highermobility. As soon as the fusion temperature isreached, macromolecules are completely freeand the entire mass acquires a totally amorphousstructure.This phenomenon is associated with an importantspecific volume increase [C]. This is the typical polymer condition beforebeing injected into the cavity mold. As it cools,macromolecules tend to organize themselvesaccording to their own nature: they recover theprimary crystalline percentage. In the newreordered areas, the free space among moleculesis lower than the amorphous areas: a concretespecific volume reduction (“shrinkage”) is thusobtained.

For this reason, the higher is the densityand the crystalline areas extension, thehigher will be the mold shrinkage.In the amorphous resins, on the contrary, thecooling has the only effect to cool the structure,without any molecular reorganization. Theresulting low shrinkage is practicallycaused by the reduction of specific volume,due to drop in temperature.The crystalline degree of the part is alsoinfluenced by other contingent factors, relatedto the filling processes (for example nucleations),to the part geometry (especially thickness), tothe transformation conditions (temperaturesand pressures).

Summarizing, in relation to technicalThermoplastics, it is necessary to considerthese variables:⟩ Derived from material:

• Resin nature;⇒ Semi-crystalline;⇒ Amorphous.

• Composition:⇒ Reinforcements;⇒ Mineral fillers;⇒ Filling processes.

⟩ Derived from part:• Mold geometry.

⟩ Derived from process:• Transformation parameters.

2 - S H R I N K A G E P H E N O M E N O N

Semi-crystalline Semi-crystalline structure

Amorphous structureWeight increase

Semi-crystallinestructure

Volumetric shrinkagedue to cooling

+Molecular organization

High shrinkage

PolymerSpecific weight connected

to temperature

Before Transformation(Granulate, in hopper)

Heating effect(Melt mass, in

plasticizing barrel)

Cooling effect(In the mold cavity)

Mold shrinkage(Influenced factors)

Amorphous Amorphous structure Amorphous structureWeight increase

Amorphous structure

Volumetric shrinkage onlydue to cooling

Low shrinkage

[C] Resume

TEMPERATURE

TEMPERATURE

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· Semi-crystalline resinsSemi-crystalline resins have a highshrinkage tendency during the cooling(1.2÷2.5% on the neat resins); theyorientate themselves on the injection flow,allowing the creation of differentialshrinkage (RD) and/or warpages(WL-WT) easier, above all if theyare filled with anisotropic fillers,such as glass and carbon fibers.

· Amorphous resinsAs amorphous resins have notmolecular regularities, which haveto be restored during the cooling,they have lower shrinkages(0,4÷1.0%) and they are moredimensionally stable.In the table D it is reported aresume about molding shrinkageindicative values of the most impor-tant neat resins, in their normaltransformation conditions.The diagram 1 represents the RL-RTcorrelation and allows to finddifferences between the two chemi-cal natures. In this diagram it ispossible to notice the diagonal brokenline, which corresponds to RD=0 (any

warpage connected to the differential shrinkage).The positioning along this directrixmeans planarity and dimensional stability.

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2.1 THE MATERIAL2.1.1 - RESIN CHEMICAL NATURE

Semi-crystalline resins

LATENE

LATAMID 6

LATAMID 66

LATER

LATAN

PP

PA6

PA66

PBT

POM

1.50÷2.00

1.25÷1.50

1.35÷1.70

2.00÷2.40

1.85÷2.35

1.80÷2.30

1.35÷1.75

1.65÷2.20

2.20÷2.40

1.85÷2.50

PRODUCT RESIN RL [%] RT [%] RD [%]

0.20÷0.30

0.10÷0.40

0.10÷0.60

0.05÷0.25

0.05÷0.25

LARPEEK PEEK 1.60÷1.85 1.90÷2.15 0.15÷0.40

Amorphous resins

LASTILAC

LARIL

LATILON

LASULF

LAPEX R

ABS

PPOm

PC

PSU

PPSU

0,45÷0.60

0,60÷0.80

0,65÷0.80

0.80÷1.00

0.90÷1.10

0,45÷0.60

0,60÷0.80

0,65÷0.80

0.80÷1.00

0.90÷1.10

0.00÷0.10

0.00÷0.10

0.00÷0.10

0.00÷0.10

0.00÷0.10

[D] - Shrinkage of the most important neat polymers- plate 120 x 80 x 3.5 mm

[1] RL RT data scattering of the most important neat polymers


· Filler/reinforcement typeglass fibre, carbon fibre, mica:

these fillers underline remarkablythe differential shrinkage (RD) phe-nomenon in semi-crystallineresins. Because of their form(length is much higher than dia-meter) fibers tend to arrangethemselves parallel to the injectionflow. This causes an across shrin-kage, which is much higher thanthe along flow. Fiber orientation isalso connected to the form factor(Ln/Tn) between the two senses.This is demonstrated by the diffe-rential shrinkage (RD) entity [2],which is an important element forthis phenomenon.Thanks to their chemical structure,amorphous resins are affected onlyin part by shrinkage differences.They keep excellent planarity levels[7].

mineral fillers, glass beads:they are isotropic in shape; theyare arranged homogeneous in themelt mass, without followingpreferential flows. They grant lowdifferential shrinkages RD [2]and low warpages WL-WT. Forthis reason, their use is availablein those applications, which needgood or excellent planarity anddimensional stability (only insemi-crystalline resins).

2.1.2 - FILLER PROCESSES, REINFORCEMENTS, FILLERS

[2] Differential Shrinkage RD as function of flow length-breadth relation, on rectangular plates

1.45÷1.75 1.40÷1.60 0.00÷0.30 1.00÷1.20 2.30÷2.50

RT [%]

0.65÷0.95

0.70÷1.25

0.70÷1.05

0.80÷0.90

1.10÷1.40

RM [%]

0.40÷0.75

0.70÷0.90

0.70÷0.85

0.70÷0.80

0.90÷1.20

RD [%]

0.50÷0.65

0.65÷1.00

0.15÷0.40

0.00÷0.25

0.30÷0.50

WL

[10- 2

mm/cm]

4.90÷5.30

1.20÷1.60

1.00÷1.20

0.55÷0.75

2.60÷3.10

WT

[10- 2

mm/cm]

2.10÷2.50

1.45÷2.70

1.25÷2.10

0.70÷0.90

3.00÷3.50

[E] - Shrinkage values with different filler reinforcement typologies (30%) - PA66; plate 120 x 80 x 3,5 mm

REINFORCEMENT

CARBON FIBER

GLASS FIBER

BLEND GLASS FIBER/MINERAL FILLER

TALC

ARAMID FIBER

GLASS BEADS

RL [%]

0.15÷0.40

0.30÷0.45

0.35÷0.40

0.65÷0.75

0.80÷1.00

1.40÷1.55

[3] RL RT data scattering of the most important reinforcement types (30%) - PA66;plate120 x 80 x 3.5 mm

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s Blend mineral fillers/glass fibers,milled glass fibers:have an intermediate behaviourbetween the two above situations,as a function of percentagere lat ions among di f ferentcompounds [2].In the table E it is reported aresume about molding shrinkageindicative values of products filledwith the most important type offillers and reinforcements, used inThermoplastics. The diagram 3,which represents the RL-RTcorrelation, underlines data scatteringand allows to individuate differencesamong different typologies.In this case too, the diagonalbroken line, which corresponds toRD=0 (any warpage connected tothe differential shrinkage) is areference for the excellent planaritysituation.

· Reinforcement/Filler quantityConnected to the resin typologythe filler percentage influences onthe longitudinal RL, across RT,medium RM and differential RDshrinkage. In the graph 4 it isreported the value trend oflongitudinal RL and across RTshrinkage, connected to the glassfiber percentage (PA66). It ispossible to notice that over 30%longitudinal variations are rather low.

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[4] Longitudinal and across shrinkage connected to the fiberpercentage PA66; plate 120 x 80 x 3,5 mm

[5] Medium shrinkage RM connected to the filler percentage.PA66 with glass fiber (LATAMID 66), mineral filler (KELON A) andPC (LATILON); plate 120 x 80 x 3,5 mm

[6] Differential shrinkage RD connected to the filler percentage.PA66 with glass f iber (LATAMID 66), mineral f i l ler(KELON A) and PC (LATILON); plate 120 x 80 x 3,5 mm

The graph 5 describes, connectedto the filler percentage, mediumshrinkages RM of a PA66 (withglass fiber and mineral filler) andof a PC (glass fiber). Thanks tothe amorphous structure, PC(glass fiber) has low values. Onthe contrary, in a PA66 thevolumetric shrinkage ispractically constant, for thesame percentage and evenchanging the filler typology.But it is associated to a differentdifferential shrinkage RD [6],maximum in the range of 20÷30%.In the table F it is reported (seedefinitions) S dimensional stabilitymedium values of the most


· Additives Thermoplastic materials contain specificadditives to ensure or improve importantfeatures such as self-extinguish, lubrication,stabilization and pigmentation. Their presencehas an effect on the shrinkage behaviour.In the table G it is reported a resume ofshrinkage values, obtained with the mostimportant types of self-extinguish compounds.

important neat resins, with 30%glass fiber or mineral filler. In thiscase too, the material chemicalstructure plays an important role;amorphous resins, even whenthey are filled, keep excellent orgood dimensional stability values.Semi-crystalline resins can reachthe same level only with mineralfillers. This phenomenon isdescribed in the histogram 7.

The diagram 8 describes the RL-RT correlation,underlines data scattering and allows to indi-viduate differences between various typologies.In this case too, it is possible to compare valueswith the broken line (RD=0), as in theprevious cases.

Semi-crystalline resins

LATENE

LATAMID 6

LATAMID 66

LATER

LATAN

PP

PA6

PA66

PBT

POM

60÷75

68÷78

72÷80

55÷65

60÷70

40÷50

52÷67

57÷71

38÷52

45÷55

PRODUCT RESIN NEAT RESIN 30 % GLASS FIBER 30 % MINERAL FILLER

71÷80

69÷80

72÷82

68÷79

-

LARPEEK PEEK 60÷70 51÷66 -

Amorphous resins

LASTILAC

LARIL

LATILON

LASULF

LAPEX R

ABS

PPOm

PC

PSU

PPSU

85÷95

80÷90

85÷95

85÷95

85÷95

78÷89

75÷83

80÷82

80÷91

80÷88

-

-

-

-

-

[F] - Dimensional stability of the most important polymers with 30% of glass fiber and 30% of mineral filler - plate 120 x 80 x 3,5 mm

[7] Dimensional stability (S) of the most important polymers with30% of glass fiber and 30% of mineral filler. Plate 120 x 80 x 3,5 mm

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2.2 THE PART GEOMETRY

Injection-molded parts representa mix view of situations,comparable to a whole ofgeometric elements, variablein form, complexity, size andsurface. Thickness and flowlength, runner size and gategeometry play an importantrole: they influence directlythe pressure entity, which isproduced during the fillingphase. The obtained shrinkageis the consequence of amore or less load loss, verifiedduring the process.

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[8] RL RT data scattering of the most important self-extinguishingagents. PA66 25% glass fiber; plate 120 x 80 x 3,5 mm

[9] Longitudinal, across and medium shrinkage connected to the part thick-ness - PA66 30% glass fiber; plate ISO 294-3 60 x 60; pressure in cavity at400 bar

RT [%]

0.75÷1.00

0.75÷1.15

1.00÷1.30

1.20÷1.40

RM [%]

0.50÷0.70

0.55÷0.85

0.70÷0.95

0.80÷1.00

RD [%]

0.40÷0.65

0.20÷0.70

0.40÷0.90

0.70÷1.00

WL

[10- 2

mm/cm]

0.60÷1.50

1.80÷2.50

2.30÷3.00

0.80÷2.00

WT

[10- 2

mm/cm]

1.30÷2.50

3.00÷4.00

1.50÷2.50

1.25÷2.50

[G] - Type of self-extinguishing influence- PA66 25% glass fiber; plate 120 x 80 x 3,5 mm

ADDITIVE

Polymeric self-extinguishing agentAlogen self-extinguishing agentSelf-extinguishing agent with

Melamine saltSelf-extinguishing agent with

red phosphorus

RL [%]

0.25÷0.40

0.35÷0.55

0.45÷0.65

0.35÷0.45


[10] Longitudinal, across shrinkage connected to the part thicknessand glass fiber percentage; PA66; plate 120 X 80 x 3,5 mm

[11] Differential shrinkage connected to the part thickness and glassfiber percentage - PA 66; plate ISO 294-3 60 x 60; cavity pressure 600 bar

[12] Warpage connected to the part thickness and glass fiber percentage- PA66; plate 120 x 80 x 3.5 mm

Differential shrinkage RD[11] describes a trend, whichis proportional to the thick-ness and reaches maxi-mum values around 20÷30%(see graph 6).

According to the sideWarpage trend WM [12] it isobtained higher and highervalues for the majorthickness because of a lit-tle increase for the lowestthickness.

2.2.1 - THICKNESSES

The results in the graph 9describe the strictly connectionbetween molding shrinkage (atthe same circumstances) andpart thickness. Moldingshrinkage is directly proportionalto thickness (it doubles withthickness doubling). The phenomenon reducesitself lenghting the flow pathor elevating the filler level. In the example [10] it is possibleto notice that, increasing thefiber percentage, the variationbetween the shrinkage measuredon the major and minorthickness tends to 0 (in thecase of across sense [RT]).

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s 2.2.2 - FLOW LENGHT, PART GEOME-TRY, INJECTION SECTION

The analysis has been carried outon 7 different types of moulded parts,with different thicknesses, flows andinjection sections. As it is possi-ble to notice [H, 13], there is a widerange o f data, in the longitudi-nal sense RL (0,19÷0,91%) and inthe across RT sense (0,78÷1,48%).The high result scattering (it hasnot been possible to indiv iduateany pract ica l correlation betweenthe independent variables and theobtained results) brings to the con-clusion that every object, with itsown geometries, has particular behav-iours of molding shrinkage. Theseare difficult to reproduce on testspecimens with different shapes,excepting through precise flowsimulation analyses.

2.3 TRANSFORMATION PARAMETERS

The material shrinkage beginsduring the holding pressureapplication and continues throughthe cooling phase, until thecomplete part solidification atroom temperature. These are thebasic phases; the pressure on thepart reduces the shrinkage of thesame, conditioning the entity.The best instrument to analyzethis aspect is the PVT diagram[I, L]: it studies the correlationamong temperature, specific

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TESTSPECIMEN SHAPE SIZE INJECTION

[mm]VOLUME

[cc]

GATEAREA[cm2]

Test specimen Rectangular

Rectangular

Rectangular

Rectangular

Rectangular

Base

Cover

125

120

120

110

60

80

80

12.7

80

80

55

60

80

80

3.2

3.5

2.0

1÷2

2.0

0.5÷6

2.5÷

Side 3.0 x 10

Laminar 1 x 80

Laminar 1 x 80

Side 2 x 12

Laminar 0,75 x 60

Capillar

Capillar

5.1

33.6

19.2

9.1

7.2

24.4

30.6

0.30

0.8

0.8

0.24

0.45

0.03

0.03

RL[%]

0.32

0.43

0.30

0.19

0.54

0.74

0.91

RT[%]

2.04

1.48

1.38

0.78

1.07

1.05

1.12

RM[%]

1.18

0.94

0.83

0.49

0.81

0.90

1.02

RD[%]

1,72

1,05

1,08

0,59

0,53

0,31

0,21

Plate

Plate

Plate

Plate ISO 294 type D2

Box

Box

[H] - Test specimens used for the measurement and obtained results; PA66 30% glass fiber

[13] Longitudinal, across and medium shrinkage calculatedon different types of test specimens-PA 66 30% glass fiber

[I] Diagram PVT in the molding injection cycle of a PA66

High Performance Thermoplastics

in the cavity [14], which decreases with the holdingpressure application. This is caused by theprogressive gate and part solidification. Because ofthe higher and higher part viscosity, there is alower transmission of hydraulic pressure, appliedby the screw (load loss).As soon as the gate solidification is reached (timeis variable in function of its section), cavity pressureis null and any further holding pressureapplication is irrelevant.

11

This is an important phenomenon because thederived molding shrinkage is directly connected tothe effective pressure in cavity.Moreover, some material features (fluidity) andsome transformation parameters (melt temperatureand/or mould temperature) allow more or lessload loss for the same applied pressure.

STEP MOLDING CYCLE PHASE

Filling startA

TEMPERATURE

Molding melt temperature

PRESSURE

Atmospheric pressure

VOLUME

Volume corresponds tothe highest expansion

Filling end- holding startB Constant (little decrease) Constant or little increase,till complete filling Little decrease

Highest pressure reached-partsolidification startC Constant (little decrease) It increases quickly It decreases quickly

Holding end- cooling pausestartD Decreases It decreases quickly Little decrease

Cooling pause- atmosphericpressure reachingE Decreases Atmospheric pressure is

reached Decreases

EjectionF Decreases Atmospheric pressure Decreases

Final stateG Room temperature Atmospheric pressure Final volume

[14] Hydraulic and cavity pressure during injection and holding phase;plate ISO 294-3 60 x 60 x 2.0 mm

[L] - Diagram phases in the injection molding

volume and pressure; it gives alsoimportant information about thematerial behavior, when it isheated/cooled under the pressureload effect.The volume difference, surveyedbetween A and G points, correspondsto the real value of moldingshrinkage.Some of the singular phases aregoing to be analyzed deeply.

2.3.1 INJECTION AND HOLDINGPHASE

· injectionIn this phase the material istransferred, through the nozzle,from the barrel to the mould. Thescrew works as piston and exertsa pressure on the polymer, whichincreases with slopes proportionalto the material viscosity andnozzle speed, until the switchingpoint [14]. The holding phasestarts. Any incorrect formulationof this parameter (advanced-delayed in comparison with theeffective mold filling), besidescreating different problems,influences on the pressure load incavity and consequently on theshrinkage entity.

· holdingDuring the holding phase, it isverified a difference between thepressure, applied by the screw(constant) and the real pressure

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s In the graph 15 and 16it is reported the medi-um shrinkage trend of aPA66, in function ofthe cavity pressure(in different times)and holding time.It is possible to noticethat shrinkage decreas-es with the pressureincrease and describes atemporal curve: beyonda certain point no realeffect exists any more.This time correspondsto the complete solidifi-cation of the injectionsection; screw pressurehas any more practicaleffect on the real pres-sure in the mould.

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[15] Medium shrinkage connected to the cavity pressure with different typeof holding - Neat PA66; plate ISO 294-3 60 x 60 2,0 mm

[16] Medium shrinkage connected to the holding t ime - Neat PA66;plate ISO 294-3 60 x 60 x 2.0mm; cavity pressure 600 bar

[17] Side warpage connected to cavity pressure- Neat PA66; plateISO 294-3 60 x 60 x 2.0 mm

WM side warpage presents,on the contrary, a trendthat is inversely proportionalto the applied pressure [17],but it is directly proportionalto its duration [18].

2.3.2 - COOLINGIn semi-crystalline resins,if mould temperature andholding pressure time arecorrect, the part will reachthe highest crystalline leveland the cooling pause willensure the completesolidification of it.In this case, moldingshrinkage will be inverselyproportional both to thecooling time and to theapplied pressure [19].


[18] Side warpage connected to the holding t ime - Neat PA 66;plate ISO 294-3 60 x 60 x 2.0 mm; cavity pressure 600 bar

[19] Medium shrinkage connected to the cooling time with different cavitypressure values - Neat PA 66; plate ISO 294-3 60x60x2.0 mm

[20] Medium shrinkage connected to melt temperature - PA 6/66self-extinguishing halogen free; plate ISO 294-3 60 x 60x 2.0 mm;with or without adjustment of cavity pressure at 600 bar

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2.3.2 TEMPERATURES · MeltMelt temperature has adirect effect on thepressure transmissionfrom the screw to thecavity (the higher is thetemperature, the higheris the material fluidity;consequently the higheris the transmittedpressure). If anyadjustment on theholding value is made tokeep constant cavitypressure, there will bean inversely relationbetween temperatureand shr inkage.

In the example [20] it isreported (for a PA6/66self-extinguish Halogen free)the medium shrinkage RMtrend connected to the Melttemperature, without andafter compensation, at 600 barin cavity. In the second case, there isnot any important variation;for th is reason Melttemperature is not directlyconnected to the shrinkage,but it has an effect on theshrinkage because it causesthe cavity pressureincrease.

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[22] Medium Across shrinkage connected to mould temperature-PA 66 30% glass fiber; plate ISO 294-3 60 X60 2.0 mm; with orwithout adjustment of cavity pressure at 400 bar

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[21] Medium Longitudinal shrinkage connected to moldingtemperature. PA 66 30% glass fiber; plate ISO 294-3 60 x 60 x 2.0 mm;with or without adjustment of cavity pressure at 400 bar

· MouldThe material structure isvery important: semi-crystalline resins need atemperature higher thantheir glass transition. Underthis temperature level materialcould freeze in an improperamorphous structure. Theresult is a low moldingshrinkage [21, 22] but bythe time the part will recoverits original crystallinestructure, creating warpageproblems (post shrinkage).This phenomenon will berelevant when the partworking temperature ishigher than mold temperatureduring the transformation.

In amorphous resins, on thecontrary, mould heating ismade to improve the meltmass flow in the cavity,without having real effectson shrinkage properties.Mould temperature,moreover, has only a littleinfluence on the pressureload in cavity. This can beverified in the graph 21-22,in which there is a littledifference among theobtained curves, with orwithout adjustment at 400 bar.


Semi-crystalline resin ↑↑ ↑↑ 1,7

Shrinkage Warpage References(Graph number)

Resin features

Amorphous resin ↑↑ ↑↑ 1,7

Glass fibre reinforcement ↑↑ 3,4,6,7,10,11,12

Mineral filler ↑↑ 3,5,6

Self extinguishing agent ↑↑ ↑↑ 8

↑↑

Thickness ↑↑ ↑↑ 9,10,11,12

Flow length ↑↑ 2

Transformation parameters

Cavity pressure ↑↑ 15,17,19,20,21,22↑↑

Holding pressure time 15,16,18↑↑

Cooling time ↑↑ 19↑↑

Melt temperature ↑↑ 20

Mould temperature ↑↑ 21,22↑↑

↑↑ ↑↑↑↑

↑↑

↑↑

Mould geometry

Key

↑↑ == directly proportional

↑↑ == directly proportional, then stable

== directly proportional, then inversely proportional

== == stable

== inversely proportional

== inversely proportional, then stable

↑↑ ↑↑

↑↑

↑↑

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ISO 294-1 Plastic - Injection moulding of testspecimens of thermoplastic materials; Generalprinciples, and moulding of multipurpose andbar test specimens

ISO 294-3 Plastics – Injection moulding oftest specimens of thermoplastic materials;Small plates

ISO 294-4 Plastics – Injection moulding oftest specimens of thermoplastic materials;Determination of moulding shrinkage

McCrum N.G., C.P. Buckley, C.B. Bucknall –Principles of Polymer Engineering

Pavan A, PVT relation in the polymertransformation. Issues of the XVI AIM SchoolConvention- Italian Association of macromoleculesscience and technology.

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DISCLAIMER

LATI does not guarantee that the data contained in this brocure are current, complete and error-free.To double check the values, users are kindly requested to contact our technical or commercial offices.

LATI Industria Termoplastici S.p.A. declines all responsability arising from any improper use of the information described in this document.

4 – REFERENCES AND BIBLIOGRAPHICAL SOURCES

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Printed in Italy 08/01/2008/C&I.002 LINK S.r.L.

Z.I. des Ebizoires, 4 Rue des Frères LumièreF - 78370 PLAISIR

tel. +33 (0)1 - 30791819fax +33 (0)1 - 30791818

http://www.lati.com - e-mail: [email protected]

FFRRAANNCCEE

LATI FRANCE S.A.S.

F

Borsigstraße, 12D - 65205 WIESBADEN - Nordenstadt

tel. +49 (0)6122 - 90820fax +49 (0)6122 - 908222


DDEEUUTTSSCCHHLLAANNDD

LATI IndustriaTermoplastici

Deutschland GmbH

D

Calle Muntaner, 270 - Atico A - DE - 08021 BARCELONA

tel. +34 93 - 2097377fax +34 93 - 2011519


IIBBEERRIIAA

LATI Ibérica, S.L.Unipersonal

E

P.O. Box 103Sandbach Cheshire CW11 2ZF

tel. +44 (0)1270 - 759490fax +44 (0)1270 - 759491


UUNNIITTEEDD KKIINNGGDDOOMM

LATI UK LIMITED

UK

Gullbergs Strangata 36 A-CS - 411 04 GÖTEBORGtel. +46 (0)31 - 7740236fax +46 (0)31 - 7740736


SSVVEERRIIGGEE

SCANDILATITERMOPLASTICI AB

S

Z.I. des Ebizoires, 4 Rue des Frères LumièreF - 78370 PLAISIR

tel. +33 (0)1 - 30791819fax +33 (0)1 - 30791818


BBEENNEELLUUXX && SSCCHHWWEEIIZZ

LATI FRANCE S.A.S.

Rua Prof. Alipio Dutra, 13405635-040 - SÃO PAULO - SP

tel. +55 (0)11 - 35024700fax +55 (0)11 - 35024698


BBRRAASSIILL

LATI TERMOPLÁSTICOSDO BRASIL LTDA

BR

Via F. Baracca, 7I - 21040 VEDANO OLONA (Va)

tel. +39 - 0332 409111fax +39 - 0332 409235


AASSIIAA

LATI IndustriaTermoplastici S.p.A.

KR

CHB

2036 eWall Street - Suite DMount Pleasant, SC 29464tel. +1 - 843 - 284 - 5551fax +1 - 843 - 881 - 8352


UUNNIITTEEDD SSTTAATTEESSooff AAMMEERRIICCAA

LATI USA Trading, inc.

USA

Via F. Baracca, 7I - 21040 VEDANO OLONA (Va)

tel. +39 - 0332 409111fax +39 - 0332 409307


IITTAALLIIAA

LATI IndustriaTermoplastici S.p.A.

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Dimensional Molding Shrinkages