Designing with Celcon acetal copolymer.pdf

8/18/2019 Designing with Celcon acetal copolymer.pdf

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Designing with Celcon ®

acetal copolymer C E

- 1 0

C e l c o n

®

a c e t a l c o

p o l y

m e r

TiconaA business of Celanese AG


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ForewordThe C elcon ® Acetal C opoly mer D esign Manual (C E-10) is w ritten for parts designers, materials engineers,mold designers and ot hers wishing to take advant age of t he unique and desirable features of t his versatile line ofthermoplastic materials.

This manual covers the basic structure and product characteristics of the broa d classes of the C elcon acetalcopoly mer product line and its phy sical, thermal, mechanical, and electrical properties. D imensional stab ility, creepand other long term properties, and resistance to the environment (including chemical resistance) are alsodiscussed. An introd uction to gear and b earing design is included. Mold design criteria, methods of assembly, andsecondary operations including machining, part bo nding and surface decoration complete the brochure.

Throughout the manual, the design information is presented primarily for product classes rather than fo rindividual grades, using a descriptive rather t han a detailed m athematical treatment. Some simple calculationexamples are included to illustrate a specific property (such as creep deflection) where appropriate.

Ticona provides additional technical literature to compliment this bro chure. Readers w ill find information o ngeneral design principles of engineering thermoplastics in Designing with Plastics: The Fundamentals (TDM-1) .Addit ional specific information on C elcon acetal copolymer can be found in Celcon acetal copolymer Short-termProperties Brochure (CE-4), Celcon acetal copolymer Processing and Troubleshooting Guide (CE-6) andCelcon acetal copolymer Ultraviolet Resistant Grades Extend Part Life in Harsh Environment (CE-UV) .These brochures are available from o ur I nternet site, w w w.ticona.com, or can be req uested t hrough TechnicalInformation at 1-800-833-4882.

C omments and suggestions fo r improvement of this and o ther Ticona technical literature are alway s w elcome, andshould b e sent to us by phone at 1-800-833-4882, or by w riting t o us at the address show n on the back cover.

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Overview

Physical and Thermal Properties

Mechanical Properties

Dimensional Stability

Environmental Resistance

Electrical Properties

Part Design Criteria

Gear Design

Bearing Design

Mold Design

Assembly

Machining and Surface Operations

Celcon ®

acetal copolymer

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Introduction

1. Overview 11

1.1 C hemistry of Acetal P oly mers 111.2 G eneral C haracteristics 111.3 P roduct Ty pes 111.4 Regulatory C odes and Agency Listings 131.5 P roduct Support 131.6 Safety and H ealth Information 13

2. Physical and Thermal Properties 15

2.1 C ry stallinity 152.2 Thermal C onductivity 152.3 Specific H eat 152.4 C oefficient of Linear Thermal Expansion 152.5 Thermal Stability 152.6 Flammability 16

3. Mechanical Properties 17

3.1 Introduction 173.2 ISO Test Standards 173.3 Short Term Mechanical P roperties 183.3.1 Tensile and Elongation 18

3.3.2 Elastic Modulus 193.3.3 Secant Modulus 193.3.4 Izod Impact 193.3.5 P oisson’s Ratio 193.3.6 Shear Modulus 193.3.7 Shear Strength 193.3.8 Weld Line Strength 203.3.9 Molding Effects 203.3.10 Anisotropy 203.3.11 Abrasion/Wear Resistance 203.3.12 Temperature Effects 213.3.13 Stress-Strain Measurements 21

3.3.14 D y namic Mechanical Analy sis 233.3.15 Deflect ion Temperature Under Load (D TUL) 233.3.16 U nderw rit ers L aborat ories (U L ) Thermal 24

Index Ratings3.4 Long Term Mechanical P roperties 253.4.1 Introduction 253.4.2 C reep 253.4.3 C reep D eflection 253.4.4 C reep Rupture 273.4.5 C reep Recovery 273.4.6 Relaxation 283.4.7 Fatigue 29

Table of Contents


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4. Dimensional Stability 31

4.1 C oefficient of Linear Thermal Expansion 314.2 Shrinkage C aused by P rocessing 31

(Injection M olding)4.3 Warpage 314.4 P ost-Molding Shrinkage 334.5 When Annealing is N ecessary 334.6 Tolerances 334.7 Moisture Absorption 34

5. Environmental Resistance 35

5.1 C hemical Resistance 355.2 Fuel Resistance 385.3 H y drolic Stability 395.4 Recommended U se Temperatures 405.5 Weathering Resistance 405.6 G as P ermeability 41

6. Electrical Properties 43

6.1 Effects of Aging 436.2 Effects of Thickness 43

7. Part Design Criteria 45

7.1 Basic P rinciples 45

7.2 Wall Thickness 457.3 Ribs 467.4 Bosses and Studs 467.5 C ores 467.6 Fillets and Radii 47

8. Gear Design 51

8.1 Spur G ear D imensions and Terminology 518.2 C o mparison of Metal and Plast ic G ear D esign 568.3 D esign C a lcula tio ns fo r C elco n ® 57

Acetal C opolymer Spur G ears

8.4 G ear Accuracy 588.5 G ear Tooth Modification 598.6 Tooth Thickness 598.7 The Long-Short Addendum Sy stem 608.8 Full Fillets Radius 618.9 Tip Modification 618.10 G ear N oise 618.11 Attaching a P lastic G ear to a Shaft 618.12 Stress C oncentration 628.13 G ear Ty pes Summary 628.14 G ear Application Q uality N umber 65

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Overview







Gear Design

Bearing Design

Mold Design

Assembly


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9. Bearing Design 67

9.1 Introduction 679.2 P roperties of C elcon ® acetal copolymer Bearings 679.3 C elcon acetal copoly mer Bearing G rades 689.4 P ressure-Velocity Relationship 699.5 B earing Wear Fact ors 709.6 C learance 719.7 Bearing Wall Thickness 719.8 Bearing Length 719.9 Bearing Attachments 719.10 O ther D esign Tips 72

10. Mold Design 73

10.1 G eneral C riteria 7310.2 Mold Bases 7310.3 Mold C avities and C ores 7310.4 Mold Surface Finish 7310.5 Sprue Bushings 7410.6 Runners 7410.7 Runnerless Molding 7410.8 G ates - Standard Injection Molding 7510.9 Vents 7710.10 C ooling C hannels 7710.11 D raft 7710.12 P arting Lines 7710.13 Molding Machine Barrels and Screw s 78

10.14 Suppliers 78

11. Assembly 79

11.1 Molded-In Assemblies 7911.2 Snap-Fit Joints 7911.3 Molded-In Threads 8011.4 P ress-Fits 8111.5 Thermal Welding 8211.6 Assembly w ith Fasteners 8311.7 Self-Tapping Screw s 8511.8 Threaded Metal Inserts 85

11.9 Sheet Metal N uts 8511.10 C hemical Bonding 86


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12. Machining and Surface Operations 87

12.1 Machining – G eneral C riteria 8712.1.1 D rilling 8712.1.2 Saw ing 8712.1.3 Turning 8712.1.4 Milling 8812.1.5 Threading and Tapping 8812.1.6 Reaming 8812.1.7 Blanking and P unching 8812.1.8 Shaping 8812.2 Automatic Screw Machines 8912.3 Finishing O perations 8912.3.1 Sanding 8912.3.2 Rotary P ow er Filing 8912.3.3 Barrel D eburring and P olishing 8912.3.4 Surface O perations 8912.3.5 P ainting 8912.3.6 P rinting 8912.3.7 H ot Stamping and D ecorating 9012.3.8 Colorability 90

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Overview







Gear Design

Bearing Design

Mold Design

Assembly


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List of FiguresFigure 3.1 C elcon ® acetal copolymer stress-strain properties (ISO 527) 18Figure 3.2 C elcon acetal copolymer tensi le st rength range (ISO 527) 18Figure 3.3 Celcon acetal copo lymer f lex modulus range (ISO 178) 18Figure 3.4 C elcon acetal copolymer secant modulus range (ISO 527) 18Figure 3.5 Stress-strain plot for 25% glass-reinforced 21

grade of C elcon acetal copoly mer (ISO 527)Figure 3.6 Stress-strain plot for unfilled 9.0 melt flow grade 21

of C elcon acetal copolymer (ISO 527)Figure 3.7 Stress-strain plot for toughened grade of C elcon 21

acetal (ISO 527)Figure 3.8 Secant mo dulus-st rain plo t fo r 25% G lass-reinfo rced 22

grade of C elcon acetal copoly merFigure 3.9 Secant modulus-strain plot for unfilled 9.0 melt 22

flow grade of C elcon acetal copolymerFigure 3.10 Secant modulus-strain plot for toughened grade 22

of C elcon acetal copoly merFigure 3.11 Typica l normalized C elcon acetal copo lymer DMA plo t 23Figure 3.12 Normalized creep modulus plots for C elcon 25

acetal copolymer gradesFigure 3.13 U -beam cross section 26Figure 3.14 C reep rupture, C elcon acetal copolymer unfilled 9.0 27

melt flow gradeFigure 3.15 C reep recovery for C elcon acetal copoly mer 27Figure 3.16 Flex fatigue plot for C elcon acetal copoly mer 29

(ASTM D 671)Figure 4.1 E ffect of molding conditions and w all thickness on 32

mold shrinkage for C elcon acetal copolymer M90 ™

F igur e 4.2 Shrinka ge d ue t o heat aging f or 9.0 st and ard melt flo w 33grade of C elcon acetal copoly mer

F igur e 4.3 Wa ter a bso rpt io n o f unf illed C elco n a cet al co po ly m er 34under various conditions

Figure 4.4 D imensional change due to w ater absorption of 34unfilled C elcon acetal copoly mer

F igur e 5.1 Tensile st rengt h at y ield f or C elco n a cet al co po ly m er 38M90™ after exposure to various fuels at 65° C

F igur e 5.2 Tensile st rengt h at y ield f or C elco n a cet al co po ly m er 38TX90P lus after exposure to vario us fuels at 65°C

F igur e 5.3 Tensile st rengt h at y ield f or C elco n a cet al co po ly m er 39EC 90P lus after exposure to various fuels at 65° C

F igur e 5.4 Tensile st rengt h at br eak f or C elco n a cet al co po ly mer 39G C 25TF aft er exposure to various fuels at 65° C

Figure 5.5 C hange in l inear dimensions at 23° C (73° F) and 3950% relative humid ity

Figure 5.6 Change in t ensile st rength a fter exposure to 82°C water 39and t ested at 23° C (73°F ) and 50% relative humidity

Figure 5.7 C hange in t ensile modulus aft er hot w at er exposure 40at 82° C and 100° C

Figure 5.8 Change in t ensile st rength a fter boiling water exposure 40at 100° C

Figure 5.9 C hange in notched Izod impact after hot w ater 40exposure at 82° C

Figure 5.10 Change in melt f low rate after hot water exposure at 82°C 40


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List of Figures (continued)

Figure 5.11 O utdoor w eather ing resistance for Celcon ® 41acetal copoly mer (black)

Figure 5.12 Simulated w eat hering resistance for C elcon acetal 42copoly mer (colored gra des)

Figure 6.1 D ielectric strength of unfilled C elcon acetal copolymer 44vs. th ickness @23° C

Figure 6.2 Dielect ric constan t o f unfilled Celcon acetal copo lymer 44vs. frequency @23° C

Figure 6.3 D issipation factor of unfilled C elcon acetal copolymer 44vs. frequency @ 23° C

Figure 7.1 Examples of uniform and non-uniform (poor) 45w all thickness

Figure 7.2 P roper rib proportions 46Figure 7.3 P oor and good rib design 46Figure 7.4a P roper draft angle for bosses 47Figure 7.4b U se of ribs w ith bosses 47Figure 7.4c P oor (left) and good (right) bosses 47Figure 7.4d Recommended ejector sy stem for bosses 47Figure 8.1 Involute curve generation 51Figure 8.2 Basic gear nomenclature 51Figure 8.3 Load bearing characteristics for grades of C elcon 57

acetal vs. load cy clesFigure 8.4 Variable center distance measuring device 58Figure 8.5 Idealized chart of measuring device radial displacements 58Figure 8.6 Backlash in a gear pair 59Figure 8.7 Tip relief 61

Figure 8.8 Some ty pical gear ty pes and arrangements 63Figure 9.1 D y namic coefficient of friction vs. speed 67Figure 9.2 D ynamic coefficient of friction vs. pressure 67Figure 9.3 PV values for unlubricated grades of C elcon acetal copolymer 69Figure 9.4 R ad ial w ear of unlub ricat ed C elco n acet al co po ly mer 70

journal bearingFigure 9.5 Recommended bearing clearances 71Figure 9.6 C learance for interference fit bearings 71Figure 10.1 Some basic gate designs suitable for Celcon acetal copolymer 76Figure 11.1 Barbed leg snap-fit 79Figure 11.2 C y lindrical snap-fit 79Figure 11.3 Ball and socket snap-fit 80

Figure 11.4 Snap-on/snap-in fits 80Figure 11.5 Molded plastic internal and external threads 81Figure 11.6 Alternative press-fit designs for a metal pin in a 81

plastic hubFigure 11.7 Ty pical ultrasonic w elding eq uipment 82Figure 11.8 Joint design for ultrasonic w elding 83Figure 11.9 U ltrasonic staking, sw aging and spot w elding 84Figure 11.10 Bolt assembly, stress problems and solutions 84Figure 11.11 U ltrasonic ty pe threaded inserts 85Figure 11.12 “ P ush-on” sty le fasteners 86Figure 12.1 Typical lathe tool bits for turning C elcon acetal copolymer 88


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Celcon ®

acetal copolymer

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Overview







Gear Design

Bearing Design

Mold Design

Assembly


List of Tables

Table 1.1 Regulatory listings 12Table 2.1 Thermal and physical propert ies of C elcon ® acetal 15

copolymer gradesTable 2.2 Flammability and burning rate of Celcon acetal copolymer 16Table 3.1 ISO /ASTM t ypical properties comparison 17Table 3.2 D TU L stress-modulus values per ISO 75 24

test methodTa ble 3.3 E xpa nd ed D TU L t ab le f or C elco n a cet al co po ly mer per 24

ISO 75 test methodTable 3.4 Summary of UL relative thermal index ratings for 25

C elcon acetal copoly merTable 3.5 I nit ial creep (flexural) modulus values for grades of 26

C elcon acetal copoly merTable 4.1 C o efficient of linear t hermal expansion (C LTE ) for 31

various grades of C elcon acetal copoly mer, 23-80°CTable 4.2 Effect of processing conditions on part shrinkage 33Table 4.3 Shrinkage before and after annealing different 34

part thicknessesTable 5.1 C hemical resistance of C elcon acetal copolymer 36

standard unfilled grad esTable 5.2 Test fuels composition 38Table 5.3 C elcon acetal copolymer grades for weather ing resistance 41Ta ble 5.4 G a s perm ea bilit y of C elco n M 25, M90 ™ and M270 ™ 41Table 6.1 Electr ical propert ies of C elcon acetal copolymer 43

(at 23° C and 50% relative humidity)Table 8.1 G ear tooth nomenclature and definitions 52Table 8.2 G ear sy mbol terminology 54

Table 8.3 Standard gear dimensions 54Table 8.4 Terms used in defining single spur gear geometry 55Table 8.5 C o nversion factors for terms used in defining single 55

gear geometryTable 8.6 Fundamental relat ionships between a spur gear 55

and pinionTa ble 8.7 D ef init io n o f lo ad char act erist ic c 57Table 8.8 Ty pical q uality number ranges for gear applications 59Ta ble 8.9 Appr oxim at e values of a dd end um f or ba lanced st rengt h 60Table 9.1 D ynamic coefficient of friction for unlubricated 67

standard C elcon acetal copolymer against other materialsTable 9.2 P V ranges for C elcon acetal copoly mer sy stems 69

Table 10.1 Runner size recommendations for C elcon acetal 75copolymer

Table 10.2 Recommended gate dimensions for rectangular 75edge gates, mm (in.)

Table 11.1 Interference guidelines for shear joints w ith 84C elcon acetal copoly mer

Table 11.2 D riving and stripping torq ues of self-tapping 85screw s in C elcon M90 ™ acetal copolymer


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List of Tables (continued)Table 11.3 P erformance of “ push-on” sty le fasteners using 86

C elcon® acetal copolymer M90 ™ studsTable 11.4 Adhesive bonding of C elcon acetal copo lymer to it self 86

and other substratesTable 12.1 R ecommended drilling speeds for C elcon acetal 87

copolymer


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1. Overview 1.1 Chemistry of Acetal PolymersAcetal polymers are chemically known aspolyo xym ethylenes (P O M). Tw o ty pes of acetalpolym ers are commercially a vailable:

Homopolymer is prepared by polymerizinganhydrous formaldehyde to form a poly mercomposed of o xymethy lene repeating units(-CH 2O ). Acetal homopoly mer products havesomewhat better short-term mechanicalproperties than copoly mer.

Copolymers, including C elcon ® acetal copoly mer,are prepared by copoly merizing trioxane (cyclictrimer of formaldehyde) with a cyclic ether(usually containing an ethoxy group) to form apolymeric chain composed of oxymethylene(-CH 2O ) and oxyethylene (-CH 2-C H 2-O-)repeating units. C opoly mers have a wider pro-cessing w indow than homopolymers, and areinherently mo re stable and resistant t o t hermaldegradation during service life. This is becausethe repeating copoly mer units block poly mer“ unzipping” under thermal stress.

Both the homopolymer and copolymer are end-capped, a nd also contain specific additives to preventirreversible thermal depolymerizat ion of the poly merbackbone d uring processing.

1.2 General CharacteristicsC elcon acetal copoly mer is a high strength, crystallineengineering thermoplastic material having a desirablebalance of excellent properties and easy processing.C elcon acetal copoly mer is a candidat e to replacemetals and t hermosets b ecause of its predictable long-term performance over a w ide range of in-servicetemperatures and harsh environments. C elcon acetalcopolymer retains properties such as creep resistance,fatigue endurance, w ear resistance and solventresistance under demanding service conditions.

C elcon acetal copoly mer can be converted easilyfrom pellet f orm into parts of different shapes using avariety of processes such as injection mo lding, blow molding, extrusion, rotational casting andcompression molding. Rod and slab stock, whichcan be machined readily into desired shapes, isalso a vailable.

1.3 Product TypesBo th standard and specialty grad es of C elcon acetalcopoly mer are designed to provide a w ide range ofproperties to meet specific applications. Standard andcustom grades of C elcon acetal copolymer can beobtained in pre-compounded form and in colorconcentrates, which may be blended with othergrad es. All colora nts used in C elcon resins are leadand cadmium-free. The most common categories ofC elcon r esins are described below.

Unfilled G eneral purpose M-series products are identified bymelt flow rate. D ivide the grade number by 10 toobt ain the melt flow rate [e.g., C elcon acetalcopolymer M90 ™ has a melt flow rate of 9.0 (gramsper 10 minutes, per ASTM D 1238)]. P rod uctsdesignated by a higher melt flow rate (i.e. C elconacetal copolymer M450) fill thinner walls andcomplex shapes more readily a nd maint ain the samestrength and stiffness, but exhibit a slight d ecrease intoughness. Products with lower melt flow rates, i.e.C elcon a cetal copoly mer M25 exhibit, increasedtoughness. C elcon acetal copoly mer C FX -0288 is anunfilled acetal polymer used for blow molding andextrusion w here high melt strength is required.

Glass Fiber Coupled G lass fiber coupled prod ucts provide higher strengthand stiffness than the unfilled grades. These productsare identified w ith a number indicating the percentageof glass in the product and are based on generalpurpose C elcon acetal poly mers. The glass fibers arechemically coupled to t he polymer matrix.

Glass Bead Filled These grades contain glass beads fo r low shrinkageand w arp resistance, especially in large, flat andthin-walled parts.


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Agency ScopePlumbing Code Bodies:International Association of Plumbing Plumbing fixtures and specific plumbing and mechanicalMechanical Officials (IAPMO) applications covered in the various codesBuilding Officials Conference of America (BOCA)Southern Standard Building Code

Canadian Standards Association Plumbing fixtures, fittings and potable water contact items

Plastic Pipe Institute (PPI) Recommended Hydrostatic Design Stress (RHDS) rating of 1,000psi at 23°C (73°F) as an injection molded plumbing fitting

Food and Drug Administration (FDA) Food contact applications including food machinery componentsconforming to 21 CFR 177.2470, Drug and Device Master Files

United States Pharmacopoeia (USP) Class VI Compliant

NSF International Standards 14, 51, 61 Items including plumbing components for contact with potable water

Underwriters Laboratories (UL) Various UL ratings for flammability, electrical, mechanical andthermal service use

Dairy and Food Industries Supply Association (DFISA) Sanitary Standards 3A compliant

United States Department of Agriculture (USDA) Approved for direct contact use with meat and poultry products

ASTM 6778 [Replaces ASTM 4181, General Material SpecificationMilitary Specification LP-392-A, Mil-P-6137A(MR)]

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Low Wear Low wear grades are chemically modified to providelow coefficient of friction and enhanced wearresistance, and are exceptional for demandingapplications requiring low surface wear andenhanced lubricity.

Mineral Coupled These products contain chemically coupled mineralfillers in varying percentages. The mineral filled gradesare recommended w henever resistance to w arpage(especially in thin sections) and dimensional stabilityare key application parameters.

Ultraviolet Resistant These grades are available in a w ide variety of co lorsand are lead- and cadmium-free. They are speciallyformulated for improved resistance to color shift andmechanical degradation from ultraviolet light and areavailable in various melt flow rates. C onsult theTicona brochure, Celcon® Acetal Ultraviolet-Resistant Grades Extend Part Life in HarshEnvironments (CE-UV) for further informationabout these products.

Weather Resistant Weather resistant products ar e formulated f ormaximum outd oor w eathering resistance. Severaldifferent melt flow rate grades are offered. Black is theonly color available.

Antistatic These products are chemically modified to decreasestatic build-up for applications such as convey er beltlinks and audio and video cassette hubs and rollers.

Electrically Conductive These grades are used for applications requiring low electrical resistance and/or rapid dissipation of staticbuild-up. Some electrically conductive grades containcarbon fibers and exhibit high strength and stiffness.

Impact Modified These products are form ulated to provide moderate tohigh levels of improvement in impact strength andgreater flexibility compared to the standard product.

Table 1.1 · Regulatory listings


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1.4 Regulatory Codes and Agency ListingsMany grades of C elcon® acetal copoly mer are incompliance with a variety of agency specifications andregulator y standard s as show n in Table 1.1. N ot a llgrades are covered by all regulatory listings. C allP rod uct Inf ormatio n Services at 1-800-833-4882 or goto w w w.ticona.com for further information.

1.5 Product Support In addit ion t o o ur t echnical publications, experienceddesign and application development engineers areavailable for assistance with part design, mold flow characterization, materials selection, specificationsand molding trials. C all Prod uct Informa tion Servicesat 1-800-833-4882 for further help.

1.6 Safety and Health InformationThe usual precautions must be observed whenprocessing any hot and molten thermoplastic.

CAUTION: Normal processing temperatures and residence times should not be exceeded. Celcon acetal copolymer should never be heated above 238°C (460°F) nor be allowed to remain above 193°C (380°F) for more than 15 minutes without purging. Excessively high temperature or long residence time in a heated chamber can cause the resin to discolor and, in time, degrade to release formaldehyde, a colorless and irritating gas. This gas can be harmful in high concentrations, so proper ventilation is essential. If venting is inadequate, high pressures could develop in the equipment which may lead to blow back through the feed area. If no exit is available for these gases, the equipment may rupture and endanger personnel.

C onsult the current C elcon Material Safety D ataSheets (MSD S) for health and safety d ata fo rspecific grades of C elcon acetal copoly mer priorto processing or otherw ise handling of theseproducts. C opies are available by calling yo ur localTicona sales representa tive or C ustomer Services

at 1-800-526-4960 or w w w.t icona.co m.

Warning – Avoid PVC and partially cross-linked thermoplastic elastomer vulcanizates Celcon acetal copolymer and polyvinyl chloride(PVC) (or other chlorinated polymers) are mutuallyincompatible and must never be allowed to mix inthe molten polymer during processing, even intrace amounts.

When heated, PVC forms acidic decomposition products which can rapidly degrade Celcon acetal copolymer at processing temperatures, releasing largequantities of irritating formaldehyde gas. Celconacetal copolymer and PVC should not be processed inthe same equipment. If this is unavoidable, thorough purging with acrylic or polyethylene or disassembling and thoroughly cleaning the machine’s components isessential prior to the introduction of the second material.

Some partially cross-linked thermoplastic elastomer vulcanizates contain catalysts that are detrimental toCelcon acetal copolymer and potentially can cause therelease of large quantities of irritating formaldehyde gas. Celcon acetal copolymer and the partially cross-linked thermoplastic elastomer vulcanizates should not be processed in the same equipment. If this isunavoidable, thorough purging with acrylic or polyethylene or disassembly and thorough cleaning of the machine’s components is essential prior to theintroduction of the second material.

It is strongly recommended that in cases of known or suspected contamination, the molding machineincluding the barrel, screw, check ring, screw tip and nozzle, be disassembled and thoroughly cleaned.


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2. Physical andThermal Properties2.1 Crystallinity C elcon® acetal copoly mer is a semicry stalline polymerconsisting of amorpho us and cry stalline regions.Molding conditions have a significant effect on thedegree of crystallization of a molded part which, inturn, affects performance. For parts with walls lessthan 1.5 mm thick, use a mold t emperature of at least82° C (180° F) to fully crystallize the part and ob tainthe o ptimum performance pro perties.

2.2 Thermal ConductivityC elcon acetal copo lymer, like other t hermoplastics, isa thermal insulator and is slow to conduct heat.The addition of inorganic materials such as glassfibers and minerals, may cause a slight increase inthermal conductivity. Some ty pical values are show nin Table 2.1.

2.3 Specific HeatSpecific heat is a parameter used in mold flow calculations for processing and also fo r part design.It measures the amount of heat energy necessary t oincrease the temperature of a given mass of materialby one degree. Ty pical values fo r C elcon acetalcopolymer in the solid and in the molten state areshow n in Table 2.1.

2.4 Coefficient of Linear Thermal ExpansionThe coefficient of linear thermal expansion (C LTE) isa measure of t he linear change in d imensions w ithtemperatur e, and fo r plastics the C LTE is generallymuch higher t han fo r metals. This is an importantdesign consideration and w ill be covered in detail inC hapter 4 (D imensional Stability).

2.5 Thermal StabilityH eating C elcon acetal copoly mer above 238° C(460° F) should be avoided. At these temperatures,formaldehyde, a colorless and irritating gas thatcan be harmf ul in high concentratio ns, is generated.Proper ventilation should always be providedw hen processing C elcon acetal copolymer atelevated temperatures.

Property Units Unfilled 25% Glass ToughenedGrades Fiber Grades Grades

Specific Gravity 23°C (73°F) — 1.41 1.58 1.37 – 1.39

Specific Heat

Solid cals/g/°C 0.35 0.27 —BTU/lb/°F 0.35 0.27 —

Melt cals/g/°C 0.56 0.41 0.49BTU/lb/°F 0.56 0.41 0.49

Coefficient of Linear Thermal ExpansionRange: 23°C to 80°CFlow Direction °C- 1.2 x 10-4 0.3 x 10-4 1.2 - 1.4 x 10-4

Thermal Conductivity BTU/hr/ft 2/°F/in. 0.00552 — —cal/sec/cm2/°C/cm 1.6 — —

Melting Point °C (°F) 165 (329) 165 (329) 165 (329)

Table 2.1 · Thermal and physical properties of Celcon acetal copolymer grades


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2.6 FlammabilityB ased on t he ASTM D 635 flammability test, C elcon ®

acetal copolymer is classified as a slow burningmaterial. Ty pical burning rat es for t he unfilled a ndglass-filled products are shown in Table 2.2.

The burning rate of C elcon acetal copoly merdecreases rapidly as thickness increases, according toFederal Motor Vehicle Safety Standard (FMVSS) 302.At a thickness of 1.5 mm, w hich is generally theminimum for C elcon acetal copoly mer molded parts,the ra te is 28 mm/min w hich is well below themaximum allowable rate of 100 mm/min.

In areas w here life support in a n occupiedenvironment can be aff ected by burning materials,factor s such as smoke generation, oxy gen depletionand t oxic vapors must b e considered w hen selectingthe proper plastic. O nce ignited, C elcon acetalcopolymer burns in air with a barely visible blueflame and little or no smoke. C ombustion prod uctsare carbon dioxide and water. If air supply islimited, incomplete combustion w ill lead t o t heformation of carbon monoxide and, possibly, smallamounts of formaldehyde.

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Flammability Product Sample Burn RateTest Thickness

ASTM D 635 Unfilled 3.2 mm 28 mm/min.25% Glass 3.2 mm 25 mm/min.

Federal Motor Unfilled 1.5 mm 28 mm/min. Vehicle Safety Unfilled 1.0 mm 51 mm/min.Standard 302

Flame ClassUL 94 Unfilled ≥ 0.71 mm HB

Table 2.2 · Flammability and burning rate of Celcon acetal copolymer


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3. Mechanical Properties3.1 IntroductionP roperly designed parts made of C elcon ® acetalcopoly mer have been used in a w ide variety ofindustrial and consumer applications for many yearsbecause of its advant ages over metals, ot herthermoplastics and acetal ho mopoly mers. To t ake fulladvant age of the superior characteristics of C elconacetal copoly mer, a know ledge of its mechanicalcharacteristics is essential. This chapter will coverbot h the short-term mechanical properties and t helong-term time and temperature dependentcharacteristics that must b e considered for properpart design.

For designers who would like a general overview ofthe principles and concepts of plastic part design,w e recommend the Ticona publication, Designingwith Plastic: The Fundamentals (TDM-1) .It may be obtained by contacting your local Ticonarepresentative, P roduct Info rmation Servicesat 1-800-833-4882 or by going to www.ticona.com.

3.2 ISO Test StandardsTicona performs its plastic testing and reportingof data according to ISO (International Organizationfor Standardization) test methods, where available.The ISO standard s provide reproducible andconsistent test data fo r C elcon acetal copolymerproducts and support the global quality standards forall of our plastic products. This brochure containsbot h ISO and ASTM dat a as indicated.

As an illustra tion, Table 3.1 presents a part ial listingof the ISO and ASTM short term property datafor three representative grades of C elcon acetalcopoly mer. A more complete listing o f ASTM datacan be found in t he brochure Celcon acetalcopolymer Short Term Properties (CE-4).*

*Note. Since ISO testing uses samples having differentspecimen geometry and different test conditions than ASTM, ISO and ASTM test results may not beequivalent for the same plastic material, even whenboth results are expressed in metric units. For example, from Table 3.1 the ASTM tensile strength value for the standard 9.0 melt flow grade is 60.7 MPa (8,800 psi): the corresponding ISO value is 66 MPa.

* All test results @ 23°C (73°F) (except for DTUL / HDT)

ISO Data* Grade/Type

Property Method Units Grade M90™

Grade TX90 Plus Grade GC25TUnfilled; Unfilled; very 25%9.0 melt flow high impact Glass-coupled

strengthTensile Strength (Yield) ISO 527 MPa 66 46 131 (Break)Tensile Modulus ISO 527 MPa 2,780 1,700 8,520Elongation @ Yield ISO 527 % 9 14 3 (Break)Flexural Modulus ISO 178 MPa 2,640 1,560 8,470Charpy Notched Impact ISO 179/1eA KJ/m2 5.8 11 8.7 Izod Notched Impact ISO 180/1eA KJ/m2 5.5 9.8 7.9

DTUL@ 1.80 MPa ISO 75/Af °C 100 80 150

ASTM Data* Grade/Type

Property Method Units Grade M90™ Grade TX90 Plus Grade GC25TUnfilled; Unfilled; very 25%9.0 melt flow high impact Glass-coupled

strengthTensile Strength D 638 psi 8,800 6,000 20,000Elongation (Yield) D 738 % 8 11 3.5 (Break)Flexural Modulus D 790 psi x 104 37.5 22.0 120Izod Impact (Notched) D 256 ft-lb/in. 1.3 2.5 1.8HDT@ 264 psi D 648 °F 230 176 325

Table 3.1 · ISO/ASTM typical properties comparison


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3.3 Short Term Mechanical Properties

3.3.1 Tensile and ElongationA ty pical C elcon® acetal copoly mer stress-straincurve per I SO 527 test co nditions is show n inFigure 3.1 for glass-coupled, unfilled, and impactmodified grad es.

For the unfilled material, the stress/strain responseis effectively linear to approximately 1% strain. Thiscorresponds to a stress of about 28 MPa indicatingan effective modulus of a bout 2,800 MPa . All of t hestandard unreinforced grades of C elcon acetalcopoly mer exhibit a strength at y ield (w hich is alsothe ultimate strength) of approximately 66 MP a.

The range of tensile strength of the various C elconacetal copoly mer grades is show n in F igure 3.2.U ltimate tensile strength values range from 133 MP afor the 25% glass-reinforced grade to approximately45 MP a fo r an unreinforced, impact modified grade.G lass reinforcement up to 25% increases tensilestrength approximately 85% over the unfilledbase polymer.

20

40

60

80

100

120

Strain, %

S t r e s s , M

P a

00 2 4 6 8 10 12 14

25% Glass Coupled

Unfilled, 9.0 Melt Flow

Toughened; Impact Modified

Fig 3.1 · Celcon acetal copolymer stress-strainproperties (ISO 527)

T e n s

i l e S t r e n g

t h , M

P a Unfilledand

SpecialtyGrades66-57

MineralCoupled

andGlassBead53-44

Toughened,Impact

Modified50-45

25% Glass-Coupled

133

Fig 3.2 · Celcon acetal copolymer tensilestrength range (ISO 527)

GlassCoupled8,520

MineralCoupled

andGlassBead

3,500-3,000

UnfilledandSpecialty

Grades,Low

AdditiveLevels2,800-2,200

Toughened,Impact

Modified2,100-1,700

F l e x

M o d u l u s ,

M P a

Fig 3.3 · Celcon acetal copolymer tensilemodulus range (ISO 527)

Strain, %

00 2 4 6 8 10 12

10,000

8,000

6,000

4,000

2,000 S e c a n t

M o d u l u s , M

P a

14

25% Glass Coupled

Unfilled,9.0 Melt Flow Toughened;

Impact Modified

Fig 3.4 · Celcon acetal copolymer secant modulus range (ISO 527)

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3.3.2 Elastic ModulusThe elastic modulus generally reported for plasticmaterials is either the tensile modulus or the flexuralmodulus according t o I SO 178. Either tensile orflexural mod ulus may be used in design calculationscalling for the elastic modulus (or Young’s modulus).Figure 3.3 depicts typical values of the tensilemodulus for various grades of C elcon ® acetalcopolymer. As expected, the fiber reinforced gradesshow the highest modulus of up to approximately8,500 MPa. The modulus of the standard grades andthose grades with low levels of various additives aretypically around 2,600-2,800 MPa. Mineral and glassbead mod ified grades are generally higher w hileimpact mo dified grades become progressively low eras impact modifier concentration increases.

3.3.3 Secant ModulusThe initial modulus is useful fo r a first approximat ionof polymer stress-strain values. Either the tensile orflexural mod ulus value can b e used a ccording t oISO or ASTM test methods. H ow ever, at strain valuesgreater than 1.0% (at room temperature), a betterapproximation of stress can be obtained by using thesecant modulus.The secant modulus is calculated bydividing the stress by the strain, so that Figure 3.4(C elcon a cetal copoly mer secant m odulus range) isderived from Figure 3.1.

Example 3-1. Predicted Stress from Secant ModulusA part made from a stand ard unfilled grade of C elconacetal copoly mer is subjected in use to a momentary3% strain. Fro m t he initial modulus of 2,800 MP a,the predicted stress would be 84 MPa, well beyondthe yield strength of approximately 66 MPa shown inFigure 3.1. H ow ever, using t he secant m odulus ofapproximately 1,800 MP a (at 3% strain) from Figure3.4, the predicted str ess w ould b e 54 MPa , w hich isless than the 66 MPa yield strength value.

3.3.4 Charpy and Izod ImpactWhile not directly used in design calculations, the

C harpy and Iz od N otched Impact Test (ISO 179 andISO 180) and similar impact tests are used as indicat ionsof t he sensitivity o f the material to sharp corners andnot ches in the molded parts. Table 3.1 show s the rangeof not ched C harpy and Izo d notched impact test resultsfor the various C elcon acetal copoly mer grades. Thehighest notched impact value of 11 kJ/m 2 is reported fo rthe grade w ith a maximum level of impact mod ifier,

while the lowest value of 2.5 kJ/m 2 is obtained for glassbead modified grade. Most standard grades of C elconacetal copolymer have notched C harpy impact values ofapproximately 5-6 kJ/m 2.

3.3.5 Poisson’s RatioP oisson’s ratio for most plastics falls betw een 0.3 and0.4. C elcon acetal copoly mer is no exception. U sing aP oisson’s ratio of 0.37 is generally adequat e for mo ststress and deflection calculations requiring this value.At elevated temperatures, a Poisson’s ratio of 0.38may be more appropriate.

3.3.6 Shear ModulusFor general design calculations, the shear moduluscan be obt ained from t he relationship betw eentensile modulus and Po isson’s ratio as given by thefollowing equation:

where G is the shear modulus, Eis the tensilemodulus, and ν is Poisson’s ratio. At a mbientconditions a good working value for shear modulusfor standard unmo dified C elcon acetal copolymergrades is 1,000 MPa.

3.3.7 Shear StrengthThe shear strength fo r standar d grad es of C elconacetal copolymer is typically given as 53 MPa (7,700psi) using the condit ions specified in ASTM D 732.(There is no co mpara ble ISO method). The testinvolves measuring the load as a ro und hole ispunched in the specimen. As a result the shearstrength as measured includes contributions bybending and compressive forces. Therefore, when theshear str ength is required, it is recommended thateither the published strength or 1/2 of the tensilestrength be used, w hichever is smaller. This is usuallyadequat e for most design calculations and applies to

all grades of C elcon acetal copoly mer.

G =E

2 (1 + ν)

19


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3.3.8 Weld Line StrengthWeld line strength of C elcon ® acetal copolymerapproaches the strength o f t he base resin in w ellmolded part s. To co mpensate fo r d ifficult moldflow conditions and complex design requirements,it is recommended that the w eld line strength b econservatively estimated as 80-90% of the publishedtensile strength for t he specific C elcon grade. Thus,the w eld line strength of m ost grades of C elcon acetalcopolymer with strengths of 66 MPa and above canbe estimated at 53-59 MPa.

This value is particularly critical for glass reinforcedresins, because the w eld line strength is considerablybelow the tensile strength of the material in the flow direction, w hich is ty pically reported. This is dueto the glass reinforcement no t cro ssing the w eld line.The designer should contact Product InformationServices at 1-800-833-4882 for information on weldline characteristics for specific grades.

3.3.9 Molding EffectsThe data show n in this manual w as generated fo r testsamples molded at the recommended processingconditions for t he various grades of C elcon acetalcopoly mer. C onsult Bulletin Celcon acetalcopolymer Processing and Troubleshooting Guide(CE-6) for ty pical molding conditions. O ccasionally,part design criteria or processing equipmentparameters such as gate size, melt temperature and

mold temperature may require the molder to deviatefrom recommended conditio ns. Moreover, actualparts are usually more complex than laboratorytensile or f lex bars. To maximize engineeringperformance, the designer, molder and rawmaterials supplier should w ork closely to getherto specify molding parameters based on actualpart performance.

3.3.10 Anisotropy Most cry stalline thermoplastic resins, includingunfilled and fiber-reinforced grad es of C elcon acetal

copoly mer, are anisotro pic; i.e. they exhibit differentproperties in the flow and t ransverse directions aft ermolding (such as different shrinkage values). Anothereffect of anisotropy is seen in differences inmechanical properties. In some cases the strength inthe transverse direction can be as little as 50% of thatreported in the machine direction. The effect is

minimal in unfilled grades of C elcon acetal copoly merand literature values for mechanical properties may beused “ as is” for d esign purposes.

H ow ever, when designing parts using glass fiber-reinforced grades of C elcon acetal copolymer w erecommend t hat t he literature values for strength andmodulus of these grades be reduced by approximately20%-25% to compensate for the effects of anisotropy.For round or cylindrical parts, less of a reductionneeds be taken.

Since our results are based primarily on testsof laboratory samples, it is recommended thatthe designer consult with his local Ticonarepresentative, or call Pro duct I nformat ion Servicesat 1-800-833-4882 fo r further info rmat ion befor efinalizing part geometry.

3.3.11 Abrasion/Wear ResistanceAbrasion resistance is commonly measured by theTaber Abrasion Test, in w hich a w eighted w heelabrad es a C elcon acetal copolymer molded disc at aconstant rat e. Per ASTM D 1044, using a 1,000 g loadand a C S-17F w heel, the abrasion resistance for bo thunfilled a nd glass-reinforced C elcon acetal copo lymergrades w as 6 mg at 1,000 cycles. O ther poly mersincluding nylon and po lyester have significantlyhigher ab rasion rat es.

Many end-use applications for C elcon acetalcopoly mer take advantage of t he inherent lubricity,smooth surface and excellent wear resistance exhibitedby the base polymer. Applications such as conveyerlinks, gears and bearings (see C hapters 8 and 9)depend on these properties for successful operation.C elcon acetal copoly mer low w ear grade, such asLW90, LW90F2 and LW90S2, can be used to furtherenhance wear resistance and reduce noise generation .


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3.3.12 Temperature EffectsShort term property data sheets generally provideinformation only at ro om t emperature. O ther testsare needed t o expand t he thermal range of mechanicalproperties. The most useful data for design is stress-strain measurements at various temperatures. O thertests including D y namic Mechanical Analysis (D MA),D eflection Temperature U nder Load (D TU L) andU nderw riters Lab orat ories (U L) Thermal Ind exRat ings are used t o compare or specify mat erials.As a general rule, copoly mers, as ty pified by C elcon ®

acetal copolymer, retain their mechanical propertiesunder thermal stress to a greater extent than acetalhomopo lymers (See C hapter 1).

3.3.13 Stress-Strain MeasurementsStress-strain plots measured at different temperaturesare useful tools for describing the thermal-mechanicalbehavior of a plastic. Figures 3.5, 3.6 and 3.7 presentthe stress-strain plots at various temperatures forthree basic grades of C elcon acetal copoly mer: 25%glass fiber reinforced, unfilled 9.0 melt f low and atoughened grade respectively.

Strain, %0 1 2

0

50 S t r e s s , M

P a

-40°C

23 °C

40 °C

80 °C

3

150

100

60 °C

120 °C100 °C

Fig 3.5 · Stress-strain plot for 25% glass-reinforcedgrade of Celcon acetal copolymer (ISO 527)

Strain, %0 2 4 6 8

0

40 S t r e s s , M

P a

-40°C

23 °C

40 °C

80 °C

120 °C

10 12

20100 °C

14

100

80

60

60 °C

Fig 3.6 · Stress-strain plot for unfilled 9.0 meltflow grade of Celcon acetal copolymer (ISO 527)

Strain, %0 5 10 15 20

80

0

60

S t r e s s ,

M P a

-40°C

23 °C

40 °C

120 °C

25

20

40

100 °C80 °C

60 °C

Fig 3.7 · Stress-strain plot for toughenedgrade of Celcon acetal copolymer (ISO 527)


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Figures 3.8, 3.9 and 3.10 respectively show thesecant modulus-strain curves generated from thestress-strain curves fo r the same three C elcon ® acetalcopoly mer grades, again plott ed versus temperature.These plots provide insight into mechanicalperformance for t y pical grades at elevatedtemperatures and may be used in par t d esign.

Strain, %0 5 10 15 20

3,000

0

2,000

2,500

S t r e s s

M o d u l u s , M

P a

40 °C

120 °C

25

1,500

500

1,000

100 °C

80 °C23 °C

-40°C60 °C

Fig 3.10 · Secant modulus-strain plot for toughened grade of Celcon acetal copolymer

Strain, %0 1 2

0

4000 S e c a n t

M o d u

l u s ,

M P a

-40°C

23 °C

40 °C

80 °C

3

12000

8000

60°C

100 °C

10000

6000

2000 120 °C

Fig 3.8 · Secant modulus-strain plot for 25%glass-reinforced grade of Celcon acetal copolymer

Strain, %0 2 4 6 80

2000 S t r e s s , M

P a

80 °C

120 °C

10 12

1000100 °C

14

5000

4000

3000

60 °C

23 °C

-40°C

40 °C

Fig 3.9 · Secant modulus-strain for unfilled 9.0melt flow grade of Celcon acetal copolymer


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3.3.14 Dynamic Mechanical AnalysisD y namic Mechanical Analysis (D MA) w as developedprimarily to investigate the morphology of materialstogether with their energy absorption characteristics.P arts designers have begun to use this technique toinvestigate elastic mod ulus behavior w ithin theiruseful temperature range. The test is most usefulw hen stress-strain curves are lacking or incompleteover the operating temperature range of the mat erial.

Test samples can be loaded in tension, bending orshear. The test imposes very small oscillatingdeflections w hile measuring the resulting f orce onthe test specimen over the temperature range of-40°C to almost t he melting point of the material.A continuous plot is generated of mod ulus (or o thercharacteristic) versus temperature.

The temperature-modulus plot is o ften no rmalized b ydividing all of t he modulus data per individual curveby the room temperature modulus value to morereadily compare different D MA tests obtained on thesame material but run und er different t est co nditions.

A semi-log plot of temperature-modulus providesaddit ional insight into modulus values at elevatedtemperatures. The beginning of the final do w nw ardcurvature at elevated temperatures is often consideredthe maximum useful temperature of the mat erial.The designer should exercise extreme care and

evaluate prototype parts whenever the operatingspecifications call for thermal exposure close to thematerial’s DMA downward point of curvature.

Figure 3.11 illustrates the normalized D MA plot ofshear mo dulus versus temperature of ty pical grades ofC elcon® acetal copolymer (measured by the torsionalpendulum method). Most grad es of C elcon acetalcopolymer will fall within the range of these plots.The data indicate that all three grades show the startof dow nw ard curvature at approximately 120° C .

The designer can use the D MA plo t to determine ashift factor to be applied to the room temperaturemodulus value to obtain a modulus at any operatingtemperature. For example, the modulus of a standardunfilled 9.0 melt flow grade of C elcon acetalcopolymer is 50% of its room temperature value atapproximately 80° C .

3.3.15 Deflection Temperature Under Load (DTUL)D TU L Values are given in Table 3.1 using ISO TestMethod 75/Af (flatwise test) for three typical gradesof C elcon acetal copoly mer: Celcon acetal copoly mer

G C -25T [25% glass-fiber reinforced] (150° C ); C elconacetal copolymer M 90 ™ [standard unfilled 9.0 meltflow ] (100°C ); and C elcon acetal copolymer TX90P LU S, [a toughened grade] (80° C ). D TU L is usefulfor co mparing different materials for their relativeresistance to mechanical stress (three-point bending)at elevated temperature.

The designer can, how ever, obta in much moreinformat ion t han just t he relative material resistanceinformation referred to above by properlyinterpreting the D TU L t est results.

-60 -40 -20 0 20 40 60 80 100 120 140 1600.01

0.1

10

1

Temperature, °C

N o r m a l

i z e d

S h e a r M o d u l u s , M

P a

Glass-Reinforced GradesStandard Unfilled GradesImpact Modified Grades

Fig 3.11 · Typical normalized Celcon acetalcopolymer DMA plot


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U nder D TU L, a t est specimen is loaded in three-point bending at a specified stress. The deflection isthen cont inuously measured as t he temperatureof t he test bar is increased at a rate of 2° C per minuteusing a heating medium such as an oil bath. Thetemperature is recorded w hen a specific deflection isreached. Since both the stress and strain (deflection)are specified, if it is assumed that the material islinearly elastic and follow s H ooke’s Law ; then thetest temperature can be measured when the flexuralmodulus dro ps to a specific value.

Table 3.2 illustrates the corresponding flexuralmodulus at the DTU L temperature for any materialtested under the three test methods specifiedin ISO 75:

U sing Method A as an example, if t he designerrequires a material w ith a flexural mod ulus of 1,520MP a, then the temperature w here the modulus hasdropped to only 930 MPa may well be of interest; asis the case with the standard unfilled grade. In thiscase Method A or B would be appropriate to use.H ow ever Method A (or B) w ould not be of muchinterest to designers requiring high modulus values(such as w ith the glass-reinforced grad e) w hich has aninitial room temperature mod ulus of 7,600 MP a,

because by the time the temperature has reached amodulus of 930 MP a one is very close to t he

crystalline melting point of the material and wellbeyond its useful temperature range. In this case onew ould choose Method C , w hich provides much moreuseful D TU L inform ation than either Methods A orB for all glass reinforced grades.

Table 3.3 provid es D TU L values for ty pical gradesof Celcon® acetal copolymer together withrecommendations as to which values to use bygrade type:

3.3.16 Underwriters Laboratories (UL)Thermal Index Ratings

The U L R elative Thermal Index (RTI), of ten referredto as the Cont inuous U se Temperature, has been

obtained for mo st grades of C elcon acetal copoly merand can be found on the U L “ Yellow C ard” or on-lineat ht tp://dat abase.ul.com. This card lists values forelectrical properties (dielectric strength), mechanicalproperties w ith impact (i.e. impact strength) andmechanical properties without impact (i.e. tensilestrength). These values are an estimate of thetemperature at w hich grades of C elcon acetalcopolymer can be continuously exposed, before losing50% of its original property value over the estimatedlife of the molded part. N ote that a mechanical load isnot imposed on the test specimen. This test is most

useful w hen comparing the performance of d ifferentplastics. U nder these conditions, ty pical values for mostgrades of C elcon acetal copolymer range from 95° C toabove 110° C .

Table 3.4 summariz es the Relative Thermal I ndexratings for gra des of C elcon acetal copolymer.

Test Method A B C

Applied Stress, MPa 1.8 0.45 8.0

Flexural Modulus @DTUL Temperature, MPa 930 230 4,100

Flexural Modulus @Room Temperature, MPa Value

Standard Unfilled Grade 2,600Toughened Grade 1,600Glass-Reinforced Grade 8,500

Table 3.2 · DTUL stress-modulus values perISO 75 test method

Grade Recommended DTUL Type ISO Test Method Temperature °C

Standard Unfilled A 100

B 155Toughened A 80

B 135

Glass-Reinforced A 150C 130

Table 3.3 · Expanded DTUL table for Celconacetal per ISO 75 test method


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In general, C elcon acetal copoly mer, because of itshigh crysta llinity, w ithstands creep stress better thanmost o ther plastics.

3.4.3 Creep DeflectionThe creep modulus may be used in place of theflexural or tensile modulus in the standard equationsof linear elasticity used in engineering design.The range of creep moduli for the standard C elconacetal grades, the impact modified grad es andthe reinforced grades are shown in Figure 3.12.

The graph w as prepared b y measuring the flexuralcreep of va rious C elcon grades at loads up to 1/3 ofthe published t ensile strength o f t he low elongatio ngrad es over the temperature range of 23-80° C . Verylittle influence from stress was seen on the creepmodulus reduction w ith time. Each regression curvewas normalized by dividing by the modulus valueat 0.1 hour.

The designer needs to estimate the actual temperaturethat the part w ill encounter during service, as w ell asthe critical mechanical and o ther properties for thespecific applicat ion before selecting C elcon acetalcopoly mer. C all Product I nforma tion Servicesat 1-800-833-4882 fo r U L informat ion f or specificgrades and approvals.

3.4 Long Term Mechanical Properties

3.4.1 IntroductionAdequat e consideration o f long term loads, especiallybased on creep and stress relaxation, is critical to thedesign of part s made from C elcon acetal copolymer.This can avoid issues such as incorrect estimates of in-use performance capability, part warranty and loss ofcustomer satisfaction.

Fatigue effects are usually considered b y partsdesigners, but must be approached w ith care toproperly mo del the realities of the end-use

environment. I mproperly d esigned t ests can pro duceerroneous results, which may be artifacts and may notreflect real end-use performance.

3.4.2 CreepThe instant any material, including metals, is loaded itbegins to creep. The viscoelastic properties of plasticsrequire that creep behavior be considered, even forroom temperature plastic parts d esign.

Several points need to be considered when dealingw ith creep. O ften, parts are subjected to relatively

low loads in which deflection is a factor but stress isnot. In o ther cases, the primary concern is mechanicalfailure of the part under long term loads with minimalconsideration of deflection. D eflection recoveryafter removal of long term loads is important insome applications.

Celcon acetal copolymer Grade Electrical Relative Thermal Index °C Mechanical-3.0 mm (1/8”) Mechanical with Impact

Standard Unfilled 110 100 90Glass fiber Reinforced 105 105 95

Unfilled Toughened 50 50 50

Table 3.4 · Summary of UL relative thermal index ratings for Celcon® acetal copolymer

0.1 1 10 100 1,000 10,000Time, Hours

N o r m a l

i z e d

M o d u l u s

0.1

1

Unfilled GradesGlass-Coupled GradesImpact Modified Grades

Fig 3.12 · Normalized creep modulus plotsfor Celcon acetal copolymer grades


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H ow ever, using the secant mod ulus plot(Figure 3.9), we see that the modulus is reduced byhalf at 70° C to a pproximately 1,300 MPa. While thestresses are unchanged the deflection is now 0.25 mm.

Finally, estimating the creep modulus at 10 years(approximately 80,000 hours) requires projectingone decade beyond the creep curve in Figure 3.12. Bydoing t his, it is estimated t hat t he creep modulusis 30% of the initia l value after 10 y ears. Thus w eestimate a new mod ulus of 30% of 1,300 MP a orapproximately 390 MP a. U sing this modulus w e now calculate the deflection in 10 years to be 0.83 mm.

If our maximum allow able deflection is 1.0 mm,the largest deflection permitted for design is 0.5 mmto maintain a safety factor of 2; the minimumsafety f actor recommended for creep calculations aspreviously d efined under C reep D eflection.Therefore, some alteration of the design conceptis needed. O ne alternative among many is to extendthe legs of the channel. If they are extended to 12 mmthe calculated deflection at 70° C after 10 y ears is0.48 mm, w hich satisfies the design requirements.

To ca lculate actual values w hen using Figure 3.12,refer to Table 3.5 w hich gives the initial va lues forcreep (flexural) modulus for the various grades ofC elcon® acetal copoly mer.

There is a considerable variation in creep deflection ofplastic assemblies in actual end-use. This is due tovariations in w all thicknesses and dimensionalvariations in the molded parts. To co mpensate forthese facto rs, it is strongly suggested that the designeruse a safety facto r of 2 whenever creep deflection isimportant in the end use application.

Example 3-2. Calculation of Long Term Deflectionfor a Part C onsider a molded part involving a U -beam 200 mmlong in cross section as illustrated in Figure 3.13.The beam w ill carry a uniform load across its lengthand t he ends w ill be designed t o snap into sockets,making the beam simply supported. The channel

supports slide-in components weighing 200 grams.The operating temperat ure of the part is 70° Cand t he service life is ten years. D ue to alignmentrequirements fo r the components, the maximumallow able deflection fo r t he beam is 1.0 mm.Would t he channel be satisfactory if fab ricatedfrom a standard grad e of C elcon acetal copolym er?

Solution: The equat ions of a U -beam cross sectionand a simply supported beam with a uniform loadmay be found in Chapter 7 of Designing WithPlastic: The Fundamentals (TDM-1). (Call Product

In format ion Services at 1-800-833-4882 fo r y our copyor see internet site at www.ticona.com). Initialanalysis of the part at room temperature assuming amodulus of 2,600 MP a show s that the stress in thecomponent is very low, (0.43 MP a) and t he deflectionis 0.12 mm. Many designers on seeing these low stressand relatively low deflection values may considerfurther analysis unnecessary.

Celcon acetal copolymer Grade Flexural Modulus, MPa

Standard Unfilled 2,600Glass fiber Reinforced 8,590Unfilled Toughened 1,700

Table 3.5 · Initial creep (flexural) modulus values for grades of Celcon acetal

0 2 4 6 8 10 12 14

14

0

2

4

6

8

10

12

10 mm(typical)

3 mm(typical)

10 mm

Fig 3.13 · U-beam cross section


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3.4.4 Creep RuptureThe second creep issue is creep rupt ure, in w hicha high continuous load is imposed. I n this caseuncontrolled part deformation or part breakage canoccur. It is typically characterized by much higherstresses than the deflection-limited creepdiscussed above.

U nfort unately, rupture considerations are not assimple as the analysis of deflection limited creep usingthe mod ulus. R upture is highly d ependent o n d esigngeometry, processing conditions, temperature andenvironmental exposure. As the start ing point f ordesigning for creep rupture, use a minimum safetyfactor of 10 applied to the short term data todetermine the design strength at the operatingtemperature of the plastic part, depending on theabove factors.

The above general rule of thumb applies to anyC elcon® acetal copolymer grade required to carry acontinuous load for an extended period of time.Figure 3.14 shows a creep rupture curve for alaborat ory test specimen. The curve is for the hoopstress for a sta ndard C elcon acetal copolymer unfilled9.0 melt f low grade molded into tubes and subjectedto hy drosta tic pressure for a n extended time atambient temperature. At 100,000 hours, (about 12.5y ears), rupture strength under this test condit ion isappro ximately 1,800 psi. This is appro ximately 1/5 of

the initial short t erm tensile strength o f t he material.Thus, a safety factor of 2 at 100,000 hours suggests adesign strength of approximately 1/10 of the initialtensile strength.

This result is based on a laboratory test specimenunder controlled conditions and falls within oursuggested guidelines of a minimum safety facto r of10. This holds w henever creep rupture isan important consideration in part design.

3.4.5 Creep Recovery When plastics are loaded for any length o f t ime, theydo not instantaneously recover to their original shapewhen the load is removed. In many applications therecovery time or the amount of deformationrecovered must be considered. Figure 3.15 shows theratio of strain recovered t o creep strain versus theratio of recovery time to creep time. At low strains,on the order of 1/4% to 1/2%, complete recoveryoccurs only when the recovery time is equal to thetime at load.

Time, Hours

H o o p

S t r e s s , p s i

1,000

10,000

10 100 1,000 10,000 100,000

5,000

Fig 3.14 · Creep rupture, Celcon acetal copolymerunfilled 9.0 melt flow grade

00.10.20.30.40.50.60.70.80.91.0

110 -5 10 -4 10 -3 10 -2 10 -1 10 1 10 210 -6Recovery Time/Creep Time

F r a c

t i o n a

l R e c o v e r e d

S t r a

i n ,

S t r a

i n R e c o v e r e

d / C r e e p

S t r a

i n

Recovery data out to2.5% strain at 10 7 seconds

Short TimeLow Strain

Long TimeHigh Strain

Fig 3.15 · Creep recovery for Celcon acetal copolyme

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Example 3-3. Snap Finger Strain RecoveryA simple snap finger is designed for a peak strain of2.5% during engagement. The finger is subjected toa definite tensile load after insertion. Thus, once it isinserted and released, it is held in position againstits retainer and can no longer recover in strain. I f itis inserted quickly, creep strain is brief and therecovery time is equally brief. What will be thestrain recovery?

Solution: The ratio of recovery time to creeptime is about 1. The snap finger may be expected torecover about 80% of the 2.5% strain; therefore,approximately 0.5% strain w ill remain. Alternatively,if the insertion t ime is slow w ith a q uick release afterengagement, the recovery to creep time may be 1:100.In this case, only 60% of the strain is recovered, sothe snap finger w ill be locked at a permanent1% strain.

3.4.6 RelaxationStress relaxation is similar to creep. In creep, aconstant stress is imposed and the strain grad uallyincreases. When a constant strain is imposed, there isan initial stress that gradually decays or relaxes withtime. Relaxation data is not as common as creep data.Fortunately, creep data give a good approximation ofthe relaxation phenomenon.

Example 3-4. Press Fit Strain Recovery A 10 mm diameter pin is pressed into a hole in a partmade of a standard grade of C elcon ® acetal copolymerw ith an int erference of 0.1 mm. The hoop stra in is0.1/10 = 0.01 or 1%. The resulting st ress at a mat erialmodulus of 2,800 MP a is 28 MP a. H ow ever, after1,000 hours the effective modulus is reduced by half.Therefore, the stress would be 14 MPa even thoughthe strain is still 1%.

N ow consider the recovery if t he pin is suddenlyremoved. The initial recovery typically follows theinitial modulus rather then the creep modulus. Thus,

as the stress drops from 14 MPa to zero when the pinis removed, the initial strain recovery is 14 MPa/2800MPa, or 0.005 (0.5%). From Figure 3.15, note that6 minutes is 1/10,000 of the stress relaxation time of1,000 hours. Examining the creep recovery curve atthis recovery time to creep time ratio, w e see that themiddle of t he colored region indicates that half(0.5%) of the st rain is recovered.

Example 3-5. Clock Gear DesignIn ma ny electric alarm clocks, C elcon acetalcopoly mer gears are insert m olded or pressed o ntosteel shafts. I f insert molded, the gears grip the shaftswith a strain equivalent to the mold shrinkage.Therefore, the strain o n the gears holding them t o t heshaft s is 0.5-2%. The strain w ith press fits is muchmore variable. This system w orks w ell in driving theclock hands as there is little load required betw een thegears and the shaft.

H ow ever, the final gear (the hour hand), oft en tripsthe alarm mechanism. This is the highest torque gearin the system requiring the tightest grip on the shaft.O ver time, the gear may relax its grip on t he shaftand slip rather than trip the alarm. This would beaccompanied b y increased gear noise. I n this case,a spline, knurled or flattened shaft ultrasonicallyinserted in the hole w ill eliminate the slippage.

At low load levels, a splined or knurled shaft may bepress fit. This requires careful control of tolerances toprevent over-stressing the plastic. A refinement of thisprocedure is to use a single or doub le “ D ” shaft andhole in the plastic and press fit the assembly together.

These changes will eliminate the problem of gearrelaxation/slippage as a cause of premature failure,and pro vide the normal lifetime of service for t heclock assembly.

Parts subjected to a continuous high strain may alsofail at some future time in a manner similar to creeprupture. Again, this failure mechanism is highlydependent on temperature, environmental exposure,design and processing conditions. In general,a continuous strain in excess of 2.5% is to beavoided in standard , unfilled C elcon acetal copoly merparts. The strain should be less than 2.5% to avoidcracking at w eld lines or und er specific environmentalexposure conditions.


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Figure 3.16 illustrates fatigue curves for glassreinforced and stand ard grad es of C elcon acetalcopoly mer tested accord ing to ASTM D 671. Thistest involves a beam w ith a unifor m taper (constantstress beam) under harmonic excitation. Note that theunreinforced grade retains approximately 1/2 of itsoriginal flexural fatigue strength o ver 10 7 cycles. Theglass reinforced grade is only slightly better then theunreinforced grad e. This is probably due to t heinteraction of the many glass ends and the notchsensitivity of the material. These curves should beused as starting points since the actual end-use

conditions may deviate considerably from thelaboratory test conditions.

Laboratory fatigue testing should be used only as aguide. For example, harmo nic excitation is ty picallyused in laboratory testing. The end-use environmentmay be a saw too th o r pulse loading. These loadingscould prod uce a very different response resulting ineither a shorter or longer life than t hat predicted bythe laboratory test.

End-use tests run cont inuously to achieve the

required life cycles oft en overheat the test part,resulting in low er fatigue life than t he part might havein the intermittent and, t herefore, low er temperatureend use. Alternatively, an accelerated fatigue test runat a contro lled, elevated temperature to mod el theend-use environment, may overestimate the f atigueperformance of the part by failing to consider agingeffects at elevated temperature.

Lo w er continuous strain exposure must be usedw ith glass reinforced grad es. It is recommendedthat no more than 33% of the elongation at break beconsidered. Also, at part w eld lines for glass-coupledgrades, the neat plastic alone must carry the load.Therefore, small strains in t he molded part can belarge stresses for the base plastic. For example, a0.5% strain on a part having a modulus of 1,000,000psi is 5,000 psi. This stress must cross t he w eld line.As previously discussed, a long term stress ofthis magnitude w ould b e excessive for mo stunreinforced plastics.

Example 3-6. Hoop Stress CalculationC onsider the 10 mm diameter pin w ith a 0.1 mminterference fit discussed in Example 3-4. Thematerial is a glass reinforced C elcon ® acetalcopoly mer grade w ith 7,000 MP a mod ulus. The hoopstress induced from 1% strain is 70 MPa. While theglass reinforced C elcon acetal copoly mer mighttolerate this stress if w ell molded, w eld lines areprobab ly present at the hole in the part. Since thefiber reinforcement does not cross the weld, only theunreinforced base resin is present at this stress point.The part will probably break in a relatively shortperiod of time, since the hoop stress exceeds thestrength of the base resin.

D rilling or heat punching the hole, or moving t hew eld line by redesign of t he mold have all been used

in various actual end-use applications to overcomethe problem and provide normal part service life.

C learly, wit h reinforced grades of C elcon acetalcopolymer, the interference strains should be keptquite low; on the order of 0.25-0.5%.

3.4.7 FatigueFatigue strength, like creep rupture strength, is highlydependent on design, processing, temperature andend-use environment. I n add ition, the nature of theload influences the fat igue performance. H armonic,

square wave, saw tooth or pulse loading can havevery d ifferent effects on plastic fat igue.

P lastics can also fa il in fatigue due to hy steresisheating and deformation rather than the fatiguecracking ty pically expected. D ue to its highlycry stalline nature, C elcon acetal copoly mer resistshy steresis heating a nd ha s superior f atigueperformance compared to other plastics.H ow ever, each application req uires careful testingunder conditions that model accurately the end-use environment.

10 3 10 4 10 5 10 6 10 7

Cycles to Failure

1,000

10,000

S t r e s s , p

s i

Glass-Reinforced GradeStandard Unfilled Grade

5,000

Fig 3.16 · Flex fatigue plot forCelcon acetal copolymer (ASTM D 671)


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4. Dimensional Stability 4.1 Coefficient of Linear Thermal ExpansionThe coefficient of linear thermal expansion (C LTE) isa measure of the change in dimension w ith changesin t emperat ure. Table 4.1 gives C LTE values forvarious grades of C elcon ® acetal copoly mer.

4.2 Shrinkage Caused by Processing(Injection Molding)Mold shrinkage can vary with several factors.The most important factor is molding conditions.Variations in mold surface temperature and moldinjection pressure, for example, can cause shrinkage intest bars mad e from o ne specific grade (C elcon acetalcopolymer M90 ™) ranging from 0.018 to 0.050mm/mm. Figure 4.1 provides a graphical illustrationof the shrinkage for this grade for the aboveparameters. O ther factor s such as mold design, w allthickness, gate size, flow length and flow direction,filler ty pe and level and polymer melt viscosity canalso affect shrinkage. As a result it is difficult topredict the exact mo ld shrinkage of a specific part.

Shrinkage of standa rd C elcon acetal copolymerproducts measured on laborat ory test specimensgenerally range from 0.004 mm/mm for glass-reinforced products to 0.022 mm/mm forunreinforced grades. Mold shrinkage as high as 0.037mm/mm has been observed o n an a ctual part. C onsult

the Celcon Short Term Properties Data Brochure(CE-4) for typical values of laboratory-tested specificC elcon grad es. This information is useful forpreliminary estimates of shrinkage, but should beused only as an initial guide in to ol construction.

It is highly recommended to begin with oversizedcores and undersized cavities to minimize retoo lingcosts. Following this, parts should be molded atsteady-state mo lding condit ions (see Celcon acetalcopolymer Processing and Troubleshooting Guide(CE-6) for recommended molding cond itions) andthen exposed t o amb ient t emperature for about 48hours. D imensions of critical areas can then bemeasured to d etermine any ad ditional machiningthat may be required. C omputer Aided D esign(C AD ) Flow Shrinkage Analysis can greatlyimprove the accuracy of mo ld dimensiondeformation. C ontact P roduct I nformation Servicesat 1-800-833-4882 for furt her informat ion.

4.3 WarpageWall thickness should be as uniform as possiblebecause differences in coo ling rates of thick and thinsections is a key cont ributor t o w arping. O therfactors affecting warpage are:

G ate size

G ate location

Mold temperature

Filler type/level

O rientation of fillers

Molded-in stresses

C onsult t he Celcon acetal copolymer Processingand Troubleshooting Guide (CE-6)for f urther informat ion on t hese parameters.

Celcon acetal copolymer Grade Description Units: 10-4/°C

M270™ Unfilled 27.0 Melt Flow 1.2

M90™ Standard Unfilled 9.0 Melt Flow 1.2M25 Unfilled 2.5 Melt Flow 1.2

GC25A™ 25% Glass Fiber Coupled 0.3

GB25 Glass-Bead Reinforced 0.9

TX90PLUS Toughened; High Impact 1.4

LW90GCS2 Low Wear; Lubricated 0.3

* Values measured in Flow Direction

Table 4.1 · Coefficient of linear thermal expansion (CLTE) for various grades of Celcon acetal copolymer, 23-


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8 12 16 20

4.0

3.6

2.8

2.4

2.0

1.6

1.2

3.2

S h r i n

k a g e

( % )

2.0 mm

8 12 16 20

4.0

3.6

2.8

2.4

2.0

1.6

1.2

3.2

4.1 mm

8 12 16 20

4.0

3.6

2.8

2.4

2.0

1.6

1.2

3.2

5.1 mm

8 12 16 20

4.0

3.6

2.8

2.4

2.0

1.6

1.2

3.2

10.2 mm

8 12 16 20

2.0

1.6

1.2

8 12 16 20

2.0

1.6

1.2

8 12 16 20

2.0

1.6

1.2

8 12 16 20

2.0

1.6

1.2

4.03.6

2.8

2.4

3.2

S h r i n

k a g e

( % )

4.03.6

2.8

2.4

3.2

4.03.6

2.8

2.4

3.2

4.03.6

2.8

2.4

3.2

8 12 16 20

4.03.6

2.8

2.4

2.0

1.6

1.2

3.2

S h r i n

k a g e

( % )

8 12 16 20

4.03.6

2.8

2.4

2.0

1.6

1.2

3.2

8 12 16 20

4.03.6

2.8

2.4

2.0

1.6

1.2

3.2

8 12 16 20

4.03.6

2.8

2.4

2.0

1.6

1.2

3.2

MoldSurfaceTemp.29°C



Injection Pressure (psi x 103)

A

B

C,DE,F,G

A

B

C,DF,G

ABC,DE,F,G

Part Wall Thickness

A,B,DG

DG

AB

DG

AB D

G

AB

D

AB

D

AB

AB,DA

B,D

ABCG

Fig 4.1 · Effect of molding conditions and wall thickness on mold shrinkage for Celcon® acetal copolymer M90™

Note. Melt Temperature: 190°C-204°C.Shrinkage measured in direction of material flow.

Gate Area mm2 Gate Area mm2

A 1.9 E 18.1B 3.9 F 23.9C 7.7 G 31.3D 12.2

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Some general observations on part shrinkage in t hemold are show n in Table 4.2.

4.4 Post-Molding ShrinkageP ost-molding shrinkage is usually related t o stressrelaxation of t he molded part, resulting in apermanent shrinkage of t he part. At ambienttemperatures this shrinkage is relatively small, on theorder of 0.1-0.2% for a standard unfilled 9.0 meltflow grade of Celcon® acetal copolymer. H ow ever,continuous exposure of the molded part to hightemperatures accelerates bot h t he rate and magnitudeof shrinkage due to stress relaxation. Figure 4.2illustrat es the shrinkage behavior o f t he standardunfilled 9.0 melt f low grade of C elcon acetalcopolymer after six months of exposure to various

temperatures (3.2 mm thickness, flow direction).

4.5 When Annealing is Necessary In many cases, properly molded parts will exhibitsatisfactory dimensional stability. A high moldtemperature (95-120° C ) w ill opt imize the dimensionalstability of an as-molded part. In some cases,prolonged and elevated in-service temperatures maynecessitate annealing.

Some general guidelines are given below:

In-service temperatures of 82° C or below –G enerally, properly molded parts w ill notrequire annealing.

Temperatures greater than 82° C – Annealing maybe necessary to improve the dimensional stab ilityof the molded part.

Recommended annealing procedure:

Time: As a general rule, use 15 minutes for each3.1 mm of w all thickness.

Parameter Effect on Part Shrinkage

Wall thickness increases Increases

Gate size increases Decreases

Injection pressure increases DecreasesMold temperature increases Increases

Melt temperature increases Decreases (for parts 3.1 mm thick or less)No effect (for parts 3.2-9.5 mm thick)

Resin Melt Viscosity Increases with increasing viscosity (when molded under similar processing conditions; i .e. ,Celcon acetal copolymer M450 has lower shrinkage than Celcon acetal copolymer M25)

Table 4.2 · Effect of processing conditions on part shrinkage

Temperature: 152 ± 2° C

Medium: Any refined or silicone oil which is notacidic. O il is preferred over air because it is a bet-

ter conductor of heat and provides a blanketto minimize or prevent oxidation.

C ooling: C ool annealed parts slow ly (one hourper 3.1 mm of wall thickness).

4.6 TolerancesD imensional to lerance can be defined as a variationabove and below a nominal mean dimension.If recommendations f or part /mold d esign andproper molding are followed, the typical tolerancesexpected are:

± 0.002 mm/mm fo r t he first 25 millimeters orfraction of the first 25 millimeters of w all thickness.

± 0.001 mm/mm for each subsequent 25 millimetersof wall thickness.

0 1 2 3 4 5

2.8

2.6

2.4

2.2

2.0

Time, Months

S h r i n

k a g e , %

3.0

Shrinkage Due to Heat Aging, 1 mm Thick SpecimenDirection of Material Flow

6

23 °C (Ambient)

82 °C Oven

115 °C Oven

Fig 4.2 · Shrinkage due to heat aging for 9.0standard melt flow grade of Celcon acetal copolym


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5. Environmental Resistance5.1 Chemical ResistanceThe part design engineer will appreciate the needto consider the chemical environment to w hich thepart w ill be exposed during its service life. C elcon ®

acetal copolymers have excellent resistance tomany chemicals and solvents when molded partsare exposed in an unstressed state. In some cases,slight discoloration is observed w ith little changein t he mechanical pro perties measured. Table 5.1summarizes the perform ance of C elcon acetalcopoly mer after exposure to a variety of chemicalsover a range of temperature and exposure times.

In general, C elcon acetal copoly mer is minimallyaffected by a wide variety of solvents and chemicals,except by strong mineral acids (sulfuric, nitric,hydrochloric, etc.) and strong oxidizing agents such asaqueous solutions containing high concentrations ofhypochlorite or permanganate ions. A summary of theperformance of t est specimens of C elcon acetalcopoly mer in various environments is given below :

Fuels: C elcon acetal copolymer show s small changesin dimensions, w eight and strength w hen exposed t ooxy genated and non-oxygenated fuels at 65° C . 1

Oils: Almost no effect is seen fo llow ing exposureto various hydrocarbon and ester oils such as

mineral oil, motor oil and brake fluids, even atelevated temperatures.

Organic Reagents: Most of the organic reagentstested did not affect C elcon acetal copoly mer. O nly aslight change wa s seen for com mon d egreasingsolvents such as carb on t etrachloride,trichloroethy lene and acetone at roo m temperature.P rolonged exposure at elevated t emperature to moreaggressive solvents such as ethylene dichloride,phenolic solutions and aniline should b e avoided,unless the application is d esigned around the pot ential

change in properties.

Aqueous Bases (Alkalies): C elcon acetal copoly meris especially resistant to strong bases (alkalies)show ing superior resistance in t his medium w hencompared to acetal homopolymer. Molded C elconacetal copolymer specimens immersed in almostboiling 60% sodium hyd roxide solution and o therstrong b ases for several months, show ed little change.

Aqueous Acids: C elcon acetal copolymer is notrecommended for use in the presence of mineral acidsor strong Lewis acids such as zinc chloride or borontrifluoride. C elcon acetal copoly mer should only b eexposed to aq ueous solutions that have a pHabo ve 4.0.

Detergents: Immersion for up to six months at 82° C(180° F) in several commercial dishw ashing detergentsolutions produced virtually no change in the tensilestrength of molded parts of C elcon acetal copolymer.

Potable Water: Prolonged or continuous exposure ofC elcon acetal copolymer in aq ueous solutionscontaining hy pochlorite ions should be limited tohy pochlorite concentrations typically found in U .S.domestic potab le w ater supplies.

Table 5.1 summariz es the exposure tests o f t hreeunfilled C elcon acetal copolymer grades to a w idespectrum o f inorganic and organic chemicals, as w ellas commercial products including automot ive fluids

and detergents. The results illustrate the resistanceshown by C elcon acetal copolymer to most commonsolvents and chemicals.

1 Reference “ P lastics and Aggressive Auto Fuels – a5,000 H our Study of Seven P lastics and N ine FuelB lends,” 01-300, March , 2001.


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Exposure Yield TensileTime Temp. Strength Modulus Length* Weight Visible

Chemical (Months) °C % Change % Change % Change % Change Effect**Control (Air) 2 23 0 0 0 0.22 N.C.Inorganic Chemicals10% Aluminum Hydroxide 6 23 0 0 0.3 0.88 Disc.

12 23 0.7 -16 0.3 1.03 Disc.6 82 -0.3 -12 0.4 0.74 Disc.

3% Hydrogen Peroxide 6 23 2 -15 0.3 0.97 N.C.12 23 3 -12 0.3 0.88 N.C.

10% Hydrochloric Acid 6 23 x x x x x10% Nitric Acid 6 23 x x x x x10% Sodium Chloride 6 23 2 -12 0.2 0.59 N.C.

12 23 3 -15 0.2 0.71 SL.Disc.6 82 4 -10 0.2 0.77 SL.Disc.

2% Sodium Carbonate 6 23 0 -9 0.2 0.77 N.C.12 23 6 -9 0.2 0.78 N.C.6 82 3 -2 0.4 0.96 N.C.

20% Sodium Carbonate 6 82 3 -2 0.2 0.61 N.C.

1% Sodium Hydroxide 6 23 1 2 0.2 0.80 N.C.12 23 2 2 0.2 0.84 N.C.10% Sodium Hydroxide 6 23 1 -8 0.2 0.49 N.C.

12 23 -2 -6 0.2 0.73 N.C.6 82 -3 -8 0.2 0.83 SL.Disc.

60% Sodium Hydroxide 6 82 -3 -6 -0.1 -0.18 SL.Disc.4-6% Sodium Hypochlorite 6 23 x x x x x26% Sodium Thiosulfate 6 82 3 -12 0.2 0.61 N.C.3% Sulfuric Acid 6 23 0 -8 0.4 0.81 N.C.

12 23 2 -14 0.2 0.82 N.C.30% Sulfuric Acid 6 23 x x x x xBuffer, pH 7.0 6 82 2 -15 0.3 0.94 SL.Disc.Buffer, pH 10.0 6 82 4 -12 0.3 0.89 SL.Disc.Buffer, pH 4.0 4 82 x x x x x

Water (Distilled) 6 23 0 -12 0.2 0.83 N.C.12 23 4 -12 0.2 0.84 N.C.12 82 0 -18 -0.1 -3.32 Disc.

Organic Ch

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