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Injection Molding Guide Start with DuPont thermoplastic polyester elastomer Hyt

Injection Molding Guide Start with DuPont thermoplastic polyester elastomer Hytrel ® e DuPont Hytrel® thermoplastic polyester elastomer was specified for these spacers for loosely fitting, recessed electrical receptacles because of its flexibility, toughness, resilience, and creep resistance. Copyright ©2000 E. I. du Pont de Nemours and Company. All rights reserved. Injection Molding Guide Start with DuPont polyester elastomer Hytrel ® e DuPont Hytrel® polyester elastomer was specified for these spacers for loosely fitting, recessed electrical receptacles because of its flexibility, toughness, resilience, and creep resistance. Identity and Trademark Standards Guidelines for Customer Use—Joint ventures and authorized resellers Only joint ventures and resellers who have signed special agreements with DuPont to resell DuPont products in their original form and/or packaging are authorized to use the Oval trademark, subject to the approval of an External Affairs representative. Guidelines for Customer Use—All other customers All other customer usage is limited to a product signature arrangement, using Times Roman typography, that allows mention of DuPont products that serve as ingredients in the customer’s products. In this signa- ture, the phrase, “Only by DuPont” follows the product name. Hytrel® Only by DuPont A registration notice ® or an asterisk referencing the registration is required. In text, “Only by DuPont” may follow the product name on the same line, separated by two letter-spaces (see above example). When a DuPont product name is used in text, a ® or a reference by use of an asterisk must follow the product name. For example, “This device is made of quality DuPont Hytrel® thermoplastic polyester elastomer for durability and corrosion resistance.” *Hytrel® is a DuPont registered trademark for its brand of thermoplastic polyester elastomer. Rev. August. 1995 thermoplastic polyester elastomer Hytrel ® d Hytrel® only by DuPont or Table of Contents General Information ............................................................................. 1 Product Description.............................................................................. 1 Melt Properties ..................................................................................... 3 Thermal Properties ............................................................................... 5 Material Handling ................................................................................. 6 Drying ................................................................................................ 6 Purging .............................................................................................. 7 Regrind .............................................................................................. 7 Adding Concentrates and Pigments ............................................... 8 Molding Equipment.............................................................................. 9 Screw Design .................................................................................... 9 Nozzle Design ................................................................................... 9 Molding Conditions .............................................................................. 10 Melt Temperature ............................................................................. 10 Cylinder Temperature Profile........................................................... 10 Nozzle Temperature.......................................................................... 10 Mold Temperature ............................................................................ 11 Injection Speed ................................................................................. 11 Injection and Holding Pressure ....................................................... 12 Screw Forward Time (SFT) .............................................................. 13 Screw Rotation Speed/Back Pressure ............................................. 13 Cycle Time ......................................................................................... 13 Quality Moldings on Fast Cycle .......................................................... 14 Shortening Injection Time ................................................................... 14 Shortening Holding Time..................................................................... 14 Mold Design .......................................................................................... 15 Materials of Construction ................................................................ 15 Mold Surface Finish ......................................................................... 15 Sprue Bushing Design ..................................................................... 15 Runners ............................................................................................. 15 Gates.................................................................................................. 15 Venting............................................................................................... 15 Undercuts .......................................................................................... 15 Part Ejection ...................................................................................... 16 Shrinkage and Post-Molding Shrinkage ............................................ 16 Post-Molding Shrinkage .................................................................. 18 Overmolding ......................................................................................... 18 Operating Precautions ......................................................................... 18 Skin Contact ...................................................................................... 18 Pressure Build-up ............................................................................. 18 Fire ..................................................................................................... 19 Fumes ................................................................................................ 19 Spills .................................................................................................. 20 Waste Disposal ................................................................................. 20 Drying ................................................................................................ 20 Static Electricity ................................................................................ 20 Injection Molding Troubleshooting Guide ......................................... 21 Hytrel ® Injection Molding Guide The grades of Hytrel® are grouped into four categories, by performance: 1. General purpose grades which exhibit versatile processing characteristics, are lowest in cost and are suitable for many applications; 2. High-performance grades generally provide an extra margin of mechanical properties for the more demanding applications; 3. Specialty grades provide special properties or processing characteristics for particular applica- tions; 4. Concentrates contain relatively high concentra- tions of specific property-enhancing additives for blending with other grades of Hytrel®. Hytrel® is supplied as cylindrical to oval-shaped pellets (approximately 3.2 mm [0.125 in] in diameter by 3.2 mm [0.125 in] long). They are packaged in 25 kg (55 lb) multi-wall paper bags with a moisture barrier inner wall. Palletized units contain 40 bags, or 1000 kg net weight, wrapped in polyolefin film on disposable wooden pallets. Most grades of Hytrel® are also available in 750 kg (1,650 lb) bulk boxes with a moisture resistant liner. Property data sheets on currently available grades can be obtained through your local sales office listed at the end of this bulletin or through your DuPont sales representative or are also available through the World Wide Web, www.dupont.com/ enggpolymers/americas. A summary of the mold- ing grades is given in Table 1. General Information Hytrel® is the DuPont registered trademark for its family of thermoplastic polyester elastomers. Hytrel® offers a unique combination of mechanical, physical and chemical properties that qualifies it for demanding applications. The various grades of Hytrel® exhibit a wide range of properties and an easy processability. This report provides detailed guidelines for injec- tion molding of Hytrel®. It reviews the type of equipment as well as the processing conditions necessary to achieve high quality parts and high productivity. Product Description Hytrel® combines many of the most desirable characteristics of high-performance elastomers and flexible plastics. It features: exceptional toughness and resilience; high resistance to creep, impact and flex fatigue; flexibility at low temperatures; and good retention of properties at elevated tempera- tures. In addition, it resists deterioration from many industrial chemicals, oils and solvents. Hytrel® is a block copolymer, consisting of a hard (crystalline) segment of polybutylene terephthalate and a soft (amorphous) segment based on long- chain glycols. Properties are determined by the ratio of hard to soft segments and by the make-up of the segments. Most grades of Hytrel® do not contain or require additives to enhance their properties, except for specific applications. 1 Provide an extra measure of strength and service to meet the needs of the most demanding applications in a wide range of hardnesses Best balance of cost and performance Table 1 Molding Grades of Hytrel® Engineering Thermoplastic Elastomer Nominal Hardness,1 Flexural Modulus,2 Grade of Hytrel® Durometer D MPa (psi) Description General Purpose G3548W 35 32.4 (4,700) G4074 40 65.5 (9,500) G4078W 40 65.5 (9,500) G4774, G4778 47 117 (17,000) G5544 55 193 (28,000) High-Performance 4056 40 62 (9,000) 4069 40 55 (8,000) 4556 45 94 (14,000) 5526 55 207 (30,000) 5556 55 207 (30,000) 6356 63 330 (48,000) 7246 72 570 (83,000) 8238 82 1210 (175,000) Specialty 3078 30 28 (4,000) Very soft, flexible grade 5555HS 55 207 (30,000) Heat-stabilized grade of 55D Hytrel® HTR6108 60 193 (28,000) Low permeability grade HTR8068 46 174 (25,200) Flame retardant grade 1 ASTM D2240 (ISO 868) 2 ASTM D790 (ISO 178), at room temperature Note: All of the values reported in this table are based on ASTM methods. ISO methods may produce different test results due to differences in test specimen dimensions and/or test procedures. 2 G3548W G4074 G4078W G4774 G5544 1000 100 10 170 180 190 200 210 220 240 230 250 260 270 Melt temperature, °C Melt viscosity, Pa⋅s G4778 Table 2 shows several attributes of the product range that should be considered in injection mold- ing. Certain grades depending on typical composi- tion may, however, not fall exactly into these generalizations. Table 2 Characteristics of Hytrel® Soft Grades Hard Grades 30–47 55–82 Durometer D Durometer D Crystallinity – + Shrinkage – • Thermal stability + ++ Wide processing window + ++ Melt temperature • + Mold temperature – • Cycle time • short – low, • medium, + high Melt Properties Hytrel® engineering thermoplastic elastomer has good flow characteristics. The melt viscosity and, hence, the melt flow varies depending on the composition of the resin. The melt viscosities of various grades of Hytrel® versus temperature are shown in Figures 1–3. Figure 1. Apparent Melt Viscosity versus Temperature—General Purpose Hytrel® Grades at Shear Rate of 1000 s–1 3 Figure 2. Apparent Melt Viscosity versus Temperature—High-Performance Hytrel® Grades at Shear Rate of 1000 s–1 4056 4069, 4556 5556 5526 6356, 7246 8238 1000 100 10 170 180 190 200 210 220 240 230 250 260 270 Melt viscosity, Pa⋅s Melt temperature, °C Figure 3. Apparent Melt Viscosity versus Temperature—Specialty Hytrel® Grades at Shear Rate of 1000 s–1 HTR6108 HTR8068 3078 1000 100 10 170 180 190 200 210 220 240 230 250 260 270 Melt temperature, °C Melt viscosity, Pa⋅s 5555HS 4 Thermal Properties When handled properly, Hytrel® has outstanding thermal stability. In the melt under normal operating conditions, the evolution of gaseous by-products is minimal for most grades. This thermal stability combined with a chemically pure polymer with no plasticizers minimizes problems such as change of viscosity with hold-up time in the injection unit or formation of black specks. An exception to this is during the molding of flame retardant grades or use of concentrates containing additives, where processing outside the optimum recommended conditions can more readily accelerate thermal decomposition. Melt temperatures and some thermal properties of the various grades are shown in Table 3. Melt temperatures are a function of the ratio of hard to soft segments. Generally, the greater the hard segment content (and thus, hardness), the higher the melting temperature. Table 3 Thermal Properties of Hytrel® Tm Tm (complete) Tc Hf Tg Grade °C (°F) °C (°F) °C (°F) J/g °C (°F) General Purpose G3548W 156 (312) 180 (356) 107 (225) 8 –40 (–40) G4074 170 (338) 190 (374) 120 (248) 17 –37 (–35) G4078W 170 (338) 190 (374) 120 (248) 17 –37 uploads/Ingenierie_Lourd/ hytrel-design-guide.pdf