注塑培训吹塑成型指导e.doc

DuPont Engineering Polymers Blow Moulding Processing Manual Start with DuPont Engineering Polymers DuPont registered trademark Blow moulding processing manual Table of contents 1 DuPont resins for blow moulding . 3 1.1 Why blow mould engineering resins. 3 1.2 ZYTEL nylon resins for blow moulding. 3 1.3 HYTREL and CRASTIN polyester resins for blow moulding. 4 2 Description of blow moulding processes. 7 2.1 General. 7 2.2 Continuous extrusion machines. 7 2.3 Accumulator head machines . 7 2.4 Co-extrusion and sequential 3-D blow moulding. 7 2.5 Injection blow moulding . 9 3 The blow moulding machine - Important considerations. 11 3.1 Screw and barrel design. 11 3.2 Manifold/adapter design. 11 3.3 Accumulator and continuous extrusion head design . 12 3.4 Die/head tooling design . 12 3.5 Parison cutters . 13 3.6 Mould clamping force . 13 3.7 Temperature control. 13 3.8 Auxiliary equipment. 13 4 Machine operating conditions . 15 4.1 Quick reference - Processing conditions . 15 4.2 Barrel temperatures . 15 4.3 Adapter, head and die temperature. 16 4.4 Accumulator push-out pressures and speeds. 16 4.5 Parison programming . 16 4.6 Mould temperature . 17 4.7 Start-up procedures. 17 4.8 Purging and shutdown. 17 4.9 Secondary operations: trimming, welding . 18 4.10 Special conditions for injection blow moulding and Pressblower operation . 19 5 Handling of blow moulding resins . 21 5.1 Effects of moisture . 21 5.2 Drying. 22 5.3 Regrind . 22 5.4 Bulk storage. 23 6 Mould design guidance . 25 6.1 General. 25 6.2 Materials of construction. 25 6.3 Blow-up (draw) ratio. 25 6.4 Mould shrinkage allowances and part dimensions. 25 6.5 Pinch-off designs. 25 6.6 Other mould considerations. 26 7 Troubleshooting guide . 27 1 1 1.1 DuPont resins for blow moulding Why blow mould engineering resins? ZYTEL blow moulding resins ZYTEL BM7300THS Unreinforced PA6 There are many reasons why engineering resins have become established in blow moulding applications, for example: Cost and weight reduction Recyclability ( replaces rubber for example) Innovation: - Multifunctional parts - Reduce number of parts in the engine compartment Higher temperature requirements Easier assembly and disassembly Reduce number of materials Improve performance Reduce noise Availability of special resin grades designed for blow moulding DuPont offers a wide range of engineering resins types for blow moulding including: HYTREL CRASTIN ZYTEL SELAR RB Polyester elastomer PBT polyester Nylons 6, 66, and alloys Barrier resin ZYTEL BM73G25THS 25% glass reinforced PA6 ZYTEL BM73G15THS 15% glass reinforced PA6 ZYTEL BM7300FN ZYTEL CFE8005HS ZYTEL EFE7340 ZYTEL EFE7341 Unreinforced, PA6 flexible nylon alloy Unreinforced PA66 15% glass reinforced hydrolysis resistant PA66 20% glass reinforced hydrolysis resistant PA66 New grades are continuously being developed, so please contact your local DuPont representative for the latest product literature. All DuPont resins are supported by comprehensive Technical Service in the areas of: Basic data Design (C.A.D.) Processing Testing. 1.2.1. ZYTEL resins - rheology ZYTEL blow moulding resins have been developed to provide excellent melt strength in the parison during the push-out and moulding operation. This requires very high viscosity at low shear rates, typically in the -1 range of shear rates from 0-10 s . At higher shear rates which are encountered in the plastification of the resin in the screw and barrel of the machine, there is a reduction in viscosity which helps to minimise the screw torque and required motor power. Figures 1 (below) and 2 (following page) show the apparent viscosity/shear rate curves for the ZYTEL blow moulding grades measured at appropriate melt temperatures. All resins were dried to a moisture level of below 0,05%. Higher levels of moisture will signifi- cantly reduce the viscosity levels across the range of shear rates. 1.2 ZYTEL nylon resins for blow moulding 100000 ZYTEL nylon resins are thermoplastic polyamides having properties that place them high on the list of engineering plastics. They are tough and chemically resistant, and moulded articles retain their performance at elevated temperatures. The ZYTEL resins listed below have excellent parison melt strength and good drawability for blow moulding. Some grades are reinforced with glass fibres to increase their tensile strength, stiffness and dimensional stability. There is also a flexible nylon alloy available. All ZYTEL blow moulding grades are especially compatible with each other for use in sequential co-extrusion blow moulding - for example in hard/soft segment air ducts etc. (see section 2.4). ZYTELBM7300THS (250C) 10000 s) . (Pa Viscosity 1000 ZYTELBM73G25THS (250C) Melt 100 10 100 Shear Rate (1/s) 1000 10000 Fig. 1 Melt viscosities of various ZYTEL nylon 6 grades 3 Table 1 Nylon type PA66 unreinforced PA66 15% glass fibre PA66 20% glass fibre PA6 unreinforced PA6 flexible alloy PA6 25% glass fibre ZYTEL grade CFE8005 BK EFE7340 BK EFE341 BK BM7300T BK BM7300FN BK BM73G25T BK Typical MFI at 21,6 kg g/10 min 25-35 30-40 50-60 20-30 40-50 25-35 Temperature 280C 280C 280C 250C 250C 250C 100000 Dynamic (flex fatigue) performance Noise reduction Excellent sealing (low creep) properties Special HYTREL grades have been developed for good parison stability and other properties required for blow moulding. Applications include: CVJ boots Suspension and steering boots Air ducts Vent pipes Listed below is part of the range of HYTREL blow moulding grades. Hardness HYTREL HTR8105 HYTREL HTR5612 HYTREL HTR8223 HYTREL HTR4275 HYTREL BM6574 HYTREL BM5576 (Shore D) 47 50 45 55 65 55 Main applications CVJ Boots Suspension and steering boots, CVJ boots CVJ boots, suspension and steering boots Air ducts, vent pipes Air ducts, vent pipes (higher temperature) Air ducts, vent pipes (higher melt strength) ZYTELCFE8005 (280C) 10000 (Pa ZYTELEFE7340 (280C) Viscosity 1000 ZYTELEFE7341 (280C) Melt 100 10 100 Shear Rate (1/s) 1000 10000 Fig. 2 Melt viscosities of various ZYTEL nylon 66 grades s) . Melt index (MFI) values have been measured on ZYTEL blow moulding resins and are shown in Table 1. The measurements were made at a weight of 21,6 kg and at a temperature close to the typical processing temperature for each grade. MFI results based on dif- ferent conditions are not comparable. Please note that MFI is not considered to be a reliable indication of melt strength for nylon materials (espe- cially glass reinforced) due to effects of moisture and other factors. For this reason it is advisable to use the values with caution. 1.3 HYTREL and CRASTIN polyester resins for blow moulding 1.3.1. HYTREL polyester elastomer HYTREL thermoplastic polyester elastomers (TEEE) are high performance, flexible polymers, with excep- tional properties such as: High and low temperature performance Excellent oil and hydrocarbon resistance Toughness and tear resistance 1.3.2 HYTREL resins - rheology Figures 3 and 4 show apparent viscosity/shear rate curves for some of the HYTREL blow moulding resins. The higher viscosity grades are designed for longer parts such as air ducts, while the lower viscosity (higher melt index) grades are formulated for use in CVJ boots, suspension and steering bellows. Melt Index (MFI) values for these HYTREL blow moul- ding resins are given in Table 2 below. Please note the test weight and temperature used as measurements made under different conditions are not comparable. 4 Table 2 HYTREL grade HTR4275 BK BM5576 BK BM6574 HTR5612 BK HTR8105 BK HTR8223 BK Hardness (Shore D) 55 55 65 50 47 45 Typical MFI at 5 kg g/10 min 2,0 1,2 - - - 2,5 Typical MFI at 2,16 kg g/10 min 0,5 0,3 0,5 3,0 2,0 0,4 Temperature 230C 230C 270C 230C 230C 230C 100000 HYTRELHTR-8105 (220C) 10000 s) . (Pa HYTRELHTR-8223 (220C) 1000 HYTRELHTR-5612 (220C) Viscosity Melt 100 10 10 100 Shear Rate (1/s) 1000 10000 Fig. 3 Melt viscosities of various HYTREL grades Good stiffness and strength, especially at elevated temperatures Excellent toughness and impact strength Good oil, hydrocarbon and overall chemical resistance Low moisture absorption and excellent dimensional stability Compatible with HYTREL in hard/soft combination mouldings Two special CRASTIN grades have been developed for blow moulding: CRASTIN ST820 (for smaller parts) CRASTIN BM6450 (high melt strength, for larger parts) 100000 10000 s) . (Pa HYTRELBM5576 (225C) Viscosity HYTRELHTR-4275 (225C) 1.3.4. CRASTIN resins - rheology The apparent viscosity/shear rate curve for CRASTIN BM6450 BK is shown in Figure 5 below. CRASTIN BM6450 BK has a typical Melt Flow Index (MFI) value of 11g/10 minutes measured with 21,6 kg weight at a temperature of 250C. 1000 Melt 0 10 100 Shear Rate (1/s) HYTRELBM6574 (250C) 1000 100000 10000 10000 s) . (Pa Fig. 4 Melt viscosities of various HYTREL grades CRASTINBM6450 BK (250C) Viscosity 1000 Melt 1.3.3 CRASTIN PBT polyester resin CRASTIN PBT polyester resins are high performance engineering polymers which are particularly useful in automotive blow moulded applications for the following reasons: 0 10 100 1000 10000 Fig. 5 Melt viscosity of CRASTIN BM6450 5 2 2.1 Description of blow moulding process General All blow moulding processes consist of 3 stages: 1. Plastification of the thermoplastic resin granules, normally by means of a single screw extruder. 2. Production of a molten pre-form- either an extruded tube or parison in the case of so called extrusion blow moulding, or an injection moulded pre-form in the case of injection blow moulding. 3. Inflation of the parison or pre-form (usually with air) in a blowing mould, followed by a demoulding and a part trimming operation. It is not intended to provide detailed descriptions of all the above processes and machine types on the mar- ket, but the following information may be useful to differentiate the more important aspects of each tech- nology in relation to the use of engineering resins in blow moulding. so that the part shot can be pushed out quite rapidly immediately before the mould closes round it to start the moulding cycle. The extruder screw can be stopped and started as required to fill the accumulator in time for the next push-out and moulding operation. The accumulator head machine, as well as helping to mini- mise the effects of parison stretching in long parts, can also be useful for moulding semi-crystalline engineering resins when rapid cooling or oxidisation of the parison surface may cause problems when those materials are moulded in continuous extrusion machines. 2.4 Co-extrusion and sequential 3-D blow moulding 2.2 Continuous extrusion machines In this process the extruder screw runs continuously, plasticising the granules and pumping the resin melt through the head and die to produce a vertical parison which hangs from the die. When the parison reaches the required length, the mould closes round it and immediately the parison is cut, while the mould is quickly transferred to the blowing position where a blowpin inflates the parison to fill the mould cavity. Meantime the next parison is being extruded. The process requires that the extrusion speed must be exactly controlled so that each parison reaches the required length in the time it takes the mould to complete its blowing and cooling cycle. Parison wall thickness and hence part wall thickness, is controlled by a multi-point parison programmer which operates via hydraulics to adjust the die gap during the extrusion process. Co-extrusion blow moulding involves the simultaneous extrusion of two or more compatible resins in layers through the parison wall. This allows, for example, the incorporation of special layers for permeation barrier, or the use of a layer of regrind material in the part wall. Multiple extruders are therefore needed to feed each material to the special co-extrusion head, which can be designed either for continuous extrusion or accumulator head operation. Sequential blow moulding can be considered as a devel- opment of co-extrusion blow moulding where the layers are switched on and off in a programmed way. This allows production of parts which combine sections made from two or more resins, for example hard, rigid sections in one material and soft flexible bellows in a different material. DuPont Engineering resins which are compatible with each other and suitable for sequential coextrusion blow moulding include the following polyamide (nylon) and polyester resin combinations: Nylons: 2.3 Accumulator head machines The continuous extrusion process, though simple and cost effective for many applications has the inherent disadvantage that the parison must hang under gravity for the full length of each moulding cycle, This demands extremely good melt strength in the resin, especially for long mouldings. By incorporating an accumulator head, which acts like a reservoir and push-out piston, it is possible to accumulate enough resin inside the head for one part, Polyesters: Hard component ZYTEL BM7300T, BM73G15T or BM73G25T CRASTIN BM6450 Soft component ZYTEL BM7300FN HYTREL HTR4275 A major disadvantage of conventional blow moulding processes is that they are not ideally suited to the blow moulding of long narrow components in 3 dimensions, such as air ducts, without producing excessive scrap and very long undesirable pinch-offs at the mould closing lines. This fact led to the development of the so-called 3-D blow moulding processes which essentially describe 3 different systems for achieving similar results. 7 The 3-D processes are normally combined with sequen- tial blow moulding to make hard-soft combinations in a single moulding. Laydow process In this system (see Fig. 6) the parison is extruded verti- cally onto a horizontally fixed mould half, in such a way that the emerging parison is made to follow the path of the mould cavity by either moving the complete extruder head and die or alternatively moving the mould half (with extruder fixed). The parison is kept partially inflated with support air to prevent its collapse, until such time as the complete cavity has been filled, when the top half of the mould is closed over the lower half and the parison is fully inflated by inserting a blowing needle. The result is a moulding with virtually no scrap (except at each end) and no inherently weak pinch-off. The disadvantage of this process for engineering poly- mers is the relatively long time during which the parison is in contact with only one half of the mould, leading to premature freezing-off of the parison surface. However, this can be mainly overcome by use of high mould temperatures which may require the use of oil heaters. Parison manipulation process This technique is a development of a conventional blow moulding (normally accumulator head) process, whereby the extruded parison in manipulated by a combination of robots and moving mould segments in order to make it conform to the 3-dimensional mould cavity. The parison is normally r