Blow Molded Parts

How is orientation introduced into an injection blow molded part Compare this to orientation in a stretch blow part ... 

Figure 11.23 Photographs of the defects for the high-speed blow-molding parts a) a large cutout from the part showing a large hole, b) a small hole defect, and c) a location with a very thin wall. The arrows show locations that have degraded resin particles...

They may be extruded or blow molded. Parts may be thermally formed and heat or solvent welded. Some applications are blow-molded containers, pipe, ventilating ducts, and molded parts. 

Empee [Monmouth Hastics] Poly-ethylenes used in wire and cable, inj. molded parts, extruded sheet, blow molded parts, shapes, tubing, elec, ai lics. 

Generally, the blow mold is a cavity representing the outside of a blow-molded part The basic structure of a blow mold consists of a cast or machined block with a cavity, cooling system, venting system, pinchoffs, flash pockets, and mounting plate. The selection of material for the construction of a blow mold is based on the consideration of such factors as thermal conductivity, durabrhty, cost of the material, the resin being processed, and the desired quality of the finished parts. Commonly used mold materials are berylHum, copper, aluminum, ampcoloy, A-2 steel, and 17-4 and 420 stainless steels. 

The production speed of blow-molded parts is generally limited by one of two factors extruder capacity or cooling time in the mold. Cooling of mold is accomplished by a water circuit into the mold. Flood cooling and cast-in tubes are most common in cast molds drilled holes and milled slots are the norm in machined blow molds. 

The third mode is the shuttle method, where usually two or more sets of molds are used. Each set of molds can have at least two or more molds. Their blowing stations are around the periphery of the extruder die head and parisons. One set of molds in the open position is located under the die. With the proper length of the parisons (a parison for each mold), the open molds underneath close. After the molds are closed, parisons are cut, usually with an electrically charged hot wire, and quickly shuttled to a blow station, where blow pins are inserted into the parison openings. Blow-molding parts solidify and are released from the molds when they open. In the meantime, the parisons continue to be extruded as another set of open molds is positioned around these parisons. Thus, the molds alternately shuttle producing molded parts. 

Blow molded parts demonstrate that, from technical and cost standpoints, BM offers a promising alternative to other processes, particularly injection molding (IM) and thermoforming. The technical evolution of BM, plus accompanying improvements and new developments in plastics, has led to new BM parts. With the coextrusion technology now established and the hardware in place, the variety of achievable properties can readily be extended by the correct combination of different materials (see Chapter 3). The potential for BM products includes much more than the simple bottles that have been made for many decades. Now the expertise and economics of the method are such that many ideas once deemed futuristic are much closer to realization (2, 96, 186-212). 

Dichlorotrifluoroethane blowing catalyst, PU foams N,N, N",N"-Pentamethyldiethylenetriamine blowing/nucleating agent, thermoplastics Sodium bicarbonate blow-molded bottles Hydroxypropylcellulose blow-molded parts Polypropylene... 

P = 10-40 MPa in the presence of Al(Ci 2, or 4)3] leads to PE having a relatively broad MWD, p = 0.910-0.935 g mL and good processability. The PE is suitable Pot the preparation of blown or cast films, blow-molded parts, extruded goods, and injection-molded products... 

Alvord, Lincoln J., Engineered Blow Molding Part Design, GE Plastics, Pittsfield, Mass., 1989. 

The design of the mold should take into consideration placement of the gates to prevent wrinkled or washed overlays. The overlay may be held in place in the mold by cutting it so that it fits snugly or by electrostatic means. Blow-molded parts can also be printed or decorated by in-mold processes. The ink or paint image is placed on a carrier film or paper and placed in the mold. As the hot plastics expands, filling the... 

Extrusion blow molded parts must meet strict dimension distribution requirements to provide the necessary strength and rigidity with minimum material usage. The final part dimension distributions are directly influenced by parison dimensions [4]. 

Parison sag (parison parting line and blow mold parting line do not overlap)... 

TPUs can be blow molded, and the requirements for the screw design are the same as for extrusion. Both injection molded and blow molded parts should be heated at 100 °C for 24 hours to reach the equihbrium structure and minimize creep and compression set. The main field of application of thermoplastic urethanes is for various casters, rollers, wheels, flexible clutches, seals and gaskets for hydraulic machines, shoe soles, printing rolls and machine parts. 

Snap fits are widely used for both temporary and permanent assemblies, principally in injection- and blow-molded parts. Besides being simple and inexpensive, snap fits have been superior qualities (see Figs. 5-41). Snap fits can be applied to any combination of materials, such as metal and plastics, glass and plastics, and others. All types of plastics can be used. 

Figure 7-53. This Navistar International truck fascia is of multiple-extrusion blow-molded parts made from Himont s HiFax polypropylene. The fascia parts, which range from 8 to 17 lbs. and come in lengths from 24 in. to 6 ft., are molded on 50-lb. accumulator head capacity machines. The ability to mold the PP in an integral color eliminates the need to paint. 

Alvord, L. J. Engineering Blow Molded Part Design. Paper presented at GE Plastics SPI Structural Plastics Conference, 1989. 

---