Application to Injection Molding

Several groups developed numerical models for the simulation of the IM process. Early works modeled the effect of temperature on the crystallization rate only and included the crystallization heat in the energy equation (see for example Hieber [171]). The effect of shear was taken into account by, for example a modified Nakamura equation where the kinetic parameters were made (shear) stress dependent [22,76,77,116,172]. 

Pantani et al. [11] gave an extensive review on available models to predict and characterize the morphology of injection-molded parts. The authors themselves proposed a model to predict the morphology of injection-molded iPP, in which flow kinematics are computed using a lubrication approximation. Polymorphism was accounted for, using the Avrami-Evans-Nakamura equation to describe the crystallization kinetics of the mesomorphic phase, while the evolution of the a phase was modeled using Kolmogorov s model [122]. 

Isayev and coworkers pubhshed a series of papers [75,76] in which they built up an increasingly advanced model for FIC in IM. Using special extrusion experiments, they parameterized the crystallization model 

Smirnova et al. [174] used a differential set of Avrami equations to predict crystalhnity and the average size of spheruhtes in IM, but in their study only temperature effects were taken into account. 

Most of these numerical models give little insight into the morphology developed, failing to provide information about the shape and dimensions of oriented crystalline structures Aey lack molecular understanding, and they do not couple FIC with melt rheology. 

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C.A. Hieber. Melt-viscosity characterization and its application to injection molding. In A.I. Isayev (Ed.), Injection and Compression Molding Fundamentals, Marcel Dekker, New York, 1987, p. 6. 

Crowson, R.J. and Folkes, M.J. (1980) Rheology of short glass fiber-reinforced thermoplastics and its application to injection molding. II. The effect of material parameters. Pdym. Eng. Sd.. 20 (14), 934-940. 

Further improvements of the orthotropic fitted closure and application to injection molding problems have been reported by VerWeyst (1998) and VerWeyst et al. (1999). 

Zoller P, Kehl TA, Starkweather HW, Jones GA (1989) The equation of state and heat of fusion of poly(ether ether ketone). J Polym Sci Part B Polym Phys 27 993-1007 Zuidema H (2000) Flow Induced Crystallization of Polymers Application to Injection Molding. 

This calculation, which holds tme for most metals, is generally applicable to injection-molded TPs. However, the designer is already familiar from previous discussions with the inherently nonlinear, anisotropic nature of most plastics, particularly the fiber-reinforced and liquid-crystal ones. 

Crowson, R. J., Folkes, M. J., and Bright, R F., Rheology of short glass fiber-reinforced thermoplastics and its applications to injection molding 1. Fiber motion and viscosity measurement, Polym. Eng. ScL, 20, 925-944 (1980). 

Akay, G., Rheology of reinforced thermoplastics and its application to injection molding IV. Transient injection capillary flow and injection molding, Polym. Eng. ScL, 22, 1027 (1982). 

The 7-form of P.V.19 is also applicable in injection-molded and extrusion-made polyamide. It satisfies not only the high thermal requirements in connection with these purposes but has the added advantage of being, like P.R.122 and 209, chemically inert to the slightly alkaline and reducing plastic melt. 

In conclusion, it is evident from the above discussion that anionic polymerization has emerged from a laboratory curiosity to an important industrial process in a relatively short span of time. Currently, over a million tons of polymers are produced by the anionic route in about twenty manufacturing plants around the world. We at Phillips are quite proud of being one of the pioneers along with Firestone and Shell in harnessing this new technology to commercial applications. The fact that our polymers find such wide ranging applications from tire treads to injection molded blood filters and from lubricant additives to solid rocket binders bears ready testimony to this. 

When processing plastics some type of tooling is usually required. Tools include molds, dies, mandrels, jigs, fixtures, punch dies, perforated forms, etc. The terms for tools are virtually synonymous in the sense that they have some type of female and/or negative cavity into or through which a molten plastic moves usually under heat and pressure or they are used in secondary operations such as cutting dies, stamping sheet dies, etc. These tools fabricate or shape products. In this chapter injection molds and extrusion dies are primarily reviewed because they represent over 95% of all tools made for the plastic industry. This chapter also includes information applicable to other molds and dies used in the other processes some of the other chapters too provide information applicable to their tools. 

Products A wide range of polypropylene products (homopolymer, random copolymer and impact copolymer) can be produced to serve many applications, including injection molding, blow molding, thermoforming, film, extrusion, sheet and fiber. Impact copolymer produced using this process exhibits a superior balance of stiffness and impact resistance over a broad temperature range. 

There are far too many applications for injection molded products to thoroughly cover here. However, a few examples will help provide an idea of some of the important mold design and machining considerations. 

Body panels with somewhat less demanding aesthetic requirements include tmck fairings. Extremely large parts such as these are often made by thermoforming as opposed to injection molding. For this reason, good melt strength is essential. Currentiy PPE/PA materials are used in these applications. 

Once the fluorescent colorant passes quality control testing, it is then distributed to compounders to be made into color concentrate. Once in solid masterbatch or liquid concentrate form, the fluorescents are used in a wide variety of applications, including injection molding, rotational molding, blow molding, extrusion, and vacuum forming. These fluorescent colorants are used primarily in polyolefins, in vinyl plastisols, and somewhat less in styrenics, acrylics, and ABS. 

This polymer is amorphous and thermoxidatively stable, with a Tg of 215°C, and it is subjected to injection molding operations at temperatures above 300°C. At these temperatures degradation reactions are likely to occur, and therefore the understanding of the thermal behavior of PEI is of crucial importance in the end-use applications. 

Thermoforming is an open process, which means the process is sensitive to environmental changes and therefore sometimes unstable and difficult to control. Because of its instability, the thermoforming process has developed more like an art than a science [9]. The settings of process parameters and the development of new thermoformed products is only based on experience [10]. Little attention has been paid to thermoforming in terms of scientific imderstanding, which makes the process critical for complex applications compared to injection molding. 

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