Warpage and shrinkage

Shrinkage during the rotational molding is caused by numerous reasons, includ- 

If we consider the dimensional change in volume, we deal with the volumetric shrinkage. The volumetric shrinkage can be defined as 

Zheng et al., Injection Molding, DOI 10.1007/978-3-642-21263-5 6, Springer-Verlag Berlin Heidelberg 2011 

Isayev (1987) proposed a slightly different definition for the volumetric shrinkage. He uses the time-average value of the initial specific volume over the packing time, and writes the volumetric shrinkage as 

Volumetric shrinkage involves the change of dimension in three spatial directions. These changes can be different for each direction. Therefore it is important to consider the dimensional change in length, i.e., the linear shrinkage, defined by 

For anisotropic shrinkage, it is customary to classify the linear shrinkage into parallel shrinkage (the linear shrinkage in the flow direction), perpendicular shrinkage (the linear in-plane shrinkage perpendicular to the flow direction) and the thickness shrinkage 5. When 5v C 1, one has 

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In engineering applications we routinely incorporate inorganic fillers, such as glass fibers and mineral particles, into nylons. In general, fillers perform three functions they reduce the cost of the product, they increase its stiffness, and they reduce shrinkage and warpage in molded products. 

Results of a study of mold shrinkage and warpage are shown in Table... 

The silicone semi-IPN structure imparts unique behavior to thermoplastic composites without affecting mechanical strength and stifihess. Apart from the direct effects associated with the incorporation of thermoset character into a thermoplastic, the structure has particular value by functioning as (1) a nonmigrating internal lubricant, (2) a shrinkage and warpage modifier, (3) a fiow modifier, and (4) a release agent. As a polymer-polymer composite,... 

PSF/PET blends show a dispersed morphology. The combination of crystalline PET and amorphous polysulfone provides chemical resistance and warp-free properties. The amount of crystalline polymer is varied to meet requirements in thermal properties and the level of reinforcement is varied to tailor the modulus. The blends have electrical and mechanical properties similar to PET but only a third of its shrinkage and warpage. Also, stress crack resistance to common solvents is improved. Similarly, the service T is upgraded compared to PET. The blends are formed by injection molding and extrusion. 

At the low concentrations 5-10 % silicone, the blend is reported to retain much of its thermoplasticity and processability. This silicone semi-IPN reportedly improves the lubricity, wear and biocompatibility of polyamide as well as reducing the shrinkage and warpage although... 

Fischer, J. M., Handbook of Molded Part Shrinkage and Warpage, William Andrew Publishing, Norwich, 2003. 

Carbon fiber-reinforced PAs may be used for conductive and electrical shielding applications where high mechanical properties are also required, and for applications requiring a measure of internal lubrication, slip and good wear-resistance. Mineral-reinforced PA (with talc or mica) offers very good dimensional stability, and low shrinkage and warpage. 

Fischer JM (2003) Handbook of molded part shrinkage and warpage. Plastics Design Library, William Andrew, Norwich, NY... 

For example, the calculation of shrinkage and warpage in (long) fiber-rein-forced plastics can be worked out ahead of time and the data can be provided to the processor as well as the structural component development engineers. The same applies to improved integration of anisotropic and viscoelastic material behavior. The generation and expansion of FE calculation models (with rational... 

CAS 12001-26-2 EINECS/ELINCS 310-127-6 Uses Reinforcing agent, filler for plastics, paints, coatings, and rubber applies., composite systems, PP,PP copolymer, PPhomo ymer, nylon, nylon 6, HOPE, HOPE copolymer, PET, and PVC Features High aspect ratio reduced shrinkage and warpage improved tens, and flex, sir., mod., HDT... 

Fischer, Handbook of Molded Part Shrinkage and Warpage,... 

The blends can be either extruded or injection molded. They show improved processability and impact strength, low shrinkage and warpage, high FfDT, good stress crack chemical and solvent resistance, and good economy. The blends find applications as molded electrical parts, viz., connectors, relays, switches, motor starters, control housings, etc. 

Moldflow introduced software for prediction of shrinkage and warpage in 1990. Since this time, analysis of fiber-reinforced materials has been introduced in which the orientation of the fibers in the molding are calculated. With the distribution of fibers known, it is possible to calculate mechanical properties of the composite material in principal directions. This data can then be used in warpage calculations or used for structural analysis of the resulting part. 

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