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This paper will cover the details of piece part design particular to the rotational molding process. Ribs, bosses, wall thicknesses, parallel walls, internal and external corners, openings, draft angles and undercuts will be discussed. Joining features, such as inserts, hinges and molded-in threads, will also be reviewed.
At first glance the Rotomold process is a fairly simple one. Its capabilities are exiting and have opened new avenues for creative industrial designs including complex shapes and rugged structural parts. Successful Rotomolded designs can be obtained by keeping a few guidelines in mind from concept through to product generation. This portion of the program will cover the areas that need to be considered during the design process. Items to be highlighted are basic design guidelines, features that can compromise, complicate and delay a project and what to ask a molder about specific designs.
Summary The static fracture toughness (Kc) and fatigue crack propagation (FCP) behavior of injection-molded short glass fiber (GF) reinforced poly(cyclohexylene-dimethylene- terephthalate) (PCT) composites were determined as a function of material parameters (with and without flame retardant) and molding conditions (injection speed and plaque thickness were varied). The anisotropy in the fracture mechanical response of GF-PCT, determined on compact tension (CT) specimens notched along and transverse to the mold filling direction (L- and T-notching, respectively) was interpreted by considering the molding-induced microstructure (GF layering and alignment). It was established that the effect of injection molding speed is negligible at the same specimen thickness. By contrast, increasing thickness strongly affected the GF structuring and thus the related fracture mechanical response.
Hygrothermally decomposed polyurethane (HD-PUR) of polyester type has been used as a cost-efficient impact modifier in tri- and tetrafunctional epoxy (EP) resins. The PUR modifier was added between 5 and 80 wt.% to the EP prior its crosslinking with a diamine compound (Diaminodiphenylsulphone, DDS). The fracture toughness (Kc) and -energy (Gc) of the modified resins were determined on static loaded compact tension (CT) specimens at ambient temperature. The mean molecular weight between crosslinks (Mc) was determined from the rubbery plateau modulus of dynamic mechanical thermal analysis (DMTA) spectra. The change in the Kc and Gc as a function of Mc followed the prediction of the rubber elasticity theory. The efficiency of the PUR modifier was compared with that of a carbonyl terminated liquid nitrile rubber (CTBN). DMTA and fractographic inspection revealed that the PUR modifier was not only present in a dispersed phase of the EP matrix but participated in the build-up of the EP crosslinked network structure. Thus HD-PUR works as active diluent and phase separating additive at the same time. As HD-PUR can be regarded as an amine-functionalized rubber, it was used as hardener alone (by replacing DDS) in some EP formulations.
Thermoplastic elastomers containing 50 wt.% poly(ethylene terephthalate) (PET) and 50 wt.% rubber with and without glycidyl methacrylate (GMA) functionalization were produced by melt blending. In some cases the method of dynamic curing was also adopted. The static tensile properties and dynamic-mechanical thermal analysis (DMTA) response of the systems were studied. The phase morphology of the blends was of interpenetrating network (IPN) type according to fractographic and DMTA results. It was established that the best mechanical performance exhibited those blends which contained a GMA-grafted nitrile rubber (NBR-g-GMA). The effect of dynamic dynamic curing, for which a two-step procedure was developed, was marginal. Cost reduction opportunities of the recipes by using high-volume polyolefins have also been explored.
Stéphane Menio, Eric Lafranche, José Pabiot, Claude Ollive, May 2000
Thanks to its qualities and performances, BMC injection molding has nowadays reached a satisfactory maturity level. But nevertheless, this technology remains complex. Thus, the aim of the present study is to determine the technological parameters capable of improving the surface quality of the molded parts. The experiments are performed with a semi-industrial mold for rectangular plate. A first Taguchi Design Of Experiments was used in order to quantify the effect of the feeding, filling, holding and curing parameters on the surface quality. It was completed by a second hybrid DOE, the aim of which was to estimate more precisely the incidence of the main key factors (mold surface temperature, injection flow rate and holding pressure) previously identified. These results have been then confirmed with a different gate location and a modified geometry.
Roto-mold is a versatile process which accomplishes many objectives which are difficult or impossible in other processes. It also has some special problems which complicate the aesthetic aspects of a design. Industrial designers working with engineers are uniquely qualified to design for this process.
Rotational molding is a plastics molding process that is noted for producing seamless, hollow parts. The process is capable of molding complex, thin-walled, hollow parts in small and extremely large sizes. This paper will explain what the process is, how it works, and why the manufacturers of durable plastic products should be aware of this process's impressive capabilities.
The influence of absorbed moisture on the performance of nylon products is well documented. Similarly, the effects of excess moisture on the processing of nylon are well established. But confusion often arises in the processing community regarding the reasons for the brittle behavior of nylon parts. This paper is designed to follow the role of moisture from the pellet through to the conditioned part and separate the fact from the fiction regarding the effects of moisture on nylon properties.
This paper reviews a study designed to determine the effect of aspect ratio on properties of mica reinforced polypropylene and nylon composites. The study was made possible by recent developments in particle analysis software that permits determination of aspect ratio of non-spherical materials.
Natti S. Rao, Guenter Schumacher, Nick R. Schott, Keith T. O’Brien, May 2000
The production rate of injection-molded articles is determined by the cooling time of the polymer melt in the mold. By using state-of-the-art numerical software the mold design can be optimized in order to achieve fast cooling. However, the efforts required to apply this software do not always justify its use in dealing with the daily design problems. Taking the changing mold wall temperature into account a straightforward analytical procedure for optimizing the cooling channel lay-out for a thermoplastic resin has been developed. The equations in the model can be easily solved by means of a hand-held calculator, thus enabling quick estimates of the effect of relevant parameters on mold design. Results of numerous simulations and a worked-out example illustrate the application of the model which has led to good results in the practice.
Rheological behavior of entangled six-arm and eight-arm 1,4-polybutadiene melts of the types A3-A-A3 and A3-A- A2-A-A3 is investigated using low amplitude oscillatory shear and viscosity measurements. Experiments covered a time (frequency) and temperature range broad enough to characterize the complete relaxation spectrum. In oscillatory shear, three separate relaxation modes are identified. At high frequencies a maximum in the loss modulus is linked with segmental relaxation. At intermediate frequencies a new relaxation mode characteristic of the arms is observed. Finally, at low frequencies a terminal relaxation process is identified. This process is characterized by a lower plateau" modulus and is thought to reflect cross-bar reptation in an enlarged tube."
M.C. Cramez, M.J. Oliveira, R.J. Crawford, May 2000
During rotational molding the plastic is subjected to relatively high temperatures for long periods of time. This often causes degradation of the polymer at the inner surface of the molded article. The resulting degraded layer is responsible for the deterioration of the mechanical properties of the part. In practice, the optimum processing temperature and/or heating time must be obtained by means of an extensive molding and testing program. Moreover, as the degradability of polyethylene depends on many factors, such as the molecular structure of the material, the type and concentration of stabilizers and the thermal history experienced during processing, an optimization program that takes into account all these variables is very expensive and time consuming. In this work the degradation of polyethylene is studied using a technique widely used in the assessment of degradation resistance in the pipe industry - Oxygen Induction Time (OIT). The method enables the onset temperature of degradation to be identified using only a few milligrams of material. The data obtained from simple and quick experiments was used to produce an empirical model to predict the optimum inner air temperature for rotational molding of the materials. It is shown that whilst the maximum internal air temperature experienced during rotational molding is a good quality control parameter, there are many other important factors, such as the heating rate of the mold, the thickness of the mold material, etc.
Polypropylene(PP)-clay composites were prepared by melt mixing in an intensive mixer. Three grades of PP's having different melt viscosities were employed to investigate the mixing characteristics of the composites with various clays which belong to organically modified montmorillonite(org-MMT). Depending on the matrix viscosity and nature of the organic layer in MMT, significant variations in the phase structure of the composites were found. In addition to the simple combination of PP and clay, modified PP's having various content of maleic anhydride were also incorporated. Major interest was focused on the effect of varying thermodynamic affinity between the components on the phase evolution and mechanical properties of the composites. Requirements for the effective dispersion of clay in the PP matrix are discussed in terms of both rheological effect and thermodynamic interaction.
It's expensive in terms of time and equipment to give students the necessary exposure to a wide variety of polymer behavior in different areas of characterization and processing. 'Virtual instruments' (VIs) consist of interactive software that simulates the response of a particular characterization instrument or a process. A characterization 'suite' contains many thermal instruments; other instruments are under development. A blown film process line has also been assembled relating film properties to operational parameters.
During the extrusion of complex plastic profiles, the parts often distort and bow during the cooling phase of the process. The traditional methods of dealing with this are to use heat lamps to re-warm certain sections to remove the bow or to apply jigs to distort the part in the opposite direction so that when it cools, it comes back into the proper shape. A method to look at the cooling requirements of a particular profile is proposed along with a method to calculate how the part should be cooled in order to avoid distortion and bow.
There is a market need for soft (35 - 70 Shore A) clear TPEs with heat resistance high enough for repeated boilable applications. Flexible PVC meets most of the requirements, but it is out of the scope of this work. Styrenic Block Copolymer based compounds have been developed to fill this need. Important parameters, such as molecular weight of the base polymer, surface quality of the molded part and rheology of the material, have been correlated with clarity and heat resistance. Some of the myths about the clarity of SBC compounds will also be discussed.
Orientation of polymers enhances many of their properties, particularly mechanical, impact, barrier and optical etc.. Orientation processes all involve extrusion prior to deformation and can generally be classified into three categories: fibers, films, and parts (sheets, bottles, rods, ...). The knowledge of the polymer orientation produced by the different processes is critical for establishing the process conditions and the final properties of the oriented polymer. There is a long history of investigations of orientation in polymers, mainly from off-line measurements, involving techniques such as birefringence, infrared spectroscopy, X-ray scattering, Raman, NMR, fluorescence, ultrasonic etc. In this presentation, we will focus on techniques which are or could be used for on-line monitoring of orientation processes. These include birefringence, spectroscopy, fluorescence and ultrasonic.
The use of innovative crosslinking agents for the preparation of thermoplastic vulcanizates (TPVs) is investigated. In this preliminary study, the most common TPVs systems, based on polypropylene (iPP) and rubber ethylene-propylene-diene terpolymer (EPDM) blends, are studied. Typical vulcanization agents, such as sulfur, phenolic resins and peroxides do not permit to crosslink saturated elastomers and, furthermore, give rise to dynamic vulcanization of the polyolefins. For this reason, the main goal of the present study is to investigate a new vulcanization agent for elastomeric matrices. This agent is based on azide derivative, 1,3-bis sulphonyl azide benzene that, for the specific behavior of the sulphonyl azide group, allows its interaction with the C-H bonds of the elastomeric phase and of the polyolefin. The study includes the dynamic vulcanization of PP-EPDM blends and their rheological, mechanical and thermal characterization. A comparison with traditional blends prepared with sulfur as vulcanization agent is also presented.
Miguel A. López, Jerico Biagiotti, Luigi Torre, José M. Kenny, May 2000
The simultaneous effects of the incorporation of different types of fibers and of the presence of EPDM on the crystallization kinetics and thermodynamics of isotactic polypropylene are presented. The study is applied to the behavior of polypropylene matrix composites reinforced with glass, PET, aramidic and sisal fibers. The results obtained show that in all cases, either the fibers and the EPDM rubber behave as effective nucleant agents for the crystallization of polypropylene. A dramatic decrease of the half time of crystallization, t1/2, and an increase of the overall crystallization rate, Kn, are observed being the aramidic fibers the most effective. It is also reported that transcrystallinity takes places in all fibers being more evident with aramidic fibers in the neat PP matrix. Only a slight transcristallinity effect is detected when fibers were incorporated in the PP-EPDM matrix.
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Any article that is cited in another manuscript or other work is required to use the correct reference style. Below is an example of the reference style for SPE articles:
Brown, H. L. and Jones, D. H. 2016, May.
"Insert title of paper here in quotes,"
ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
Available: www.4spe.org.
Note: if there are more than three authors you may use the first author's name and et al. EG Brown, H. L. et al.
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