Case Studies
Roto-blow Molding, a Rotational Molding Hybrid
Ever increasing customer demands and expectations are pushing the process of rotational molding to new limits. This has resulted in the once simple process developing many varied hybrids and a range of processing options. One such hybrid is to pressurize the internal atmosphere of the mold during the molding cycle….
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Investigation of the Rheological Properties of Rotomolding Resins
There are many influential factors and processing variables that can impact the mechanical and aesthetic properties of a rotomolded part. One of the main variables is the resin being processed and its associated rheological properties…
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Improving the Performance of Rotomolding Resins
Rotational molding industry growth has been somewhat restricted by the number of and types of resins available to the molder. This paper outlines methods to improve the performance of rotomolding resins using processing techniques, modifying the design of the part and by the inclusion of strengthening additives in the polymer matrix…
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The Importance of Monitoring Mold Pressure During Rotational Molding
During the rotational molding of plastic parts, the pressure inside the mold can become positive or negative, depending on a variety of factors. This paper reviews the effects of pressure variations on the quality of rotomolded parts and, using experimental data, demonstrates the importance of monitoring the pressure inside the mold throughout the cycle…
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Rotational Molding Process Control
Process control for the rotational molding industry has continually evolved in recent years. Impact strength and bubble content of the wall were initially used to gauge level of cure and also to control the process. The development of the Rotolog process control device has provided a more scientific means to ensuring good process control…
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Effects of Pigmentation on the Impact Strength of Rotationally Molded Polyethylene
Rotational molding does not benefit from the high shear which is present in other processing methods such as injection molding or extrusion. Hence, rotational molders have a dilemma because there are distinct advantages in doing in-house coloring but it is difficult to get good dispersion of the color…
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Mold Pressure Control in Rotational Molding
The next major advance in rotational molding will be made when the benefits of controlling the pressure inside the mold are fully utilized. This paper explains why mold pressure control throughout the molding cycle is crucial to the rotational molding industry in terms of, firstly, achieving good part quality and, secondly, reducing cycle times…
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Removal of Pinholes and Bubbles from Rotationally Molded Products
A drawback of the rotational molding process has always been the surface pinholes and internal bubbles which occur in the products due to the inherent nature of the process. This paper describes how bubbles in rotationally molded products can be removed by pressurizing the inner atmosphere of the mold…
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Process Control for Rotational Molding of Plastics
Rotational molding has become more sophisticated in terms of equipment design and the complexity of the molded products. However, a major drawback has been the lack of precise control due to the difficulty of getting information about what is happening to the powder as it coats the inside surface of the rotating mold. To overcome this problem, a new control system has been developed whereby temperature measurements are taken from inside the mold as it rotates…
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The Effect of Processing Variables on the Formation and Removal of Bubbles in Rotationally Molded Products
The rotational molding processing method for plastics is steadily expanding its’ product range and market areas. However, a drawback of the process has always been the surface pin-holes and internal bubbles that occur in the products because of the inherent nature of the process. In an attempt to alleviate this problem, a program of research has been carried out to investigate the factors that affect the formation of the bubbles and, more importantly, that influence their removal. This paper describes the results of the first stage of this work…
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