Rotational Moulding Research Articles

Determination of the Heat Transfer Coefficient at the Metal-Mold Interface During Centrifugal Casting

The heat transfer coefficient at the metal-mold interface (h MM) has been determined for the first time during the centrifugal casting of a Fe-C alloy tube using the inverse solution method. To apply this method, a centrifugal casting experiment was carried out to measure cooling curves within the tube wall under a mold rotation speed of 900 rpm, imposing a centrifugal force 106 times as large as the gravity force (106 G). As part of the solution method, a comprehensive heat transfer model of the centrifugal casting was also developed and coupled to an optimization algorithm. Finally, the evolution of h MM with time that gives the minimum squared error between measured and calculated cooling curves was obtained. The determined h MM is approximately 870 W m−2 K−1 immediately after melt pouring, decreasing to about 50 W m−2 K−1 when the average temperature of the tube is ~973 K (700 °C), after the end of solidification. Despite the existence of a centrifugal force that could enhance the metal-mold contact, these values are lower than those generally reported for static molds with or without an insulating coating at the mold inner surface. The implemented model shows that the heat loss by radiation is dominant over that by convection at the tube inner surface, causing the formation of a solidification front that meets another front coming from the outer surface of the tube.

Simulation of the Reactive Rotational Molding Using Smoothed Particle Hydrodynamics

Simulation of the Reactive Rotational Molding Using Smoothed Particle Hydrodynamics

Prediction of heating cycle time in Rotational Moulding

In rotational moulding, due to bi-axial nature of mould rotation, there is a dearth of accurate and cost-effective thermal data measurement techniques and equipment. This necessitates reliable prediction of thickness for different temperatures and critical timings of the process like switching off the oven. Therefore, an attempt has been made to estimate the appropriate heating cycle time and thickness variation using process simulation. The thickness of polymer layer during intermediate temperatures and cycle time can be perceived from the simulation. It is also predicted that, a rotomoulded product of thickness 5mm requires an overall heating cycle time of 24.5minutes.

Effects of Mould Rotation on Element Segregation and Compact Density of Electroslag Ingots during Electroslag Remelting Process

AbstractSteel solidification process control, especially in the solidification process of high-alloy steel, and improving the solidification structure have been increasingly gaining interest among metallurgists, particularly the electroslag workers. To further develop the electroslag remelting (ESR) process and to improve the ingot solidification structure, the effects of mould rotation on chemical element distribution and the compact density were investigated in this study. The experimental results showed that chemical element distribution would become more uniform when the mould keeps the reasonable rotation rate. However, the excessive rotation rate would deteriorate the solidification structure of steel. When mould rotation rate was between 0 and 28 r/min, maximum segregation of carbon could decrease from 3.19 to 1.084, and statistical segregation decreased from 0.2636 to 0.0554. Maximum segregation of chromium could decrease from 1.316 to 1.131, and statistical segregation decreased from 0.2753 to 0.0657. The compact density increased from 0.7693 to 0.94. But element segregation would become bigger and compact density would become smaller if rotation rate further increased. The improvement in the solidification structure could be attributed to reasonable mould rotation rate which could initiate movement in the slag pool and further increase the uniformity of the temperature in the slag pool. At the same time, the movement in the slag pool could also affect the metal molten droplet, scattering the liquid drop randomly in the metal pool. But the excessive rotation rate made the slag pool violent motion, so as to drive the molten metal pool to rotate which would carry off enriched steel surrounding the dendrites in the mushy zone and reduce the solute content in the region. As a result, the element segregation would occur.

Basic Finite Element Analysis of Para-periodontal Ligament in All-ceramic Zirconia Fixed Partial Denture.

The purpose of the present study was to investigate the validity of incorporating a para-periodontal ligament in the test mold used in a basic fracture test of a zirconia all-ceramic fixed partial denture (FPD). A simplified three-dimensional finite element analysis model was designed based on the three-unit FPD fracture test. Two types of model, one with and one without a para-periodontal ligament between the abutment and base mold, were fabricated. Microfocus CT of the missing first molar area in a dry human mandible was performed. A three-dimensional model was then fabricated based on the data obtained. A load of 600 N was applied to the center of the pontic and stress distribution observed. The model with the para-periodontal ligament showed stress dispersion to the dental root with rotation of the abutment mold. Stress distribution in the finite element analysis model with a para-periodontal ligament showed greater similarity with that in the mandibular model than with that in the other two models without a para-periodontal ligament.

Contribution to Study of the Sintering Mechanism

In all process based in powder and in particular in the rotational moulding process, the major physical phenomenon during the flow of the powders is the sintering and grains growth. The sintering is the formation of only one particle starting from two or many particles under the effect of the temperature and the forces of surface tension. We interest in this study in particular at the mechanism of Polyvinylidene fluoride (PVDF) sintering. The results of this study can enable us to maximize our knowledge about sintering mechanism and enable us to determine parameters such as the speed of sintering for the optimization of the process.

Rotational Molding Informs “Learning Gardens”

Plastics EngineeringVolume 70, Issue 8 p. 10-14 Cover Focus Rotational Molding Informs “Learning Gardens” Rotomolding makes a unique learning experience come to life for thousands of young people Jamie Wirkler, Jamie Wirkler Boulder, Colorado, USASearch for more papers by this authorJen Lewin Studio, Jen Lewin Studio Boulder, Colorado, USASearch for more papers by this author Jamie Wirkler, Jamie Wirkler Boulder, Colorado, USASearch for more papers by this authorJen Lewin Studio, Jen Lewin Studio Boulder, Colorado, USASearch for more papers by this author First published: 01 September 2014 https://doi.org/10.1002/j.1941-9635.2014.tb01226.xAboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume70, Issue8September 2014Pages 10-14 RelatedInformation

Effect of Mechanical Vibration during the Solidification Process of an Aluminium Alloy A356

The treatment with mechanical vibrations during the solidification process promote microstructural changes in metallic alloys, in order to have a better understanding on this matter mechanical vibration were applied to an aluminum alloy A356, while teeming in order to evaluate the morphological changes on αAl primary phase in the solidification process. Two routes were analyzed, a cooling slope and a rotational mold. This paper shows the results of quantify the effect of mechanical vibration and the specific characteristic of casting to obtain a spherical morphology on the αAl primary, that allow to obtain thixoformable raw material.

Parametric and mechanical characterization of linear low density polyethylene (LLDPE) using rotational moulding technology

In this research work, extensive literature review of the rotational moulding process using linear low density polythene (LLDPE) has been carried out to summarize the present status of the characterization in order to maintain quality and reliability of the products. The present characterization of rotomoulded products using LLDPE is based on the mechanical properties which are being altered by changing process parameters. However, it is observed that in the majority of applications of the products made of LLDPE using rotational moulding technology are prone to cracking failure due to manufacturing defects at room temperature. Therefore, study of fracture characterization of the material is equally important in relation to quality and reliability. In this article, the present characterization of the rotational moulded products using different polymers is summarized in the form of review and the importance of evaluation of the fracture behaviour of rotomoulded products is emphasized.

Simulation and Analysis of Dynamic Characteristics of Rolling Motion of Rotational Molding Ship

Parametric resonance can lead to roll motions and endanger the ship, cargo and crew. The QR-factorization method for calculating lyapunov characteristic exponents (LCEs) was introduced. And then, parametric resonance stability of ships in longitudinal waves was analyzed by taking the fishing-entertainment rotational molding boat as an example. Simulation results show that, this method can be used to analyze ship stability and to accurately identify safe and unsafe operating conditions for a ship in longitudinal waves.

Impact response of polyethylene sandwich panel obtained by rotational moulding

ABSTRACTSandwich panels are more and more used in load bearing structures because of their high specific stiffness and high specific strength. Impact energy absorption is a characteristic required for some specific application, that is, in high‐speed transportations. In this article, the impact response of a new sandwich panel made up of two polyethylene skins separated by lightweight polyethylene foam, built with an innovative manufacturing process called rotational moulding, is investigated by both the impact test and the finite element analysis. To characterize the low‐velocity impact response of this new material, three homogenous polyethylene sandwich panels, 44 ± 1 mm thick, are studied under seven impact test energy levels, from 5 to 70 J. Experimental tests have allowed obtaining absorbed energy and the load–time plot for each impact energy level. Furthermore, a quantitative analysis of the damage is presented. Finally, a finite element model was implemented to evaluate the damping effect of the core.

Influence of Gravity and Mold Shape on Molding of Aluminum Foams

A molding process of aluminum foams by using a rotating mold is proposed in order to improve the mold filling and forming process for light-weight parts of vehicles. Aluminum powder mixed with a foaming agent is extruded into the mold through the die heated to a temperature higher than the melting point, and the mold is filled with the aluminum foam. When the diameter of a cylindrical mold is large, the influence of gravity is significant and the mold is not filled successfully. In the proposed molding, the aluminum foam is extruded into the rotating mold of large diameter and the volumetric ratio of foam to mold cavity is improved. However, the effect of the mold rotation on the mold filling is limited due to friction.

Effects of relative motion between consumable electrodes and mould on solidification structure of electroslag ingots during electroslag remelting process

Steel solidification process control, especially in the solidification process of high alloy steel, and improvement of the solidification structure have been increasingly gaining interest among metallurgists, particularly the electroslag workers. To further develop the electroslag remelting (ESR) process and to improve the advantage of the ingot solidification structure, the effects of relative motion between the consumable electrodes and the mould (namely, mould rotation) on chemical element distribution were observed in this study, as well as the compact density changes in electroslag ingots. Experiment results show that applying relative motion between the mould and the consumable electrodes in ESR results in a more uniform chemical element distribution in the electroslag ingots. Compared with the electroslag ingot of conventional ESR, maximum segregation of carbon could decrease from 3·19 to 1·146, and statistical segregation decreased from 0·2636 to 0·0608. Maximum segregation of chromium could decrease from 1·316 to 1·253, and statistical segregation decreased from 0·2753 to 0·1201. The compact density for the stationary mould increased from 0·7693 to a compact density of 0·9501 for the rotating mould. The improvement in the solidification structure of the electroslag ingot can be attributed to mould motion, which led to the generation of a shallow pool and the improvement of the solidification structure. But the excessive rotation rate is harmful to solidification structure instead due to the molten metal pool motion caused by violent slag pool motion.

Investigation of Melt Flow Index and Impact Strength of Foamed LLDPE for Rotational Moulding Process

Rotational molding of foamed polyethylene has increasingly become an important process in industry because of its thicker walls, low sound transfer, high stiffness and good thermal insulation. However, the foaming process of polyethylene during rotational molding has not been well studied. The focus of thisarticle is to assess the rotomoldability of foamed polyethylene and to investigate how LLDPE foam influence the process of rotational molding and the final product quality. Rotational molding experiments are carriedout in a laboratory scale biaxial machine. Impact tests and melt flow property are performed on the rotationally molded parts. It is found that the MFI and impact strength of rotomoulded product increases as the foam percentage increases up to 6% after which both decreases. Therefore it is concluded that 6% of foam is the optimum level to obtain sufficient melt flow index and better impact strength.

回転成形用エラストマー材料

回転成形用エラストマー材料

Forming of Aluminum Foams by Using Rotating Mold

In order to improve the mold filling in molding of aluminum foams, a molding process by using a rotating mold is proposed. Aluminum powder mixed with a foaming agent is formed to a precursor by hot powder extrusion and extruded into the mold through the die heated to a temperature higher than the melting point, and then the mold is filled with the aluminum foam. When the diameter of a cylindrical mold is large, the influence of gravity is significant and the mold is not filled successfully. In the proposed process, the aluminum foam is extruded into the rotating mold of large diameter and the shape of foam is improved. However, the effect of the mold rotation on the mold filling is limited.

Regional Rotomolders Ride the Storm

Plastics EngineeringVolume 69, Issue 9 p. 28-32 Rotational Molding: Special Report Regional Rotomolders Ride the Storm Peter J. Mooney, Peter J. MooneySearch for more papers by this author Peter J. Mooney, Peter J. MooneySearch for more papers by this author First published: 01 October 2013 https://doi.org/10.1002/j.1941-9635.2013.tb01069.xCitations: 1AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume69, Issue9October 2013Pages 28-32 RelatedInformation

INVESTIGATION OF THE INFLUENCE OF MOLD ROTATIONAL SPEED ON THE CAST WALL THICKNESS IN THE ROTATIONAL MOLDING PROCESS

This paper presents the rotational molding process. The general principles of this polymer processing technology have been described. The main applications have been introduced and leading advantages and typical disadvantages of rotational molding process have been discussed. Based on the conducted experimental tests, the influ ence of changing one selected technological parameter, which characterized rotational molding process, on selected geometrical features of the polymer cast has been determined. Rotational mold’s speed around axes was changed and a thickness of cast walls has been measured. Laboratory test stand, processing properties of polymer, also test program and experimental test methodology have been described.

The Research on the Heating Time of Rotational Molding

In the process of rotational molding, there are two important parameters, temperatures in the rotational molding machine’s oven and in the mold. It is the crux of the evaluation about the molding efficiency and products’ quality to control the time of the temperatures to reach the top. This article puts forward to two time parameters C1, C2 to show temperatures’ change in machine’s oven and in the mold during the molding processing. Besides, these two time parameters are applied to direct the structure design of rotational molding machines and molds. Meanwhile, the theoretical analysis agrees well with the experimental data from the comparison between them. Hence, the efficacy and practicality of the two parameters are well verified.

A Numerical Investigation on Temperature Field in the Oven of a Rotational Molding Machine

A simplified 3D model of a rotational molding machine oven was built, and a numerical investigation was carried out with the RNG k-ε approach in FLUENT. Since the temperature field in the original oven structure was distributed unevenly, three types of reformed designs were proposed and numerically studied. Results showed that by changing the inclined angle of inlet flow to 30° downward, hot air flowed onto the mold surface directly, the temperature field around the mold became more uniform but temperature in the bottom of the mold was still a little bit low. By changing the inclined angle of hot air to 30° downward and 45° rightward and leftward, or by changing both the cross sectional dimension of the inlet to 900mm×400mm and the inclined angle of hot air to 30° downward, the temperature field became more uniform and the average temperature around the mold remained relatively high, these two reformed designs were effective with good feasibility and economic efficiency, which could be considered in the future design of rotational molding machine.