The effect of pressure variations on the formation of gas inclusions in the rotational molding process

2015 ◽  
Vol 35 (5) ◽  
pp. 481-491 ◽  
Author(s):  
Martin Löhner ◽  
Dietmar Drummer
Keyword(s):  
Cycle Time ◽  
Polymer Melt ◽  
Low Pressure ◽  
Rotational Molding ◽  
Molding Process ◽  
Inclusion Removal ◽  
Heating And Cooling ◽  
Polymer Powder ◽  
Major Disadvantage ◽  
Plastic Processing

Abstract The major disadvantage of rotational molding is the cycle time, which is very long compared to other plastic processing methods. A major percentage of the cycle time besides heating and cooling results from the time necessary to remove gas inclusions from the polymer melt, which are trapped while sintering the polymer powder. In this work the formation of gas inclusions is investigated by conducting a cycle time variation on a uniaxial rotational molding machine. The influence of low pressure during melting on the formation of inclusions is investigated by examining sintering experiments with a pressure variation during the melting of the polymer. Sintering experiments are conducted with different melt residence times to investigate the mechanisms of gas inclusion removal. By comparing the time to reach a pore-free polymeric melt, the cycle time reduction potential under low-pressure application while melting the polymeric powder is estimated.

Dynamic Modeling of Thermal Processes in Rotational Molding

Volume 3 ◽  
2004 ◽  
Author(s):  
Kalyanjit Ghosh ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Energy Consumption ◽  
Plastic Material ◽  
Liquid Pool ◽  
Transient Heat Transfer ◽  
Rotational Molding ◽  
Molding Process ◽  
Heating And Cooling ◽  
Consumption Rates ◽  
Plastic Parts

Transient heat transfer phenomena in the rotational molding of plastic parts are modeled in this study. Natural convection and radiation from the furnace and flue gases to the mold housing are analyzed. Other models include transient heat transfer through the mold, single-phase conduction through the particulate plastic material prior to phase change, melting of the plastic, and heating of the liquid pool. Subsequent staged cooling and solidification of the mold and plastic using a combination of free and forced convection and radiation is also modeled. Information about the properties of the plastic in powder, liquid and solid forms is obtained from the literature. Assumptions about the behavior of the plastic powder and the molten plastic during the rotational operations are also made in accordance with the available literature. The mold wall, melt and solidified plastic regions are divided into a number of finite segments to track the temperature variation with time during the molding process. The corresponding variations in masses and thicknesses of the melt and solidified plastic regions are also estimated. Consequently, the energy consumption rates in the process are estimated. The model is applied to a specific molding process in a commercial rotational molding plant. Parametric studies of the effect of heating and cooling durations on the plastic temperatures and the energy consumption rates are also conducted. These analyses provide insights about opportunities for optimization of the heating and cooling schedules to reduce overall energy consumption and also improve throughput.

Numerical study of the effect of operating parameter on rapid heat cycle molding process

2016 ◽  
Vol 231 (5) ◽  
pp. 1075-1084 ◽  
Author(s):  
Moez Hammami ◽  
Fatma Kria ◽  
Mounir Baccar
Keyword(s):  
Product Quality ◽  
Cycle Time ◽  
Numerical Study ◽  
Operating Parameter ◽  
Operating Conditions ◽  
Cycle Performance ◽  
Three Dimensional Model ◽  
Molding Process ◽  
Heat Cycle ◽  
Heating And Cooling

Recently, rapid heat cycle molding technology has been developed based on the mold heating before each polymer injection stage. For this process, successful heating and cooling phases are of great importance to ensure the cycle productivity and product quality. In this study, a three-dimensional model was developed to investigate the thermal response during the rapid heat cycle molding process. The procedure uses the finite volume method and the fractional area volume obstacle representation to obtain the thermal behavior of both polymer and mold until reaching the regular cyclic regime. The authors’ objective was to determine the operating parameter effect on rapid heat cycle molding process. Thus, four parameters were studied: the heating and cooling temperatures, the heat transfer coefficient of the cooling phase, and the fouling resistance at the channels. To investigate the influence of these parameters on the product quality and the process productivity and profitability, four criteria were selected: cycle time, consumed energy, temperature gap at the surface cavity, and temperature homogeneity in the polymer part. It was found that the operating conditions had a significant effect on the rapid heat cycle molding cycle performance. It was demonstrated that the heating medium temperature affects only the heating time; however, the cooling water temperature affects both heating and cooling times. In particular, the cooling temperature range of 50–60 ℃ reduces the consumed energy compared with the lowest temperatures, without a significant increase in the cycle time.

Cycle time predictions for the rotational molding process with and without mold/part separation

1999 ◽  
Vol 39 (4) ◽  
pp. 617-629 ◽  
Author(s):  
G. Gogos ◽  
X. Liu ◽  
L. G. Olson
Keyword(s):  
Cycle Time ◽  
Rotational Molding ◽  
Molding Process ◽  
Mold Part

scholarly journals A Novel Automated System for the Handling of Car Seat Wires on Plastic Over-Injection Molding Machines

Machines ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 141
Author(s):  
F. J. G. Silva ◽  
M. R. Soares ◽  
L. P. Ferreira ◽  
A. C. Alves ◽  
M. Brito ◽  
...  
Keyword(s):  
Cycle Time ◽  
Added Value ◽  
Automated System ◽  
Production Cycle ◽  
Labor Costs ◽  
Molding Process ◽  
Car Seats ◽  
Car Seat ◽  
Productivity And Competitiveness ◽  
Plastic Injection

The structure of car seats is becoming increasingly complex, with mixing of wire conformation and plastic injection. The plastic over-molding process implies some labor, which can be reduced if novel solutions are applied in this manufacturing area. The handling of the wires used in car seats is the main problem identified in the process, wasting time both in the feeding and in the extraction of the molds used in the wire over-molding process. However, these machines are usually extremely compact and the free space around them is too short. In classic molding injection machines, there are just two half-molds, the female, and the male. In the over-molding process of wires used in car seats, three half-molds are used in order to increase the cycle time. Thus, to solve this problem, the classic robotic solutions are not appliable due to lack of space and elevated cost. This work describes the development of an automated solution able to handle the wires in both the feeding and the extracting phases of the production cycle, avoiding the traditional labor costs associated with this type of machine. Departing from an industrial need, the developed novel solution is described in detail and can be successfully adapted to other situations of low added-value products where it is needed to increase the productivity and competitiveness of the product. The system developed uses mechanical and pneumatic solutions which, combined, can be used to solve the identified problem, occupying a restricted space and requiring a small budget. This solution can be translated into guidelines that will allow the analysis of situations where the same system can be applied.

Simplified Version of Polymer Rotational Molding Manufacturing Method

2016 ◽  
Vol 699 ◽  
pp. 97-103 ◽  
Author(s):  
Laurenţiu Slătineanu ◽  
Oana Dodun ◽  
Margareta Coteaţă ◽  
Gheorghe Nagîţ ◽  
Irina Beşliu
Keyword(s):  
Liquid Phase ◽  
Rotation Speed ◽  
Rotational Molding ◽  
Slow Speed ◽  
Molding Process ◽  
Manufacturing Method ◽  
Polyurethane Resin ◽  
Liquid Material ◽  
Complex Equipment ◽  
Plastic Parts

Rotational molding is a manufacturing method which supposes the rotation of the mold, during the solidification of the liquid phase material, so that finally a part having a hollow could be obtained. The method could be applied in manufacturing of metallic and nonmetallic parts. Usually, the equipment for rotational molding ensures slow speed rotating of the mold around two axes placed perpendicularly each other and this fact led to relatively complex equipment for achieving rotational molding. The capacity of the liquid material to entirely cover the internal walls of the mold depends essentially on the liquid material viscosity, on the rotation speed and on the movements applied to the mold. Simplified equipment including a single rotation movement could be materialized. In order to test such a solution, a preliminary experiment was designed and materialized, by using a device adapted on universal lathe. Thus, the objective of the research presented in the paper was to study if it is possible to achieve plastic parts made by rotational molding using a single rotation movement. A polyurethane resin obtained from two liquid components was used in order to obtain the liquid material that could be introduced in the mold. The research results proved the possibility to use simplified equipment for achieving a rotational molding process, at least in certain cases and with some technological limits.

Influence of Moisture on Flax Fiber in Polyethylene Composite Product Manufactured by Rotational Molding Process

2002 ◽  
Author(s):  
S. Panigrahi ◽  
L. G. Tabil ◽  
W. J. Crerar ◽  
S. Sokansanj ◽  
T. Powell ◽  
...  
Keyword(s):  
Flax Fiber ◽  
Rotational Molding ◽  
Molding Process ◽  
Polyethylene Composite ◽  
Composite Product

Design and Testing of Innovative Rotational Mould Heated by Thermal Fluid

2010 ◽  
Author(s):  
M. D. Monzo´n ◽  
A. N. Beni´tez ◽  
P. Bordo´n ◽  
P. M. Herna´ndez ◽  
M. D. Marrero ◽  
...  
Keyword(s):  
Cycle Time ◽  
Energetic Efficiency ◽  
Internal Stresses ◽  
Cycle Times ◽  
Transfer Processes ◽  
Computational Fluids Dynamics ◽  
Heating And Cooling ◽  
Computational Fluids ◽  
Plastic Parts ◽  
Design And Testing

Rotomoulded plastic parts have no internal stresses, as it is a process carried out at lower temperatures than injection moulding and no pressure is applied. The main disadvantage is the high cycle times needed. This paper focuses on reducing this cycle time and in producing a mould using standardized parts. For cycle time reducing, it is proposed to heat the mould by thermal fluid in continuous circulation; heat transfer processes have been studied for over 20 different configurations of the oil’s inlet – outlet, obtaining acceptable results with a manifold with 25 perforations in the front and rear faces. This configuration has been optimized by computational fluids dynamics, allowing reducing heating and cooling time and improving the energetic efficiency and the uniformity of heating. Design, simulations and testing of a 100 mm3 cube have been carried out in order to produce a standardized mould; this mould consists in some standardized parts and a nickel shell, obtained by rapid prototyping and electroforming process. This shell can be removed from the rest of elements in the mould, allowing thus to obtain parts with any other geometry just by changing the nickel shell. An experimental machine for testing has been developed as well.

Banana and Abaca Fiber-Reinforced Plastic Composites Obtained by Rotational Molding Process

2013 ◽  
pp. 130614085148001 ◽  
Author(s):  
Z. Ortega ◽  
M. D. Monzón ◽  
A. N. Benítez ◽  
M. Kearns ◽  
M. McCourt ◽  
...  
Keyword(s):  
Fiber Reinforced ◽  
Rotational Molding ◽  
Molding Process ◽  
Fiber Reinforced Plastic ◽  
Plastic Composites ◽  
Reinforced Plastic

Evaluation of a Piezoelectric Energy Extraction Device for Cavity Pressure Sensing in Injection Molding

2003 ◽  
Author(s):  
Charles B. Theurer ◽  
Li Zhang ◽  
David Kazmer ◽  
Robert X. Gao
Keyword(s):  
Injection Molding ◽  
Mechanical Strain ◽  
Piezoelectric Element ◽  
Polymer Melt ◽  
High Energy ◽  
Injection Molding Process ◽  
Molding Process ◽  
Transient Model ◽  
Piezoelectric Energy ◽  
Wide Range

This paper presents the design, analysis, and validation of a self-energized piezoelectric pressure sensor that extracts energy from the pressure differential of the polymer melt during the injection molding process. To enable a self-energized sensor design, an analytical study has been conducted to establish a quantitative relationship between the polymer melt pressure and the energy that can be extracted through a piezoelectric converter. Temperature and pressure are monitored during an injection molding cycle and the performance of the piezoelectric element is evaluated with respect to a mechanically static, electrically transient model. In addition to corroboration of the proposed model, valuable statistical information about the working temperature in the prototype sensor will prove very useful in the package design of molding cavity sensors. A linear model examining the energy conversion mechanism due to interactions between the mechanical strain and the electric field developed within the piezoelectric device is established. This model is compared to the functional prototype design to evaluate the relevance of the assumptions and accuracy. The presented design enables a new generation of self-energized sensors that can be employed for the condition monitoring of a wide range of high-energy manufacturing processes.

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