Optimisation of multi-layer rotationally moulded foamed structures

2018 ◽  
Author(s):  
A. J. Pritchard ◽  
M. P. McCourt ◽  
M. P. Kearns ◽  
P. J. Martin ◽  
E. Cunningham
Keyword(s):  
Rotationally Moulded

Rotational Moulding of Liquid Polymers

1996 ◽  
Vol 210 (5) ◽  
pp. 437-447 ◽  
Author(s):  
E Harkin-Jones ◽  
R J Crawford
Keyword(s):  
Ring Opening ◽  
Material Handling ◽  
Bubble Formation ◽  
Rotational Moulding ◽  
Polymer Systems ◽  
Moulding Process ◽  
Cycle Times ◽  
Liquid Polymer ◽  
Liquid Polymers ◽  
Rotationally Moulded

The vast majority of rotationally moulded articles are produced from powdered polymers. However, the moulding process developed originally from the use of liquid polymers and nowadays there is a renewed interest in such systems because of some unique advantages that they offer. This paper compares the behaviour of three different liquid polymer systems—nylon 6 by ring-opening caprolactam, polyvinyl chloride plastisol and polyurethane. The flow behaviour of each material is examined with particular reference to wall thickness distributions and bubble formation in the product. On the basis of this, criteria for the production of fault-free mouldings have been established. The interrelationships between mould shape and resin viscosity are also examined and an ideal viscosity—time—temperature profile is proposed for liquid polymer systems. Finally, a general comparison of the materials is made with regard to material handling, safety, cycle times, etc.

Use of virgin/recycled polyethylene blends in rotational moulding

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sibele Piedade Cestari ◽  
Peter J. Martin ◽  
Paul R. Hanna ◽  
Mark P. Kearns ◽  
Luis Claudio Mendes ◽  
...  
Keyword(s):  
Impact Resistance ◽  
Degree Of Crystallinity ◽  
Household Waste ◽  
Flow Index ◽  
Melt Flow ◽  
Rotational Moulding ◽  
Plastics Recycling ◽  
Recycled Polyethylene ◽  
Rotationally Moulded ◽  
The Impact

Abstract Aiming to further plastics recycling via rotational moulding plastics processing, blends of virgin and recycled polyethylene sourced from post-consumer plastics were developed. Three different kinds of recycled high density polyethylene – from bottles, pipes and mixed household waste – were compounded with virgin medium density polyethylene in an extruder. The ideal amount of recyclate was chosen based upon the impact resistance of different contents (25, 50 and 75%) of recycled plastic with the 50/50 blend found to have the best performance. Compression-moulded and rotationally-moulded samples were analysed through falling dart impact test, flexural test, melt flow rate and differential scanning calorimetry analysis. The impact results of the compression-moulded samples showed an increase in the impact resistance of the blends with a higher melt flow index and lower degree of crystallinity. The rotationally-moulded specimens displayed much lower impact resistance than the pure virgin plastic and a 20–30% reduction in the flexural moduli, which were ascribed to the crystalline structure of the part and issues in the blends’ rotomoulding process. It was concluded that blending virgin and recycled polyethylene for rotational moulding can be an effective way to further plastics recycling inside the Circular Economy context.

scholarly journals Development and testing of thermoplastic structural components for modular prostheses

1988 ◽  
Vol 12 (1) ◽  
pp. 19-40 ◽  
Author(s):  
A. G. A. Coombes ◽  
J. Maccoughlan
Keyword(s):  
Service Use ◽  
Structural Integrity ◽  
Static Load ◽  
Fatigue Testing ◽  
Load Level ◽  
Structural Components ◽  
Knee Prostheses ◽  
Static Test ◽  
Structural Deterioration ◽  
Rotationally Moulded

The wider use of thermoplastic structural components in modular artificial limbs would enable their general properties of low density, corrosion resistance and mouldability and more specific properties of certain thermoplastics such as shock absorption, fatigue and wear resistance to be used to the advantage of patients and manufacturers. They provide an alternative to metal and carbon fibre reinforced resin systems. Emphasis has been placed on the development of rotationally moulded Nylon 11 shank sections, using Philadelphia recommended load levels as the design criteria for structural integrity. Laboratory testing underlined the importance of fatigue testing of thermoplastic components since structural deterioration due to creep-a time dependent mechanical property of thermoplastics-can be ascertained in fatigue testing but would not be evident on the shorter timescale of the static test. Experimental below-knee prostheses incorporating suitably designed plastic shanks and alignment devices can withstand high static loads and exhibit long fatigue lifetimes in excess of 2 million cycles. The shank design offered an opportunity for testing under service conditions the validity of the Philadelphia Static Load level (2.5 kN) since shank failure loads are around this figure. Patient trials of experimental prostheses based on various combinations of plastic shanks and alignment devices and conducted over 33 months indicate that the Static Load Level along with fatigue testing is a satisfactory test criterion for general service use of thermoplastic prosthetic components.

Morphology of Rotationally Moulded Microfibril Reinforced Composites and its Effect on Product Performance

2007 ◽  
Vol 334-335 ◽  
pp. 349-352 ◽  
Author(s):  
Richard Lin ◽  
Debes Bhattacharyya ◽  
S. Fakirov
Keyword(s):  
Ethylene Terephthalate ◽  
Mechanical Characteristics ◽  
Raw Materials ◽  
Product Performance ◽  
Manufacturing Processes ◽  
Reinforced Composites ◽  
Rotational Moulding ◽  
Poly Ethylene Terephthalate ◽  
Poly Ethylene ◽  
Rotationally Moulded

Rotational moulding (rotomoulding) is one of the fastest growing plastics manufacturing processes using linear polyethylenes dominantly as raw materials. However, due to their modest mechanical properties, rotational moulders worldwide are keen to develop stronger and stiffer materials. In the present study, an attempt was undertaken to apply the concept of microfibril reinforced composites (MFCs) for improving the material performance. Melt blended and subsequently cold drawn and undrawn linear medium density polyethylene (LMDPE) with either poly(ethylene terephthalate) or poly(ethylene naphthalate) possessing MFC structure were mixed with neat LMDPE and thereafter processed via rotational moulding. The rotomoulded samples were characterised morphologically and tested mechanically. The obtained unsatisfactory mechanical characteristics led to the subsequent morphological study which revealed some interesting phenomena for the rotomoulded products containing MFC blends.

Removal of Pinholes and Bubbles from Rotationally Moulded Products

1996 ◽  
Vol 210 (6) ◽  
pp. 521-533 ◽  
Author(s):  
A G Spence ◽  
R J Crawford
Keyword(s):  
Butyl Acetate ◽  
Time Pressure ◽  
Ethylene Vinyl Acetate ◽  
Processing Method ◽  
Rotational Moulding ◽  
Nylon 12 ◽  
Market Areas ◽  
Inherent Nature ◽  
Rotationally Moulded ◽  
The Impact

The rotational moulding processing method for plastics is steadily expanding its product range and market areas. However, a drawback of the process has always been the surface pinholes and internal bubbles which occur in the products due to the inherent nature of the process. In an attempt to alleviate this problem, a programme of research has been carried out to investigate the factors that affect the formation of the bubbles and more importantly influence their removal. This paper describes how bubbles in rotationally moulded products can be removed by pressurizing the inner atmosphere of the mould. It has been shown that bubbles were successfully removed from MDPE (medium density polyethylene) by introducing a low pressure (0.5 bar) inside the mould after the polymer had melted. The removal of bubbles using pressure was shown to increase the impact properties (25 per cent) and the tensile properties (5 per cent) of the moulding while also reducing the cycle time. Pressure was successfully used to remove bubbles from other rotational moulding materials, such as polypropylene, Nylon 12, polycarbonate, ethylene vinyl acetate and ethylene butyl acetate.

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