Strona głównaThe usage of rotational molding technology to replace laminated products
Developed by: M. Eng. Adam Bernacki
Plastipol Poland Sp. z.o.o
Abstract:
The presented article focuses on illustrating the benefits that will result from replacing the method of laminating plastics with rotational molding technology Comparative analysis indicates direct advantages of the rotational molding method, which will bring a range of benefits in terms of systematization and standardization of production in industrial and decorative sectors. Both technologies share the use of similar processing capabilities. Therefore, based on a common produced items, we are able to identify effective and direct advantages of rotational molding The direct benefits include high production repeatability, standardization of mechanical and functional properties of the product, lower unit cost, high aesthetics of the products, and several times increased process efficiency. The low implementation costs of laminating do not compensate for the mentioned benefits, as the molds used in rotational molding, despite often large dimensions, remain cost-effective. The company Plastipol Poland sp. z. o. o has carried out numerous successful projects using the above solution in the industrial, agglomerative, and domestic wastewater treatment sectors, as well as in the energy and food industries.
Introduction to Rotational Molding and Laminating Technologies.
Rotational moulding
Rotational molding is one of the modern forms of plastic processing that is gaining increasing popularity. In the rotational molding process, also known as rotational or centrifugal molding, gravity force is utilized on the molded material . The material is introduced into the mold, usually in the form of powder, and then, under the influence of mold heating, it melts in its cavity. The solidification or hardening of the material occurs in the rotating mold, which is then stopped, opened, and the molded product is removed from its cavity.
att.1 Rotational Molding Diagram
A characteristic feature of planetary casting, presented in the att.1 1, is the even distribution of molten material on all walls of the forming cavity due to the gravity and centrifugal force generated by the simultaneous rotation around at least two axes. The shape of the forming cavity in rotational molding molds reflects the external surface of the molded object (in the form of a container), while the internal surface of the casting is freely shaped by the movement of the material under the influence of centrifugal force.
The molds for rotational molding technology are made of steel and aluminum alloys. The production costs of molds vary from 10,000 PLN for smaller details to 60-80,000 PLN for large, complex details with dimensions exceeding 1.5 meters.
Laminating
In a general sense, laminating involves covering structural objects with a polymer material. Laminat jest to rodzaj kompozytu powstający z połączenia co najmniej dwóch materiałów o różnych właściwościach mechanicznych, fizycznych i technologicznych. In laminates, the reinforcing component (so-called reinforcement) is arranged in the form of layers, between which there is a filler – resin, serving as an adhesive. The reinforcing layers can take the form of continuous fibers arranged unidirectionally (known as roving) as well as woven fabrics or mats made from chopped fibers (att. 2)
att. 2. The appearance of the surfaces of products obtained through lamination depends on the different forms of reinforcing components: a) mat, b) roving, c) glass fiber
This technology utilizes molds that range from 1000 to 10,000 PLN.
Advantages and disadvantages of the technology.
Rotational moulding
Advantages:
- Low cost of production preparation, driven by the low cost of manufacturing casting molds, cost-effectiveness for small and large production batches.
- zero-waste processing method,
- The possibility of attaching additional elements (sleeves, pins, connectors, rings) in the mold, which are covered with molten material and become an integral part of the casting after the process is completed. There is also the possibility of incorporating stiffening ribs in the mold, which increase the rigidity of the walls in very large castings.
- The entire process (heating, melting, molding, and cooling) takes place in the mold and does not involve any external pressure. There are no seam lines on the surface of the products.
- The ability to produce objects with a mass ranging from tens to several hundred kilograms, which is impossible to achieve in injection molding or extrusion technology due to the structural limitations of these processing machines.
Disadvantages:
- relatively long cycle time for casting production – low efficiency,
- Low efficiency and high energy consumption of the process, caused by heating and cooling the mold using air.
- The cost of preparing materials is further increased by the need to convert them into powder or pellets.
Laminating of plastics
Advantages:
- very simple method
- does not require expensive equipment
- the curing of the formed laminate takes place under normal pressure and at room temperature.
- cost-effective for the production of individual items or in small batches.
- the ability to produce products of very large dimensions.
Disadvantages
- labor-intensive, significant resin and filler losses, low filler content in the laminate.”
- uneven saturation
- harmful effects of substances on the human body.
- high unit cost of the product.
- the quality of the detail depends on the competence of the worker.
- limited variety of materials used.
Summary
Comparative analysis indicates unequivocal advantages of the rotational molding method, which will bring a range of benefits in terms of systematization and standardization of production in industrial and decorative sectors. Both technologies share the use of similar processing capabilities. Therefore, based on a common denominator of produced items, we can identify effective and unequivocal advantages of rotational molding. The direct benefits include – high production repeatability, standardization of mechanical and functional properties of the product, lower unit cost, high aesthetics of the products, and several times increased process efficiency. The low implementation costs of laminating do not compensate for the aforementioned benefits, as the molds used in rotational molding, despite often large dimensions, remain cost-effective.
Selected implementations
Dwg. 1 Comparison of rotational molding and manual laminating technologies based on underground manhole covers.
Dwg. 2 Defects arising from manual lamination of the cover
Literature:
http://bc.pollub.pl/Content/1368/PDF/polimery2.pdf
http://www.qenos.com/internet/home.nsf/(LUImages)/TG6Roto/$File/TG6Roto.pdf
