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SMC/BMC materials offer ideal solutions for the highly demanding building and construction industry. Combining properties that can be found only separately in traditional materials like metals or concrete, they offer great design versatility. Cost-wise, they are also an excellent choice, because they offer a good return on investment and cost-in-use benefits for manufactured elements.
(Published on July-August 2008 – JEC Magazine #43)
BILL RAM, SALES MANAGER UK, MENZOLIT LTD. AND
XAVIER PAPASSEIT, SALES IBERIA, MENZOLIT VITROPLAST S.L.
Composite materials have been used in construction since early human history. The first bricks were made with clay as the matrix and straw as reinforcement. In today’s plastic age, fibre-reinforced plastics (FRP) have been used extensively over the years for big, complex structures – like bridges, towers, and more recently, windmills – where high properties and low weight are required. In more recent years, FRP have also been used for certain medium-sized and small parts where weight savings as well as mechanical properties, durability and cost are important. The main technologies for such applications are hand lamination, pultrusion (profiles) and RTM.
Sheet moulding compounds (SMC) and bulk moulding compounds (BMC) are fibre-reinforced plastics that provide an excellent balance between weight, performance and cost, due to their low density, high stiffness, resistance to atmospheric agents and paintability. They are established materials in the building and construction industry. Menzolit offers a variety of products to serve the special needs of the building industry, from mechanical properties to resistance against water, chemicals or even fire.
Features and benefits of SMC and BMC
SMC and BMC can be formulated to withstand atmospheric agents in a wide range of climates. A surface treatment can further improve their weatherability. They can be painted without expensive primer pre-treatments, or self-coloured to avoid the need to paint over minor nicks and scratches to a surface paint layer.
Due the low density (1.90 kg/dm3) and high stiffness of these materials, the parts are much lighter than concrete or metal parts. This means that it costs less to transport, handle and install parts, eliminating the need for heavy or sophisticated handling equipment.
In SMC/BMC processing, moulds are filled under high pressure. Almost any shape of mould can be used, including curved or textured surfaces and complex geometries. This means that designers have an excellent material to play with to create new and revolutionary shapes. The number of separate parts can be reduced, for instance, to create façade panels to replace cladding made out of concrete outer panels plus metal fittings. With SMC compression technology, separate parts can be integrated into a one-shot moulding process. SMC and BMC can be formulated to virtually zero shrinkage and no shape or dimensional distortion.
The initial investment for SMC and BMC technologies is heavy, as it involves hydraulic presses, or injectors and steel tools. However, for series from 10,000 parts per year on up, tooling costs are quickly recouped, while the press/injection operation can be outsourced.
The mechanical performance, density, corrosion resistance and very low moisture absorption of these compounds make them extremely competitive compared to steel or concrete. By nature, composites provide excellent thermal insulation, so SMC and BMC elements can play a significant role in the thermal insulation of buildings, reducing the need for other insulating elements like PU foam.
Typical applications include water tank panels, door skins, housings, canopies, streetlights, waste bins and advertising columns.
Water tank panels
Sectional tanks are made of a series of modular panels bolted together on site to give an infinite range of sizes and capacities. They are particularly functional in confined spaces, and can be conveniently packed, easily transported to remote areas, and readily assembled with only some skilled supervision. They play a vital role in combating drought conditions in developing countries and rural areas.
These panels ensure excellent quality of stored water, and help to retard the growth of algae and fungi. They have a smooth inner and outer finish and a high strength-to-weight ratio. They also offer good resistance to most chemicals, excellent UV resistance, and constant, proven mechanical properties. They require very low maintenance and ensure long service life. Figure 1 shows different configuration of water tanks thanks to its versability.
SMC and BMC manhole covers are very strong and can withstand loads up to 12.5 tonnes (EN124 standard). They are safe to handle compared to traditional cast iron parts and make an ideal replacement for cast iron covers (less likely to be stolen). They are suitable for both aesthetic and functional outdoor applications and available in a variety of colours to suit corporate identities/utilities services. (figure 2)
The STAKKAbox™ consists of 150-mm-deep ring sections stacked on top of each other to form chambers of varying depths. Each ring is made of twin walls with vertical ribs spanning between the walls, and is castellated to positively interlock with the neighbouring rings (figure 3). Installing this system takes far less time than traditional methods – as little as 30 minutes for an average chamber size of 900 mm x 900 mm x 900 mm. The material’s additional cost compared to concrete is far outweighed by the savings on labour and on-site costs. In addition to the significant potential savings on construction costs, site safety is greatly improved. Each section falls below the 25 kg internationally recognized safe weight-lifting limit for one man.
Roof-integrated solar panels
Several roof-integrated solar panel systems have been developed. SMC offers mechanical stiffness, weather resistance and function integration, among other advantages. By using an appropriate design, builders can get a combined energy-source and roof function, saving on installation time and materials. Figure 4 shows the assembling scheme of the solar roof by combination of only 2 types of parts.
Nowadays, to meet environmental requirements, any new industrial application must take the lifetime of the part being manufactured into consideration. There are several different ways that building elements made of Menzolit compounds can be recycled at the end of their service life. The most recent and innovative method is
illustrated by a project carried out jointly with Ranger for the manufacture of swimming pool panels, which are moulded with BMC containing 30% recycled composites. Figure 5 shows on the left rectangular swimming pool set and on the right a single panel.