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Innovative, underground access manhole and drain covers, so lightweight that even the largest can be lifted by hand, have been developed by UK manufacturer Structural Science Composites (SSC) using Scott Bader’s Crestopol acrylic resin.
According to Scott Bader, the SSC composite design uses its patented Thrubeam design which produces a stiffer beam in combination with glass fibre reinforcement and the high performance properties of Scott Bader’s Crestapol acrylic resin. Durable, high quality, lightweight composite manhole covers, with load bearing properties to match the much heavier, traditional ductile, steel or concrete covers, are cost effectively manufactured by SSC. A full resin transfer moulding (RTM) process is used, which gives both the strength-to-weight ratio and the surface details and anti-slip finish required for these types of access covers, along with high productivity. Being made of composite materials, SSC covers are also inherently non-corrosive, non-conductive, and avoid problems relating to theft for their scrap value, which is a real issue with metal covers.
Scott Bader explains that the SSC Thrubeam composite design produces covers which are typically three to four times lighter than an equivalent steel or reinforced concrete cover, yet still provides the long term performance and mechanical properties required for this type of application. This includes very high load bearing capabilities to meet BS EN124:1994 Standards Group 4 Class D400. This standard specifies that an access cover must be able to cope with static loading from cars, vans, lorries and HGVs if installed in areas such as carriageways, hard shoulders, factory sites and industrial estates; to pass BS EN124 Class D400 an access cover or grating must withstand a 40 tonne test load.
It says all SSC composite manhole covers are fabricated in SSC’s UK factory in Barrow in Furness. The full RTM closed moulding process and tooling used by SSC is well-suited for high volume production of 100 to 10,000 units per annum. Given the wide variety of standard and bespoke product types and dimensions produced, having a flexible volume manufacturing process, with high productivity, is a critical success factor.
SSC claims that, in addition to being lighter than steel and concrete covers, by combining its unique Thrubeam technology with a ‘custom grade’ Crestapol resin specially developed for SSC by Scott Bader, has resulted in SSC being able to produce GRP composite covers which are more than 20% lighter than other composite covers currently available, based on independent test data. This has been achieved due to the high mechanical properties of the Crestapol resin, along with more precision and control through using an RTM injection process; a thinner, so overall much lighter, Crestapol glass fibre laminate is needed to encapsulate the Thrubeam stiffener beams used in all SSC covers, with no loss of performance in use.
The SSC production team has also benefited from improved Quality Assurance (QA) and productivity targets. In addition to being easy to infuse, covers can be de-moulded in less than one hour due to the rapid cure at room temperature of the Crestapol resin. Andrew Burton, General Manager of SSC explains: “After extensive new product development trials and testing different UPR and epoxy resin systems, we were very pleased that Scott Bader was able to develop a special grade of its Crestapol high performance acrylic resin for SSC that met all our needs. The custom Crestapol grade we now use firstly provides a level of physical properties to match our Thrubeam® technology and meet BS EN124 test standards. Secondly, the resin’s rheology and very fast cure rate at moderately elevated temperatures enables us to manufacture our composite covers consistently, and with a high level of confidence that parts will meet our quality standards.”
The durable, long term performance properties of SSC composite access covers, alongside the benefits of easy installation and in-situ opening and closing due to being so light, has gained SSC orders across the UK, and internationally with a rapidly growing export business. SSC customers include utility companies, builders, contractors, local authorities, and infrastructure developers located in Europe, Asia and North America. SSC Thrubeam access covers are now installed in a variety of demanding locations such as petrol forecourts, highways, factories and industrial areas, as well as in towns and cities.
As required, SSC also incorporate additional product features into its covers such as: secure locking systems; venting; watertight sealing; colour coding; and conductivity. Recently, one of the major utilities companies in the North West of England, United Utilities, had an issue with noise from an underground pumping station close to local residents. The original metal installed covers were replaced with SSC’s DM6 manhole covers, which include a unique watertight seal as part of the design; this solved the noise problem immediately.
Photo provided by Scott Bader.
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