CoxGomyl bears load in Paddington

10 November 2010

At a new development in Paddington Basin, London, CoxGomyl Integral have designed an elegant, hidden, system to support building maintenance units. The Merchant Square development contrasts modern architecture with the canal boats in the Paddington Basin. At the centre of this development is the Carmine building where it is essential that its clean triangular lines are not spoilt by the building maintenance units used externally for cleaning and access. Rather than to simply park the units on the skyline, they are withdrawn from the edge and then dropped behind the façade by a lifting system designed by CoxGomyl Integral of Sheffield. The lifts handle 9 tonnes of the building maintenance unit and its carriage using a complete drive system with screw jacks supplied by Lenze.

CoxGomyl Integral are part of the SCX Group and are experts on façade access and fall arrest systems. They are the sole UK representative for the CoxGomyl range of Building Maintenance Units (BMU’s) and are able to supply both standard access systems or, as in this case, bespoke solutions. They have handled many high profile façade access projects such as 30 St Mary Axe (the Gherkin) and Albion Wharf on the South Bank of the Thames. The Carmine Building is a centrepiece to the brand new Merchant Square development. It rises up from the canal edge with a striking triangular profile. Building work started in 2007, it was topped out by Boris Johnson in 2009 and completed in Autumn 2010. The design and shape of the building dictates that three BMU’s are required to access all the façades.

The BMU sits on a railed carriage that runs around the top of the building powered from busbars. The carriage holds a crane and the cradle that can be swung out and lowered down the façade. Each BMU has a parking position where rails at 90º to the façade take the carriage some 7m back into the lowering position. The carriage is driven by inverter controlled Lenze geared motors, three stage models with a ratio of 177 and an output speed of 5r/min. They are fitted with spring-applied brakes to hold position, blowers to permit continuous operation at low speed, and anti-condensation heaters for the often cold temperatures at this exposed location.

The lifting system is based on a conventional ‘H’ configuration with screw jacks at each corner and motive power from a motor and gearbox in the centre bar of the ‘H’. In this case the motor is standard, albeit with holding brake, blower and condensation heaters, and is rated at 3kW. This connects into a bevel box with twin outputs at 375 r/min rated speed. This configuration was chosen over the more common alternative where a motor has an output at the non-drive and is fitted in-line, without a gearbox. In such cases the motors become non-standard, and the output speeds may be undesirably fast.

Connection from the motor gearbox out to the two side arms of the ‘H’ is made with Lenze universal joint spacer couplings built to SAE automotive standards. These can accommodate misalignment and expansions with a telescopic section. At the end of each spacer coupling is another bevel gearbox to turn the drive through 90º and split it with two output shafts. All the bevel gearboxes were supplied by Lenze from partner company Vogel. They have a rating of 120Nm and low backlash at 10 arcmins.

A further four spacer couplings connect the drive to the four screw jacks mounted at each corner. These were manufactured by another Lenze partner company, Servomech of Bologna, and are rated for lifting 50kN. These are ‘travelling screw’ designs where the acme screw passes through the body of the jack. In this case the screw sits in a fixed axial position and the jack body moves up and down it with the carriage. Performance is 6 mm/s travelling through 1350 mm with the four screw jacks supporting the load of 11 tones. An additional feature is a safety nut which is a back-up to prevent the load dropping in an uncontrolled manner should there be extreme wear or a catastrophic failure. The safety nuts provide a wear indication for the internal gearing of the screw jack.

The motor, gearboxes, couplings and screw jacks were all supplied by Lenze as a complete lifting system with a design life of 25 years. CoxGomyl Integral were able to get support and technical advice from a single source saving their time and letting them focus on their skills with the building maintenance units.