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Hydraulics’ role in the rolling mill

11 March 2011

Hagglunds Drives achieved its first successful hydraulic drive installation at a sheet metal rolling mill back in 1998. Since that time, the company has been involved in several others around the UK and overseas. Here, we discover how Hagglunds’ customer, the sheet lead manufacturer Jamestown Metals, rejected a high-maintenance geared power train in favour of a direct hydraulic drive for a new mill at its Barnsley plant

Jamestown Metals is a specialist manufacturer of high quality lead products and, in particular, the processing of lead sheet for the construction industry. The company was established by members of the Sherling family who brought with them more than 150 years of experience in this industry, with rolling mills in Ireland (Dublin), England (Barnsley), Wales (Ebbw Vale) and the USA (Houston).

The manufacture of rolled lead sheet lead starts with an eight-tonne billet, cast from materials often recycled from building waste and lead acid car batteries. The billet is reduced in size to the required thicknesses by making a number of passes through a heavy duty reversing rolling mill. After each pass the gap between the rolls is adjusted using powered screws and the rolled sheet is coiled at each end as it lengthens, until the correct thickness is achieved. As the billet enters the rolls their speed and torque have to be carefully controlled in order to create sheet material that is BSEN 12588: 1999 compliant.

Towards the end of the 1990s, the company took the decision to install a two-tiered reversing mill at its Barnsley plant. With this came the opportunity to re-think the roll drive, a power train traditionally comprising large dedicated gearboxes with splitter gears to the two work rolls. Past experience had shown that gearbox failures caused long and expensive production shutdowns due to the length of time required to repair or replace components.

Jamestown discovered that a viable alternative – hydraulic drives – were readily available from stock for immediate delivery, so the decision was taken to use slow-speed, high-torque hydraulic motors, one for each of the work rolls on the new mill. A trawl of the market led Jamestown to Hagglunds, whose motors best fit the bill, providing a simple, compact drive that could be coupled directly to the roll shafts with no gearboxes needed – an arrangement that allows far easier adjustment of the mill roll gap during the milling process. Hagglunds was also able to provide a complete drive system, with power unit, control system and all the necessary hydraulic lines and hoses.

Direct hydraulic drives can absorb the shocks that might otherwise compromise mechanical drive trains. They also provide a highly efficient drive system that can be easily adjusted and controlled to suit a variety of requirements and materials. The drive motors themselves have a very low inertia so they are very responsive; moreover, the load on the rolls is precisely controlled by pressure adjustments at the hydraulic pumps, so that the whole system is protected from damage.

Both the reversing action and speed of the mill are controlled by the pumps, rather than the electric motors, so there is no restriction to the number of times the mill can be reversed. The ramp times during reversing can also be very short, going from almost full speed in one direction to full speed in the opposite direction, instantaneously, thus improving productivity compared with that of a mill based on geared drives.

Hagglunds’ axial piston pumps produce variable flow in relation to the angle of the swash plate and therefore variable speed at the drive motors. If the swash plate is controlled over centre, then the direction of flow is reversed thus reversing the drive motor direction. If the load is too high the pressure increases to the set pump compensator level and at that point, the pump will back off, stopping the drive to maintain safe operation and keep the loads under control.

The pumps are directly coupled to the electric motors - standard squirrel cage induction units that run at a constant speed of 1,475rpm to make full power available throughout the speed range. In fact, the power units used on Jamestown’s reversing mills are completely standard Hagglunds units housed within soundproofed enclosures. They are particularly easy to maintain, a task that usually involves a change of filter elements and oil quality check, with access provided via doors into the enclosure.

Jamestown’s power unit is positioned in a convenient place close by the mill with short hydraulic lines, just three or four lines needed per motor to connect them up in a normal configuration. The power units and controls were all fully tested before delivery so the installation and commissioning took little time on site.

Since its installation m ore than twelve years ago, this drive system has proved a complete success and, according to Hagglunds, it demonstrates once more the superior performance of hydraulic power trains in tough industrial duties.

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