Belt-driven unit used to upgrade strip rolling mill

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Dolgarrog Aluminium has used a biparting HepcoMotion profile driven unit (PDU2) to upgrade a cold rolling mill so that the strip is centred fully automatically as it enters the mill.

Belt-driven unit used to upgrade strip rolling millThe HepcoMotion profile driven unit (PDU2) linear transmission was introduced as a high-performance, cost-efficient belt-driven package and one example where the double-acting version of the system is demonstrating these characteristics is in an aluminium coil manufacturing plant in Conwy.

Dolgarrog Aluminium is an independent and fully integrated rolling mill that prides itself on flexibility, good service and on-time delivery. Short lead times, low minimum order quantities and bespoke products are its speciality. Based in North Wales, the company's capability is not limited to aluminium. Investment in a wide range of plant allows it to roll a variety of metals such as alloys of zinc and magnesium.

The DAPDU2 belt-driven system is used on the company's four-high cold mill process line, which, as its name suggests, is a finishing rolling mill consisting of four rollers. It receives aluminium coils that are approximately 800mm in diameter with a strip thickness of 5–8mm. After several passes, the material is reduced to its desired finish gauge that is upwards of 0.5mm. This process can generate loads of 1400 tons at up to 150m/min.

Automatic sequencing

A recent upgrade introduced a new system to ensure the coil or strip enters the rollers centrally to within +/-5mm of the centreline of the mill. As Dolgarrog products are available in a variety of widths, an automatic sequence was required to maintain productivity and it was for the resultant mechanism that the DAPDU2 system was specified.

The coil centring system comprises the DAPDU2 actuator that spans the width of the in-going side of the mill, two reflecting lasers mounted on each carriage and two pull wire encoders. The coil centring sequence is activated once the strip has been fed into the mill and is stationary. The drive is responsible for bringing the lasers in from the edges of the mill at a speed of 100mm/s, while the encoders measure the distance travelled; full stroke for each carriage is approximately 500mm.

Once the lasers detect the edge of the strip either simultaneously or independently, the measured encoder travel for each side is transmitted to the control. The software automatically calculates the offset between the two edges and the error value is determined. This information is then fed back to the decoiler heads that are automatically adjusted via hydraulic rams to rectify the coil position to +/-2mm. The finishing process then continues.

The HepcoMotion belt-driven system was chosen by Dolgarrog for its speed and response and because its physical size was sufficiently small for the limited mounting space available. And, as it has proven, the sound performance of the DAPDU2 has been unaffected by its fairly hostile operating environment of kerosene oil mist.

Central to this linear system is a slotted and highly robust aluminium beam of one-piece construction into which fits the belt drive and two carriages. The arrangement effectively seals the unit on three sides, offering it protection in harsh conditions.

Virtually friction-free

The carriages use Herculane wheels that run virtually friction-free on the inside surface of the profile, yet still provide stable support. Without motivation, even a light load on the system would accelerate under gravity on an incline of just 8mm/m. The carriages are driven by a strong and accurate toothed belt that allows them to move symmetrically or together.

Mark Jones, the project engineer, explains: "This capability was central to our application. The option to request a total length and stroke length for the system was also very appealing. The price and delivery lead time for the DAPDU2 fitted well into our plans."

Installed during December 2006, the DAPDU2 is working well and has suffered zero downtime. The entire auto-centring sequence on the four-high cold mill occupies just six seconds, enabling the operator to continue his production duties during this quality procedure.

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