Metal component manufacturer goes for AC drive

Edited by the Engineeringtalk editorial team Sep 29, 2000

Doncasters FVC of Sheffield made the switch from a DC drive system to an AC one, opting for a 75kW motor and a control panel with a VT210S drive from Meiden Europe

Faced with the need to upgrade a centrifuge casting machine to ensure product integrity for a major contract, Doncasters FVC of Sheffield made the switch from a DC drive system to an AC one.

The centrifuge is used to cast 2.72 diameter steel rings for power generation turbines and the total weight of the cast and mould is 30t.

For the new higher specification, the centrifuge is required to produce 100g to ensure the rings are of highest integrity, with all impurities (oxides, gases, non-metal inclusions etc.) being excluded from the steel.

The high 'g' forces also mean that the steel ring is cast to a higher density than was previously achieved eliminating any porosity.

Before the upgrade, the centrifuge was belt driven by a 35kW DC motor.

To meet the new specification demands, including larger ring size, the power unit had to be changed to a 75kW motor.

This presented two problems.

The first was the size of a 75kW DC motor and the second was the 12 week delivery time.

Because the centrifuge is built below ground level major civil engineering work would have been required to install it, which would have been both costly and time consuming.

Add to this the lengthy delivery time, plus commissioning, this option looked very unattractive, according to Adrian Burgin, Works Engineer for Doncasters.

Via electrical engineers ECC Central, Rotherham, Burgin explored the AC alternative.

The outcome was a 75kW motor that would fit into the existing space envelope and a control panel with a VT210S drive from Meiden Europe that provides control characteristics that achieve significant operational time savings.

Further, the AC package was delivered, installed and commissioned inside one and half weeks.

The control provided by the Meiden drive enabled motor speed to be ramped up to speed (100rpm) in 4.5 minutes compared to the 35 mins previously with DC system and stopping time was cut from 1.5 hours to 25 mins.

In addition, the switch to an AC motor has eliminated all the maintenance problems experienced with the previous DC units (brush repair and maintenance, and damage to the tachometer feedback cable).

Also, unlike the ventilated DC unit, the AC motor is fully enclosed, preventing the ingress of grit.

"The short delivery/commissioning time made the AC route very attractive", said Adrian Burgin, "and the massive time savings on the start-up and stop operations play a significant role in helping us to achieve the five rings a week programme, bearing in mind the long cooling period, machining and x-ray operations that follow casting." Doncasters FVC is a leading supplier of high integrity 'centrispun' components in a variety of alloys including, corrosion resistant and duplex alloy steels, heat resistant stainless steel and nickel based super alloys.