Furnace instrumentation improves quality of heat treated products and simplifies furnace operation

Citation

(1999), "Furnace instrumentation improves quality of heat treated products and simplifies furnace operation", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 4. https://doi.org/10.1108/aeat.1999.12771dab.005

Furnace instrumentation improves quality of heat treated products and simplifies furnace operation

Furnace instrumentation improves quality of heat treated products and simplifies furnace operation

Keywords: Honeywell, Furnaces

Doncasters Blaenavon reports that it has raised the quality of its heat treated products through greatly improved furnace temperature control, a direct result of replacing obsolete instrumentation on seven heat treatment furnaces by new Honeywell recorders and digital controllers (Plate 7). Other benefits of the new instrumentation include simpler furnace operation, clearer and more accurate chart recordings and a reduced number of instruments which, in turn, means less downtime and maintenance.

Cardiff-based INSTeng Process Automation supplied seven Honeywell DPR250 chart recorders - one for each furnace - and 16 Honeywell UDC3300 digital controllers. INSTeng, with the Doncasters Blaenavon's electrical department, also designed and installed the furnace control system.

Doncasters Blaenavon, a part of Doncasters plc, specialises in precision forging and ring rolling services for aero engines, aero structures, industrial gas turbines and defence applications. Its products, made from materials including nickel and titanium alloys, aluminium, stainless steels and specialist alloys, must be finished to the most exacting metallurgical specifications by heat treatment in the factory's electric or natural gas furnaces.

Plate 7 Honeywell instruments at Doncasters Blaenavon

"The new furnace instrumentation provides much better control and keeps a tighter tolerance band, resulting in a higher quality of heat treated products", reported Dave Heward, electrical engineer, of Doncasters Blaenavon.

The Honeywell instrumentation has also simplified operation: whereas prior to each furnace run operators used to enter ramp and dwell set points for every part of the heat treatment cycle - which may include several temperature ramps and dwells - with the new Honeywell UDC controllers there is just one program which is simple to access and to adjust through the controller keypad.

Over-temperature alarm trips, independent of the temperature controllers, are essential to furnace operation at Doncasters Blaenavon. INSTeng and Doncasters Blaenavon together devised a means to provide these trips through the Honeywell DPR250 recorders, rather than by installing additional controllers. Each furnace zone needs to be constantly monitored, so the recorder associated with a furnace uses a built-in "group maximum'' function to monitor all the zone temperatures within its related furnace, and compares these with a set point value provided by the furnace's controller.

When a zone temperature exceeds its set point temperature plus the allowed tolerance, the recorder applies the trip and shuts off the furnace at the same time as bringing in an audible/visible alarm.

The recorders have also added to the efficiency of furnace operation. The furnaces each contain between three to six thermocouples. A "group minimum'" function within the Honeywell recorders starts the timer for each temperature soak when all the thermocouples reach the required temperature - no sooner, no later. All the guesswork has been taken out of furnace operation.

According to Doncasters Blaenavon, it has discovered several other bonuses from the new instrumentation. The LCD displays, on both the recorders and controllers, are big and bright enough to be read clearly from the supervisor's desk, situated at the other end of the room. The chart recordings are far superior to those from the previous recorders: the DPR250s' clear, accurate traces and their superimposed alphanumeric data - such as the time, date and chart speed - make them much easier to interpret. As Doncasters Blaenavon's laboratory keeps all heat treatment charts for 25 years, long-term legibility is a prerequisite.

Details from Honeywell Control Systems Ltd, Tel: +44 (0)1344 656000; Fax: +44 (0)1344 656240; E-mail: info.centre@uk.honeywell.com