Russian Project (continued)
Part 1 can be read here.
The second problem was that the recuperative burners were in a very poor condition. Of six straight-through roller-hearth furnaces with eight burners per side with recuperation, 40% were in a less-than-functional manner and not operating. In addition, there were (because of burner flame and mixture settings) significant temperature variances in the furnaces’ operational chambers.
The primary reason was simply that the recuperative burners were left in a state of disrepair and totally non-functional. The furnaces were shut down, all of the burners and recuperators were refurbished, and the furnace hearths were thoroughly cleaned out of fallen iron-oxide scale. New hanging chains in the entry and exit vestibules were fitted to ensure an almost day-one condition. This proved to be very successful and an economical improvement on both furnace performance and throughput.
The next part of the project was to set up a practical (but frequent) maintenance program. In order to prove the benefits of the refurbishment, the following items were monitored:
- Mechanicals (roller-hearth drive systems and variable-speed drives)
- Temperature uniformity was measured once again, and the appropriate thermocouples and instrumentation were upgraded to ensure temperature uniformity and thermocouple calibration. A program of thermocouple inspection and millivoltage was conducted on a biweekly basis.
- An automatic loading system was designed and installed based on the production forgings' size to ensure part temperature uniformity and the appropriate discharge temperature. The company had been previously working on a one-speed-fits-all-forgings system, but the forgings varied in individual mass.
- All of the gas burner systems were measured to establish and accomplish the correct air-to-gas ratio as well as the chamber process combustion-gas analysis.
- An initial analysis of the quench-oil medium was conducted and the oil cleaned. The quench-tank oils were then analyzed on a six-month basis.
- A scheduled maintenance program was developed for a monthly inspection and preventive maintenance.
H13 Forging Dies
The life expectancy of the H13 forging dies was minimal, and the dies were washing out on a very frequent basis, which meant that die maintenance costs were excessively high. The pre-heat treatment of H13 dies was accomplished in an open gas-fired furnace with no atmosphere. Once again, the quenching practice left a great deal to be desired. The net effect was that the pre-heat-treatment die metallurgy was inconsistent.
The process techniques were monitored, and there were similar practices being conducted as was conducted on the roller-heath gas-fired forging heat-treatment furnaces. Once the appropriate thermal-processing conditions were obtained and uniform, die life improvements were then observed.
The next part of the project was to develop improved performance of the dies by a combination of pre-heat treatment in conjunction with surface treatment.