Here’s a chance for you, the reader, to comment on a topic that I consider of relevance to the industry.
A question came to me through a
commercial heat treater operating batch integral-quench (IQ) furnaces produced
by the same manufacturer. The furnaces have only one apparent difference
between them, that being the radiant-tube material. Both furnaces are pulse-fired
running natural gas. Furnace 1 has vertical 8-inch-diameter radiant (“U”)
tubes, and Furnace 2 has vertical 6-inch-diameter silicon-carbide tubes. The
temperature uniformity and carbon uniformity is reported to be well below the
However, the heat treater reports
a 20% increase in demand for additive gas on the silicon-carbide-heated
furnace. The results of increased additive gas are reported to be across the
board – irrespective of the recipes run in the furnaces.
The additive-gas usage is
determined by setting the furnaces at the same 930°C (1700°F) temperature –
empty of product – and manually increasing the carbon potential to 1.20%C and
recording the gas flow required to keep the chamber at setpoint. The endothermic
carrier gas flows at a rate of 650 cfh (18 m3/hour) with a
controlled dew point of +5°C (+9°F) and a target dew point of 2°C (+3.5°F). The
enrichment gas is propane. The furnaces are controlled by oxygen probes.
The heat-treater’s investigation (through
other plants in its organization) claims that the reason for this added
consumption is because the alloy tubes act as a catalyst to the additive
gas where the silicon carbide tubes do not. So, here are the questions:
1. Is it reasonable to assume that
the alloy tubes act as a catalyst?
2.Do the tests run prove this or is
there a better test?
3.What are the true advantages and
disadvantages of one type of tube over another with respect to gas consumption?
With respect to other factors?
4.As more and more alloy (roller
rails, chain guides, muffles, etc.) is being eliminated from furnaces, will
this result in less-optimum carburizing gas consumption?
is the market headed and why?
I await your answers!
An Open Question to Readers
Dan Herring is president of THE HERRING GROUP Inc., which specializes in consulting services (heat treatment and metallurgy) and technical services (industrial education/training and process/equipment assistance). He is also a research associate professor at the Illinois Institute of Technology/Thermal Processing Technology Center. tel: 630-834-3017; e-mail: firstname.lastname@example.org; web: www.heat-treat-doctor.com
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