Si-SiC Radiant Tubes

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“ Faster, Cheaper, Better ”

What is a Si-SiC Composite?

50% Si + 50% SiC by volume, metallurgical grade Silicon metal with 80 mesh SiC particles

Rationale for  Si-SiC Radiant Tubes

  • Conventional = Very Long Life
  • Enabling = Very High Temp
  • Productivity = Higher Throughput

Conventional Savings

  • Excellent creep properties to 1343°C (2450°F) = No tube droop or distortion
  • Excellent resistance to carburization = No tube corrosion or embrittlement
  • Excellent thermal shock & low CTE = No fracture in heat-up or cool-down

18+ Years Continuous Carburizing Service

Compare Alloys to Si-SiC at 1343°C (2450°F) = ~8.5 KPSI Stress at <0.6% Strain

Si-SiC Composite vs. 600 Alloy (after just 1 hour)

No deformation for the INEX tube tested 360 hours at 1343°C (2450°F).

Metal Alloy Tubes after < 24 Months

Si-SiC Enables Processing > 982°C (1800°F)

  • Stainless Steel Aging
  • Powdered Metal Sintering
  • Minerals Processing

What Limits Furnace Throughput ?

  • Metallurgical objectives
  • Mechanical constraints
  • Radiant tube heat flux
  • NOT refractory or burners

What is Heat Flux ?

Heat flux or thermal flux is the rate of heat energy transfer through a given surface,
per unit surface.
(BTU/hour)/inch2
kW/meter2    =   2.2 BTU/hr/in2

Design Criteria for Radiant Tubes

Metal Alloy Tubes at 982°C (1800°F) :

  • Conservative = 50 BTU/hr/in2
  • Nominal = 55 BTU/hr/in2
  • Aggressive = 60 BTU/hr/in2

Max Service temperature depends on Alloy & Atmosphere

Si-SiC Composite Tubes @ 982°C (1800°F) :

Nominal = 110 BTU/hr/in2
Maximum Service Temp is 1343°C (2450°F)

SANKEY DIAGRAM Typical Pusher Furnace

Parasitic or Standing Losses average ~20%

  • Wall Losses
  • Opening Losses
  • Cooling & Conveyor Losses
  • Fixtures, Trays, Baskets
  • Storage Losses (Batch Furnace)

FASTER Cycle Time

  • Increases furnace throughput
  • Reduces per unit standing (parasitic) losses
  • Does NOT reduce process energy required
  • Does NOT improve combustion  efficiency

Compare Alloys to Si-SiC at 1343°C (2450°F) = ~8.5 KPSI Stress @ <0.6% Strain

CHEAPER Furnace Operation

  • 25% Increase in Throughput  = 25% More Load (Reducing Furnace Operating Hours by 20%)
  • Process Energy Required Remains the Same i.e. Work on Load is Unchanged = 0.0
  • Standing Energy Losses of 20% Eliminated  for the 20% of Furnace Hours Reduced  = +4.0%
  • Offset Somewhat by Higher Exhaust Losses (1906°F > 1999°F) Available Heat   =  -2.0%

“SAME-WORK” SCENARIO

“Back of the Envelope” Savings

1200 more hours/year/furnace
5.2 hours/cycle
231 cycles/year
2,000 lbs/cycle
461,538 lbs/year
$1.10 Sales Value / lb
$507,692 Increased Sales
50% Variable Cost
$253,846 EBIT / furnace

Compare with:

  • New Si-SiC Radiant Tubes
  • New EGR-type Burners, if Needed
  • Used or New Furnace

Why Are Si-SiC Tubes BETTER ?

  • Proven Life >18 Years in Carburizing
  • High Temp Processing to 2300°F
  • 25% More Product Throughput

FASTER, CHEAPER, BETTER @ 1400°F – 2300°F