Page 225 - Mechanical Engineers' Handbook (Volume 4)

214 Furnaces

Table 2 Conversion of Metric to English Units
Length 1 m 3.281 ft
1cm 0.394 in
2
Area 1 m 10.765 ft 2
3
Volume 1 m 35.32 ft 3
Weight 1 kg 2.205 lb
3
Density 1 g/cm 62.43 lb/ft 2
2
2
Pressure 1 g/cm 2.048 lb/ft 0.0142 psi
Heat 1 kcal 3.968 Btu
1 kwh 3413 Btu
Heat content 1 cal/g 1.8 Btu/lb
2
1 kcal/m 0.1123 Btu/ft 3
2
Heat flux 1 W/cm 3170 Btu/hr ft 2
Thermal conductivity 1 cal 242 Btu

s cm C hr ft F
Heat transfer 1 cal 7373 Btu

2
2
s cm C hr ft F
Thermal diffusivity 1 cal/s cm C 3.874 Btu/hr ft F

C g/cm 3 C lb/ft 3
By function:
Heating for forming in solid state (rolling, forging)
Melting metals or glass
Heat treatment to improve physical properties
Preheating for high-temperature coating processes, galvanizing, vitreous enameling,
other coatings
Smelting for reduction of metallic ores
Firing of ceramic materials
Incineration

By method of load handling:
Batch furnaces for cyclic heating, including forge furnaces arranged to heat one end
of a bar or billet inserted through a wall opening, side door, stationary-hearth-type
car bottom designs
Continuous furnaces with loads pushed through or carried by a conveyor
Tilting-type furnace

To avoid the problem of door warpage or leakage in large batch-type furnaces, the
furnace can be a refractory-lined box with an associated firing system, mounted above a
stationary hearth, and arranged to be tilted around one edge of the hearth for loading and
unloading by manual handling, forklift trucks, or overhead crane manipulators.
For handling heavy loads by overhead crane, without door problems, the furnace can
be a portable cover unit with integral firing and temperature control. Consider a cover-type
furnace for annealing steel strip coils in a controlled atmosphere. The load is a stack of coils
with a common vertical axis, surrounded by a protective inner cover and an external heating
cover. To improve heat transfer parallel to coil laminations, they are loaded with open coil