Specifications

Section 1
1-6 LA-306 Operation & Theory
Zones. The heating chamber is partitioned into 3 separate zones using ceramic fiber dividers. The dividers are
designed with the smallest possible opening consistent with the part parts clearance specifications. This
partitioning assures very high thermal isolation between zones. Although the heating profile across the belt is
extremely uniform, heat losses through the furnace side walls and at the belt edge supports produce a
temperature drop near the edges of the transport belt. Away from the extreme edges of the belt, overall
temperature uniformity across the belt will be ±3 ⁰C.
Temperature Measurement. Inside the furnace chamber, at the top center of each zone a type K thermocouple
measures the temperature in that zone and provides feedback to each respective zone PID controller to determine
the amount of power necessary to maintain setpoint temperatures. However useful these thermocouples are for
controlling the temperature in each zone, the actual part is exposed to three heat transfer methods. As with any
furnace, the most accurate way to determine what temperature product on the belt actually sees from these three
methods of heat is to profile the furnace with a thermocouple placed directly on the product surface.
Heat Transfer Methods. Transfer of heat in the furnace is by three different methods: Radiation, Convection
and Conduction. In order of their contribution to heating the product, these methods are:
A. Radiation
The furnace lamps emit infrared electromagnetic waves which, when striking and absorbed by product on the
belt, cause its temperature to rise. This is the way “heat lamps” and microwave ovens work, and also the way the
sun heats the Earth. The infrared radiation does not directly heat the process gas within the furnace.
B. Convection
During operation, lamp radiation heats the chamber top, bottom and side wall insulation. As the process gas
enters the furnace through the porous ceramic insulation, it is heated to near the setpoint temperature of the zone.
This flow of heated gas transfers heat to the product on the belt. This is how a hair dryer or home forced air
heating works.
C. Conduction
Lamp radiation heats the transport belt which becomes a heat source for the product supported on the belt. This
is how a hot plate heater works.
1.3.5 Controlled Atmosphere
LCI furnaces are equipped with the ability to supply constant streams of a supplied process gas. This feature
allows the user to reduce product oxidation or contamination, remove process effluents or reduce other
potentially negative effects of ambient air at high temperatures.
A controlled atmosphere also helps establish higher consistency in thermal processes. When a product travels
through the process section, slight changes in the atmospheric conditions in a non-controlled atmosphere
environment can affect the stability and consistency of the product temperature profile.
1.3.6 Transition Tunnel
The transition tunnel separates the furnace chamber from the closed atmosphere cooling tunnel. The transition
tunnel is constructed using the same materials as the furnace section to minimize thermal stresses to the product
caused by excessive cooling rates. Convective gas cooling of product is produced by the controlled flow of
process gas into this tunnel. A series of hanging stainless steel baffle plates serve to act as a thermal barrier and
help contain the furnace atmosphere.
1.3.7 Closed Atmosphere Cooling Tunnel (CACT)
This section is constructed of extruded aluminum heat sink material and is not insulated. Inside, a carefully
controlled atmosphere of CDA or N2 gas is maintained to cool the product to a safe temperature. Fans mounted
on the exterior of the CACT transfer heat to the air inside of the furnace cabinet. This cabinet air is then
exhausted by cabinet fan through an opening in the furnace top cover into the room or for removal by facility
exhaust ducting.
To prevent drafts and ambient air from entering the CACT, a hanging stainless steel baffle plate is mounted
directly to the CACT exit.