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INTEGRAL BATCH FURNACES
With the development of a new high temperature single polymer
quenchant, new dimensions have been reached in the use of polymer quenchants in
integral batch type furnaces. In the past single polymer quenchants have been
used in integral quench furnaces successfully, however in some cases the furnace
load size had to be reduced to prevent a high heat rise from occurring and
causing spotty hardness to parts being processed. The ability of the new high
temperature quenchant to operate at higher temperatures have eliminated this
situation and allow for repeatedly good results.
When converting a
batch integral furnace to polymer the following parameters must be followed:
- The work load to gallon of quench ratio on existing furnace equipment should
not exceed a 1 lb. work to 1 gallon quenchant ratio. In the case where new
equipment is being ordered, it would be advisable to have the quench tank built
to a 1 lb. Work to 1-1/2 gallon quenchant ratio.
- Agitation of the quenchant should be such as to provide a good volume flow
with directional flow baffles to maintain fluid flow through load work
areas.
The fluid flow from the agitation must provide surface movement
of the quench fluid and this flow must be constant while the furnace is in
operation. The reason for this flow is to prevent the quench fluid from being
heated by the hot vestibule gases which will cause vaporization of the water in
the quenchant. This vaporization can cause an atmosphere upset which is
detrimental to carburizing operations.
When the fluid is constantly in
circulation, the top fluid will not become heated to the point where this
vaporization will take place and in turn will not affect the furnace atmosphere.
- Heat exchanging of the quenchant to maintain the proper operating
temperature of the polymer quenchant is also important to the operation. If the
quench system cooling was originally sized for oil quench the cooling capacity
will usually be more than adequate for cooling the polymer quenchant. If a new
system is being designed the cooling capacity can be calculated based on the
amount of BTU to be removed for heat exchange sizing.
- Other criteria to be considered is a tight fitting inner door to prevent
excessive pressure or leakage to the vestibule and also prevent a feed back when
vestibule chamber goes under suction during quenching cycles. Also a slight
increase in the gas pressures is a good idea to prevent any possible feed back
to the furnace of water vapors.
- Some of the older type batch integral quench furnaces have what is know as a
weir overflow reserve tank feature. With the use of polymer quenches, we
recommend that these be removed to provide the additional added volume, to
prevent foaming from entrapped gases and to eliminate the potential of explosion
from trapped gases in the reserve tank.
ILLUSTRATION #2
Shows an integral
quench furnace with the proper
modifications for a batch type
furnace.
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ILLUSTRATION #3
Shows a furnace with a
reserve tank system and
the area which has been removed.
Proceed to Section 3 of Operational
Principles
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