THE LINING OF THE CARS OF SHORT TUNNEL FURNACES
T. F. Baranova,
I. B. Mal’kov,
and V. A. Poklad
Translated from Novye Ogneupory, No. 10, pp. 8 – 10, October, 2011.
Original article submitted March 11, 2011.
A new design has been developed for the cars of PG-30 tunnel furnaces used to fire ceramic parts employed in
the casting of aircraft engines. The refractory layer of the cars’ lining is made of several slabs that are joined to
one another. The slabs are made of a specially developed mullite-corundum material with improved heat resis
tance. Use of the new cars has lengthened the time between routine repairs and reduced maintenance costs.
The service life of the cars at temperatures up to 1600°C has been increased by a factor of 1.5.
Keywords: tunnel furnace, furnace car, refractory layer of car lining, slab.
The quality of the firing of refractory products in tunnel
furnaces depends to a large extent on the regime used to heat
them. The extent to which the regime is executed properly in
turn depends on many factors, including the length of the fur-
nace and the design of the rolling stock (the cars used with
these furnaces). The design of the rolling stock is especially
important for short furnaces (such as the 18-m-long PG-30
furnace), in which the cars move at high speeds. Short tunnel
furnaces are often used to fire ceramic equipment (melting
crucibles, cores, molds, capsules, pouring funnels, etc.) that
is employed in the casting of heat-resistant alloys as part of
the process of making aircraft engine parts. When the pre
scribed heating regime is observed in short tunnel furnaces,
the length of time that the refractory products are held at the
maximum temperature may range up to 8 – 12 h. In two spe
cific cases, the products are fired at 1350 and 1580°C and the
cooling zone is shortened accordingly. In connection with
this, the lining of the car should ensure that the products
placed in it remain intact and in good condition; being the
base element, the top layer of the lining should be made of a
refractory material and be reliable in service because the
products being fired are located directly on it and because
this layer is subjected to the most severe temperature load.
The top layer of the lining undergoes the greatest amount
of linear expansion as it is acted upon by high temperatures
while the products being fired are held in the furnace. This
expansion destabilizes the dimensions of elements of the lin
ing, which is one possible cause of crack formation in the lin
ing’s refractory layer with its repeated heatings and coolings.
The thermal stability of the materials of the lining’s top layer
is one of the deciding factors that determine the energy effi-
ciency and cost effectiveness attained in the firing of ceramic
In accordance with the data sheet , the lining of the
cars of a PG-30 furnace is composed of two layers: the bot-
tom layer is a heat-insulating layer, while the top layer is a
refractory layer composed of corundum products (see
Fig. 1a ). The refractory layer itself is also composed of two
parts: two lower courses of corundum products installed to-
gether with a heat-insulating layer on a standard lining-grade
mortar and two upper courses of corundum products in
stalled without a mortar. The use of mortar with the two
lower courses keeps the hot air in the space where the semi
finished products are being fired from reaching the bottom of
the car. The highest temperature used in firing refractory
products in PG-30 tunnel furnaces is in the range from 1000
to 1600°C, the exact temperature depending on the type of
product being made.
The serially-produced corundum bricks used for the re
fractory layer of the lining have a dense fine-grained struc
ture. This structure, together with the high coefficient of lin
ear expansion of corundum, accounts for the low heat resis
tance of these bricks. The bricks cannot withstand the ther
mal loads created by intensive firing regimes involving high
temperatures or fast movement of the cars. It should be men
tioned that the most demanding service conditions for the
cars in a PG-30 furnace are created during the firing of
foundry molds at 1000°C, since in this case the cars move at
a speed five times greater than their speed during the firing
of crucibles (to cite one example) at 1550°C.
Refractories and Industrial Ceramics Vol. 52, No. 5, January, 2012
1083-4877/12/05205-0316 © 2012 Springer Science+Business Media, Inc.
”Salyum” Scientific-Industrial Center for Gas Turbine Construc
tion, Moscow, Russia.