BASKET FURNACES

HTE-Novac designed and installed several basket furnaces for the T6 and T4 heat treatment of aluminum alloy castings, with sand or without sand.

SPECIAL PLANT FEATURES AND MAIN CHARACTERISTICS

This furnaces reflect the result of extensive experience of the best foundries in the thermal treatment of light aluminium alloys. In addition power saving and easy maintenance are some of the main features taken in high consideration during the design of the plants.

The choice of using an “index beam” for baskets movement through the furnace was taken to have a simple, but strong plant, with the possibility of future increase of productivity. This particular index system was developed to work 24 hours/day in a foundry environment, where the sand is always present.

Here after a description of the main characteristics of the typical plant:

 Index beam transport system; the main characteristics of this system are:

very simple maintenance operations – all the components subject to maintenance are placed outside of the hot zone;

the lower trays (base plate) move on free wheels – no rollers are installed, which means: no thermal bridges, less heat-up of steel, no bending of rollers, easy maintenance (i.e. exchange of wheels is very simple, needs just few seconds and must be made only after several years of continuous operations);

the basket positions inside the furnace are well defined.   It is not possible that baskets could be in a wrong position;

our system with the double index beam allows the independent movement of the load on the load bench and for the loads positioned in the furnace;

with our system, it will never happen that the front and the rear doors are opened at the same time;

the index beam system allows to move only one basket through the system even if it is alone in the furnace

Plant module design for future production expansion: the two furnaces are designed to be able to increase the production adding a module with supplementary zones in the central part of each furnace. All the transport systems, the connection cable, the electric cabinet with free space are already dimensioned to support the future enlargement. The external fixtures, such as pipes and the index beam are flanged in the zone in which the extra module(s) will be inserted.

Easy maintenance of the entire plant:

the burners and the open tubes are placed on a removable fixture for easy removal

on the roof of the furnace a manual crane can be installed  for easy removal of the burners, and fans (optional)

the baskets are loaded/unloaded by means of forklift trucks in order to reduce maintenance operations, but an automatic system for the return of the base plates in the loading position can be installed (optional)

all movement units are designed to work continuously in a foundry environment

the internal re-circulation fans are placed on easily removable fixtures to be extracted for maintenance operations. It is also possible to install a special crane (optional) directly on top of the furnace roof

the ball bearings of the re-circulation fans are air cooled to avoid the problems with water cooling

NESSy - Novac Energy Saving System; The aging furnace , which normally operates in the range of 150° to 250°C, is heated by the hot fumes coming out from the solution furnace operating at approx 540°C. This system allows to save all the energy normally used to heat up the aging furnace with a power recovery in the range of 25-30% of the total plant consumption, in comparison with a traditional furnace.  To achieve this result, it is necessary to collect all these fumes in one insulated duct leading to an exhaust fan made of stainless steel suitable for high temperatures. From this point, the fumes are conveyed to nozzles that heat up each zone of the aging furnace. The necessary heat in the different zones of the aging furnace is controlled by valves which adjust the hot air capacity of the nozzles. Moreover there are other advantages, such as easy maintenance due to the fact that there are no further burners installed for this aging furnace which need adjustment and operation checks. Notice should be taken to the fact that an auxiliary burner and a fan (booster) are installed in the exchanger fume duct, suitable to heat the aging furnace in case the solution heat treat furnace is switched off.   Our patented N.E.S.Sy. heating system, able to save all the energy necessary for heating of the aging furnace, has no rivals all over the world.  In connection with other technical choices (i.e. the absence of rolls passing through the furnace walls) guarantees a reduction of gas consumption more than 50% compared to the most qualified competitors.  It is important to underline that with this recuperative heating and energy saving system a temperature uniformity of +/-3°C in the aging furnace will be achieved.

Independent opening of the doors in the continuous solution and aging furnace

Intermediate doors in the continuous solution furnace and in the continuous aging furnace;the installation of the intermediate doors avoid loss of temperature during the critical heat-up phase

Double fan system; the installation of the double fan system in the inner and ending zones will drastically reduce the "opening door" effect, it will reduce the heat-up time, and it will improve the uniformity of the charge.

 Water/sand separator device;it is possible to install a water/sand separator system in order to remove the rest sand which is washed out from the pieces and which is settling in the tank. The bottom of the water tank is provided with a sand trap; the wet sand is pumped by a special pump into a drainage “big bag”, where the filtered water drains out and is returned into the quench tank.  Once the “big bag” is full of sand, it is easily removed by a forklift truck and is replaced by an empty one.   The tank remains always clean and it must be emptied only once a year, for periodical controls.

Blowing/cooling section;a blow-off air cooling section is placed above the quench tank to remove rest water from the cavities of the castings. This system consists of a support structure with a high performance fan and blades to direct the air flow to the castings. This way, not only the water is removed from the castings, but also an improved heat uniformity of the pieces is obtained in the following ageing treatment. The entire zone is confined by sound proof panels.

Heated/cooled quench tank;the heating of the tank will reduce the thermal shock otherwise created by immersion of the pieces in non-controlled water. This is particularly important when the products require specific conditions for certification.  The heating of the water is obtained by a gas burner that fires into a submerged radiant pipe. If necessary, a water/water heat exchanger will reduce the water temperature. The temperature control is obtained by a thermo regulator integrated into the control system.

Lower tray (basket base plate);the use of a strong lower tray (basket base plate) carrying the baskets through the furnaces permits great flexibility of the loading arrangements. It is possible to load onto this base plate only 1 big basket or up to 4 smaller baskets, to use the maximum clearance of the furnace tunnel passage.  Another advantage for the use of a base plate in the furnace system is that bended baskets will not present any problem for the furnace index transport systems.