At many prominent aluminium producers, a combination of continuous and batch homogenizing systems is a common sight for ultimate flexibility.

In case batch homogenizing equipment, which has become obsolete, is replaced with  continuous homogenizers, most customers retain some of the existing batch plants to specifically process certain special alloys.

Operating labour for a combined plant is typically limited to:

  • Data storage on log entry
  • Quality control at visual/UT inspection station
  • Billet Saw

The range comprises furnaces for round logs, rolling slabs and combined furnaces (slab & logs).

  • Single chamber furnace up to 60t
  • Double chamber furnace up to 120t

Reliable, maximum homogenizing quality is achieved through accurate temperature regime (+/-3°) and reversing air flow for almost uniform heating and cooling.

Typical plant layout (Batch&Conti)
Typical plant layout (Batch&Conti)
 
2x Stack Storage / 2x Homogenizer 1x Cooler
2x Stack Storage / 2x Homogenizer 1x Cooler
 

Automatic Log Handling:

Modern plants include automated stacking and destacking equipment for lean operating labour requirement and enhanced safety. Automated plants may comprise spacer manipulator, spacer magazines and a crane for handling of log layers.

Spacers made of heat resistant steel square-tube are well suited for automation of the process, and are extremely durable. Spacers supplied in 1990 are still in use today.

HE variable spacer system:

In combination with a moveable bottom in furnace and cooler single spacers are placed equidistant  for best possible log support and optimized to avoid overhanging of log ends.

Heat expansion or contraction is compensated by the moveable bottom to avoid surface marks on logs. The lower weight of single spacers vs. heavy spacer frames also contributes to lower energy consumption.

Plant overview
Plant overview
 
Automatic Log Handling
Automatic Log Handling
 

Furnace design:

Conventional batch homogenizing furnaces are designed upon mono-directional airflow as shown on the illustration to the right. The disadvantage of unequal heating of logs in a stack is known.

Some 20 % faster heating is achieved with the new generation of furnaces with reversing air. The reversing airflow drastically reduces temperature deviation between outer and inner logs. Important of course is an intensive air flow and best heat distribution to achieve near uniform log temperature throughout the stack.

Typically reversing air batch homogenizing furnaces are equipped with reversing type ventilators. This method of reversing the air flow is not particularly efficient, as every change in flow direction causes unnecessary time loss and mechanical strain on motors and fan wheels, etc.

Bidirectional fan wheels are less efficient and reach only around 70% of the nominal airflow in one direction.

Hertwich high efficiency furnaces and cooling stations are equipped with flaps, to switch the air-flow direction within 3 – 5 seconds and without extra strain on motors and fan wheels.

Heat-up time gain is 15 - 20 %.

 
Monodirectional airflow furnace
Monodirectional airflow furnace
 
Bidirectional airflow furnace
Bidirectional airflow furnace
 

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