Dummy Block

The dummy block is the most critical element of the aluminium extrusion process. Both the product quality and the efficiency depend on this part. Damatool has developed a dummy block with a high performance as a result of the development works is performed on this issue and 3 dimensional numeric modelling.

Of course will the dummy block act as a part of a system and its performance depends on a series of factors. E.g. on the centering adjustment of the press, the temperature and physical facture, the proper performance of the lubrication, regular maintenance etc. The most important factor except these is a container with a homogenous heat balance achieved container with a measuremental consistency, where an efficient stability is provided.


The Functions of the Dummy Block

The function of the dummy block might seem to be very simple at the first sight. This part, which is the extension of the stem, is used to press the softened alloy through the die. A producer, targeting full quality and high performance, will expect the following performance criterion from a dummy block;

  • To transfer the power of the press on the alloy again and again under high temperatures.
  • To rapidly expand and stop at a safe limit under pressure and to leave only a thin alloy film layer on the liner surface.
  • To detach from the billet cleanly after the pressing.
  • Not to cause any gas entrapments. Gas entrapments may cause damages on the liner or the dummy block.
  • To contribute to the solving of minor press centering problems.
  • To be able to be detached and attached rapidly.
  • To continue performing its task until the completion of the production process.




Damatool dummy block is one of the best dummy blocks developed. It has solved a problem frequently faced at conventional blocks. For example; the most wearing incurs at the front part of the dummy block. As a result of this, the dummy block needs to be replaced or repaired. But at Damatool, the front part of the dummy block is being produced out of high resistant steel. The rapid replacement of the ring part only and to continue with the utilization of the rest part contributes economically to our customers.


The dummy block needs to operate freely inside the container in order to obtain the maximum product efficiency. For that, the press centering must be good. The centre relocation can be easily perceived since an unequal wearing will be seen on the dummy block ring. The key for the press centering is the regular and carefull control.


The dummy block is a part faced with high pressure. It is produced out of hot work tool steel and H13 is commonly as the material. The dummy block needs to be heated prior to the usage. The pre-heating will increase the resistance of the steel and prevent cracks during thermal shocks.  The dummy block should be heated up to 300°C at least.

As the dummy block, also the billet, container and die temperatures affect the operation.

An excessive heated billet (above 500°C) will reduce the pressure during the pressing and may limit the expansion function of the dummy block. This may result in an escape of billet behind the dummy block. This situation may result in a decrease of the life-time, and even to serious deformations. In the same way, similar results can be faced with containers with different heated regions.


The adhesion of the dummy block to the billet is really a serious problem. This is particularly seen frequently at large billets and soft alloys. A considerable benefit can be achieved by using boron nitride.



Possible Problems

The dummy blocks are forced during operation.

The dummy blocks are subjected to influences like temperature, pressure differences, mechanical pressure and the problems below can be frequently faced with.


• Wear at the sides.

• Increase, expansion of the dimension.

• Flexibility losses.

• Faulty centering, unequal wearing.


We can accept the dummy block as normal. The problem is the rapidity of such wearing. The wearing of the dummy block will increase the costs in several ways;

• The cost of the dummy block itself.

• The costs due to production stops and human power usage.


In addition to these; the interruption of the production will affect the performance of other parts and the plant. All these negative conditions will cause production costs.


Dummy Block Maintenance

The dummy block should be controlled daily. The possible aluminium accumulation can be determined by a visual check. The free movement of the mandrel and the ring, the fixation of the screws should be controlled. The dummy block should be detached from the stem and cleaned with caustic weekly. Its dimensions should be controlled and compared with the values of the date of the order. There may be a widening during the usage and the fixation of the expansion by time should be controlled. The increase of the diameter will seriously decrease the life-time.