Method for breaking down steel slag blocks (skulls)

The invention relates to the field of processing so-called steel slag blocks or skulls that are obtained in blast furnace operations during the production of steel from ore. Such steel slag blocks constitute a by-product that consists of slags mixed with residual steel. They weigh between approximately 20 tonne and 50 tonne each. As a result of the way in which they originate they usually have a round, somewhat pear-shaped form. Generally attempts are made to recover the iron from these steel slag blocks, for which purpose this iron has to be separated from the slags. In practice, efforts are made in a first processing step to reduce these steel slag blocks to smaller fragments. To this end cranes are generally used that are equipped with a hoist line to which a magnet is attached. A so-called breaking ball that is made of forged steel and has a weight of, for example, 20 tonne is picked up with the aid of this magnet. The breaking ball is hoisted on the magnet, for example to a height of about 15 m. At that height the electromagnet is deactivated, as a result of which the potential energy of the breaking ball is converted to kinetic energy. This energy is released when the breaking ball collides with the steel slag block made ready on the ground, so that this should shatter into more or less relatively large fragments.

However, this practice that has been in existence for some time has the disadvantage that the breaking ball has to be dropped onto the steel slag block very many times before breaking down to the desired proportions is achieved. This means that this process can be very time-consuming.

An additional disadvantage of hoisting the breaking ball by means of a magnet is that the magnet becomes too hot in the course of time. Furthermore, fragments break off the breaking ball when used for a long time; it is also possible that crack formation occurs with a forged breaking ball.

Consequently, many other attempts have already been made to break down steel slag blocks. Examples that may be mentioned are boring through the steel slag blocks, cutting them up with torches, and attempts have also been made to break down the steel slag blocks by pressing. Furthermore, breaking down the steel slag blocks by means of explosive has been tried. However, all these attempts have not led to the desired result, so that the only usable method in practice up to now is breaking down the steel slag blocks by dropping the said breaking ball on them.

The aim of the invention is to provide a method of the abovementioned type with which it is possible to break down the steel slag blocks concerned in a more efficient manner. Said aim is achieved by means of a method for breaking down steel slag blocks, which are obtained by the making of iron and steel from ore and which have the form of a hardened mixture of iron and slags, comprising the following steps:

- provision of a static collision means,

- hoisting of a steel slag block or portion thereof,

- allowing said steel slag block or portion thereof to fall under the influence of gravity onto the onto said collision means, - shattering of at least a part of said steel slag block or portion thereof as a result of the collision forces.

With the method according to the invention, in contrast to in the state of the art, use is made of the steel slag blocks themselves or portions thereof to achieve breaking down. With this method, according to a first possibility a suitable, for example especially hardened base is selected. By allowing the hoisted steel slag block or portion thereof to collide onto this, such a collision force can be generated that said steel slag block is shattered.

According to a second possibility an additional steel slag block or portion thereof is provided as collision means, which can be made ready on a suitable base. In addition, it can be established by trial and error which of the steel slag blocks themselves is sufficiently hard to be able to exert an impact of the desired magnitude on the steel slag block located on the base. However, no special measures have to be taken to select such a steel slag block with sufficient hardness and mass. The fact is that steel slag blocks that are less hard and fall from a specific height onto other steel slag blocks will themselves also readily shatter and then can no longer be used for hoisting and then being allowed to fall once more. Furthermore, the advantage is that with the latter method according to the invention two steel slag blocks can be treated at the same time per time unit in each case. That is to say the one steel slag block or portion thereof that is hoisted and the other steel slag block or portion thereof that is the target of the falling steel slag block. As a result, the process of breaking down the steel slag blocks can be carried out much more quickly. The treatment of the steel slag blocks can be carried out by means of various hoisting machines, such as a crane or a dragline. Of course hoisting and allowing a steel slag block, or alternatively portions of said steel slag block, to fall under the influence of gravity is

continued until the steel slag block made ready on the base is broken down into fragments of predetermined sizes.

In order to avoid the disadvantages that are associated with the use of an electromagnet, the steel slag blocks are preferably grasped by means of a grabbing implement, such as a grab or clamshell. This grab or clamshell can optionally be designed such that this, in addition to a steel slag block, can also pick up a breaking ball of, for example, 50 tonne.

Various hoisting installations are suitable for treating the steel slag blocks. Such installations must be capable of withstanding large, suddenly changing loads. If, for example, a relatively heavy steel slag block, for example of 50 tonne, is suddenly lowered, care must be taken that the hoisting installation is able to withstand such a sudden reduction in the load. In this respect a portal crane could be used in particular, but other cranes that are able to withstand such sudden changes in load are also suitable. In this respect it is also possible to consider the use of a boom or jib.