HANDLING INSTRUCTIONS

1. Like other fused cast refractories, KORVISIT-A is a rigid material by nature containing some glassy phase. Its moving on rollers, turning over the edges and corners may result in pieces splitting off. Impact of the blocks against each other should be avoided.

2. The blocks have to be stored in a dry, covered place. Water absorbed by the shrinkage cavity and the open pores may cause blocks to shatter when heated up or to burst if exposed to frost.

3. Further machining of the blocks can only be carried out safely by using diamond or silicon carbide tools.

4. Better embedding and strong bond of the blocks is ensured by laying refractory mass as thick as 20 to 30 mm under the skid rails or bottom. For installation of KORVISIT-A refractory blocks, we recommend refractory mass KORKOM PLAST.

5. In case of steel rail/fused cast block junctions in a pusher type furnace, the fused cast bottom has to be by 10 mm lower than the steel rails' upper edge.

6. When laying a bottom, expansion gaps of 8-10 mm per meter should be left in all directions by putting cardboard, styrene, plywood or simple iron sheet between the blocks (Iron sheets must be removed before heating up of the furnace.) It is forbidden to fill the gaps with mortar or mass.

7. In addition to the bottom blocks ramming or castable refractory masses can be applied along both sides of the furnace (in a width of 200 to 300 mm) and along the charging and the discharging end (in a width of 50 to 250 mm).

8. Once the bottom is laid, it must be carefully cleaned. Mortar or scrap, if any, must be removed from the joints by compressed air and the clean joints should be sealed with paper or foil strips.

9. When the spaces between fused cast skid rails or bottom blocks are lined with KORVISIT-A, the instructions given under the points 6-8 are to be followed. In case this lining is made of other type of refractories, expansion gaps should be allowed in accordance with the expansion coefficient of the type used.

When laying a new bottom, the mortar prepared from the ramming mix is being spread in a thin layer on the surface, carefully cleaned previously. Then the KORVISIT-A blocks are laid so that the expansion gaps remain empty.

10. There are three phases when heating up the furnaces in the iron and steel industry:

1. 1. drying

2. 2. pre-heating

3. 3. heating as far as operation temperature is reached.

The length of each phase is subject to the quality of the refractory materials, their expansion and the thickness of the furnace wall. Depending on the thickness of mortar or stamping mass, the prepared furnace bottom should be dried. When repairing damaged bottoms, the damaged part has to be cleaned (or mortised if necessary) and then stamped with the said stamping mass. If the layer of mass is thinner than 20 mm, slow drying may be omitted.

For the purpose of drying, the furnace is heated up to 140-150 °C at a rate of 10°C/h in order to expel humidity. Fused cast refractory blocks need not be cared for in this phase. During drying operation only other refractories must be controlled. The phase of pre-heating stretches as far as the temperature limit 600°C; usually auxiliary burners are used, rate of heating is 20-30 °C/h. Holding should preferably be in the range of 340 to 580 °C depending on and with a view to the various refractory materials of walls and crown, their phase changes and their expansion anomalies (SiO2).

When the temperature of 600 °C is reached, the heating up is continued with the main burners instead of the auxiliary ones at a constant rate of max. 60 °C/h. It is imperative to avoid local overheatings. Fused cast materials should not be exposed to jet flame, and also the flow-in of cold air should be eliminated.

11. The temperature of fused cast rails or bottom should not change more quickly than 60 °C/h, preferably 40 to 50 °C/h. Temperature may be increased at a rate of maximum 100 °C/h in exceptional cases.

12. Charging should not be started before the working temperature or at least 1000 °C is reached.

13. The liquid scale occurring results in quicker wearing of the KORVISIT-A blocks. In the presence of not dry scale as well as at temperatures higher than 1300 °C, scale sticking is to be expected.

14. In the case of short standstills (weekends, intermediate repairs) the furnaces shall be cooled down and then heated back to working temperature. The rate of temperature change cannot exceed the values given in point 11. Furnaces cooled down to ambient temperature, should be reheated as in the case of the first heating up. (See points 10 to 12).

15. When scale removal is necessary, the furnace should be cooled down below 800 °C. Rapid cooling with compressed air or water spray may cause the fused cast blocks to shatter. Scraping slabs or hand tools are generally used for scaling. Pusher type furnaces reheating billets, which are not heavy enough to remove the scale by their weight, are generally scaled with the help of hollow scraping slabs. They make it also possible to reach into the furnace with iron rods from the sides and to loosen and remove the scale.

The cleaning of the bottom can also be done, depending on material to be reheated, by pushing heavy and easier slabs by turns through the furnace. Especially unwelcome are scale deposits between slabs pushed through in parallel rows. The scale accumulated in the middle can be removed by means of a heavy slab the length of which conforms to the width of the furnace. Using of rough pneumatic tools and/or fluxing materials is not allowed.

Due to the heavy weight of the ingots and slabs, significant quantities of even denser and harder scale may accumulate on the bottom of soaking pit furnaces.

Likewise to the abovementioned, their scaling should be done in cold state, in no case the application of the thermit method, blowing or water spraying is allowed.

16. In pit furnaces by using a protective magnesite or olivine layer on the clean KORVISIT-A bottoms, scale sticking to the paving can be avoided (or at least slowed down). In case of pit furnaces coke layer can also be applied.

17. In reheating furnaces, the maintaining of slightly oxydizing or neutral atmosphere reduces the scale sticking.

It is recommended to build the fused cast part of reheating furnaces from standardised blocks. Almost every kind of paving and side walls can be built from these standardized blocks and shapes. Other blocks will also be manufactured by MOTIM on request, provided the shapes and sizes are within the production capability.