Frequently asked questions to our concrete gunning machines

GUNMIX is a moistening system for dry gunning machines, which is developed by VELCO and patented (EP 1153861).
With dry gunning, the gunning material is poured dry into the machine, pneumatically conveyed without adding moisture and only moistened at the mixing nozzle (It is also called gunite or dry shotcrete).
With wet gunning (sometimes as well called spraying), the gunning material is mixed homogeneously with water in a mixing unit and then pumped through a hose as a pasty compound. Screw pumps, hose pumps or piston pumps are used here. At the nozzle, the material flow is sprayed with an auxiliary gas flow (wet spraying) and sometimes a liquid binder is added (It is also called (wet) shotcrete).
Dry gunning is used for gunning onto hot refractory bricks (hot repair) or when a highly compacted (“dense”) gunning material layer has to be applied (low porosity).
If the gunning material has to be applied as light as possible (high insulation) and still has to be smoothed after it has been applied to the wall, wet spraying is the best option.
The better the dry gunning compound is mixed with the liquid (water, binder etc.) the less dust is generated and the rebound is less.
Dust occurs when the liquid added to the mixing nozzle does not reach all of the dry material particles. The cause can be that the gunning mix has a very high proportion of fine particles in the µm range, that too little water is added to the nozzle or that the mixing of water and material is too poor.
Rebound occurs when gunning material particles hit the wall and do not stick there. This means that the particles do not have a sufficient adhesive effect, e.g. because there is too little binder, the binder has not been activated or the impact speed (gunning pressure) on the wall is so high that the particles do not adhere to the wall. This can be remedied by better humidification, adapting the gunning pressure and good nozzle movement by an experienced operator.
Hot repairs refer to the application of gunning material to hot bricks or cast refractory linings that are used in furnaces, ladles or other components. The repair time is very short. So there are only low production and therefor low heat losses. As a result it is required less energy and time for reheating and drying. There are also fewer thermal stresses and cracks. The disadvantage is the high stress on the operator due to the radiant heat. That is why spray manipulators are used.
A gunning manipulator is a machine that leads a gunning lance and is operated by a worker via radio- or cable control.
A gunning robot is a machine that applies a gunning layer, the movements are controlled by a PLC. Either pre-programmed paths can be used or the gunning zones are calculated using a measuring system such as a laser measurement.

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