A locally developed and manufactured industrial cleaning machine that uses dry ice to clean and prepare surfaces is undergoing testing before being launched onto the South African market at the Electra Mining Africa trade show, in Johannesburg, next month.
Pretoria- and Durban-based dry-ice specialist company Dry Ice International owner Deon Roux tells Engineering News the new machine is the first of its kind to be manufactured in South Africa. “We have designed the machine to operate without a power source, so it is ideal for use throughout Africa, where electricity is unreliable or not even available,” he says.
The machine can operate using only a supply of compressed air of varying pressures.
“We have been working with seven different models of dry-ice blasting machines that are manufactured by companies from the US, Europe and Eastern countries,” he says, adding that all these overseas units are expensive, which creates difficulties in justifying the cost of purchase.
“During the past year, we have developed the new blasting machine, which is virtually maintenance free,” says Roux, adding that the prototype machines have passed numerous tests in difficult scenarios, such as operating in dirty and high-temperature environments.
The product has been enhanced in the past six months and will be geared towards an international market launch shortly after the local launch.
The company’s offering of full in-house maintenance, with the supply of a backup unit when a client’s unit has to be removed for maintenance or repair, adds further value.
The new machine will be for sale or can be rented for three years from Dry Ice International.
Cleaning with Dry Ice
Roux explains that dry ice can be used to blast surfaces clean, owing to the medium’s cold and brittle properties. “When dry ice comes into contact with the surface, it sublimates, turning into carbon dioxide,” he says, adding that kinetic energy from the high-pressure airflow initially removes any dust or other nonembedded material.
As the dry ice impacts on the surface – and owing to the medium’s frozen nature – thermal shock occurs, which dislodges embedded materials on the surface being cleaned.
At this point of the process, the thermal shock penetrates only the top layer of the surface, resulting in a low temperature drop of the material being cleaned. Roux says the temperature on a metal surface after dry-ice blasting has taken place will drop by about 7 ºC to 10 ºC, adding that the temperature drop will not compromise the material being cleaned.
Dry-ice blasters use a 3 mm dry-ice pellet for the blasting process. “However, not just any dry ice can be used to form pellets,” he notes, adding that Dry Ice International manufactures pellets to a high industrial-standard density, giving the pellets a hard, yet brittle, quality.
Blasting machines require at least 200 cubic feet of air a minute to operate and they require air pressure in the range of 200 kPa to 1 600 kPa, depending on the degree of work to be performed.
Pellet flow rates can also be adjusted from 20 kg/h to 100 kg/h and light rust can be removed from a metal surface using the highest setting.
“Dry ice is always at a temperature of –80 ºC, unlike normal ice which can have different temperatures,” says Roux.
Roux tells Engineering News that one of the best applications of dry-ice blasting is the cleaning of sensitive electrical equipment.
“We have noted a keen interest in our dry-ice blasters being used to clean sensitive electrical components such as stators and rotors in generators.”
Further, maintenance work on electrical substations can be done faster where cleaning has previously been done using dry-ice blasters.
Roux says the company’s dry-ice blasting systems have been excellent in disaster recovery operations of electrical infrastructure, where electric flashes have occurred.
An electrical flash occurs when high-voltage circuits arc – creating explosive sparks – when they are tampered with - typically when cable thieves break into substations to steal the cables or when electrical faults occur, subsequently creating an electrical fire, which produces large amounts of carbon. This carbon residue coats the interior of substations and is difficult to remove from the walls and electrical equipment.
Previous methods of cleaning the carbon from walls and electrical components involved a large team of cleaners with liquid detergents and manual tools such as brushes. “This manual cleaning was labour intensive and took several days to complete,” says Roux.
The company offers six fully trained cleaning teams, supported by a fleet of 20 delivery vehicles that supply the company’s services and products to Southern African countries.