In the field of shipbuilding and maintenance, the quality of deck surface treatment is crucial, as it directly affects the lifespan of the ship's anti-corrosion coating and the reliability of the hull structure. Currently, the primary methods for cleaning ship decks are shot blasting and sandblasting. Although both techniques use high-speed impact to clean, they differ significantly in their working principles, cleaning efficiency, and application scenarios.

1. The equipment difference between shot blasting and sandblasting process on deck rust removal

① Deck shot blasting machine

The deck shot blasting machine relies on the centrifugal force of the high-speed rotating impeller to eject steel balls (casting balls, cutting balls or stainless steel balls) to the deck surface at high speed. The power source is a motor, which can achieve large-area coverage through single shot blasting or double shot blasting operation. The surface treatment is performed with a deck shot blasting machine, which has a strong impact force and obvious cleaning effect. While removing the oxide scale on the surface of the ship's deck, the repeated impact of the steel balls will undergo plastic deformation without damaging the surface of the deck, forming a reinforced layer of a certain thickness, thereby significantly improving the metal's fatigue resistance and extending the working life.

② Deck sandblasting machine

The deck sandblasting machine uses compressed air as power and sprays abrasives such as quartz sand, ore sand or corundum to the surface of the ship's deck at high speed to achieve the cleaning effect. The deck sandblasting machine is more flexible than the shot blasting machine. The spray gun can penetrate deep into complex welds or corners, and has a good cleaning effect. It is suitable for cleaning deck areas with high surface cleanliness. After sandblasting, dirt on the deck surface is removed and the metal surface is slightly damaged, forming a rough surface to enhance the adhesion of the coating, but there is almost no reinforcement effect.

2. Comparison of application scenarios for anti-corrosion and rust removal on ship decks

The choice of two cleaning processes for ship rust removal and corrosion protection depends on the operation stage and deck structure. Generally speaking, cleaning and maintaining ship decks can use three models: deck shot blasting machine, vertical shot blasting machine and deck sandblasting machine.

① Deck shot blasting machine

The deck shot blasting machine is suitable for cleaning the flat area of the deck and can efficiently remove the oxide scale and rust layer on the flat surface of the ship's deck, with an hourly processing capacity of up to 80 square meters.

② Vertical shot blasting machine

The vertical shot blasting machine can clean the vertical surface rust and painted surface of the ship's side, which can achieve the surface cleanliness and roughness required for corrosion protection. It uses a 11KW main shot blasting device, which can achieve about 60 square meters per hour.

③ Ship deck sandblasting machine

Ship deck sandblasting machine is suitable for cleaning ship curved surfaces, pipeline welds and narrow and complex parts. Compared with shot blasting, the sandblasting process has better cleaning effect and can accurately treat local rust areas of the ship deck, but its working efficiency is less than half of the shot blasting, and it will produce a large amount of dust, so it needs to be equipped with a dust removal system.

3. The cleanliness level of ship decks for deck shot blasting machines and deck sandblasting machines

The quality of the pre-coating treatment of the ship is related to the service life of the paint, so the importance of surface cleanliness before painting has been recognized by people for a long time. Many countries around the world have formulated standards for metal surface cleaning, which are also applicable to ship decks. There are two representative international standards: the (Sa) standard formulated by Sweden in 1976 and the (SSPC) standard formulated by the United States in 1985. The two can correspond to the cleanliness of metal surfaces one by one.

Sa1/SSPC-SP7 (non-complete cleaning grade): The surface of the ship's deck has been completely cleaned, and oily, loose scale, floating rust has been removed. The scale, rust, paint and coating that is firmly combined with the deck and cannot be removed with a spatula allows remaining on the surface after cleaning.

Sa2/SSPC-SP6 (more thorough cleaning): The cleaned ship deck surface is free of oil, rust and other impurities, allowing for mild shadows or color difference due to insufficient rust and scale removal, with an area of no more than 33%.

Sa2.5/SSPC-SP10 (very thorough cleaning): The cleaned deck surface does not contain oil, scale, rust and other impurities. Only no more than 5% of the surfaces are allowed to have shadows or color differences due to incomplete cleaning.

Sa3/SSPC-SP5 (most thorough cleaning level): The cleaned deck surface is completely consistent with metallic silver grey, with a certain surface roughness to improve the adhesion of the coating. The grease, dirt, oxide scale, corrosion, corrosion products, oxides and other impurities on the surface of the deck are completely removed.

Ship decks treated by deck shot blasting machines or deck sandblasting machines usually require surface cleanliness of Sa2.5 or above. After testing the roughness thickness gauge, it is determined that the shot blasting process is easier to achieve Sa2.5-Sa3 levels stably, while sandblasting is prone to unevenness due to manual operation. In order to solve the uneven sandblasting phenomenon caused by artificial factors, we have developed a crawling robot that drives the sandblasting machine, which can achieve uniform sandblasting and rust removal.

4. In ship rust removal and corrosion protection projects, appropriate strategies should be selected according to the different positions of ship rust removal (deck removal, calder removal, ship side, pipeline, etc.).

① Mobile shot blasting machine-clean the deck surface

Mobile shot blasting machine is a preferred equipment for cleaning the plane area of the ship's deck. It has high cleaning efficiency, good cleaning effect, strengthens the substrate and no dust spillage. It only requires a single pass to reach the Sa2.5 level.

When selecting mobile shot blasting machines, it is recommended to choose ROPW550, 500E, and 500S. Among them, the working width of ROPW550 is 550mm, which is suitable for cleaning of flat decks, and the processing efficiency is 75-100m²/h. Since the height from the horizontal surface can be controlled at 20mm when working, it can be used for the horizontal deck or for the cleaning of anti-slip slope surface. The working width is 500mm and the processing efficiency is 50-140m²/h.

② Deck sandblasting machine-cleans complex structures such as ship side

Deck sandblasters can exert flexibility in the maintenance of ships or handling ship locations with complex structures. In order to meet environmental protection requirements, a dust collector can be used for the sandblasting machine or a dust-free sandblasting machine can be used.

In terms of the selection of deck sandblasting machine, it is recommended to choose the circulating sandblasting machine ROVAN Recovery-BRS25 and dust-free sandblasting machine DB500. The advantages of the circulating sandblasting machine ROVAN Recovery-BRS25 are that it is easy to move, no dust spillage, automatic abrasive recycling, and cleaning efficiency is 6-15m²/h. The dust-free sandblasting machine DB500 is a wet sandblasting machine. There is no dust during sandblasting operation and can work continuously for 60 minutes. If you need to extend your working hours, you can also choose DB800 and DB1500 with larger capacity.

Sandblasting and shot blasting are not simple substitutes for each other in deck cleaning of ships; only by matching the appropriate process according to the working scenario can high-efficiency and high-quality cleaning be achieved.