The world of hull surface preparation witnessed the launch of an innovative hull surface preparation system product at the recent Ship Repair and Conversion 2002 exhibition in London.
British specialists Aquablast have introduced the Superstripper, a hand-held unit that utilises Ultra High Pressure (UHP) water with a pressurised wet abrasive system to give what is hoped to be a tool that will enhance hand-held hull blasting productivity whilst complying with strict environmental guidelines.
This is the result of a detailed period of research and development, as Donald Blair, Aquablast’s managing director, explains:
“We’ve recently developed a system of wet abrasive blasting where we pressurise the pot with water and deliver abrasive at a differential pressure – in other words, in a normal blast system you have air pressurising the pot all the way through. With this technique, we’ve got a method of mixing the slurry in the pot, so we can deliver a much better pattern of abrasives. We get a much better delivery to the target than the old dry blasting system, and when we found we could use less abrasives, it meant we could go to the much harder abrasives which are more efficient.”
In fact, this new system averages around 15kg of garnet abrasive per m2 compared to the average of 40 to 50kg of grit for the same surface area. Garnet is effective but expensive, and this reduction in the amount required should make its use cheaper for repair yards.
This wet abrasive blast system was then married to a hand-held UHP system, and tests carried out in both Rotterdam and Dubai proved encouraging. In these trials, a Superstripper averaged around 20m2 per hour whilst conventional dry blasting tools alongside could only manage on average 10m2 per hour. Previous hand held UHP systems were often seen as being too slow to be efficient on large surface areas. ‘Now we’ve got a hand held UHP system which is fast enough to be a viable product in a shiprepair yard,’ says Donald Blair. Earlier tools had been suitable only for smaller areas such as sections of decks, bulwarks, winches and ballast tanks.
Previously, robotic technology was considered one of the most effective ways of tackling large areas. Vacuum assisted robotic blasting is certainly viable; as such systems can cover large, flat areas quickly and efficiently. UHP robotic systems also have an advantage in that they can suck away moisture and waste material very effectively and can hold the blast much more accurately than manual systems. But they are handicapped by the fact that they can only access some 85% of a ship’s surface area, leaving many areas they can only be reached by hand held tools.
Donald Blair says one of the other crucial drawbacks of previous hand held UHP blast systems has been addressed by this new development: ‘One of the difficulties with previous high pressure systems was that the lower pressure systems were generally pumping higher volumes of water, and it is volume of water that reaction force rather than pressure. We’ve now got equipment that operates at 55,000 lbs/in2, operators can get hold of it and use it effectively.’
Such systems will almost certainly prove increasingly popular in shipyards where environmental issues are becoming an ever-increasing concern. Dry blasting methods produces masses of copper slag dust, whereas UHP systems are dramatically cleaner. Dryblasting has long been considered by many shiprepair yards to be somewhat of a ‘bogeyman’. A ship undergoing any form of dryblasting has to be virtually shut down because the debris produced gets into spaces and can cause considerable difficulties. With UHP systems, it is possible to carry out other jobs on a vessel in very close proximity to the blasting operation, resulting in quicker turnaround times and lower costs. This is understandably a significant factor for many Western yards facing up to an onslaught of cheap competition from Eastern Europe and the Far East. Another advantage is that waste disposal costs are said to be reduced by as much as 60% with UHP systems.
But many industry experts believe advances in UHP technology will not spell the end for the older, less environmentally sound dry blasting methods. Many yards, for example, in some East European countries, are not bound by environmental legislation which makes dry blasting much less cost-effective in countries with tighter laws on pollution.
The development of the UHP technology behind equipment such as the Superstripper relied on convincing paint manufacturers that UHP had the capability to remove rust, corrosion and old coatings to expose the original blast profile, which is vital for the adherence of a primer coat.
If it could be demonstrated to be capable of exposing the original hull profile, then there would be no justification for reblasting and using a lot of wasteful copper slag blasting material. UHP also has the ability to remove chlorides from the surface to a much greater extent than conventional dry blasting. In fact, the residual chloride values in micrograms per square cm is typically 10 – 20, and today values of below 10 are the norm. This is a very attractive aspect to ship repair firms and shipowners alike because it gives a very clean surface to apply the new coat of protective paint onto. UHP and wet abrasive systems will often create a new profile, and that can be advantageous because the existing profile might be damaged.
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