A UCL Guide To The Industrial Abrasive Cleaning Process
Universal Coatings UK provides a complete coating solution for a wide range of clients and customers with varying requirements. The first stage in any of our complete coating processes, and arguably the most important, is the surface preparation. It is vital to allocate a correct level of preparation to ensure that a high quality and long-lasting final coat can be achieved which is only as durable as the base surface it is originally applied to.
Surface Analysis & Profile
Depending on the project and its current condition we allocate an overview of the surface condition to determine the level of abrasive blasting required. Roughly speaking there are four grades to judge the supplied surface by.
A. Surface largely covered with adhering mill scale, little rust present
B. Surface has begun to rust, causing mill scale to begin to flake
C. Mill scale has rusted away or can be scraped, light pitting visibly present
D. Mill scale has rusted away, and general pitting is now easily visible
Abrasive Blast Cleaning
This is the main method we utilise throughout most of our projects, both on-site and in our workshop. Abrasive blasting is the process of mechanical cleaning by the continuous impact of abrasive particles propelled at high velocities to the steel surface via compressed air. This process is 100% efficient at removing mill scale and rust.
There are four standard grades of cleanliness for abrasive cleaning as follows.
A. SA1 Light blast cleaning
B. SA2 Thorough blast cleaning
C. SA2.5 Very thorough blast cleaning
D. SA3 Blast cleaning to a visually clean steel surface
The majority of work we undertake is to SA2.5 or SA3, this is predominantly required when preparing bridge steelwork and other similar structures. Before any abrasive cleaning work is signed off as completed, we compare original images against the cleaned surfaces to ensure an optimum surface has been achieved before we begin the initial coating process.
The abrasive we use most often, also known as media is chilled iron, highly effective and can be reclaimed and recycled throughout its use which improves efficiency and helps to reduce our environmental impact by reducing contaminated waste.
The size of the abrasive media used during the blast cleaning process is vital in achieving the desired surface profile, as well as the surface cleanliness it is important to achieve the suitable ‘roughness’ required to facilitate a mechanical key suitable to the coating method that will be applied. Paint coatings that are made up of several dense layers or thermal metal sprays require a coarse surface comprising of minute angles to establish an effective mechanical key to strengthen the coatings bond to the substrate surfaces.
Predominantly the category of blast media most used is G17 which achieves a surface profile of between 75-100 microns, this is absolutely ideal for the vast amount of high build coating processes we apply in daily operations.
Abrasive Blasting Environment
In our workshop, we have a main dedicated blast bay suitable for handling very large items in a controlled environment. Over-head cranes coupled with a retractable roof allow us to easily and quickly move and rotate items, enabling the blasting process to be completed efficiently and to the high standards we require.
The blast bay itself can be sealed and is suitably extracted to improve air conditions whilst also improving visibility during the process. We also have an underfloor mounted elevator to reclaim the blast media, this system carries the media through various filters and cleaners and collects it to be reused.
Surface Condition Before Coating
Once the surface has been both cleaned and profiled to the required specification, we must ensure the exposed surface is not allowed to deteriorate. Depending on moisture and temperature levels re-rusting can occur very rapidly. We have a heated and temperature-controlled workshop which does help throughout this process, as well as during the coating application itself. Any rusting, scale or other imperfections are classed as contaminates and will require re-blasting before proceeding any further.
Ideally, we aim to coat all blast cleaned surfaces as soon as possible and never any longer than 4 hours from completed abrasive blasting.
Site Abrasive Cleaning
Universal Coatings UK carries out a complete abrasive cleaning and painting process across sites anywhere in the country. Working with specialised sub-contractors we design and install encapsulation to the required area to be the blast cleaned. This ensures that no matter where we operate, we can create a clean, safe and environmentally friendly environment whilst dealing with all kinds of contaminates.
Conventional abrasive blasting is commonly used but we also deploy our sponge-blasting system to deal with unique requirements.
Sponge-blasting utilises a softer, sponge-based media propelled using compressed air, on impact the sponge compresses and begins to slide across the surface creating a scrubbing motion to clean surfaces. The main benefits of this system are that they produce much less dust, which is hugely beneficial when working in small spaces, or encapsulation. The initial impact of the sponge-based media is much more easily absorbed on impact meaning less bounces back at the operatives in confined spaces and does not simply rip through plastic sheeting and encapsulation where conventional blasting would breakthrough immediately.
Throughout the sponge blasting process, reclamation can easily be achieved which in turn reduces waste all whilst creating usually less than 10% of the airborne dust when compared to conventional abrasive blasting.
The sponge media itself also has the ability to collect salt contaminates and other foreign deposits from cleaned surfaces, this reduces the requirement to wash down and clean surfaces after blasting, on certain sites, for example when working on or near waterways this system reduces the use of fluids to clean the surfaces and helps mitigate the risk of contaminating watercourses.
Whatever the requirements, Universal Coatings UK has both the techniques and the experience required to achieve a long-lasting and reliable coating solution, wherever and whatever you need.
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01427 891 141
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