Abrasive Blast Cleaning: Part Three

Sommario:

Abrasive blast cleaning is a varied but common process for the removal of unwanted matter like particulates, paints, rusts and even for de-burring through the use of kinetic energy.
Wheel blasting and air blasting are two common methods of abrasive cleaning that can deliver good quality results. Air blasting can be used in two main forms including suction and pressure and the choice of the method is closely related to the surface and particulate being treated.

Blast cleaning can be used for applications from simple oil or particulate removal to deburring and removing cured paints, rust, or oxide. Methods like carbon dioxide (CO2) or ice blasting sometimes incur some form of brief chemical effect immediately on impact. However, the bulk of the work is done as a function of the kinetic energy delivered by the impacting media. Kinetic energy is defined as ½mv2, where m = mass and v = velocity of the media.

There are several methods and equipment options available for delivering blast media -- again, these depend on the application. Different applications require different media – and there are many media choices from which to select. In all cases, some form of contaminant and abrasive containment and/or treatment system should be employed to not only reduce safety risks, but to reduce media recycling and reclaiming costs. For example, in applications involving CO2 or baking soda blasting, media is either vaporized immediately or can be sent to the sewer, depending on the contaminants.

Blast cleaning is line-of-sight in nature. As such, only those surfaces that can be impacted by the blast spray may be effectively cleaned. This can present a challenge when cleaning blind holes and spaces. Blast cleaning may be used in many cases as a pre- or post-treatment for liquid cleaning methods. Liquid cleaning methods also are used prior to blast cleaning to remove oils and greases, which can foul the media and make it more difficult to recycle. Suppliers of blast media systems can assist manufacturers in determining what type will work best for different applications.

There are numerous delivery mechanisms for blast cleaning. Choice depends on both the media being used and the finish desired from the blasting process.

Wheel blasting operates by using a high-rpm bladed wheel to deliver media to the surface being blasted. The media is delivered to the wheel where it is then accelerated centrifugally toward the surface. Wheel blasting can operate with almost any type of media but excels in efficiency over other techniques when using heavy media and shot.

Air blasting can be accomplished via two methods: suction and pressure.

Suction systems work on the premise that by passing air over an orifice (eduction), a vacuum is created that will draw media into the air stream. Pressure systems operate by feeding media directly into a pressurized air stream such that it then accelerates toward the surface to be blasted. Both systems carry a number of options that can be utilized to obtain a custom fit for almost any application. Air blasting is typically best suited for lighter-weight media that will respond well to air acceleration.

The introduction of the airless blast wheel was a major revolution for the blast cleaning industry. Instead of using compressed air to propel abrasive, the abrasive is thrown from a rapidly rotating wheel onto the work to be cleaned. The throwing action is achieved through a centrifugal force, where a wheel with radially located blades is rotated at high speed. Onto the revolving wheel, abrasive is fed in such a mariner that it travels along the radial length of the blades and is thrown off in a high velocity stream at the surface to be cleaned.



Figure 1: Airless Shot Blasting Systems



Figure 2: Abrasive Blast Cleaning System for Train Passenger Carriages

Blastman Robotics Ltd has secured a major contract to supply a fully automated abrasive blast cleaning system to AYO TVT Torzhok Russia.

The fully automated robotic crane type system uses the very latest technology to accurately and repetitively blast clean train passenger carriage's after manufacture, and before the painting procedure takes place. The company in Finland's scope of supply is to install their proven fully automatic B20C robot in an enclosed and extracted blast cleaning chamber.

Blastman will provide the train carriage work handling system that presents the carriage to the B20C robot and remove it from the chamber after the blast cleaning operation is complete. Also Blastman are providing the air compressor unit in this turnkey contract.

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