Theory of Shotblasting
The basic principle of the blasting operation is performed by abrasive being thrown at a high velocity against the surface to be cleaned. The throwing action is achieved through centrifugal force, where a wheel with paddle-type blades attached radially, is revolved at a continuous shaft speed. Onto this wheel, abrasive is fed in such a manner 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. The energy placed into the abrasive is sufficient to enable it to rebound from the work surface. The rebound (kinetic energy) is used to recover the abrasive for re-use.
e machine is designed so that the blast wheel is throwing abrasive at an inclined angle relative to the work surface. This means after striking the work surface, the abrasive rebounds at a similar angle into the reclaim duty which directs it back into the hopper for re-use. Assisting with the reclaim cycle, the airflow created by the dust collector enters the machine through a brush screen at the real of the cabinet and flows across the work surface, up the reclaim duct, through the separators, and in the dust collector. Then it moves through the fan and into the atmosphere. All of the surface contamination which has been collected in the dust collector must be disposed of under the COSHH and Health and Safety guidelines.
- there are some restrictions when it comes to application, so can't blast a surface that is contaminated with oil or grease or heavy dirt, or any wet damp surfaces or sometimes any rubber-based paints and coatings.
- The Shot is loaded in the hopper of the machine. The hopper acts as a funnel to direct the shot to the shot valve
- The shot valve (butterfly valve) controls the volume of shot that is allowed to flow down a spout and into the blast housing. The shot valve is controlled by a cable or lever located in the operator’s position for easy accessibility
- After passing through the shot valve the flow of shot is directed by a ‘Control Cage’. This allows the shot to fall on the optimal position of the blast wheel. The Control Cage can be calibrated (adjusted) to ensure that the shot blaster is achieving an even blast pattern across the width of the machine
- After passing through the Control Cage, the shot is impacted by the Blast Wheel and travels at a high velocity towards the floor. Depending on the size of the machine, the blast wheel can either be a one-piece unit or made up of a center housing with a series of blades (paddles)
- The abrasive impact force of the shot hitting the floor removes surface contaminants and leaves a clean, dry profile
- The rebounded shot and debris then travel up the reclaim channel and land on a shelf located directly above the hopper. Once the shelf becomes full, the shot and debris overflow off the shelf. The lighter debris particles are removed by the suction provided by dust collector and the heavier shot is recycled back into the hopper
- The process described above is a continuous cycle. Over time the shot breaks down (wears away) and new shot needs to be added to the hopper