Shot blasting is an effective process to remove surface contaminant or clean and roughen a smooth surface before applying a primer or coating. Rust and mill skin are two surface contaminants which need to be removed at the shot blasting process to ensure a reliant adhesion of the primer or coating afterwards. Voortman offers pre-fabrication shot blasters which are able to shot blast individual plates and beams but not assembled constructions. The degree of surface contaminant is defined in ISO 8501-1. Sa 2,5 is required for most coating processes which is possible with the VSB Range of shot blasting systems.
Shot blasting video
|Standard||Method||Description of finish|
|Sa 1||Light blast cleaning||When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and from poorly adhering mill scale, rust, paint coatings and foreign matter.|
|Sa 2||Thorough blast cleaning||When viewed without magnification, the surface shall be free from visible oil, grease and dirt and from most of the mill scale, rust, paint coatings and foreign matter. Any residual contamination shall be firmly adhering.|
|Sa 2,5||Very thorough blast cleaning||When viewed without magnification, the surface shall be free from visible oil, grease and dirt and from mill scale, rust, paint coatings and foreign matter. Any remaining traces of contamination shall show only as slight stains in the form of spots or stripes.|
|3||Blast cleaning to visually clean steel||When viewed without magnification, the surface shall be free from visible oil, grease and dirt and shall be free from mill scale, rust, paint coatings and foreign matter. It shall have a uniform metallic color.|
The VSB Range of shot blasting systems is based on the wheel blasting principle which uses a kinetic abrasive energy to shot blast the material. The number of turbines and the turbine capacity is based on the desired shot blasting area, throughput and the desired degree of surface contaminant.
|Power of turbine||Abrasive amount per turbine||Turbines|
|7,5||10||90 - 160||200 - 350|
|11||15||130 - 170||285 - 375|
|15||20||210 - 250||460 - 550||VSB1500 (4x and 6x) VSB2500 (6x)|
|18||24||270 - 320||600 - 700|
The VACAM control software on the VSB Range of shot blasting systems fully utilizes the ricocheting effect of the shot blasting material with pre-calculated loading schemes.
Maximum distance from the turbine to the material surface is set at 1,65 m (5,5 ft) to ensure a shot blasting speed at the surface of the beam of 61 m/s (200 ft/s) with a minimum angle of impact of 26 degrees. This speed and angle of impact will fully utilize an effective shot blasting process but will also keep the abrasive detract to a minimum.
Shot blasting operating mix
The shot blasting operating mix is of primary importance when blasting steel profiles and plates. A well-distributed mix of small and larger particles will give the best shot blasting results and is key to achieving maximum quality and output. Big particles with a lot of kinetic energy can break the upper mill skin and remove large contaminants while the smaller particles are able to reach the pores and remove the smaller and remaining contaminants. The shot blasting systems are equipped with a separator which separates the inoperable abrasive or dust from the rest of the abrasive. It also checks the size and number of particles of the rest of the shot blasting mix. Without the separator the shot blasting system would be very inefficient because the operating mix would be far from optimal.
Particles decrease in size after each cycle. The larger sized particles will become medium sized particles. The medium sized particles become smaller sized particles and the smaller sized particles become dust. This is called the flaking or onion effect. The remaining dust is extracted by a fume extraction unit. When using steel shot it is required to add a average of 11 kg (24 lbs) (4 x 15 kW (20 Hp) turbines), 15 kg (33lbs) (6 x 15 kW (20 Hp) turbines) or 30 kg (66 lbs) (8 x 22 kW(30 Hp) turbines) of the larger sized (SAE J 444 - S390) particles per shot blasting hour, to keep a relatively constant shot blasting mix.