What you should know to specify Blasting

To specify a blasting equipment it is necessary to know the various systems usually adopted and their specific applications.

Firstly, the material to be used in the blasting must be defined.
The first twelve TECHNICAL INFORMATION, in particular the second, summarize the main characteristics of the most common materials, facilitating their choice.


Defined the material, the choice between Suction Guns, Pressure Nozzles or Turbines, depends not only on the type of work as efficiency, regularity and availability of compressed air.

Suction Pistols

They operate with compressed air. It is introduced into the gun through the nozzle and exits through the ejector creating a vacuum in the internal venturi chamber, sucking air and abrasive from the dosing valve. It is the most widely used cabinet system for its maneuverability and low consumption of compressed air.

Operates on all materials including aqueous suspension (wet jet).

1- The nozzle diameter defines long air consumption and remains constant throughout the life of the gun.

2- Rated power absorbed from a compressed air network. Using a team-specific compressor a slightly higher capacity (15-20%) is recommended.

3- Comparative reference with the production of the 1/8 ”diameter nozzle gun.

No.

Injector
Nozzle
Consumption of compressed air HP

Approx.


80 psi
Efficiency
40 60 80 106
2 1/16 3.1 4.2 5.3 6.4 1.2 0.2
4 1/8 12.3 16.8 21.2 25.7 4 1.0
5th 5/32 20.0 26.2 33.0 40.1 6.5 1.4
6th 3/16 27.5 37.5 47.5 57.9 9th 2.1
8th 1/4 49.0 67.0 85.0 10 3 15 4.0

Pressure systems

It consists of a pressure vessel that is fed through a shut-off valve. During operation, the vessel is pressurized and the material, along with the long air, is dragged through the hose and expelled through the nozzle at high speed.

It is a more energy efficient process than with suction guns. It can be used in cabinets (BP series) but is most commonly used in cabins or open blasting.

The vessels are manufactured with capacities between 40 and 4500 liters, with outputs for one or more operators, direct or remote controls, with discontinuous or continuous operation (double chamber), finally, with several operational options and the hoses can be longer than 30m, allowing to operate long distance of the equipment.

The diameter of the nozzle defines the compressed air consumption indicated on the side. Its progressive wear increases consumption and it is recommended to provide air capacity up to 20% higher than indicated.

Rated power absorbed from a compressed air network for new nozzles.
For a compressor directly connected to the pressure vessel, capacities of 15 to 20% higher are recommended.

Comparative reference to the production of the 1/8 ”diameter pressure nozzle.

No.

Injector
Nozzle
Consumption of compressed air HP

Approx.


80 psi
Efficiency
60 80 90 100
2 1/8 14th 17 19 21 5th 1.0
3 3/16 30 39 42 46 10 2.1
4 1/4 55 70 75 83 17 4.0
5th 5/16 90 115 127 140 30 6.5
6th 3/8 130 163 175 200 40 9.5
7th 7/16 175 220 245 260 55 13.0
8th 1/2 225 285 312 342 70 16.8

Turbines

They are rotary devices provided with blades that accelerate by centrifugation particles of abrasives fed continuously by the center. They are much more energy efficient than suction guns and pressure nozzles, ie with the same power installed they can perform a much larger service volume.

Basically they are composed of a radial vane rotor that generally rotates between 1500 and 3000rpm. , and a metering valve that can regulate the volume fed and the direction of this feed in the center of the turbine.

Depending on the angle at which the abrasive is released into the turbine, it is fan-thrown over a given area, ie the flow can be directed with some precision. The most commonly used abrasives in turbines are spherical steel grits, but they can also operate on lighter ones, including walnut shells.

Depending on the purpose they are manufactured with various diameters in the range of 150 550mm with also varying widths.

Just to illustrate the efficiency, it is worth mentioning that a 550mm diameter turbine, rotating at 2600 rpm, driven by a 75hp engine throws over 600kg / min. of steel shot.

They are constructed from special alloys of high abrasion resistant steel, which ensures wear parts have over 300 hours of service life.

In the drawing, the shape of the array of thrown abrasives covering an elongated area that may be more than one meter long is outlined.

The large surface area associated with the high volume of material thrown at high speeds gives turbines a wide range of applications, usually for large parts such as sheet and profile stripping, forged or cast parts (with or without sand), shot peening in torsion bars etc.

Since it was developed more than 100 years ago, the blasting process has always proved to be a highly efficient resource and its applications have multiplied rapidly and are even absorbed by various industrial sectors.

However, application technology was primitive, with three basic drawbacks:

– Environmental pollution, creating problems of dusty atmosphere that hit and damaged buildings and even machinery inside, as well as the health of operators.


– Even with the development of more efficient and less polluting abrasives, their use was prohibitive due to the difficulties of their recovery.


– Finally, even recovered, these abrasives gradually contaminated, impairing the repeatability and efficiency of the process.

Solutions have emerged and improved over a century of evolution, radically changing the image of blasting equipment, once relegated to the confines of factories, today found on production lines, alongside sophisticated conventional mechanical equipment, fully meeting the most stringent safety requirements and uniformity of production.

Open-air operations tend to disappear completely not only because of pressure from official or internal company security bodies, but also for economic reasons regarding direct costs, transportation and operational efficiency.


The modern design of blasting equipment always includes, with greater or less sophistication, the following components:

1) Containment of the blasting operation itself

Accelerated particles (suction guns, pressure nozzles, turbines, etc.) and the parts they fall into are always confined indoors as simple cabinets or large booths where operators also enter the environments.

2) Abrasive Collection

These are gravity, mechanical or pneumatic devices that collect and concentrate the materials in silos, returning them to the process.

3) Abrasive Scrubbers

These are intermediate devices of greater or less complexity according to the operational requirements, which remove from the materials, after blasting, the contaminations removed, the operating dust and eventual larger debris, returning them to the process with constitution and particle size similar to initials.

4) Exhaust Systems

Its main function is to drag dust from confined environments and separate it from abrasives.
When properly sized, they ensure good internal visibility and decompression (negative pressure) on all system components, increasing safety against dust leakage into the outdoor environment.

5) Dust collectors

Separate the exhaust air from the dust, trapping it and returning the first purifier to the atmosphere.

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