Measuring blasting involves assessing various parameters to ensure efficiency, safety, and desired outcomes, from monitoring operational pressure within the blast system to evaluating the impact and efficacy of the blasting process on materials or the surrounding environment.
Understanding Blasting Measurement
Accurate measurement is crucial in both abrasive blasting and explosive blasting operations for quality control, safety compliance, and performance optimization. It helps operators fine-tune processes, prevent equipment damage, and meet project specifications.
Measuring Abrasive Blasting Performance
Abrasive blasting, used for surface preparation, requires precise control over several factors to achieve the desired surface profile and cleanliness.
Blast System Pressure
Maintaining optimal pressure is vital for effective abrasive blasting. Pressure directly impacts the abrasive velocity, which in turn affects cleaning speed and surface profile.
To precisely measure pressure within an abrasive blasting system, particularly in the flexible hose delivering the abrasive, a specialized pressure gauge is employed. The typical procedure involves:
- Gauge Preparation: Securely attach the hypodermic needle onto the designated nipple at the bottom of the pressure gauge.
- Hose Insertion: Carefully insert the needle into the rubber hose a few inches back from the nozzle holder. Ensure the needle is aimed slightly towards the end of the nozzle, at a slight angle, to get an accurate reading of the dynamic pressure.
- Reading and Removal: Observe and record the pressure reading displayed on the gauge. Once the reading is taken, gently remove the needle from the hose and properly pack away the gauge for its next use.
Surface Profile and Cleanliness
The surface profile (or anchor pattern) is the texture created by the abrasive, while cleanliness refers to the removal of contaminants.
- Surface Profile Measurement:
- Replica Tape (Testex Tape): A common method involves placing a compressible film over the blasted surface, rubbing it to capture the profile, and then measuring the impressed replica with a micrometer.
- Digital Profilometers: Electronic devices that use a sharp stylus or laser to trace the surface and provide digital readings of peak-to-valley height.
- Cleanliness Assessment:
- Visual Standards: Comparing the blasted surface to photographic standards (e.g., SSPC/NACE standards, ISO 8501-1) to determine the degree of rust, mill scale, and coating removal.
- Dust Tape Test: A method to quantify the amount of dust remaining on a blasted surface.
Abrasive Consumption and Material Removal Rate
- Abrasive Consumption: Measured by tracking the weight or volume of abrasive used per unit of time or per unit of blasted surface area.
- Material Removal Rate (MRR): Quantified by measuring the weight or volume of material removed from the substrate over a specific time, indicating the blasting efficiency.
Assessing Explosive Blasting Outcomes
Explosive blasting, used in mining, quarrying, and construction, focuses on controlling ground vibrations, air blast, and achieving desired rock fragmentation.
Ground Vibration and Air Overpressure
These are critical safety and environmental parameters.
- Ground Vibration: Measured as Peak Particle Velocity (PPV) using seismographs placed at various distances from the blast site. These instruments record ground motion in three orthogonal directions. Regulations often set limits for PPV to prevent damage to structures and ensure public safety, following guidelines from bodies like the Office of Surface Mining Reclamation and Enforcement (OSMRE).
- Air Overpressure (Air Blast): Also measured by seismographs, but with specialized microphones that detect pressure waves in the atmosphere. High overpressure can cause annoyance and minor structural damage.
Fragmentation Analysis
The size distribution of blasted rock (fragmentation) significantly impacts downstream processes like crushing and hauling.
- Image Analysis Software: Digital photographs of the muck pile are analyzed to estimate particle size distribution.
- Sieving (Laboratory): Samples of blasted rock are sieved through a series of screens to determine precise particle size distribution.
Muck Pile Characteristics
The geometry and looseness of the muck pile (the pile of blasted rock) are important for efficient loading.
- Visual Inspection: Qualitative assessment of pile height, spread, and uniformity.
- Volume Estimation: Using laser scanners or drone photogrammetry to create 3D models and calculate the precise volume of the muck pile.
Rock Displacement
Measuring how far the rock mass moves after a blast helps optimize blast patterns.
- Laser Scanners & GPS: Used to map the rock mass before and after the blast to calculate displacement.
- Pre-marked Targets: Physical markers placed on the rock face whose positions are recorded before and after blasting.
Tools and Technologies for Blasting Measurement
| Measurement Parameter | Primary Tools / Technologies | Application |
|---|---|---|
| Abrasive Blasting | ||
| System Pressure | Pressure gauges (with hypodermic needle) | Monitoring hose/pot pressure for consistent abrasive flow |
| Surface Profile | Replica tape, Digital profilometers | Quantifying peak-to-valley height for coating adhesion |
| Surface Cleanliness | Visual standards (SSPC, ISO), Dust tape | Assessing contaminant removal |
| Abrasive Consumption | Weighing scales, Flow meters | Tracking abrasive usage efficiency |
| Explosive Blasting | ||
| Ground Vibration & Air Overpressure | Seismographs (with geophones & microphones) | Monitoring blast effects on structures and environment |
| Fragmentation Analysis | Image analysis software, Sieves | Determining rock particle size distribution for downstream processes |
| Muck Pile Characteristics | Laser scanners, Drone photogrammetry | Assessing blast efficacy and optimizing loading |
| Rock Displacement | Laser scanners, GPS, Surveying equipment | Understanding rock movement for blast design improvements |
