Sampling Procedures
Representative sampling is the foundation of any valid abrasive testing program. Abrasive materials are heterogeneous — particle size, shape, and contamination levels vary throughout bulk containers, storage piles, and production streams. A poorly collected sample will yield misleading results regardless of analytical precision.
Sampling Principles (ASTM D75)
Three key principles govern representative sampling: (1) every particle in the lot must have an equal probability of being selected; (2) samples must be collected in increments throughout the bulk — not taken from the surface or top layer; (3) increment collection must be conducted uniformly — same device, same procedure, same operator technique for every increment in the set.
Sampling by Container Type
| Container Type | Sampling Tool | Minimum Increments | Min. Total Sample Mass | Sampling Points |
|---|---|---|---|---|
| 25 kg sack | Sampling trier / probe | 3 per sack; 1 in 10 sacks from lot | 300 g per sampled sack | Top, middle, bottom diagonal |
| 1-tonne bulk bag (FIBC) | Sampling probe (900 mm) | 5 increments per bag | 500 g composite | 4 corners + centre at mid-depth |
| Bulk tanker discharge | Mechanical cross-stream cutter | 1 increment per 2 minutes of discharge | Minimum 1 kg composite | Full stream cross-cuts at timed intervals |
| Blast pot (in-service) | Catch container at nozzle | 3 catches per test | 200 g minimum composite | 0%, 50%, 100% through pot cycle |
| Wheel blast machine mix | Sample spout / catch | 5 timed increments | 300 g composite | At separator discharge during operation |
| Outdoor bulk storage pile | Sampling shovel or tube sampler | 10 increments minimum | 2 kg composite | Grid pattern; avoid weathered surface layer |
Sample Reduction — Riffle Splitter
Composite field samples are typically too large for direct laboratory testing. Sample reduction using a riffle splitter (Jones splitter) reduces sample size while preserving representativeness. Cone-and-quarter methods are not acceptable for abrasive testing — they introduce systematic segregation bias.
Riffle Splitter Procedure
Equipment Selection
Select riffle splitter with slot width at least 3× the maximum particle size. For fine abrasives (all passing No. 16 sieve), use 6 mm slots. For coarse abrasives (> 2 mm nominal size), use 19 mm or larger slots. Clean all slots before use — trapped particles from previous samples invalidate results.
Splitting Operation
Pour composite sample uniformly and slowly across the full width of the riffle feed chute. Do not tilt or concentrate flow to one side. Collect both halves. Discard one half (record which). Repeat splitting of retained half until target sub-sample mass is achieved (typically 300–500 g for most tests).
Verification
Weigh both halves from the final split. Mass ratio should be 50 ± 5%. Greater deviation indicates equipment fault (blocked slot or uneven pour) — clean splitter and repeat. Label sub-sample with original sample ID, split number, and date.
Equipment Calibration Schedule
All measurement equipment used in abrasive testing must be maintained on a documented calibration program using NIST-traceable reference standards. The following schedule represents minimum requirements; specific project specifications may impose tighter intervals.
| Equipment | Calibration Frequency | Reference Standard | Acceptance Criteria | Action if Failed |
|---|---|---|---|---|
| Analytical balance | Daily verification; Annual external cal. | NIST Class F weights | ±0.1% of NIST weight value at 3 points | Remove from service; recalibrate |
| Conductivity meter | Before each test session | 1413 µS/cm KCl standard (NIST-traceable) | ±2% of standard value | Recalibrate probe; replace if non-responsive |
| Test sieves (ASTM E11) | Annual; after any damage | NIST-traceable sieve calibration service | Max aperture ≤ 1.25× nominal | Remove sieve; replace with new certified sieve |
| Oven | Quarterly temperature verification | Calibrated NIST thermocouple | ±5°C at 110°C set point | Adjust controller; service if unable to calibrate |
| Surface profile gauge (D4417C) | Daily zero/span; Annual NIST-traceable | Certified reference shims/foils | ±10% at mid-range reference | Remove from service; factory recalibration |
| Depth micrometer (tape method) | Before each use | Gauge blocks (NIST-traceable) | ±2.5 µm (±0.1 mil) | Adjustment per manufacturer; replace if worn |
| Spectrophotometer (D516) | Calibration curve each batch | Certified sulfate standards | R² ≥ 0.999 on calibration curve | Remake standards; check wavelength calibration |
| pH/ion meter (D512) | Before each test session | NIST-traceable buffer/ion standards | ±0.5 mV at verification point | Replace electrode; recalibrate |
Complete Laboratory Equipment List
The following equipment is required for a fully equipped abrasive testing laboratory capable of performing all ASTM test methods referenced in this hub.
Particle Size Testing
- Mechanical sieve shaker (ASTM E11 compliant)
- Test sieve set — No. 7 through No. 200 (SS, 200 mm)
- Collection pan and cover
- Analytical balance (2000 g, 0.1 g resolution)
- Drying oven (forced-air, 50–150°C)
- Desiccator with silica gel
- Sample riffle splitter (6 mm and 19 mm slot)
- Sampling trier / probe (stainless steel)
Contamination Testing
- Conductivity meter with ATC probe (0–2000 µS/cm)
- DI water system (≥ 1 MΩ·cm)
- DI water conductivity monitor
- Polypropylene mixing containers (1 L × 6)
- 0.45 µm membrane filter system (polypropylene)
- Conductivity calibration standards (1413 µS/cm KCl)
- White blotter paper (ASTM D4285)
- Spectrophotometer (420 nm, for D516 sulfate)
- Ion meter / potentiometric titrator (D512 chloride)
Physical Property Testing
- Surface profile gauge (ASTM D4417 Method C)
- Testex Press-O-Film tape (Coarse + X-Coarse)
- Spring-loaded micrometer for tape reading
- Keane-Tator visual comparator (Method A)
- Density measure (1 L calibrated cylinder)
- Pycnometer set (specific gravity)
- Hardness reference specimens (Mohs set)
- Vickers hardness tester (laboratory)
- Metallographic mounting press + polisher
General Laboratory
- NIST-traceable calibration weight set (Class F)
- Calibrated thermocouple (for oven verification)
- Stainless steel weighing dishes (100 mm × 12)
- Inspection tray (white, 400 × 300 mm)
- Magnifying glass (10×) and inspection lamp
- Laboratory notebook + test record forms
- Personal protective equipment (nitrile gloves, safety glasses)
- Chemical waste disposal containers (acid-washed)
Recyclability Testing
Recyclable abrasives (primarily metallic — steel shot and grit) are used multiple times in wheel blast and recirculating pot systems. Recyclability testing characterizes how the abrasive degrades over service cycles, to establish replenishment rates and predict in-service gradation shift.
Breakdown Resistance Test
Baseline Gradation
Establish initial particle size distribution of a 500 g sample of new abrasive per ASTM C136 procedure. Record cumulative percent passing each sieve. This is the T₀ baseline.
Simulated Blasting Cycles
Subject sample to simulated blasting in a standardized blast chamber (fixed nozzle, fixed distance, fixed pressure, 30 seconds per pass). One pass = one simulated "cycle." Conduct tests at 0, 5, 10, 20, and 50 simulated cycles. Recover all abrasive after each cycle for gradation measurement.
Degradation Analysis
Plot cumulative percent passing vs. sieve size for each cycle. Calculate "Breakdown Index" = (% passing No. 40 at 50 cycles) − (% passing No. 40 at 0 cycles). Lower values indicate better recyclability. Compare results to manufacturer's stated recyclability data and project requirements.
Laboratory Records Management
All test records must be traceable from the raw data through to the final reported result. The following minimum information must be recorded for every test:
Sample ID: Unique identifier traceable to delivery lot and sampling event
Abrasive type: Material, trade name, supplier, grade, nominal size designation
Sample source: Container ID, sampling date/time, sampler name
Test date/time: Date and time of test performance
Test method: ASTM standard and revision year
Equipment IDs: All instruments used, with current calibration status confirmed
Raw data: All individual measurements before averaging
Calculations: Shown step-by-step or via validated spreadsheet with audit trail
Result: Final reported value with units
Acceptance status: PASS / FAIL / CONDITIONAL with specification reference
Operator signature: Printed name + signature + date
RETENTION: Minimum 5 years; longer if project specification requires
Laboratory Setup Guidance
Environmental Requirements
| Parameter | Requirement | Reason |
|---|---|---|
| Temperature | 20–25°C (±2°C preferred) | Conductivity and density are temperature-dependent |
| Relative humidity | < 60% RH | Prevents sample moisture absorption during testing |
| Ventilation | Local exhaust at dust-generating operations | Dust exposure control; prevent cross-contamination |
| Vibration isolation | Balance on vibration-damping mat | Balance accuracy during weighing operations |
| Lighting | Minimum 500 lux general; 1000+ lux at inspection areas | Visual inspection per D7393; microscopy work |
| DI water system | Dedicated lab-grade system, ≥ 1 MΩ·cm output | D4940 contamination testing validity |