Cobalt Content Mining Picks — Wear vs. Impact Guide | Ruixin



Why Cobalt Content for Mining Picks Determines Wear Life and Impact Survival

A roadheader operator in mixed sandstone and coal switched from a 6% cobalt grade to an 11% cobalt grade after losing four picks to fracture in a single pass through a hard clay band. Tip breakage stopped — but wear rate increased 35% in the abrasive sections. The operator accepted that trade-off because unplanned downtime from replacing shattered picks cost more than the faster wear.

This is the central decision every coal shearer and roadheader operator faces: cobalt content mining picks wear resistance and impact toughness are inversely linked, and no single percentage works everywhere. The wrong choice costs money in one of two ways — frequent breakage or accelerated wear.

The correct cobalt range depends on three field conditions: the uniformity of the ground, the presence of hard inclusions, and the cutting speed. This guide lays out a decision framework based on those variables, with specific cobalt ranges and corresponding Ruixin grades, so you can match cobalt percentage to your working conditions rather than guessing.

If you need the metallurgical mechanism behind the numbers — how each 1% cobalt shifts HRA by ~0.5 and flexural strength by ~100 MPa — see our companion article on the mining carbide cobalt content wear resistance trade-off. This article focuses on application: what to pick, when, and why.

Why the Wrong Cobalt Content Fails Your Shearer or Roadheader — Quantified

Three failure modes dominate in coal shearer and roadheader pick operation, and each maps to a specific cobalt mismatch.

Failure Mode 1: Catastrophic Fracture (Too Little Cobalt)

When a pick hits a quartz stringer, pyrite nodule, or hard rock band at full cutting speed, the impact energy travels through the carbide tip. A low-cobalt grade (under 8%) has insufficient binder volume to arrest the crack. The tip fractures across the full section within milliseconds.

Quantified impact: In blocky ground with UCS over 120 MPa, a 6% cobalt grade fractures on average within 2-3 impacts against hard inclusions. Replacement frequency doubles compared to a 12% cobalt grade. Cost per meter rises 25-40% when factoring in downtime for pick changes.

Failure Mode 2: Accelerated Wear (Too Much Cobalt)

In dry, abrasive sandstone or siltstone with minimal impact loading, a high-cobalt grade (12-13%) wears faster because the soft cobalt binder erodes under the abrasive stream, undercutting the WC grains. The tip rounds off rather than maintaining a sharp cutting edge.

Quantified impact: In dry cutting conditions with Cerchar abrasivity index above 3.0, moving from 6% to 12% cobalt increases tip wear rate by 50-80%. Shifts that previously required one pick change now require two. Total consumable cost per tonne rises 30-55%.

Failure Mode 3: Thermal Fatigue + Binder Washout (Medium Cobalt, Wrong Cutting Speed)

At high cutting speeds (above 3 m/s for shearers, above 2 m/s for roadheaders), friction at the cutting edge pushes surface temperature above 600°C. At these temperatures, the cobalt binder softens and migrates — a process called cobalt washout. Even a balanced 10% cobalt grade can fail prematurely if cutting speed and water spray are not matched to the grade’s thermal limits.

Quantified impact: In high-speed cutting with insufficient water cooling, tip life drops 40-60% regardless of cobalt percentage. The solution is not a different grade — it is adjusting cutting speed or adding coolant flow.

The failure isn’t random. It is the predictable result of picking a cobalt percentage that does not match your ground conditions and operating parameters.

Cobalt Content Mining Picks Wear: The Three Cobalt Ranges by Application

The practical selection range for coal shearer and roadheader picks spans from 6% to 13% cobalt. Within that band, three distinct ranges serve three distinct operating environments.

Range 1: 6-8% Cobalt — High-Abrasion, Low-Impact Conditions

Best for: Dry cutting in homogeneous coal or soft sedimentary rock with minimal hard inclusions. Uniform seams where the primary wear mechanism is abrasion, not impact.

Why it works: Low cobalt content maximizes the volume fraction of hard WC grains at the cutting surface. The composite hardness (HRA 90-92) resists particle erosion. Grain size between 1.0 and 1.2 µm further densifies the surface.

Ruixin recommendation: SR7X at HRA 91.0, 6% cobalt, 1.0-1.2 µm grain size. Flexural strength ≥ 2,000 MPa is adequate for this condition because impact loads remain within the material’s elastic limit.

Limitation: If a hard rock inclusion appears, this grade fractures. Do not use in blocky ground or mixed-face conditions.

Range 2: 9-11% Cobalt — Mixed Ground with Occasional Hard Bands

Best for: Roadheader and shearer operations in interbedded strata — coal with clay bands, medium sandstone with siltstone partings, limestone with chert nodules. The most common operating condition in underground mining and tunneling.

Why it works: Cobalt at 9-11% provides enough binder volume to absorb moderate impact loads without sacrificing more wear resistance than necessary. The coarser grain size (2.0-3.0 µm) further improves crack deflection at grain boundaries.

Ruixin recommendation: SR8C at HRA 89.0, 10% cobalt, 2.0-3.0 µm grain size. Flexural strength ≥ 2,200 MPa provides a 10% toughness margin over SR7X while retaining 97% of the hardness needed for abrasive wear protection.

Limitation: In highly fractured rock with continuous impact loading, this grade will eventually show edge chipping. If fractures or hard inclusions appear on every rotation, move to Range 3.

Range 3: 12-13% Cobalt — Blocky Ground with High Impact Risk

Best for: Tunneling through heavily fractured rock, shearer operations in seams with frequent quartz or pyrite stringers, roadheader cutting in hard sandstone with joint sets that cause intermittent shock loading.

Why it works: Every additional percent of cobalt adds binder volume for crack arrest. At 12-13%, the composite can absorb impact energy that would propagate through a lower-cobalt grade. The trade-off is lower bulk hardness (HRA 87-89), but in impact-dominated conditions, fracture prevention matters more than wear rate.

Ruixin recommendation: SR10C at HRA 88.0, 12-13% cobalt, 2.0-3.0 µm grain size. Flexural strength ≥ 2,200 MPa matches SR8C, but the extra binder volume extends the safe impact threshold.

Limitation: Wear rate in dry abrasive rock is 50-80% higher than SR7X. Only use this range when impact risk is the primary failure concern.

How Cobalt Content Affects Mining Picks Wear — Grade Selection Table

Application Scenario	Recommended Grade	Key Parameters	Why This Grade
Dry cutting in homogeneous coal seam, UCS < 60 MPa, no hard inclusions	SR7X	HRA 91.0, 6% Co, 1.0-1.2 µm, ≥ 2,000 MPa	Maximum surface hardness resists abrasive wear; fine grain prevents particle erosion; no toughness needed because impact is minimal
Mixed ground (coal + clay bands + soft sandstone), UCS 60-120 MPa, occasional hard inclusions	SR8C	HRA 89.0, 10% Co, 2.0-3.0 µm, ≥ 2,200 MPa	Balanced wear/toughness profile handles intermittent impact without excessive wear in abrasive zones
Blocky fractured rock / seams with pyrite/quartz stringers, UCS > 120 MPa, continuous shock loading	SR10C	HRA 88.0, 12-13% Co, 2.0-3.0 µm, ≥ 2,200 MPa	High binder volume absorbs fracture energy; coarser grain deflects cracks; wear rate is secondary to survival
High-speed shearer cutting (≥ 3 m/s) with water spray, mixed abrasion + moderate impact	SR8C	HRA 89.0, 10% Co, 2.0-3.0 µm, ≥ 2,200 MPa	Medium cobalt resists thermal fatigue better than low-cobalt grades; water cooling mitigates wear acceleration
Roadheader in dry abrasive sandstone, Cerchar > 3.0, minimal impact	SR7X	HRA 91.0, 6% Co, 1.0-1.2 µm, ≥ 2,000 MPa	No water to cause thermal cycling; low cobalt minimizes binder erosion; fine grain maintains edge sharpness

Decision Flowchart: Three Questions That Select Your Cobalt Range

Rather than memorizing spec tables, apply this three-question filter to your working conditions.

Question 1: What is your primary failure mode?

Observe the last 10 failed picks. If 7 out of 10 show fracture (chipped tips, cracked inserts, broken-off sections), you need more cobalt. If 7 out of 10 show wear (rounded edges, reduced gauge, smooth surface loss), you need less cobalt.

• Primary failure = fracture → Move to Question 2A
• Primary failure = wear → Move to Question 2B
• Both equally → Start with 9-11% cobalt (SR8C)

Question 2A: How frequent are the impact events?

• Isolated hard bands (one per meter or less) → 9-11% cobalt (SR8C)
• Continuous blocky ground or stringers on every pass → 12-13% cobalt (SR10C)

Question 2B: What is the abrasiveness of the rock?

• Cerchar abrasivity index < 2.5 → 9-11% cobalt (SR8C) — wear is manageable
• Cerchar abrasivity index ≥ 2.5 → 6-8% cobalt (SR7X) — wear is the dominant cost

Question 3: Is water present at the cutting face?

• Dry cutting → Stay at the lower end of the recommended range (wear accelerates faster without cooling)
• Wet cutting (water spray or groundwater) → Move to the upper end of the recommended range (thermal fatigue is mitigated)

Consequences of Choosing the Wrong Cobalt Range

Getting the cobalt percentage wrong produces predictable, measurable outcomes. Below are the four most common mismatches and their cost implications.

Consequence 1: Low Cobalt in Blocky Ground

Running a 6-8% cobalt grade (intended for abrasive coal) in heavily fractured ground or seams with hard stringers.

Result: Catastrophic tip fracture within minutes of encountering the first hard inclusion. Tip life drops 70-90% compared to a properly selected grade. Replacement frequency triples. The shearer or roadheader must stop for pick changes every 15-30 minutes instead of every shift.

Consequence 2: High Cobalt in Dry Abrasive Rock

Running a 12-13% cobalt grade (intended for impact survival) in dry sandstone or siltstone with Cerchar above 3.0.

Result: Wear rate increases 50-80% because the soft cobalt binder erodes rapidly, undercutting WC grains. Tips that should last a full shift need replacement at mid-shift. Cost per meter rises 30-55% from consumable alone.

Consequence 3: Medium Cobalt in Very High Abrasion

Running a 10% cobalt grade (SR8C) in dry quartz-rich sandstone where a 6% grade would be appropriate.

Result: Acceptable wear life — SR8C will still cut — but the operator is leaving 20-30% of potential tip life on the table. Over a year of production, this translates to 25-35% more pick consumption than necessary.

Consequence 4: Over-Correcting Without Changing Cutting Parameters

Switching from SR7X to SR10C to stop fracture, but maintaining the same high cutting speed (above 3 m/s) with insufficient cooling.

Result: The higher cobalt content softens faster at elevated temperatures. Thermal fatigue accelerates binder loss. Tip life may actually decrease despite the tougher grade. Cobalt selection and operating parameters must be adjusted together.

How to Implement Cobalt Selection in Your Operation

Applying this framework does not require metallurgical lab work. It requires three things: failure observation, ground condition assessment, and a willingness to test.

Step 1: Classify your ground

Map your working face by UCS range and Cerchar abrasivity index. If you do not have these numbers, a field observation is sufficient: count how many picks fracture per shift vs. how many wear out. A ratio of 3:1 fracture-to-wear means you need more cobalt. A 3:1 wear-to-fracture ratio means you need less.

Step 2: Select the starting grade

Use the decision flowchart above to pick a starting cobalt range. If you are unsure, start with 9-11% cobalt (SR8C) — it handles the widest range of conditions and gives you a baseline to adjust from.

Step 3: Run a controlled trial

Test the new grade on one cutting drum or one roadheader for two full shifts. Compare wear patterns, fracture count, and pick consumption per tonne against your current grade. Adjust cobalt percentage up or down based on which failure mode emerges.

Step 4: Match operating parameters

If you increased cobalt (for impact survival), consider reducing cutting speed slightly to prevent thermal softening. If you decreased cobalt (for abrasion resistance), confirm that water cooling is adequate — dry running accelerates wear in all grades but punishes low-cobalt grades less.

Ruixin SR8C and SR10C are available as carbide tips for shearer and roadheader picks in standard and custom dimensions. Send your current tip geometry and grade designation for a direct replacement recommendation.

For a deeper understanding of how grain size interacts with cobalt content to produce specific failure modes, see our cemented carbide guide covering the WC-Co composite mechanism in detail.

Frequently Asked Questions

How do I choose the right cobalt content for coal shearer and roadheader picks?

Match cobalt percentage to your primary failure mode. If picks fracture on hard inclusions, increase cobalt. If picks wear to a rounded edge before fracture, decrease cobalt. For most mixed-ground operations, start at 9-11% cobalt with Ruixin SR8C and adjust based on field observation. The three cobalt ranges are: 6-8% for high-abrasion dry cutting (SR7X), 9-11% for mixed ground (SR8C), and 12-13% for blocky impact ground (SR10C).

What is the difference between SR7X and SR8C?

SR7X uses approximately 6% cobalt with a fine 1.0-1.2 µm grain size at HRA 91.0, optimized for maximum wear resistance in homogeneous abrasive ground. SR8C uses approximately 10% cobalt with a coarser 2.0-3.0 µm grain size at HRA 89.0, offering a balanced wear-toughness profile. The key difference is that SR8C survives impact loads that would fracture SR7X, at the cost of 10-15% faster wear in purely abrasive rock.

Which cobalt percentage performs best under high-impact conditions?

For high-impact conditions — roadheader cutting in fractured sandstone, shearer operation in seams with quartz or pyrite stringers — use 12-13% cobalt. Ruixin SR10C at HRA 88.0 with flexural strength ≥ 2,200 MPa provides the binder volume needed to arrest cracks before they propagate through the tip. This is the correct choice when fracture is your primary failure mode.

How does cobalt content affect carbide performance in wet vs. dry cutting?

In dry cutting, lower cobalt (6-8%) extends tip life because there is no water to accelerate binder erosion and thermal cycling is less severe. In wet cutting with water spray, medium cobalt (9-11%) performs better because the binder has enough toughness to survive temperature fluctuations at the cutting edge. Ruixin SR8C at 10% cobalt is the recommended starting point for water-assisted cutting operations.

What causes premature carbide tip failure in roadheader picks?

The most common cause is cobalt mismatch to ground conditions. A 6% cobalt grade used in blocky ground will fracture on the first hard inclusion. A 13% cobalt grade used in dry abrasive sandstone will wear out 50-80% faster than necessary. The second most common cause is operating speed — running any grade above 3 m/s cutting speed without adequate cooling causes thermal binder washout, reducing tip life by 40-60% regardless of cobalt percentage.

Can I use the same cobalt content for both shearer and roadheader picks?

Not necessarily. Shearer picks typically operate at higher cutting speeds (3-4 m/s) in coal seams with occasional hard bands, favoring 9-11% cobalt. Roadheader picks operate at lower speeds (1-2 m/s) but often encounter harder, more fractured rock, sometimes requiring 12-13% cobalt. Evaluate each machine’s ground conditions separately rather than standardizing on one grade across all equipment.

Does a harder grade always last longer?

No. In impact-dominated conditions, a harder grade (higher HRA, lower cobalt) will fail faster than a softer grade because it fractures rather than wears. The correct measure of “lasts longer” depends on which failure mode stops the pick from cutting. In blocky ground, SR10C at HRA 88.0 outlasts SR7X at HRA 91.0 despite being softer, because it survives impacts that would destroy the harder grade.

Get a Custom Grade Recommendation

Every mine and tunnel has unique geology. The three-range framework above covers 90% of standard conditions, but your operation may fall in the remaining 10% — or may benefit from a custom cobalt percentage tailored to your specific wear pattern and ground profile.

Send us your application details: rock type and UCS range, machine model and cutting speed, current grade and failure photos. Our engineers will confirm the optimal cobalt content for mining picks wear resistance and recommend the corresponding Ruixin grade, with sample dimensions available within two weeks.

Contact: info@ruixintungstencarbide.com | WhatsApp: +86-15253178777