In coal mining, the rapid wear and tear of picks is often the invisible killer that causes high equipment maintenance costs - choosing the wrong material may cause the purchase price difference to be swallowed up by the cost of frequent replacement within three months.
1. Why is the material selection of coal picks more important than imagined?
Coal shearer picks are in direct contact with coal seams and rock formations, and their failure modes usually show three types:
- Alloy head fragmentation: Commonly seen when working in hard rock formations, it is directly related to the cemented carbide material grade of the pick.
- Tooth shank wear: more likely to occur in medium-soft coal seams, related to the hardenability of the steel and the surface treatment process
- Overall fracture: mostly due to the impact load exceeding the design endurance range, involving structural strength and welding quality. Among them, early failures caused by material problems account for the highest proportion. For example, when dealing with sandstone gangue layers, the hardness of the alloy head of ordinary coal picks is less than HRC40, which may cause chain damage.
Key conclusion: Picks are not consumables. Choosing the right material can extend the service life by 3-5 times
2. Conversion logic from coal seam hardness to pick parameters
Pick performance matching needs to consider two dimensions at the same time:
- Coal seam characteristics
- Lignite/bituminous coal: focus on the bending strength of the shank
- Anthracite/Hard Rock: Prioritize alloy head hardness and impact resistance
- Equipment parameters
- Cutting power determines shank diameter
- Drum speed affects tooth head geometry
For example, the U92 sandstone pick adopts a 42CrMo steel shank and an HRC40+ alloy head, which is specially designed to deal with gangue inclusion conditions in mining areas. The streamlined design of the pick-shaped pick is more suitable for coal crushing operations of high-speed drums.
Key conclusion: It is only scientific to measure the Mohs hardness of the coal seam first and then back-deduct the parameters of the pick
3. How to avoid the pick selection trap under different working conditions?
Based on the risk of failure in common scenarios, you can choose from the following triage options:
- Hard rock fire protection conditions
- When choosing hard rock anti-spark picks or alloy picks, focus on checking:
- The alloy head contains tungsten ≥30%
- Tooth shank with quenching hardened layer
- Overall impact resistance test report
- High water content coal seam
Wear-resistant shearer gear sleeves are required to avoid corrosion and wear:
- The service life of the stainless steel gear sleeve is 2 times that of the ordinary model
- Pay attention to the matching tolerance with the gear seat
- Composite rock formation excavation
- Tunnel boring machine picks and shearer picks cannot be mixed:
- Excavation tooth impact frequency is higher
- The design difference between the intercept distance is obvious
Key conclusion: The more complex the working conditions, the more customized parameter combinations are needed
4. Pick peripheral accessories that are easily overlooked
The performance of cutting picks depends on the coordination of supporting systems, and these links are often underestimated:
- Gear seat matching
- If the tolerance of the circlip groove of the pick holder exceeds the standard, it will cause:
- Radial runout after pick installation
- Abnormal vibration accelerates wear
- It is recommended to check the gear seat wear every 500 hours
- Welding process
Automated pick welding equipment can ensure:
- The brazing temperature is stable at 650±10℃
- Metallurgical bonding strength of alloy head and tooth shank
- 40% longer life than manual welding
Key conclusion: The accuracy of the supporting system determines the actual performance of the pick
5. How does the welding process affect the service life of the pick?
Three detailed misunderstandings in on-site operations:
- Insufficient preheating
Direct high-temperature welding will cause the grains of the 42CrMo steel shank to become coarse. It is recommended:
- Preheat at 250℃ for 30 minutes
- Gradient heating to brazing temperature
- Cooling too fast
- Naturally cool to 150℃ and then air cool
- Water cooling or compressed air quenching is prohibited
- Missing post-weld treatment
- Stress relief annealing is required
- Check welds for pore defects
Key conclusion: No matter how good the material is, it will be in vain if the pick has poor welding quality
The essence of purchasing coal picks is to calculate the general ledger - the initial purchase cost savings may be doubled in downtime and replacement frequency three months later. For high-working-condition products such as hard rock anti-spark picks, it is recommended to evaluate the comprehensive cost based on annual ton coal consumption, rather than simply comparing unit prices.
