coal crusher hammer manufactured from

Manufacturing the Hammer for Coal Crushers: Materials, Processes, and Critical Choices

The hammer is the core wearing component of a coal crusher, directly determining its crushing efficiency, service life, and operational economy. Its manufacturing is not a simple forging or casting job but a precise engineering process that involves selecting appropriate materials, employing specific heat treatment technologies, and implementing rigorous quality control. This article provides a detailed overview of how coal crusher hammers are manufactured, focusing on material selection, production processes, and the rationale behind these critical choices.

1. Core Material Selection

The primary requirement for coal crusher hammer materials is high wear resistance to withstand the abrasion from coal and impurities like rocks and shale. Simultaneously, they must possess sufficient toughness to resist impact fracture. Common materials fall into two main categories:

• High Manganese Steel (e.g., ZGMn13): This is a traditional material known for its exceptional work-hardening capability. Under strong impact pressure, its surface hardness increases significantly while maintaining good toughness in its core. It is particularly suitable for crushers handling large lumps or those with higher impurity content.
• Alloy Steel with High Chromium Content (High-Chromium Cast Iron/Steel): This type of material offers superior initial hardness and wear resistance compared to high manganese steel. Its wear resistance is typically 2-3 times higher under abrasive conditions. However, its toughness is relatively lower, making it more suitable for crushing smaller coal sizes or where impact conditions are less severe.

The choice between these materials depends on the specific operating conditions of the crusher (feed size, coal hardness, moisture content) and economic considerations regarding initial cost versus service life.

2. Manufacturing and Heat Treatment Process

The manufacturing process varies slightly depending on the chosen material but generally follows these key stages:

1. Casting/Forging: Hammers are primarily produced through casting (especially for high-chromium alloys and complex shapes) or forging (common for certain alloy steel hammers to achieve denser internal structure).
2. Machining: Critical mounting holes and surfaces are machined to ensure precise dimensions and balance, which is vital to prevent excessive vibration during crusher operation.
3. Heat Treatment: This is the most critical step defining the final properties of the hammer.
   • For High Manganese Steel, "Water Toughening Treatment" is essential. It involves heating the castings to around 1050-1100°C, holding them until fully austenitized, and then rapidly quenching in water. This results in a uniform austenitic structure that provides optimal toughness and work-hardening potential.
   • For High-Chromium Alloy Hammers, heat treatment typically involves quenching at high temperatures (950-1000°C) followed by tempering at 200-450°C. This process precipitates hard carbides within a martensitic matrix, achieving an excellent combination of hardness and some toughness.
4. Quality Inspection: Finished hammers undergo inspection for dimensional accuracy, hardness testing (e.g., using Brinell or Rockwell methods), and sometimes non-destructive testing like magnetic particle inspection to check for surface cracks.

3. Material Comparison Table

Feature	High Manganese Steel (e.g., ZGMn13)	High-Chromium Alloy Cast Iron/Steel
Primary Advantage	Excellent impact toughness & work-hardening ability	Superior initial hardness & wear resistance
Typical Hardness	~200 HB (as-cast), can increase to >500 HB on surface under impact	58-65 HRC (after heat treatment)
Toughness	Very High	Moderate to Good
Best Suited For	Large lump coal, high impact conditions, uncertain impurity content	Highly abrasive coal/impurities, smaller feed size, consistent conditions
Cost Consideration	Generally lower initial cost; life depends on impact for hardening	Higher initial cost; longer predictable life in suitable applications

4. Real-World Application Case: Power Plant Crusher Hammer Upgrade

Scenario: A mid-sized coal-fired power plant experienced short hammer life (approximately 600 hours) in its ring hammer crusher processing run-of-mine coal with variable shale content. Frequent replacements caused high maintenance costs and downtime.

Solution & Implementation: After analyzing failed hammers (showing both abrasion and minor impact cracks), the plant collaborated with a manufacturer to trial hammers made from a composite material. The hammer body was crafted from tough alloy steel to absorb impacts, while the wearing edges/faces were embedded with high-chromium alloy cast iron blocks.

Result: The service life of the composite hammers increased to over 1500 hours—a 2.5-fold improvement. While the unit cost per hammer was about 40% higher than the standard high manganese steel version used previously, the total cost per operating hour was reduced by approximately 35% due to fewer changeouts and less downtime. This case highlights that selecting or designing a hammer based on specific feed material analysis can yield significant economic benefits.

FAQ Section

Q1: Can we simply use harder steel to make hammers last longer?
A: Not necessarily. Excessive hardness often comes at the expense of toughness. A very hard but brittle hammer is prone to catastrophic fracture upon encountering an uncrushable object (like tramp metal), potentially causing severe secondary damage to the crusher rotor and housing.

Q2: Why do some hammers have symmetrical or reversible designs?
A: Many hammers are designed with symmetrical ends or are reversible. Once one wearing edge or corner is worn down during operation,the hammer can be rotated or flipped in place to utilize a fresh edge.This effectively doubles its usable life before requiring replacement.

Q3: How often should crusher hammers be inspected?
A: Regular visual inspection during routine maintenance shutdowns is crucial.The frequency depends on operating hours and abrasiveness of the coal.It's common practice to inspecthammer wear,cracks,and balance after processing every 50，000to100，000 tons of material，or as recommended bythe manufacturer.Wornhammers should be replaced in complete sets tomaintain rotor balance.

Q4: Is welding a viable method for repairing worn hammers?
A: Repair welding worn hammers with hardfacing electrodesisapracticed technique，particularlyforlargeand expensivehammers。However，it requires expertise.Pre-heatingand controlled post-weld coolingareessential topreventcrack formation，especiallyforhigh manganese steel.The repairedhammer must also bere-balanced.It isoften moreeconomicalforstandardhammersto simply replace them。

Q5: What role does rotor speed play in hammer selection?
A: Rotor speed significantly affectstheimpact energy.Higherspeedsgenerategreaterimpactforce，which benefits work-hardeningofhighmanganesesteelbut mayexceedthefracturetoughnessofveryhardmaterials likehigh-chromium alloys.Manufacturer's guidelines regardingoperatingspeed formaterial compatibilityshould always be followed。