Jaw Crusher eccentric Shafts

Detailed Introduction to the Eccentric Shaft Component of Jaw Crushers

I. Composition and Structure of the Eccentric Shaft

1. Shaft Necks: Divided into the main shaft neck and eccentric shaft neck. The main shaft neck is a cylindrical part matching the frame's bearing housing, serving as the rotation center, requiring high cylindricity and surface precision. The eccentric shaft neck connects to the swing jaw bearing, with its axis offset from the main shaft neck's axis by an eccentricity (typically 1/4–1/3 of the shaft diameter). This eccentricity converts rotational motion into the swing of the movable jaw.
2. Shaft Body: The intermediate part connecting the main shaft neck and eccentric shaft neck, often stepped or cylindrical. Large eccentric shafts may have weight-reduction grooves on the shaft body (reducing weight without compromising strength). Some shaft bodies feature keyways for positioning keys of flywheels or pulleys.
3. Transition Fillets: Connections between the main shaft neck, eccentric shaft neck, and shaft body use large-radius transition fillets (usually R ≥ 5 mm) to reduce stress concentration and prevent fatigue fracture (these are structurally weak areas).
4. End Faces: Both end faces of the shaft are machined flat to serve as positioning references for flywheels and pulleys. Some end faces have center holes (for thimble positioning during machining).

II. Casting Process of the Eccentric Shaft

1. Mold Preparation

• Sand casting (resin sand) is used. Wooden or metal patterns are made based on the shaft structure, with an 8–12 mm allowance for forging/machining (accounting for casting shrinkage and subsequent processing needs).

• The mold cavity is equipped with a reasonable gating and riser system to ensure full filling of molten metal. Large shafts use stepwise pouring to avoid shrinkage cavities and porosity.

2. Melting and Pouring

• High-quality pig iron and scrap steel with low phosphorus and sulfur content are melted in a medium-frequency furnace, producing alloy cast steel (e.g., ZG35CrMo) with controlled chemical composition (C: 0.32–0.40%, Cr: 0.8–1.1%, Mo: 0.15–0.25%).

• Pouring temperature is controlled at 1520–1560°C, using bottom pouring to ensure stable filling and prevent gas entrainment or inclusions.

3. Shakeout and Heat Treatment

• The casting is shakeout after cooling to below 300°C. Risers are removed, and annealing is performed (heated to 650–700°C, held for 4–6 hours, then slowly cooled) to eliminate casting stress.

• After rough machining, quenching and tempering are conducted: heating to 850–880°C for oil quenching, followed by tempering at 550–580°C to obtain a tempered sorbite structure with hardness 220–260 HBW and tensile strength ≥ 700 MPa.

III. Manufacturing Process of the Eccentric Shaft (Forged Parts)

1. Forging Process

• High-quality alloy structural steel billets (e.g., 40CrNiMo) are heated to 1100–1200°C and subjected to free forging, using drawing and upsetting processes to form the shape, ensuring internal density and freedom from forging cracks.

• Spheroidizing annealing (held at 780–800°C, slowly cooled) is performed after forging to reduce hardness and improve machinability.

2. Rough Machining

• The main shaft neck, eccentric shaft neck, and shaft body are rough-turned on a lathe or CNC lathe, leaving a 3–5 mm finishing allowance, with diameter tolerance controlled at ±1 mm.

• Center holes are drilled in the shaft ends as positioning references for subsequent processing.

3. Semi-Finishing

• Using center holes for positioning, the main and eccentric shaft necks are finish-turned to near-design dimensions (0.5–1 mm grinding allowance remaining), ensuring cylindricity ≤ 0.1 mm and eccentricity deviation ≤ 0.05 mm.

• Keyways are milled: machined on the shaft body or ends with width tolerance ±0.05 mm, depth tolerance ±0.1 mm, and groove bottom roughness Ra ≤ 6.3 μm.

4. Finishing

• Grinding of main and eccentric shaft necks: External cylindrical grinding machines are used to achieve IT6 dimensional tolerance, surface roughness Ra ≤ 0.8 μm, roundness ≤ 0.005 mm, and axis straightness ≤ 0.01 mm/m.

• Precision grinding of end faces: Ensuring perpendicularity to the axis ≤ 0.02 mm/100 mm.

IV. Quality Control Process of the Eccentric Shaft

1. Material Inspection

• Spectral analysis of raw materials is conducted before forging/casting to verify chemical composition compliance. Tensile and impact tests are performed on samples to ensure mechanical properties meet standards (e.g., 40CrNiMo after tempering requires impact energy ≥ 60 J).

2. Internal Quality Testing

• 100% ultrasonic testing (UT) is performed on forgings, prohibiting internal defects ≥ φ2 mm. Magnetic particle testing (MT) is applied to stress concentration areas such as shaft neck transition fillets to ensure no surface cracks.

3. Machining Precision Inspection

• Shaft neck diameters are measured with micrometers, and roundness/cylindricity with dial indicators. Eccentricity is checked with an eccentricity gauge, requiring deviation within ±0.03 mm of the design value.

• A coordinate measuring machine verifies keyway position accuracy, ensuring symmetry error with the axis ≤ 0.05 mm.

4. Pre-Assembly Verification

• Dynamic balance testing is conducted (rotational speed ≥ 1500 r/min) with residual unbalance ≤ 10 g·cm. Trial assembly with bearings and flywheels ensures proper fit clearance (H7/js6 for main shaft neck and bearing).