Coke Vibration Screen Maker Specification: Engineering Parameters, Design Criteria, and Operational Considerations

Introduction

In the metallurgical and chemical industries, coke serves as both a fuel and a reducing agent in blast furnaces and foundry cupolas. The physical quality of coke—specifically its size distribution, uniformity, and mechanical strength—directly influences permeability in the furnace burden and the efficiency of the smelting process. To achieve the required size fractions (typically 25–40 mm for blast furnace use, 10–25 mm for foundry, and 0–10 mm for fines), coke must undergo rigorous screening after quenching and crushing. The equipment responsible for this separation is the coke vibration screen—a heavy-duty, high-capacity, linear or circular motion screening machine engineered to handle abrasive, hot, and impact-laden feed.

This article provides a comprehensive specification framework for a coke vibration screen maker, detailing the mechanical design, material selection, motion characteristics, screening efficiency, safety features, and quality assurance protocols. The specification is intended for manufacturers, procurement engineers, and plant operators who require a standardized, performance-based technical document.

1. Scope and Application

The specification covers the design, fabrication, testing, and supply of a single-deck or multi-deck vibrating screen specifically for coke classification. The screen shall be capable of processing feed material with the following characteristics:

• Feed size: 0–80 mm (run-of-crush coke)
• Bulk density: 450–600 kg/m³
• Moisture content: ≤ 5% (surface moisture after quenching)
• Temperature at feed point: ≤ 80°C (peak transient up to 120°C)
• Abrasiveness: High (due to coke ash and sharp edges)

The screen must separate the feed into two or three product streams, typically:

• Oversize (>40 mm) – recirculated to crusher
• Mid-size (25–40 mm) – blast furnace grade
• Undersize (<25 mm) – further screened or sold as nut coke / fines

2. Design Basis and Performance Requirements

2.1 Capacity

The nominal capacity shall be defined at a specific feed rate (e.g., 200 t/h) with a separation efficiency of ≥ 90% for the critical cut point. The maker must provide a capacity curve based on:

• Screen width and length
• Deck inclination (typically 15°–25° for circular motion, 0°–10° for linear motion)
• Stroke amplitude (6–12 mm)
• Vibration frequency (700–1000 rpm for circular; 800–1200 rpm for linear)

2.2 Separation Efficiency

The screen shall achieve a partition curve with a sharpness index (S.I.) of ≥ 1.5, where S.I. = d75/d25 (the size at 75% and 25% recovery to oversize). The maker must guarantee that the oversize fraction contains less than 5% of undersize material (by weight) and that the undersize fraction contains less than 3% of oversize material.

2.3 Screening Area

The effective screening area (m²) is calculated using the standard formula:
A = (Q × F) / (C × K)
Where:

• Q = feed rate (t/h)
• F = material factor (for coke, 0.8–1.0)
• C = base capacity per m² (t/h/m²) at 50% oversize and 25 mm aperture
• K = correction factor for aperture size, deck slope, and moisture

The maker shall provide a detailed calculation sheet with all correction factors.

3. Mechanical Construction and Materials

3.1 Screen Body (Deck Frame)

The screen body shall be fabricated from high-strength structural steel (e.g., S355J2+N or equivalent) with a minimum yield strength of 355 MPa. The side plates shall be at least 10 mm thick, reinforced with welded stiffeners to prevent flexural fatigue. All welds shall be continuous, full-penetration, and subject to magnetic particle inspection (MPI) for critical joints.

3.2 Screen Mesh / Panels

Coke screening demands wear-resistant, impact-tolerant media. The maker shall offer the following options:

• Polyurethane panels with a hardness of 90–95 Shore A, reinforced with steel inserts. Aperture tolerance: ±0.5 mm. Recommended for final sizing (25 mm and below).
• Self-cleaning rubber panels (tensioned or modular) with a Shore A hardness of 60–70, designed to reduce blinding from sticky fines.
• Woven wire mesh (high-carbon spring steel, 65Mn) for coarse screening (>40 mm), with a wire diameter of 8–12 mm and a crimped or welded construction.

All panels must be easily replaceable from the top side, with a quick-release fastening system (wedge or pin type) to minimize downtime.

3.3 Vibration Mechanism

Two types of vibration exciters are acceptable:

• Circular motion – achieved by a single eccentric shaft with two bearings, mounted at the center of gravity. The shaft shall be forged from alloy steel (42CrMo4), heat-treated to 280–320 HB, and dynamically balanced.
• Linear motion – achieved by two counter-rotating vibrator motors or a single exciter with two shafts. The resultant motion angle shall be 45° ± 5° relative to the deck surface.

The exciter shall be protected by a labyrinth seal and a positive-pressure oil lubrication system (or grease for smaller units). Bearing life (L10) shall be ≥ 30,000 hours at full load.

3.4 Springs and Suspension

The screen shall be supported on four or eight helical steel springs (or rubber shear mounts) designed to isolate 90% of the dynamic forces from the supporting structure. The natural frequency of the spring system shall be at least 3 times lower than the operating frequency to avoid resonance. Spring material: chrome-silicon steel (55CrSi) with shot-peened surfaces.

3.5 Drive System

• V-belt drive with a guard, powered by a TEFC (totally enclosed fan-cooled) induction motor (IP55, F-class insulation).
• Motor power: calculated based on total vibrating mass (screen body + material) and required acceleration (typically 4–6 g).
• A flexible coupling (or cardan shaft) shall be used between the motor and the exciter to accommodate misalignment.

4. Operational and Safety Features

4.1 Dust and Noise Control

• The screen shall be supplied with a fully enclosed dust cover, fitted with rubber-lined inspection doors.
• Noise level at 1 meter distance shall not exceed 85 dB(A) under normal operating conditions. If exceeded, the maker must provide acoustic cladding.

4.2 Safety Interlocks

• Emergency stop buttons on both sides of the screen.
• Vibration sensors (accelerometers) with a trip setpoint at 120% of normal amplitude.
• Temperature sensors on bearings with alarm at 70°C and shutdown at 85°C.
• A safety lockout system for maintenance access to the exciter and deck.

4.3 Maintenance Accessibility

• The deck panels shall be accessible via a walkway and handrails (supplied as optional).
• The exciter shall have a removable top cover for bearing inspection without dismantling the shaft.
• Grease nipples or oil fill/drain points shall be located at the highest and lowest points of the lubrication circuit.

5. Quality Assurance and Testing

5.1 Material Certificates

The maker shall provide EN 10204 3.1 certificates for all structural steel plates, shafts, and springs. For critical welds, a welding procedure qualification record (WPQR) and welder qualification certificates must be submitted.

5.2 Factory Acceptance Test (FAT)

Before dispatch, the screen shall undergo a no-load test for a minimum of 8 hours, verifying:

• Vibration amplitude and frequency (measured with a vibrometer)
• Bearing temperature rise (≤ 40°C above ambient)
• Noise level
• Uniformity of motion across all four corners
• No abnormal resonance or vibration of the support frame

5.3 Performance Test (Optional)

If required, a wet or dry test with actual coke (or a surrogate material) shall be conducted at the maker’s facility. The test shall confirm the separation efficiency and capacity as per Section 2. The test protocol shall be agreed upon in writing prior to manufacturing.

6. Documentation and Deliverables

The maker shall supply the following documents:

• General arrangement drawing (GA) with all dimensions and weights
• Foundation plan with dynamic load data (static + dynamic forces)
• P&ID (piping and instrumentation diagram) for lubrication system
• Operation and maintenance manual (including lubrication schedule, spare parts list, and troubleshooting guide)
• CE declaration of conformity (if applicable) or compliance with local safety standards (e.g., ISO 9001, ISO 14001)

7. Warranty and After-Sales Support

• Warranty period: 24 months from commissioning or 30 months from delivery, whichever is earlier.
• The maker shall guarantee the availability of spare parts (screen panels, springs, bearings, exciter components) for a minimum of 10 years.
• On-site commissioning support: one engineer for a maximum of 5 working days, including operator training.

8. Conclusion

A coke vibration screen is not a generic screening unit; it is a specialized machine that must withstand severe impact, abrasion, and thermal cycling while maintaining precise size separation. The specification outlined above provides a rigorous, performance-based framework for a maker to design, build, and test such equipment. Adherence to these parameters ensures not only high screening efficiency and long service life but also operational safety and maintainability. For any coke plant—whether greenfield or retrofit—this specification serves as the definitive technical baseline for procurement and quality control.

Appendix: Key Specification Summary Table

This specification is intended for engineering procurement purposes. Any deviation from the stated values must be approved in writing by the purchaser’s engineering department.