JB/T 7687.2-2008 Crane Drum Brake Standard Guide
JB/T 7687.2-2008 "Lifting Appliances — Brakes — Part 2: Drum Brakes" is the dedicated standard for drum brakes used in cranes. It specifies the structural types, technical requirements, performance parameters, test methods, and inspection rules for drum brakes, and is applicable to normally closed type drum brakes used in various mechanisms of lifting appliances.
JB/T 7687.2-2008 is Part 2 of the JB/T 7687 series for drum brakes in lifting appliances, specifically defining the technical specification for this brake type. Drum brakes are among the most widely used braking devices across crane mechanisms. This article provides a systematic review of the key technical requirements set out in the standard.
Standard Scope and Drum Brake Characteristics
JB/T 7687.2-2008 is the second part of the JB/T 7687 series, dedicated to the technical requirements for drum brakes. Also known as brake shoe brakes, drum brakes are the most traditional and commonly used brake type on cranes — the brake shoes are pressed against the outer cylindrical surface of the brake wheel by spring force to generate braking torque, and the brake is released by an electromagnet or hydraulic push rod that overcomes the spring force. The advantages of drum brakes include a simple and reliable structure, high braking torque, low manufacturing cost, and ease of adjustment and maintenance. Their main drawback is poor heat dissipation from the brake wheel — continuous braking causes temperature rise that can reduce the friction coefficient of the brake lining — making them suitable for non-frequent braking applications such as cranes in duty classes A1 to A5. Drum brake wheels range from 160 mm to 800 mm in diameter, with corresponding braking torque from 100 N·m to 20,000 N·m.
Structural Types
The standard defines two primary structural types of drum brakes: short-stroke electromagnet drum brakes and long-stroke electromagnet drum brakes. In a short-stroke electromagnet drum brake, the electromagnet is mounted directly on the brake arm (stroke ≤ 5 mm), offering a compact structure and fast response (pick-up time ≤ 0.2 s); this type suits applications requiring low braking torque (brake wheel diameter ≤ 400 mm). In a long-stroke electromagnet drum brake, the electromagnet drives the brake arm through a lever system, providing a larger braking stroke (10–50 mm); this type is intended for high braking torque applications (brake wheel diameter 400–800 mm). Hydraulic push rod drum brakes use a hydraulic push rod instead of an electromagnet as the releasing actuator. The hydraulic push rod operates smoothly without impact and with low noise, but has a longer response time (≥ 0.5 s), making it suitable for applications requiring smooth braking, such as VFD-controlled cranes.
Technical Requirements
The standard sets out specific performance requirements for drum brakes: Braking torque — at rated opening clearance, the braking torque must not be less than 90% of the nominal value. Brake spring — spring material 60Si2Mn or 50CrVA, with a quenched hardness of HRC 42–47 after heat treatment. The spring must withstand 300,000 compression cycles at maximum working load without permanent deformation. Brake lining — friction coefficient μ ≥ 0.35 (at temperatures ≤ 200 °C and pressure ≤ 1.0 MPa). Lining thickness ≥ 5 mm. Brake wheel — material ZG 310-570 or 45# steel, surface hardened to HB 280–350, with a hardened layer depth of ≥ 2 mm. The working surface roughness of the brake wheel must be Ra ≤ 1.6 μm.
Testing and Inspection
Before delivery, each drum brake must pass the following tests: braking torque test (actual torque ≥ nominal value), open-close test (100 consecutive cycles without failure), spring life test, and insulation resistance measurement (≥ 1 MΩ). After installation, the user should make the following adjustments: brake shoe-to-wheel clearance of 0.5–1.5 mm on each side, and spring compression adjusted to the specified torque per the manufacturer's manual. Kelude heavy industry cranes are equipped with high-quality drum brakes, and the hoisting mechanism is fitted with a double-brake system — two independent brakes operating simultaneously, so that if either brake fails, the other can independently brake the rated load.
Drum Brake Technical Parameter Comparison Table
The comparison table below lists the core parameter configurations for drum brakes, for reference during selection and operation.
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| Specification | Braking torque(N-m) | Brake wheel Span(mm) | applicable mechanism |
|---|---|---|---|
| YWZ-200 | 160-250 | 200 | Hoisting mechanism |
| YWZ-300 | 400-630 | 300 | Long Travel / Bridge Travel |
| YWZ-400 | 1000-1600 | 400 | Crane Bridge/Trolley |
| YWZ-500 | 2500-4000 | 500 | crane travel |
