The shear bolt is an inconspicuous yet central component in demolition and extraction technology. As a mechanical safety component, it protects power units and attachments from overload by failing at a defined shear load, thus acting as a predetermined breaking point. Especially under harsh operating conditions—such as in concrete demolition, rock demolition and tunnel construction, or natural stone extraction—the shear bolt prevents consequential damage to expensive assemblies. In applications with concrete demolition shears and stone and concrete splitters, it often provides an additional safety layer alongside hydraulic pressure limiting, ensuring planned downtimes instead of uncontrolled failures.
Definition: What is meant by a shear bolt
A shear bolt is a pin, bolt, or special screw deliberately designed to break when a specific shear force is exceeded. This function as a mechanical overload protection prevents damage to shafts, couplings, levers, linkages, or housings. Unlike fatigue-resistant fasteners, the shear bolt is intentionally sized weaker and is inexpensive to replace, setting defined limits for torque, axial, or transverse loads. In practice, cylindrical dowel pins, locating pins, shear bolts, or shear screws are used; they operate in single or double shear depending on the support and component stack-up.
Function and use in demolition technology
In demolition and extraction practice, the shear bolt protects machines, attachments, and hydraulic power units from load spikes caused by blockages, operator error, material inhomogeneities, or impact loads. It operates purely mechanically and responds immediately, even when sensors or hydraulic valves do not react quickly enough. The combination of hydraulic pressure limiting and a shear bolt has proven effective in creating redundancy and lowering the risk of costly structural or gearbox damage.
Shear bolt in concrete demolition shears
In concrete demolition shears, load spikes are caused, for example, by reinforcement layers, embedded components, or skewed component geometries. Shear bolts are typically found in kinematic chains, bolted joints, or couplings to protect lever arms, bearing locations, and cylinder connections from overload. In addition to pressure limiting in the hydraulic system, the shear bolt limits the mechanical ultimate load of the shear—if it breaks in a controlled manner, cylinders, bearing blocks, and jaws remain protected.
Shear bolt in stone and concrete splitters
When splitting concrete or rock in a controlled manner, high local stresses act on wedges, spreading elements, and cylinder supports. A shear bolt can serve as a predetermined breaking point in the force transmission (e.g., between the cylinder and the wedge pack). This concept protects the load paths when the splitting process is unexpectedly impeded by cracks, inclusions, or edge hang-ups.
Use in other product groups
Combination shears, steel shears, tank cutters, and multi cutters may also incorporate shear bolts, for example in drive or joint connections, to compensate for shock-like torque peaks. In hydraulic power units, shear bolts are found on couplings between the drive and the pump, preventing a seizing driven component from damaging the entire drivetrain.
Design, materials, and manufacturing
The configuration of a shear bolt follows a clear target metric: the defined break torque or break force. Geometry, material, and surface condition are selected so that shear stress governs over tensile and bending stresses and the fracture occurs cleanly and predictably.
Geometry and fit
- Cylindrical pin shape with constant diameter for reproducible shear planes.
- Single or double shear depending on support; double shear increases the allowable limit load.
- Fit matched to the bore (clearance or transition fit) to minimize notch effects and unintended bending moments.
- Targeted neck-downs where appropriate for clearly defined fracture locations.
Materials and heat treatment
- Quenched-and-tempered steels for reproducible shear strength and controlled fracture behavior.
- Stainless steels for corrosive environments (e.g., concrete slurry, salt-laden air in tunnel construction).
- Surfaces free of sharp notches; chamfered edges and suitable roughness to avoid crack initiation sites.
Corrosion and wear protection
Corrosion can reduce the effective cross-sectional area and unintentionally lower the fracture level. An appropriate material selection, corrosion protection (e.g., coated surfaces), and regular inspection are essential, particularly for equipment frequently exposed to water, sludge, and fine dust.
Design and calculation
Sizing is based on the force to be limited or the maximum permissible torque. Key influencing factors include the shear area (diameter, number of shear planes), the material’s shear strength, the static or dynamic load profile, and the temperature and environmental conditions. A safety factor is chosen so that the shear bolt reliably fails before costly components, while avoiding nuisance trips under normal loads.
Interaction with hydraulic systems
For hydraulically actuated tools—such as concrete demolition shears or stone and concrete splitters—the shear bolt’s fracture load must be coordinated with the set system pressure and the effective piston area. Pressure spikes due to impacts (e.g., from jamming) can far exceed static pressure; therefore, the combination of a pressure relief valve and a mechanical shear bolt is a robust solution for shock loads.
Influence of support
Eccentric loads or clearance in the bore introduce bending moments in the pin, altering the fracture behavior. The most centralized force introduction possible and suitable bushings or sleeves improve the reproducibility of actuation.
Installation, replacement, and maintenance
The greatest benefit of a shear bolt lies in its quick, safe replacement. A clearly defined procedure increases availability and prevents secondary damage.
- Identification: Document type, dimensions, material designation, and fracture load unambiguously.
- Depressurize: De-energize the tool, set down the load, secure energy accumulators.
- Removal: Fully remove fracture remnants, clean the bore, and check for spalling, burrs, or out-of-roundness.
- Inspection: Check attachments (bushings, lugs, levers) for cracks, plastic deformation, and wear marks.
- Installation: Insert the bolt without stress, ensure correct alignment, and properly install retaining elements (e.g., cotter pin).
- Documentation: Record installation time and part batch to analyze service life.
Typical failure patterns and diagnosis
- Inclined fracture: Indicates bending due to clearance or eccentricity.
- Ragged fracture surface: Possible crack initiation and growth due to vibration or corrosion.
- Premature fracture: Fracture load too low, wrong material, section loss due to corrosion, or pressure spikes outside design.
- No fracture despite overload: Shear area too large, material too high-strength, unintended load bypass.
Safety and legal aspects
As a safety component, the shear bolt is part of a machine’s overall safety concept. Adhering to the intended specification, using suitable spare parts, and proper installation are essential. Information on inspection intervals and operating limits should always be understood as general guidance; it does not replace manufacturer-specific instructions or legal requirements. Modifications to protective devices may only be undertaken after careful evaluation and within applicable regulations.
Practical relevance in application areas
Concrete demolition and special deconstruction
During selective deconstruction, unpredictable load jumps occur when components are removed unevenly or reinforcement tears. Shear bolts reduce the risk of damage to pin bearings or jaws on concrete demolition shears.
Strip-out and cutting
When cutting profiles, tanks, and pipelines, edge hang-ups and springback can cause blockages. Shear bolts protect the kinematics of combination shears, steel shears, multi cutters, and tank cutters from torque spikes.
Rock demolition and tunnel construction
In rock, wedges can jam or stresses can redistribute abruptly. In stone and concrete splitters, the shear bolt acts as a defined mechanical safety valve to preserve cylinder connections and wedge packs.
Natural stone extraction
When separating natural stone slabs, controlled load limiting is important to protect the workpiece, tool, and equipment. A correctly designed shear bolt enables reproducible interventions without compromising process quality.
Special applications
For special tasks with atypical materials or temperature ranges, the shear bolt provides simple, reliable, and passive protection—independent of sensors or controls.
Distinction from alternative protection concepts
- Hydraulic pressure limiting: Protects the hydraulic circuit but may not always respond sufficiently to very rapid shock loads.
- Slip clutches/torque limiters: Effective continuously and repeatedly, but more complex and maintenance-intensive.
- Electronic monitoring: Detects trends (e.g., pressure, displacement, force) but does not replace a mechanical predetermined breaking point.
In practice, these measures complement each other. A robust overall concept combines hydraulic, mechanical, and organizational protection layers.
Service life, spare parts inventory, and operating costs
The cost of a shear bolt is low compared to damage to cylinders, jaws, or housings. A sensible spare parts inventory includes graded fracture loads for different use cases, corrosion-resistant variants for wet environments, and documented installation instructions. By evaluating replacement history, both design and operating practices can be optimized.
Relevance for the Darda GmbH product world
In the Darda GmbH product world, the shear bolt primarily serves as a protective mechanism where high forces are transmitted via levers and joints: in concrete demolition shears for controlled fragmentation and in splitting with stone and concrete splitters. Additionally, shear bolts can be used in drive connections of hydraulic power units as well as in combination shears, steel shears, multi cutters, and tank cutters to safeguard critical components against shock overloads. This assignment serves for technical classification and does not replace product- or series-specific details.
Planning and training
Proper operator training reduces misuse that leads to unnecessary activations. In deployment planning, choosing the correct fracture load—tailored to concrete strength, reinforcement ratio, rock characteristics, and tool geometry—helps balance protection and availability. Clear labeling of bolts and standardized replacement procedures shorten downtimes.
Quality assurance and documentation
For reproducible behavior, batch traceability, dimensional inspections, and visual inspections of fracture surfaces are helpful. Deviations—such as unusual fracture appearances or widely fluctuating service lives—should be documented and investigated for causes such as corrosion, geometric deviations, or changed process forces.