Toothing / interlock describes both the coupling of teeth for power and motion transmission (for example in gears, pinions, and racks) and the deliberate toothing of gripping and cutting edges on tools. In the context of concrete demolition, special demolition, rock excavation, and natural stone extraction, toothing determines how reliably forces are introduced, components are held, and materials are separated. In tools and equipment from Darda GmbH—such as concrete demolition shears or stone and concrete splitters—the correct toothing in the form of tooth profiles, serrations, or form-fit drives is a key factor for process reliability, precision, and service life.
Definition: What is meant by toothing / interlock
Toothing refers to the periodic profile of teeth and tooth spaces that is brought into mutual form-fit engagement on at least two components. The aim is to transmit torque, force, or motion with defined backlash and controlled contact stresses. Classic examples are spur gear pairs, helical gears, bevel and planetary gear sets, as well as rack–pinion. In a broader sense, toothing also includes functional gripping tooth patterns on jaws, blades, or shear edges that increase frictional and form-fit locking, minimize slippage, and thereby introduce controlled load paths into the workpiece.
Fundamentals of force transmission in toothing
In mesh, tooth flanks contact along a defined line. The involute geometry ensures an almost constant transmission ratio and a uniform distribution of rolling and sliding. Decisive factors are contact pressures, surface pressure, and the micro-slip fraction; they determine efficiency, heating, noise, and wear. In gripping toothing, the tooth tip acts as a micro-wedge: it increases local pressure, creates micro-notches in the material composite (e.g., the concrete matrix), and stabilizes the grip against transverse forces.
Geometry and terminology of toothing
The performance of a toothing is defined by its macro- and micro-geometry. Important features include:
- Pitch and module: define tooth size and load capacity
- Pressure angle and profile shift: influence contact pattern, backlash, and root strength
- Helix angle and face width: determine smooth running and load distribution
- Addendum and dedendum diameters, tip clearance: avoid interference and scuffing
- Lead and profile modifications: compensate deflection, temperature, and manufacturing tolerances
- Surface roughness, hardness profile, and surface layer strength: govern wear behavior and pitting resistance
Toothing / interlock in concrete demolition and special demolition
In concrete demolition shears, combi shears, and multi cutters, gripping and cutting edges are often executed with a functional toothing. It increases holding force on highly heterogeneous surfaces, guides the bite in a controlled manner, and protects against unintended slipping. When severing reinforced concrete, the toothing stabilizes the position relative to the component, while the blades progressively cut through the matrix and reinforcement. In thick members, a defined load path is established via the toothing, which safely channels transverse and torsional loads into the tool body.
Concrete demolition shears: teeth, gripping edges, and load paths
The geometry of the gripping teeth (tooth form, pitch, rake/attack angle) influences bite, crack initiation in concrete, and control over reinforcing bars (rebar). Finer-toothed areas grip reliably on smooth surfaces; coarser teeth generate greater penetration depth in rough material. Rounded tooth edges reduce notch stresses in the tool, while defined tips improve the form-fit. A balanced tooth height minimizes local over-pressures and reduces edge wear.
Stone and concrete splitters: toothed contact surfaces and wedge action
Stone and concrete splitters work on a wedge-based principle. Toothed or ribbed support surfaces on struts and counter-bearings increase frictional grip and prevent the tool from wandering under load. The toothing directs the input forces into the rock body, while the splitting wedge expands in a controlled manner and the separation joint grows along existing planes of weakness.
Application in strip-out and cutting
When dismantling sheets, tanks, or profiles—e.g., with steel shears or tank cutters—serrated gripping surfaces stabilize the workpiece ahead of the cut. The toothing reduces the need for additional holders by channeling transverse forces into the component and keeping the cutting edges in position. In building strip-out, this enables clean separations with minimal rework.
Toothing in hydraulically driven tools
Hydraulic tools utilize toothing on two levels: as drive toothing in gearboxes, slew drives, or (depending on power unit type) gear pumps, and as functional toothing on gripping or cutting edges. Rotary modules can operate via ring gears and pinion torque; this is how shear heads are positioned or workpieces are oriented. In hydraulic power units, toothing in pumps or couplings shapes power transmission. The execution of the toothing determines starting torque, response speed, and smooth running.
Tolerances, backlash, and noise
Backlash is necessary to compensate thermal expansion, lubricant films, and manufacturing scatter. Too little backlash increases the risk of scuffing and noise; too much backlash causes impact, degraded contact pattern, and positioning errors. In gripping toothing, excessive play manifests as fluctuating grip and uncontrolled load spikes.
Load transmission, wear, and lubrication
Typical wear mechanisms include abrasion, micro-pitting, and adhesive scuffing. Dust, slurries, and corrosive media from concrete and rock burden flanks and tooth backs. A hard, tough surface layer with suitable lubrication reduces material removal. For gripping toothing, periodic cleaning is essential: sintered-in particles alter contact conditions and heighten uncontrolled notch effects.
- Regularly perform visual inspections of teeth and flanks; assess the contact pattern
- Document wear dimensions; define limit values on a project-specific basis
- Gently rework damaged tooth areas; break sharp burr edges
- Keep lubrication points clean; apply suitable lubricants as required
- If unusual noises or vibrations occur, systematically narrow down the root cause
Materials and heat treatment
Alloyed quenched-and-tempered or case-hardening steels are used for highly loaded toothing. A hard surface with a tough core (e.g., by case hardening, induction hardening, or nitrocarburizing) increases pitting and wear resistance without compromising fracture safety. For gripping toothing, replaceable wear strips enable economical maintenance.
Manufacturing and quality assurance
Tooth profiles are produced by, among other methods, hobbing, shaping, broaching, or grinding. Micro-geometric modifications are deliberately introduced to avoid peak loads. Quality assurance includes measurements of pitch, lead, and profile, contact pattern checks, and surface inspections. For gripping toothing, reproducibility of tooth shape, edge radius, and roughness depth are decisive, as they determine bite and service life.
Failure modes and diagnostics
Unusual noises, increased power loss, uneven chips, or crumbling edges indicate faulty toothing. In gripping toothing, polished areas point to slip, while dull, torn surfaces signal overload or abrasive media.
- Local breakouts at the tooth root: indication of notch stresses or vibratory fatigue cracks
- Streaky material removal: foreign particles, contaminated lubricants
- Blotchy contact pattern: misalignment, inadequate modifications
- Hollow sound, rattling: excessive backlash, bearing tolerances exceeded
Planning and selection for use
The correct toothing depends on material, component geometry, and process control. In concrete demolition and special demolition, robust gripping toothing with a resistant surface layer is advantageous. For stone and concrete splitters, slip-resistant tooth profiles support wedge action. In strip-out and cutting, defined tooth forms secure the cutting position on sheets and profiles. For rotating assemblies, a toothing with smooth running, tailored modifications, and sufficient backlash is recommended for changing temperature and load conditions.