Xylan coating is an established means in industrial practice to equip metallic components with a dry-lubricating, chemical- and corrosion-resistant surface. In the context of high-performance hydraulic tools from Darda GmbH—such as concrete demolition shears or hydraulic rock and concrete splitters—such thin-film systems act as functional protective and sliding layers on fasteners, pivot pins, slideways, and fittings. They help reduce friction, define assembly forces, and increase the service life of components under abrasive, moist, and alkaline operating conditions in concrete demolition, building gutting, or tunnel construction.
Definition: What is meant by xylan coating
A xylan coating is a fluoropolymer-containing thin film that is applied as an organically bound multilayer system to metal surfaces and cured at elevated temperature. Typical features include a low friction coefficient, corrosion protection, anti-stick properties, good chemical resistance, and a low film thickness often in the 10–40 µm range. Substrates include steel, stainless steel, aluminum, or cast iron; the coating is typically applied by spraying, dipping, or a drum process followed by thermal crosslinking. Primer and topcoat are often combined to specifically adjust adhesion, barrier effect, and tribological properties.
Properties and mode of action
The mode of action is based on embedded fluoropolymers that create extremely low surface energy and very good lubricity. Within an organic matrix, this yields a low-wear surface that resists moisture, chlorides, alkalis from the concrete environment, and many oils or greases. Owing to the small film thickness, component geometries are largely retained, but tolerances must be considered in design. In practice, this results in defined assembly and breakaway torques, reduced cold welding (galling) on screws and pins, and easier disassembly during service.
Relevance in concrete demolition, building gutting, and tunnel construction
In concrete demolition and special demolition, in strip-out and cutting operations, in rock excavation and tunnel construction, and in special deployments, components are continuously exposed to moisture, fine concrete dust, alkaline media, and fluctuating temperatures. Xylan coatings create a robust barrier against corrosive media and reduce buildup of cement laitance and stone flour on metallic surfaces. This particularly applies to fasteners and moving parts on concrete demolition shears, stone and concrete splitters, combi shears, multi cutters, steel shears, tank cutters, as well as on hydraulic power packs.
Application areas on concrete demolition shears and stone and concrete splitters
The application focuses on components whose function can be improved through sliding and protective effects or where assembly processes should be made reproducible. Functional surfaces that deliberately require high friction or sharp edges (for example, cutting and jaw edges) are excluded.
Suitable components
- Bolts, nuts, threaded studs: defined tightening torque, reduced embedment effects thanks to improved friction stability
- Pins, dowels, bearing surfaces: reduced galling and easier release in service
- Hydraulic fittings and adapters: anti-stick effect against dirt buildup, additional barrier against underfilm corrosion
- Covers, clamps, brackets: improved weather and splash-water protection
Not suitable zones
- Cutting, pressing, and gripping edges of concrete demolition shears
- Wedge and pressure faces on rock splitter cylinders
- Calibrated slideways where film thickness would unduly reduce clearance
Advantages and limits in harsh use
- Advantages: low friction values, controlled assembly, corrosion and chemical resistance, anti-stick against cement pastes, low film thickness, good disassemblability.
- Limits: limited temperature resistance compared with ceramic coatings, abrasive wear possible under sand/dust exposure, meticulous surface preparation is essential, masking of functional edges required.
Coating thickness, tolerances, and design notes
The film thickness should be considered early in design. For fits on pin–bearing connections or threads, the added material must be checked. In practice, the following guidelines have proven effective:
- Check and, if necessary, adjust clearance and fit conditions for coated pin/bearing surfaces with an additional 10–40 µm layer.
- Design bolted joints with friction-dependent preload using coating-specific friction values; plan for trial tightenings.
- Mask areas with line contacts or sharp edges to avoid chipping of the coating.
Friction values during assembly
Coated threads typically achieve lower and more stable friction values than untreated ones. This allows a more defined tightening torque, especially on large fasteners on concrete demolition shears or housings of stone and concrete splitters. Preferably, torque-and-angle or preload-controlled tightening methods are used to minimize scatter.
Surface preparation and application process
Durability stands or falls with the pretreatment. The following process steps have proven themselves:
- Degreasing and cleaning to remove oils, greases, and particles completely
- Abrasive blasting (e.g., alumina) to achieve uniform roughness and activation
- Application by spraying, dipping, or drum coating—depending on component geometry
- Curing at process-specific temperatures for full crosslinking
- Inspection of film thickness, adhesion, and appearance; documentation of process parameters
Masking and component handling
Functional edges on gripping and cutting tools are masked. Reproducible component handling prevents holidays, runs, or uneven film thickness—particularly relevant on long pins, threaded pieces, and hydraulic adapters.
Quality assurance and test methods
- Film thickness measurement (magnetic or eddy current) on planar reference surfaces
- Cross-cut test or pull-off dolly to assess adhesion on steel/stainless steel
- Corrosion tests in condensing humidity or salt spray for comparison purposes
- Tribological comparison tests (e.g., breakaway torque on bolts)
Maintenance, cleaning, and servicing
Coated components on combi shears, multi cutters, steel shears, tank cutters, and hydraulic power units should be cleaned of concrete residues with mild cleaners. Highly alkaline or strongly abrasive cleaners can accelerate coating aging. In the event of visible damage (flaking, deep scoring), replacement of the affected component or controlled recoating is recommended. Lubricants should continue to be applied where provided by design, since xylan coatings provide dry lubrication but do not fully replace every hydraulic or bearing application.
Occupational safety and environmental aspects
Application takes place in industrial processes with defined curing temperatures. The respective safety data and emission specifications of the coating facility are decisive. During tool operation, when used correctly, there are no additional requirements compared with untreated components; removed material must be disposed of in accordance with local regulations.
Selection criteria and specification
For use in concrete demolition and natural stone extraction, specifications should realistically reflect the environmental conditions. Key criteria:
- Media resistance to water, chlorides, alkaline concrete solutions, hydraulic oils
- Temperature window of the component (typical: ambient up to elevated oil temperatures)
- Required friction values for assembly/disassembly
- Permissible film thickness in fits
- Expected abrasive loading from dust/stone flour
Typical damage patterns and causes
- Chipping at edges: insufficient edge rounding or missing masking
- Underfilm corrosion: inadequate pretreatment, damaged coating
- Early wear: very high abrasive load, unsuitable application site (e.g., active slideway)
- Non-uniform torques: friction scatter due to contaminated threads or damaged coating
Combinations and alternatives
Depending on the component, xylan coatings can be combined with metallic base protection systems (e.g., zinc alloys) or with phosphating to increase adhesion and barrier performance. For highly loaded sliding surfaces, alternative hard-material or conversion coatings may be considered. For cutting and gripping edges on concrete demolition shears, steel shears, and tank cutters, wear-optimized materials and heat treatments take precedence; here, xylan serves the periphery (screws, covers, adapters).
Practical recommendations for Darda GmbH tools
- Concrete demolition shears: coat screws, pins, and hydraulic fittings; do not coat gripping and cutting edges.
- Stone and concrete splitters: protect housing screws, retaining clips, and covers; mask wedge and pressure faces.
- Combi shears, multi cutters, steel shears, and tank cutters: anti-stick for threads and cover parts to facilitate service disassembly.
- Hydraulic power packs: corrosion protection on fittings, clamps, and housing fasteners in splash-exposed zones.