Hot-dip galvanizing

Hot-dip galvanizing is a proven method for permanently protecting steel against corrosion-especially where tools and attachments operate under moisture, dirt, chlorides, and mechanical stress. In the environment of concrete demolition and special deconstruction, strip-out and cutting, rock excavation and tunnel construction, natural stone extraction as well as special applications, components of concrete pulverizers, stone and concrete splitters, combination shears, Multi Cutters, steel shears, tank cutters, and hydraulic power packs are often subjected to extreme loads. A high-quality zinc coating provides cathodic protection here and extends the service life of frames, brackets, housings, adapter plates, transport racks, and other steel components without impairing the function of moving, wear-exposed parts. In practice, this results in robust corrosion protection against splash water, de-icing salts, alkaline concrete residues, and abrasive dust, with proven resistance to chipping and underfilm corrosion at cut edges.

Definition: What is meant by hot-dip galvanizing?

Hot-dip galvanizing (batch hot-dip galvanizing) involves immersing pretreated steel components in a bath of molten zinc at about 450 °C. A firmly adhering multi-layer iron-zinc structure made of intermetallic phases with an outer zinc layer is formed through a metallurgical reaction. This composite provides both barrier and cathodic corrosion protection: even with minor surface damage, the zinc electrochemically protects the steel from rust. In contrast to electroplated galvanizing (electrolytic) or zinc lamella/flake systems, the coating in hot-dip galvanizing is usually thicker, extremely robust, and positively bonded to the base material. Common requirements and tests are described in relevant standards such as DIN EN ISO 1461 and application-related guidelines (e.g., DIN EN ISO 14713, ISO 9223). The diffusion-bonded layer build-up ensures durable adhesion without delamination; optical surface effects (e.g., spangle or slight matting) are functional and do not reduce protection.

Functionality and process steps of hot-dip galvanizing

The process begins with surface preparation: degreasing and cleaning remove oils, fats, and particles; subsequent pickling dissolves scale layers and rust; and a flux (often based on zinc and ammonium chloride) prepares the steel surface for reaction with the zinc. After drying, the components are fully immersed in the zinc bath. A multilayer composite of iron-zinc phases (gamma, delta, zeta phase) and an outer, zinc-rich eta layer is formed. Depending on steel chemistry (especially silicon and phosphorus content), material thickness, and dwell time in the bath, coating thicknesses vary. After lifting out, the parts cool down under control; a light passivation is often applied to reduce initial white rust formation. For high-quality results, uniform bath movement, adequately sized drain and vent openings, and design suitable for galvanizing are crucial, so that cavities are safely emptied and no inadmissible zinc accumulations occur that could impair tolerances, balance, or assembly. Where component size requires, staged immersion or double dipping is used; subsequent minor dressing of runs and spikes is part of the finishing routine.

Process steps at a glance

• Degreasing and cleaning
• Pickling and rinsing
• Flux application and drying
• Immersion in the zinc bath (~450 °C)
• Draining, cooling, passivation
• Final inspection (visual inspection, coating thickness measurement)
• Optional post-treatment (sealing or passivation tuned to storage and transport)

Advantages and limits in deconstruction and extraction environments

In the harsh use of concrete pulverizers and stone and concrete splitters, moisture meets abrasive dust, alkalis from concrete, and fluctuating temperatures. Hot-dip galvanized frames, mounts, protective covers, supports, and transport racks withstand these conditions in the long term. Zinc coatings are insensitive to localized damage and also provide protection at cut edges. Limits exist where sliding surfaces, precision fits, sealing faces, or highly loaded cutting edges are concerned: these functional surfaces are generally not galvanized or are masked before the bath. In highly abrasive zones, sacrificial wear of zinc must be expected; where longer optical durability or defined color coding is needed, a duplex system with an organic topcoat is appropriate.

Typical components on tools and power units

• Load and side frames, adapter plates and mounting plates
• Protective and cover sheets of hydraulic power packs
• Anchorage and pickup points, lifting eyes, brackets
• Transport and storage racks for stone split cylinders and concrete pulverizers
• Housing components of tank cutters as well as holders for hoses
• Bumpers, guards, skids, and guide plates exposed to splash water and impact

Design guidelines: draining, venting, tolerances

A design suitable for galvanizing prevents entrapment, minimizes distortion, and ensures dimensional accuracy. Adequately sized openings on hollow sections are important for zinc inflow and outflow as well as steam venting. Overlaps, crevices, and double plates are to be avoided or welded tight. Threads, precision bores, bearing seats, sealing and sliding surfaces are masked prior to galvanizing or reworked afterwards. Weld seams should be continuous and free of slag to prevent underfilm corrosion. Generous radii on edges, clear marking of masked zones, and well-placed lifting points promote uniform layer formation and facilitate safe handling during dipping.

Material selection and heat treatment

• Higher-strength, quenched and tempered steels and hardened tool components (e.g., cutting edges, pressing wedges) are generally not hot-dip galvanized to avoid microstructural changes at ~450 °C.
• For fasteners: hot-dip galvanizing is common up to strength class 8.8; for 10.9/12.9, alternative zinc systems are often used to minimize risks.
• The silicon and phosphorus content of the steel influences coating thickness (Sandelin/Sebisty effect); this should be considered for components with visual and dimensional requirements.
• Cast steels and complex weldments can be galvanized, but reactivity and residual stresses should be evaluated; the risk of hydrogen uptake is lower than with electroplating, yet brittle base materials require particular care.

Fit and assembly

• Threaded joints: internal threads are often retapped after galvanizing or masked in advance; external threads are preferably applied afterwards.
• Hydraulic connections and sealing faces must be free of zinc; careful masking is mandatory.
• Moving assemblies (e.g., joints on concrete pulverizers) are typically assembled only after galvanizing.
• Allowances for layer thickness should be considered for press fits and holes; slight oversizing and generous edge radii help maintain assembly tolerances.

Coating thickness, corrosivity categories, and service life

The service life of a hot-dip galvanized surface depends largely on coating thickness and environmental exposure. In many applications, zinc coatings range between 70 and 150 µm. In corrosivity categories according to common assessment procedures (e.g., ISO 9223), the expected time to first maintenance in moderate environments is often several decades; in highly stressed zones (spray water, chlorides, construction site traffic), mechanical loading can reduce protection time. Duplex systems (hot-dip galvanizing with subsequent coating, such as powder coating) significantly increase service life and improve the visual durability of power unit housings, mounts, and protective sheets. Local wear at edges and impact points should be taken into account in maintenance planning, with measurement on representative flat areas and critical geometries.

Quality assurance and standards

The execution and testing of hot-dip galvanized components frequently follows DIN EN ISO 1461 (steel parts batch hot-dip galvanized after fabrication) as well as guidelines for design and service life such as DIN EN ISO 14713. For environmental assessment and coating selection, categories and guidelines that classify corrosivity and protection systems are additionally used. In projects involving concrete demolition, tunnel construction, or special applications, it is advisable to clearly specify the areas to be protected, coating thickness ranges, and acceptance tests. Defined sampling plans, traceable measurement protocols, and agreed acceptance criteria for runs and local touch-ups support reliable quality across batches.

Practical inspection criteria

• Visual inspection for uniformity, runs, drips, and zinc dross
• Coating thickness measurement (magnetic induction) on representative areas
• Edge and cavity inspection for adequate wetting
• Verification of masking quality on functional surfaces and threads

Repair and maintenance in operation

Damage caused by impacts, cutting, or welding can generally be repaired using suitable methods: zinc-rich repair paints, thermal zinc spraying, or zinc repair sticks are common approaches. Preparation includes a clean, metallically bright surface and removal of loosely adhering residues. For concrete pulverizers, steel shears, and tank cutters, regular visual checks are recommended at edges, support points, lifting gear, and transport surfaces. Contaminants are removed with mild cleaners; aggressive media should be avoided. For acceptability, repair methods and film thicknesses should align with common guidelines to ensure continuous cathodic protection.

Inspection and maintenance intervals

• Regular visual inspections as part of scheduled equipment maintenance
• Documentation of repairs on highly stressed contact surfaces
• For duplex systems: check the coating condition for underfilm corrosion and flaking
• Additional inspections after heavy impact, thermal cutting, or structural modifications

Interfaces: welding, drilling, and cutting hot-dip galvanized components

When welding hot-dip galvanized components, the zinc coating in the seam area is removed beforehand and repaired after joining. The same applies to drilling and cutting. Zinc oxide fumes may be generated during processing; suitable extraction and adequate ventilation are required. Reworking adapter plates, mounts, or housings of hydraulic power packs should therefore be planned to quickly restore the protective effect of the zinc coating. Clean removal of zinc around the joint zone and subsequent surface conditioning support consistent weld quality and reliable post-repair protection.

Application on tools and components

In practice, hot-dip galvanized steel parts are primarily used on load-bearing, protective, or transport-relevant components. For concrete pulverizers, this often includes base frames, protective covers, mounting brackets, and lifting eyes; for stone and concrete splitters, among others, tripods, supports, and storage and transport racks. On Multi Cutters, steel shears, and combination shears, housing and cover parts are suitable candidates. Tank cutters benefit from corrosion-resistant mounts, guides, and racks, especially under alternating indoor and outdoor conditions. Functionally highly loaded cutting and pressing components generally remain ungalvanized and receive other function-appropriate surfaces or are protected by assembly. Uniform edge preparation and generous radii improve zinc flow and reduce the risk of thin edges in exposed areas.

Hydraulic power packs and peripherals

• Housings and frames hot-dip galvanized to prevent rust during outdoor storage
• Mounting plates, cable and hose guides executed for corrosion resistance
• Fasteners and clamps matched to zinc coating thicknesses and contact corrosion
• Defined earthing points and reference contact areas kept free of zinc for reliable electrical connections

Galvanic corrosion and material pairing

When hot-dip galvanized components contact stainless steel or aluminum, the area ratio and moisture exposure must be considered. In many applications the pairing is uncritical; in permanently moist environments a separating layer (e.g., gasket, coating) can be useful. For fasteners, electroplated or stainless screws are often used, with the combination adapted to the service environment. Insulating washers, compatible sealing pastes, and targeted drainage reduce the risk of galvanic cells in splash and salt-laden zones.

Alternatives and combinations

In addition to hot-dip galvanizing, other systems are used depending on functional requirements and tolerance needs: electroplated zinc coatings for precise fits, zinc flake coatings for high-strength fasteners, sherardizing for complex small parts, as well as thermal spraying of zinc for local repairs or large, heat-sensitive structures. Duplex systems-i.e., hot-dip galvanizing plus an organic coating-are common for power unit housings and exposed frames when extended protection duration and specific color requirements are desired. Inorganic zinc-rich primers and mechanically applied zinc systems can complement the portfolio where bath immersion is not feasible.

Sustainability and resource efficiency

Hot-dip galvanizing contributes to high resource efficiency through long maintenance intervals. Steel and zinc are highly recyclable; modern galvanizing processes operate with closed loops for process chemicals. Longer protection means reduced downtime in the use of concrete pulverizers, stone and concrete splitters, and other tools, as well as reduced spare parts and maintenance logistics for transport and mounting racks. Durable surfaces support circular economy strategies by extending service life and lowering total material and energy demand across multiple use cycles.

Practice-oriented planning: steps to a suitable execution

1. Application analysis: assess corrosivity environment, mechanical loads, cleaning and maintenance cycles.
2. Design check: define drain and vent openings, masking, and functional surfaces.
3. Material and fastener selection: coordinate steel chemistry, heat treatment, fasteners, and mating partners.
4. Define process sequence: welding before galvanizing, assembly only after galvanizing; plan rework.
5. Quality assurance: define checkpoints for coating thickness, visual surfaces, and critical edges; keep repair materials on hand.
6. Pilot part: validate design-for-galvanizing and masking on a sample component prior to series execution.