Galvanized Crossarms for Cable Trays: Analysis of Functions, Processes and Applications
Galvanized crossarms for cable trays are typically made of Q235 low-carbon steel via rolling. Their cross-sectional forms are mostly U-shaped or L-shaped, and their thickness is classified into three categories (2.5mm, 3mm, and 4mm) based on load levels. The standard length matches the width of the cable tray, with common specifications including 300mm, 400mm, and 500mm. They are fixed to the connectors on the side of the cable tray using bolts, forming support nodes with a spacing of 500–1000mm.
In terms of design, they must meet both static load and dynamic load requirements: According to GB 50217 Code for Design of Cables in Electric Power Engineering, it is clearly specified that the deflection of the crossarm shall be ≤ L/200 (where L is the support spacing). That is, the maximum sag of a crossarm with a 1000mm spacing shall not exceed 5mm. For light-duty cable trays used for laying control cables, the design load value of the crossarm is 50N/m; for power cable trays, it needs to reach 150–200N/m. For heavy-load scenarios (such as metallurgical workshops), the load requirement shall be upgraded to over 300N/m, in which case the crossarm must adopt a stiffened structure, and the flange width shall be increased to 60–80mm.
The galvanization of crossarms adopts the hot-dip galvanization process, with the workflow including:
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Pickling for rust removal: Using a 10% hydrochloric acid solution at 40°C for 15 minutes to remove oxide scale;
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Fluxing treatment: Using a zinc chloride-ammonium chloride solution to prevent secondary oxidation;
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Hot-dip galvanizing: Immersing in 450°C molten zinc for 3–5 minutes to form a zinc coating with a thickness of 85–120μm;
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Final steps: Cooling, followed by passivation (chromate treatment) to seal the pores of the zinc coating.
Quality inspection must comply with GB/T 13912-2022 Metallic Coatings - Technical Requirements and Test Methods for Hot-Dip Zinc Coatings on Iron and Steel Products:
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Zinc coating adhesion: Pass the bending test (no peeling of the zinc coating after 180° bending);
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Salt spray test: Withstand 96 hours in a neutral 5% NaCl solution without red rust;
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Minimum local thickness: Not less than 65μm.
Compared with the electrogalvanization process, the zinc coating thickness of hot-dip galvanization is 3–5 times that of electrogalvanization, and its corrosion resistance life is extended to 15–20 years, making it particularly suitable for humid or outdoor environments.
The galvanized coating forms a sacrificial anode protection mechanism. When the crossarm is scratched or locally corroded, zinc corrodes preferentially to protect the base steel. In the high-humidity environment of industrial plants, the corrosion rate of galvanized crossarms is only 1/20 that of ordinary carbon steel; in the salt spray environment of coastal areas, the annual corrosion loss is ≤ 5μm, far lower than the 30μm/year of untreated steel.
Its application scenarios are wide-ranging:
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For the weak current cable tray systems in office buildings, 300mm-wide crossarms are used, matching trough-type cable trays to lay network cables and telephone lines;
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For power cable trays in industrial workshops (e.g., 800mm-wide), thickened crossarms are used to support multiple 10kV cables;
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For cable trays in outdoor photovoltaic power stations, crossarms with drainage holes must be selected to prevent water accumulation from accelerating corrosion;
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In chemical industrial parks, passivation treatment must be added on the basis of galvanization to improve acid and alkali resistance.
During installation, the connecting bolts between the two ends of the crossarm and the side plates of the cable tray shall be 8.8-grade galvanized bolts, with the torque controlled at 30–40N·m to ensure no loosening. The spacing setting shall be calculated based on the total weight of the cables: When the weight per meter of control cables is ≤ 10kg, the spacing can be set to 1000mm; when the weight per meter of power cables is 15–25kg, the spacing shall be reduced to 600–800mm.
Routine maintenance requires regular inspection (once a year):
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Remove accumulated dust and debris on the surface to avoid local overheating;
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Check whether white rust (early corrosion product) appears on the zinc coating. If so, wipe it with a dry cloth and repair it by applying cold-spray zinc agent with a zinc content ≥ 95%;
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Tighten loose bolts in a timely manner to prevent fatigue fracture caused by resonance.
As the "skeleton" of the cable tray system, the quality of galvanized crossarms directly affects the safety and durability of cable laying. Selecting hot-dip galvanized products that meet standards, following installation specifications, and conducting proper maintenance can effectively reduce the risk of electrical failures and ensure the long-term stable operation of the cable system. In the construction of green buildings and smart factories, high-corrosion-resistance galvanized crossarms are becoming a key component to extend the service life of infrastructure.
