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The powder coating process for slotted cable trays, commonly known as electrostatic powder coating, utilizes an electrostatic generator to charge plastic powder. This charged powder adheres to the surface of iron plates, and after baking at 180 to 220°C, the powder melts and adheres to the metal surface. The powder-coated products are often used for indoor enclosures, presenting a matte or glossy finish. Common powders used include acrylic powder and polyester powder.

Process Flow for Electrostatic Powder Coating of Slotted Cable Trays:

• Pre-treatment:

  • Objective: Remove oil, dust, and rust from the surface of the workpiece, and generate a corrosion-resistant "phosphating layer" that enhances the adhesion of the coating.

  • Main Process Steps: Degreasing, rust removal, phosphating, passivation. After pre-treatment, the surface is not only free of oil, rust, and dust, but also has a uniform and rough gray phosphating film that prevents rust and enhances the adhesion of the powder coating.

• Electrostatic Spraying:

  • Objective: Uniformly apply powder coating to the surface of the workpiece. Specialized electrostatic spraying machines are recommended for spraying on specific parts, including those prone to static shielding.

  • Process Steps: Use the principle of electrostatic adsorption to evenly spray a layer of powder coating on the surface of the workpiece. The fallen powder is recycled through the recovery system and can be reused after sieving.

• High-Temperature Curing:

  • Objective: Heat the powder coating on the surface of the workpiece to a specified temperature and maintain the temperature for a certain period to melt, level, and cure, achieving the desired surface effect.

  • Process Steps: Place the sprayed workpiece into the curing oven, heat it to the specified temperature (usually 185°C), and maintain the temperature for the required time (15 minutes). After cooling, the finished product is obtained.

  • Note: The heating and control system (including electric heating, fuel oil, gas, coal, etc.) + insulation box = curing oven.

• Decorative Treatment:

  • Objective: Achieve a specific appearance effect on the workpiece after electrostatic spraying, such as various wood grain patterns, textures, gloss enhancement, etc.

During the indoor installation of cable trays, it is essential to ensure that the trays are straight, aesthetically pleasing, and consistently aligned. The horizontal deformation in the horizontal direction of the cable tray generally needs to be controlled within 4 millimeters. Depending on the selected width of the cable tray and the required horizontal load deformation, one can refer to the load characteristic curves of corresponding structural forms. If the deformation requirements cannot be met, adjustments such as increasing the side height of the tray or reducing the support spacing can be made to meet the specifications.

Cable trays are stamped from thin steel plates, and their load-bearing capacity is limited. Overloading the tray can result in deformation, affecting both the aesthetics of the tray and the safe operation of the cables. Typically, the load-bearing capacity of cable trays is represented by the load characteristic curve. From the load curve, it is evident that the load capacity is related to the tray specifications and support spacing. For the same support distance and bending deformation amount, trays with greater side heights have higher load-bearing capacities. When the load capacity is the same, cable trays of the same specifications have smaller bending deformation with smaller support spacing.

We are aware that the load on cable trays can be categorized into three aspects: static load, dynamic load, and additional load. Let's delve into the specific differences and characteristics of these three types of loads.

• Static Load:

  • Definition: Static load refers to the weight of various types of cables, the number of cables, and the outer diameter weight per unit length laid inside the cable tray.

  • Characteristics: These fundamental parameters must be rigorously accounted for based on the different routing of cable installations. Static load considerations are essential for routine cable tray operation.

• Dynamic Load:

  • Definition: Dynamic load pertains to the weight of construction and maintenance personnel during the installation and upkeep of cable trays.

  • Characteristics: For lightweight cable trays, we typically do not factor in dynamic loads, meaning that personnel are not allowed to stand on the tray. If it becomes necessary to consider personnel standing, the span should be appropriately reduced to meet safety requirements.

• Additional Load:

  • Definition: Additional load, applicable only outdoors, includes the loads induced by ice, snow, wind, and electromagnetic forces.

  • Characteristics: It is influenced by the natural weather conditions of the installation site and the nature of charged elements. The design should incorporate calculations based on these conditions to address the impact of external factors on the cable tray.

The method for correctly selecting cable tray types is as follows:

• Electromagnetic Interference Shielding and Protection Requirements:

  • When there is a need to shield electromagnetic interference in cable networks or external protection requirements (e.g., exposure to corrosive liquids, environments with combustible dust), choose (FB) type slotted composite corrosion-resistant shielded cable trays (with cover).

• Highly Corrosive Environments:

  • In highly corrosive environments, opt for (F) type composite epoxy resin corrosion-resistant and flame-retardant cable trays. Choose support arms and brackets made of the same material to enhance the lifespan of the tray and accessories. In environments prone to dust accumulation and requiring coverage, it is advisable to use cover plates.

• General Environmental and Technical Requirements:

  • In other cases, select tray types such as tray-style, slotted, ladder-style, glass corrosion-resistant flame-retardant cable trays, or standard steel trays based on site conditions and technical requirements. In environments prone to dust accumulation and requiring coverage, consider using cover plates.

• Public Walkways and Outdoor Crossings:

  • For public walkways or outdoor road crossings, consider adding base plates to the bottom of the lower ladder rungs or use trays in that segment. For long spans crossing public walkways, it is possible to increase the load capacity of the tray or use supports according to user requirements.

• Selection for Long Spans:

  • For long spans (>3m), choose composite trays (FB).

• Outdoor Environments:

  • For outdoor use, choose composite epoxy resin trays (F).

Cable trays exhibit high mechanical strength, combining the rigidity of metal trays with the flexibility of fiberglass-reinforced plastic (FRP) trays. They boast excellent corrosion resistance, strong aging resistance, aesthetic design, easy installation, and a long service life. Epoxy resin and epoxy resin composite cable trays are suitable for use in highly corrosive environments, large spans, and under heavy loads.

Types and Structural Classification:

• Trough Type (C)

• Ladder Type (T)

• Tray Type (P)

Specification Selection:

The cable filling rate should not exceed the specified standard value, with power cables taking 40-50% and control cables taking 50-70%. Additionally, a 10-25% engineering development margin should be reserved. The selection of the cross-sectional area of the tray is shown in the table. Various bends and accessories should comply with engineering layout conditions and be compatible with the tray.

In addition to its own weight, the cable tray should also consider the mechanical load of the wires and cables it can bear. The uniformly distributed load should not exceed the rated uniformly distributed load for the selected load level. The relative deflection of the cable tray under the rated uniformly distributed load should not exceed 1/200 for epoxy resin and epoxy resin composite types.

Tray-type cable trays can be equipped with covers. If a cover is required, it should be specified when ordering, and all accessories are compatible with ladder-type and trough-type trays.

Trough-type cable trays come with matching covers, and other accessories are compatible with ladder-type and tray-type trays. If users require other specifications for trough-type cable trays, they can specify by drawing or inquiry.

For long-span cable trays, cover plates are available. If a cover plate is needed, it should be specified when ordering or ordered according to the cover plate model.

• The arrangement of cable tray tiers from top to bottom is as follows: computer cable tray, shielded cable tray, general control cable tray, low-voltage power, and lighting cable tray, high-voltage cable tray. If two different-purpose cables must be placed in the same tray, a partition should be used in the middle of the tray with a cover.

• For ease of maintenance and installation, the total width of trays on the same level should not exceed 2m, and the vertical spacing between trays is generally 300mm.

• The distance from the side of the cable tray to the wall should be 50-100mm, and the horizontal spacing between adjacent trays should be 50mm.

• The vertical distance from the bottom of the cable tray to the wall or column should be 25-50mm, and the distance from the top of the tray to the ceiling, beams, and other obstacles' bottom should be greater than 150mm. If the bottom distance of the tray from the top of electrical devices is less than 450mm, non-combustible baffles should be installed at the bottom of the tray.

• The span between cable tray supports is generally less than 3m, with 1.5m or 2m commonly used in actual projects. Expansion bolts are usually used to fix the support arms and columns. The fixation position and strength are determined through calculations. To avoid drilling into rebars, a rebar detector can be used beforehand, and main rebars should be avoided as much as possible. For places using trays in cable trenches or tunnels, embedded parts should be used, and expansion bolts should not be used. Embedded parts generally use flat steel with a thickness of 8-16mm and a width of 80-200mm, and the support arms are welded directly onto the flat steel.

• Cable tray installation paths should avoid areas where high-temperature process equipment or high-temperature pipelines may generate heat. Heat-insulating baffles should be added when necessary.

• When using cross-linked cables and all-plastic cables, rollers should be used on the straight sections of the tray during construction, and rollers or wheels should be used at turns or appropriate locations to assist in cable laying, reducing friction between the cable and the tray and protecting the cable sheath. When leading cables from the main support frame to electrical equipment, it is advisable to use narrow trays or steel pipes to support and protect them.

• Cables inside cable tray trays should be fixed with fixtures or nylon ties. The fixing interval is 1.5-3m, and large cross-section single-core cables from the same power circuit should be fixed in a zigzag shape. Iron clips should not be used to tie single-core cables to prevent eddy currents from causing high-temperature damage to the insulation.

• When cable trays pass through fire-resistant walls or partitions, the cable segment should be treated with fire prevention, such as applying fire-resistant coatings or sealing the tray segment with a metal casing filled with fire-resistant material. To prevent rainwater erosion, when entering or leaving the building walls, a waterproof slope of 1/100 should be created from inside to outside.

• To ensure the safe operation of electrical circuits, the cable tray system should be well grounded. There are two specific methods: one is to connect each section of the metal tray with multi-strand steel wire and then ground it; the other is to separately set grounding lines or zero lines along the entire length of the tray, and each tray segment should have at least one point reliably connected to it. Ground or zero lines should be led to electrical equipment for grounding.

Common Issues in Cable Tray Usage and Maintenance Methods

During the use of cable trays, various problems may arise, requiring timely inspection and maintenance. Here are some common issues and corresponding inspection and maintenance methods:

Possible Problems:

1. Short circuits in various parts of the cable: Manifested by the operation of current relays on distribution cabinets, causing severe damage to the cables.

2. Internal short circuits in the cable: Typically caused by poor cable quality, with no visible signs on the surface.

3. Entire cable or a section of the cable burnt: Resulting in significant damage.

4. Only one short circuit in the cable tray: The cable is damaged at the fault location, but there are still clear traces.

Possible Causes:

These issues may be caused by excessive current or poor cable quality.

Inspection and Maintenance Methods:

1. Regularly inspect the action status of the balance cylinder, oil lubrication system, oil circuit, joints, and other components of the cable tray equipment, and perform necessary tests.

2. Adjust and correct the friction between the slider and guide rail of the cable tray equipment regularly. Check the lubrication of the joints and ensure smooth operation.

3. Periodically lubricate the gear components of the cable tray equipment. Since the gearbox and internal components are in constant motion, they are prone to damage and loosening. Regular checks and lubrication are necessary.

4. These inspection and maintenance methods help ensure the proper functioning of cable tray equipment, extending its operational life.