What should be paid attention to when processing building accessories

The processing of building accessories involves various types such as concrete components, steel structural components, door and window accessories, pipeline accessories, etc. The processing quality directly affects the safety, functional realization, and service life of building structures. The following provides a detailed explanation of key precautions during processing from the perspectives of materials, processes, safety, etc

1、 Material selection and pretreatment

1. Material selection and quality verification

Steel/Metal Accessories: 

        Strictly verify the material certification (such as the yield strength, elongation and other mechanical performance indicators of Q235B and Q355B steel), and avoid using inferior steel (such as high sulfur content that can lead to hot brittleness).

        For welded parts, it is necessary to ensure the weldability of the steel (such as carbon equivalent ≤ 0.4%, to avoid welding cracks).

Concrete components:

       Cement should be selected from Portland cement that meets the GB 175 standard, and the grading of sand and stone should comply with the "Quality and Inspection Methods Standards for Sand and Stone Used in Ordinary Concrete" to avoid excessive mud content affecting strength.

Plastic/composite material accessories:

        For PVC pipe fittings, it is necessary to confirm that the raw materials meet the GB/T 10002.1 standard and that the aging resistance performance (such as thermal stability testing) meets the standard.

2. Material pretreatment requirements

Metal surface treatment: 

        Before welding, it is necessary to remove rust and oil stains on the surface of the steel (such as sandblasting to Sa2.5 level) to avoid welding pores; The cutting edge needs to be polished smooth to prevent stress concentration.

Concrete batching control:

        Strictly weigh according to the mix proportion (cement, water, sand, gravel error ≤ 2%), and conduct a trial mixing test before using additives (improper addition of water reducing agent can lead to abnormal setting time).

2、 Processing technology and precision control

1. Dimensional and positional tolerance requirements

Steel structure accessories:

        The deviation of bolt hole position is ≤ 1mm (if the distance error of high-strength bolt connection holes is too large, it may lead to uneven stress), and the bending degree of the component is ≤ L/1000 (L is the length of the component).

        Example: When welding H-beams, the vertical deviation between the flange plate and the web plate should be ≤ b/100 (where b is the width of the flange plate), otherwise it will affect the installation accuracy.

Concrete prefabricated components:

        The length and width deviation of prefabricated floor slabs should be controlled within ± 5mm, and the surface flatness should be ≤ 3mm/2m to avoid leakage caused by loose joints during installation.

2. Key processing technology points

Cutting and welding:

        Prioritize using CNC plasma cutting machines (accuracy ≤ ± 0.5mm) for metal cutting to avoid edge burrs caused by manual cutting; Welding needs to be carried out according to the process evaluation parameters (such as current, voltage, gas flow rate of carbon dioxide gas shielded welding), and important welds require non-destructive testing (UT/RT).

Pouring and maintenance:

       When pouring concrete components, they need to be compacted by vibration (to avoid honeycomb and rough surfaces), and the curing period should maintain a humidity of ≥ 90% and a temperature of ≥ 15 ℃ (standard curing for 28 days, or steam curing accelerated hardening).

Mechanical processing (such as bolts and nuts):

       The thread accuracy should reach 6g/6H level (GB/T 197) to avoid loose connections caused by poor thread fit; After cutting, burrs need to be removed to prevent scratching the installation personnel.

3、 Surface treatment and protection

1. Anti corrosion treatment of metal accessories

Rust prevention of steel structures: 

         Adopting the "primer+intermediate coat+topcoat" system (such as epoxy zinc rich primer with a zinc content of ≥ 80% and a dry film thickness of ≥ 60 μ m); The intermediate paint should be epoxy mica iron, and the topcoat should be polyurethane or fluorocarbon paint, with a total film thickness of ≥ 150 μ m. In coastal areas, the thickness should be increased to over 200 μ m.

Galvanizing treatment:

        The thickness of hot-dip galvanized layer is ≥ 85 μ m (GB/T 13912), suitable for outdoor embedded parts, to avoid corrosion caused by zinc layer leakage (such as bolt heads and threads that need to be inspected carefully).

2. Surface treatment of concrete components

        The bubble rate of the plain concrete components should be controlled to be ≤ 5%, and the surface should not be repaired arbitrarily (if repair is required, it needs to be confirmed by the design) to ensure the decorative effect; Waterproof sealing (such as applying silane waterproof coating) should be done around the pre embedded metal parts to prevent moisture from infiltrating and rusting.

4、 Safety and environmental requirements

1. Processing safety control

Mechanical operation:

         Cutting machines, punching machines and other equipment need to be equipped with safety protective covers, and operators need to wear protective goggles and gloves; During welding operations, a smoke exhaust system must be equipped to avoid inhaling metal smoke and dust. For hot work operations, a permit must be obtained and a fire extinguisher must be equipped.

High altitude operations (such as processing large components):

         Scaffolding construction must comply with JGJ 130 standards, with a working platform bearing capacity of ≥ 2.0kN/m ², and operators must wear safety belts.

2. Environmental Protection and Waste Management

         The cutting fluid generated during metal processing needs to be treated with oil-water separation (COD ≤ 500mg/L), and welding fumes need to be purified through a filter cartridge dust collector (emission concentration ≤ 30mg/m ³); The concrete mixing plant needs to be equipped with a closed silo, and the dust emission should comply with the GB 25972 standard (particle size ≤ 30mg/m ³).

5、 Quality inspection and acceptance

1. Key points of process inspection

         First piece inspection: Before processing each batch of accessories, the first piece must be made and undergo size, appearance, and performance inspections (such as UT testing of steel structure welds) before mass production can begin.

Sampling inspection:

         Concrete test blocks shall be made according to GB/T 50081, and the compressive strength shall be tested after 28 days of standard curing (deviation ≤± 15%); Mechanical performance testing of metal fittings (such as tensile testing, bending testing) shall be sampled by batch (1 piece per 100 pieces).

2. Finished product acceptance criteria

         Steel structure accessories need to be accompanied by factory certificates of conformity, inspection reports, and anti-corrosion coating testing reports (such as dry film thickness testing records); Concrete prefabricated components require strength reports and appearance quality acceptance forms (such as crack width ≤ 0.2mm).