W-shaped Steel Strip Testing

W-type steel strip inspection mainly conducts scientific testing and analysis on the geometric dimension testing, mechanical property testing, chemical composition analysis, surface quality inspection, coating/plating quality testing and weldability evaluation, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Geometric dimension testing: Mainly including the measurement of the key parameters such as the section dimensions, strip heights, strip thicknesses, edge widths and hole spacings. Through the precise measurement, whether the section shapes and dimension tolerances of the W-type steel strips meet the design requirements is ensured. This is the basis of guaranteeing the precise matching with the supporting components such as the trays and supports and the load-bearing capabilities.

Mechanical property testing: This is the key of evaluating the load-bearing and deformation resistance capabilities of the W-type steel strips. The main testing items include the yield strengths, tensile strengths, elongations after fracture and reduction of area. Through the tensile testing to obtain the data, it is ensured that the plastic deformation or brittle fracture does not occur in the high-stress environments.

Chemical composition analysis: Mainly testing the contents of the elements such as the carbon (C), silicon (Si), manganese (Mn), phosphorus (P) and sulfur (S). The chemical compositions directly affect the strengths, toughness, weldability and corrosion resistance of the steel. The control of the harmful elements such as the phosphorus and sulfur is crucial for preventing the cold brittleness and hot brittleness phenomena.

Surface quality inspection: Including the visual or instrumental inspection of the surface cracks, scars, laps, pits, oxide scales and rust degrees. The surface defects will form the stress concentration points, significantly reducing the fatigue lives and load-bearing safety of the material, and must be strictly controlled.

Coating/plating quality testing: For the W-type steel strips with the hot-dip galvanizing, electro-galvanizing or other anti-corrosion coatings, the coating thicknesses, uniformity, adhesion and corrosion resistance need to be tested. The commonly used methods include the magnetic thickness gauge measurement, bending testing, cross-cut testing and salt spray testing, to ensure their long-term anti-corrosion effects.

Weldability evaluation: For the W-type steel strips that need the on-site welding connections, their weldability needs to be evaluated. Mainly carried out through the carbon equivalent (CE) calculation and welding procedure qualification testing. The excessively high carbon equivalents will increase the hardening tendency and cold crack risks of the welding heat-affected zones.

Testing Scope

Raw material incoming inspection: Before the production of the W-type steel strips, the preliminary inspection of the chemical compositions, dimension specifications and surface qualities is carried out on the purchased steel coils or plates, controlling the product quality from the sources and ensuring the stability of the subsequent roll forming.

Production process quality control: The online or sampling testing carried out after the key processes such as the cold roll forming, punching and welding (if any). The key monitoring of the dimension changes, surface damages and welding qualities, timely finding and adjusting the process parameters, preventing the batch defects.

Finished product factory delivery inspection: The comprehensive inspection carried out before the product warehousing or delivery. Covering all the key testing items, and issuing the qualification certificate documents according to the relevant product standards (such as YB/T 5003). It is the final confirmation link that the products meet the standards.

Engineering application on-site testing: At the application sites such as the coal mine roadway support and tunnel engineering, the sampling re-inspection is carried out on the arrived W-type steel strips, checking whether the deformations, rust or damages occur during the transportation and storage, ensuring the reliable quality of the materials used for the engineering entities.

Used part safety evaluation testing: For the recovered or reused W-type steel strips, the strict damage evaluation testing needs to be carried out. The key checks are whether the plastic deformations, cracks, severe rust and coating peeling exist. Through the mechanical property re-testing, their remaining load-bearing capabilities are judged, determining whether they can be used with the degraded grades or scrapped.

Comparative analysis and arbitration testing: When the disputes over the product qualities occur between the supply and demand parties, the qualified third-party testing institutions carry out the testing according to the standard methods. The testing results of this type have the legal effects, often used for the arbitration and determination of the quality disputes.

Testing Methods

Dimension measurement method: The tools such as the high-precision vernier callipers, micrometers, tapes, templates and optical projectors are used for the manual measurement. For the batch testing or complex profiles, the laser scanning or machine vision automatic measurement systems can be used, realizing the efficient and non-contact high-precision data acquisition.

Tensile testing method: According to the GB/T 228.1 standard, carried out on the universal material testing machines. The W-type steel strips are processed into the rectangular or circular cross-section specimens of the standard proportions, clamped and loaded at the uniform speeds until the fracture. The load-displacement curves are automatically recorded, thereby calculating the various mechanical property indicators.

Spectroscopic analysis method: The direct-reading spectrometers (OES) or X-ray fluorescence spectrometers (XRF) are used for the fast quantitative analysis of the chemical compositions. This method has the simple pre-treatment, fast analysis speeds and high precision, and is the routine testing means of the steel material composition control.

Macro and micro inspection method: The macro inspection includes the acid immersion low-power inspection and fracture analysis, used to find the internal defects such as the shrinkage cavities, porosity and white spots. The micro inspection is the metallographic analysis. Through the specimen preparation and etching, the observation is carried out under the metallographic microscopes, analysing the micro-structures, grain sizes and the contents and grades of the non-metallic inclusions.

Non-destructive testing method: Detecting the internal and surface defects under the premise of not destroying the material. The commonly used methods include the ultrasonic flaw detection (UT) for the internal cracks and lamination, and the magnetic particle flaw detection (MT) or penetrant flaw detection (PT) for the surface and near-surface open defects. Suitable for the key components with the extremely high safety requirements.

Coating property testing method: The coating thicknesses are measured with the magnetic method (galvanized layers) or eddy current method (non-magnetic coatings); the adhesion is commonly evaluated with the cross-cut method or bending method; the corrosion resistance is evaluated by simulating the accelerated corrosion environments through the methods such as the neutral salt spray testing (NSS) and copper-accelerated acetic acid salt spray testing (CASS).

Testing Standards

Domestic Standards:

1. YB/T 5003, W-type steel strips for coal mine

2. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

3. GB/T 232-2010, Metallic materials — Bend test method

4. GB/T 10125-2021, Corrosion tests in artificial atmospheres — Salt spray tests

International Standards:

1. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

2. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Universal material testing machine: The core equipment of carrying out the mechanical property testing such as the tensile, bending and compression. The modern models are usually equipped with the computer control systems, which can automatically collect the data, draw the curves and generate the reports. The testing force ranges need to cover the strength requirements of the W-type steel strips to be tested.

Direct-reading spectrometer: The precision instrument used for the fast analysis of the chemical compositions. Through the excitation of the samples to generate the characteristic spectra, the photomultiplier tubes or CCD detectors receive them after the grating dispersion. Compared with the spectral intensities of the standard samples, the contents of the multiple elements in the steel can be simultaneously determined within tens of seconds.

Metallographic microscope and sample preparation equipment: The key equipment of the metallographic analysis. Including the specimen cutting machines, mounting machines, grinding and polishing machines, as well as the inverted or upright metallographic microscopes with the image analysis systems. Through the image analysis software, the parameters such as the grain sizes and phase ratios can be quantitatively measured.

Ultrasonic flaw detector and magnetic particle flaw detector: The main equipment of the non-destructive testing. The ultrasonic flaw detectors use the high-frequency sound wave reflection principle to detect the internal defects; the magnetic particle flaw detectors magnetize the workpieces and apply the magnetic suspensions on the surfaces, using the leakage magnetic fields to adsorb the magnetic particles and display the surface cracks. The portable equipment is suitable for the on-site testing.

Coating thickness gauge and salt spray test chamber: The dedicated equipment of the coating quality testing. The magnetic/eddy current thickness gauges are used for the fast on-site measurement of the coating thicknesses; the salt spray test chambers simulate the marine or industrial atmospheric environments to accelerate the evaluation of the coating corrosion resistance. It is the important means of verifying the effectiveness of the anti-corrosion processes.

High-precision dimension measuring tools: Including the digital vernier callipers (resolution 0.01mm), outer diameter micrometers, wall thickness gauges, radius gauges, as well as the large platforms and height gauges. For the complex cross-sections, the coordinate measuring machines (CMM) can provide the high-precision dimension, shape and position tolerance data in the three-dimensional spaces.