Flame Cutting Nozzle Testing

Flame cutting nozzle inspection mainly conducts scientific testing and analysis on the appearance and dimension testing, orifice geometry shape and smoothness testing, material composition and hardness testing, air tightness testing, gas flow characteristic testing, and thermal cycling and ablation resistance testing, 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

Appearance and dimension testing: The visual inspection and dimension measurement are carried out on the flame cutting nozzles. The inspection contents include whether the nozzle bodies have the mechanical damages such as the cracks, indentations and deformations, whether the concentricity of the preheating orifices and cutting orifices meets the requirements, as well as whether the dimension tolerances of the various key parts meet the design drawing requirements. This testing is the basis of judging whether the nozzles are qualified.

Orifice geometry shape and smoothness testing: The endoscopes or high-power microscopes are used to observe the internal structures of the preheating orifices, cutting orifices and mixing chambers of the nozzles. The key checks are whether the orifices are smooth, without the burrs and blockages, and whether the internal contours are regular, to ensure the smooth gas flow and uniform mixing.

Material composition and hardness testing: The spectroscopic analysers are used to carry out the chemical composition analysis of the nozzle materials, confirming whether they are the specified alloys such as the red copper and chromium-zirconium copper. At the same time, the Rockwell or Vickers hardness testers are used to measure the hardness values at the specified positions, to evaluate the wear resistance and high-temperature resistance of the materials.

Air tightness testing: Under the specific pressures, the air tightness testing is separately carried out on the oxygen and fuel gas channels of the nozzles. The water immersion bubble method or precision pressure gauge pressure-holding method is usually adopted to check whether the various connection threads, bodies and internal channels have the leakages, ensuring that the gases do not escape unexpectedly.

Gas flow characteristic testing: On the dedicated test benches, the working states are simulated to test the gas flow rates, flow velocity distributions and outlet gas flow patterns of the nozzles (such as whether they are the standard straight or swirling patterns). This item is directly related to the preheating efficiencies and the purity and stiffness of the cutting oxygen flows.

Thermal cycling and ablation resistance testing: By simulating the actual cutting working conditions, the nozzles undergo the multiple cycles of the "ignition-preheating-cutting-extinguishing" processes, and then the ablation, oxidation and deformation conditions of their key parts (especially the cutting orifice outlets) are checked, evaluating their service lives.

Testing Scope

Nozzles for the conventional manual cutting torches: Suitable for the nozzles of the handheld torches such as the common oxy-acetylene and oxy-propane. The testing emphases are their versatility, durability and operation safety. This type of nozzles has the numerous models, and the common specifications from the thin plate to thick plate cutting need to be covered.

Nozzles for the CNC and machine cutting: The high-precision nozzles specially designed for the CNC cutting machines and copying cutting machines. In addition to the basic items, the testing scope focuses more on the dimension consistency, high repeatability precision, excellent gas flow characteristics and stable properties suitable for the high-speed cutting.

Special gas nozzles: For the nozzles using the non-acetylene fuel gases such as the propane, natural gas, MAPP gas and hydrogen. Since the combustion characteristics of the different fuel gases are different, the testing needs to verify whether their internal structures (such as the mixing chamber designs) are optimized for the specific fuel gases, to achieve the best cutting effects.

Integral and split nozzles: The testing scope covers the integral nozzles which integrally form the mixing chambers and nozzles, as well as the split (also known as the equal-pressure type) nozzles in which the preheating oxygen, fuel gas and cutting oxygen enter separately. The testing methods and emphases of the two types are different due to the different structural principles.

Nozzle series of the different orifice sizes and numbers: From the small orifice nozzles for the fine cutting to the multi-orifice nozzles for the large thickness cutting (such as the plum-blossom type), the testing needs to cover the complete number series. Each number corresponds to the specific gas pressures and cutting capabilities, and needs to be verified one by one.

Newly delivered and in-service old nozzles: The testing is not only for the factory delivery quality inspection of the newly produced nozzles, but also applicable to the condition evaluation and life judgment of the old nozzles in use at the sites, providing the technical basis for the maintenance and replacement.

Testing Methods

Visual and magnifying glass inspection method: The most basic and direct testing method. Under the good lighting, the defects of the nozzle end faces, orifices and surfaces are observed with the help of the 3-10 times magnifying glasses. This method is fast and simple, and can effectively find the macro cracks, severe ablation and blockages.

Precision dimension measurement method: The micrometers, digital callipers, inside diameter dial gauges, projectors or coordinate measuring machines (CMM) are used for the precise measurement of the total lengths, outer diameters, various step dimensions, orifice diameters and depths of the nozzles, ensuring that they meet the manufacturing tolerance requirements.

Gas flow rate and pressure testing method: The nozzles are installed on the standard cutting torches, connected with the calibrated flow meters and pressure gauges. Under the specified inlet pressures, the flow rates of the preheating oxygen, fuel gas and cutting oxygen are separately measured and compared with the standard values, judging whether the flow channels are unobstructed and the resistances are normal.

Water immersion bubble air tightness testing method: The channels to be tested of the nozzles are sealed and connected to the compressed air or nitrogen sources, pressurized to about 1.5 times the working pressures, and then immersed in the clean water. Whether the continuous bubbles emerge within the specific time is observed, thereby judging the leakage points and leakage rates.

Cutting kerf specimen cutting evaluation method: A comprehensive performance testing method. The nozzles to be tested are used for the straight cutting on the standard thickness test plates, and then the kerf widths are measured, the cut verticalities are observed, the slag adhesion conditions are checked, and the definition of the back edges is inspected, intuitively evaluating their cutting qualities.

Metallographic analysis and hardness testing method: For the nozzles suspected of the material problems, the specimens can be taken to make the metallographic samples, and the micro-structures are observed under the microscopes. Combined with the multi-point testing of the hardness testers, whether the material has undergone the appropriate heat treatments and whether the internal casting defects exist is comprehensively judged.

Testing Standards

Domestic Standards:

1. JB/T 6969, Injection type cutting blowpipes

2. JB/T 6970, Injection type welding blowpipes

3. GB/T 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

4. GB/T 4340.1-2009, Metallic materials — Vickers hardness test — Part 1: Test method

International Standards:

1. ISO 5172, Gas welding equipment — Blowpipes for gas welding, heating and cutting — Specifications and 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

Optical measuring instruments: Including the tool microscopes, image measuring instruments and optical projectors. These equipment can non-contactingly measure the complex geometric parameters such as the tiny orifice diameters, orifice spacings and angles of the nozzles with the high precision, and generate the test reports. They are the core equipment of the dimension testing.

Gas parameter test bench: An integrated dedicated testing platform, usually including the stabilized gas sources, high-precision gas mass flow controllers (or rotameter flow meters), pressure transducers and data acquisition systems. It can automatically complete the mapping of the flow-pressure characteristic curves, with the high efficiency and objective data.

Endoscope and video microscope: The industrial video endoscopes can extend the probes into the internal orifices of the nozzles, transmitting the inner wall images to the displays in real time, convenient for observing the deep conditions. The high-power video microscopes are used for the meticulous observation of the micro morphologies and ablation states of the orifice edges.

Hardness tester: The portable Leeb hardness testers or benchtop Rockwell/Vickers hardness testers are commonly used. For the relatively soft materials such as the red copper, attention needs to be paid to selecting the appropriate scales (such as the HRF or HV), and the testing should be carried out at the ground and flattened test points, to ensure the accuracy of the readings.

Air tightness testing device: Consisting of the pressure regulating valves, precision pressure gauges (or pressure transducers), timers, sealing fixtures and water tanks. The advanced helium mass spectrometry leak detectors have the extremely high sensitivity, and can be used for the micro leakage detection of the high-end nozzles with the extremely strict requirements, but the costs are higher.

Material analysis instruments: The handheld X-ray fluorescence spectrometers (XRF) can carry out the non-destructive material composition analysis. For the more in-depth analysis, the laboratory direct-reading spectrometers (OES) or inductively coupled plasma optical emission spectrometers (ICP-OES) may be needed to obtain the precise element contents.

Cutting performance testing machine: The equipment simulating the actual cutting processes, which can clamp the nozzles and move on the test plates at the set speeds, while precisely controlling the gas pressures and switching sequences. It provides the repeatable testing conditions for the standardized cutting quality evaluation.