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Gasworld US Edition, Vol 60, No 06 (June) - Hydrogen Issue

By Rob Cockerill 2022-04-21T08:56:00+01:00

Metal cutting processes with laser technology are more efficient and successful methods in many aspects compared to other known methods. The laser cutting method is frequently preferred in the industry in order to achieve high surface quality, precise and fast cutting.

In principle, laser cutting is based upon local combustion, melting, and evaporation of the material by sending focused and amplified rays to the surface to be cut. The directed strong rays break the bonds of the material and thus, the cutting process takes place.

There are some parameters in laser cutting technology that increase production efficiency and directly affect product quality. One of these parameters concerns the used gases that directly contact with the material during the cutting process. Various gases are used in the laser cutting process, depending on the material type, in order to remove the melted material from the surfaces and to achieve better cutting edges. Burrs are removed from the cutting area by using pressurised nitrogen gas (on average 12-20 barg) by creating a mechanical force. The quality of nitrogen gas that contacts with the cut material is very important. If the percentage of oxygen as an impurity in nitrogen gas increases, the material is oxidised, and the cutting quality deteriorates.

Pure nitrogen gas acts as a barrier between the air and the product during the cutting process and prevents corrosion of the product. Thus, the problems such as rusting, darkening, and burrs caused by contact with oxygen during cutting or colour change (yellowing) due to corrosion are minimised. Since there will be a slower cutting process, especially in thick materials, the material surface has the capacity to come into contact with oxygen more. Therefore, in order to obtain a high-quality cutting surface, the minimum nitrogen purity is typically 99.995% in metal cutting processes. It should be noted that certain metal cutting that does not require a smooth finish can accept lower nitrogen purities, at the risk of the aforementioned problems.

Using nitrogen gas in metal cutting processes also increases the production speed. In the material that is cut with oxygen gas, the heat is released as a result of the exothermic reaction during the cutting process. In terms of being a controlled cutting, the cutting process speed with oxygen gas should be much slower than the processing speed with nitrogen gas.

Airline design from compressor to gas drying system

As aforementioned, using nitrogen gas has lots of beneficial aspects in metal cutting plants. However, using manifolds as nitrogen sources for these systems is not always the most cost-effective means of doing so. As also widely known, nitrogen gas is the most important expensive utility for those companies.

Mikropor Nitrogen Generators (MNG Series) can easily supply high-quality and cost-effective nitrogen gas for such applications. Mikropor MNG Series systems use PSA (pressure swing adsorption) technology for generating nitrogen and thus, the gas can be supplied to the customer onsite and at the desired capacity, with purity a range from 95% to 99.999%.

In a PSA system, there could be 0.5% and 0.1% oxygen in the 99.5% and 99.9% purity nitrogen, respectively. In some metal laser cutting processes, the contaminants in the pure nitrogen must be very low, where the purity level is expected to be 99.999%. For such high purity nitrogen gas, the air: nitrogen ratio is generally 8-9 when it is produced by PSA method. However, the smaller the air: nitrogen ratio, the smaller the capacity of the compressor, filter, or nitrogen generator. For this reason, to reduce this ratio it is better to use a nitrogen purification system which incorporates a deoxo unit addition to the PSA system. In this configuration, 99.5% or 99.9% pure nitrogen produced by PSA means can be increased to 99.999% with an air: nitrogen ratio of just 3.0. This results in significant reductions of both investment costs and energy consumption.

With 35+ years of experience, Mikropor knows these customer application requirements and has created the Mikropor Deoxo System (MDX) for customers who need 99.999% pure nitrogen gas. In this series, 99.999% pure nitrogen can be produced with a dew point <3°C. The air: nitrogen ratio of this machines is 3.0, which means the end-user requires a smaller size air compressor compared to traditional nitrogen production systems. For that reason, the investment cost and energy consumption of the machine decreases remarkably. The long-term service life of the deoxo catalyser and the high efficiency of nitrogen production further underline the strength of the MDX series.

MMDX-60-1110-150-W-40C-7015.

In addition, Mikropor can provide 99.999% pure nitrogen production with -40°C dew point too. In this way, any corrosion caused by water in the laser cutting process is also eliminated. To produce such a low dew point, nitrogen dryer units should be added after the deoxo system. Mikropor Dryer Systems (MGD Series) lower the dew point up to -40°C, without loss of pure nitrogen gas during the regeneration process.

A -40 °C dew point and 99.99% pure nitrogen produced by the PSA nitrogen generator can be given to the system without any loss in production, and a high-quality cutting surface can be obtained and sustained in the customer system.

GAZ SYSTEMES designs and manufactures a wide range of medical gases production and distribution equipment.

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