CAV - Nitrogen in the production of additives for the casting of metals

Article CAV 06/2019

Nitrogen atmosphere for explosion prevention

ASK Chemicals, a supplier of foundry chemicals and tools for the foundry industry, overlays its solids mixer for mixing the additives with nitrogen, thereby avoiding the risk of dust explosions. Nitrogen is produced directly on-site to ensure its constant supply.

Additives play an important role as excipients in the foundry industry. They are used in foundries to avoid casting defects such as veining, metal penetration, scabbing or stress cracks. It is often the case that their addition significantly reduces the proportion of expensive special sands, such as chromite sand, which are used as basic mould materials in foundries for the production of moulds and cores, or it replaces such sands completely. Moreover, additives provide an improved casting surface and therefore enable "plain- free" casting, in which cast parts are coated in an energy-intensive process in order to create smooth surfaces. ASK Chemicals uses a solids mixer with a capacity of 3 m³ for production. In this context, different powdery materials, such as wood flour and graphite, are mixed with each other. This creates a dust atmosphere which, in combination with oxygen, results in an explosion risk. Prior to each filling of the mixer a flush with nitrogen is carried out to completely free the mixer contents of oxygen. To this end, nitrogen is pressed into the mixer in two passes of six minutes each with a volume of 90 m³ per hour. This is then filled with 80 percent useful content and 20 percent nitrogen. The nitrogen for the mixer, which is operated in two-shift operation, has a purity of 99.8%.

The INMATEC nitrogen generator PN 1650 Ontouch with pressure swing adsorption (PSA) technology is also located in the production hall and produces the requisite nitrogen in a quantity of up to 23 m³ per hour. To this end, ambient air is first forced under pressure through an activated carbon filter and a dust filter. The dry and clean air is then passed through a valve block, which is connected to two activated carbon tanks. The valve block automatically regulates the alternating filling of the two adsorption vessels filled with a carbon molecular strainer. The vessels switch alternately from production to regeneration mode. Thus, oxygen and carbon dioxide molecules from the ambient air are adsorbed in one filter, while the filter in the second vessel regenerates under compressed air relief. The generated nitrogen is then buffered in a product tank with a volume of 1000 l. The adsorbed oxygen is led outside via a pipe with a silencer. Pressure swing adsorption, with its two parallel phases of adsorption at high air pressure and desorption at low pressure, provides a continuous flow of nitrogen. The technology allows the PN 1650 Ontouch Generator to produce nitrogen with a purity of up to 99.999% (5.0). The generator at ASK Chemicals is connected to the company’s compressed air system, which also supplies the factory with control air. The on-site nitrogen production is significantly cheaper than using cylinders. Moreover, the CO2 balance is reduced as there is no need for delivery by truck.

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published in CAV CHEMIE PRODUKTION ANLAGEN VERFAHREN 06/2019