There are several terms used to describe fire and explosion risk. Terms Used to Describe Fire and Explosion Risk The fire triangle and explosion pentagon 2. Well in case of fire explosion which can harm that should be resist or plan to resist. This thought process of appreciating you are one criterion away from a fire is useful, if sobering, to bear in mind when working with these powders. When the metal is being processed with a high power laser, it is done in an inert atmosphere at very low Oxygen levels. When not processing the powder in the machine, it is often subject to ambient oxygen content and thus all precautions are taken to prevent an ignition source (an ESD spark, for example). When handling reactive metal alloy powders, it is important to remember that two of the three requirements for a fire are almost always met and the key lies in avoiding the other criterion. Fire and Explosion Criteriaįigure 2 is a commonly used representation of the criteria that need to be met to initiate a fire (fuel, oxygen and an ignition source) and an explosion (the same three criteria for a fire, plus a dust cloud and confined space). To truly understand the risk associated with powder metals, we must first understand a few basic concepts. Reactivity in this process really pertains to the likelihood of the alloy in question serving as a fuel for a fire and/or an explosion, which are two related but distinct phenomena. The question is: what classifies them as such in the context of this process? Figure 1. Typical metal alloys available for the laser-based powder bed fusion process (from Concept Laser), classified as Non-Reactive and Reactive The reactive metal alloys on the other hand are Aluminum or Titanium based. The former includes steels, Inconels, bronze and CoCrW alloys. I have separated these into non-reactive and reactive metal alloys. Ultimately, this boils down to a safety issue and I believe it is important that we, the users of these technologies, truly understand the fundamentals behind the measures we are trained to follow.įigure 1 below is indicative of the range of materials available currently for the laser-based powder bed fusion process (this selection is from Concept Laser). A more sophisticated calculation involving electrode potentials is required to make accurate predictions in this area.One of the first concepts you come across in metal 3D printing is the notion of reactivity of the powder metal alloys – in this post, I investigate why some of these powder alloys are classified as reactive and others as non-reactive, and briefly touch upon the implications of this to the user of metal 3D printing tools, scoping the discussion to laser-based powder bed fusion. For example, calcium is quite reactive with water, whereas magnesium does not react with cold water but does displace hydrogen from steam. The boundary between the metals that react with water and those that don't is harder to spot. Those metals that can displace H + ions from acids are easily recognized by their position above H in the activity series. Less active metals like iron or zinc cannot displace hydrogen from water but do readily react with acids: Sodium is highly active and is able to displace hydrogen from water: It is important to distinguish between the displacement of hydrogen from an acid and hydrogen from water. However, silver cannot displace copper ions from solution.
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