Essential Precautions for Ash Content Testing in Resistance Furnaces

A resistance furnace is an industrial heating system that warms workpieces or materials by passing current through heating elements or a heating medium, generating heat via electrical resistance. In mechanical industries, resistance furnaces are used for preheating before metal forging, heat treatment of metals, brazing, sintering of powder metallurgy components, firing and annealing of glass and ceramics, melting of low-melting-point metals, and drying of sand molds and paint films. When conducting ash content testing in a resistance furnace, follow these precautions to ensure accuracy and safety: 1) After the initial ignition (pre-ashing), cool the sample, then carefully add a small amount of deionized water along the inner edge of the crucible (do not pour directly onto the residue to prevent ash from dispersing). This dissolves water-soluble salts and exposes trapped carbon particles. Evaporate the water on a water bath, then dry thoroughly in an oven at 120–130 ℃ to remove moisture (preventing ash from dispersing during subsequent ashing). Ignite again to constant mass. 2) When placing a crucible into, or removing it from, a muffle furnace, pause briefly at the furnace mouth to preheat or cool the crucible. This helps avoid thermal shock and potential crucible cracking. 3) Preheat the crucible tongs by holding them briefly over the electric or muffle furnace before gripping a hot crucible, reducing thermal stress and slippage risk. 4) After ignition, allow the crucible to cool below 200 ℃ before transferring it into a desiccator. Placing it inside while too hot can cause convection that disperses ash, slow the cooling rate, and create a strong vacuum upon cooling, making the lid difficult to open. 5) Once the crucible is in the desiccator, place the lid on first, then gently crack it open to release air. Repeat this venting action several times, then seal the lid and cool to room temperature to prevent ash disturbance. 6) When removing the crucible from the desiccator, remember a partial vacuum may have formed. Open the lid gently to restore atmospheric pressure slowly, allowing air to enter gradually to avoid disturbing or dispersing the ash.

This article was originally published on our Chinese website. You can view the original version below: