Different Signs of Sintering Failures

February 28, 2018

In place of superfluous text, we’re digging straight into the indicators that signal a sintering failure. There are different symptoms, signs that crop us with different cues, and it’s our job to clearly identify each one. Where do we start? Well, a deeper look at metal porosity seems logical. After all, that spongy metal structure may not support a specified load.

Reviewing Structural Failures 

The sintering process mixes a lubricant into an accumulated quantity of powder metal. Brass or iron, the sintering alloy distributes the oily substance, then the next stage in the process compresses the mix into a solid shape. If this mix/compression procedure is conducted erroneously, expect a network of microcracks to propagate through the component. Weakened drastically by these multiplying fracture paths, a product failure is in the cards. Heavier loads and drive misalignment errors will likely take advantage of the weakened microstructure. Correct this issue by balancing the mix and boosting particle-to-particle fusing. In that latter case, more pressure or heat will augment the sintering process.

Non-Uniform Additive Distribution 

An uncontrollable grain-growth incident is taking place in the equipment line. The metal is shrinking, growing, experiencing dimensional alterations, and a peculiar homogenization effect. The finished product won’t fit its shaft. Worse still, it’s sitting loose in its housing. If this is a bearing, the drive shaft isn’t going to align properly. The entire rotating shaft, plus it is attached rotor parts, will experience dramatic lifespan fall-offs. This is a scenario that occurs when the alloy mix isn’t properly blended. Special additives help control this material-fusing stage. They regulate the grain boundary, increase product capillary action, and ensure lubricant uptake.

Spotting Signs of Post-Processing Difficulties 

Manufactured to meet precise dimensional tolerances, sintered components sometimes require post-processing machine work. The machinery works its activities, a notch is cut, a bevelled edge is trimmed, and the product is improved by a surface finishing station. Dimensional deformations occur when the machinery is poorly operated. If the tooling isn’t configured properly, the sintered parts won’t fulfil their role. That’s not acceptable, not if the application relies on its high-tolerance rotational behaviour.

Complex shapes and high dimensional tolerances aside, sintering failures often occur at a microscopic level. The sponge-like microstructure fractures, then those fracture paths expand. Like the ingredients in a gourmet meal, the additives, lubricants, and powder metal must blend according to a specially determined formula. From here, the equipment heats and presses the mix until it fuses. Grain size, lubricant type, thermal treatment times, all of these treatment ingredients will impact the final product.

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