The Role of Binders and Lubricants in Powder Metallurgy

March 19, 2019

Exotic recipes blend to create hardened products in the powder metallurgy sector. They’re packed with enigmatic chemical compounds. They flow in and around the metal particles so that the granules disseminate evenly and easily find their way into a die assembly. There’s no clumping, no material friction or substance stickiness to impede the process, not when the ingredients include process-augmenting binders and lubricants.

Incorporating Compaction Improving Compounds

A compaction mechanism applies pressure, then the particles smoothly gather into the desired shape. That product form is dimensionally accurate and free of discontinuities. If those actions were carried out under ideal conditions, that’s how the process would take place. However, as all engineers know, we don’t live in an ideal world. In the real world, the compaction operation encounters die wall friction and unpredictable material stresses. To counteract those opposing energies, exotic chemicals pave the way for the interfacial bonding phase. Applied before the sintering stage, those binders and lubricants boost product green strength.

Binding Different Alloying Elements

Even in its granular state, powder metal isn’t classed as a fully homogenized substance. The granules are loaded with carbon and coarse alloying elements. Complicating matters even more, there are special carbon-adhering stages, which exist to add alloying strength to the mix. All of those different material types flow in different ways. They have different masses and chemical compositions, so they segregate, they split away from the uniformly mixed powder. Binders stop segregation and dusting problems from breaking down the powder mix. Tackling these issues, oily and waxy phases hold the powder base in a semi-rigid state, which assures a segregation-less blend, even when those granules exhibit a natural inclination for separating.

Removed Before the Sintering Phase

All-in-all, the process is going well so far. The alloy granules are evenly distributed but they’re not powdering or segregating into structure-weakening clumps. The binder is doing its job. Die wall friction is under control, too, as a result of the pressing lubricant. On exiting the compaction mechanism, the component is loaded with details, and it’s displaying superior green strength. Only, before the heating elements trigger the necking stage, those binders and lubricants need to be removed. They can’t be left in the mix, for they’ll impede the sintering process.

Solvent evaporation treatments and pre-processing heaters are used to remove the superfluous chemicals before the sintering operation starts. The pressing oils and binders were invaluable during the compaction work, but they’re not required anymore. To the contrary, their presence will seriously inhibit the sintering process. Again, as was said right at the start of this post, powder metallurgy recipes are loaded with exotic ingredients, not just self-lubricating oils and powdered alloys.

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