POLYOX™ Additives for Powder Metallurgy
POLYOX™ polymers serve as ideal binders and lubricant additives for powder metallurgy processes. They are high–molecular weight thermoplastic polyethylene oxide polymers with several key properties that make them ideal for improving the efficiency, durability, and quality of parts made via powder metallurgy.
POLYOX™ helps prevent segregation that may occur when alloy-based metal powders are sintered during powder metallurgy processes. It accomplishes this due to a very high-binding efficiency for metal powders, which enables more precise metal-part geometries to be formed. This also allows for increased green strength of compacts after compaction and fewer rejects due to breaking and cracking.
POLYOX™ polymers provide high lubricity to metal alloy powders, facilitating less wear on dies and simpler ejection of parts from the die or mold. As a result, a lower volume of classical lubricants is needed. This lubricating property reduces adhesion and friction between powder particles, which also facilitates easier compaction that requires lower power consumption.
POLYOX™ is a thermoplastic polymer compatible with various part formation techniques, ranging from thermoplastic extrusion to injection molding processes. POLYOX™ also ensures clean burn-off with little to no tendency to char or create ash because it begins to melt at relatively low temperatures (90°C–120°C).
Powder metallurgy manufacturers can use less energy-intensive methods to remove POLYOX™ from prefired compacts before firing due to its ready solubility in some organic solvents and water. This helps provide an alternative to burning out the polymer and is another way to ensure complete binder removal for controlled porosity.
Powder Metallurgy Overview
Powder metallurgy is a more sustainable metal-part manufacturing process that provides manufacturers the advantages of higher production speeds, reduced waste, lower costs, and better accuracy than other processes like liquid metal molding. As such, many metal parts, tools, and equipment used in the automotive, aerospace, and agriculture industries are now being made using powder metallurgy.
The powder metallurgy process begins by combining elemental metal or metal alloy powders with additives such as binders and lubricants that are consolidated into molds. Green bodies, or compacts, which have the intended shape of the part but low mechanical strength, are then formed. After this, the metal particles are sintered, meaning they are bonded metallurgically just below their melting point. The final step increases strength and density when cooled.
Lubricant and binder additives play a significant role in the success of powder metallurgy, even though they make up a small portion of the process by weight. Lubricants assist in clean separation from molds and dies after pressing and are critical during compaction to ensure that metal particles easily slide into place. Binders help control porosity, increase the green strength of compacts, and reduce defects from breaks or cracks. Thus, it is especially important to use high-quality lubricant and binder additives to ensure quality, efficiency, and durability since some parts made from powder metallurgy can be intricately shaped or thin walled. The best-performing additives will allow many types of parts to be reliably and accurately formed using powder metallurgy with excellent quality and efficiency.
Selecting a POLYOX™ Grade
Grade
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Molecular Weight (g/mol)
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100,000
|
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200,000
|
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300,000
|
|
4,000,000
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Use Rate (wt%)
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Injection molding binder: 10–20
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Thermoplastic extrusion binder: 10
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Lubricant: Less than 3
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Generally, the molecular weight coincides with the melting temperature of POLYOX™. Therefore, if a lower burnout temperature is needed, a grade with a lower molecular weight is required. The above grades of POLYOX™ and recommended use rates per application may also be considered for specific uses within the powder metallurgy manufacturing process.
Summary
POLYOX™ provides the necessary lubrication and binding for metal powders, allowing for the highly efficient production of metal parts with various shapes, thicknesses, and complexity. POLYOX™ can be burned off cleanly and at low temperatures or washed out using water or alcohol, giving manufacturers flexibility and ease of removal before sintering. When choosing a binder or lubricant additive for accurate and efficient powder metallurgy processes, choose POLYOX™ polymers.