Blending in Powder Metallurgy

Blending in Powder Metallurgy

What is blending in powder metallurgy?

Combine powders, alloying elements, and lubricants to determine the characteristics of finished product. This process is referred to as blending or mixing.

This blog takes a deep look at powder metallurgy blending process. You will learn the following.

  • Blending Steps in Powder Metallurgy
  • Testing Mixed Metal Powder
  • Factors Affecting Blending process
  • Main Powder Blending Equipment

Blending Steps in Powder Metallurgy

Blending process usually has the following steps.

1. Choose Metal Powders

Choose the raw material for blending process, including basic metal powders and alloying elements.

Metal powders are the cornerstone of the powder metallurgy process, influencing the performance of the finished component. And alloying elements directly improves the corrosion resistance and mechanical strength of parts.

Commonly used powdered metals include:

  • Iron
  • Copper
  • Aluminum
  • Tungsten
  • Stainless steel

Main alloying elements are as follows.

  • Nickel (Ni)
  • Chromium (Cr)
  • Molybdenum (Mo)
  • Manganese (Mn)

2. Weight and Proportioning

After selecting the powders, calculate the weight percentages for each material based on the final product’s requirements. Here are the powder metallurgy material standards in the United States, Japan, and Germany.

Metal Powder Industries Federation (MPIF)

MPIF Standard 35: This standard defines the right materials for making powder metal parts.

Japanese Standards Association (JSA)

JIS Z 2500: It specifies the requirements for sintered metal materials, including their chemical composition and mechanical features.

German Institute for StandardizationDIN

DIN 30910: This standard specifies the general characteristics, classification, examining, and quality requirements of sintered metal materials excluding hard metals.

3. Blending

During blending process, metal powders are mixed by blending equipment, such as V mixer. The purpose of blending process in powder metallurgy is to make even metal powders.

According to the needs, you can adjust the speed and swing amplitude appropriately to achieve a better mixing effect.

Powder metallurgy mixers have a feed inlet and an outlet for easy operation. And it can mix raw materials ranging from several hundred kilograms to a ton at a time. Usually, mixing 1,000 kg of metal powder takes about 1 hour.

The time and speed of powder blending process are carefully controlled to prevent demixing. This is when powders separate because of differences in density or particle size. In addition, mixed metal powders are typically kept for no more than a week.

4. Adding Binder and Lubricant

Binders offer essential adhesion between the particles. This helps mixed powders remain intact during the following compaction process.

Main binders are as follows:

  • Polyvinyl alcohol (PVA). This blinder provides excellent adhesion and burns off cleanly during sintering.
  • Acrylic resins. These deliver good green strength and are easily removed in the sintering process.
  • Cellulose-based binders. Such as carboxymethyl cellulose (CMC), are biodegradable, reducing environmental impact.

Lubricants reduce the friction between metal particles, which makes it easier for the powders to flow when mixed. It makes the mixing process smoother and more efficient.

  • Zinc Stearate. It lowers friction during compacting, thereby extending die life.
  • This lubricant provides excellent lubricity at high temperatures.
  • Stearic Acid. It’s frequently used for its good lubrication and evaporates cleanly during sintering, leaving no residue.

Testing Mixed Metal Powder

Metal Powder attributes such as flow rate and density are examined to ensure compliance with standards. Evaluate

Testing mainly include:

  • Flow rate

Flow rate shows how fast the powder flows through a funnel or orifice. A higher flow rate indicates easier handling. Factors such as particle shape, size, and texture affect it.

Bulk density measures the mass per unit volume of the powder when poured into a container. It shows how densely the powder will pack together when compacted. A higher bulk density suggests the powder will form denser, more stable parts.

  • Particle Size:

The size of powder particle influences how they mix, flow, and pack together. When particle sizes are similar throughout, it assists the mixture stay even and ensures the final product is consistent. Particle size analysis uses techniques like sieving or laser diffraction to ensure consistency.

  • Chemical Composition

Contaminants such as sulfur, phosphorus or oxygen can lead to poor mechanical properties and other defects. Analyze chemical composition to avoid defects.

The following are the parameters of several metal powders.

Material

Flow Rate

Bulk Density

Particle Size

Chemical Composition

Copper powder

/

3.76 g / cm3

45 µm / 325 mesh/ 0.045 mm

Cu 99,96%

(Al) Aluminium : 0.004% Max

(Cd) Cadmium: 0.001% Max

(Pb) Lead : 0.001% Max

Iron powder

26.3 s/50g

2.94 g / cm3

140 µm / 105 mesh / 0.140 mm

Carbon (C) : 0.004%

Sulfur (S) : 0.0101%

Oxygen content (O): 0.08%

Manganese (Mn): 0.179%

Stainless steel powder 316L

/

2.82 g / cm3

45 µm / 325 mesh / 0.045mm

Ot: 0.39

Carbon (C) : 0.038%

Molybdenum (Mo): 2.90%

Silicon (Si) : 0.48%

Chromium (Cr): 16.00%

Nickel (Ni): 13.40%

Source: Wide Range Metals

Factors Affecting Blending in Powder Metallurgy

Several key factors influence the powder metallurgy mixing process:

Powder Size and Distribution

Uniform particle distribution promotes better powder cohesion, reduces voids, and results in a more balanced mixture. Smaller particles mix more smoothly, improving powder flow and compaction. This helps powder metal parts reach consistent mechanical properties.

Powder Shape

Spherical particles easily slide over each other and blend well. Their smooth shape lowers friction, helping them to move and mix better.

Meanwhile, irregular or angular particles are different. They tend to lock together, forming a strong bond that makes the final product stronger. However, these irregular shapes can also disrupt smooth mixing, causing uneven blending.

Main Powder Mixing Equipment

  • Tumbler Mixer

A tumbler mixer features a cylindrical container that rotates on a platform. Its smooth interior stops powders from sticking and makes sure they mix evenly. It’s gentle and perfect for mixing fine metal powders without damaging them.

  • Double Cone Mixer

This mixer has two conical sections joined at the bases, forming a diamond shape. It rotates horizontally along its axis. This design is good for mixing powders of different sizes and densities. So it’s effective at creating uniform mixtures and preventing separation.

  • V Mixer

V mixer has a V-shaped chamber that spins around a horizontal axis. The V shape makes powders to slide and mix back and forth. This motion helps distribute the powders evenly and Precludes clumping.

 V Mixer for Powder Metallurgy

  • Ribbon Blender

It has a U-shaped trough with two ribbon-like blades rotating in opposite directions, ensuring balanced distribution of powders. The blades push the powders back and forth, mixing them along the trough. This design is effective for large batches, minimizing segregation.

  • Planetary Mixer

Planetary mixers have a central mixing blade that spins on its axis while orbiting the container. This dual movement ensures thorough mixing and avoids segregation, creating a consistent blend. The mixer also ensures that the powders reach all areas of the container, reducing Inconsistent mixing.

 

From our insights, traditional powder metallurgy mixing process works well for base metal powders like iron and copper. However, for metal powders that contain alloying elements, we usually use prefabricated powders. This is due to the fact that these elements typically have a higher melting point than base metals. As a result, it becomes challenging for the alloying elements to reach a molten state during sintering.

 

FAQ

 

1. Is the Powder Metallurgy Mixing Process Eco-friendly?

Powder metallurgy mixing process is beneficial to the environment in some ways. It uses recyclable and Biodegradable materials, which helps minimize environmental damage.

Also, using mixing techniques that waste less and energy-efficient mixers facilitates in lower the carbon footprint

2. Does the Powder Metallurgy Blending Process Require a Separate Space?

Yes, the powder metallurgy mixing

needs a separate space. Dust can spread and harm air quality, so a dedicated area is important.

This space should include air purification and dust removal equipment to reduce the impact on the environment. Moreover, this process is a key concern for the China Environmental Protection Bureau.

3. Will the Powder Metallurgy Mixing Process Cause Physical Harm to the Operator?

Yes, handling metal powders can be harmful. Breathing in the fine dust can cause lungs problems. Besides, the powders can irritate skin or result allergies. That’s why it’s important to wear masks and gloves. It’s equally important to keep the workplace well-ventilated to protect workers’ health.

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