Tungsten Carbide Rods: A Comprehensive Guide

Tungsten carbide rods are extremely versatile tools used in a wide range of manufacturing and engineering applications. This hard metal possesses excellent hardness, wear resistance, strength, and durability properties that make it an ideal material for applications requiring high precision and performance.

What is Tungsten Carbide?

Tungsten carbide, also known as cemented carbide, is a composite material made by combining tungsten metal powder and carbon. Tungsten carbide is one of the hardest metals commercially used today. It scores about 9 on the Mohs hardness scale, which is slightly higher than titanium, chromium, and cobalt alloys.

Tungsten has the highest melting point of all metals, at 3422°C. By weight, it is comparable to steel, but it is much denser, weighing almost twice as much. The extreme hardness of tungsten carbide allows it to retain its shape at high temperatures and makes it very resistant to wear and tear.

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Key Properties of Tungsten Carbide

  • Extreme hardness and high hot hardness
  • Excellent wear and abrasion resistance
  • High Young’s modulus
  • Low thermal expansion coefficient
  • Resistance to deformation
  • Strength and toughness
  • Corrosion resistance

These unique properties make tungsten carbide an ideal material for applications that involve high temperatures, friction, corrosion, and wear and tear. Some notable properties that set it apart from other materials:

Hardness

Tungsten carbide scores about 9 on the Mohs scale, which makes it extremely hard and rigid. Diamond is the only material that’s harder. The hardness comes from tungsten carbide’s interlocked crystal structure and the covalent bonding between carbon and tungsten atoms.

The hardness makes tungsten carbide highly resistant to wearing, abrasion, scratching, chipping, and deformation under load. This is incredibly useful for parts that interact with abrasive surfaces or hard materials.

Strength

Tungsten carbide has high strength and toughness despite its extreme hardness. The strength comes from the chemical bonds between tungsten and carbon atoms. Parts made from tungsten carbide can withstand high impacts without fracturing.

Thermal properties

Tungsten carbide retains its hardness even at extremely high temperatures. The strength remains constant up to 1000°C. It has a low thermal expansion coefficient, so it resists thermal shock stress.

Corrosion resistance

Tungsten carbide exhibits excellent corrosion resistance and chemical inertness. It resists corrosion from most mineral acids found in the manufacturing and chemical processing industries. However, it can be attacked by hydrofluoric acid.

Manufacturing Tungsten Carbide Rods

Tungsten carbide is challenging to manufacture into parts like rods and requires powder metallurgy processes. Here are the main steps:

Milling and mixing

High purity tungsten metal powder and carbon powder are milled together in a ball mill to obtain a homogeneous mixture of particles. The milling breaks down the particle size and intimately mixes the powders. The ratio of tungsten to carbon determines the final grade of tungsten carbide.

Pressing into a green compact

The milled powder is pressed into the desired shape using a process called cold isostatic pressing. Enormous pressure is applied evenly in all directions to form a solid mass called the green compact. The green compact has the shape of the final part but is porous and fragile.

Sintering

The green compact is heated to just below tungsten’s melting point in a controlled atmosphere of hydrogen. This causes the tungsten and carbon particles to bond metallurgically into a dense, solid part through a process called liquid phase sintering. The end result is a consolidated tungsten carbide material with exceptional hardness.

Secondary processing

The sintered tungsten carbide material may require additional processes like grinding, lathing, milling or other finishing operations to achieve the final rod dimensions, surface finish, straightness, and roundness.

Grades of Tungsten Carbide Rods

Tungsten carbide rods are available in several grades that contain different ratios of tungsten to carbon. The different grades offer a balance between hardness, toughness, and strength. Some common tungsten carbide grades for rods include:

  • K grades (K01, K05, K10, K20) – Contains 3-25% cobalt as a binder. Higher cobalt increases toughness.
  • P grades (P01, P10, P20) – Similar to K grades but has a finer grain structure for added hardness.
  • C grades (C1, C2, C3, C4) – Pure tungsten carbide without cobalt binder. Hardness increases from C1 to C4 as carbon content increases.
  • H grades (H10, H20, H30) – Similar to C grades but with better hardness uniformity for high wear resistance.
  • N grades – Nickel-bonded grades used for corrosion resistance.
  • M grades – Molybdenum carbide-tungsten carbide alloys. Better high temp hardness than pure WC.

Applications of Tungsten Carbide Rods

Tungsten carbide rods offer unmatched wear resistance and durability in the most demanding applications. Here are some of the most common applications:

Machine and tooling components

  • Cutting tools like drill bits, router bits, circular saws, turning inserts
  • Punch and dies
  • Draw dies for wire drawing
  • Extrusion dies for plastics and metals
  • Forming and stamping tools
  • Mandrels, nozzles, and other components

Tungsten carbide allows these tools and components to withstand intense friction, abrasion, and temperatures without wearing down quickly. The hardness also allows for extremely tight tolerances and precision.

Wear parts and surfaces

  • Bearings and bearing surfaces
  • Seal faces
  • Ball valve balls and seats
  • Nozzles
  • Pump impellers and casings
  • Linings for hoppers, chutes, cyclones

WC rods are ideal for rebuilding and hardfacing these high wear parts to extend service life. The corrosion resistance also helps them perform reliably in harsh environments.

Mining and construction

  • Rock drilling buttons and tunnel boring heads
  • Crushing and pulverizing equipment
  • Mining screens
  • Conveyor rollers
  • Grader and snowplow blades

The extreme hardness of tungsten carbide allows these parts to withstand the high impacts and abrasion involved in mining, earthmoving, and construction work.

Metal cutting and machining

  • Guide rods for machine tools
  • Collets and toolholders
  • Grippers and end effectors for robots
  • Profile knives for metal cutting
  • Extruder screws and shafts
  • Embossing rollers

Tungsten carbide’s stiffness, hardness, and thermal resistance enable it to withstand aggressive machining applications without excessive wear or deflection.

Structural Characteristics of Tungsten Carbide Rods

Tungsten carbide rods have unique structural and geometric attributes that enable their exceptional performance:

Grain size

The tungsten carbide grain size affects hardness and toughness. Finer grain sizes below 1 micron result in optimal hardness. Coarser grains improve toughness. Rods use a fine grain size for hardness but add cobalt for needed toughness.

Porosity

Tungsten carbide consolidation during sintering aims to reduce porosity as much as possible. Complete elimination of pores is difficult. Some amount of microscopic porosity remains but engineers try to limit it to under 1% to prevent crack initiation points.

Percent weight tungsten

Higher tungsten content increases hardness and Young’s modulus. But it reduces fracture toughness. Cobalt or nickel binders flex and bridge microcracks. The grade of tungsten carbide balances tungsten percentage and binder to optimize properties.

Density

The theoretical density of tungsten carbide is 15.63 g/cc but practical densities range from 13.5 to 15.1 g/cc. Higher density indicates less porosity. Most grades aim for near full density to maximize hardness and strength.

Grain shape

Grains can have rounded, angular, or irregular shapes depending on how the powders were milled. Angular and interlocking grains improve shear strength. Rounded grains increase resistance to crack propagation.

Surface finish

Rod surface finish is controlled according to application needs. Precision rods have excellent surface finish of under 32 microinches. Rough unfinished rods have higher hardness ideal for wear applications.

Dimensional tolerance

Rod dimensions like straightness, roundness, and diameter are held to tight tolerances. Precision grade carbide rods hold tolerances of +.0002/-.0000 inches on the diameter. This ensures performance in precision instruments.

How to Select the Right Grade of Tungsten Carbide

Choosing the optimal tungsten carbide grade depends primarily on the application requirements. Here are key factors to consider:

Hardness level

Harder grades with higher tungsten content are needed for extreme abrasion and wear resistance. Softer grades are tougher for high impact applications.

Temperature

Higher cobalt content improves high temperature hardness. Pure tungsten carbide is brittle above 600°C.

Corrosion conditions

Nickel binder grades offer the best corrosion protection. Cobalt/tungsten grades resist dilute acids.

Precision needs

Finer grain grades like P and H grades offer maximum precision, flatness, and straightness.

Shock and impact forces

Higher cobalt and nickel binders produce greater fracture resistance for applications with high cyclical stresses.

Always consult the manufacturer’s recommendations based on your operating conditions. They can suggest the optimal grade or custom formulation to maximize service life.

Best Practices for Machining Tungsten Carbide Rods

Tungsten carbide is extremely challenging to machine due to its hardness. However, rod suppliers use the following techniques to achieve precision tolerances:

Diamond grinding

Diamond is one of the only abrasives hard enough to grind tungsten carbide. Diamond wheels and belts grind carbide rods to final dimensions and surface finish. Coolants are critical to minimize thermal damage.

Electrical discharge machining (EDM)

EDM uses high energy electrical sparks to melt and vaporize material. It is highly effective at machining complex or delicate features in carbide rods. A graphite or copper electrode makes the cuts.

Laser cutting

Lasers offer high precision cutting of tungsten carbide rods and enable complex internal geometries. The laser locally melts the carbide along the kerf. Excess heat can alter material properties.

Hard turning

Carbide turning inserts with polycrystalline diamond or cubic boron nitride can hard turn carbide rods. Rigid setups with minimal runout are essential to prevent vibration and chatter.

Hole drilling

Small diameter holes in carbide rods require diamond-coated micro drills. High pressure coolant is used to extract heat and chips. Peck drilling and frequent drill changes are recommended.

WEDM

Wire EDM allows accurate cutting, holes, and slots in carbide rods without tool forces or heat. The wire never contacts the workpiece so there is no tool wear. Extremely fine wires enable small precision features.

How to Care for Tungsten Carbide Rods

To maximize the working life of tungsten carbide rods, proper care and maintenance are essential:

  • Use appropriate cutting parameters – Avoid excessive heat, feeds, and speeds
  • Use flooded coolant – Prevents thermal microcracking during machining
  • Handle carefully – Prevent chips, dings, scratches that reduce strength
  • Clean thoroughly – Remove all oils, greases, grit, grime, and residues
  • Store properly – Keep rods in clean, dry conditions away from vibration
  • Inspect periodically – Check for chips, cracks, corrosion or damage
  • Recondition when worn – EDM, grind, or otherwise refinish worn surfaces
  • Replace when damaged – Do not attempt to reuse fractured, cracked or broken rods

With proper care, tungsten carbide rods can deliver years of reliable high performance even in the most demanding applications. Consult the manufacturer’s recommendations for the ideal handling, maintenance, and storage procedures for your specific grade of tungsten carbide.

Frequently Asked Questions

What are the main advantages of tungsten carbide rods?

The extreme hardness, wear resistance, strength, and thermal resistance allow tungsten carbide rods to outperform other tool materials in demanding applications. The precision and stiffness enable accurate performance even in high precision instrumentation.

Why is tungsten carbide so hard?

The hardness comes from the tightly interlocked crystal structure and strong covalent bonds between tungsten and carbon atoms. Few materials in nature match this atomic bonding strength, so tungsten carbide is exceptionally hard and rigid.

What industries use tungsten carbide rods?

The primary industries include manufacturing, aerospace, automotive, electronics, textiles, oil and gas, mining, construction, medical, and more. Any application that involves wear, friction, abrasion, or high precision utilizes tungsten carbide.

Can you machine tungsten carbide rods?

Yes, tungsten carbide can be machined using diamond grinding, EDM, or laser cutting. Hard turning with CBN or PCD inserts is also possible for finishing cuts. The hardness necessitates slow feeds/speeds and more frequent tool changes.

How long do tungsten carbide rods last?

Properly selected grades used within their design parameters can last for years even decades in extreme environments. Cobalt content and quality of manufacturing determine working life. Periodic reconditioning can extend service life indefinitely.

How are tungsten carbide rods made?

Manufacturing involves milling tungsten and carbon powders, pressing them into a compact, and sintering at high temperature to form a solid consolidated part. Secondary machining processes like grinding achieve the final rod dimensions and finish.

Can tungsten carbide rods be welded or brazed?

Yes, tungsten carbide can be joined to itself or other materials using specialized welding methods. Brazing with high silver content alloys is common. Strict process controls are needed to prevent carbon migration from the carbide.

Are tungsten carbide rods expensive?

Tungsten carbide is more expensive than steel because of material and manufacturing costs. However, the long working life often makes it more cost effective in the long run for extreme wear applications. Cost depends on grade, size, and quality.

What is the difference between tungsten and tungsten carbide?

Tungsten is a pure hard metal whereas tungsten carbide is a composite made with tungsten powder and carbon. Tungsten carbide is much harder due to the tungsten-carbon matrix. Pure tungsten is softer but has excellent high temperature properties.

Is tungsten carbide hazardous?

Like most carbide materials, tungsten carbide rods pose few health or environmental risks in solid form. However, breathing fine WC dust when grinding should be avoided. Always follow safety protocols and ensure proper ventilation when machining tungsten carbide.

Conclusion

With its supreme hardness rating and unrivaled wear resistance, tungsten carbide in the form of rods, bars, plates or其他工具 has become the material of choice for some of the most demanding applications across every industry. Choosing the optimal grade for each application, and caring for tungsten carbide properly allows manufacturers to reduce downtime, extend equipment lifetime, and boost productivity. As material engineers continue innovating new grades and nano-scale carbide composites, the future looks bright for wider adoption of this versatile and durable material.

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