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Creating smooth steel bar surfaces by removal of thick black scale (oxidation scale)

Processing details

  • remove
  • Scraping

What is the “removal of oxide scale of steel bars” by wet blasting?

This process scrapes off oxide scale (oxide films, black scale) of steel bars generated by heat treatment such as annealing, by using an abrasive. It can be used for pretreatment for cold drawing and surface finishing.

Three features of wet blasting

  • Processing by small diameter SUS grit
    The water transport effect enables precise treatment using fine abrasives
  • Degreasing and descaling performed in one process
    No need for pre-degreasing because the abrasive scrapes the surface off together with dirt. Water also prevents re-transfer of the oil.
  •  Improved work environment
    No dust is generated in the wet process

Picture of wet blasting

Wet blasting is a technique to project a mixture of abrasive and water at high speed with compressed air against a material to clean, process, and modify its surfaces. This technique allows fine abrasives to be used due to wet processing, and is good at forming a fine uneven surfaces while grinding the surface of the workpiece together with dirt and foreign matter.

Comparison with conventional methods

Comparison with shot blasting
  Shot blasting Wet blast
Projection method Projecting steel balls with the rotating impeller Projecting a mixture of small-diameter grit abrasive and water with compressed air
Quality Abrasives and debris remain on the scale as residues. No residues → Abrasives scrape off the oxide scale
Dents are large, requiring finishing
  • Reduced surface roughness after drawing
  • Improved processability → Improved lubricant retention and reduced residual stress due to fine roughened surfaces
Costs Many consumables are used for projecting over a wide area Limited consumables due to projection aimed at the workpieces → Maintenance costs reduced by 1/2
Environment There is a risk due to dust (fire, poor working environment) No need to take measures against dust due to wet method
Comparison with “pickling (chemical treatment)”
  Pickling (chemical treatment) Wet blast
Quality Contact areas between workpieces are not uniformly processed
  • No uneven processing → Each workpiece is fed by roller to be processed individually
  • Inline processing up to drawing is possible
Costs It takes time to etch the alloy material for the removal of scale Since abrasives scrape off the oxide scale, allowing processing regardless of the material.
Environment Generation of neutralized sludge Sludge of 1/20 or less → No acid or alkali used
It is difficult to install new equipment because a large and heavy chemical bath is required. It is easy to build new production lines → Space saving, no notification required

Problems in conventional scale removal processes

Descaling of annealed materials and alloy steels is difficult
Mechanical descaling Pickling (chemical treatment)
Shot blasting Peening
  • Contact areas between workpieces are not uniformly processed
  • Energy costs are huge
  • A large amount of inventory is necessary because a huge amount of time is required to process
    • Cannot be used before finishing because of remaining scale
    • Embeds scale into the bar surface
    • Uniform processing is not possible due to misalignment
    • Machining allowance is large

Application example of wet blasting

Application example of wet blasting

Three points

  • Sharpshooting with compact guns ensures descaling
  • Reduced maintenance costs due to the use of the sharpshooting nozzles resulting in limited wear and tear
  • The descaling method that does not use acid or alkali results in reduced sludge