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MECHANICAL DESCALING

To cold reduce hot rolled mill rod it is most advantageous to thoroughly remove the mill scale, heat treatment oxide if present and oxidation from the atmosphere (rust) the rod is exposed to after it leave the producing mill.

For most purposes the operational preferred way to clean hot rod is batch acid cleaning.  The product quality is excellent and fully serves a broad range of wire mill products.  We feel that the high standard of cleaned rod is properly acid cleaned rod.

For many applications an overcoat is applied to the acid cleaned rod, such as borax, lime, proprietary pre-coats, phosphate, and other rod surface chemicals.  The applied coating must be thoroughly dried.

 Mechanical descaling comes into consideration for many reasons.

-        Total costs of acid cleaning are too high.

-        Not enough volume for an efficient acid cleaning line.

-        Geographic location of the wire processing plant is not open to acid use.

-       Disposal costs are too high.

-        Incremental capacity cleaning capacity required greater than the acid capacity.

-   High-speed direct drawing of diameters less than 0.040”

Advantages of mechanical descaling

    -    Environmentally friendly

    -    Disposal costs are predictable

    -    No hazardous materials in plant for cleaning.

    -    No variable costs when down.

    -    Low investment per ton processed

    -    Low maintenance.

    -    In line cleaning assures fresh rod.

    -    The process is conducive to strand coating.

    -    Surface enhancement

 Discussion

To effectively and efficiently cold form the wire rods we must remove the hot rolling and if applicable the heat treatment scales. For this discussion will explore mechanical descaling via reverse bending in line with cold reduction.   

Rod for reverse bending mechanical descaling must be ordered from the producer, as rod for mechanical descaling, should be free of rust and dry.   In this case a simple reverse bending descaler will in certain applications work satisfactorily for low speed cold drawing of less than 75 % R/A and for cold rolling of low carbon rods. 

REVERSE BENDING

  For efficient further processing a second step is often required:

  Brushing

This type of loose scale removal is employed for steel to be cold rolled, the removal is not considered sufficiently efficient for die drawing.  The rod passes through the center of the four rotating bushes.  This process is primarily for cold rolling of concrete reinforcement products.

Side Brush

Flat Brush

Sanding

The second operation adds space and requires capital investment and adds variable costs for the power consumed and the replacement of the wear items.  It allows for higher throughput drawing speeds, better die life, and better finish due to the loose scale remaining on the rod being removed.

 Caution!

Consider the back pull and power demand on your wire drawing machine!

Third Operation

For long machines to achieve reductions in area of greater than 80%, higher tensile materials and higher speeds many applications demand a coating over the rod prior to the ripper die.

Dry Lubricant or Dry Carrier Applicator

Wet Applicator

Considerations

    -    Not suitable for all applications such as plating quality

    -    Scale dust control, may need a vacuum system.

    -    Higher power required on the drawing machine. 

    -    Not all rod reacts the same, rod for mechanical descaling should be ordered.

    -    Indoor storage for minimum one-day turnover

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