G01Presentation 4 by f0GA99A


									                       Thermal Diffusion

    A Cost Effective, Environment Friendly

By: Moshe Moked
    Unstain North America
    617-566 0058
• First:
• Why am I here?????
• What is Thermal Diffusion Galvanizing?

 It is a method of applying a metallic
 (Zinc alloys) coating to Steel, using
 a metallurgical diffusion process
 rather than hot dip.
• How is it applied?
• It is applied by tumbling the parts to be
  treated in a cylinder which rotates inside
  a furnace, with a powder composed of
  Zinc + alloying elements. The process
  takes place at elevated temperatures,
  between 3000C and 5000C (5700F-
  9300F), over a period of 2-4 Hrs,
  depending on process requirements.
• Illustration of the process:

                Step 1
• Pre treatment – mainly light cleaning.
  – Light Oils Acceptable
  – Light Corrosion Acceptable
Step 1-Pretreatment
Step 2-Loading
         Step 3-
Treatment in a slow rotating
   cylinder in the oven
Step 4 – Cooling
Step 5-Unloading parts
–Filtration system absorbs dust and excess powder
Step 6 - Rinse/Polish/Passivation
Step 7 - dry
 Step 8 – Second
Step 9 – Final drying
      Characteristics of the coating
• The Thermo-Diffusion zinc coating is
  anodic in relation to ferrous metals and
  provides for electrochemical protection of
  steel against corrosion (Sacrificial
  protection – Galvanic action).
• One of the main advantages of this
  method, in comparison with the Hot Dip
  process, is the absence of hydrogen
•The coating obtained follows exactly the contours of the article.
 It’s thickness is uniform over the whole surface of the part,
 including complex-shaped articles (threaded connections, etc.)
• When applying the coating, the parts are placed
  in a container. Since the size of the parts is
  restricted by the size of the container, this
  process is most economic for small-sized
  articles which can be packed closely in the
  container. For long and relatively narrow parts,
  the process works well by providing long
• The coating has strong adhesion to base metal
  due to mutual diffusion of zinc and iron. Zinc
  penetrates to the base metal to about 1/3 of the
  coating thickness.
Typical cross section

          5. FeZn7 + Zn

          4. FeZn7

          3. Fe11Zn40 zinc rich layer

          2. Solid solution Zn in Fe

          1. Base Steel
           US 14-09 Elemental Analysis Shank Diffusion Section





      171 175 179 183 187 191 195 199 203 207 211 215 219
• The corrosion resistance of the
  Thermo-Diffusion zinc coating is
  significantly higher than that of the
  Electro plating and higher than that
  of Hot Dip Galvanizing as well, in
  exposure to industrial and marine
• The coating consists mainly of the
  iron-zinc d1-phase containing 7 to
  10 % Iron.
•   The coating is harder than other zinc coatings
    and offers a good resistance to abrasive wear.
•   The coating provides an excellent substrate
    for additional surface treatment (painting,
    rubberizing, etc.).
• The processing temperature is not high,
  and therefore the coating can be applied
  to parts made of spring or other special
• The process can be used for coating
  parts made by powder metallurgy,
  castings, porous parts, and also to
  preassembled units.
          Where does the process fit in
                your Industry?
• The process is cost competitive with
• Following are some samples of typical
  parts that are coated with thermal
  diffusion. Many similar parts are found
  on towers, poles and various hardware.

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