3 Fundamentals of press design

462 Solid forming (Forging)
phide is used when large deformations, i.e. large true strains, are present.
In addition, molybdenum disulphide creates fewer problems as
regards the accumulation of surplus lubricant in the dies. The upper
application temperature limit is around 350 °C. At higher temperatures,
molybdenum trisulphide is created, which is ineffective as a lubricant.
Molybdenum disulphide is also applied in an immersion bath, and
in some cases sprayed or applied by tumbling. The coated billets should
be stored for one day prior to processing. A storage period of one week
should not be exceeded.
As a rough guideline, the overall sequence of surface treatment with
the respective functions of different baths, bath composition, times
and temperatures is summarized below:
1. Degreasing: Chemical degreasing in a 5% sodium hydroxide
solution at 80 to 95 °C for around 5 to
10 min.
2. Cold rinsing: Removal of sodium solution residues, cold rinsing
in running water for approx. 2 min (water
surface must always be clean).
3. Pickling: Pickling in 12 % sulphuric acid or 18 % hydrochloric
acid at approx. 50 to 65 °C, duration
approx. 10 to 18 min (acid content is correct if
the pickle effervesces).
4. Cold rinsing: Removal of acid residues, cold rising in running
water for approx. 2 min.
5. Hot rinsing: Hot rinsing to pre-heat the parts – influences
the phosphate layer thickness, 70 – 90 °C, for
around 2 to 3 min (at lower temperatures, a
lower layer thickness results).
6. Phosphating: Mainly using zinc phosphate, for rustproof
steels with iron oxolate, 70 to 80 °C for around
8 to 10 min (phosphating comprises an initial
pickling reaction and a subsequent layer
forming reaction, layer thickness approx. 8 to
15 mm).
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998