Cold extrusion surface preparation — verify the pretreatment sequence Consider the following sequence for preparing a steel billet before cold extrusion: pickling → alkaline cleaning → phosphate coating → lubrication with reactive soap. Is this the correct order for a standard phosphate–soap system?

Introduction / Context:
Surface preparation before cold extrusion (or cold drawing) is critical for friction control and die life. For steels, a common pretreatment is the phosphate–soap system. The order of degreasing, pickling, conversion coating, and lubrication must be correct to ensure a clean, chemically active surface that will hold lubricant.

Given Data / Assumptions:

• Work material: steel billet.
• Target: phosphate conversion coat plus reactive soap (stearate) lubrication.
• Operations involved: alkaline cleaning, pickling, phosphate, soaping.

Concept / Approach:
The generally recommended order is: 1) alkaline cleaning (degrease) to remove oils; 2) water rinse; 3) acid pickling to remove oxides/scale; 4) rinse/neutralize; 5) phosphate conversion coating; 6) lubrication in reactive soap. Performing pickling before degreasing allows oil films to hinder acid action and produce uneven activation. Therefore, the proposed order (pickling before alkaline cleaning) is not correct.

Step-by-Step Solution:

Verification / Alternative check:
Process sheets for wire drawing and cold extrusion lines list degrease → pickle → phosphate → soap as the standard flow, sometimes with intermediate rinses and neutralization.

Why Other Options Are Wrong:

• “Yes”: reverses degreasing and pickling.
• Aluminium requires different treatments (e.g., zincate for plating), not phosphate–soap.
• Omitting alkaline cleaning leaves oils that impede coating formation.

Common Pitfalls:
Skipping rinses; mixing up order; applying soap on unconverted steel surfaces resulting in poor lubricant retention.

Final Answer: