Process For Coating Discrete Articles With A Zinc-based Alloyed Layer

Abstract

The present disclosure concerns a process suitable for coating discrete articles with a zinc-rich, fully alloyed layer. A known method for the corrosion-protection of such articles comprises the steps of hot-dip galvannealing, typically followed by painting. This hot-dip process has however to be performed at a high temperature, thereby submitting the articles to severe thermal stress. A novel vacuum deposition process of Zn is therefore presented. It is characterized in that, in the step of contacting the article with metallic Zn vapor, the temperature of the article is equal to or higher than the dew point of the Zn vapor. The process results in a coating having a uniform thickness, even on less accessible surfaces. The surface roughness is well adapted for the adhesion of paint.

Description

[0001] This application is a divisional application of a Chinese invention patent application with an application date of February 4, 2010, an application number of 201080006697.3, and an invention title of "Process for Coating Discrete Workpieces with a Zinc-Based Alloyed Layer". technical field [0002] The present invention relates to a process for coating discrete workpieces with a zinc-based alloying layer. In particular, the present disclosure relates to a process suitable for plating workpieces, especially discrete articles, with a zinc-rich fully alloyed layer. Background technique [0003] Discrete workpieces refer to discontinuous workpieces, which generally have at least one concave surface. They usually contain a combination of connected parts. [0004] The disclosed process is suitable for applying a zinc-based protective coating on iron or steel, wherein Zn-Fe intermetallics are formed throughout the thickness of the coating. This coating is similar to the la...

AI Technical Summary

Problems solved by technology

[0013] However, hot dip coating at such high temperatures can lead to potentially harmful thermal stresses in the workpiece

Also, the characteristics of the steel itself may be adversely affected

Compounding the problem is a typical hot dip rack with multiple discrete workpieces made of different steel grades

This makes it impossible to determine suitable process parameters for all workpieces, such as bath temperature or immersion time

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