Electroplating by the Numbers

About this book

Most engineers meet electroplating as a line on a drawing: “zinc plate”, “bright nickel”, “hard chrome”. The line hides a manufacturing process with its own physics, chemistry, defects, hazards and costs. A plated part can arrive with half the coating the designer intended, with bare metal in a recess, with blisters that lift in a month, or with a coating that is perfect while the steel underneath has been made brittle by hydrogen. Almost all of those outcomes can be predicted, specified against and checked, if the numbers behind the process are understood.

This book is for the people who write that line on the drawing or answer for what comes back: design, manufacturing and quality engineers, buyers and supervisors. It assumes school chemistry and physics, simple algebra and SI units. It does not teach how to run a plating line; that needs trained platers, chemical suppliers and the controls that regulators require. It teaches what a plater’s numbers mean, so a specification can be written clearly, a supplier’s process questioned sensibly and a result checked on evidence.

A 1917 treatise as the starting point

Applied Electrochemistry and Welding, published in Chicago by the American Technical Society, with copyrights of 1914 and 1917, was a practical textbook for engineers and tradespeople. Its first part, by Charles F. Burgess, a former professor of chemical engineering and applied electrochemistry at the University of Wisconsin, explains the electrolytic cell, Faraday’s laws, electroplating, electrolytic refining and the industrial chemistry of the day. Its second part, by George W. Cravens, covers welding.

The plating chapters are short, but almost every principle in them still governs the process: the amount deposited follows the current and the time; the current density decides whether the deposit is sound or burned; a deposit is only as good as the cleanliness of the surface beneath it; plating roughens rather than smooths; and the cost lies mainly in the labour of preparing, racking and finishing. Each chapter of this book takes one of those principles, restates it in modern terms with current units and standards, and works it through a modern case.

The running case

This is an illustration. A sheet-metal workshop orders zinc electroplating with a trivalent passivate for 4,000 mild steel mounting brackets. Each bracket has about 2.0 dm² of surface, including a formed channel that creates a recess, and the drawing calls for a minimum of 8 µm of zinc on significant surfaces. A smaller order of 400 hardened spring clips joins the case in Chapter 7. Through the book the brackets are specified, their plating time calculated, their current efficiency measured, their thickness distribution examined, their preparation, life, rinsing and cost worked out, and the result recorded. The workshop, the plater, the parts, the process settings, prices and results are invented for teaching. They are not KEVOS® work and not data for any real plating process or product.

How to use the book

Read Chapters 1 to 5 in order to understand how a specification turns into current, time and thickness. Chapters 6 and 7 deal with adhesion and hydrogen embrittlement, the two failures that a thickness measurement cannot detect. Chapters 8 to 10 cover service life, the plating line’s chemistry and waste, and cost and inspection. Each chapter ends with an exercise and its worked answer. Current densities are given in amperes per square decimetre (A/dm²), the unit used by most modern platers; the 1917 figures in amperes per square foot are converted where they appear.

Limits and professional responsibility

This book is educational. Electroplating uses corrosive, toxic and in some cases carcinogenic chemicals, high currents, heat and heavy plant, and it produces regulated wastes. In Australia it is governed by work health and safety laws and regulations, Safe Work Australia’s guidance on electroplating, state and territory environmental and trade-waste requirements, Australian and international coating standards, and the chemical suppliers’ safety data sheets. The 1917 solutions and practices, some of which used cyanide openly, are described only as history. Coating standards are named by number and scope; their requirements must be read from the current editions. Where a figure comes from a published source it is cited; where it comes from the running case it is labelled as an illustration and must be replaced with real specification, supplier and measured data before any decision is made.

An original treatment

READOS already compares coating systems in Protecting metals from corrosion and wear, which places electroplating beside galvanising, paint and other treatments. This book goes inside the electroplating process itself. The explanations, the bracket case, the calculations, figures and exercises are original KEVOS® writing. The 1917 treatise is a public-domain historical work; its ideas are summarised and analysed in new words, and none of its text, tables or illustrations is reproduced.