Hydrogen Embrittlement and the Process of Electroplating Compression Springs
Very frequently – throughout different walks of life – we hear the term “it is plated.” When referring to jewelry, this usually means that it is not really gold but is made of some cheaper material and gold-plated to look like gold. Springs are very often plated for the same reason.
The Process of Electroplating
Many times springs are quite visible and “ordinary” spring steel lacks luster. To respond to the aesthetic needs, the spring is often plated with a nice, shiny material.
Compression springs are also often plated with other finishes for the purpose of rust prevention. But the purpose is the same. If a spring is in a toxic environment it will oxidize quickly. That same spring could be made out of stainless steel but stainless steel is more expensive. Consequently, a spring is often plated not for aesthetic reasons but purely for rust prevention.
The term plating is a shortened form of the term “electroplating”. When a spring is plated, it is dropped in a bath that contains the desired finish. Baths could have zinc, silver, or gold in them. Once the spring is immersed in the appropriate bath, a charge is sent through the water which lines up the ions such that the material in the bath adheres to the spring. In order for this to happen properly hydrogen is created.
What is Hydrogen Embrittlement?
Because hydrogen is the smallest element, if the spring is in any way porous the smallest element worms its way into the porous surface. As the spring is removed from the bath, the hydrogen can actually cause micro-cracks in the material. When the spring is deflected these micro-cracks can expand and actually lead to spring failure and breakage. This failure is known as hydrogen embrittlement. Heating the spring immediately after the electroplating process thereby “boiling” off the hydrogen before it can cause any damage may prevent hydrogen embrittlement. However, this process is not 100% effective and hydrogen embrittlement may persist.
Not all spring materials are porous. There are basically two types of spring materials –
oil-tempered and cold-reduced.
The first type is heated in a high temperature oven and then immersed in oil and then sent into a second oven at a lower temperature. These materials are called oil-tempered. There are many different alloys such as oil tempered chrome vanadium or oil tempered medium basic. The point is they are all heated and then immersed in oil and then heated again at a lower temperature. This is the type of material that has a porous finish and can be subject to the hydrogen atom working its way into the structure and causing hydrogen embrittlement.
The other type of spring material is known as cold-reduced material. This family of materials starts out as a larger size and is then pulled through cone-shaped dies. As it is pulled through these dies the wire becomes smaller and longer. In order to reach spring-tempered status the wire may have to be pulled through and reduced seven times. In doing so, sheen develops on the surface of the material, which makes the material much less porous and therefore not as susceptible to the hydrogen ion working its way into the body of the spring.
For many years, oil-tempered wire springs were frequently electroplated and even if they were heated directly after the plating process, they frequently failed. The failure rate was so prevalent that the national trade association of the spring industry (known as the Spring Manufacturers Institute) now defines hydrogen embrittlement of oil-tempered wires as a design flaw rather than a manufacturing flaw.
With today’s higher precision manufacturing, most spring companies will warn their customers that they should redesign their oil-tempered springs to hard-drawn springs if those springs are to be electroplated.
In spring manufacturing, we have the capacity to create virtually any shape and type of spring with a wide variety of compression springs, possessing many properties, for an array of uses. We are running our 150th anniversary special "Springs for $150" for the remainder of the calendar year (2016), so take advantage of our special promotion and contact one of our Springs Geeks today to find out which compression spring will work best for your next project!