Dayon Spring Finishes

Dayon Spring offers and extensive selection of micro and miniature spring finishes and plating options. In addition, a Dayon Spring engineer can assist with selecting the right finish and plating options for your application.

Micro and Miniature Spring Finishes and Plating

• Passivation
• Tumbling
• Electopolishing
• Shot Peening
• Electroplating
• Electroless Plating
• Chemical Coatings

When designing a custom spring, there are often two primary decisions to make beyond the spring physical dimensions: 1) spring material and 2) spring finish and/or surface treatments. There are a number of spring finish and treatment options depending on the use requirements of your spring. The information below will help to guide you through some common finish and surface treatment options.

Go to Spring Materials to learn about materials right for your custom spring design. An experienced Dayon Spring Engineer can help you at stage in your design process with suggestions.

Shot Peening

Shot peening is a method of cold working metal in which compressive stresses are induced in the exposed surface of metallic parts using a stream of shot. The shot is directed at the metal surface at a high velocity. This process is different from blast cleaning to the extent to which it is controlled to yield accurate and a reproducible result. Shot peening will clean the surface during the process and in the area that is being peened. Achieving fatigue strength is the purpose of shot peeing.

Media or material used for peening can be steel, iron, glass, cut steel or stainless steel wire. Metallic shot is designated by numbers according to size. Shot numbers, as standardized by MIL-S-13165, range from S70 to S780. The shot number is approximately the same as the nominal diameter of the individual pellets in ten thousandths of an inch. The effectiveness of a shot peening operation can measured using an almen strip. An almen strip is a thin flat piece of steel that is clamped to a solid block and exposed to the blast of shot, which will produce a curvature that can be measured. The amount of curvature on a standard almen strip serves as a means of measurement of the intensity of the shot peen process.

Tumbling

A tumbling machine is an open-topped bowl or tub which holds springs. Tumbling and vibration action can deburr metals, clean parts, and help to give springs a brighter finish. The major advantage of bowl vibrators is that a separation system can be incorporated to separate parts from the tumbling and vibration media.

Chemical Coatings

The most common chemical treatments for springs and metal parts range from a phosphoric acid wash on steel that provides limited and short-term oxida­tion resistance, to paints of various types designed to give more lasting corrosion pro­tection. Black oxide is a lower cost option to form a corrosion protective barrier over various types of steel, stainless steel or copper substrates. Black oxide can also dull surfaces where light reflection is not desirable.

Electroplating

Electroplating is the creation of a galvanic cell in which the spring to be plated is the cathode and the plating material is the anode. The two metals go into an electrolyte bath and a direct current is applied from anode to cathode. Ions of the plating material are driven to the plating substrate through the electrolyte and cover the part with a thin coating of the plating material.

Steels, nickel and copper based alloys, as well as other metals are easily electroplated. Nickel, tin and chromium are often used to electroplate steel for corrosion resistance. Chrome plating also offers an increase in surface hardness to HRC 70, which is above that from many hardened alloy steels. Pits in the plating can provide nodes for galvanic action if conductive media, like water, are present. Because the substrate is less noble than the plating, it becomes the sacrificial anode and corrodes rapidly. Electroplating with metals more noble than the substrate is seldom used for parts that will be immersed in water or other electrolytes.

Alternatively, a less noble metal can be plated onto the substrate to serve as a sacrificial anode which will corrode instead of the substrate. A common example of this is a zinc coating on steel, which is also known as galvanizing. The zinc or cadmium coating will gradually corrode and protect the more noble steel substrate until the coating is used up, after which the steel will start to oxidize. Zinc coating can be applied by a process known as hot dipping rather than via electroplating. This will result in a thicker more protective coating and gives a more "mother-of-pearl" type appearance. Electroplated coatings can cause hydrogen embrittlement of the substrate to occur, causing a loss in strength. Electroplated finishes should not be used on parts that are fatigue loaded. Electroplating reduces the fatigue strength of metals and can cause early failure.

Hydrogen Embrittlement occurs whenever carbon steel is pickled in preparation for plating or during an electroplating processes and hydrogen can become absorbed into the material. Cracks can develop in the pickling or plating bath, more often they appear when the plated springs are used in service. The hazard of hydrogen embrittlement becomes more acute when there is high stress concentration, high Rockwell hardness, or a high carbon content. Tempered materials are particularly susceptible to this occurring. To relieve embrittlement, the springs should be baked immediately after plating to drive the hydrogen out of the material.

Electropolishing

Electropolishing is a finishing process used for the polishing of springs made of metal. The idea is essentially the reverse of electroplating. The workpiece is made the anode in an electrolyte, with a cathode added to complete an electrical circuit. In the resulting de-plating, the material is removed most rapidly from raised, rough portions, which creates smooth and polished surface. This process is primarily used for obtaining a mirror-like finish, when starting from smooth surfaces. A final finish of less than 0.05 µm can be obtained if the initial surface roughness (root mean square) does not exceed 0.18 to 0.20 µm. Electropolishing is used for polishing stainless steel sheets and parts.

Electroless Plating

Electroless plating puts a coating of nickel on the substrate without using electric current. The substrate "cathode" in this case (there is no anode) acts as a catalyst to start a chemical reaction that causes nickel ions in the electrolyte solution to be reduced and deposited on the substrate. The nickel coating also acts as a catalyst and keeps the reaction going until the part is removed from the bath. This process can produce a relatively thick coating. Coatings are typically between 0.001 in and 0.002 in thick. Unlike the electroplating process, the electroless nickel plate is totally uniform and will enter holes and crevices. The plating is dense and relatively hard at around 43 HRC. Nickel is the most common material that is electroless plated but this process will work with other materials.