Spring Finishes and Surface Treatments
Quick Spring provides an extensive array of finishing and plating options for rapid custom springs. Our team of experienced engineers is available to assist you in selecting the most suitable finish, plating and surface treatment options tailored to your specific application.
When designing a custom spring, aside from its physical dimensions, two critical decisions often need to be made: the choice of spring material and the selection of appropriate finishes or surface treatments. The following information will guide you through common finish and surface treatment options commonly used for custom spring designs.
Common Spring Finish and Surface Treatment Options
Shot Peening: Shot peening is a cold working method applied to metal, inducing compressive stresses on the exposed surface of metallic components using high-velocity shot. This controlled process differs from standard blast cleaning, ensuring accurate and reproducible results. Shot peening simultaneously cleans and strengthens the surface, with the primary goal of enhancing fatigue strength. Various materials, such as steel, iron, glass, cut steel, or stainless steel wire, can be used for peening. Shot types are classified by standardized numbers ranging from S70 to S780, reflecting the nominal diameter of individual pellets in ten thousandths of an inch. The process's effectiveness can be measured using an Almen strip—a thin piece of steel that, when exposed to shot, forms a measurable curvature. The curvature on an Almen strip quantifies the intensity of the shot peening process.
Tumbling: Shot Tumbling involves the use of an open-topped bowl or tub that holds springs, subjecting them to vibration and tumbling action. This process serves multiple purposes, including deburring metals, cleaning parts, and giving springs a more polished finish. Bowl vibrators offer the advantage of incorporating a separation system to distinguish parts from the tumbling and vibration media.
Chemical Coatings: Shot Common chemical treatments for springs and metal parts range from phosphoric acid washes for limited and short-term oxidation resistance to various paint types that provide long-lasting corrosion protection. Black oxide, for instance, offers a cost-effective solution to create a corrosion-resistant barrier on steel, stainless steel, or copper substrates. It can also reduce surface reflectivity where needed.
Electroplating: Shot Electroplating involves the creation of a galvanic cell where the spring to be plated acts as the cathode, and the plating material serves as the anode. These two metals are immersed in an electrolyte bath, and direct current drives ions of the plating material to deposit a thin coating on the part's surface. Electroplating is suitable for various metals, including steels, nickel, copper-based alloys, and more. It is often used to enhance corrosion resistance, with nickel, tin, and chromium being common choices. However, caution is required when using electroplated finishes on fatigue-loaded parts, as it can reduce their strength and potentially cause early failure.
Hydrogen Embrittlement: Shot This phenomenon can occur during electroplating, particularly with carbon steel, as hydrogen is absorbed into the material. This can lead to cracks, especially under high-stress conditions. Baking the plated springs immediately after plating can alleviate hydrogen embrittlement by expelling the hydrogen from the material.
Electropolishing: Shot Electropolishing is a finishing process for polishing metal springs. In this process, the workpiece becomes the anode in an electrolyte bath, with a cathode added to complete the electrical circuit. Material is removed more rapidly from raised, rough portions, resulting in a smooth and polished surface. Electropolishing is primarily used to achieve a mirror-like finish, particularly when starting from smooth surfaces. A final finish with a roughness of less than 0.05 µm is achievable when the initial surface roughness does not exceed 0.18 to 0.20 µm. It is commonly used for polishing stainless steel sheets and parts.
Electroless Plating: Shot Electroless plating deposits a nickel coating onto the substrate without the need for electric current. The substrate acts as a catalyst, initiating a chemical reaction that reduces nickel ions in the electrolyte solution, depositing them uniformly on the part. This process results in a relatively thick and uniform coating, typically between 0.001 and 0.002 inches thick. Unlike electroplating, electroless nickel plating can cover holes and crevices, making it suitable for intricate parts. The resulting coating is dense and relatively hard, around 43 HRC. While nickel is the most common material used, this process can work with other materials.
