Various surface treatments, surface finishes and surface coatings give metal springs such as Form springs, Flat springs, Spring clips , Stamped and bent parts and Laser parts Subsequent additional properties – for example, they are more resilient, more conductive, metallically pure, rust- or heat-resistant. Gutekunst Formfedern GmbH In addition to classic processes such as pickling, burnishing, electropolishing, bright galvanizing, shot peening, passivating, phosphating, chrome plating, nickel plating and galvanizing, it also offers a variety of special surface finishes for its product range. These include thick-film passivations, powder coatings, Delta®-Tone and Delta®-Seal corrosion protection systems, glass bead blasting, PTFE-Teflon coatings, gold plating, copper plating or galvanized chromating.
Table of Contents
An overview of the most important surface treatments, surface finishes and surface coatings:
Pickling (dry cleaning)
Pickling is a process that removes all contamination from stainless steel surfaces chemically – i.e. by acid. The result is a metallically pure surface of the metal springs, mould springs and metal mould parts. Only then can the protective passive layer form in the next step.
Burnishing (optical, low corrosion protection)
Burnishing is one of the classic surface finishing processes and is a non-layer-forming process in which oxygen is incorporated into the outermost layer. This surface treatment creates a black, thin and non-metallic coating of iron oxide on a low-alloy spring steel. This covering, which is usually less than a micrometer thick, not only enhances the appearance of the material, but also protects it. The process takes place at low temperatures below 150 degrees Celsius. This means that there is no thermal load. The structure and roughness of the shaped spring, the punched part and the laser part are only changed insignificantly. The dimensional accuracy of the coated workpieces remains the same.
Delta®-Tone and Delta®-Seal coating (very good corrosion protection, good sliding)
Due to the structure of the base and top coat, tailor-made solutions can be achieved with regard to the functional properties, the friction behavior and the corrosion resistance of surfaces.
Delta®-Tone (basecoat)
In the Delta®-Tone process, an inorganic and micro-layer-forming base layer is applied to the shaped spring, flat spring, spring clip or the punched and bent and laser part, which contains zinc and aluminum flakes. The subsequent baking process creates a silver-metallic, glossy coating with a uniform thickness. This has excellent corrosion protection properties and at the same time ensures very good electrical conductivity. This enables cathodic protection and avoids the risk of hydrogen embrittlement.
The right basecoat depending on the requirements:
- Delta®-Tone 9000 is especially suitable for springs, spring band clamps and stamped and bent parts.
- Delta-Protekt® KL 100 was specifically developed for threaded parts and is often used in the automotive industry. The base layer can withstand constant temperatures of 96 hours at 180 degrees Celsius.
- With its integrated lubricant, Delta-Protekt® KL 105 makes the use of a topcoat superfluous. The coating is adjusted to the specific coefficient of friction and thus enables cost savings as a 2-in-1 system.
- Delta-Protekt® KL 130 is dark gray and predestined as a substrate for black covering shades, because impact points are no longer visible.
- Delta-Protekt® KL 120 is particularly suitable for connecting elements with threads and for springs or spring band clamps. The red and white corrosion resistance goes far beyond the requirements of other surface finishes.
Delta®-Seal (Topcoat)
Delta®-Seal is a top coat made of organically highly cross-linked, micro-layer-forming material. It optimally complements the previously applied base layer. The coating and baking process leaves a firm, chemical-resistant covering. Excellent resistance to external influences is achieved through the use of certain resins such as acrylate, epoxy and polyurethane resin with an adapted curing.
The Delta®-Seal variants, the black Delta-Protekt® VL 450 or Delta-Protekt® VT 600 and the silver Delta-Protekt® VL 411 GZ.
Thick-film passivation (good corrosion protection, chromium VI free)
The process of this surface treatment is also called transparent passivation. The thick-film passivation is a passivation layer on a zinc layer that has been galvanically applied beforehand. The thick layer passivation creates a clear, iridescent surface that offers good corrosion protection, much better than a zinc layer alone. The process is also known as transparent passivation. Here, a non-metallic protective layer is created on a metallic material such as a steel spring. The coating is absolutely free of chromium VI and is mainly used where conventional chromating cannot be used. This type of surface treatment is very suitable for higher coatings
Electropolishing (visual, good corrosion protection, good sliding)
Electropolishing consists of a single operation in which a very thin layer of the surface is removed by means of anodic dissolution. Impurities, particles, micro-cracks as well as structural disturbances and local stresses are also cleaned up. The treated surfaces are characterized by various properties: They are metallically pure and shiny, free of burrs and particles, closed in the microscopic range and have optimal properties of the base material. Another advantage: The process is particularly gentle and metal molded parts such as molded springs, spring clips, spring clips and stamped and bent parts are neither thermally nor mechanically stressed.
Advantages over other processes are also good corrosion resistance, minimized micro-roughness, improved fatigue strength and a reduced coefficient of friction. Treated surfaces also impress with their low product adhesion and reduced build-up of deposits. They can therefore be cleaned very easily and quickly. This surface technology method is often used in medical devices, for example.
Bright galvanizing (visual, good corrosion protection, heat-resistant)
Bright galvanizing is a galvanically generated protection system for steel surfaces. During the process, a very thin zinc metal layer is created; the layer thicknesses can be adjusted between 2 µm and 30 µm over the length of time in the zinc bath. In order to adequately protect the metal from corrosion, the layer is also passivated or chromated (see section Passivation or Galvanizing + Passivation). This makes the material much more durable. Traces of corrosion, also known as white rust, can be prevented with gloss galvanizing. The surface is also more adhesive, more thermally stable, impresses with its high functionality and looks more appealing.
Glass bead blasting (optical, metal-free cleaning)
With glass bead blasting, compressed air, wheel blasting or injector blasting systems throw very small glass beads at high speed against the steel surface. The process creates very homogeneous surfaces with excellent optical properties on the shaped springs, flat springs, spring clips, stamped and bent parts and laser parts. Glass bead blasting is therefore used for iron-free cleaning and for decorative surfaces.
Shot peening (increased fatigue strength)
Shot peening is a special type of surface treatment. In this process, compressed air or centrifugal wheels shoot the abrasive at high speed at the shaped springs, flat springs and spring clips. The abrasive consists of round or rounded grains that give the process its name.
The aim of shot peening is to increase the surface volume of the material and to generate residual compressive stress. The result is a compression of the material and thus the solidification of the surface. With this process, the fatigue strength of the metal spring is significantly improved.
Passivation (good corrosion protection, self-regenerating)
Passivations arise as a natural reaction on almost every metallic surface and offer more or less good protection against corrosion. In surface technology, artificially created passivation often takes place on zinc, aluminum, magnesium, cadmium or stainless steels. The special form of passivation is the so-called chromating, which used to contain Cr VI compounds and provided very good corrosion protection on zinc, aluminum and cadmium layers. The classic chromating on zinc has been replaced in recent years by the development of Cr VI-free passivations, and the new developments such as blue, yellow, black and thick-film passivations are in no way inferior to the earlier processes in corrosion protection and optical properties. Today, passivations are based on harmless Cr-III compounds and other additives such as fluorides, zirconium compounds or organic complexes. In addition to zinc and aluminum layers, steels, especially stainless steels, can also be chemically passivated.
Phosphating (temporary corrosion protection, primer, low-friction)
Phosphating, also known as bonding, atramentizing or Parkerizing, is one of the most common process technologies in the surface treatment of molded metal parts made of normal steel. Here, a conversion layer of firmly adhering metal phosphates is formed by means of chemical reactions between the metallic surface and a phosphate solution. These surfaces are interesting for applications in which value is placed on temporary corrosion protection, good adhesion for subsequent paintwork, friction and wear reduction or electrical insulation. Phosphating is also very economical and inexpensive.
Powder coating (optical, colourfast in 180 RAL colors, shock and scratch resistant)
In order to process steel springs in this way, the corresponding colored powder is electrostatically charged and applied to the material using a so-called powder gun. The powder coatings are based on various binders such as acrylate, epoxy and polyester resin. They are offered in all RAL colors and in any desired intermediate shade. The only requirement: The shaped spring, flat spring, spring clip, the punched and bent part and the laser part must be electrically conductive. This is true if it is made of steel or aluminum, for example. The powder is then burned into the material in a furnace at temperatures between 140 and 200 degrees Celsius. This creates an evenly dense coating. This impresses with its high light and weather resistance and is also shock and scratch resistant.
Teflon coating – PTFE (optical, very good corrosion protection, heat-resistant, easy sliding, non-stick)
Coatings made of Teflon, also called PTFE (polytetrafluoroethylene), have various properties: In addition to very good corrosion resistance and optimal non-stick properties, they also include low coefficients of friction and resistance to high temperatures. They are used, among other things, in the food industry, in clean room applications, in the textile and paper industry as well as in plant and mechanical engineering.
Chrome plating (visual, good corrosion protection, heat-resistant, easy sliding)
Chrome-plated surfaces are built up in several layers. They protect molded metal parts such as shaped springs, flat springs, stamped and bent parts and laser parts from corrosion and have low static friction. They can be mechanically reworked, are resistant even at high temperatures and do not tarnish. Chrome-plated surfaces are used across all sectors in many areas of the technical industry.
Gold plating (optical, very good conductive, solderable)
With chemical gold plating, the contact spring is coated with a thin layer of pure gold. This means that the solderability of the material is retained and is further improved. Gold-plated materials are not only particularly conductive, they also prevent excessive switching sparks. Gold-plated metal springs are therefore preferably used in the electrical industry. The areas of application also include decorative areas.
Copper plating (very good conductivity, corrosion-resistant, paintable)
With copper plating, a thin layer of copper covers the metallic springs and molded parts. This coating is a popular basis for many corrosion protection systems – including nickel or chrome coatings. Because the covering ensures permanent protection. The layer is usually 5-15 µm. Copper-plated springs also offer improved thermal and electrical conductivity. Another advantage: They can be painted without any problems.
Nickel-plating (optical, corrosion-resistant, slightly acid-resistant, easy to slide)
Nickel is suitable for a variety of different applications and is part of electroplated metal coatings. In order to nickel-plate metal molded parts, they are immersed in a nickel electrolyte – an aqueous solution containing nickel salts – after a special pretreatment. When an electrical voltage is applied, a fine layer is formed on the surface of the molded spring and the molded metal part. The coating is resistant to air and water as well as diluted acids and some alkalis. On the other hand, nickel is unsuitable in contact with nitric acid, concentrated hydrochloric acids and ammonia. The transition metal has a light silver color with a slightly yellowish hue. Due to its characteristic color, it differs very well from chrome-plated surfaces. However, nickel is not resistant to tarnishing and can take on a dark color over time.
Galvanizing (good corrosion protection, insulating, mechanical protection)
When galvanizing, shaped springs, flat springs, metal molded parts and laser parts made of steel are provided with a metallic coating made of zinc. Frequent processes are continuous and discontinuous hot-dip galvanizing, thermal spraying with zinc and galvanizing. The processes differ on the one hand in the production of the protective layer and in their layer thickness. The duration of protection and the mechanical load-bearing capacity of the workpiece also depend on this. Hot-dip galvanizing and thermal spraying produce layer thicknesses of well over 50 µm, with electro-galvanizing the layer thickness of up to 30 µm can be selected individually. Electroplated zinc layers are also only offered with an additional passivation layer, on the one hand these serve to increase the corrosion protection and are offered in different colors (transparent / blue, yellow, black, olive) for optical reasons.
In addition to its shielding effect, zinc is corrosion-resistant. Galvanized workpieces are often used as a sacrificial anode against contact corrosion. This makes them suitable for applications in which more noble metals with different potential for dissolution are conductively connected. The galvanized material prevents the metals from corroding up to a distance of five millimeters. Exposed cut edges and imperfections in the zinc coating can be optimally protected.
Galvanized + passivated (very good corrosion protection, partly with chrome VI)
The passivation (previously chromating) of galvanized shaped springs, flat springs, metal molded parts and laser parts creates a functional and optical surface treatment. It offers a high level of corrosion protection and is available in blue, yellow, black and olive. Before passivation, the steel springs must be galvanized. Only in the next step do they immerse in a solution of passivation solutions with various additives (Cr-III, fluorides, acids). This creates a very thin chemical conversion layer, also known as a conversion layer – without the application of an electrical voltage. The different passivations can be differentiated according to color. Blue (transparent), yellow, black and olive are possible. Most passivations today are Cr-VI-free and RoHS-compliant. RoHS stands for Restriction of Hazardous Substances, i.e. the restriction of the use of certain hazardous substances. Passivations / chromates containing Cr-VI are therefore not suitable, for example, in sectors such as the automotive industry.
A particularly good alternative to chromium (VI) -containing chromates are thick-film passivations. This process creates a clear, iridescent surface with good protection against corrosion.
The following colors and properties are offered galvanized and passivated:
- Blue: The hue turns slightly bluish. There is usually a smooth transition to the transparent. The corrosion protection of blue passivated surfaces is relatively good, the layer is Cr (VI) -free and thus conforms to the RoHS 2002/95 / EC directive.
- Yellow: The color is similar to brass or an impure gold tone. This type of passivation provides corrosion protection comparable to that of blue passivation and is often used when the appearance of the yellow chromating, which was often used in the past, is desired. The layer is Cr (VI) -free and therefore conforms to the RoHS 2002/95 / EC directive.
- Black: With this coloring, the metallic character of the surface is retained in places. Because the color is not as strong as with a paint job. The corrosion protection of the layer is medium to good. The coating is Cr (VI) -free and therefore conforms to the RoHS 2002/95 / EC directive.
- Olive: The color olive is very strong, which means that the metallic character of the upper layer is largely lost. This layer contains chromium (VI) and is therefore not RoHS-compliant.
- Thick film: Thick-film passivation is the latest development in passivation layers on galvanized surfaces and, with regard to corrosion protection, is a worthy replacement for the yellow chromating containing Cr-VI, which was often used in the past. The thick-film passivation is transparent to slightly iridescent, it is Cr-VI-free and therefore conforms to the RoHS 2002/95 / EC directive.
Tin-plating (very good conductivity, chemical-resistant and food-safe)
Tinned Technical springs are particularly interesting for the electrical and food industries. With this type of surface treatment, an even material coating with a very good layer thickness distribution is applied to the metal spring with the aid of electricity. The process can be used with spring steel, stainless steel, brass or copper. Tin-plated components are chemical and corrosion resistant, have high conductivity and can be just solder . They have a low contact resistance and very good sliding properties.
Do you need more information about surface treatment, surface finishing and surface coating of shaped springs, flat springs, spring clips, stamped bent and laser parts? You can reach the technical department of Gutekunst Formfedern GmbH by phone at (+49) 07445 85160 or by email at info@gutekunst-formfedern.de .
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