Epoxy Painting
This process is used on virtually all substrates including aluminum, steel, stainless steel, and more. You need to determine whether pretreatment is necessary before applying the epoxy. In the case of aluminum, it is advisable to apply a chromate or non-chromate conversion coating such as Alodine which is manufactured by Henkel. Equivalent pretreatments are available from other companies. In the case of stainless steel it is recommended that a pretreatment primer, such as a vinyl butyral wash primer be applied before using the epoxy primer. However, the wash primer must be formulated specifically for purposes of slightly etching the stainless steel. You should contact your local industrial paint store (not your local hardware store) to identify the most appropriate wash primer for your application.
If you have a production line in which you already treat aluminum then you might be able to avoid the use of a wash primer by passing the stainless steel through a chemical etching process.
Please bear in mind that it is extremely important to rinse the stainless steel well and then allow it to thoroughly dry before applying the epoxy. Epoxy primers should not be applied at temperatures below 60°F or above approximately 100°F. At the higher temperature the potlife will be dramatically shortened.
In service epoxies can be used at both low and high temperatures, but I would imagine that you would not want to expose it to temperatures much above 300°F for any length of time.
Passivation
Passivation is a widely-used metal finishing process to prevent corrosion. In stainless steel, the passivation process uses nitric acid or citric acid to remove free iron from the surface. The chemical treatment leads to a protective oxide layer, or passivation film, that is less likely to chemically react with air and cause corrosion. Passivated stainless steel resists rust.
For manufacturers, the industry standards ASTM A967 and AMS 2700 represent the most widely used standards for passivating stainless steel.
oday the industry standards for surface passivation offer three types of passivation. Each type is based on what chemical is used for passivation. The three types of passivation are:
Nitric acid
Nitric acid with sodium dichromate
Citric acid.
Choice of which chemical to use for passivation often depends on customer requirements. Each passivation type has its own advantages and disadvantages.
Chemical conversion coating
The process of applying a chromate conversion coating is referred to as chromating.
Chromate conversion coatings are a type of chemical conversion coating. In chemical conversion coatings, the metal undergoes a chemical reaction at the surface. Unlike plating, which adds a new layer to the metal surface, a chemical conversion coating transforms the existing metal surface into a protective layer via chemical reaction.
The primary benefit of an Alodine coating is aluminum corrosion protection. But chemical film coating with Alodine offers other benefits. The chemical film or Alodine coating leaves a base that provides better adhesion for organic coatings, and it can protect against the loss of electrical conductivity.
Chromate conversion coatings are used for heat sinks, automotive wheels, and everyday aluminum hardware and components. In aerospace applications, chromate conversion coatings are used on aircraft hulls, including shock absorbers, side and torsion struts, landing gear, and flight control systems such as rudder systems and wing parts.
Chem film is applied by dipping, brushing or spraying, and the chromate conversion coating thickness does not change the dimensions of the part. The layer of transformed metal is very thin: Alodine coating thickness is typically only 0.00001-0.00004 inches (0.25-1 μm). Aluminum conversion coating improves the adhesion of both paint and primer if it is applied to an aluminum surface prior to the primer.
Anodize treatment
Turning is a machining process performed by a lathe; the lathe spins the workpiece as the cutting tools move across it. The cutting tools work along two axes of motion to create cuts with precise depth and width. Lathes are available in two different types, the traditional, manual type, and the automated, computer numerical controlled (CNC) type.
The turning process can be performed on either the exterior or interior of a material. When performed on the inside, it is known as "boring”—this method (which can be either horizontal or vertical depending on the orientation of the spindle) is most commonly applied to create tubular components. Another part of the turning process is called "facing” and occurs when the cutting tool moves across the end of the workpiece – it is typically performed during the first and last stages of the turning process. Facing can only be applied if the lathe features a fitted cross-slide. It used to produce a datum on the face of a casting or stock shape that is perpendicular to the rotational axis.
Lathes are generally identified as one of three different sub-types – turret lathes, engine lathes, and special purpose lathes. Engine lathes are the most common type found in use by the general machinist or hobbyist. Turret lathes and special purpose lathes are more commonly used for applications that require repeated manufacturing of parts. A turret lathe features a tool holder that enables the machine to perform a number of cutting operations in succession without interference from the operator. Special purpose lathes include, for example, disc and drum lathes, which an automotive garage would use to reface the surfaces of brake components.
CNC mill-turning centers combine head and tail stocks of traditional lathes with additional spindle axes to enable the efficient machining of parts that have rotational symmetry (pump impellers, for instance) combined with the milling cutter’s ability to produce complex features. Complex curves can be created by rotating the workpiece through an arc as the milling cutter moves along a separate path, a process known as 5-axis machining.
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