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The following article is reprinted with the permission of Pneumadyne, Inc. TECO has placed this document on our web page because it is a very good summary of metals and finishes. For more information on the products and services Pneumadyne offers, visit their website: www.pneumadyne.com.
The Pneumadyne Advantage
Pneumadyne uses a variety of metal finishes, chemical finishes and anodizing to enhance our product line. The plating process provides corrosion resistance and the result is a pleasing appearance. In this issue we discuss the procedures and benefits of the finishes used by Pneumadyne.
Materials
When discussing any type of finish it is important to first address the material to be treated. Pneumadyne uses a variety of materials in the production of pneumatic components; often a single valve contains multiple materials and finishes. The following is a brief description of each material and the type of finish we use to protect and enhance its’ appearance. There are five basic materials used in the production of our product lines:
Aluminum: one of the chemical elements, a silvery, lightweight, easily worked metal that resists corrosion and is found in abundance: symbol: Al.
Aluminum is light in weight compared to steel, brass, nickel and copper and it resists corrosion and readily accepts a wide range of surface finishes. Pneumadyne uses aluminum in the manufacture of manifolds and larger valve bodies.
When newly machined aluminum surfaces are exposed to the atmosphere, a thin invisible oxide skin forms immediately which protects the metal from further oxidation. This self protecting characteristic gives aluminum its high resistance to corrosion. A variety of finishes can be applied to aluminum for protection against substances and conditions that destroy the natural oxidated layer.
Brass: a yellowish metal that is essentially an alloy of copper and zinc.
Brass offers numerous characteristics that make it a practical choice of material. It is a semi soft non-ferrous alloy that is easy to machine and rather inexpensive. Pneumadyne uses brass for fittings, valve stems, end caps and spools, porting, mounting nuts and smaller valve bodies.
Steel: a hard, tough metal composed of iron alloyed with small percentages of carbon and other metals to produce hardness and resistance to rusting.
Cold rolled steel offers strength and durability yet is ductile and can be shaped and formed. Pneumadyne uses cold rolled steel for cam actuators and mounting brackets.
Stainless Steel: Steel alloyed with chromium, making it virtually immune to rust and corrosion.
Many different types of stainless steel are used by Pneumadyne:
302: for spring wire, spiral pins, snap rings- tough and ductile.
303 (Carpenter Project 70 brand): free machining steel suited for automatic screw machine work.
302 -grade 25: for ball bearings and for plugging holes.
Zinc: a bluish-white, metallic chemical element, usually found in combination, used as a protective coating for iron, as a constituent in various alloys, as an electrode in electric batteries, and in the form of salts, in medicines: symbol Zn.
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| The above photo illustrates the wide variety of materials and finishes used for Pneumadyne components |
Zinc is a plentiful metal with physical attributes which allow it to be cast into very intricate shapes, with closer dimensional limits and thinner walls than aluminum. Zinc casts are produced with extremely smooth surfaces that readily accept plating and other finishing methods. Pneumadyne uses die cast zinc for "O" Series normally closed valve bodies (also available in nickel plated brass), this process allows for high volume runs to be produced in a short amount of time.
Finishes and Processes
All finishes used by Pneumadyne are high quality and within MIL (Military) specifications and the ASTM (American Society for Testing Materials) standards. The application of a finish involves a degreasing preparation and a series of bath solutions and rinses with cleanliness and temperature closely monitored throughout the process. There are a variety of finishes and processes used by Pneumadyne:
Bright dip, chromate on brass, is a common procedure used to treat raw brass. This is a chemical rinse that removes oxides from the surface, however, it offers the least resistance to corrosion. This process improves the appearance of brass and provides increased resistance from tarnish.
Zinc dichromate provides a finish used to protect brass and zinc cast parts from corrosion. Zinc plating is applied first for corrosion resistance and then dyed various colors. Pneumadyne uses black dichromate with an additional layer of lacquer which provides further protection from corrosive agents as well as a lustrous shine.
Electroless nickel plating can be applied to brass and aluminum to produce a hard, smooth surface which protects against oxidation, corrosion, and wear. In this process the product is electro cleaned, acid dipped and is submerged into an autocatalytic plating solution containing nickel. Under specified conditions, the bath automatically coats external surface and internal cavities with a thickness of .0002" to .0003". The coating is so thin 2-56 UNC threads can be uniformly covered. After every batch the bath pH is adjusted to the appropriate alkali level and nickel is added.
Electroless nickel with PTFE is a plating used on brass and aluminum, it provides lubricity without the need for additional lubricants. In this plating process ENI and PTFE are mixed to form a slippery, corrosion resistant coating.
Anodizing is a controlled oxidation process, it effectively insulates aluminum from electricity providing durable protection in environments corrosive to aluminum. In testing for corrosion to the base metal, anodizing can withstand 400 hours of salt spray testing!
Pneumadyne uses anodizing, a clear, thick, hard, impervious film of aluminum oxide processed in an acid electrolyte and then sealed in boiling water. Anodic coatings can be dyed a variety of colors, the final seal for color anodizing is a nickel acetate bath. Pneumadyne uses black anodizing as the standard color on components, however there are over thirty colors available for large quantity orders (contact factory).
Black Anodizing with a PTFE coating can be applied to aluminum and adds lubricity to the advantages of the anodized finish.
Passivating is a cleaning procedure performed on stainless steel to remove surface contamination and foreign matter, primarily iron, and to promote a complete oxide film naturally acquired from the atmosphere. This controlled process allows stainless steel to achieve its’ optimum corrosion resistance.
The passivating process includes cleaning (either degreasing or alkali cleaning) immersion in 20% nitric acid at 1200/1400 F for thirty minutes, a water rinse and dry. Cleanliness throughout and water softness are important.
Electro nickel plating is a process that uses electricity to apply a thick, durable, corrosion resistant nickel surface. Electro nickel is ideal for use on products where dimensions are not critical. Pneumadyne uses electro nickel on cam actuators and mounting brackets, these products are stamped out of steel sheets, shaped and then plated.
We have discussed several of the standard finishes used by Pneumadyne, however we are not limited to those mentioned. Pneumadyne has provided special finishes on medical devices which can actually been implanted in the human body!
Pneumadyne cares about the protection of our environment. All our finishing processes comply with MIL- Q-45208 and all waste fluids are in full compliance with EPA regulations.
