Finishing Services

Polishing and buffing are finishing processes for smoothing a work piece’s surface using an abrasive and a work wheel. Technically polishing refers to processes that use an abrasive that is glued to the work wheel, while buffing uses a loose abrasive applied to the work wheel. Polishing is a more aggressive processes while buffing is less harsh, which leads to a smoother and brighter finish. A common misconception is that a polished surface has a mirror bright finish, however most mirror bright finishes are actually buffed.

 

Polishing is often used to enhance the looks of an item, prevent contamination of medical instruments, remove oxidation, create a reflective surface or prevent corrosion in pipes. In metallography and metallurgy, polishing is used to create a flat, defect-free surface for examination of a metal's micro structure under a microscope. Silicon-based polishing pads or a diamond solution can be used in the polishing process.

 

The removal of oxidization (tarnish) from metal objects are accomplished using a metal polish or tarnish remover; this is also called polishing. To prevent further unwanted oxidization, polished metal surfaces may be coated with wax, oil or lacquer. This is of particular concern for copper alloy products such as brass and bronze.

Steel is an iron based alloy that is often combined with small amounts of carbon and other alloys to stabilize the metal structure to enhance its strength, machining and forming properties. The hard structure of steel requires aggressive buffing to achieve a high luster. Because carbon steel is prone to oxidation and corrosion it is most often plated after buffing to retain the luster and bright aesthetic quality.

When chromium is added to iron based alloy it produces a tough corrosion resistant metal called stainless steel. When other alloys like nickel and molybdenum are added it produces grades of stainless that not only have the great wear and corrosion properties but often can be buffed to a beautiful and high luster.

Before steel or stainless steel can be buffed to a high luster it usually needs to have scratches, forming marks, tool lines removed and smoothed out. Often a steel part can have a surface roughness of 100 to 150 µ inch after a normal bending, forming or press operation. This roughness, usually measured in Ra, needs to be reduced by polishing to about 10 to 12 µ inch before it should be buffed. This is most often accomplished by polishing with a progressively finer series of abrasive belts or flap wheels.

The high temperature and pressure of aggressive tangential buffing is common for steel and stainless buffing applications. Heat does not bother steel and stainless since they have very high melt points (2500 to 2700 °F). These parts normally need 9,000 to 10,000 surface feet per minute (SFPM) in the initial cut buff operations to be effective and efficient. In addition, it will often use a sisal or combination cloth & sisal bias buff with a steel cut compound to smooth the part. This is then followed up with a cut & color operation using either a dip treated buff or a mill treated cotton buff to provide a good shine to the metal part. The buffing step can reduces the surface roughness to a surface roughness Ra of <1 µ inch.

For stainless steel or in critical high luster applications a final color buff operation is the final step. This uses a regular or loose weave cotton buff along with a high color compound using a color grain like red oxide mixed with a fine grade of alumina. When this is combined with a color stroke it can produce a beautiful and high luster that brings out the natural luster of the metal.

Electro Less nickel (EN) Plating is a chemical reduction process which depends on the catalytic reduction process of nickel ions in an aqueous solution (containing a chemical reducing agent) and the subsequent deposition of nickel metal without the use of electrical energy. Due to its exceptional corrosion resistance and high hardness, the process finds wide application on items such as valves, pump parts and many others. It is used to enhance the life of components exposed to severe conditions of service, particularly in the oil field and marine sector. With correct pretreatment sequence and accurate process control, good adhesion and excellent service performance can be obtained from EN deposited on a multitude of metallic and non-metallic substrates.

 

In the EN plating process, the driving force for the reduction of nickel metal ions and their deposition is supplied by a chemical reducing agent in solution. This driving potential is essentially constant at all points of the surface of the component, provided the agitation is sufficient to ensure an uniform concentration of metal ions and reducing agents. Electro less deposits are therefore very uniform in thickness all over the part's shape and size. This process offers distinct advantages when plating irregularly shaped objects, holes, recesses, internal surfaces, valves or threaded parts. Distinct advantages of EN plating are:

Uniformity of the deposits, even on complex shapes:

 

• Deposits are often less porous and thus provide better barrier corrosion protection to steel substrates, much superior to that of electroplated nickel and hard chrome
• The deposits cause about 1/5th as much hydrogen absorption as electrolytic nickel and about 1/10th as much hard chrome
• Deposits can be plated with zero or compressive stress
• Deposits have inherent lubricity and non-galling characteristics, unlike electrolytic nickel
• Deposits have the good wet ability for oils
• In general low phosphorus and especially electro less nickel boron is considered solder able. Mid and high phosphorus EN's are far worse for solder ability
• Deposits are much harder with as-plated micro hardness of 450 - 600 VPN which can be increased to 1000-1100 VHN by a suitable heat-treatment

 

The versatility of electro less nickel plating is demonstrated by the wide range of coatings possible. The following are important types of coatings industrially available (reference):

 

Low phosphorous (Hard) : An unique bath providing an as-plated deposit hardness of up to 60 Rockwell. This bath provides a deposit nearly as hard as hard chrome, with the advantage of an uniform thickness inside complex configurations as well as outside. The deposit is so uniform that grinding after plating is eliminated. Low phosphorous electro less nickel offers excellent resistance to alkaline corrosive environments.

Electro polishing is an electrochemical process similar to, but the reverse of electroplating. The electro polishing process smooths and streamlines the microscopic surface of a metal object. As a result, the surface of the metal is microscopically featureless with not even the smallest speck of a torn surface remaining.

 

In electro polishing, the metal is removed ion by ion from the surface of the metal object being polished. Electro chemistry and the fundamental principles of electrolysis (Faraday's Law) replace traditional mechanical finishing techniques including grinding, milling, blasting and buffing as the final finish. In basic terms, the metal object to be electro polished is immersed in an electrolyte and subjected to a direct electrical current. The object is maintained anodic, with the cathodic connection being made to a nearby metal conductor.

 

During electro polishing, the polarized surface film is subjected to the combined effects of gassing (oxygen), which occurs with electrochemical metal removal, saturation of the surface with dissolved metal, the agitation and temperature of the electrolyte.

 

Smoothness of the metal surface is one of the primary and most advantageous effects of electro polishing. During the process, a film of varying thickness covers the surfaces of the metal. This film is thickest over micro depressions and thinnest over micro projections. Electrical resistance is at a minimum wherever the film is thinnest, resulting in the greatest rate of metallic dissolution. Electro polishing selectively removes microscopic high points or "peaks" faster than the rate of attack on the corresponding micro-depressions or "valleys." Stock is removed as metallic salt. Metal removal under certain circumstances are controllable and can be held to 0.0001 to 0.0025 inch.

 

In summary, electro polishing removes metal. It does not move it or wipe it. As a result, the surface of the metal is microscopically featureless, with not even the smallest speck of a torn surface remaining. The basic metal surface is subsequently revealed — bright, clean and microscopically smooth. By contrast, even a very fine mechanically finished surface will continues to show smears and other directionally oriented patterns or effects.

Chemical etching, also known as metal etching, is a process of dissolving metals or glasses in acids to make them into a particular shape. There are two main types of chemical etching: the process as it was first developed and a more modern method known as photochemical machining.

 

The etching process is preferred for fine metalwork and metal panels, especially those that need specific designs like panels used in making computer parts. Originally, such pieces needed to be made by hand or with expensive machines that took time to calibrate and maintain, but chemical etching vastly reduced the time and expense it took to create fine metal work.

We provide Coating, which is designed in conformation with international quality standards.  Our range is installed with servo motor drive that controls the coating speed. Based on advanced technology, this machine has a pneumatic fine adjustment for pressure and toggle movements of coating scoop.