BACK TO THE BASICS OF SURFACE FINISHING

By
A.F. Kenton

   There are only five ways to do surface removal or modification. Of these five, three are mechanical systems that use abrasives. Mechanical means that energy is used or required to apply pressure to the abrasive and/or material to work together to remove or modify surface features. To do this material removal and modification, all equipment systems use energy in different ways to produce these results.

   Albert Einstein developed a famous formula of E=MC2 to explain what energy is in physical reality. Most people don’t care what it is, but they understand what it can do. Basically, energy translates into power or the speed of movement to effect, change, transfer, or transmute something into a linear progression of something else.

   In mechanical surface finishing, speed is a relationship of where one is to where one wants to be, over a given period of time. It is a negative process of material removal for a positive result. To accomplish this negative task, there is a need for an abrasive material to make surface contact with that which needs to be modified. The best way to increase speed is by pressure and this can be best accomplished by weight, mass, or a combination of both. So, in mechanical surface finishing, we have the two ingredients of Einstein’s formula, energy and mass.

   Now with all of the above information, we can create our own formula for mechanical surface finishing as follows: E+M=S. Meaning, energy plus mass equals the speed of material removal.

   The term speed is correct as an end result; however, speed is a result of pressure. Therefore, a more correct formula would be pressure or E+M=P.

   When energy is applied to mass, movement results. As a result of movement, pressure and abrasive friction occurs resulting in a negative breakdown of the abrasive and the materials being processed within the energize mass. The larger the size of an abrasive particle, the greater the mass. Also, the greater the density of the particles within the mass the greater the weight of the mass.

   How energy and force are applied to the mass is very important and does translate into the speed of the negative material removal. Given the same abrasive mass in different equipment processing systems, the amount of speed or pressure created is significant and/or the surface finishing results are or can be different.

   There are three different types of equipment that energize abrasives. Four if you include hand working of parts. These systems are: 1. Wheel and belt systems, 2. Blasting systems, and 3. Mass finishing systems. Of these methods, mass finishing systems are normally the fastest, best surface improvement, and least labor intensive and expensive processing method for large quantity parts.

   Wheel and belt systems are the best systems for mirror finishes and are good systems for large parts, contour parts, and small quantities. In these systems, energy is applied to an abrasive medium or tool and transferred to the mass or finished part. Energy in the way of pressure is normally applied directly by hand through the tool or part perpendicular to the movement of rotational energy. These systems are the most labor intensive but are capable of removing the most amount of material and produce the smoothest surface finishes.

   Abrasive blasting systems are also good for large parts, contour parts, and surface areas, but not necessarily edges. This process leaves the roughest surface finish of all the mechanical systems. Energy in the way pressure is applied to the abrasive particle medium though air at an optimum angle of 60 degrees to the material being processed. These systems are also labor intensive and controlled by hand and do not necessarily produce repeatable uniform finishes unless these systems are automated. They do produce the best finishes for heavy protective paint like coatings.

   Mass finishing systems are good for most materials and parts under two feet in size or less than two pounds in weight, provided proper media is used. These systems do not require any hand orientation or operations and therefore they are the least expensive systems to produce repeatable uniform surface finishes. Energy is applied through an energize rotational abrasive mass that exerts pressure to the entire contents of the work chamber.

   There has been relatively little changes in the way energy is applied to either wheel and belt systems as well as blasting methods; however, there have been significant advances in mass finishing systems to improve energy forces. For over 2000 years the rotational barrel was the only method of surface finishing parts with abrasive media. Energy is use to rotate the barrel and that energy is transferred to the mass within the barrel by gravity to a portion of the barrel’s contents that moves; therefore, processing is very limited to a small working area within the barrel. Because of simplicity, these systems are still used today.

   With the invention of electric motors and the knowledge of eccentric energy forces came the advent of vibratory equipment to create greater energy and abrasive forces to the entire mass of the work chamber. Instead of the primarily one direction of movement and pressure of 1 force of gravity, vibratory systems produce equal x, y, and z axis movement and pressure of up to 8 times the force of gravity. Vibratory systems improve speed of processing times of 10 to 1 over the old barrel systems.

   The third generation of mass finishing is based upon high energy centrifugal equipment systems. Although the technology has been around for some time, it hasn’t been until fairly recently in the last 20-25 years that these systems have really started to become more popular. The main reason for this to catch on is the cost of the equipment. These machines operate at energy forces of 22-28 times the force of gravity that are applied on the mass and the equipment; therefore, they are expensive to build. Processing time equates to about another 10 to 1 improvement over the vibratory systems.  

   Basically, there are two versions of centrifugal equipment in use today. One is similar to the old 1 g barrel type system; however, instead of one barrel rotating in one direction, the centrifugal system spins 2 to 4 barrels in two different directions at the same time. This movement increases gravity or pressure within the barrels of up to 28 g’s. On the negative side, these barrels are small and they still require hand loading and unloading  the same way as to old barrels. These systems are extremely good for working small parts and producing mirror finish results similar to hand buffing. 

   The second centrifugal system is called the disc finisher. This is more similar to the vibratory machine in appearance, but the only moving part in this system is a spinning disc located in the bottom of the work chamber. This system produces between 20-22 g’s of energy force to the work mass. Like the centrifugal barrel, these machines produce excellent quality finishes. Unlike the closed barrel systems, these machines can be made to automatically loaded and unloaded.

   For more complete information on ALL FIVE metal removal systems and equipment, I just released a new revised second edition copy of my book called “Understanding Deburring /Polishing and Mass Finishing Systems”. This is a 250 page technical book with visuals of all surface finishing equipment, machine classifications, comparisons,  specifications, evaluations, performance charts, standards, supplies, applications and alternatives. For more information go to www.novafinishing.com or call A.F.Kenton 1-800-444-4159.