Vibratory Surface Finishing Technology

 

Vibration

Vibration is defined as mechanical oscillations around a point of equilibrium or low-frequency, high-amplitude mechanical vibrations. Two fundamental parameters we need to mention when discussing vibration are "amplitude" and "frequency". The distance from the peak to the trough of a wave divided by two is called "Amplitude", while the number of waves (vibrations) passing through a fixed point in a given time is called "Frequency". Vibration can be measured by many different measurement methods and is generally at the top of unwanted conditions in mechanical constructions. Vibratory surface finishing machines produce this unwanted phenomenon as a controllable energy and create a method that can deliver very fast, effective, efficient and high-quality results for the surface finishing industry.

Vibratory Surface Finishing Machines

These are machines that create vibration through a motor that rotates at speeds determined by unbalanced loads, moving the parts contained within. In vibratory surface finishing, energy is imparted to abrasives through vibration and rotational movements. With this energy, the abrasives move and create a micro-grinding effect on the part surface. There are several important parameters that control the motion. These are vibration amplitude (3-5mm), frequency and rotational speed.

Surface Roughness

Parts have a surface quality represented by Ra and Rz values known as surface roughness. These values indicate how smooth the part is, and each surface finishing operation has achievable Ra and Rz values for parts. The selected finishing operation, the desired Ra and Rz value, part geometry, and material type all result in different outcomes.

Surface Finishing

Surface finishing is the method applied to give the part surface the desired properties and can be of different qualities and methods depending on the desired properties of the part after finishing. After surface finishing, the part is either directly put into final use or subjected to a coating-type operation. Vibratory surface finishing is a general term used to bring the surfaces and edges of many different metal and non-metal parts to the desired level.

The most common part surface expectations are;

• Burr removal, • Scale removal, • Surface smoothing, • Edge breaking, • Radius application, • Surface polishing, • Preparation before painting and coating, • Natural stone aging, • Cleaning surface waste from heat treatment. General vibratory surface finishing processes are carried out in the following machines: Circular vibratory machines, Linear vibratory machines, Centrifugal machines and Rotary barrels.

Surface Finishing Consumables

Surface finishing consumables are divided into two main categories: abrasives and process chemicals. Abrasives are subdivided into ceramic abrasives and plastic abrasives, while process chemicals are divided into three main groups: liquid, powder and paste (semi-fluid) forms. In any surface finishing process, abrasives and surface finishing chemicals are used together.

Abrasives

• Abrasives provide the desired level on the surface through mechanical action. They bring the part surface to the desired roughness level by grinding away material in micro-chip form from the part surface. • Chemicals generally serve a lubrication function to reduce friction forces, reduce wear, create corrosion protection effects on the part, facilitate the removal of particles that break away and are cleaned from the surface, and clean the part surface. In addition to these, abrasive geometry also directly affects the quality of the targeted surface finishing process. Abrasive geometry is critically important depending on the shape and complexity of the part. Holes, corners and recesses on the part must be compatible with the shape of the abrasives.

Examples of Abrasive Geometries

Ceramic abrasives are products from the technical ceramics group in which synthetic abrasive powders are contained and various ceramic-based products are used as binders. This structure, prepared at a specific moisture level, is shaped in presses into various forms and sizes and is fired at high temperatures (approx. 1250-1350ºC) to obtain the final product. They are mostly used on iron and iron-derivative metals. In plastic abrasive stones, abrasive particles are held within polyester resin. Compared to ceramic stones, they have lower density and are softer. Plastic abrasive stones are mostly used on non-ferrous metals (aluminum, brass, zinc alloy, gold, copper, silver, etc.) and plastic-based materials for operations such as burr removal, rust removal, degreasing, scale removal and edge breaking.

Chemicals

The operations performed in vibration and centrifugal machines are physico-chemical processes. Besides abrasives, these operations have two fundamental pillars: chemicals. Without either of these two fundamentals or with incorrect selection, it is not possible to achieve the desired surface quality.

Functions of surface finishing chemicals

1. Degreasing and cleaning, 2. Scale and rust removal, 3. Polishing, 4. Corrosion protection.

Chemical selection parameters

1. Type of metal, 2. Causes of contamination on the metal surface (oil, rust, scale, etc.), 3. Desired surface quality.

pH value in surface finishing chemicalsIf pH = 1 to 6.5;

• Acidic, • No corrosion protection properties, • Generally used for scale removal on metals, • Darkens the metal surface.

If pH = 6.5 to 7.5;

• Neutral.

If pH = 7.5 to 14;

• Alkaline, • Has corrosion protection properties. To achieve the best results in the surface finishing process, the correct combination is very important. To determine the correct combination, selections should be made by considering each of the following parameters: • Production method of the workpiece, • Applications to be performed on the workpiece after the surface finishing process, • Shape, material type and weight of the workpiece, • Geometry and dimensions of surface finishing abrasives, • Surface finishing chemicals, • Machine type and capacity, • Screening method and screen size, • Grinding and polishing requirements.

İlker Er

Technical Deputy General Manager Kromaş Makine San. ve Tic. Ltd. Şti.