Essential tool for car body polishing

The appearance of a car body today is of great importance to many car enthusiasts. In order to maintain the appearance of the car in perfect condition, polishing or painting work is used. In both cases, a tool for grinding and polishing is necessary, without which both processes would be long and ineffective.

Definition of polishing and grinding

Before moving on to studying the tools used for grinding and polishing, it is necessary to define these two fundamentally different concepts. Almost the same tool can be used for both, but the purpose of these procedures is different.

So, sanding the body. This process is used to prepare the car body for painting. That is, grinding involves removing the old coating, traces of corrosion and rot to bare metal.

Polishing is a procedure that involves either applying a protective layer to the surface of the paintwork, or partially removing the varnish in order to remove small scratches and chips that did not reach the metal.

Mechanical polishing method

For many years, a mechanical method of processing the surface of a metal product has been used. Special sets of abrasive wheels and belts, when combined with GOI polishing pastes, make it possible to obtain a material with a roughness index Ra = 0.05–0.12 microns.

The features of this password encryption method include:

1. to automate the process, special machines are used that are equipped with fabric or felt circles;
2. a certain amount of GOI paste is applied to the abrasive;
3. the goyi paste in question is a special powder consisting of an active substance that has an activating effect on the surface of the product;
4. A typical paste consists of approximately 60% abrasive and 40% binder. content of activating additive 2%.

Finish grinding can only be achieved using GOI paste. In this case, a soft wheel and GOI paste with a fine abrasive are used. For such work, the material consumption is quite large: per 1 square meter of surface there are 0.3 felt wheels and an abrasive substance such as GOI, approximately 100 grams. When processing complex surfaces, a belt type of material and the same GOI abrasive are used.

Special attention should be paid to GOI paste. It is a special substance that is based on chromium oxide. The substance from the GOI category is produced in the form of a green bar. Special GOI sets contain bars with different abrasive grain sizes.

Tools and Supplies

The following tools and consumables are used for grinding to metal:

• grinding machine with attachments for metal;
• brushes for metal of varying hardness;
• special holder for sandpaper;
• coarse sandpaper.

For grinding to metal, a household grinder or an angle grinder is usually used as a machine.

At the same time, for the process of removing paint and varnish to metal, its main parameter when choosing is power. The greater the power and spindle speed, the faster and more efficient the procedure for removing paint and stripping down to bare metal will be.

For polishing, the requirements for the tool are somewhat different, since this procedure requires special care and precision. Depending on the type of polishing, which will be discussed below, the following tools and consumables are used:

• grinding machine (more about their varieties below);
• attachments for securing polishing wheels;
• polishing wheels made of foam rubber or other material;
• polishing liquids or pastes (depending on the type of polishing and its purpose).

Since polishing a car body is a process somewhat more varied and complex than simply removing paint, the approach to choosing a tool is slightly different.

Description and properties of the polishing process

GOST 9.301-86 regulates the requirements for the quality of processing of metal products as a result of polishing work. There are no special instructions regarding the gloss of surfaces after grinding, however, after polishing various defects, grooves, scratches, burrs, corrosion, etc. should be excluded.

In a word, polishing activities are designed to give the product an attractive appearance and consumer qualities.

In production there is such a thing as “polishing class”. The level of surface roughness of a particular part is determined using special equipment (microscopes and profilographs) down to 1 micrometer (μm, 1 mm = 1000 μm). If metal grinding is carried out at home, then the depth of the unevenness is determined by eye.

There are 14 roughness classes, which are indicated in special drawings in accordance with GOST 2789-59.

Polishing classes and requirements for them are presented in the table below.

Types of polishing tools

So, to polish a car body, grinding machines are used as a tool. Today the market offers consumers several options. They are all used equally often, having their positive qualities along with the negative ones.

The simplest tool for polishing a car body is a grinder. Almost every owner has it, and therefore it is often adapted for these purposes. Using an angle grinder allows you to save a little money and not have to buy a special tool designed specifically for polishing a car body.

However, the grinder is a very inconvenient and capricious tool. Firstly, even the smallest household grinder is quite heavy and uncomfortable. You can easily feel this on yourself after working with it for more than 10 minutes. And since polishing the body is a rather lengthy task, using an angle grinder for this purpose makes it even more tedious.

Most grinders do not have the ability to adjust the spindle speed. And for polishing, excessively high speeds can lead to overheating of the paintwork and its subsequent clouding. This especially often happens among inexperienced car enthusiasts who do not yet feel how hard they need to press the tool against the surface of the body.

However, the grinder is often used for polishing. To do this, in stores you can purchase a special attachment in the form of a circle, on the bottom of which there are micro hooks for the so-called Velcro. It is easy to attach special grinding wheels to the sole, and thus turn the grinder into a polishing machine.

But, of course, special polishing machines are a more convenient tool for polishing a car body. Some of them look similar to a regular angle grinder, however, they have much less power and the ability to adjust the spindle speed. Also on sale you can find polishing machines similar to an angle grinder with two spindles. Similar two polishing wheels are attached to these two spindles.

Also in great demand are polishing machines with a direct attachment. This tool has two convenient handles for gripping with your hands, and it is pressed against the surface of the body from above.

This tool is more convenient, since its weight does not have to be constantly held in your hands. In addition, such machines are quite light in themselves.

Separately, it should be said about the now widespread cordless tool. This technology has come a long way and continues to evolve. However, today it is cost-effective to buy such a tool only for protective polishing, that is, for quickly applying and rubbing wax. Such a tool is absolutely not suitable for high-quality rubbing of abrasive polishing paste, since its operating time is limited by the battery capacity.

Electrolyte-plasma method

In recent years, the electrolyte-plasma processing method has become increasingly popular.

Special sets of devices, which are quite difficult to create with your own hands, provide the effect of a charge on the part. Design features include:

1. the workpiece becomes the anode;
2. the part is supplied with positive potential from a powerful power source;
3. The working bath acts as a cathode.

To treat stainless steel and copper alloys, use a special solution consisting of ammonium sulfate and ammonium chloride. Their concentration is approximately 5%. Provided that the product is made of another metal or alloy, a solution with a concentration of the given substances of 10% is used. Polishing metal when using a similar kit and method is completed within 2-5 minutes, the burr can be removed in about 20 seconds. Such indicators determine the high productivity of this metal polishing method.

Types of polishing

Now a few words about the types of car body polishing. Here, as mentioned above, everything can be divided into two types. Simple polishing with preliminary application of liquid wax. This polishing is designed to apply a protective layer of wax to the paintwork. Such protection will repel water, dirt, dust and other external factors.

A more serious process is restorative polishing. This process requires much more time and effort than protective polishing. In addition, special abrasive pastes are needed, which also differ in the degree of impact on the top layer of paintwork. Both of these processes differ slightly, so it will be useful for every car enthusiast to know in general terms how and what to do in both cases.

Types of jobs

Metal polishing can be carried out using the following methods:

1. mechanical or abrasive polishing of products;
2. chemical treatment using special substances, for example, paste;
3. electrochemical method;
4. electrolyte-plasma method.

Some types of finishing sanding are simple and do not require special materials or equipment. For example, the mechanical method can be used at home. However, it is practically impossible to achieve significant results when using them.

Disadvantages of traditional methods

Polishing metal using traditional methods, abrasive and chemical effects on the surface, has a certain number of limitations in application. These include:

1. lack of possibility to automate the process. When carrying out work to obtain gloss, many enterprises introduce automatic processing technology, which can significantly reduce the time it takes to obtain a whole batch. Chemical, mechanical, electrochemical polishing have features that make it difficult to automate the technological process;
2. the difficulty of obtaining a mirror surface when using the considered types of impact on metal concerns technological and electrical reasons. Economic reasons are primarily associated with the high cost of production robots and machines that operate on a numerical control system. Technological factors determine the impossibility of incorporating traditional methods of polishing metal products to obtain a mirror surface.

Polishing stainless steel with a felt polishing disc

Often the above problems lead to the fact that the work in question is done by hand using a special paste under mechanical influence. This point determines a significant decrease in productivity, since processing on an automated line is impossible. Due to the use of outdated methods, the production line often results in a conveyor failure, and this negatively affects the cost of obtaining the product and reduces the competitiveness of the enterprise.

Protective polishing

This polishing takes very little time. If you have a sanding machine, you can apply and polish the wax in just twenty minutes. Here are some rough instructions for this process:

• First of all, the car is thoroughly washed using special detergents. This process should be taken very seriously, since polishing on a dirty car will lead to the opposite process - the polishing machine in combination with particles of dust and sand will become an excellent abrasive that will lead the car to a deplorable state.
• The car should not be exposed to direct sunlight. Ideally, polishing is carried out in a cool, closed room.
• The room should be free from drafts that raise dust and well lit from all sides. The situation with dust is the same as with a dirty car. But the light will help prevent defects during polishing.
• Next, the car is conventionally divided into parts - this could be the roof, hood, and so on. Applying wax to these parts step by step, it is rubbed with a polishing machine until the desired shine is obtained.

If deep shine does not work, then there are several options:

• the wax used is of low quality or expired;
• the paintwork does not have varnish (this happens on repainted old cars);
• Insufficient time was given for polishing;
• The paintwork is excessively damaged and requires restorative polishing.

Electromechanical method

Mechanical and chemical polishing of metal often does not lead to the desired result. This is due to the fact that the product may have increased resistance to changes in structure. The electrochemical method is an exposure procedure that involves immersing parts in an electrolyte. Carrying out such work with your own hands is often quite difficult, since the electrolyte is represented by an acid solution. The impact occurs when the tank is connected to a power source with a voltage of about 20 V.

This type of processing determines the appearance of a passivating film, which leads to a decrease in the roughness index. The degree of change in the quality of the surface structure depends on the applied voltage. The achieved quality depends on the type of metal, the indicator of residual deformation, the thickness of the workpiece and other factors.

Purpose and types of grinding machines

There are quite a lot of varieties of modern grinding machines - surface grinding, cylindrical grinding, internal grinding, centerless grinding, belt grinding and honing machines are actively used in industry. Each of these types of grinding equipment has its own purpose and is used to process a specific group of parts.

In principle, the purpose of a particular grinding machine can be judged by its name. For example, a cylindrical grinding machine is used to process surfaces that have a cylindrical shape, a surface grinding machine easily copes with smooth surfaces, internal grinding machines process internal holes, and the field of activity of honing machines includes fine grinding, which is equated to the polishing process.

Most modern grinding machines are equipped with numerical software to achieve greater productivity and processing accuracy. Although the use of CNC automates the production process, it does not completely exclude human participation. In this regard, programmable grinding machines are the most capricious - the operator constantly has to monitor the process and make timely adjustments to the program for the rapidly wearing grinding wheel.