Metal can be sanded. What cloth is better to polish metal. Do-it-yourself metal polishing to a mirror finish. Metal processing methods using etching

Metal polishing will help to significantly improve the aesthetic appearance of the product. If it is not possible to turn to professionals, then you can polish yourself, at home, the main thing is to follow the technological process.

The process of polishing to a mirror at home

There are several proven methods for polishing metal at home. One of them is chemical (without the use of mechanisms). It does not require much effort, the main thing is that it follows the safety requirements. Metal polishing at home by a chemical method occurs in the following order:

1. Sulfuric acid is diluted with water in a ratio of 1:20. The volume of the resulting mixture should be sufficient to completely cover the thing to be polished;
2. We lower the polished object into the resulting solution for several minutes, and, having taken it out, wash it in running water. Next, place in a container filled with sawdust;
3. We lower the metal object dried in sawdust for 2-3 seconds into nitric acid, after which we again thoroughly rinse;
4. After another drying in sawdust, carefully wipe the metal.

After such simple procedures, the metal object will look like new. A smooth and shiny surface will be perceived by the eye as a mirror.

TIP: Before lowering a metal thing into acid, you need to remove all elements made of other materials from it. Other materials can be adversely affected by acid and destroyed.

One of the most popular types of home metal polishing is processing with GOI paste. This paste was created in the last century and has been successfully used to this day. Initially, it has a solid shape and comes in varying degrees of granularity. For better application, it is recommended to dilute it with a few drops of machine oil.

For manual polishing of soft metals, it is recommended to use a soft flannel cloth coated with a fine-grained paste. Ferrous metal can be polished with a piece of canvas or denim with a coarse paste. For faster results, instead of a rag, you can use a felt circle attached to a hand drill, or a small wooden block.

Required equipment and chemicals

To get a good result at home, you will have to spend a little money and stock up on some chemicals, fixtures and mechanisms. Depending on the method by which the metal will be polished to a mirror finish with your own hands, you will need several items from this list:

• Sulphuric acid;
• Nitric acid;
• Water;
• Sawdust;
• Paste GOI;
• Felt circle;
• Drill;
• Wooden block;
• Textile.

polishing process

Polishing metal to a mirror finish at home is a rather lengthy process, the main thing here is not speed. If the process (mechanical) is carried out without the use of electrical assistants (after all, some metal objects can be “wiped”), then each square centimeter of the product should be carefully and for quite a long time, with extreme caution.

Advice! For items with recesses, you can use an old toothbrush smeared with GOI paste. It is convenient for her to get to hard-to-reach places.

Safety

When using a chemical polishing method, be sure to use special gloves, respiratory protection, special dishes that do not react with acid. Polishing metal to a mirror finish with a grinder or drill should be carried out using eye protection. And most importantly, it is necessary to strictly adhere to the technological process. It is necessary to always have a first-aid kit on hand, with which you can provide first aid before the arrival of the ambulance, although it is advisable to prevent such cases.

Result

Grinding and polishing of metal at home, carried out in compliance with all technical requirements, is able to completely restore the appearance of a metal object. With minimal financial costs and a certain skill, you can achieve high results.

If you need to compare your work with the ideal result, then you can always watch a video on the Internet - “Grinding and polishing metal at home”, where you can find lessons on various polishing methods. They tell in detail about all the nuances of polishing metals at home.

Stainless steel is rarely used in households. Metal is expensive. Processing is difficult. Resistant to corrosion. Polished to a mirror finish. Hence the main places of its application: as an interior and everyday life of kitchens, bathrooms, as well as complex power elements included in the interior of a house or premises. Kitchens, bathrooms, door handles, railings - something that is always in sight and catches the eye with sparkling beauty. Proper and timely polishing of such items will keep expensive decoration.

Time and moisture vapor affect the structure of the metal. The first sign of corrosion is a slight clouding of the surface. At this stage, the restoration of the mirror shine of stainless steel is easy.

Polishing methods at home

A small list of interior and household items made of stainless steel, due to the complexity of the forms of products, limits the mechanization of the polishing process. At the same time, the high hardness of the alloy, due to the high labor intensity, does not allow relying solely on manual labor. The best option is a reasonable combination of both methods. Stainless steel stair railings are a good example of the scope of such work. Small-scale mechanization is indispensable here. Difficult terrain will not allow cleaning with a single tool. There will be many places where this process will have to be completed manually.

An angle grinder can be considered as a tool for polishing stainless steel at home. Better known as "Bulgarian". The procedure is as follows:

• a special fabric circle is installed on the machine;
• a thin layer of polishing paste is applied to a part of the treated surface. During the operation of the tool, the polishing agent is evenly distributed on the wheel and transferred to other parts of the workpiece;
• as the cleaning properties decrease, the paste is added, and the stainless steel polishing process is repeated in a new place.

The dimensions of the grinder and equipment limit access to the entire surface of the workpiece. Such places have to be polished by hand. For this, a piece of felt and abrasive paste are suitable. The cleaning agent is applied to a rag and rubbed onto the treatment site until the desired surface specularity is obtained. The process is lengthy. It takes patience.

In 2016, our company introduced a new process of electrochemical polishing of metals. electro or electrochemical polishing, as well as chemical polishing is a process in which roughness is selectively etched, which allows you to level the surface with a mirror finish.

Thanks to this method, it was possible to weld aesthetic seams, to become smooth and shiny. For example, about 100-200 microns are removed during about 30 minutes of polishing stainless steel.

On average, stainless steel is shiny after 5-10 minutes, but if preliminary mechanical preparation has been done, you can get a mirror finish within 5 minutes. Electropolishing can also be used on complex parts where mechanical polishing is nearly impossible.
electrochemical polishing This is an anodizing treatment of metal to create a smooth and shiny surface.

The product, which has a micro and macro screen, is the anode of the cell. A cathode is a metal that is chemically insoluble in an electrolyte solution.

Polishing metal with glossy glossy hands

Such as electrolytes, solutions using phosphoric acid, chromic acid, sulfuric acid, acetic acid, hydrofluoric acid and others. In the process of electropolishing, anodic dissolution of the metal occurs on macro and microcircuits, where the surface becomes smooth and shiny. Hydrogen is released at the cathode. The mechanism of electroporation has not been fully elucidated.

electropolishing. The effect is usually associated with the action of a viscous film formed in the anode layer, a barrier to dissolution in the metal in the recesses compared to dissolution in the protrusions and alternating activation and passivation of the metal.

Electropolishing of steels is the best type of electrochemical anode pickling. This process combines the operations of removing corrosion, smoothing the surface and giving it a shine, passivation, as well as increasing the adhesion strength of electroplated coatings to the treated surface.

It should only be taken into account that the initial cleanliness of processing should not be lower than the 7-8th grade so that, in addition to obtaining gloss, the effect of smoothing the surface is also observed. Carbon and low-alloy steels are electropolished with alternating current of industrial frequency in an electrolyte of composition, % (by mass): 96.5 phosphoric acid (p = 1.54 g / cm3), 2.0 technical oxalic acid, 1.5 joiner's glue in tiles.

Operating temperature 15-30°C current density 15-20 A/dm2. Exposure depending on the state of the surface is 1-5 minutes. Before preparing the electrolyte, the adhesive and oxalic acid are dissolved separately. The electrodes are the parts themselves, hung on rods of three-phase or two-phase alternating current with a voltage of 12-15 V ...

For anodic polishing of carbon steels with direct current, an electrolyte of composition is used,% (by mass): 65 phosphoric acid (p = 1.67 g / cm3), 20 sulfuric acid (p = 1.84 g / cm3) and 15 water (total content ). Inhibitor PB-5 is introduced in an amount of 5% of the volume of the mixture of acids, it dissolves slowly with stirring (within two days). Working temperature<15-25°С, корпус ванны имеет рубашку для водяного охлаждения.

Anode current density >20 A/dm2, exposure up to 20 min. at voltages up to 30 V. Lead cathodes are periodically cleaned.

Electrolytic polishing and etching

For most alloys, the normal process of grinding on sandpaper, wet polishing and etching by dipping or wetting will give quite satisfactory results. However, in some cases, electropolishing should be preferred, especially if there is a risk that the work hardening resulting from the polishing process will affect the surface structure.

The first to use electropolishing for metallographic work was, apparently, Jacquet. His method includes mechanical processing of the sample, which is usual at the first stage, in order to obtain a sufficiently smooth surface.

Then they make up a circuit in which the sample is made the anode; the electrolyte is selected so that the metal of the sample is only slightly soluble in it. Under these conditions, the concentration of metal ions on the surface quickly reaches saturation, after which the current mainly depends on the concentration gradient of metal ions perpendicular to the surface. The ridges on the surface are associated with a large concentration gradient and tend to dissolve faster than the pits.

Thus, electrolysis leads to smoothing, and under appropriate conditions, a fine polished surface can be obtained without plastic deformation. The process is regulated mainly by the concentration of polarized ions, and this causes a characteristic relationship between the current density and the applied voltage (Fig. 132). With increasing voltage, the current density first increases to a certain maximum, then decreases somewhat and remains constant until a new process begins in the electrolyte (usually oxygen evolution).

The most satisfactory results are usually obtained at a voltage that corresponds to the right edge of the horizontal section of the above curve, as indicated by the arrow in Fig. 132.

The apparatus for electrolytic polishing is comparatively simple; one of the possible options is shown in Fig. 133. The device is an overturned jar, through the neck of which the sample holder 3 and positive input are inserted; the holder and parts of the sample that are not subject to polishing are protected by varnish.

The top of the vessel is closed with a wide rubber or cork lid, through which cathode 1 is introduced; depending on the electrolyte used, the cathode can be copper or stainless steel.

The liberated hydrogen exits through a wide tube; the same tube serves to remove the electrolyte from the apparatus.

Electropolishing is most suitable for single-phase alloys, for which it is usually sufficient to prepare the surface on sanding paper 00 or

132. Relationship between current density and applied voltage in an electropolishing bath

Rice. 133. Device for electropolishing: 1 - cathode; 2 - outlet tube for evolving hydrogen; 3 - sample

Multiphase alloys are more difficult to polish in this way, for them a light mechanical polishing with water and aluminum powder or magnesium oxide can give the best result.

Before electropolishing, the surface of the sample must in all cases be completely free of grease; it is desirable to wash it in carbon tetrachloride.

The processes of electrolytic polishing and etching require a wide range of voltage changes. According to the literature, the intervals and 50-110 in. are most often used. The current density also varies over a wide range - from 1 to 500 A / cm2, so it is recommended to make a stationary control panel that works with

adjustable voltage transformer and current rectifier.

Relatively little is known about good electropolishing chemicals. Most of the early work was done with mixtures of perchloric acid and acetic anhydride. This reagent, however, is explosive.

Polishing stainless steel - a mirror in 5 minutes is real!

For many metals, orthophosphoric or pyrophosphoric acid solutions were also used.

The electrolytic method, in addition to polishing, can be used for etching metals and alloys; in some cases, both processes can be carried out in the same electrolyte.

For polishing, a relatively higher voltage is used, and at the end of this process, the voltage is reduced to a certain value and etching is performed. Electrolytic etching can also be applied to samples whose surface has been mechanically polished.

This method should always be used when conventional polishing does not give satisfactory results. Apparatus suitable for this purpose is shown in Fig.

133. The literature provides a lot of data on samples electrolytically etched in aqueous or alcoholic solutions.

Metal polishing with an angle grinder

Polishing is a type of metal treatment that restores the shine to the metal surface. At the present stage, the following grinding methods are distinguished:

What tools and machines are used? Mechanical methods involve the use of the following tools and devices:

• polishing machine;
• Grinder;
• electric grinder;
• drills with clamps.

This finishing method has a number of advantages. Firstly, it allows you to change the frequency of rotation of circles and tapes, which has a positive effect on the quality of processing a metal plane; secondly, additional nozzles made of fabric, leather, wool, etc. can be installed on the polishing machine.

Special grinder - angle grinder

Manual grinding differs from automated grinding in that its effectiveness depends on the quality of polishing consumables. In manual finishing, diamond paste and additives based on chromium or iron oxide are used. Smooth metal surfaces are polished with an ordinary file - a wooden block covered with a cloth, on which a polishing paste is applied.

Metal polishing with a special tool

Combined processing methods

Metal polishing can be carried out by combined methods, in the case of an unprepared and rough surface with a rough relief. In this case, a long-term electrolytic-plasma finishing is prescribed, which consists of removing a significant layer of metal.

This processing method is used in extreme cases when a quick restoration of the gloss of a metal product is required. Among the shortcomings of the technology, one should highlight the high energy intensity, especially at the initial stage of processing, when 100% more energy is used than usual.

The electrolytic-plasma polishing machine processes the part in two stages. On the first one, the surface is degreased, and on the second, the grinding itself, which, in turn, also consists of two cycles: cutting the rough layer and grinding the metal. Grease removal is mandatory, since the viscous surface leads to oxidation of the metal and a deterioration in the quality of its finish.

Classification of metal polishing pastes

You can bring the metal surface to a mirror state with your own hands without the use of machines, it is enough to pay attention to special tools that are divided into the following groups:

• Water. The substance does not contain fat and does its job perfectly;
• Organic products - contain paraffin and a variety of oils. They are diluted with various oils and fatty acids;
• Diamond paste is a revolutionary solution that allows you to instantly achieve a shine on any metal surface.

Let us dwell in more detail on the last version of grinding. Diamond paste is so effective that it completely replaces the polishing machine. Diamond Substance is available in two types: ASN and ACM (expensive).

Diamond paste has the following advantages:

• Accuracy. Synthetic diamonds allow you to polish any metal product to a shine as accurately as possible;
• Wide range of grain sizes. More than 12 types of grit can be found on the market today;
• Simple operation allows you to carry out cleaning procedures with your own hands without the use of a special tool;
• Diamond paste requires a minimal tool: a rag, water and rubber gloves.

The main disadvantage of this cleaning agent is its high price. On average, diamond paste on the consumables market costs more than 500 rubles per 35 grams of the substance.

Working principle of diamond paste

Diamond paste acts on a metal product mechanically and chemically, forming dispersed films. The composition of the cleaning agent includes active substances that promote the flow of adsorbing processes, which facilitates the grinding of the material.

Diamond paste is applied to various types of fabrics (felt, microfiber or jeans), paper, rubber, plastic and other types of non-metallic materials. It should be noted that diamond paste can also be applied to polishing wheels to improve the efficiency of metal surface treatment. In this way, you can achieve a mirror effect. Circles made of felt, felt or leather are installed on the polishing machine.

Description of the polishing process

To grind a metal surface, you will need: lapping laps and several tubes of diamond mixture with different grain sizes. Diamond paste is evenly distributed over the working surface of a rag or other material. Experts have noticed an interesting pattern that improves the quality of metal processing.

It turns out that castor or olive oil must be added to the polishing agent. The ideal ratio is considered to be a mixture consisting of 40% diamond dust and 60% oil. After dilution, the mixture is immediately applied to the metal surface.

Experts recommend starting work only with large grains, gradually moving to abrasive products. During processing, make sure that no extra elements get into the mixture - dust, sawdust, hair or pieces of rags. The presence of third-party objects greatly impairs polishing to a shine. It is also recommended to wash your hands after changing from one grit to another.

Types of diamond dust

On the modern market, you can find tools not only for polishing metal, but also other materials, such as wood, glass, stone, etc. You can classify them by color, for example:

Huge range of diamond paste

• Yellow packaging indicates that the substance is intended for grinding ceramic materials and glass products. It should be noted that this dust can also be used for metal finishing;
• Blue packaging. This type of product is used for glass finishing. The grinding tool has a fairly wide selection of abrasive elements - from 60 to 10 levels;
• The red packaging is suitable exclusively for the treatment of metal surfaces.

As for the packaging itself, diamond paste is sold in compact plastic jars, 35–45 grams in volume. The average cost of a jar depends on the size and quality of abrasive materials. The finer and better the polishing material, the cheaper the paste is. The average price is 450-600 rubles.

Paste GOI

Chrome paste GOI is a universal tool for polishing metal and non-metal surfaces. Although it was invented in the early 1930s, it is used to polish metals even today.

Polishing paste GOI

The GOI tool comes in different grain sizes (classified by the size of the abrasive materials). There are three types of grit: fine, medium, and coarse. Fine dust is used for polishing soft and non-ferrous metals, coarse grain - for rough finishing of ferrous metals and steel.

Features of use. Initially, the polishing agent has a solid structure, which can be diluted with a few drops of machine oil. If you need to polish an uneven metal surface with bends, then it is recommended to apply the paste in a diluted form to a rag.

The second polishing method is designed for smooth metal surfaces. Its peculiarity lies in the fact that a small amount of abrasive material is applied to a wooden block. Then it is recommended to make methodical movements back and forth on the surface to be treated.

Video: Polishing aluminum

Metal polishing: features of the preparatory and main processes. Metal polishing classes according to GOST. Various methods, tools and machines for polishing and grinding metal to a mirror finish.

Metal polishing is the final stage in the manufacture of metal and alloy products, which consists in removing the thinnest layer of material from the surface of the part. There are a large number of ways in which you can polish the product to a shine both at home and in industrial production. They are discussed in detail in this article.

GOST 9.301-86 regulates the requirements for the quality of processing 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 measures are designed to give the product an attractive appearance and consumer qualities.

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

Surface Description	Roughness size (up to µm)	Polishing class	Mechanical processing method
Traces of processing are very noticeable	320	1	Planing, sharpening and milling
	160	2
	80	3
Traces of processing are very faintly visible	40	4	Soft abrasive, semi-finishing
	20	5
	10	6
Processing marks are not visible at all	6,3	7	Fine flow, grinding
	3,2	8
	1,3	9
The surface of the metal product is perfectly smooth and has a characteristic mirror shine.	0,8	10	Finish polishing, soft polishing
	0,4	11
	0,2	12
	0,1	13
	0,05	14

Preparatory stages

Industrial enterprises that are engaged in various types of metal processing carry out a check on the condition of surfaces before grinding. Before using various chemical reagents and polishing machines, the part must be prepared for further polishing stages, for this, the product is affected by one of the mechanical methods:

• treatment of the part with compressed air together with special coarse abrasive elements that remove large corrosion and rust growths from the surface;
• cleaning the surface of the product with brushes with hard bristles to remove signs of oxidation and sludge (dust formed as a result of cleaning with a coarse abrasive);
• degreasing surfaces from traces of previous polishing agents by treating them with warm organic solvents;
• the use of alkaline solutions to remove mineral residues containing oil;
• electrochemical degreasing (immersion of a metal product in an electrolyte).

All these methods are most often used in industrial production. At home, to prepare a metal product for polishing, it is enough to treat the surface with sandpaper of various hardness.

Metal polishing methods

To polish metal to a mirror finish at home, most often they use a special paste, such as GOI or diamond, popular among home craftsmen, as well as a polishing machine with an abrasive wheel.

The following types of polishing are used at metal processing enterprises:

• mechanical;
• chemical;
• electrochemical;
• with the help of plasma;
• laser;
• ultrasonic.

mechanical method

One of the most effective ways to self-polish metal is to treat the surface of the product with a polishing machine.

A grinding machine is an indispensable tool for high-quality polishing of metal until the initial shine appears. The polishing machine has a so-called abrasive wheel, the coverage of which will depend on the nature of the work and the material.

The process of metal processing using a grinding machine will take place as follows:

1. Polishing wheels and the area of ​​metal to be treated are wetted with water. For metal processing, the disk must rotate at a speed of 1400 revolutions per minute. It must be foreseen that at this speed of rotation the spray will scatter 1-1.5 meters, therefore, it is necessary to take care of the appropriate protection of the face and clothing.
2. The surface to be treated will begin to heat up as a result of friction, and the water will evaporate. As a result of such interaction, irregularities and roughness will be removed, forming blockages from metal particles and water on the basis of the abrasive wheel. Every few minutes it is necessary to turn off the machine and rinse the disc under running water. Metal particles should be removed not only from the tool, but also from the surface of the product.
3. To achieve a mirror finish, it is recommended to use felt material. Such a nozzle is put on the grinding disc so that the edges protrude 1–1.5 cm beyond the circle. The felt and the surface of the metal part must be moistened with water, after which the metal is polished.

If a special machine is not available, you can use a polishing agent such as sandpaper. First you need to treat the surface with sandpaper of a large abrasive, and then a softer one. After switching from one grain size to another, you can proceed to the finishing stage of processing.

At the final stage, a polish is used. For metal products, as well as for stone surfaces, diamond paste is excellent, which can restore ideal smoothness and mirror shine to surfaces. The surface of the metal product is carefully processed with a cloth on which the polishing paste is applied.

Chemical polishing is the most effective solution for metal and alloy products that have a decorative function.

The essence of the chemical method of cleaning metal is that all the work to restore the surface of the product is performed by special solutions of chemical reagents and acids. The solution must be heated to a certain temperature, which depends on the components of the metal alloy, after which the metal product is immersed in the solution for several minutes. A reaction occurs between the metal and the chemical solution, as a result of which the defective layer of the product is destroyed.

In order to immerse the part in the solution, special holders are used. There is no need to use manual labor, and metal processing occurs evenly over the entire surface.

However, this method has a drawback: after the procedure, the surface of the product is more matte than shiny. In addition, this method requires compliance with a number of safety rules.

Electrochemical metal polishing

At first glance, electrochemical polishing of metal takes place in the same way as chemical polishing. The part must be lowered to the bottom of the tank with the solution, but it is necessary to ensure the passage of electric current through the product. The current accelerates the destruction of the oxide layer even in barely noticeable depressions on the metal surface.

As a result, the product acquires perfect smoothness. This method is perfect for those who are looking for an answer to the question of how to polish metal to a mirror finish.

The disadvantage of this method is the high cost of electricity and the need for regular replacement of the chemical solution.

Plasma polishing

Polishing a metal with a plasma is similar to an electrochemical cleaning method: the product is also immersed in a chemical solution, followed by an electric discharge through it. However, the electrolytic-plasma method does not involve the use of a mixture of chemicals and acids, but a harmless solution obtained from ammonium salts.

The result of electroplasma polishing will be not only a mirror shine and perfect smoothness, but also additional protection against corrosion.

Metal laser polishing

The process of polishing metal using a laser machine eliminates the need for the use of various polishes, solvents and abrasive particles.

The laser device acts on the surface of metal products by applying light pulses. Energy, in contact with the metal, is converted into plasma, its particles decay, which leads to the appearance of a shock wave. The light pulse is not long enough to damage the product, but it splits the damaged metal particles. Due to this feature of the laser beam, if the product requires deep cleaning, the same area of ​​the metal surface will have to be affected several times.

The laser machine, made of steel, has such a feature as self-limitation. The device itself reduces the intensity of exposure and beam power as soon as the laser reaches a layer of metal that does not need to be polished.

Ultrasonic metal polishing

Metal polishing by ultrasound is one of the types of processing of various surfaces by crushing, that is, the destruction of the defective surface layer is carried out after applying a load to the material. Oscillations of the ultrasonic wave form chips and cracks, as a result of which the upper layer of metal leaves by itself, like an eggshell.

This method helps out if the material is not a conductor of electric current and cannot act as an anode during electrochemical cleaning. It is also excellent for grinding thin and fragile items, including precious stones and metals.

The technology of ultrasonic metal processing is as follows:

1. A composition of abrasive elements is placed in a special working sector of the device.
2. The device is located in close proximity to the treated surface.
3. The vibrating device causes the abrasive elements to vibrate, while affecting the top layer of the product.
4. The defective layer under the influence of vibrations cracks and collapses.

Silicon or carbide-based boron particles can act as abrasive elements, and fresh water supply can act as a vibrating factor.

If you have experience in polishing metal using industrial and improvised methods, share it in the comments.

Polishing is the final process of manufacturing a part, carried out using various methods to remove a minimum layer of metal to achieve a mirror finish. These are interrelated physical, chemical, electrical influences, the choice of which depends on the type of material, the tool used and the characteristics of the external environment. The required quality is achieved by replacing abrasives and methods of exposure. Polishing time depends on the initial quality of the metal.

GOST requirements for metal polishing

Requirements for the quality of metal and coatings are defined in GOST 9.301-86. Surfaces must be free of pits, pores, rust, cracks after grinding, scale, and burrs. There are no regulatory requirements for the degree of gloss.

At enterprises engaged in metal processing, input control of surfaces is carried out. If necessary, the following is carried out:

• treatment with compressed air containing an abrasive (steel shot) (rust and scale are removed);
• metal brushing to remove oxides and pickling sludge;
• degreasing heated in organic solvents (chlorinated carbons) to remove grease;
• degreasing in alkali solutions (removal of mineral oils);
• degreasing in electrolyte (electrochemical).

At home, surfaces are wiped with a solvent, treated with a file or a grinder with a disk with the appropriate grain size.

Metal polishing class

The polishing class is determined by the surface roughness (roughness in microns) of a particular part. The roughness corresponds to the area of ​​use. In total, there are 14 purity classes, which are indicated in the drawings by an equilateral triangle. Numerical values ​​of roughness after metal polishing are specified in GOST 2789-59.

Metal polishing class

Surface appearance	Irregularity height (up to mcr)	Class	Type of processing
Traces of processing are clearly visible			Turning, milling, planing
Processing marks are almost invisible		fourth	Semi-finishing
Processing marks are not visible			Fine turning, grinding
Surface with a mirror finish			Finishing polishing
		eleventh
		twelfth
		thirteenth
		fourteenth

In industry, special instruments are used to measure the height of irregularities: profilers and microscopes. At home, the roughness is determined "by eye".

Existing metal polishing methods

The most common ways to polish metal:

• mechanical (abrasive);
• chemical (pastes, solutions);
• electrochemical (in electrolytes);
• ultrasonic.

Mechanical polishing of metal can be dry or wet.

The process can be carried out:

• manually;
• in semi-automatic mode;
• automatically.

Important! With manual processing, you can monitor the process and influence the result. It is impossible to achieve high quality and productivity.

Semi-automatic is a special equipment and a qualified specialist. Processing is carried out on metal polishing machines, technological parameters are changed manually. With automatic processing in batch production, human participation is not required. The work is carried out very quickly and with high precision. The amount of scrap is minimized.

Hand polishing small parts at home. The paste is applied to a rag and rubbed on the surface in a circular motion. For large surfaces, grinders (grinders) or drills equipped with nozzles of various grain sizes are most often used.

Various attachments can be installed on the disc. If the nozzle is made of felt or fabric, it is moistened with paste. A professional tool is used in auto repair shops, as it allows you to process surfaces of sufficiently large sizes. In small metalworking enterprises, machines equipped with polishing belts or felt (cloth) circles are used.

Mechanical methods also include abrasive technology for polishing metal in vibrating drums filled with dry abrasive or solution. Rotation and vibration can quickly reduce roughness. If the method is dry, then the solution is replaced with oak or ash sawdust, pieces of felt or suede. If a solution is used, then in addition to polishing steel balls, alkali can be added to it (for example, a solution of laundry soap), which speeds up the process.

But mechanical polishing has a number of disadvantages:

• there is a possibility of the introduction of abrasives into the structure of the metal;
• high installation and resource costs;
• processing consists of several stages;
• the process is difficult to manage;
• Requires a significant amount of manual labor and time.

Important! Chemical polishing has a higher potential, especially when it comes to elements of decorative interior decoration made of various alloys or expensive metals.

When using this method, metal products are immersed in solutions of a certain temperature. During the passage of chemical reactions, the roughness melts within a few minutes. There is almost no manual labor, power tools and metal polishing devices are not required. The surface is processed uniformly, the configuration of the part does not matter.

But there are also disadvantages. Mirror gloss is not achieved (the surface is rather matte), the solution needs to be changed frequently, it is quite aggressive (most often it is an acid). Work can be carried out only in overalls, the room must be equipped with a high-quality ventilation system.

In electrochemical polishing, parts are also immersed in a solution, but an electric current is passed through it. Since the surface is uneven, the oxide film is thicker in the micropits. The solution processes even parts of the surface with a thin layer of oxide faster. At the end of the process, the surface is perfectly smooth. Small time costs give an opportunity to increase productivity.

The disadvantage is the high consumption of electricity. If the surface is rough, mechanical grinding is required. It is necessary to carefully monitor the quality and temperature of the solution, the current density. Solutions are created from acids, so safety regulations must be observed. To reduce costs, it is desirable to pre-process the material by mechanical means.

At large enterprises, they try to automate and robotize polishing. This can be done using ultrasound, which increases productivity by 30 times and allows you not to purchase circles and pastes. Energy consumption is lower than when using a chemical or electrochemical method.

Metal polishing products

The technology of manual polishing of metal requires the purchase of equipment (drills, grinders) and various nozzles.

The main means for mechanically polishing metals are various pastes containing silicon, zirconium or titanium carbide, diamond chips, chromium oxide. Hard pastes must be diluted with oil. The costs are high, since the process consists of several stages, each of which requires different nozzles.

If a chemical or electrochemical method is used, large containers and acids are needed for the preparation of solutions, overalls. Nitric, hydrochloric, sulfuric, phosphoric acid, glycerin, benzyl alcohol are used. For a household, these are quite expensive purchases, so chemicals are used only in enterprises.

Metal polishing machines

All polishing machines are divided into 2 groups: with circles and tapes. Belts and circles consist of abrasives, the choice takes into account the requirements for surface roughness after processing. The equipment is semi-automatic or automatic. Automatic machines can become part of the lines used in mass production.

Any machine is equipped with a bed (platform) that does not change position during operation. An electric motor is mounted on the platform, which drives the shaft. You can work with grinding abrasives and circles. The sharpening angle is adjusted manually or automatically. Some designs are equipped with a water tank needed for cooling.

Available machines for processing raw materials (sheets of steel, aluminium, brass, profiles) and finished products:

• ship fittings;
• plumbing equipment;
• metal cornices and railings;
• door handles, parts of candlesticks;
• bicycle parts;
• tables and chairs;
• mufflers for motorcycles and cars.

The power of industrial models is 700-950 W, they are connected to a 220 V network. The rotational speed is 90-150 rpm. Adjustment is made depending on the characteristics of the material being processed and the format of the circle. At the first stages of processing, large circles are used, small ones are used for refinement. The package includes a cable and an extension cord. During operation, tools for measuring angles, stabilizers, pastes may be required.