Contents
GOI paste was invented at the State Optical Institute. It was named after the first letters of the name of this organization. So there is no decryption as such. In the article, we will consider how to use GOI paste, what and how to polish it.
Numbers and Grain
GOI paste is based on chromium oxide. That’s what gives it the green color. There are four numbers that differ in the size of the abrasive particles. Their parameters are described in TU 6-18-36-85. They are intended for grinding of varying degrees of “subtlety”.
- № 4. Used for rough grinding, removing small scratches. Contains 75-85% chromium oxide, 10% stearin, 5% fat, 2% kerosene and silica gel. You can’t polish it to a shine with this composition, only to a matte surface.
Paste GOI: numbers, granularity, composition and purpose - № 3. Needed for medium sanding. You can achieve a soft even shine. The composition contains less chromium oxide – 70-80%, but more fats (10% fat and stearin each), silica gel and kerosene the same amount (2% each).
- No.2 and #1 used for fine polishing (successively). Soda is added to the composition, which gives a finer polishing.
There are three types of GOI paste release. Often found in the form of solid green bars (see photo above). Before use, apply to a soft cloth or skin. There is also a paste that is easier to apply, as it has the consistency of thick sour cream. Grinding wheels are also sold, on which this paste has already been applied.
Sometimes dyes are added to the composition. This is done to quickly determine the number “by eye”. But this is not always the case. The “normal” color is green, regardless of the number and grit.
How to apply to fabric/leather
For polishing various kinds of materials with the help of GOI paste, soft, slightly fleecy materials are used. These are felt (for a rougher finish), flannel for a finer finish, suede (sometimes shaved) and fine leather for a mirror finish.
In general, the “fresh” GOI paste is well applied to a fleecy fabric. Just rub the bar over the fabric/felt/leather until it is covered with a layer of compound. To speed up the process, clean machine oil (for sewing machines), transformer oil, etc. is applied to the fabric, and then rubbed with a bar.
How to soften or dilute
With constant use, it is easier to work when the composition looks like thick sour cream. It is easier to spread it on a fabric or a strip of leather (on the back). You can soften a bar of GOI paste in several ways:
- The GOI bar is melted in a water bath. When the composition becomes liquid, add kerosene or machine oil (pure), stir well and cool. The amount of thinner or oil depends on the desired consistency, but start with about 50% by weight of the GOI paste.
- Grate the pasta or cut with a knife. Place the shavings in a non-oxidizing container, fill with a solvent (for example, 367) and mix vigorously until it dissolves. If the consistency is too liquid, leave for a while in an open container so that part of the solvent evaporates. When the desired consistency is reached, transfer to a container with a lid.
Can be made into a paste or even a liquid solution - You can also dissolve the chips of GOI paste with machine oil. Without heating, it will take longer, but the composition will hardly dry out.
Any softening method is acceptable. Just choose the one that suits you best. By changing the amount of solvent or oil, select the consistency.
Once the paste has been applied to the fabric, lightly polish an unwanted piece of the same or similar material. You can work a little on the back of the part. First, remove too large abrasive fragments. Secondly, you will understand how this type of paste affects the material and whether the grain size is chosen correctly.
How to use
GOI paste is needed for polishing metal, glass or plastic products. This means that grinding (removal of large defects) has already been done and only small scratches remain. Polishing with GOI paste is used for grinding (exact match) parts. Here it is important to achieve not shine, but a perfect match between the surfaces of the two parts.
According to the rules, it is necessary to polish alternately with two or three numbers of GOI paste. It’s better to start with number 4. When all scratches are gone, go to #3, then to #2 or #1. How long to polish? Until you are satisfied with the result. This is a general principle that varies depending on the hardness of the materials being machined. For example, for plastic and soft metals, only “two” and “one” are used. “Four” and “three” are more likely to harm and add scratches than polish.
Polishing technique
Polishing can be done by hand or with felt and felt nozzles on a screwdriver, drill or grinder with adjustable speed. A grinder or a drill without speed control can only be used for hard metals or for glass, otherwise the surface may be damaged.
Manually polishing with GOI paste is simple, but long.
If we are polishing a flat surface, we stretch / stuff the fabric / leather with the paste applied onto a flat board. It is possible with a handle. Translational movements (circular or forward / backward) three details. No need to press. It requires a lot of effort, and as a result, you can not grind, but make a recess.
When the metal is polished, a greenish-gray layer forms on the surface. We wash it off with alcohol or a solvent. Plaque can be cleaned with soft paper or rags. After the solvent has dried, we can continue polishing. Don’t forget about cleaning. Plaque is a mixture of polishing paste and small fragments of the polished material. These “fragments” are abrasive and are usually larger than the grain of the polishing paste. That is, the part is not polished, but scratched.
How to polish plastic, plexiglass (headlights)
Headlights in most modern cars are made of plastic. So all of the above is true for plastic products. If you need to remove small scratches from the headlights, first we work with GOI No. 2 paste. In this case, it is better to apply it without oil or solvent. Just rub the felt or felt and sand until the damage disappears. Remember to clean periodically.
From a power tool, it is better to use a screwdriver with adjustable speed or a grinder. You need to work at the lowest speed. If there is no possibility of adjustment, do not hold the disc for a long time in one place. When overheated, microcracks form in the plastic, which greatly reduce transparency. They are no longer removed.
When polishing plastic, do not rub with the edge of the circle, only with its flat part. You will make dents with a rib.
You can return transparency to plastic or achieve a brighter shine, you can GOI No. 1. This is where WD-40 oil or grease comes in handy. If you are polishing with a power tool attachment, you can put a few drops on the polishing pad. The oil film speeds up the process many times even with manual polishing. When finished, wash off the remaining paste with a lubricant (gasoline usually helps, then soapy water), wipe dry and bring to transparency with a car polish. Shiny plastic parts are polished in the same way.
Glass polishing
Glass is polished in the same way as plastic, but much longer. It takes a very long time to remove even a not very deep scratch with your hands. Glass is easier to polish with power tools and nozzles. And do not forget about cleansing when grinding – it is advisable to carry it out even more often.
Tempered glass requires even more time than usual.
The difference with plastic is that we start polishing with the most granular GOI No. 4 paste. We use it without oil. With No. 3 we also work without additives until we remove the scratches. Then, one by one, we pass to an increasingly finer particle size. Here you can already add a few drops of pure engine oil. This brings shine and returns transparency.
If you are polishing a small object with a smooth surface, and it is highly desirable that the surface remain even, it is better to change the way. Make a polishing table. It can be a small piece of metal or thick glass with a perfectly flat surface. A fabric/leather with applied GOI paste is placed on this “table” and a polished object is driven over it. This is how glasses of watches and mobile phones are polished. Just don’t rub the body. It is better to seal it with masking tape.
How to work with metals
We work with hard metals just like with glass: starting from #4 and up to #2 or #1, depending on the desired result. To speed up the process, you can heat the paste or parts – it is polished faster. The principle is the same: while it is necessary to remove scratches, we work without oil, when we bring shine, add a little (drops) pure machine oil.
If you are rubbing parts for equipment, rub dry only. Free from oils, solvents, alcohol and even running water. You can use distilled water to clean up the remaining paste. When the part is absolutely clean, grease can be removed with alcohol and then rinsed with distilled water.
We polish soft metals (aluminum, silver, gold, etc.) like plastic – starting with GOI 2 pastes. The difference is that you don’t have to think about overheating. Increasing the temperature only speeds up the polishing process.
Embossed products
Polishing with GOI paste is mechanical-chemical. This means that some layer of material is physically erased. Therefore, jewelry and coins cannot be cleaned in this way. This reduces their cost. If you need to restore shine, just rub with a soft cloth without adding abrasive pastes.
Tarnished buckles, plaques, cutlery or appliances are processed by hand. You need the most gentle GOI paste – No. 1 – and a soft cloth. The fabric is rubbed with a bar without any additives and the products are rubbed for some time. You can wash off the paste with water or alcohol.