Guide to electrical materials for all. Part 7

Continuing guidance on electrical materials. In this part, we begin to disassemble the dielectrics: glass fiber, varnished cloth, rubber and ebonite.

Welcome to CAT (TRAFFIC)

Glass fiber

A kind of PCB that uses fiberglass and most often epoxy resin. Usually light yellow. A widespread composite material, combines lightness, strength, elasticity, does not rot, it is difficult to burn.

In the form of sheets - the main material of printed circuit boards, has the name FR-4 abroad. durable enough and stable for the manufacture of multilayer printed circuit boards. Outside the form of sheets, fiberglass is often referred to as fiberglass.

Application examples

The main material for the manufacture of printed circuit boards. Already produced with pre-glued copper foil on one or both sides, referred to as "fiberglass foil GOST 10316-78".

PCB blanks from 1.5 mm foil fiberglass.

Construction material. In the form of sheets of various thickness, “Structural textolite GOST 10292-74” Mandrel coils, electrode holders, body elements.

Scraps of sheet fiberglass of various thickness. The detail in the foreground was specially broken - a textile material is visible on the break.

Insulating material. As gaskets, separators, holders, protective plates.

What should be added

Fiberglass and fiberglass in general are very interesting materials. Fiberglass reinforcement rings when falling onto a concrete floor, which indicates a high elasticity of the material. The material is lighter than steel, while in many respects comparable with her strength.

The material is anisotropic. Since it is layered, with a load perpendicular to the layers, it is much stronger than with a load aimed at the separation of layers. In the manufacture of products by molding fiberglass with epoxy, this is taken into account when choosing the directions of laying the fabric.

Material is deceptively easily handled. It is easy to cut with a hacksaw, sawed with a file, drilled. But the glass fibers in the composition very quickly wear out the working edge of the tool. Conventional high speed steel drills are blunt after already two or three dozen holes, so fiberglass laminate in the production of printed circuit boards is drilled with tungsten carbide carbide drills. But these drills are very fragile and they can be drilled only in the machine.

The material is destroyed irreversibly, this behavior (like a crash when breaking fibers) strongly resembles wood. If the steel part bends when exceeded, then it can be straightened with the help of a hammer and some mother there, then the fiberglass part loses its shape when the load is exceeded and cannot be repaired, only replaced.

Steklotekstolit does not decay, it is resistant to atmospheric influences (however, it can stratify due to freezing of water that has entered random pores in winter) and is transparent to radio waves. Therefore, it makes various fairings for antennas, covers, enclosures. The flip side of the coin is that the material is not recyclable. In general, he goes to landfill and will lie there for centuries.

The manufacture of products of complex shape is a non-automated process with an abundance of manual labor. Correctly spread out the fabric, cut, smooth folds, apply resin, expel air bubbles - all by hand. Therefore, products made of fiberglass, carbon fiber (carbon fiber cloth) are expensive and are unlikely to ever become cheaper. This, in fact, put an end to the fiberglass auto body - for a long time, it is expensive to produce them and not to be processed into scrap metal later, although such a body is almost eternal and will not rust. Some products are obtained by automated winding of glass yarn - gas cylinders, fittings.

Varnished cloth

Varnish is a flexible insulating material, consists of a fabric (cotton, synthetic fiberglass) impregnated with an elastic binder (varnishes, resins). There is GOST 28034-89 on varnished cloth.

A piece of varnished cloth. Often can be found in transformers.

Since the layer of fabric is only one - the varnishcloth is flexible and durable, and often translucent. Sometimes the binder is specially made sticky, the layers of such fabric adhere well forming with time an almost monolithic layer.

It is often used to isolate layers of windings in transformers, in windings of electric motors, generators.


Elastic material obtained by the vulcanization of rubber. In general, rubber is often called any elastic material, not focusing on the difference in composition, although silicone rubber differs from isoprene quite strongly.

Rubber insulated cable, V-ribbed belt, O-rings - rubber products.

Before the invention of vulcanization, natural rubber was a specific material - sticky in the heat, brittle in the cold, fragile. The discovery of vulcanization Goodyear allowed to deprive the rubber of natural defects. If 1–2% of sulfur is introduced into the feedstock, when heated between the molecules of rubber, bridges form through the sulfur atoms, as a result of which the rubber becomes elastic. If you introduce a lot of sulfur (30%), then the bridges will be so much that the rubber will become hard, you get a material called ebonite. By adjusting the degree of vulcanization, you can adjust the properties of the material over a wide range.

Application examples

Insulation wires. Occasion in rubber insulation has a number of advantages over fellow PVC insulation, rubber in the cold dubeet not so much, does not melt. Heating devices that do not exclude contact with the supply wire have a wire made of heat-resistant insulation, for example, irons. Rubber Wire Extension Cable -
Good solution for harsh environments. Unfortunately, the copper wires of such a wire are very often oxidized, which complicates installation.

Seals. Rubber rings, pads, cuffs, often not only provide
tightness, but also eliminate unpleasant backlash and vibrations in the products.

Driving belts. Flexible belts round (belt), square, flat, wedge,
poly V-sections, cog ... and many other forms. They are intended for transmitting rotation in different mechanisms, for example, from an electric motor shaft to a rack and pinion tray extension drive on a DVD drive.

Voltage protection means. Rubber gloves, boots, mats - all to protect the electrician from electric shock.


Ebonite is a highly vulcanized rubber with a high (up to 30%) sulfur content, due to which, unlike the usual rubber, it has hardness. There is GOST 2748-77 for ebonite.

Ebonite bar. I cut off a piece of bar for the visibility of the material itself.

Application examples

Insulating material. Before the wide distribution of synthetic plastics was in progress, now completely replaced by plastics, surpassing its properties.
Ornamental material - handles of knives, mouthpieces of tubes, decorative elements.

Links to parts of the manual:

1 : Conductors: Silver, Copper, Aluminum.
2 : Conductors: Iron, Gold, Nickel, Tungsten, Mercury.
3 : Conductors: Carbon, nichrome, thermostable alloys, solders, transparent conductors.
4 : Inorganic dielectrics: Porcelain, glass, mica, ceramics, asbestos, gas and water.
5 : Organic semi-synthetic dielectrics: Paper, click, paraffin, oil and wood.
6 : Synthetic dielectrics based on phenol-formaldehyde resins: carbolite (bakelite), getinax, textolite.
7 : Dielectrics: Glass fiber (FR-4), varnished cloth, rubber and ebonite.
8 : Plastics: polyethylene, polypropylene and polystyrene.
9 : Plastics: polytetrafluoroethylene, polyvinyl chloride, polyethylene terephthalate and silicones.
10 : Plastics: polyamides, polyimides, polymethyl methacrylate and polycarbonate. History of the use of plastics.
11 : Insulating tapes and tubes.
12 : Final


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