It is easy to imagine the front line, even in the conditions of the modern "civilized" world. There are a lot of dangerous zones where you have to dodge bullets in this world. In such circumstances, special assistance is required, which modern technologies ready to offer. However, not only the sniper's bullet may require protection, but also in other cases when the need to dissipate the energy of movement becomes relevant. In any case, the idea of ​​bulletproof glass seems like a good fit. Therefore, let's consider (just in case "fireman") what constitutes bulletproof, how other moments are produced.

Everyone once had to catch a ball flying fast in the air. The trick of it easy way energy damping is when the hand moves along the motion vector of the flying object, gently stopping the flying ball.

This reduces the strength of the obstacle (arm). As a result, hitting the ball is perceived completely painless. Speaking scientific language- the force of the ball acting on the palm of the hand is equal to the moment of speed of movement.

However, unlike the palm of the hand, a piece of glass does not have the properties of synchronous movement. If a piece is fired from a firearm, it becomes obvious that this object is not able to bend and absorb energy.

As a result, the glass simply collapses, and the bullet overcomes the obstacle with virtually no loss of momentum. This is why ordinary glass is not capable of protecting against bullets, and in such cases, a bulletproof design is required that is more effective in terms of absorbing motion energy.

How bulletproof glass works

Ordinary and bulletproof glass are two completely different things. In any case, one design differs radically from the other. Meanwhile, bulletproof glass is not a completely bulletproof structure. Restrictions, of course, exist, as there are firearms with different recoil strengths.

Bulletproof glass is made up of multiple layers of tough transparent material with "layers" made on the basis of various kinds plastics. Some designs of bulletproof glass contain a final inner layer made of polycarbonate (a hard type of plastic) or plastic film.

This layer prevents the "splint" effect (when pieces of glass or plastic break off when hit by a bullet). Such a "sandwich" of layers is called a laminate. A kind of bulletproof laminate is an order of magnitude thicker than ordinary glass, but at the same time it has a relatively small weight.

Energy absorbing design property

When a bullet hits bulletproof glass, it impacts the existing layers. Since the energy is distributed between the various layers of bulletproof glass and plastic interlayers, the spread of force occurs over a large area, which is accompanied by a rapid absorption of energy.

The movement of the bullet is slowed down to such a level of energy that the forces to overcome the obstacle are completely lost and are not able to cause significant damage. Bulletproof glass panels are, of course, damaged, but the plastic layers do not allow the panels to break into small fragments. Therefore, bulletproof glass should be considered rather as an energy-absorbing object in order to clearly understand the operation of this protective device.

How is bulletproof glass made?

The traditional execution of bulletproof glass, as already noted, is represented by alternating glass panels (3–10 mm thick) and plastic. In this case, the plastic is present in the form of a thin film (thickness 1-3 mm) made on the basis of polyvinyl butyral (PVB). Modern durable types of bulletproof glass represent a similar kind of "sandwich", containing:

• acrylic glass,
• ionoplastic polymer (for example, SentryGlas),
• ethylene vinyl acetate or polycarbonate.

In this case, thick layers of glass and plastic are separated by thinner films of various plastic materials, such as polyvinyl butyrol or polyurethane.

To make a simple PVB-based bulletproof glass, a thin film of PVB is sandwiched between thicker glass to form a laminate. The formed laminate is heated and compressed until the plastic begins to melt, making it with a glass panel.

Typically, this process is done under vacuum to prevent air from getting in between the layers. The penetration of air into the interlayer contributes to the weakening of the laminate structure, affects the optical properties (distorts the transmitted light).

The device is then placed in an autoclave and brought to full readiness under conditions of higher temperature (150°C) and pressure (13-15 ATI). The main difficulty of this process is to ensure proper adhesion of the plastic and glass layers. It is necessary to remove air from the space between the layers, to exclude possible deformation of the plastic from overheating and overpressure.

Where is bulletproof glass used?

The product is manufactured in a variety of shapes and sizes, which allows you to provide various levels protection for emergencies. Most often, the use of bulletproof glass is seen as a characteristic phenomenon in the banking sector.

Cash rooms are usually equipped with bulletproof ones, and bulletproof boxes for the exchange of documents and money are also used.

The quality of protection depends on the thickness of the product. The thicker the glass (the more layers), the better the absorption of energy is provided, respectively, the level of protection increases. The base bulletproof glass has a thickness of 30-40 mm, but if necessary, this parameter can be doubled.

The only problem is that increasing the thickness of the bulletproof glass inevitably leads to an increase in weight. Perhaps this is a minor problem for equipping a bank's cash desk, but becomes a significant problem, for example, in the case of the production of bulletproof glazing.

Increasing the thickness of the bulletproof glass also reduces the transparency factor as the light is "dimmed" by the additional layers of construction. Sometimes this design creates additional difficulties, for example, in a car, when bulletproof glass impairs the driver's visibility.

The process of coating the glass of a car from the inside with a thick film that provides protection and strength is called glass armoring. This coating withstands the impact of a hammer, bats and other heavy objects. The booking system itself came from a business. The earliest films were invented for industrial buildings and commercial premises where protection against robbers and vandals is necessary. In this article, you will learn how to apply such a film yourself, what advantages and disadvantages this system has, and how effective it is.

Film varieties

There are different armored films designed for:

• Autoglass. Thickness from 250 to 310 microns. Free sale. Glued on the principle of tinting. It will take 1 month for complete drying. After that, the film withstands blows with a stone, a hammer, a bat. It saves the car and its passengers both from stones that can fly off on the highway, and he also robs.
• office buildings. Thickness, as well as at a film for an auto glasses. Suitable for offices, shop windows, workshops, large shopping centers. Rolls of material are much larger in width than for auto glass.
• especially important objects. Thickness is about 550 microns. This is necessary for especially important facilities in any state in order to protect themselves from possible terrorists. Such glass is absolutely impossible to break and penetrate into the room.
• Bulletproof for auto glass. Withstands shooting not from any firearm. The standard film is bulletproof, capable of withstanding .38 caliber bullets from a pistol. The thickness of the glass must be at least 12 mm, as well as multi-layered, exactly like the windshield of a car. Automata, this reservation will not be able to withstand.

Whatever the booking film, it is difficult to give a 100% guarantee of strength. The name "bulletproof" is conditional. Studies have shown that this glass will not break through if they shoot from a pistol of the specified caliber and into different parts of the glass. In the event that bullets of the required caliber hit the same place, the glass will be pierced through and not a single film can save it.

Pros and cons of booking a windshield with a film

Often, car enthusiasts believe that car tinting and booking are related to each other. In addition, there is an opinion that such a windshield coating will impair visibility and interfere with driving. All this is completely wrong. The main features and advantages of such a film:

• Quality visibility;
• Does not mix with tinting;
• Perfectly tolerates auto chemicals;
• A thick film covers the windshield, a thin film covers everything else;
• Coating with polarized film - reducing glare;
• Uniform distribution of impact;
• Protection against petty vandalism.

It is also worth remembering about the headlights, which also need protection from foreign objects.

Before you go to the service station, it is important to know the disadvantages of film booking:

• When driving or parking, dust settles on the surface of the windshield. When the car owner turns on the wipers, significant damage is caused to the film in the form of scratches. To reduce damage, avoid heavy dusting and wipe the windshield more often.
• Bubbles can appear anywhere. If they appear in front of the driver's eyes, they will usually be very annoying and reduce the quality of visibility. In addition, suffering appearance car.

The price of booking car windows with a tint film starts around 3,500 rubles.

DIY booking

Glass armor is usually used by motorists who have become victims of broken glass for any reason: someone because of the stones that often fly off the wheels, and someone because of a robbery.

The appearance of the film is similar to tinted with the highest level of transparency. You can buy it in auto stores or through online stores. The procedure for applying the film is as follows.

1. You need to remove the side windows. It is necessary to follow everything according to the instructions based on the make and model of your machine. You should carefully get to the latches and remove the glass, before that, do not forget to unscrew the door cards.

2. Removal of dirt and grease. Important point- this is the degreasing of each glass completely. To do this, lay the glass on a pre-cleaned flat surface. Be careful with abrasive particles that can scratch the glass. Next, you should clean the inside of the side glass, where the booking film will be applied. To clear you can use detergent special for glasses and a lint-free cloth. It is important to understand here that any dust or lint, if it suddenly remains on the surface of the glass, will not remain under the film at all, and the view of the glass from the inside of the cabin will be far from aesthetic.

3. Preparation. The film itself consists of an adhesive layer and a protective colorless substrate. First you need to measure the glass and cut right amount stock films.

4. Now apply to the clean inner side of the glass. The film must be positioned so that the substrate is at the bottom. Using masking tape, you can perfectly fix the film on the glass. Make sure that there is at least 1 cm of film peeking out from all sides.

5. Preparation special means to remove the adhesive part from the film. For cooking, you need to take plain water And liquid soap. The proportion is 20% soap and 80% water. Shampoo should be used with minimal fragrances and additives. Otherwise, these additives will most likely enter into a chemical reaction with the adhesive layer, which will turn out to be unknown. The resulting solution must be filled with a garden sprayer

6. We glue the film and smooth it. Carefully remove the protective backing, keeping the foam only where the edges will not come into contact with the glass. Pour the prepared solution over the surface of the glass and the adhesive layer of the film. Now you should attach the armored film with the sticky side to the inside of the side window. The first film will ride on the surface, this is necessary to smooth out the bumps with a special mini-spatula (it can be changed to bank card). With simple movements from the center to the edges, it is necessary to expel all air bubbles. If this is not done, then bubbles will form, which will no longer be possible to remove.

7. Drying with a building hair dryer. After straightening the entire film, it must be thoroughly dried with a hairdryer. It has a high air t and a thinner jet. The hot film will be able to stretch over the surface. Then take a break for an hour so that the film has time to cool.

8. Removing excess. Initially, at least 1 cm extra was left in order for the film to be enough. Now that it has sat down well and cooled down, you can cut off the extra parts with a clerical knife. It is best to hold the knife at an angle of 45 degrees. It is also desirable to hold the film with a spatula.

Final drying lasts far from one day. The highest degree of protection will appear in a month. Based on experiments, it is possible to break through glass with only 4-5 hits in one place with a heavy object.

Reservation of car windows with film (video)

Outcome

Thus, armoring car windows with a film very well protects not only from foreign objects flying from under the wheels, but also from possible robbers and vandals. But, as a rule, car owners begin to think about it only when something like this happens and the glass is damaged.

One day in 1903, the French chemist Edouard Benedict was preparing for another experiment in the laboratory - without looking, he reached out for a clean flask that was on a shelf in the closet and dropped it. Taking a broom and a scoop to remove the fragments, Eduard went to the closet and found with surprise that the flask, although it had broken, all its fragments remained in place, they were connected to each other by some kind of film. The chemist called a laboratory assistant - he was obliged to wash glassware after the experiments - and tried to find out what was in the flask. It turned out that this container was used a few days ago during experiments with cellulose nitrate (nitrocellulose) - an alcohol solution of liquid plastic, a small amount of which, after the alcohol evaporated, remained on the walls of the flask and froze with a film. And since the plastic layer was thin and transparent enough, the laboratory assistant decided that the container was empty.

A couple of weeks after the story with the flask that did not shatter into fragments, Edward Benedict caught the eye of an article in the morning newspaper, which described the consequences of head-on collisions of a new type of transport in those years - cars. The windshield shattered into fragments, inflicting multiple cuts on drivers, depriving them of vision and normal appearance. The photographs of the victims made a painful impression on Benedict, and then he remembered the "unbreakable" flask. Rushing to the laboratory, the French chemist dedicated the next 24 hours of his life to creating unbreakable glass. He applied nitrocellulose to glass, dried a layer of plastic, and tossed the composite onto the stone floor—over and over and over again. So Edward Benedict invented the first triplex glass.

laminated glass

Glass formed by several layers of silicate or organic glass, connected by a special polymer film, is called triplex. Polyvinyl butyral (PVB) is commonly used as the glass bonding polymer. There are two main ways to produce triplex laminated glass - pouring and laminating (autoclave or vacuum).

Filled triplex technology. Sheets are cut to size, if necessary, they are given a curved shape (bending is performed). After thoroughly cleaning the glass surfaces, they are stacked on top of each other so that there is a gap (cavity) between them no more than 2 mm high - the distance is fixed using a special rubber strip. Combined sheets of glass are set at an angle to horizontal surface, polyvinyl butyral is poured into the cavity between them, a rubber insert around the perimeter prevents it from flowing out. To achieve the uniformity of the polymer layer, the glasses are placed under a press. The final connection of glass sheets due to the curing of polyvinyl butyral occurs under ultraviolet radiation in a special chamber, inside which the temperature is maintained in the range from 25 to 30 ° C. After the formation of the triplex, a rubber band is removed from it and the edge is turned.

Autoclave lamination of triplex. After cutting glass sheets, processing edges and bending, they are cleaned of contamination. Upon completion of the preparation of float glass sheets, a PVB film is laid between them, the formed “sandwich” is placed in a plastic shell - air is completely removed from the bag in a vacuum installation. The final connection of the “sandwich” layers takes place in an autoclave, under a pressure of 12.5 bar and a temperature of 150 ° C.

Vacuum lamination of triplex. Compared to autoclave technology, vacuum triplexing is performed at lower pressure and temperature. The sequence of working operations they have is similar: glass cutting, shaping in a bending furnace, turning edges, thorough cleaning and degreasing of surfaces. When forming a “sandwich”, an ethylene vinyl acetate (EVA) or PVB film is placed between the glasses, then they are placed in a vacuum machine, previously placed in a plastic bag. The soldering of glass sheets takes place in this installation: air is pumped out; "sandwich" is heated to a maximum of 130 ° C, the film polymerizes; the triplex is cooled to 55°C. Polymerization is carried out in a rarefied atmosphere (-0.95 bar), when the temperature drops to 55°C, the pressure in the chamber equalizes to atmospheric pressure and, as soon as the temperature of the laminated glass reaches 45°C, the formation of the triplex is completed.

Laminated glass, created by poured technology, is stronger, but less transparent than laminated triplex.

Windshields of cars are made from glass sandwiches made using one of the triplex technologies, they are necessary for glazing high-rise buildings, in building partitions inside offices and residential buildings. Triplex is popular with designers - products from it are an integral element of modern style.

But, despite the absence of fragments when hitting a multi-layer "sandwich" of silicate glass and polymer, it will not stop the bullet. But the triplex glass discussed below will do this quite successfully.

Armored glass - history of creation

In 1928, German chemists create new material, which immediately interested aircraft designers - plexiglass. In 1935, the head of the Research Institute "Plastmass" Sergei Ushakov managed to get a sample of "flexible glass" in Germany, Soviet scientists began to study it and develop mass production technology. A year later, the production of organic glass from polymethyl methacrylate began at the K-4 plant in Leningrad. At the same time, experiments were begun aimed at creating armored glass.

Tempered glass, created in 1929 by the French company SSG, was produced in the USSR in the mid-30s under the name "stalinite". The hardening technology was as follows - sheets of the most common silicate glass were heated to temperatures in the range from 600 to 720 ° C, i.e. above the glass softening temperature. Then the glass sheet was subjected to rapid cooling - cold air flows lowered its temperature to 350-450 ° C in a few minutes. Thanks to tempering, the glass received high strength properties: impact resistance increased by 5-10 times; bending strength - not less than twice; heat resistance - three to four times.

However, despite its high strength, "stalinite" was not suitable for bending to form an aircraft cockpit canopy - hardening did not allow it to bend. In addition, tempered glass contains a significant number of internal stress zones, a light blow to them led to the complete destruction of the entire sheet. "Stalinite" cannot be cut, processed and drilled. Then the Soviet designers decided to combine plastic plexiglass and "stalinite", turning their shortcomings into dignity. Preformed aircraft canopy coated small tiles made of tempered glass, polyvinyl butyral served as glue.

The entry of the former Soviet republics into capitalism since the early 1990s has sharply increased the demand for armored glass protection for vehicles of collectors and currency exchange offices. At the same time, there was a need for "transparent armor" for cars businessmen. Since the production of real armored glass was expensive, as well as the final product, a number of companies launched the production of imitation armored glass - it was a triplex of rather mediocre quality, the polymerization of PVB film was carried out in an accelerated mode, using ultraviolet irradiation. Finished products was able to withstand a pistol bullet from a distance of 5 meters, i.e. corresponded only to the 2nd class of protection (there are six in total). Massive armored glass of this type could not withstand temperature fluctuations of more than +20 and below -22 ° C - after six months, the layers of triplex partially delaminated, their already low transparency was seriously reduced.

transparent armor

Modern bulletproof glass, also called transparent armor, is a multilayer composite formed by sheets of silicate glass, plexiglass, polyurethane, and polycarbonate. Also, the composition of the armored triplex may include quartz and ceramic glass, synthetic sapphire.

European armored glass manufacturers mainly produce triplex, consisting of several “raw” float glasses and polycarbonate. By the way, non-tempered glass among companies producing transparent armor is called "raw" - it is "raw" glass that is used in triplex with polycarbonate.

A polycarbonate sheet in such laminated glass is installed on the side facing the inside of the protected room. The task of plastic is to dampen the vibrations caused by the shock wave when a bullet collides with bulletproof glass in order to avoid the formation of new fragments in sheets of "raw" glass. If there is no polycarbonate in the composition of the triplex, then the shock wave moving in front of the bullet will break the glass even before it actually comes into contact with them and the bullet will pass through such a “sandwich” without hindrance. The disadvantages of armored glass with a polycarbonate insert (as well as with any polymer in the composition of the triplex): a significant weight of the composite, especially in classes 5-6a (reaches 210 kg per m 2); low resistance of plastic to abrasive wear; exfoliation of polycarbonate over time due to temperature changes.

quartz glass. It is produced from silicon oxide (silica) of natural origin (quartz sand, rock crystal, vein quartz) or artificially synthesized silicon dioxide. It has high heat resistance and light transmission, its strength is higher than that of silicate glass (50 N/mm2 versus 9.81 N/mm2).

ceramic glass. It is made of aluminum oxynitride, developed in the USA for the needs of the army, the patented name is ALON. The density of this transparent material is higher than that of quartz glass (3.69 g / cm 3 versus 2.21 g / cm 3), the strength characteristics are also high (Young's modulus is 334 GPa, the average bending stress limit is 380 MPa, which is practically 7-9 times higher than similar indicators of silicon oxide glasses).

Artificial sapphire (leucosapphire). It is a monocrystal made of aluminum oxide, as part of armored glass it gives the triplex the maximum strength properties possible. Some of its characteristics: density - 3.97 g / cm 3; average bending stress limit - 742 MPa; Young's modulus - 344 GPa. The disadvantage of leucosapphire lies in its significant cost due to high production energy costs, the need for complex machining and polishing.

Chemically strengthened glass. "Raw" silicate glass is immersed in a bath with an aqueous solution of hydrofluoric (hydrofluoric) acid. After chemical hardening, the glass becomes 3-6 times stronger, its impact strength increases six-fold. The disadvantage is that the strength characteristics of toughened glass are lower than those of thermally hardened glass.

Armored glass frame

The use of armored triplex in glazing does not mean that the opening blocked by it will be bulletproof - a frame of a special design is required. It is made mainly from metal profiles, most often aluminium. In the grooves located along the junction line of the triplex and the frame profile, steel linings are installed to protect the weakest point in the armored window structure from impact or contact with a bullet.

Protective armor plates can also be installed outside the frame structure, however, this will reduce the aesthetic characteristics of the window. To achieve the maximum level of protection, the frames can be made entirely of steel profiles (linings are not needed in this case), but they will become very bulky and costly.

The weight of an armored window often exceeds 300 kg per m 2, not every building and construction material is able to withstand it. Therefore, the installation of an armored window structure is only permissible for reinforced concrete and brick walls. Opening the sash of an armored window is not easy due to its high weight; servo drives are used for this purpose.

Armored windows are widely used in various fields: they can be found in banks, residential buildings, shops, cars. The design is a thick glass made of triplex and polycarbonate. The layers are superimposed on each other and glued together in a special way, due to which a thick, heavy, but very strong structure is obtained.

Product varieties

Armored glass is similar in properties to tempered glass. Read what is the advantage of this type of glass.

Using an armored window

Not so long ago, armored windows were used exclusively in places associated with material or historical values, such as museums and banks, but later armored windows became more affordable, and it became possible to meet them in ordinary private houses, and not necessarily government officials.

Modern windows have become much more technologically advanced, more affordable and more functional. They can be installed instead of . Armored windows for the home are superior to standard double-glazed windows not only in terms of strength, but also in all other indicators, such as protection from cold and noise.

armored windows

What should be considered when buying an armored window?

Before you buy armored windows in an apartment, you need to determine what you need it for. You may not be able to get by with the cheapest option that can withstand the impact of a stone, or you may not have to pay extra since you do not need a bulletproof window.

Product functions may be as follows:

• Protection against stone ingress, accidental mechanical damage.
• Security from criminal encroachments, attempts to purposefully break a window.
• Protection against shots from firearms.

The difference between the designs lies not only in strength and cost, but also in functionality.

Possible options when choosing a window

Reservation of double-glazed windows with a film makes them more durable, triplex glass does not spill out when broken, since all the fragments remain on the film. Such a strong desire can be broken, but it will take a vandal quite a lot of time. Bullying teenagers can not be afraid. Glass can prevent a thief from getting into the house, it will last much longer than usual, but it will not provide protection from a bullet.

Armored plastic windows for the home - this is most often the usual triplex, fastening several thin glasses. It makes the window stronger and safer, but such a product cannot be fully called armor. A double-glazed window of such a plan is suitable for standard plastic frames and is inexpensive.

Types and designs of frames

Bulletproof double-glazed window is quite expensive, but it can be different options, from one relatively thin glass to a thick complex. It is worth noting that the lowest-class double-glazed windows can freeze and produce condensation. Thicker double-glazed windows will cope with a shot from a more powerful weapon and hold heat better, but they will weigh quite a lot. The higher the class of double-glazed windows, the stronger it is. To make it clear, a class 5 product can withstand a shot from a 7.62 caliber.

Armored windows in the house can be different designs and meet different requirements and standards, which affects their thickness and price. Such windows are quite affordable to a wide range of buyers.

Bulletproof glass — layered construction, consisting of several M1 glasses and several layers of a polymeric photocurable composition. Depending on the required protection class, the design can be either with or without a film. This design structure provides protection against bullets fired from different kind weapons, depending on the required protection class.

The armored glass design is transparent and provides protection according to classes B1, B2, B3, B4, B5 (bullet resistance class 1, 2, 3, 4 and 5) according to GOST R 51136-2008 while simultaneously transmitting light. Suitable for both internal and external glazing.

The complete set of a double-glazed window for preservation of a temperature condition is possible.

Armored glass- a guarantee of security, it was created in order to protect people and their property. That is why it is especially important that the glass is of excellent quality. You need to be sure that you and your property are fully protected. The first, second, third, fourth, fifth or sixth class of armored glass protection is selected based on the conditions and wishes of the customer.

Scope of bulletproof glass

• currency exchange points;
• places for issuing money at the cash desks of large organizations, enterprises;
• internal security posts in banks, jewelry stores, shooting galleries;
• workplaces of petrol station operators;
• workplaces of bank tellers working in operating rooms;
• workplaces of employees of duty units of internal affairs bodies;
• equipment of banks and cash collection machines;
• other buildings, structures and objects that need to be protected from burglary, strikes and shelling.

Double-glazed windows made of laminated armored glass, made using mirrored, tinted glass of various colors, have unique properties that not only protect the room from impacts and shelling, but also reduce heat loss in the cold season, protect against the harmful effects of sunlight and noise.

A mirror made of laminated glass, along with high strength characteristics and aesthetic properties, ensures its long-term and safe use in rooms with high humidity(in bathrooms and pools).

Armored laminated protective glass (bulletproof glass) is intended for use on vehicles, in administrative and residential buildings, where there is a need to protect human life and material values.

Characteristics of bulletproof glass

Characteristics bulletproof glass correspond to GOST R 51136-2008 "Protective multilayer glasses". The total light transmission of glass is at least 70%. Glass must be heat and moisture resistant, withstand a temperature of 60 ° C and a humidity of 95%. Its frost resistance is minus 40 °C.

Defensive Ability bulletproof glass depends on its thickness. 37 mm thick glass holds PS-43 bullets of 7.62 mm caliber from AKM. According to the certificate issued by the State Standard of Russia, such glass corresponds to the third class of protection and, in addition, is able to hold bullets from PM, TT pistols, AK-74 assault rifles and fragments from RGD-5, F-1 and RG-42 hand grenades.

Armored glass has protective properties

• withstands repeated impact of a freely falling body;
• resistant to penetration;
• withstands the impact of firearms (PM, TT pistols, AKM submachine gun, SVD rifle) and prevents through penetration of the damaging element.

Technologies for the production of armored glass

For the manufacture of bulletproof glass, flat or curved polished blanks with a thickness of 5 to 10 mm are used. In order to increase strength, they are glued together in a certain combination. Polyvinyl butyral film is used as fastening materials. Then a layer is glued to the inner surface of the glass, which protects against damage by secondary glass fragments. In this way, not only extremely strong, but also shatterproof glass is obtained.

Protective film in armored glass

The protective film has a very high transverse tensile strength. When applied to glass, it gives it the same properties: it greatly weakens deformations transverse to the glass surface, including microvibrations. If even a small transverse deflection occurs, the viscous polymer film quickly returns the glass (providing elastic deformation) to its normal position. Of course, a sufficiently strong impact can deflect the glass with the film from its undeformed position by the distance necessary for the fragile glass to still break. But at the same time, it remains in place, glued to the protective film.

Properties of the protective film of bulletproof glass

• strengthening glass - glass does not break when not too strong blows (when hit by a soft body, foot, stone or bottle);
• shatterproof - the film prevents fragments from entering the room even when the glass does break (therefore, the protective film is applied to the armored windows from the back);
• penetration protection - maintaining the integrity of the window (even after breaking) prevents an intruder from entering the room, providing protection similar to gratings;
• the possibility of listening is almost completely excluded by removing sound vibrations from the glass with special equipment;
• soundproofing properties (sound enters the room through the window due to mechanical vibrations of the glass, retransmitting street noise);
• well absorbs ultraviolet, keeping the interior from fading and providing protection from one type of heat transfer. As a result, the thermal insulation of the room increases from external environment and as a result, the cost of heating the premises in winter and cooling in summer is reduced;
• with similar protective qualities, glass with a protective film can be knocked out from the inside of the room.

Requirements for installing bulletproof glazing

Protective panels must have a stability class not lower than the stability class of the protective glazing used. For class B1 (P1), the panels must be made of sheet steel with a thickness of at least 6 mm. For class B3 (P3) - from sheets of armored alloy with a thickness of at least 4.57 mm.

Trays for transferring money or documents, openings for negotiating must be designed to prevent the penetration of a bullet into the protected area when fired from outside.

Vertical supports must be securely fixed at ceiling and floor level. Horizontal structural members must be securely fastened at each joint and, if possible, fastened to the walls.

Doors to the protected area should provide the same level of protection as the bulletproof glazing used. In addition, they must open outward and be equipped with a self-locking lock.

Any window in the protected area must be protected by bulletproof glazing of the same class as that installed inside the premises.

Test methods for bulletproof glass

The essence of this method is to determine the resistance of laminated glass to the effects of certain types of firearms. The tests are carried out on three samples of laminated glass measuring 500×500 mm. Draw an equilateral triangle at the center of the test specimen with sides 120 mm long. Three shots are fired at the vertices of this triangle. Glass is considered to have passed the test in the absence of through penetration.

Test requirements for bulletproof glass

• the test sample is installed in a rigid frame with clamping devices;
• the rigid frame should not move under the impact of bullets;
• the test sample must be installed perpendicular to the direction of movement of the bullet;
• all four edges of the glass must be evenly clamped, the width of the clamp must be (30 ± 5) mm, while the target area must be at least 440 × 440 mm;
• clamping forces must prevent displacement of the sample during the test, while no stress should occur that affects the result.

Behind the test sample, a fragment storage box is installed, which is a chamber that serves to collect glass fragments separated from the rear surface of the test sample and a bullet that has passed through the test sample.

The bullet velocity measurement device is an electronic system that measures the time of flight of a bullet between two sensors - targets located at a fixed distance of 300500 mm along the bullet's flight path. When a bullet passes through the first target sensor, a pulse is generated, which turns on a frequency meter that counts the number of pulses generated by the high-frequency generator of the device. When the bullet passes through the second target sensor, the pulse is stopped. The speed of a bullet is determined by calculation. The bullet velocity is measured at a distance of not more than 2.5 m in front of the test specimen. The measurement error should not exceed 1.0 m/s.

When a bullet hits an obstacle, the bullet and the protection material itself are damaged: the huge kinetic energy of the bullet's movement is extinguished due to the deformation of the material being compressed and torn by it (inelastic deformation). Most bullets (for submachine guns or rifles) contain a very strong, heavy steel core that, after flattening the shell, penetrates deep into the material.

For the purity of the test, a sheet of thin metal foil is placed behind the test sample, by damage to which the test results can be determined. The protection class depends not only on the means of destruction, but also on the selected cartridge and bullet.

Testing bulletproof glass

• weapons and ammunition are selected according to the protection class for which the laminated glass is to be tested;
• before testing, several preliminary shots are fired to determine whether the actual impact speed is acceptable;
• the sample is installed in the frame with the attacked side to the weapon;
• three shots are fired at the test sample in accordance with the test conditions. The impact speed and the distance between the centers of three impacts are determined with an accuracy of 1 mm;
• inspect the test sample for the presence of through holes;
• check for the presence of glass fragments and fragments that have separated from the rear surface of the test sample in the box - the fragment accumulator;
• the nature of the lesion is controlled after each shot according to the state of the control screen and the back of the sample;
• lumbago is considered through penetration of the sample by a bullet or its fragment;
• glass is considered to have passed the test if there is no penetration of the control screen by a bullet or glass fragments.

Bulletproof glass classification according to bullet resistance

Video about armored glass

The bulletproof glass video was commissioned by the How It Works program.