History
Bulletproof vest is a kind of modern light armor, which is specially designed to protect the wearer’s important organs from bullets. For many manufacturers and wearers of protective armor, the term “bulletproof vest” is not used properly. The term “safety vest is not the first choice for the wearer because the item will not be impacted by bullets”
Over the centuries, different cultures have developed bulletproof vests for combat. The Mycenaeans in the 16th century B.C. and the Persians and Greeks around the 5th century B.C. used up to 14 layers of linen, while the Micronesian residents of Gilbert and Ellis islands did not use coconut palm fabric until the 19th century
Elsewhere, armor is made from animal skins: as early as the 11th century BC, the Chinese wore five to seven layers of rhinoceros skin, and Shoshone Indians in North America also developed jackets with several layers of animal skins, which were glued or sewn together. Quilted armour was found in Central America before Cortes, Britain in the 17th century and India before the 19th century.
The earliest armor consisted of links or wires made of iron, steel or brass. It was successfully developed in Europe as early as 400 BC. The Roman Empire used mail shirts, which were the main dress in Europe until the 14th century.
Subsequently, Japan, India, Persia, Sudan and Nigeria also developed ancient armor. An overlapping scale consisting of metal, horn, bone, leather, or scales of an appropriately sized animal, such as a scaled anteater, used throughout the old hemisphere from 1600 BC to modern times. Sometimes, as in China, the scales are sewn in cloth pockets.
Brigandine armor – sleeveless quilted jacket consists of small rectangular iron or steel plates fixed to overlapping leather strips like roof tiles. The result is a relatively light and flexible jacket. (the steel plate coating in early 12th century Europe was heavier and more complete. This led to the familiar all steel plate armor of 16th century and 16th century.) Many people believe that armor is the pioneer of today’s bulletproof vest.
Around 700 ad, Chinese and Koreans had similar armor. In Europe in the 14th century, it was a common form of human armor. After 1360, the bra inside a bra became the norm. Until 1600, the short brigandine coat with bra was popular in Europe.
With the introduction of firearms, armored craftsmen initially tried to compensate by strengthening the breastplate or trunk cover, covering the breastplate with a thicker steel plate and a second heavier steel plate to provide some gun protection. However, in general, heavy armor is discarded wherever firearms are used in military use.
Experimental research on effective bulletproof vests continued, most notably during the American Civil War, World War I and World War II, but it was not until the plastic revolution in the 1940s that effective bulletproof vests began to be provided to law enforcement personnel, military personnel and others. At that time, the bulletproof vest was made of bulletproof nylon, supplemented by glass fiber, steel, ceramics, titanium, duolong and composite materials of ceramics and glass fiber. The last one was the most effective. Bulletproof nylon has always been the standard fabric of bulletproof vest.
Until the 1970s. In 1965, DuPont chemist Stephanie goleck invented Kevlar, which is a trademark of poly-p-phthalamide. It is a liquid polymer that can be spun into aramid fiber and woven into cloth. Initially, Kevlar was developed for tires, and later used in a variety of products such as ropes, gaskets and various parts of aircraft and ships. In 1971, Lester Shubin of the National Institute of law enforcement and criminal justice advocated using it to replace the bulky bulletproof nylon in bulletproof vests. Since then, Kevlar has been the standard material. In 1989, United signal developed a competitor for Kevlar, called spectral. Originally used in canvas, polyethylene fiber is now used to make lighter and stronger nonwovens and bulletproof vests next to traditional Kevlar fibers.
Raw Materials
The bulletproof vest consists of a panel and a vest shaped sheet made of advanced plastic polymer, which is composed of multiple layers of Kevlar, spectrum shield or Twaron (similar to Kevlar) or bynema (similar to spectrum).
The woven Kevlar layer is sewn together with Kevlar thread, while the nonwoven spectral shielding layer is coated and bonded with resin such as Kraton, and then sealed between two polyethylene films.
The panel provides protection but is not very comfortable.
It is placed in a fabric shell usually made of polyester / cotton blend or nylon. The side of the shell facing the body is usually sewn with a layer of water absorbent material, such as kumax, to make it more comfortable. Bulletproof vests may also have nylon padding to provide additional protection.
For bulletproof vests intended to be worn in particularly dangerous situations, built-in bags are provided to accommodate plates made of metal or ceramic bonded to fiberglass. The vest can also provide protection in the event of a car accident or stab injury.
Various devices are used to tie vests. Sometimes both sides are connected with elastic webbing.
However, they are usually fixed with cloth straps or elastic bands, with metal or Velcro fasteners.
The Manufacturing Process
Some bulletproof vests are customized to meet the customer’s protection needs or dimensions. However, most of them comply with standard protection regulations, have standard clothing industry sizes (such as 38 long and 32 short), and are sold in large quantities.
Making panel cloth
- To manufacture Kevlar, the polymer polyethylene terephthalate must first be produced in the laboratory.
This is done through a process called polymerization, which involves binding molecules to long chains. Then, the crystalline liquid containing the rod-shaped polymer is extruded through the spinneret (a small metal plate filled with small holes, which looks like a shower head) to form Kevlar yarn.
Kevlar fibers are then hardened through cooling tanks. After spraying water, the synthetic fiber is wound on the reel. Then, Kevlar fiber manufacturers usually send the fibers to the spinner, which twists the yarn to make it suitable for weaving.
In order to make Kevlar cloth, the yarn is woven with the simplest pattern, plain or plain, which is only the upper and lower patterns of alternately interlaced threads. - Unlike Kevlar, the spectrum used in bulletproof vests is usually not fabric.
Instead, strong polyethylene polymer filaments are spun into fibers and laid parallel to each other. Resin is used to cover the fibers and seal them together to form a cloth. Then the two pieces of this cloth are placed perpendicular to each other and bonded again to form a non-woven cloth, which is then sandwiched between the two pieces of polyethylene film. The vest shape can then be cut from the material.
Cutting panel - Kevlab is sent to the bulletproof vest manufacturer in large rolls. First, unfold the fabric onto the cutting table, which must be long enough to cut multiple panels at one time; Sometimes it can be like this
Secondly, Kevlar has always been the most widely used material in bulletproof vests. In order to make Kevlar, we must first produce polymer solution. Then the liquid produced is extruded from the spinneret, cooled with water, stretched on the drum, and then rolled into cloth.
Kevlar’s latest competitor is spectras shield. Unlike Kevlar, spectrum shield is not woven, but spun into fibers parallel to each other. The fibers are coated with resin and layered to form a cloth.
Up to 32.79 yards (30 meters). Lay as many layers of material as necessary on the cutting table (as few as eight layers or as many as 25 layers depending on the level of protection required).
- Then put a piece of cut paper on several layers of cloth, similar to the model of home sewing. In order to maximize the use of materials, some manufacturers use computer graphics systems to determine the best position for cutting plates.
- Using a hand-held machine, except that there is a 5.91 inch (15 cm) cutting wheel (similar to the cutting wheel at the end of the Pizza Cutter) instead of the cutting line, its performance is similar to a puzzle. Workers cut around the cut plates to form plates, and then stack them accurately.
- Although spectrum shield usually does not need to be sewn, because its panels are usually cut and stacked into one layer and then put into the tight fitting pocket in the vest, the bulletproof vest made of Kevlar can be sewn by quilt or box.
Quilted sewing forms a small diamond cloth, which is sewn separately, while box sewing forms a large single frame in the vest. Stitching the quilt requires more labor intensity and difficulty, and it provides a hard panel, which is difficult to remove from the vulnerable area. On the other hand, box stitching is fast and simple, allowing the vest to move freely. - In order to sew the layers together, the workers placed a template on the top of each layer and rubbed chalk on the exposed area of the panel,
After the cloth is made, it must be cut into appropriate patterns. These parts are then sewn together with accessories (such as shoulder straps) to form a finished vest.
Draw a dotted line on the cloth. The sewer then stitches the layers together in a chalk pattern. Next, sew a size label on the panel.
The last is to tidy up the vest
- The panel shell is sewn together in the same factory using standard industrial sewing machine and standard sewing procedures. Then slide the panel into the housing and sew accessories such as belts. The finished bulletproof vest is packed and delivered to the customer.
Quality Control
Bulletproof vests undergo many of the same tests as ordinary clothes.
Fiber manufacturers test the tensile strength of fibers and yarns, and weavers test the tensile strength of synthetic fabrics. The manufacturer also tested the tensile strength of nonwovens.
Vest manufacturers test the strength of panel materials (whether Kevlar or spectra), and production quality control requires trained observers to check the vest after panel stitching.
Unlike ordinary clothing, bulletproof vests must undergo strict protection tests in accordance with the requirements of the National Institute of Justice (NIJ). Not all bulletproof vests are the same.
Some can prevent lead bullets at low speed, while others can prevent all metal jacketed bullets at high speed. Vests are classified from the lowest to the highest by number: I, II-A, II, III-A, III, IV and special cases (cases requiring protection specified by the customer).
Each category specifies which bullet will not penetrate the vest at what speed. Although it seems logical to choose the highest rated vest (such as III or IV), this vest is heavy and the wearer’s needs may think that a lighter vest is more suitable. For police use, the general rule suggested by experts is to buy a vest in case the police usually carry guns.
The size label on the vest is very important. It includes not only the size, model, style, manufacturer’s logo and care instructions. Just like ordinary clothing, it must also include the protection grade, batch number, release date, which side should face outward, serial number, notes indicating that it meets the NIJ approval standards. For type I to type III a vests – this is a huge warning that the vests will not protect the wearer from sharp instruments or rifle shots.
The bulletproof vest has been tested dry and wet. This is because the fibers used to make vests behave differently when wet.
The test vest (wet or dry) needs to be wrapped around the modeled clay dummy. Then, the correct type of gun and the correct type of bullet are fired at a speed suitable for vest classification. Each shot is 3 inches (7.6 cm) from the edge of the vest and nearly 2 inches (5 cm) from the previous shots. Six bullets were fired, two at an incident angle of 30 degrees and four at an incident angle of 0 degrees. One shot should fall on the seam.
This shooting method forms a large triangular bullet hole. Then turn the vest over and shoot in the same way, this time forming a narrow triangular bullet hole. In order to pass the test, the vest should show no signs of penetration. In other words, the clay dummy should not have holes, vest pieces or bullets. Although the bullet will leave a dent, the depth should not exceed 1.7 inches (4.4 cm).
When the vest passes the inspection, the model is certified and the manufacturer can make an accurate copy of the vest. After testing the vest, put it into the file so that you can easily check the same model of vest according to the prototype in the future.
It is not feasible to manipulate the field test for the bulletproof vest, but in a sense, the wearer (such as the police) will test it every day. Research on injured police shows that bulletproof vests save hundreds of lives every year.
