Lightweight and strong: ballistic panels protect cars, ships, airplanes
Wars, terror, piracy: In a troubled world, people want to protect themselves. The first armor made of fiber composite dates back to antiquity. Back then, several layers of linen were joined with glue to form a stiff fabric laminate that fighters wore around their bodies. Even Alexander the Great protected himself with such a linothorax.
Nowadays, ballistic plates help protect against all kinds of projectiles. They consist of materials such as aramids and high-performance polyethylenes. Together with glass, ceramic and metal fibers made of aluminum oxide, silicon carbide, boron carbide, aluminum and armor steel, they are heated in composite presses from Wickert and formed into fiber composite plates.
This is done by specialist companies that produce ballistic panels tailored to specific applications. These include sensitive areas on warships, container ships and military trucks as well as the bodies of luxury limousines and the outer skins of helicopters. The linings are designed to provide the greatest possible protection against bullets, explosive, fragmentation and ricochet projectiles, while at the same time being very lightweight.
Uncertainty in the world increases demand for ballistic plates
Wickert is directly affected by the current increase in demand for protection: "We have been manufacturing composite presses for the production of ballistic plates since the 1980s. In recent years, however, the market has picked up noticeably and has been growing continuously ever since," observes managing partner Stefan Herzinger.
Composite presses for ballistic plates must meet three requirements:
In them, the blanks and semi-finished products must be heated and cooled as uniformly as possible.
The pressure of the press must be as equal as possible at all points of the entire sheet.
In the press, the die must close precisely. For this, it is important that the upper and lower halves of the die meet as precisely as possible - the so-called plane parallelism must be particularly accurate.
Only three degrees temperature deviation
In our WKP 52000 composite press, heating/cooling plates with an output of 360 kW ensure uniform temperature distribution. Separate channel systems for hot and cold thermal oil are responsible for maintaining the correct temperature. Although this type of temperature control involves a great deal of effort, it is worth it: the deviation in temperature distribution over the entire plate is just ±3 ºC.
High force density and sensitive pressure adjustment
The very high force density is generated by six press cylinders made of high-strength steel. For a project in Australia, we have included the option of fine pressure adjustment at just 960 kN as an additional equipment variant. This is less than a fifth of what a press can normally work with. This is because the minimum press force is usually ten percent of the maximum output, which would otherwise be 5,200 kN for the WKP 52000.
At 40 mm/s, the hydraulics also work not only quickly but also precisely. An axial piston high-pressure pump serves as the drive, and force and speed can be freely preselected for all travel functions. This makes the hydraulics fast, sensitive, reliable and precise - important for repeatable production.
High-precision press run
The accuracy of the press is also important for the quality of production. "The use of high-quality standard components and our expertise in integrating peripheral components are important," Herzinger cites. "Not to mention our more than 110 years of experience in press and plant engineering. With our presses, plane parallelism of up to 0.025 mm/m is possible, so the upper and lower dies close exactly."
Production of ballistic plates takes one to two hours
To produce ballistic sheets, blanks of up to 60 layers of fibers are impregnated with a special plastic and loaded into the press. Its temperature control system heats them in the mold first to 40 ºC and then, in a second step, to 160 ºC. The plastic melts during this process. This melts the plastic, and the press presses the blank into the desired shape under pressure. It then cools back down to 40 ºC in the mold. It is then removed and cooled to room temperature.
This cycle takes between one and two hours. After that, the 1,600 x 2,500 mm ballistic plates only have to be cut to the required size.