There are four main manufacturing methods for steel fiber used in steel fiber concrete (please refer to Figure 3), the following is the detailed information:
1. Steel wire cutting method
This processing method is relatively simple. Generally, cold-drawn steel wire with a small diameter of 0.4-0.8mm is used as raw material, and the steel wire is cut into short fibers according to the specified length. The tensile strength of steel fiber produced by this method is much higher than that of steel fiber processed by other methods, which can reach 1000-2000MPa.
The processing means can be cutter and punch press. In order to improve efficiency, rotary cutter is often used for cutting. Since cold-drawn steel wire is expensive, the cost of steel fiber produced by this method is relatively high. Another disadvantage of this method of producing steel fiber is that the surface is relatively smooth and the bonding strength with the substrate such as concrete is relatively low. In order to increase the bonding strength between steel fiber and the substrate such as concrete, it is often solved by changing the shape of steel fiber, that is, by producing special-shaped steel fiber. There are three common methods: ⑴ Edge pressing method: Before cutting the steel wire, use the feeding roller of the feed wire to press out the angular pit on the steel wire.
⑵ Waveform method: Before cutting the steel wire, use the feeding roller of the steel wire to press the steel wire into a waveform before cutting it.
⑶ Hook method: Before cutting the steel wire, use the feeding roller of the steel wire to press out the hook shape at equal distances before cutting it.
The steel fiber shown in Figure 1e is called "DRAM Ⅸ" in foreign countries. During production, water-soluble adhesives are often used to bundle and bond them together, thereby reducing the aspect ratio (Figure 1h). After this bundled steel fiber is put into the concrete mixer, the adhesive quickly dissolves in water, and the steel fiber is evenly distributed in the concrete.
2. Thin plate shearing method
The thin plate shearing method is a method of cutting cold-rolled thin steel plates into steel fibers. Before shearing, a special small longitudinal shearing machine is used to cut the thin cold-rolled coil into a strip steel coil. The width of the strip steel coil is the same as the length of the steel fiber. Then the strip steel coil is continuously fed into a rotating tool or a common punching machine for cutting. The axis of the rotating tool is perpendicular to the feeding direction of the thin plate. The raw material is generally annealed cold-rolled steel plate, and unannealed cold-rolled steel plate can also be used to improve strength.
3. Ingot milling method
The raw material used is thick steel plate or ingot, and the steel fiber is cut by a rotating flat-blade iron knife. During cutting, the steel fiber will produce a lot of plastic deformation, and the axis will be twisted, which can increase the bonding force with the matrix such as concrete. If ordinary low-carbon steel is used as the raw material, the curvature of the cut steel fiber is about two and a half times that of the parent material after hardening, becoming a high-strength and high-hardness steel fiber.
4. Molten steel wire drawing method
The scrap steel is melted into 1500-1600℃ molten steel in an electric furnace, and then a high-speed rotating melting wheel is approached to the molten steel on the surface of the molten steel. Many grooves are engraved on the melting wheel according to the requirements of the required steel fiber. When the melting wheel descends to the liquid surface, the molten steel is scraped out by the groove and thrown out by the centrifugal force of the high-speed rotating melting wheel, and is cooled and formed at a speed of 10,000°C/second. Water must be passed through the melting wheel to maintain the cooling speed. The melting method for producing steel fiber is currently the most promising method for producing steel fiber in the world. Its raw materials come from a wide range of sources, and all kinds of scrap steel can be used. Due to the low cost of raw materials, simple manufacturing process and high production efficiency, this type of steel fiber is the cheapest. Since the melting method uses an electric furnace to melt molten steel, it is relatively easy to adjust the chemical composition of the molten steel, thereby producing steel fibers and other metal fibers of various materials. By changing the size of the grooves on the melting wheel, the rotation speed of the melting wheel and the immersion depth, the geometric dimensions of the steel fiber can be changed. This method eliminates the complicated processes of the above three methods from steelmaking to steel rolling, wire drawing (or plate rolling), etc., so that the molten steel is formed in one time and processed into the final product, and its economic effect is very significant. At present, only the United States, the United Kingdom, Japan and China in the world have mastered the production technology of steel fiber production by melting method. The complete set of melt-drawn steel fiber production technology and equipment was officially put into production on July 9, 1997. The various stainless steel fibers, ordinary carbon steel fibers, ultrafine steel fibers, and aluminum fibers produced have been supplied to the market in large quantities.