Il metodo di produzione dei tubi senza saldatura è grosso modo suddiviso in metodo di laminazione incrociata (metodo Mennesmann) e metodo di estrusione. Il primo metodo consiste nel perforare prima il tubo con un rullo obliquo e poi estenderlo con un laminatoio. Questo metodo ha una velocità di produzione elevata, ma richiede una maggiore lavorabilità del tubo grezzo ed è adatto principalmente per la produzione di tubi in acciaio al carbonio e bassolegato. Quest'ultimo metodo consiste nel forare il tubo grezzo o il lingotto con una macchina perforatrice, quindi estruderlo in un tubo d'acciaio con un estrusore. Questo metodo è meno efficiente del metodo di laminazione obliqua ed è adatto per la produzione di tubi in acciaio legato ad alta resistenza. Sia il metodo di laminazione obliqua che il metodo di estrusione devono prima riscaldare il tubo grezzo o il lingotto e il tubo d'acciaio prodotto è chiamato tubo laminato a caldo. I tubi d'acciaio prodotti con metodi di lavorazione a caldo possono talvolta essere lavorati a freddo secondo necessità.

TUBO PER PRESSIONE

There are two methods of cold working: one is the cold drawing method, which is to draw the steel pipe through a drawing die to gradually thin and elongate the steel pipe; the other method is the cold rolling method, which is invented by the Mennesmann brothers. The method of hot rolling mill applied in cold working. The cold working of seamless steel pipe can improve the dimensional accuracy and processing finish of the steel pipe, and improve the mechanical properties of the seamless pipe material.

Second, the production method

hot rolling is hot working

Cold drawing is cold working

The main difference: hot rolling is rolling above the recrystallization temperature, and cold rolling is rolling below the recrystallization temperature.

Cold rolling is sometimes heated, but the temperature is relatively low, because work hardening will occur after cold rolling. If the forming requirements of the material are relatively high, annealing is required.

Cold-rolled and hot-rolled are generally sheets or profiles, while cold-drawing is generally a cylindrical section of wire. In addition, hot-rolled sheets are generally steels with high alloy content and high strength, while cold-rolled steels are low-carbon and low-alloy steels. Cold rolling can improve the strength and ensure the surface quality of the materials.

The difference between cold-drawn seamless steel pipe and hot-rolled seamless steel pipe is different from that of plate. Seamless steel pipes are divided into hot-rolled (extruded) seamless steel pipes and cold-drawn (rolled) seamless steel pipes because of their different manufacturing processes. Cold drawn (rolled) tubes are divided into two types: round tubes and special-shaped tubes:

Cold-drawn steel pipes generally need to be drawn several times, and corresponding stress relief annealing should be performed between each drawing to ensure the smooth progress of the next cold drawing.

From the outside, cold-rolled seamless steel pipes are often small in diameter, and hot-rolled seamless steel pipes are often large in diameter. The precision of cold-rolled seamless steel pipe is higher than that of hot-rolled seamless steel pipe, and the price is also higher than that of hot-rolled seamless steel pipe. Cold-drawn seamless pipes generally have a small diameter, mostly below 127mm, especially the accuracy of the outer diameter of cold-drawn seamless pipes is very high, and the length of cold-drawn seamless pipes is generally shorter than that of hot-rolled seamless pipes. In terms of wall thickness, cold-drawn seamless pipes are more uniform than hot-rolled seamless pipes.

3. Performance hot rolling and cold drawing are the difference between production processes. Hot rolling is processed at high temperature and will not change the structural properties of the metal. Cold drawing is to perforate round steel at high temperature, and then cold-draw on a pipe drawing machine. Processing, in the untempered state, can affect the crystal structure of the metal. In general, hot rolling has better mechanical properties than cold rolling. After heat treatment, its tensile strength, yield strength, plasticity and toughness will be improved. In addition, heat treatment can eliminate residual stress, while cold rolling may Due to the uneven deformation of the steel during the processing, residual stress will be generated, and this residual stress has a great influence on the stability.