I. Preparation of raw materials
The production of seamless steel tubes begins with high-quality steel billets, usually made of carbon steel, alloy steel or stainless steel. These raw materials are subjected to stringent chemical composition analysis and visual quality checks to ensure that they meet the production requirements. The billets are also truncated and centered for subsequent piercing operations.
II. Heating and piercing
The billets are heated to 1200°C to 1300°C in a heating furnace to soften them for subsequent processing. The heated billet is fed into the piercing machine, and under the action of the rotating head and rolls, the center of the billet gradually forms a hollow tube. The piercing process requires precise control of temperature, speed and pressure to ensure wall thickness uniformity and quality of the burrs.
III. Rolling and Reduction
After piercing, the burr pipe enters the rolling stage, which is mainly divided into two processes:
Hot rolling: the burr pipe is rolled under high temperature in several passes to gradually reduce the outer diameter and wall thickness, forming a steel pipe with a certain size and shape. Hot rolling process not only improves the production efficiency, but also improves the organizational structure and mechanical properties of the material.
Cold Rolling/Cold Drawing: It is carried out at room temperature and further processed by cold rolling mill or cold drawing machine to obtain higher dimensional accuracy and better surface quality. Cold processed steel tubes are usually used in scenarios where high precision is required.
The rolled steel tubes are further reduced to the final size through a size reduction machine to meet customer requirements.
IV. Heat Treatment and Straightening
After rolling, steel pipes need to be heat treated to eliminate internal stress, improve organizational structure and enhance mechanical properties. Commonly used heat treatment methods include annealing, normalizing and quenching. After heat treatment, the steel pipe needs to be straightened to eliminate bending and twisting, and to ensure the straightness and roundness of the steel pipe.
V. Finishing and inspection
After straightening, the steel pipe enters the finishing stage, including cutting head and tail, grinding surface, removing burrs and other processes, in order to improve the appearance quality and dimensional accuracy. Subsequently, the tubes are subject to strict inspection procedures, including non-destructive testing (e.g. ultrasonic flaw detection, eddy current flaw detection), physical and chemical testing (e.g. tensile test, impact test) and dimensional inspection. These inspections ensure that the quality of seamless steel pipes meets the relevant standards and customer requirements.
VI. Storage and shipment
Qualified steel pipes will be labeled, specification arranged and put into storage. Before shipment, final inspection and packaging of the steel pipes are also required to ensure safety during transportation.