The main substandard hot-rolled ribbed steel bars (commonly known as rebar) on the market today are not qualified by the following factors.
1. The actual size is about one specification smaller than the nominal size, and the dealers make profiteering by buying the actual weight and delivering the theoretical weight to earn the amount of metal.
2. The strength is low.
3, chemical composition failure rate is high. The main reason for this is that small rolling mills are not qualified in terms of raw materials and use clay billets to roll the it.
When buying it, the first thing to do is to look at the size of the it from the outside, using a vernier card gauge to simply measure whether the actual size is smaller than the stated size (generally the rebar is rolled with a specification mark) by about one specification or more (e.g. the standard internal diameter of a 12 rebar is 11.5±0.4mm, while the internal diameter of a shoddy it is mostly about 10mm). Also, some shoddy it is rolled flat to deceive the eye, so that the end face of the bar is observed to be flat and oval, whereas the end face of regular material should be basically round.
Secondly, the surface quality is poor due to the use of adobe, often with defects such as scars and an overall roughness. At the same time, some small rolling mills have a reddish surface colour due to insufficient heating temperature and rolling speed.
Third, most of the regular steel in the factory when the factory large bundles of packaging, bundles of steel are hung with the actual corresponding metal tags, indicating the manufacturer, steel grade, batch number, specifications and inspection code, etc.. As for the shoddy steel bars, most of them are packed in small bundles (about ten bundles) or loose due to the poor production conditions and no large lifting equipment, no metal tags, no quality guarantee.
To avoid buying shoddy rebar at all, it is advisable to go to the direct agent of the brand name manufacturer, especially in the province where the brand name rebar (Minguang rebar from Sansteel) is not only of stable quality, but also easy to deal with even in case of dispute. Experienced people can also distinguish other chemical components by spark.
When buying it, users are advised to go to a regular steel business unit or point of sale, obtain a certificate of steel quality and carry out an inspection. Those with quality doubts can go to a professional inspection agency for quality advice and testing.
General it specifications shall include standard brand (type code), nominal diameter, nominal weight (mass), specified length and allowable deviation of the above indicators.
it series with nominal diameters of 6, 8, 10, 12, 16, 20, 25, 32, 40 and 50mm are recommended in Chinese standards. The supply length is divided into fixed length and double length.
The selection range of fixed length of deformed steel bars exported from China is 6 ~ 12M, and that of deformed steel bars produced in Japan is 3.5 ~ 10m; If there are no requirements specified in the contract, the length of domestic screw thread steel is usually 9m and 12m.
① Surface quality. The surface quality of deformed steel bar is specified in relevant standards. It is required that the end shall be cut straight, and the surface shall be free of cracks, scabs and folds, harmful defects in use, etc.
② Allowable deviation of overall dimension. The requirements for the bending degree of deformed bar and the geometry of reinforcement are specified in relevant standards.
