1、 Inspection (type inspection report)
The type inspection report is used to inspect whether the sleeves produced by the sleeve manufacturer are qualified under the conditions of specific materials, appearance dimensions and thread parameters. The validity period of the type inspection report is four years. If the materials are inconsistent with the materials in the type inspection report, the type inspection report is invalid, and the corresponding sleeves cannot be regarded as national standard sleeves.
2、 Check whether the raw materials of the sleeve are qualified
Compare the sleeve raw materials provided by the manufacturer according to the sleeve raw material category and steel grade marked in the type inspection report. If they are inconsistent, they shall be regarded as unqualified products.
The sleeve raw materials on the market are generally divided into two categories: No. 45 steel and low carbon steel. No matter which material is used, its annealing test report shall be checked. If these two materials are not annealed, they can meet the requirements of qualified tensile strength. If the purchaser only submits qualified tensile strength for inspection, it will create an opportunity for defective businesses to cut corners. If the 45 # steel is not annealed, the tensile strength can also be submitted for inspection, but it can not meet the deformation index, another important performance index of the joint. The mild steel is not annealed, and the tensile strength is also qualified for inspection. However, once a fire occurs, the sleeve is heated, the stress disappears, and the sleeve tensile strength drops to about 400Mpa, the sleeve will break into two sections, that is, the low carbon steel sleeve has poor fire resistance, and it is difficult to meet the requirements of the building fire rating. Therefore, the inspection of sleeve raw materials is particularly important. As for how to distinguish 45 # steel and low carbon steel, it requires a deep professional knowledge, which will be explained in detail.
3、 Check whether the sleeve size is qualified
Reasonable and sufficient length, outer diameter and inner diameter are the necessary factors for selecting the national standard sleeve. As we all know, the sleeve used for rebar connection will have corresponding size specifications. When most customers buy the sleeve, they just see whether the specifications quoted by the seller conform to the size of their own rebar, which often gives some bad businesses an opportunity to take advantage of. As the price of raw materials increases, the profits of the national standard sleeve will decline, In order to obtain higher profits, many businesses will cheat on the specification and size of the sleeve, cutting corners on materials. The outer diameter of the produced sleeve is less than the minimum value required by the specification. Although it can meet the tension requirements, it reduces the safety factor of the joint, which has structural hidden dangers. At this time, we should understand that the outer diameter of the sleeve should not be less than the minimum value specified in the industry standard, and there should be no negative tolerance. On the contrary, it is unqualified and belongs to non-standard products.
4、 Check sleeve identification
The qualified national standard sleeve shall be marked with the manufacturer's identification and production batch number, and the production batch number shall be consistent with the production batch number marked in the raw material inspection report and the factory tensile strength inspection report. To ensure the true traceability of the product, otherwise it is also a non-standard product.
5、 Check whether the product certification documents are complete, true and effective
As a safety product of engineering structure, the quality certificate document of the sleeve is particularly important, which is the basic basis for the responsibility analysis, accountability and traceability of engineering quality accidents. If the lack of information is not noticed when purchasing the sleeve, it will lead to the failure of the engineering to verify whether the quality of the sleeve used in the project is qualified or not, and the failure of acceptance. In case of any quality accident, it is impossible to analyze the quality accident and hold the sleeve manufacturer accountable. Therefore, it is recommended that when purchasing sleeves, it is better to sign a contract with the client in the sleeve type inspection report to provide more responsibility guarantee; The sleeve manufacturer is required to provide authentic, effective and complete quality certificates. If trading companies, hardware stores, etc. are selected as the suppliers of sleeves, the information provided by them is basically invalid, untrue, and incomplete, which requires careful selection.
