The security check and requirements of rail fishplate and rail bolt overview

The railway fishplate is an important connection between two rails. It is mostly known with another name - rail joint. Combined with rail bolt, it becomes a system to connect and fasten the two rail tracks. So if the quality of the railway fishplate is poor or the manufacture happens to occur any error, the caused consequence would be unimaginable. To reduce the risk of security, the surface of railway fishplate has a strict requirement during the manufacture.

Firstly, the surface of railway fishplate should be clean and smooth without any defect such as cracks, scarring, scratches and so on. And there are no shrinkage cavity mark or intercalation on the end faces. As for the allowed surface defects and relative geometrical quantity of light/heavy rail, it should be in the range of standard provisions.
Secondly, after rolling process, the railway fish plate should be straight without significant bending or torsion. 

To ensure the fine use of railway accessories, we need to maintain the railway fishplate from time to time in order to improve quality and avoid any accidents.

1.the bolts well fastened and no wounds or cracks on the assembling device of railway fishplate. 
2.No wounds or cracks on each connected rod or out-lock device. No grinding or corrosion on the rod body and abrasion pin hole less than 1mm with good insulation.
3. All iron rods’ connection is with good insulation and the insulation link between out-lock iron and gauge rod are both fine. At uninsulated condition, 3mm gap should be kept and not into other parts. And bolts are fastened well.
4. To ensure no cracks on the shell of the switch machine to assembling railway fish plate, and the installation is firm under good lock condition.
5. To ensure the oil tank circuit in good protection without damage or being buried by ballasts or other debris.

It is difficult to recognize the condition that the common railway bolts are fastened or not only through the surface. Therefore, no twist or fastened twice times can be regular. The maintenance includes exhaustive test and sampling survey.
Firstly, the exhaustive test is the process of using a hammer to knock the railway fish plate one by one. According to the differences of sound, we can find the no twist bolt to twist it again.
Secondly, the sampling survey is the process of checking the fastening axial force meet the standard requirements or not. We check every joint one by one. The number of joint bolts participated in the sampling survey should account for 10% of the total and less than two. After the sampling survey, if the bolts don’t pass the check, we should check it again with the number twice as large as before. If the bolts still don’t pass the check in the second time, some measures will be implemented: To loose twist bolts, we should twist them again with the torque 10% larger than before. As for tight twist bolts, we should replace them all.
The fastening bolt should be in a certain order, because sometimes the common connection plates can be unsmooth. Arbitrary fastening or fastening at one or two ends can produce additional internal force and empty drum on the rubbing surface, thus affect the transfer of friction.

In general, rails are fastened with bolts, but if the chosen of the bolt is improper or the quality is poor, it would lead to the fault. So the quality check of railway bolts is necessary before leaving the factory.
The detection includes human check and machine check. Human check is an original way generally used in our life. In order to reduce the outflow of the defective products, the producers always check packaging or deliver products by means of visual inspection.
Machine check is a full-automation way, it is mainly consist of magnetic particle inspection. Magnetic particle inspection uses the interaction between magnetic flux leakage and magnetic particle of bolts’ defect, aiming at the difference between steel permeability and permeability of defects of bolt such as crack, slag inclusion, mixing material, etc. After magnetization, the magnetic field of discontinuities will be distorted. And magnetic flux leakage occurs on the surface of workpiece which formed part of magnetic flux leak, so as to attract the magnetic particle to form magnetic particle accumulation in the defects--magnetic particle indication. Then in the condition of proper lighting, it can reveal defects’ location and shape. After observation and interpretation on the accumulation of these magnetic particle, the purpose of reducing the outflow of the defective products is realized.