The standards and procedures for quality inspection of brake shoes are as follows:

Testing standards

Appearance quality:The surface of the brake shoe should be smooth and flat,without obvious defects such as cracks,sand holes,pores,missing materials,flying edges,burrs,etc.The color of the brake shoes should be uniform and consistent,with no obvious color difference.

Dimensional accuracy:The external dimensions of the brake shoe should meet the requirements of the design drawings,and the dimensional deviation should be within the specified range.For example,the deviation of dimensions such as thickness,width,and length of brake shoes is usually required to be controlled within±1mm or±2mm.

Material properties:For synthetic brake shoes,the raw materials such as resin,fibers,and fillers used should meet the corresponding quality standards,and their composition and properties should meet the specified requirements.For example,the curing performance of resins,the strength and modulus of fibers,the particle size and hardness of fillers,etc.For cast iron brake shoes,their chemical composition should comply with relevant standards,such as the content of carbon,silicon,manganese,phosphorus,sulfur and other elements should be within the specified range to ensure the hardness,strength and wear resistance of the brake shoes.

Physical and mechanical properties:including hardness,compressive strength,compressive modulus,impact strength,friction coefficient,wear rate,etc.For example,the Rockwell hardness of composite brake shoes is usually required to be within a certain range,and the friction coefficient should remain stable under different braking speeds and pressure conditions,and meet the specified numerical range;The wear rate should be lower than a certain indicator to ensure the service life of the brake shoes.

Restriction of harmful substances:The content of harmful substances in brake shoes should comply with relevant standards,such as lead,mercury,cadmium,hexavalent chromium,polybrominated biphenyls and their ethers,etc.The content of harmful substances should not exceed the prescribed limits to protect the environment and human health.

Detection Process

Appearance inspection:Use the naked eye or a magnifying glass or other tools to check whether there are cracks,sand holes,air holes,missing materials,flying edges,burrs and other defects on the surface of the brake shoe,as well as whether the color is uniform,whether the edges of the brake shoe are neat,and whether there is deformation,damage and other conditions.

Dimensional measurement:Use measuring tools such as calipers,micrometers,rulers,etc.to measure key dimensions such as thickness,width,length,and arc radius of the brake shoe,ensuring that the dimensions meet the design requirements and the dimensional deviation is within the specified tolerance range.

Material testing:Chemical analysis,spectral analysis and other methods are used to detect the chemical composition of the brake shoe material,ensuring that it meets relevant standards.For synthetic brake shoes,it is also necessary to check whether the quality and proportion of raw materials such as resin,fiber,and filler are correct.By means of metallographic analysis and other methods,the microstructure of the brake shoe material can be observed to determine whether it is uniform,whether there are defects,and whether the microstructure meets the requirements.

Physical and mechanical performance testing:Use a hardness tester to measure the hardness of the brake shoe;Conduct compression tests using a universal material testing machine to determine the compressive strength and modulus of the brake shoe;Conduct impact testing using an impact testing machine to obtain the impact strength of the brake shoe;Simulate actual braking conditions on the brake test bench and test the friction coefficient and wear rate of brake shoes under different braking speeds,pressures,temperatures,and other conditions.

Hazardous substance detection:Professional detection equipment and methods,such as inductively coupled plasma mass spectrometer(ICP-MS),gas chromatography-mass spectrometer(GC-MS),etc.,are used to detect harmful substances in brake shoes to ensure that their content does not exceed the specified limit.

Comprehensive judgment:Based on the results of appearance inspection,size measurement,material testing,physical and mechanical performance testing,and hazardous substance testing,the quality of the brake shoe is comprehensively judged according to relevant standards and technical requirements.If all indicators meet the standard requirements,the quality of the brake shoe is qualified;If one or more indicators do not meet the requirements,the quality of the brake shoe is unqualified,and the reasons need to be analyzed to take corresponding measures for improvement or scrapping.