Hardness is the core mechanical property of materials, which refers to the ability of solid materials to resist elastic deformation, plastic deformation and physical failure, and is a key index for evaluating the processability and safety of materials in machinery manufacturing and material research and development.
Hardness test method
Common methods are divided into static method, dynamic method, and electromagnetic method, among which the static pressing method is the most commonly used, and there are three mainstream methods.
Rockwell hardness test - according to GB/T 230.1, using diamond cone/steel ball indenter, in two steps, measuring the residual depth of indentation, adapting to different hardness materials (such as HRC measuring quenched steel), fast operation.
Brinell hardness test - according to GB/T 231.1, using a cemented carbide ball indenter, measuring the diameter of the indentation mark to calculate the average pressure, the data is stable, but the indentation is large, not suitable for thin plates or high hard materials.
Vickers hardness test - according to GB/T 4340.1, using a 136° diamond tetragonal pyramid indenter to measure the diagonal of the indentation mark to calculate the hardness, the ruler is unified, suitable for the detection of small areas, but the requirements for the finish of the specimen are high.
Hardness measurement transfer system
our country establish hardness benchmarks for all categories such as Rockwell, Brinell and Vickers, and the measurement values are transmitted according to the "national benchmark→ working benchmark→ standard hardness block →working hardness tester" to ensure that the national measurement value is accurate and traceable, and avoid the accumulation of errors.
Installation, use, maintenance and verification of hardness testing machines
Installation: room temperature 10~30°C, humidity ≤65%, away from vibration source; The horizontality error of the equipment is ≤ 1mm/m to ensure the stability of the test force.
Use: Select the pressure head and test force according to the material, load without impact, and the indentation spacing is up to standard to avoid interference with the result.
Maintenance: Regularly clean moving parts, add lubricating oil, protect the indenter, and check the displayed value with standard blocks every month.
Verification: According to the corresponding regulations (such as Rockwell JJG112), once a year for weekly inspection, after repair, it must be verified before it can be used.
Common faults and troubleshooting methods of hardness testing machines
Troubleshooting needs to be combined with equipment principles, core problems and solutions.
Load mechanism failure
Load override - adjust weight quality, leverage ratio or boom length.
Unstable loads - tightening loose parts, grinding/replacing worn edges, cleaning spindles, calibrating the balance thallium position.
Abnormal load holding indication - wipe off the oil stains of the contact plate; Replace damaged bulbs/resistors, repair insulation or connect broken wires.
Faulty loading and buffering systems
Loading shock/abnormal speed - buffer lack of oil refueling, spring replacement; Change the adapted fluid, clean the buffer or change the piston.
buffer rotation - grinding spring end face; If the piston is unstable, it will be exhausted or the working face of the cylinder will be studied.
Transmission and table failure
The lead screw lifting is inflexible - repairing the keyway, straightening the lead screw, and cleaning surface debris.
The worktable does not reset - cleaning the reset lever fulcrum bearing; When the lead screw moves, the lead screw is replaced, and when it is rotated, the key is changed or tightened.
Indicates a fault with the optical system
Abnormal pointer/display value - tighten the pointer or support plate to correct the pointer position; Replace the chipping missing pressure head and remake the unqualified specimen.
Indentation observation problems - scrubbing optical components, adjusting focus/bulb position; The objective lens is corrected for coaxiality with the spindle.
Electrical and auxiliary system failures
abnormal motor/oil pump - replace the reverse power cord; Refill the tank, seal the tubing or clean the oil filter.
Noise of the machine is electrified/reducer - ensure that the body is grounded; Add lubricating oil or adjust the coaxiality of the shaft.
summary
This chapter sorts out the core knowledge of hardness testing machines, clarifies the definition of hardness, mainstream test methods and measurement value transmission system, and refines the requirements for equipment installation, use, maintenance and verification; At the same time, specific troubleshooting plans are provided for common faults of load, loading, transmission and other systems. These contents provide clear guidance for the accuracy of hardness testing, stable operation of equipment, and help control material quality and industrial production accuracy.
