Paper Cutter Blade Testing

Paper cutter blade inspection mainly conducts scientific testing and analysis on the blade hardness testing, cutting edge straightness testing, cutting edge sharpness testing, blade body flatness testing, blade geometric angle testing and wear resistance and coating testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Blade hardness testing: Through the measurement of the Rockwell hardness (HRC) or Vickers hardness (HV) of the cutting edges and different parts of the blade bodies, the uniformity and effectiveness of their heat treatment processes are evaluated. The hardness directly affects the wear resistance and sharpness retention of the blade, and is the core indicator determining the blade service lives. Usually, the cutting edge hardness is required to be between HRC 58-62, to ensure the sufficient sharpness and moderate toughness.

Cutting edge straightness testing: The high-precision marble platforms or laser straightness measuring instruments are used to detect the straightness errors within the full lengths of the blade cutting edges. The unqualified straightness will cause the uneven pressures during the cutting, producing the paper burrs or partial uncut phenomena. For the large paper cutters, the straightness tolerance is usually required to be controlled within ±0.02mm per metre length.

Cutting edge sharpness testing: Evaluated through the professional paper trial cutting method or dedicated sharpness testers. By observing the smoothness and finish of the cut edges when cutting the standard papers of the specific grammage and materials, and whether the paper fuzz and scraps are produced, the sharpness is judged. The sharp cutting edges should produce the clean and non-sticking cut edges.

Blade body flatness testing: The dial indicators or optical flat interferometers are used to detect the flatness of the blade installation reference surfaces. The poor blade body flatness will cause the distortion or stress of the blade after the installation, which not only affects the cutting qualities, but also accelerates the blade wear, and even causes the equipment vibration and noise.

Blade geometric angle testing: The universal protractors or optical projectors are used to precisely measure the blade edge angles (rake angles, clearance angles and wedge angles) and micro morphologies of the cutting edges. The reasonable geometric angles are the key to balancing the sharpness, strength and chip removal abilities. The different cutting materials (such as the paper, leather and cardboards) have the different requirements for the edge angles.

Wear resistance and coating testing: Through the simulated wear testing or the thickness, hardness and adhesion testing of the surface coatings (such as TiN, TiCN and DLC), the durability of the blade is evaluated. The coatings can significantly improve the surface hardnesses and reduce the friction coefficients. The testing of their uniformity and integrity is crucial for predicting the blade lives.

Testing Scope

New blade incoming inspection: The comprehensive first-article and batch sampling testing is carried out on the purchased new blades, ensuring that the key parameters such as their materials, dimensions, hardness and precision meet the purchase technical agreements. It is the first gate of the quality control, aiming to prevent the unqualified products from entering the production links.

In-service blade condition monitoring: Within the normal service cycles of the blades, the on-site fast testing of the cutting edge sharpness, wear amounts and whether the chipping and edge rolling occur is regularly carried out (such as after each cutting of a certain quantity or operation for a certain time). Through the monitoring data, the blade re-sharpening cycles can be scientifically formulated, avoiding the sudden failures.

Post-re-sharpening blade quality verification: After the blades are re-sharpened by the professional equipment, the cutting edge straightness, sharpness, geometric angles and re-sharpening allowances must be re-tested. Ensuring that the re-sharpening processes restore the original performances of the blades, and the excessive re-sharpening does not affect the structural strengths and service lives of the blades.

Targeted testing of the blades of the different materials: For the blades of the different materials such as the high-speed steel (HSS), alloy tool steel, powder metallurgy steel and cemented carbide, the testing emphases and standards are different. For example, the cemented carbide blades need to emphatically test their micro porosity and cutting edge chipping tendencies.

Dedicated blade testing for cutting the specific materials: For the blades used to cut the special materials such as the special papers (containing the mineral fillers), composite materials, self-adhesive labels and leather, the special testing of the cutting edge corrosion resistance, special coating properties and compatibility with the materials needs to be added.

Blade failure analysis testing: For the failed blades with the early wear, chipping or fracture, through the means such as the macro morphology observation, metallographic analysis and fracture scanning electron microscopy (SEM) observation, the failure roots (such as the material defects, improper heat treatment and overload) are traced, providing the basis for the improvements.

Testing Methods

Non-destructive testing methods: Mainly including the magnetic particle flaw detection and ultrasonic flaw detection. The magnetic particle flaw detection is used to detect the defects such as the micro cracks on the surfaces and near the surfaces of the blade; the ultrasonic flaw detection is used to detect whether the internal defects such as the inclusions, blowholes or delamination exist inside the blade, ensuring the structural integrity of the blade.

Dimension and geometric tolerance measurement method: The high-precision outer diameter micrometers and vernier callipers are used to measure the basic dimensions such as the total lengths, widths and thicknesses of the blades; the laser trackers or coordinate measuring machines (CMM) are used for the digital precision measurement of the geometric tolerances of the blades (such as the straightness, flatness and parallelism).

Hardness gradient testing method: On the blade cross-sections, the Vickers hardness (HV) is tested point by point from the cutting edges toward the blade bodies at the fixed spacings, drawing the hardness distribution curves. This method can effectively evaluate the qualities of the heat treatment processes (such as the quenching and tempering), ensuring the reasonable hardness transitions from the cutting edges to the cores.

Micro morphology analysis method: With the help of the stereomicroscopes, metallographic microscopes or scanning electron microscopes (SEM), the micro states of the cutting edge areas are observed, such as whether the cutting edges are smooth, and whether the micro chipping, edge rolling and wear morphologies (abrasive wear and adhesive wear, etc.) exist, providing the micro evidence for the process improvements.

Actual cutting trial method: The tested blade is installed on the paper cutters, and the continuous or interval cutting is carried out on the standard test materials under the specified pressures and speeds. Through the evaluation of the cut edge qualities, equipment operation stability and blade temperature rises, etc., the comprehensive performance is evaluated. It is the most intuitive testing method.

Vibration and noise monitoring method: During the operation of the paper cutters, the vibration analyzers and sound level meters are used to monitor the vibration spectra and noise levels of the blade holders and spindles. The abnormal vibrations and noises are often the signs of the blade imbalance, improper installation or local cutting edge damages, belonging to the online indirect testing means.

Testing Standards

Domestic Standards:

1. GB/T 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

2. GB/T 4340.1-2009, Metallic materials — Vickers hardness test — Part 1: Test method

3. GB/T 1299, Tool and die steels

International Standards:

1. ISO 6508-1, Metallic materials — Rockwell hardness test — Part 1: Test method

2. ISO 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Hardness tester: The Rockwell hardness testers (HRC) and Vickers hardness testers (HV) are the core equipment. The Rockwell hardness testers are fast to operate and suitable for the fast batch testing; the Vickers hardness testers have the small indentations, can be used to measure the thin layer hardnesses and hardness gradients, with the higher precision.

Precision measurement platform and measuring tools: Including the grade 00 marble platforms, lever dial indicators, electronic height gauges and laser straightness measuring instruments, etc. These equipment jointly constitute the reference frames and measurement systems for detecting the geometric tolerances such as the straightness, flatness and parallelism of the blades, requiring the extremely high stability and precision.

Optical testing instruments: The tool microscopes and optical projectors are used to precisely measure the geometric angles and micro dimensions of the blades. For the finer analysis, the metallographic microscopes and scanning electron microscopes (SEM) with the image analysis software need to be used.

Surface roughness tester: Used to measure the surface roughness (Ra values) of the blade edge lands and installation reference surfaces. The excessively large roughness will increase the cutting resistance and friction heat, accelerating the wear; the appropriate roughness is helpful for the adhesion of the lubricating oils.

Dynamic balancing machine: For the long blades used for the high-speed or large paper cutters, the dynamic balancing testing and correction need to be carried out before the installation. Through the dynamic balancing machines, the positions and magnitudes of the mass imbalance are found, and the counterweight adjustment is carried out, to prevent the harmful vibrations during the high-speed rotation.

Dedicated blade testing bench and trial cutting machine: The dedicated testing equipment simulating the actual working conditions. The testing benches can fix the blades and carry out the multiple static parameter measurements; the small trial cutting machines can carry out the controllable cutting trials with the standard papers in the laboratory environments, which is safe and has the strong repeatability.