اخبار شرکت How to Grind a Circular Blade with a Damaged Cutting Edge

In industrial slitting (e.g., paper, metal foil, film) and food processing (e.g., meat, pastries), circular knives are prone to cutting edge damage due to contact with hard objects (such as metal impurities, bones), improper operation (e.g., high-speed impact), or long-term use. Common damages include small chipping (depth ≤0.5mm), local notches (depth 0.5-2mm), or uneven edge wear. These damages directly affect slitting results: for example, burrs occur when slitting films, "drag marks" appear when cutting food ingredients, and severe damage can lead to expanded defects due to stress concentration, shortening the tool life. However, most mild to moderate damages do not require immediate tool replacement. Through "phased grinding repair" (rough grinding to fill defects → fine grinding to calibrate the edge angle → polishing to enhance sharpness) combined with suitable tools (especially for high-hardness materials like tungsten carbide), the damaged cutting edge can be restored to usable performance. This article breaks down the grinding method for damaged circular knife edges from three dimensions: "preliminary evaluation and tool preparation," "core grinding steps," and "special notes for tungsten carbide circular knives." The steps are clear and easy to understand, suitable for operators in workshops or industry novices.

The core of pre-grinding is to "clarify the damage degree" (which determines the grinding plan) and "select suitable tools." Tungsten carbide and other cemented carbide circular knives (hardness HRA 88-93) require diamond abrasives, as ordinary grinding wheels cannot grind them effectively and may damage the knife body.

First, observe the damage with "visual inspection + magnifying glass (10-20x)" and classify it by depth and scope to determine whether grinding is suitable (severe damage is recommended to be replaced):

Note: If the damage depth of a tungsten carbide circular knife exceeds 1/3 of the total edge thickness (e.g., edge thickness 3mm, damage ＞1mm), even after grinding repair, the edge is prone to chipping again during use, so direct replacement is recommended.

Tool selection varies greatly by circular knife material—tungsten carbide and other cemented carbides must use diamond tools, while high-speed steel and stainless steel can use ordinary grinding wheels, but with lower efficiency. The following is a general tool list classified by "grinding phase," clearly indicating usage and specifications:

Whether it is mild chipping or moderate notching, the logic of "first repair defects → then calibrate angle → finally enhance sharpness" must be followed. The operation method and precautions vary for each phase, especially the need to control grinding force and angle.

Goal: Grind off the damaged area of the cutting edge, restore the basic continuous shape of the edge, and lay the foundation for fine grinding.

• Operation Method:
  ① Fix the circular knife: Place the circular knife in a fixture with rubber lining, ensuring the center of the knife body is aligned with the spindle of the grinding equipment (deviation ≤0.1mm) to avoid eccentricity during grinding;
  ② Select tools: Use an 80-120 mesh diamond grinding wheel for tungsten carbide circular knives, and an 80-mesh white corundum grinding wheel for high-speed steel circular knives;
  ③ Adjust the angle: According to the original edge angle (measured with an angle gauge, e.g., 15°-25° commonly used for slitting knives), tilt the grinding wheel to the corresponding angle and lightly touch the damaged area;
  ④ Start grinding: Turn on the equipment (rotational speed 2000-2500r/min), turn on water cooling at the same time (the nozzle is aligned with the grinding point, distance 5-8cm), move the grinding wheel slowly, each grinding time ≤10 seconds, and repeat until the damage is completely removed (observe with a magnifying glass, no obvious notches on the edge);
• Key Precautions:
  • Dry grinding is prohibited: Tungsten carbide is prone to softening at high temperatures (>600℃). Dry grinding will cause the grinding wheel to stick to the material and damage the hardness of the knife body;
  • Force control: The contact pressure between the grinding wheel and the edge ≤5N (approximately the force of "lightly pressing a mobile phone screen"). Excessive pressure will cause new chipping;
  • Check progress: Observe with a magnifying glass every 3 grinding times to avoid excessive grinding leading to an overly thin edge.

Goal: Calibrate the edge angle to the original design value (error ≤1°), remove deep scratches left by rough grinding (depth ≤0.01mm), and ensure the edge is flat.

• Operation Method:
  ① Replace tools: For tungsten carbide circular knives, replace with a 400-600 mesh diamond grinding wheel (or 600-mesh diamond grinding disc); for high-speed steel circular knives, replace with a 400-mesh white corundum grinding wheel;
  ② Angle calibration: Attach the cutting edge angle gauge to the edge to confirm the deviation between the current angle and the original design value. If the deviation >1°, fine-tune the grinding wheel angle (adjust 0.5° each time);
  ③ Precision grinding: Reduce the equipment rotational speed to 1500-2000r/min, maintain water cooling, lightly touch the edge with the grinding wheel, and move uniformly along the circumferential direction of the edge (speed 5-10cm/min). After each full-circle grinding, touch the edge with a gloved hand to feel for "burrs";
  ④ Dimensional inspection: If the circular knife has slitting dimensional requirements (e.g., inner diameter, outer diameter), measure with a digital micrometer to ensure the dimension after grinding is within the tolerance range (e.g., ±0.02mm);
• Key Precautions:
  • Grinding disc calibration: When using a diamond grinding disc, first calibrate the flatness of the grinding disc (≤0.005mm), otherwise the edge will be ground askew;
  • Avoid local over-grinding: If there are still scratches on a certain part of the edge, grind that part separately, but the time ≤5 seconds to prevent angle deformation.

Goal: Remove fine grinding scratches, reduce the edge surface roughness to Ra ≤0.05μm, enhance sharpness (e.g., no resistance when slitting films), and reduce adhesion of food ingredients or materials.

• Operation Method:
  ① Prepare tools: Evenly apply 1-3μm diamond polishing paste on a wool polishing wheel (dosage ≤0.1g per square centimeter), or directly use a 1200-1500 mesh diamond polishing wheel;
  ② Adjust parameters: Reduce the equipment rotational speed to 800-1200r/min and turn off water cooling (polishing does not require high temperature, dry polishing is acceptable);
  ③ Gentle polishing: Lightly touch the edge with the polishing wheel and move slowly along the circumferential direction of the edge (speed 3-5cm/min), polish each part for 20-30 seconds, and repeat 2-3 times;
  ④ Effect inspection: Test the sharpness with a tissue—lay the tissue flat, lightly touch the tissue with the circular knife edge. If it can be "cut without resistance" and the cut is flat, the polishing is qualified;
• Key Precautions:
  • Polishing paste dosage: Excessive dosage will cause residual paste on the edge, contaminating materials during subsequent use;
  • Force control: Pressure ≤2N. Excessive force will blunt the edge (the polishing wheel will squeeze the edge instead of grinding).

Tungsten carbide circular knives (containing cobalt/nickel binders) have high hardness but high brittleness. Extra attention should be paid to 3 points during grinding to avoid damage to the knife body:

The hardness of ordinary white corundum and brown corundum grinding wheels (HV 1800-2200) is lower than that of diamond (HV 10000+), although they can grind tungsten carbide (HV 1300-1800), the efficiency is extremely low. Moreover, the "falling of grinding wheel particles" is likely to impact the edge, causing new chipping. Therefore, diamond tools (grinding wheels, grinding discs, polishing paste) must be used throughout the process from rough grinding to polishing.

Tungsten carbide edges are brittle. If the grinding wheel only contacts a single point of the edge (e.g., the edge of a notch) during grinding, local stress concentration will occur, resulting in "corner chipping." The correct approach is:

• During rough grinding, the contact width between the grinding wheel and the edge ≥3mm (covering the damaged area and surrounding areas);
• During fine grinding and polishing, move the tool "uniformly and smoothly" along the circumferential direction of the edge, avoiding pauses or sudden acceleration.

After grinding the tungsten carbide circular knife, observe the edge with a 20x magnifying glass:

• If "microcracks" are found (usually small white lines), it indicates that the temperature was too high or the force was too large during grinding. Such tools cannot be used continuously (prone to fracture during slitting);
• If there are no cracks or burrs on the edge and the angle meets the requirements, perform a test cut (e.g., test the slitting effect with waste film or food ingredients) and put it into production only after confirming it is qualified.

A1: Not recommended. Even for small chips, rough grinding (80-120 mesh) can quickly "level" the damaged area. If fine grinding is performed directly with a fine grinding wheel, it is not only time-consuming (may be 3 times that of rough grinding) but also unable to completely remove the damage marks due to the weak grinding force of the fine grinding wheel, leading to easy wear of the edge during subsequent use.

A2: It is most likely due to edge angle deviation. For example, the original design angle is 20°, but the actual angle after grinding is 18°, and the edge is too thin and prone to "rolling"; or the angle is 22°, and the edge is too thick, causing material extrusion during slitting. Re-calibrate with an angle gauge and fine-tune the angle with a 400-mesh grinding wheel.

A3: There may be 2 reasons: ① The damage depth exceeds 1/3 of the edge thickness, and the edge strength is insufficient after grinding; ② There are still hard objects (such as metal impurities) in the slitting material. It is recommended to install an "impurity filtering device" before the slitting equipment and check the incoming material quality.

Grinding damaged circular knife edges is not a "one-step" operation. Instead, through the phased process of "rough grinding repair → fine grinding calibration → polishing efficiency improvement" combined with "material-adapted" tools (diamond for tungsten carbide, white corundum for high-speed steel), defects can be repaired while ensuring edge strength and sharpness. For practitioners in the tungsten carbide industry, it is also necessary to pay attention to: regularly check the edge status of circular knives (recommended once a week), promptly grind mild damages to avoid expanded defects; if the damage is too severe, do not force grinding, replace the tool in time to avoid safety accidents or material scrap during slitting.

If you need to customize a grinding plan for "specific specifications of tungsten carbide circular knives" (e.g., large-diameter slitting knives, ultra-thin edge circular knives) or want to learn about the selection details of diamond grinding tools, feel free to communicate—we can provide tool parameter tables and on-site operation guidance to help optimize the grinding process and extend the tool service life.