You selected the right AGMA Class gearbox . You calculated the belt tension perfectly. But the moment you hit "Start," the belt snaps or the gearbox makes a terrifying clunk. The culprit is likely your Starting Method . In conveyor systems, the starting torque profile matters more than steady-state power. Note: We previously discussed VFDs as Energy Savers for pumps and fans. For conveyors, however, the goal is not lowering your electric bill—it is preventing your gearbox from exploding. Table of Contents 1. The Physics of Shock Loads 2. Why Soft Starters Stall Conveyors 3. The VFD Torque Advantage 4. Comparison: Cost vs. Protection 5. Final Verdict Advertisement 1. The Physics of Shock Loads When an AC induction motor starts Direct-On-Line (DOL), it draws 600% to 800% of its rated current (Inrush Current). More importantly, it produces a sudden spike known as Locked-Rotor Torqu...
Figure 1: Surface hardening creates a wear-resistant "case" while preserving a ductile "core" to absorb impact.
Many engineering applications require high surface hardness to resist wear, while complex service conditions demand adequate core strength and toughness to withstand impact and cyclic loading.
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To obtain this combination of properties, two general approaches are commonly used:
- Method 1: Chemical Modification. Diffusing elements into the surface (Carburizing, Nitriding, Cyaniding).
- Method 2: Localized Heating. Hardening only the surface via rapid heating/quenching (Flame, Induction).
1. Carburizing: The Industry Standard
Carburizing is a thermochemical process where carbon is diffused into the surface of low-carbon steel (typically <0.30% C) by heating it in a carbon-rich environment. The result is a high-carbon surface that becomes hard after quenching, while the core remains tough.
Figure 2: Gas carburizing allows precise control over carbon potential and case depth.
The Three Common Methods:
- Gas Carburizing: Uses a controlled atmosphere (methane/propane). Most common for mass production.
- Liquid Carburizing: Uses molten cyanide salts. Fast, but involves hazardous chemicals.
- Pack Carburizing: Parts are sealed in a box with charcoal. Slower, but requires less equipment.
2. Nitriding: Distortion Control
Nitriding heats steel (900°F – 1150°F) in an ammonia atmosphere. Unlike carburizing, it does not require quenching to harden.
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Engineering Advantage:
Because no quenching is involved, Nitriding produces minimal distortion. Parts can often be machined to final dimensions before treatment.
Because no quenching is involved, Nitriding produces minimal distortion. Parts can often be machined to final dimensions before treatment.
3. Cyaniding & Carbonitriding
Cyaniding heats parts in molten salt to diffuse both carbon and nitrogen. It produces a thin, hard case ideal for screws and nuts.
Carbonitriding is similar but uses a gaseous atmosphere (ammonia + hydrocarbons). It is often preferred over cyaniding because it avoids liquid cyanide waste disposal issues.
4. Flame & Induction Hardening
These methods do not change chemical composition. Instead, they use intense localized heat to austenitize just the surface layer before quenching.
Figure 3: Induction hardening offers rapid, repeatable hardening for shafts and gears.
- Flame Hardening: Uses oxy-fuel torches. Good for large, irregular parts (e.g., large gears, lathe ways).
- Induction Hardening: Uses high-frequency electric coils. Excellent for automation and high-volume shafts. Precise depth control is achieved by adjusting frequency.
Source: Adapted from Google Books & Engineering Standards.
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