Under Crank Shearing Machine

An Under Crank Shearing Machine is a type of industrial machine used for cutting or shearing metal sheets and plates. It's named "under crank" because its crankshaft mechanism, which drives the cutting action, is located beneath the machine's bed. This design offers several advantages and defines its operational characteristics.

Here's a detailed description:

Core Function: The primary function of an under crank shearing machine is to cut large pieces of sheet metal into smaller, desired sizes with clean, straight edges. It operates by a scissor-like action, where a moving upper blade descends past a fixed lower blade to shear the material.

Key Components and Their Function:

• Frame/Body: A robust, rigid steel welded frame that provides stability and support for all other components, ensuring minimal deflection during shearing.

• Blades (Knives): Two sets of high-carbon, high-chromium steel blades are used. The top blade moves in a guided path, while the bottom blade remains stationary. These blades are precisely ground and hardened for sharp, long-lasting cuts.

• Crankshaft Mechanism: This is the heart of the machine. An eccentric crankshaft, located below the bed, converts the rotational motion of the motor into the reciprocating (up and down) motion required for the upper blade.

• Flywheel: Stores kinetic energy and smooths out the power delivery from the motor to the crankshaft, especially during the peak cutting load.

• Clutch: Engages and disengages the power from the motor to the flywheel/crankshaft, allowing for controlled starting and stopping of the shearing action. Can be mechanical (dog clutch) or pneumatic/hydraulic.

• Hold-downs: A series of hydraulic or spring-loaded cylinders located just in front of the blades. They firmly clamp the metal sheet against the machine bed before and during the cut, preventing it from lifting or slipping, which ensures accurate and burr-free cuts.

• Back Gauge: An adjustable stopper located at the rear of the machine bed. It's used to precisely position the metal sheet to achieve the desired cutting width. Can be manual, motorized, or CNC controlled for higher accuracy and automation.

• Motor: Provides the power to drive the crankshaft through a system of pulleys and belts.

• Foot Pedal/Control Panel: Allows the operator to initiate the shearing cycle. Modern machines often have a control panel for setting back gauge positions, stroke length, and other parameters.

• Lubrication System: Essential for reducing friction and wear on moving parts, extending the machine's lifespan.

Working Principle:

1. The metal sheet is fed onto the machine bed and positioned against the back gauge to achieve the desired cut length.

2. The operator activates the machine (usually via a foot pedal).

3. The clutch engages, transferring power from the motor to the flywheel and then to the crankshaft.

4. The eccentric motion of the crankshaft causes the connecting rods to push the upper blade assembly downwards.

5. Simultaneously, the hold-downs descend and firmly clamp the sheet metal.

6. As the upper blade descends past the fixed lower blade, the shearing action occurs, cleanly cutting the metal.

7. After the cut, the crankshaft continues its rotation, lifting the upper blade back to its starting position, and the hold-downs release, allowing the cut piece to be removed.

Advantages of Under Crank Design:

• Compactness: The under-crank design generally leads to a more compact machine footprint as the driving mechanism is housed beneath.

• Lower Center of Gravity: This contributes to greater stability and reduced vibration during operation.

• Ease of Material Handling: The clear working area above the bed often facilitates easier loading and unloading of sheets.

• Cost-Effectiveness: Often more economical than equivalent over-crank or hydraulic shearing machines for certain applications, particularly for thinner to medium gauge materials.

Applications:

Under crank shearing machines are widely used in:

• Sheet metal fabrication shops

• Manufacturing industries (automotive, appliance, HVAC)

• Workshops involved in general metal cutting

• Industries requiring precise cutting of mild steel, stainless steel, aluminum, and other non-ferrous metals.

Maintenance:

Regular maintenance is crucial for optimal performance and longevity. This includes:

• Lubrication of moving parts.

• Checking and adjusting blade clearance (gap between upper and lower blades).

• Sharpening or replacing dull blades.

• Inspecting electrical and mechanical components.

In summary, an Under Crank Shearing Machine is a reliable and essential piece of equipment in metalworking, valued for its efficient and precise cutting capabilities for a wide range of sheet metal applications.