Description

Flexible shafts provide rotary power transmission along curved or adjustable axes. They are used in a wide variety of remote control, valve actuation, and power transmission applications. 

Types of Flexible Shafts

There are two basic types of flexible shafts:

• Unidirectional shafts rotate in a clockwise or counterclockwise direction as viewed from the motor or drive-end of the shaft. They are used for power transmission along non-linear axes in industrial automation, heavy-duty, and specialized applications such as agricultural equipment, speedometers, dentistry, woodworking, and jewelry tools.
• Bidirectional flexible shafts can be rotated in either direction or reversed. They are well-balanced in both directions and suitable for cyclic applications. Some flexible shafts are corrosion resistant or can withstand environmental contaminants such as dust, fluid, and oil. Others have a casing around the shaft for protection and safety.

Specifications

   
Specifications for flexible shafts include

• Maximum speed
• Torque capacity
• Diameter
• Minimum bend radius
• Length, stiffness
• Torsional deflection
• Axial stretch

 Maximum speed is the maximum, rated rotational speed under load. Units of measure include

• Revolutions per minute (rpm)
• Revolutions per second (rps)
• Revolutions per hour (rph)

Some Important Measurements for selection are:

• Torque capacity is the maximum, continuous torque transmission for which flexible shafts are designed. Torque, the measure of force applied to a member to produce rotation, is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied.
• Shaft diameter includes the shaft casing and helps determine speed and torque requirements.
• Minimum bend radius is measured during shaft operation.
• End-to-end length is measured along the centerline of the shaft. 

Applications and Materials

Materials

Flexible shafts differ in terms of materials and applications. Most products are made of

• Carbon steel
• Stainless steel
• Tempered steel
• Music wire
• Rocket wire
• Bronze alloys
• Copper alloys

Aerospace Applications

The aerospace industry uses flexible shafts in

• Thrust reverser actuation
• Variable bleed valve
• Magazine drive shaft
• Rescue pump
• Scavenger pump
• Flap actuation systems.

Automotive Applications

Automotive applications include

• Automatic pedal adjustment,
• Sliding door adjustments, a
• Power seating tracks

Industrial and Medical

Flexible shafts are also used in industrial power tools and reach rods for valve removal. In the medical field, flexible shafts are used in

• Biopsy probes
• Magnetic resonance imaging (MRI) drug delivery
• Orthopedic instruments
• Eye surgery.

Related Standards

DIN 75532-2 - Transmission of rotary motions; flexible drive shafts

DIN 75532-1 - Transmission of rotary motions; types of connection to gears, intermediate gears, flexible gears, fexible drive shafts and equpment

JIS D 5602 - Flexible shafts for speedometers and tachographs of automobiles

Resources

Image Credits:

Berg W.M., Inc. | CEF Industries, LLC | S.S. White Technologies, Inc.