What is torque screwdriver?

A torque screwdriver is a quality control device used in production and manufacturing environments. All torque screwdrivers include a variable torque range, and all have a unique torque limiting clutch that disengages once the preset torque has been reached. This prevents over-tightening which can cause possible damage to components and the final product.
Torque screwdrivers measure torque ranges from 6 inch ounces to 190 inch pounds. Currently, no single tool measures this entire range. Thus, torque screwdriver manufacturers offer tools within segments of this range. Some tools are rated for low torque while others are rated to cover a mid to high torque range.

Clutch Types

Torque screwdrivers also include several clutch types, including “cam-over”, “cushion clutch”, and “auto-shut off”. Most of these clutch styles can be found in electric screwdrivers, air screwdrivers, impulse screwdrivers, manual torque screwdrivers, and cordless torque screwdrivers. Each style includes the ability to preset a specific torque value. In some cases, the necessity may arise to certify the tool in a calibration lab to verify the torque output of that tool and provide an NIST certificate.

Cam Over

A Cam-over clutch is usually found in a manual torque screwdriver where the clutch simply “cams-over”, meaning that it signals the maximum torque has been achieved.

Cushion Clutch

Cushion clutch or “slip clutch” styles are found in both electric screwdrivers and air screwdrivers. This clutch style is similar to the “cam-over” when once the final torque is reached because the clutch continues to cam over and slip. It will continue to run until the operator releases the throttle.

Auto-Shut Off

Auto-shut off clutches are designed for fastening of critical applications. Auto shut off clutches provide precision torque control and reduce energy consumption because, once the maximum torque is reached, the tool automatically turns off.

Components

Torque Limiting Clutch

The clutch is the key component that makes up a torque screwdriver. This is achieved with steel balls rolling between indented plates, compressed by a spring at one end, and the other side driving a screw or fastener. The torque limiting clutch is the part of the tool that limits the amount of torque being applied to the fastener at the receiving end of the tool.

Drive Source

Another key component of torque screwdrivers is the drive source. In a manual torque screwdriver the drive source is the operator’s wrist. There are also a variety of torque screwdrivers powered by electric or pneumatic motor drives.

Manual Torque Screwdriver

The manual torque screwdriver is made in two popular designs: inline and pistol grip. Modern manual torque screwdrivers are ergonomic in design and ever offer a rubber grip for decreased fatigue. A manual torque screwdriver can have a range of 6.0 In Oz to 170.0 In Lb.

Electric Torque Screwdriver

The electric torque screwdriver is commonly found in three different designs: pistol grip, angle and inline. The electric application is the mostly used for industrial assembly applications—such as electronic assembly and small parts assembly. Traditional brushed electric motors and the more efficient brush-less motors are found in electric torque screwdrivers. The torque range for an electric torque screwdriver typically is 0.18 In Lb to 60.0 In Lb, with speeds in excess of 2000 RPM.

Cordless Torque Screwdriver

Another form of electric torque screwdriver is the cordless. The cordless torque screwdriver is powered by 9v, 12v and the modern 14.4v Lithium Ion battery pack. These are great for odd jobs that require mobility and flexibility. Popular designs are pistol grip and angle style.

Pneumatic Torque Screwdriver

The pneumatic torque screwdriver is still widely used for assembly requiring higher levels of torque. They are commonly found in assembly designs like automotive assemblies, aerospace and marine. Pneumatic tools require a pressurized air source that provides a constant supply to be effective. Torque ranges for this type of torque screwdriver 1.5 In Lb to 265.0 In Lb and can reach speeds of 800 to 2600 RPM.

Quoted from: http://en.wikipedia.org/wiki/Torque_screwdriver

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