Torque tools

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Hand-held torque tools

Hand torque tools are precision instruments that measure the tightening torque of bolts. Therefore, they are used to tighten bolts with a specific force, the value of which is optimized for a given type of joint. They are used in industry and mechanical services: vehicles, machinery, etc., as well as in the energy sector.

Types of torque tools

Torque tools can be divided into manual and mechanical tools. The former includes torque wrenches and screwdrivers, while the latter includes electrically or pneumatically driven torque wrenches and screwdrivers. Hand-held torque tools can measure the tightening torque of bolts and then they are called indicating tools, or they can be used only to tighten them to a specific torque, the so-called adjustable tools. Among torque indicating tools there are:

  • wrenches with a twist or bend shank (Class A),

  • rigid body wrenches with graduation or dial indicator or display (class B),

  • keys with rigid body with electronic measurement (class C),

  • screwdrivers with scale or dial indicator or display (class D),

  • screwdrivers with electronic measurement (class E).

On the other hand, adjustable torque tools include:

  • graduated wrenches (Class A),

  • fixed setting wrenches (class B),

  • keys without graduation (class C),

  • slotted screwdrivers (class D),

  • fixed blade screwdrivers (class E),

  • screws without graduation (class F).

Design and principle of operation of hand-held torque tools

Torque tools of the indicating class A are based on an elastic arm or a round bolt which requires a torque to be bent or, in the case of a bolt, twisted. The respective tightening torque values indicated on the scale are assigned to the respective bending or twisting angles. The torque indicating tools of classes B and D work on the torsion bar principle and differ from their class A counterparts in that the torque is measured using a scale or dial indicator or a display. Class C and E indicating tools are complex electronic measuring devices with many additional functions, e.g. torque control, memory for measurements, computer capability, etc.

Adjustable torque wrenches of classes A, B and C work on the principle of a tension lever. When a pre-set torque or higher is applied to them, their arm tensions (actually bends). The tension effect is obtained by means of a special mechanism, with which the value of the tightening torque required can be adjusted. This mechanism is built from two, pressed together by a spring and a screw pendulum arms, between which in a special ratchet there is a small cubic cube. So if we work with the wrench with a tightening torque exceeding the force of pressing the arms against each other, the value of which we have previously set as such a torque, these arms will bend (release) at the point where they are joined by the cube and a characteristic click will be heard. When we release the force, the arms of the wrench tighten, i.e. they return to their previous position. Adjustable torque screwdrivers of grades D, E and F work on a similar principle. They only have a ratchet mechanism, the so-called overload clutch, in which instead of arms there are two torsion elements pressed together by a spring and a screw, connected by a ball placed in a special ratchet. Thus, if we operate the screwdriver with a tightening torque exceeding the force of pressing its torsion elements to each other, the value of which we have previously set as such a torque, these elements will rotate in relation to each other, making a characteristic clicking sound.

Class A adjustable wrenches and class D screwdrivers have a scale that serves to set the tightening torque value. Class C wrenches and Class F screwdrivers, on the other hand, are adjusted on a torque gauge. Class B wrenches and Class E screwdrivers have a fixed tightening torque preset at the factory.

Main technical data of torque hand tools

The technical data that characterizes torque hand tools are: Torque range or torque (Nm), accuracy (%), square drive size or screwdriver bit type and size, overall length (mm), overall weight (g).

Applications for hand-held torque tools

Hand-held torque tools are used for responsible screw assembly. They are therefore used in factories assembling vehicles, aircraft, machinery, various types of equipment (e.g. white goods) and in the power industry, as well as in various types of mechanical services (automotive, aircraft, machinery, railway, etc.) and energy services and in factory departments or maintenance companies. They are manufactured by Bahco, Facom, Gedore, Hazet, Wiha and many others.