When do I need a torque wrench and which torque wrench is the best?
Location: Wissen an der Sieg - Published on: 15.03.2023 - Author: F. Berger
From our daily conversations with our customers, we regularly hear an uncertainty in the formulation of their initial situation. Most of the time, this results from a lack of experience with bolting in the high (and low) torque range. Furthermore, the market of torque wrenches (also called power wrench, nut runner, torque multipliers, torque gun or high-torque wrench) is versatile and offers some possibilities to buy the right but also the wrong thing. Also, from a financial point of view, hesitation should not be underestimated when it comes to an investment object like a torque wrench. We would like to look at when a classic torque spanner is used and when you should decide for a torque gun.
We would like to provide you with a guide that will help you to eliminate the first uncertainties so that you can start the consultation on an equal footing and answer the questions: "Do I need a torque wrench?" or "What is the best torque wrench?" to find a suitable answer for you.
Picture 1: Torque Wrench
Picture 2: Torque Spanner
Structure and content
The first question is usually, "Do I need a torque wrench?" - When do you need a torque wrench and when do you need a screwdriver? Is both also possible? What are the advantages and disadvantages of the two screwing instruments? In this article we want to get to the bottom of these questions:
Summary
Drehmomentschlüssel | Torque Spanner | Drehmomentschrauber | Torque wrench | ||
|---|---|---|---|---|---|
+ | Kostengünstiger als Drehmomentschrauber | More cost-effective than torque wrenches | + | Kraftanstrengung des Anwenders kann dank elektrischem, pneumatischen oder hydraulischen Antrieb auf ein Minimum reduziert werden | Exertion of the user can be reduced to a minimum thanks to electric, pneumatic or hydraulic drive |
+ | Ggf. geringeres Gewicht bei gleicher/höherer Leistung | Possibly lower weight with the same/higher performance | + | Fest programmierte Drehmomentwerte, bei denen Drehschrauber automatisch abschalten garantieren ein hohes Maß an Prozesssicherheit | Fixed programmed torque values, at which torque wrenches automatically switch off, guarantee a high degree of process reliability |
+ / - | Keine Abstützung für die Erzeugung eines Gegenmoments. Platzeinsparung, aber geringere Sicherheit | No support for generating a counter-torque. Space saving, but lower safety | + | Bessere Schraubfrequenz- und geschwindigkeit dank verschiedenster Antriebsarten. | Better screwing frequency and speed thanks to a wide range of drive types. |
- | Maximales Drehmoment von ca. 3.000 Nm limitiert Anwendungsspielraum | Maximum torque of approx. 3,000 Nm limits scope of application | - | Bei pneumatischen und hydraulischen Drehschraubern zusätzliches Equipment benötigt | Additional equipment required for pneumatic and hydraulic torque wrenches |
- | Ergonomische Konflikte (z.B. Kraftaufbringung in schlechter Körperhaltung) führen zur Gesundheitsgefährdungen des Werkzeugführers | Ergonomic conflicts (excessive weight of the spanner, application of force in poor posture) lead to health hazards for the tool operator | - | Ggf. Schulung notwendig, um Anwender vorzubereiten | Training may be necessary to prepare users. |
- | Ggf. Geschwindigkeitsabnahme/Zeitverlust bei mehreren Verschraubung auf Grund menschlicher Belastungsgrenze | Possible speed reduction/time loss with multiple bolting due to human load limit | - | Teurer als Drehmomentschlüssel | More expensive than torque spanner |
For some applications, there are arguments in favour of using a torque spanner and/or a torque gun. As a rule, the bolting cases have to be assessed individually. Nevertheless, there are certain criteria that can be considered fixed. It is always important to involve all parties in the consultation process: The people who do the work and those who pay the instruments for the work.
Torque spanners are usually inexpensive tools for making a secure and accurate bolted joint. They prove to be a particularly helpful tool for small torques and low tightening frequencies. As soon as the torque and the frequency of tightening increases, the switch to a torque wrench is usually unavoidable. In addition, it offers decisive advantages in ergonomics and work safety.
We have summarised the most important parameters in this article to prepare you as well as possible for your first consultation.
Initial situation: Do I need a torque wrench or torque spanner?
In order to assess this question, we would like to consider and explain the following aspects:
Torque
The torque (in Newton metres) results from the multiplication of a force (in Newton) and a lever arm (in metres). The force in turn results from multiplying a mass (in kilograms) by the acceleration due to gravity (approx. factor 10 for multiplication by weight). What does this mean for us? With this knowledge, we can determine a theoretical limit to the maximum torque values a person can be expected to exert in their daily work. To get a feel for how many kilos they can exert on a lever arm, press down on a standard house scale with both hands. Approximately 100 kg are certainly possible here for a trained person (approx. 1,000 N). But even low forces can quickly become (over)demanding if they have to be applied quickly and several times in succession. If these forces have to be applied overhead or in places that are difficult to access, this increases the risk of accidents.
force (N) x Lever arm (m) = torque (Nm)
Picture 3: Neither a variation of the force nor the lever arm would be possible here due to the limited space without risk of injury.
Screw
Of course, the screw and the type of thread play a role in choosing the right tool. Basically, the required torque increases with the screw size and strength class. This means that as the screw size increases, the consideration of buying a torque gun becomes more important. However, even small screws with low torque (e.g. 100 - 200 Nm) can be screwed better with a torque gun if they are screwed frequently and regularly.
Furthermore, the thread should not be neglected: with some torque spanners it is not possible to screw in left-hand threads (read your operating instructions here). Fine threads usually require higher torques and more frequent cranking due to the pitch of the thread. Both cases are predestined applications for the use of torque guns.
Screw environment
As we explained when looking at the first factor (the torque), the torque is made up of a force and a lever arm. The length of the lever arm must be increased to increase the torque if the force is constant; the calculation is simple: If you have only limited space for the lever arm, then you need more force (note here the possibilities for force application by the person using the tool). If you do not have this force available (for physical reasons or because of the space available), you have to increase the size of the lever arm. Depending on the surrounding components, there are clear dimensional limits.
In addition, please note the risk of damage to surrounding components or persons due to slipping! When using torque spanners, at least two users are recommended and required for large torques (from approx. 1000 Nm). Since the torque spanner does not have its own support, it must be additionally stabilised. This becomes particularly important with allen screws, as the force application here is clearly less favourable than with an external hexagon. When the torque spanner slips, nearby components and the screw can be damaged and people can be injured. Abrupt blows on the lever arm of the torque spanner (e.g. with a hammer for short-term force generation) additionally increase the risk of slipping, destruction of the spanner and the screw.
Picture 4: Cordless torque wrench in tight spaces
Picture 5: Electric torque wrench in tight spaces
Occupational safety and health
The more often you have to carry out tightening with a torque spanner, the more strenuous and tiring it becomes for the person using the tool. Consideration of this aspect increases with increasing torque. If tightening is carried out overhead or on screws that are difficult to reach, an ergonomic application of force by the person using the tool is only possible to a limited extent or not at all. As already discussed in the section on the screwdriving environment, there is also the risk of slipping due to insufficient support possibilities for the torque spanner.
Tighten and/or loosen screws?
Often this aspect is not included in the decision to purchase. The loosening of components without destroying them is a decisive advantage of bolting compared to other types of joining such as welding.
Torque spanners are assembly tools and are not suitable for loosening screws. If you loosen bolts anyway, the calibration values can become misaligned or the torque spanner can be damaged.
Counter torque
A support (also called a reaction arm) is necessary to stabilise the nut runner. This is applied to a suitable component near the screw. It offers the user decisive advantages: The reaction arm favours the vertical placement of the torque screwdriver on the screw. This drastically improves the flow of force and prevents damage to the screw (e.g. abrasion of the inner edges of Allen screws). In addition, the support protects the user from damage caused by slipping of the torque gun. The suitable position of a support is not always given at first go - for this case there are special designs of reaction arms.
A torque spanner does not have such a support. This can be an advantage if there is no space available for any supports. However, for large torques it has significant disadvantages.
If you are unsure about individual critics, please feel free to contact us for a free consultation.
Picture 6: Support of a pneumatic torque wrench
Deciding on a torque wrench - which drive?
Once you have decided on a torque wrench, you have a variety of options: The torque guns are available with battery-powered, electric, pneumatic, hydraulic and mechanical drives. So how do you find the right torque wrench? And which is the best torque wrench? First of all - the one that suits your application! In addition, you can look at the following criteria:
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screw environment
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access to external power sources (electricity, compressed air, oil pressure)
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frequency and frequency of screwing
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time of screwing
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documentation/accuracy requirements
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budget
In the following we look at the different types of drive and define the advantages and disadvantages of the respective devices.
Mechanical torque multiplier
Range of functions
Similar to a torque spanner, the input torque is applied by the force of the person using it via a lever arm. Mechanical torque multipliers are probably the cheapest alternative to a torque spanner. However, thanks to the gear technology, you can achieve the same or higher output torques (i.e. effective torque on the bolt head) with less effort than with a torque spanner. In addition, you have a support to generate the counter-torque to protect the screw and the user. Torques between 100 and 15,000 Nm can be easily handled with JUWEL torque multipliers.
Please note!
Any installation space limitations due to des and the overexertion of the operator must also be taken into account.
Vorteile | Advantages | Nachteile | Disadvantages |
|---|---|---|---|
Kleine sowie große Drehmomente möglich | Small as well as large torques possible | Ermüdung des Anwenders | User tiredness |
Keine externe Antriebsquelle benötigt (wie Strom, Öl oder Pneumatik) | No external drive source required (such as electricity, oil or pneumatics) | Ggf. Platzprobleme zur Bedienung des Hebels zur Einleitung des Drehmoments | If necessary, space problems for operating the lever to initiate the torque |
Kostengünstiger Drehmomentschrauber | Cost-effective torque wrench | Langsamer als alternative Antriebe | Slower than alternative drives |
Electric torque wrench
Range of functions
On the contrary to the mechanical torque wrenches the drive and the generation of the input torque is taken over by an electric motor. This is where decisive advantages arise in terms of speed, ergonomics and consistency. The electric drive also enables you to achieve torques of up to 15,000 Nm. The torque is switched off by firmly defined torque stages. When the target torque is reached, the torque wrench switches off automatically.
Please note!
To assess which electric torque wrench is right for you, ask yourself the following questions:
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Do I have a constant power source? (Note that generator operations may cause complications if there are significant fluctuations in current)
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Do I have the option of making the power source available near the bolting area?
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Are there any complications with a power cable in the bolting environment?
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Do I work outside and am I exposed to the elements (e.g. rain, extreme cold or heat, dust/sand) or in an enclosed space?
Vorteile | Advantages | Nachteile | Disadvantages |
|---|---|---|---|
Wesentlich schneller als mechanische Alternativen | Much faster than mechanical alternatives | Ggf. Platzkonflikte mit dem Stromkabel | Possible space conflicts with the power cable |
Reduzierung der körperlichen Aktivität auf das bloße Halten des Drehschraubers | Reduction of physical activity to just holding the torque wrench | Konstante Stromquelle benötigt | Constant current source required |
Große Drehmoment (bei JUWEL bis 15.000 Nm) möglich | High torque (up to 15,000 Nm with JUWEL) possible | Elektrik witterungsanfällig | Electrics susceptible to weather |
Battery-operated torque wrench
Range of functions
The battery-operated torque wrench offers almost the same advantages as the electric torque gun. Crucially though, you can bolt without a directly connected power source. The drive unit is powered by the battery. This means there is no power cable to get in your way and the risk of damage to the electrical system from power fluctuations is eliminated.
You can charge the batteries in construction site vehicles, for example. In addition, batteries and their capacities are constantly being further developed. The current limits of battery technology clearly represent a snapshot.
Please note!
With all the advantages, there must be a disadvantage, right? Yes the battery powered screwdriver due to the battery technology, they can only be used up to 7,000 Nm according to our recommendation. Of course, you can also get a cordless tool with 10,000 Nm - but the speed decreases as the torque increases. In addition, you must ensure that the batteries are charged regularly. This is particularly important if you are planning extensive screwdriving sessions: It is best to recharge the second battery immediately after changing it!
Vorteile | Nachteile | Advantages | Disadvantages |
|---|---|---|---|
Keine störenden Kabel oder Schläuche in der Schraubumgebung | Maximales Drehmoment nicht so hoch wie bei alternativen Antriebsarten (Grenze bei JUWEL bei ca. 7.000 Nm im Vergleich zur Hydraulik (72.000 Nm)) | No disturbing cables or hoses in the screwing environment | Maximum torque not as high as with alternative drive types (limit at JUWEL at approx. 7,000 Nm compared to hydraulics (72,000 Nm)) |
Absolute Flexibilität dank im Betrieb befindlicher Energiequelle (Antrieb durch Akku) | Akkus m üssen stets nachgeladen werden | Absolute flexibility thanks to energy source in operation (drive by rechargeable battery) | Batteries must always be recharged |
Kleine sowie große Drehmomente möglich | Small as well as large torques possible |
Digital battery-operated torque wrench
Range of functions
In times of Industry 4.0, digitization is also finding its way into the field of bolting. What does that mean specifically? Thanks to digital controls you can:
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Electrically program and document screw connection parameters such as torque, angle of rotation, revolutions and speed
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Provide torque wrenches with fixed programs and protect them with a password. Application errors are kept to a minimum and process reliability is significantly improved
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Control the torque wrench not only on the device itself, but also with the help of a mobile phone or PC/laptop
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Send data fully automatically eg via BUS to a central storage unit or via USB cable
Please note!
Ask carefully whether you need the additional functions. Digital drives are usually more expensive than analog drives with the same performance. Even if the displays and software are usually very user-friendly, displays and control buttons represent an additional source of damage if used incorrectly. The gearbox can still be used without problems, but you are forced to send in the device due to a fault in the control unit. Therefore, in any case, find out about the proper operation and possible training of your colleagues.
Vorteile | Nachteile | Advantages | Disadvantages |
|---|---|---|---|
Verschraubungsparameter (Drehmoment, Drehwinkel, Anzahl der Umdrehungen) genau einstell- und überwachbar | Akkus müssen stets nachgeladen werden | Bolting parameters (torque, angle of rotation, number of revolutions) can be precisely set and monitored | Batteries must always be recharged |
Schraubergebnisse nachhaltig speicherbar (auf dem Gerät, auf PC/Handy oder per BUS-Verfahren auf einer zentralen Steuerungseinheit) | Maximales Drehmoment nicht so hoch wie bei alternativen Antriebsarten (Grenze bei ca. 7.000 Nm im Vergleich zur Hydraulik (72.000 Nm)) | Bolting results can be stored permanently (on the unit, on PC/mobile phone or via BUS procedure on a central control unit) | Maximum torque not as high as with alternative types of drive (limit at approx. 7,000 Nm compared to hydraulics (72,000 Nm)) |
Kleine sowie große Drehmomente möglich | Höhere Kostenaufwand auf Grund digitaler Technologie | Small as well as large torques possible | Higher costs due to digital technology |
Höchstes Maß an Genauigkeit und Prozesssicherheit | Display und Bedienknöpfe anfällig für Schäden / kompletter Gerätedefekt droht bei Beschädigung | Highest level of accuracy and process reliability | Display and control knobs susceptible to damage / complete unit defect threatened if damaged |
Keine störenden Kabel oder Schläuche in der Schraubumgebung | No disturbing cables or hoses in the screwing environment | ||
Absolute Flexibilität dank im Betrieb befindlicher Energiequelle (Antrieb durch Akku) | Absolute flexibility thanks to energy source in operation (drive by rechargeable battery) |
Pneumatic torque wrench
Range of functions
Contrary to electrical/battery-powered nut runners the transmission is not driven by electricity but by pneumatics, ie compressed air. This means that torques of up to 15,000 Nm can be achieved. Thanks to the regulation by the compressed air, the pneumatic nut runner can be regulated very gently - this clearly reduces vibrations and leads to more user-friendliness.
Please note!
A compressor and a compressed air hose are required to generate the compressed air. Similar to operating an electric torque wrench possible space conflicts in the screw environment can occur here.
Vorteile | Advantages | Nachteile | Disadvantages |
|---|---|---|---|
Vibrationsfrei und geräuscharm | Vibration-free and low-noise | Ggf. keine Druckluft verfügbar | Compressed air may not be available |
Sanftes Anfahr- und Abbremsverhalten ermöglicht auch bereits angezogene Schrauben nachzuziehen | Smooth start-up and braking behaviour also allows screws that have already been tightened to be retightened | Ggf. Platzkonflikte mit Druckschlauch | Possible space conflicts with pressure hose |
Konstant vorherrschender Überdruck in Antriebseinheit begünstigt Arbeit in verstaubten Umgebungen | Constantly prevailing overpressure in drive unit favours work in dusty environments | ||
Besonders geeignet für Verschraubungen in Brennstoff-Umgebungen | Particularly suitable for fittings in fuel environments |
Hydraulic torque wrench
Range of functions
When using one hydraulic wrench the input torque is generated using oil pressure. To do this, you need an oil pump (e.g. electric or petrol-driven). Similar to pneumatics, the drive is generated by a compressed fluid. Immense torques are possible with this.
With hydraulic wrenches you have the choice between so-called cassette wrenches and square drive wrenches. For hydraulic wrenches with cassettes, place the device on the screw to be tightened and the cassette, on which the torque acts, encloses the screw head. Square drive wrenches have similar to electric power wrench a square drive. Using a socket (ie a component that has a square at the connection to the drive and a hex at the bottom) you can finally tighten your bolts.
Please note!
To generate the pressure you need hoses and a pump. Similar to the operation of a pneumatic nutrunner, possible space conflicts in the screwdriving environment can occur here. In addition, please note that the oil pressure is approx. 800 bar. Hydraulic wrenches, valves and hoses require regular maintenance to avoid injury to users, damage to components and crushing.
Vorteile | Advantages | Nachteile | Disadvantages |
|---|---|---|---|
Kaum Grenzen bei der Schlüsselweite gesetzt | Hardly any limits set for the width across flats | Energiequelle für den Antrieb der Ölpumpe notwendig (z.B. Benzin oder Strom) | Energy source required to drive the oil pump (e.g. petrol or electricity) |
Hohe Drehmomente bis über 70.000 Nm möglich | High torques up to over 70,000 Nm possible | Pumpe benötigt | Pump needed |
Geeignet für enge Bauraumverhältnisse | Suitable for tight installation spaces | Ggf. Platzkonflikte mit hydraulischen Schläuchen | Possible space conflicts with hydraulic hoses |
Umständlich bei mehreren Verschraubungen, die nicht in einem engen Umkreis liegen | Exhausting several screw connections that are not within a close radius |
The company E. Berger JUWEL-Schraubtechnik has been offering torque wrenches from Wissen an der Sieg for over 40 years. As an expert in the field of bolting technology, we will be happy to advise you on your next application. Based on your requirements, we offer you the suitable torque wrench including any accessories.
This article does not replace personal, technical advice by a trained person. If you are not sure, please arrange a personal meeting in any case.