Measurement system of the tension of tightening of screw: the TRAXX-M2


The TRAXX-M2 is a bolt tension measuring system which tests and manages the tightening of bolted assemblies to a very high degree of precision.

The TRAXX system :

1 – Designed to be used on industrial sites

  • Portable : Weight: 3Kg, Battery life : 5 h
  • Solidity : IP64, shock resistant
  • User-Friendliness : Touch-screen, intuitive interface


2 – Is suitable for many types of screws/bolts

  • Bolt/screws : un-surfaced screws
  • Length: 5 mm to 14 m
  • Diameter : 3mm to 300mm or more


3 – Provides bolt tension measurements with up to 1% accuracy

  •  Measurements are expressed in kN
  • The unit automatically applies a temperature correction to the measurements
  • TRAXX is a non-invasive technique: the measurement modifies neither the condition nor the nature of the assembly


Additionally, the TRAXX-M2 is modular, a number of options are available and specific functions can be developed on demand. The TRAXX-M2’s  software is being constantly developed and is regularly updated.

TRAXX-M2: measurement tool tension tightening of a screw

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When should the TRAXX-M2 unit be used?


1. Control the tension applied to your assemblies

The solidity of a bolted assembly depends on the force holding its component parts together.  This force depends on the tension applied to the screws or bolts which hold it together. The TRAXX-M2 system measures this bolt tension independently to the tool used to tighten the bolts (screw driver, torque wrench or hydraulic tensioner). TRAXX-M2 unit users apply tension in direct relation to the tension measurement reading: while tightening they can monitor the tension applied live on the TRAXX unit display, regardless of which tool they are using.

2 - Guarantee the effectiveness of your seals by applying equal bolt tension to all of the assembled parts

Given that it is the seal that guarantees that an assembly is watertight, the screws or bolts used to maintain the pressure on the seal are as much the guarantee that the seal is watertight as they can be the cause of its failure. Why? If the bolt tension is not distributed evenly over the whole of the seal then the structure’s integrity will be compromised. Seals are sensitive to pressure, the application of an even tension to the parts through using the TRAXX system to guarantee effective tightening, will ensure that the assembly is correctly sealed.


3. Reduce prototype production times

The development of a prototype assembled using torque tightening is generally a process of trial and error. Let’s use a new cylinder head seal design as an example. Its performance will have a very close relation to the tension of the cylinder head bolts. If they are torque tightened, it is difficult to tell what comes from the tightening and what comes from the seal itself. You will need to use a process of trial and error to identify the seal’s performance while statistically eliminating any dispersion caused by tightening.

On the other hand, if you have full control of the bolt tension, you will be able to analyze the performance of the seal without the influence of the dispersions caused by tightening. Being able to monitor and control the tension as it is applied, will allow you to disassociate the two variables: consequently you will have just one variable to analyses instead of two.

4. Optimize the design of your assemblies

In design offices, engineers think in terms of tension (kN) when designing assemblies, whilst assemblers will tighten to torque (N.m) when assembling the parts on the production line. This difference between the design and production procedures generates a barrier between product development and production. To cope with this discontinuity, designers tend to double the safety margins on all of the parts they design and the designated screws or bolts to be used on them.

The consequences of this generate additional costs:

– Over-sized and over-complicated assemblies

– As a result the assembly process is longer and more complicated

– Maintenance and operating costs will be higher.

Managing the bolt tension can reduce these factors and will re-establish continuity between the different departments: this way all of the teams will work with bolt tension.

– During the design process, the TRAXX system provides a way to test  the strength of the assemblies and monitor their properties and mechanical thresholds. In the end this will lead to improved design for the parts to be assembled.

– During assembly, the TRAXX system can be used to check that the tension applied to the parts complies with that prescribed by the design teams.


5. Monitor assemblies over time

In industry these days the maintenance of bolted assemblies generally involves entirely disassembling and then re-assembling the units (as is the case in refineries) or a section of the installation (for the wind turbine industry this represents 20% of bolted assemblies) on a yearly basis. This process is long and repetitive, and let’s be honest, a little outdated.

A second method, re-tightening to torque, involves slightly unscrewing the assembly and then re-tightening it. In this case it is possible that the bolts will be re-tightened to a higher tension than before, potentially leading to a risk of exceeding the bolt’s elastic threshold and its potential plasticization. 

In all cases, maintenance will be noticeably quicker and more effective when a bolt tension measurement unit is used. Why? With the TRAXX method, there is no need to actually unscrew the assemblies. It is a non-invasive procedure which can read the tension force present between two parts by simply placing a sensor on the screw or bolt.

In this way, the TRAXX unit can be used to monitor changes to the tension in the screws over periods of time (1 month, 5 years, 10 years). By comparing the initial tightening data with that measured after a specified period of time (t), for the first servicing for example, it is very easy to observe if the assembly is becoming loose or any other anomalies arise.

In this case, the TRAXX-M2 unit is used as a tool to check, monitor and survey assemblies over long periods of time.

6. Checking the quality of your bolted assemblies by checking the tension force applied by your tightening robots

Your objective is to find out if your screwdrivers apply your pre-defined tightening tension and if this tension remains steady over time.

With TRAXX units you can:

– Statistically check that the torque/angle settings of the screwdrivers are such that the tension force will remain constant.

– Correct the settings as required to guarantee acceptable tightening tension during production.

This was the case for PSA, for example.



7. Assess your tightening problems using controlled disassembly techniques

If you have a suspected tension drop in one or more screws. Before disassembly, simply measure the tightening tension of the screw or screws in question to find out their residual tension. Then compare this tension with the theoretically expected tension to find out if there been a tension drop and by how much if any. From there on you will be able to discover the causes of the tension drop.

TRAXX also proposes a wide range of tightening services :

  • Mounting and tightening an assembly on-site
  • Monitoring the performance of an assembly
  • Tightening consulting and expertise
  • Training in the use of the ultrasound bolt tension measurement method

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