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Air tools and air motors are still assumed to be safe for use in explosive environments and in underground mines, but are they really?  How safe is “safe”?

The simple answer is yes, in general air tools are safe for use in hazardous areas, but not always.  Many types of cutting & grinding tools are not safe no matter what type of motor they use – for example grinders.  Other tools like drills, hacksaws, impact wrenches and air motors are widely considered to be safe. The issue is how safe are they really?

ATEX approvals show that motors and tools have been tested and are safe to use in the indicated temperature zones.

Depending on the cutting speed, some drills and air hacksaws are not safe for use in hazardous areas at all.  Also the quality of the motor and it’s components can lead to overheating of the bearings.

Some gases and dusts can explode at very low temperatures, for example carbon disulfide can ignite at 90 degC.

So what temperature does the air tool or air motor run at?

Do all air powered motors run at the same temperature?

Of course of course they don’t.

ATEX approvals were introduced in the EU to certify the safety of equipment that is going to be used in hazardous areas.  All tools and equipment that have ATEX approvals are marked with a code that identifies:

• Which zone the equipment is safe to be used
• What temperature range the tool operates
• If the tool is suitable for operations where explosive gas and/or dust is present
• Whether the tools is safe for underground or general industrial use

ATEX approvals clarify whether or not an air tool or air motor is safe to use in a particular hazardous area thereby avoiding assumptions about safety that can lead to serious injuries or catastrophic explosions.

Our full range of air hacksaws are ATEX approved some for underground, but most for above ground use.

Most of our air motors in the Advanced Line and Basic Line ranges are ATEX approved for use around explosive gases and dusts.

Our Undergound mining impact wrenches are also ATEX approved for use in underground coal mines.

Deprag’s Green Energy Turbine generator can be used in either a direct or an indirect configuration.

Direct Configuration:

Direct use of gas turbine generator for green energy

In a direct configuration a high pressure gas is run through the turbine. Electricity, lower pressure and lower temperature gas is the result.

Some examples include:

• Energy recovery in metal smelters
  

  Turn wasted hot compressed air into electricty

   

  • often molten metal is cooled by compressed air.  The compressed air flows through cooling tubes and is normally exhausted to the atmosphere.  The hot, compressed air can be run through the GET and the recovered electricity can be either used by the smelter or fed back to the grid

• Pressure regulation in gas mains
  

  We can recover wasted energy from reducing the pressure in gas pipelines

   

  • natural gas is transported long distances at high pressure.  When it reaches regional areas, the gas pressure has to be lowered.  The pressure is lowered again when before it reaches homes at a local station.  A GET can be used to recover the energy wasted in the pressure reduction.
  • Note, the gas will cool though the process so, it is necessary to pre-heat it before entering the turbine.

• Carbon sequestration / geothermal
  • Carbon dioxide that is captured from power stations can be compressed and injected into underground reservoirs.  Whilst being stored in the underground caverns the Carbon dioxide is heated by geothermal energy.  The heated carbon dioxide can be expanded through a GET and then re-injected into the reservoir.

Indirect Configuration:

The Green Energy Turbine can be used indirectly, for example as a part of an ORC process to capture waste heat.

In an indirect configuration the GET is used as part of a waste heat recovery system – for example an ORC (organic rankine cycle).  In such a system a refrigerant gas extracts heat from an object or medium which increases the temperature and pressure of the gas.  This pressurised gas is directed through a GET, which turns the turbine and results in lower temperature, lower pressure gas and electricity.

Some examples include:

• Biogas waste heat recovery
  

  Systems already exist for large Biogas producers, however Deprag’s GET helps small producers to recover energy

  • Deprag supplies low power (from 5kW) units to help smaller producers extract electricity from heat that would normally be wasted.

• Recovering heat out of industrial hot water
  • Deprag is supplying the GET to a company who can extract electricity from hot water.  Hot water is produced in various industrial processes, for example large ship engines, geothermal energy, solar energy and the power industry.  The potential for this already proven technology is enormous and game changing in the green energy and energy recovery industries.

Deprag’s Green Energy Turbine generator can be used in either a direct or an indirect configuration.

Direct Configuration:

Direct use of gas turbine generator for green energy

In a direct configuration a high pressure gas is run through the turbine. Electricity, lower pressure and lower temperature gas is the result.

Some examples include:

• Energy recovery in metal smelters
  

  Turn wasted hot compressed air into electricty

  • often molten metal is cooled by compressed air.  The compressed air flows through cooling tubes and is normally exhausted to the atmosphere.  The hot, compressed air can be run through the GET and the recovered electricity can be either used by the smelter or fed back to the grid

• Pressure regulation in gas mains
  

  We can recover wasted energy from reducing the pressure in gas pipelines

  • natural gas is transported long distances at high pressure.  When it reaches regional areas, the gas pressure has to be lowered.  The pressure is lowered again when before it reaches homes at a local station.  A GET can be used to recover the energy wasted in the pressure reduction.
  • Note, the gas will cool though the process so, it is necessary to pre-heat it before entering the turbine.

• Carbon sequestration / geothermal
  • Carbon dioxide that is captured from power stations can be compressed and injected into underground reservoirs.  Whilst being stored in the underground caverns the Carbon dioxide is heated by geothermal energy.  The heated carbon dioxide can be expanded through a GET and then re-injected into the reservoir.

Indirect Configuration:

The Green Energy Turbine can be used indirectly, for example as a part of an ORC process to capture waste heat.

In an indirect configuration the GET is used as part of a waste heat recovery system – for example an ORC (organic rankine cycle).  In such a system a refrigerant gas extracts heat from an object or medium which increases the temperature and pressure of the gas.  This pressurised gas is directed through a GET, which turns the turbine and results in lower temperature, lower pressure gas and electricity.

Some examples include:

• Biogas waste heat recovery
  

  Systems already exist for large Biogas producers, however Deprag’s GET helps small producers to recover energy

  • Deprag supplies low power (from 5kW) units to help smaller producers extract electricity from heat that would normally be wasted.

• Recovering heat out of industrial hot water
  • Deprag is supplying the GET to a company who can extract electricity from hot water.  Hot water is produced in various industrial processes, for example large ship engines, geothermal energy, solar energy and the power industry.  The potential for this already proven technology is enormous and game changing in the green energy and energy recovery industries.

Torque controlled screw tightening has always been the most reliable and easily applied method to produce a quality screw joint.  But is torque control really going to give the perfect assembly every time?

Torque curve based on a friction controlled screw joint

Firstly, what is a perfect screw joint? What do we want to achieve by assembling a screw in a product?

We normally need to join two parts together, but more than that we want to induce tension in the joint so that the parts do not come apart.  Sometimes we also need to seal the parts together to prevent leakage or keep dust and water out.

So the aim for a screw joint is not simply to assemble the screw to a target torque within a set tolerance, but it is to induce a constant clamping or pre-load force.

When we apply torque to a screw joint we can calculate the amount of tension induced in the joint assuming that there is no friction in the joint.  In a low friction assembly (eg machine thread screw into a pre-tapped hole) almost all of the torque will induce tension in the joint.  If you know the pitch of the thread and the torque applied you can then calculate the tension.

Fluctuating screw-in torque influences pre-load force!

What about thread forming and self tapping screws?  We know that a portion of the torque is lost to friction and by doing some analysis we can subtract the friction and figure out the average torque used to clamp the parts.  In most cases this will be enough, but what if the friction is not the same in every assembly?

What if a screw with a thread diameter at the high end of it’s tolerance meets a part with a hole dia that is at the low end of the tolerance?  In this case less torque will be used to clamp the joint and it may not be enough.  At the other end of the spectrum, there could be too much torque which could strip the joint or damage the part.

The solution is Friction Tightening.  The advent of EC and EC servo screwdrivers has paved the way to improving the quality of screw joints.  Today we can assemble the screw, calculate the friction torque and then add the pre-determined tightening torque.  So if the friction torque varies, the actual clamping torque and consequently the clamping force will still be constant on every assembly.

Using the friction torque measurement we cannot use the final torque for statistical analysis anymore.  The final tightening torque is the sum of the friction torque and the clamping torque the final torque accuracy will depend on the quality of the joint and the screws.  We now have to look at the clamping torque only for statistical analysis.

EC screwdriver controller AST40 and friction controlled torque curve

The friction torque method is already well established in the international automotive industry as well as the electronic, mobile technology, household goods and medical industries.

Friction tightening modules are optionally available on Deprag’s Hand Held programmable screwdrivers and machine mountable electric screwdrivers.

For more information or if you would like to discuss an application, please don’t hesitate to contact us.

Fully automated assembly systems not only offer fast assembly, but they also guarantee a higher level of quality control. Unfortunately, professionally designed, reliable automated assembly equipment is expensive and often inflexible. Unless there are very large volumes over a length of time, many automatic assembly automation projects are not viable.

The solution?  Intelligent – Manual – Assembly cells.

Increasingly manufacturers are finding a middle ground between hand assembly and fully automated assembly cells.  Unknown product life cycles, unpredictable demand and sudden downturns means that manufacturers are looking for the most flexible system possible.  With modern screwdriving, screwfeeders and controllers we able to guarantee complete process control, minimize assembly time and provide flexibility at the same time.

A typical Intelligent Manual Assembly Cell will consist of one or more hand guided screwdrivers mounted in a position control stand connected to one or more screw feeders.

• The screwdriver is typically freely programmable and different torques can be called up depending on the part to be assembled and the position of the screwdriver.
• The torque of each screw is monitored and recorded.  If a screw is not assembled to torque or depth the operator will be alerted.
• Screws can be automatically fed to the screwdriver after every assembly. We can even feed and assemble different screws for the one part.
• The torque, angle and assembly time of each screw can be monitored
• Other assembly tasks can be monitored by the controller and additional sensors
• The workstation can be designed for the assembly of numerous different parts

   

  

  Flexible screw assembly with full quality control

Peter Smith, production engineer at a well-known manufacturer of heating control units explained his requirements:

“Our heating control units are available, according to type and size of heating system, in the most varied of designs. With the recent introduction of our new control units we are starting three separate series, our HCU25, HCU50 and HCU100. When launching our new series onto the market we are unable to estimate the expected production amounts accurately. It is also difficult to plan out how the quantities required of each individual version will develop in relation to one other. It is for exactly this reason that we require highly flexible assembly equipment. Ideally production should be able to be simply, reliably and economically adapted to each of the product versions. Additionally for our HCU assembly we have the highest requirements for processing reliability as is usual for electronic components. The sequential order of assembly must be guaranteed and each step must be documented and integrated into our manufacturing execution systems”.

Normally this requirement of a strict sequence and documentation calls for automation.  However in the costs of automation and unknown production numbers excluded automation.

Deprag were able to offer an intelligent manual assembly cell that could be used to assemble all three HCU’s even though they each used different parts, sequence of assembly, different screws and torques.

Using interchangeable adapters, assembly can be easily converted to the various sizes of HCU25, HCU50 and HCU100. Work piece adapters are equipped with integrated sensor technology and communicate with a superior controller.

Furthermore the assembly required ESD safe and technical cleanliness.  The screws were fed with sword feeders instead of vibratory feeders and the assembly and positioning of the screws was done with vacuum pick up and particle killers.

Mr Smith says –

“The collaboration with DEPRAG has been impressive. All our technical requirements were realised with already existing harmonised standard components within the shortest space of time. And what is particularly important for us, all system components come to us from one source.  When we need to increase our production capacity we can flexibly expand our assembly line”.

If you would like to know more, or to discuss your project, please contact us here.