Mechanical Engineering

This looks like one of the City of Cape Town Plants. Southern Region, maybe Cape Flats or Macassar. Speak to a man by the name of Garth Aspeling. He works in Design and Contracts. He will help you.

This may help you.

Three Proven Methods of Verifying Torque Specifications

Synopsis

Once a torque specification is determined, the joint should be audited to verify the product has been fastened to the specified torque. It is important to audit the joint for accuracy and to ensure your product's quality, safety and...

Details

Once a torque specification is determined, the joint should be audited to verify the product has been fastened to the specified torque. It is important to audit the joint for accuracy and to ensure your product's quality, safety and reliability isn't compromised. The failure of a three-cent fastener that isn't properly tightened can lead to catastrophic or latent failures. Fasteners that are insufficiently torqued can vibrate loose and excessive torque can strip threaded fasteners. It is important for many companies to ensure that proper torque is being applied and maintains gauge requirements associated with the ISO 9001 Quality Standard.

To perform this test, there are three common methods that have been established to provide an accurate reference to the applied torque.

1) First Movement Test - Once the fastener has been tightened, employ the use of torque measuring tool. Mark the tightened fastener and surrounding application. In the tightening direction, begin to slowly apply force to the tool until the first movement in the fastener is noted. The reading recorded is a good indication of the original torque applied to the joint. This is the best way to determine residual torque.

2) Loosening Test - This is a similar process to the first movement test described above, except instead of the tightening the fastener, the torque is applied in the direction that loosens the fastener. At the point the fastener breaks loose, the torque reading is recorded. The torque value to loosen the fastener is the approximate torque that was applied to the joint.

3) Marking Test - Once the fastener tightened, mark clearly the surface of the fastener, nut or bolt and continuing the mark onto the surface being clamped for reference. This time loosen the fastener and retighten until the marks on both application and fastener are aligned. The torque required to return the fastener to its original location is the reference to the original torque applied to the fastener.

What is Residual Torque? It is the amount of tension that remains in a joint after fastening a threaded fastener.

Many users may want to verify residual torque. By checking the torque after assembly, you not only verify adequate torque was delivered to the fastener, but may also detect missed or loose fasteners, or joint relaxation. But since the application is already seated and friction during rundown is different than the friction in a static joint, the torque reading will vary from those in the tool crib and from the dynamic values. These differences will need to be accounted for when engineering a residual torque specification.

The equipment used for these testing methods would be:

Dial Screwdrivers

Dial Wrenches 

Digital Torque Wrenches 

Torque tester with a Rotary Torque Sensor, Torque Screwdriver Sensor or Torque Wrench Sensor to move the fastener.

Hi Patrick, I'll tell you two alternatives.

The one you mention applying a force (to be measured) on a lever of known length (1 meter, for example) is a very effective and direct method, as long as you have the necessary elements at hand. In fact, we do not know if the length of the lever "1m" is adequate or if it will require too much force for the device with which it can be applied.

Another way to "approach the solution" is through theory, since the designer who defined the diameter of the input shaft did so based on the MAXIMUM TORQUE "M" it would handle, and the stress of the MAXIMUM SHEAR STRESS to which he would be willing to submit the material (with a certain degree of security regarding its ALLOWABLE SHEAR STRESS).

These two magnitudes are linked by the POLAR MODULE of the circular section of the axis "Wp":

                         Wp = pi()*d^3/16

If you measure the diameter "d" in centimeters and put it in the formula, you will obtain the polar module Wp in cm^3, and you will be able to apply the formula that relates these three magnitudes:

               M [Kg.cm] = Wp [cm^3] * TAU [Kg/cm^2]

TAU is approx. 0.5 of the elastic limit of the material. For example, if the material is SAE1045 steel, its elastic limit is 5400 Kg/cm^2, with which TAU = 2700 Kg/cm^2. If it is a low carbon steel, such as SAE1020 these values would be reduced to 3500 Kg/cm^2 and TAU = 1750 Kg/cm^2 ... but it is unlikely that a machine shaft would be made with this type low carbon steel.

Example: SAE 1045 steel shaft of 5cm in diameter, will have a "Wp":

                  Wp=3.14*5^3/16=24.5 cm^3

And it will resist, at most, a torque "Mmax":

      Mmax = 24.5cm^3 * 2700 Kg/cm^2 = 66.150 Kg.cm = 661 Kg.m

But, since the designer will have stipulated a minimum safety factor FS of 2 (and it can be 3, 5 or much more if the machine works roughly), then you can conclude that your allowable torrent moment M = Mmax/FS = 330 Kg.m (or less if the FS is higher).

If you had done the test with a one meter lever, you would have had to apply 330 kg to it to obtain that torque!

PS: of course, this theoretical estimation has the uncertainty of the applied FS, from which the effective torque of the machine could be much lower. But IT CONSTITUTES A UPPER Boundary useful for the purpose of estimating the size of the reducer, motor, etc.

There is nothing more precise than "directly measuring" the torque consumed by the machine to move, but... if this is complicated and we do not have the necessary elements, theory can help.

You can use a small manual hydraulic jack, to which you will have to connect a pressure gauge (if it does not have one incorporated) and gently apply force until you detect that the lever starts to move. Perhaps the hardest part is getting grip against the axle without damaging it.

If you have the pressure and the diameter (therefore, the area) of the piston, then you will have the force exerted in Kg and with the length of the lever "L" in cm or meters you will be able to estimate the torque M = F*L

PS: when using a hydraulic jack you will not need a long lever (with 30 cm you may have enough). With any luck, your jack may have a built-in pressure gauge with a scale for direct measurement of "forces" instead of pressures...so even those calculations won't need to be done!

It is important to understand that, in this way, you are applying "in addition to a torque" a vertical force on the shaft that tends to flex it (this is an unwanted effect!).

Therefore, try to apply this simple lever as close as possible to the bearing of the axle in its bearing... instead of applying it at its free end.

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Me pregunto si habré perdido mi tiempo (por enésima vez en GC) respondiendo esta consulta...

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Did you solve the problem? How?

There are many who could benefit from the solution, if you have the courtesy to comment on it. By the way, could you say something about other help that your GC colleagues gave you (it is also an elementary matter of courtesy).

Unfortunately I don't have the right equipment to test required torque specifically I don't a lever arm that I can used to clamp the shaft.

I understand.

But what do you need to define? an electric motor? a reducer?

Because "if there is still any component from the original installation" even if it is damaged, it could give us data on the necessary power and torque. For example, if there is a "mechanical coupling", "any electrical component", or something that was ever used to drive the system, it may help determine the values needed.

PS: From what I see in the first photo, there are some electrical cables that would surely be from the drive motor of the system.

Their capacity can give you an idea (at least an upper bound) of the power that has been handled in the drive.

If you have the wire, then you have the current "I" that it is capable of withstanding. You can use the following formula to find the Power "Pw" of the drive.

Source: Electrotec | CÁLCULO DEL CALIBRE DEL CABLE PARA UN MOTOR TRIFASICO

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