Torque surface

Torque = surface area of rotating body x radius of rotating body x shear stress... 

Between the bit and the surface, where the torque is generated, we find the drill string (Fig. 3.9). While being mainly a means for power transmission, the drill string fulfils several other functions, and if we move up from the bit we can see what those are. 

Figure 5,16. It is assumed that by using an exactly symmetric cone a shear rate distribution, which is very nearly uniform, within the equilibrium (i.e. steady state) flow held can be generated (Tanner, 1985). Therefore in this type of viscometry the applied torque required for the steady rotation of the cone is related to the uniform shearing stress on its surface by a simplihed theoretical equation given as...

The stress field corresponding to this regime is shown in Figure 6.18. As this figure shows the measuring surface of the cone is affected by these secondary stresses and hence not all of the measured torque is spent on generation of the primary (i.e, viscometric) flow in the circumferential direction. 

For dry traction more contact is desired and the stopping distance is directiy related, ie, the more contact area the shorter the stopping distance. A softer, more pHable compound conforms to the road surface topography. Too soft a compound (low mechanical strength) abrades more easily and can therefore acts as a roUer and not allow sufficient contact area to be maintained. This is not readily encountered in nominal tires and conditions but has been encountered in cases of extremely high torque conditions for very fast acceleration and sudden stops. 

The use of wind as a renewable energy source involves the conversion of power contained in moving air masses to rotating shaft power. These air masses represent the complex circulation of winds near the surface of Earth caused by Earth s rotation and by convective heating from the sun. The actual conversion process utilizes basic aerodynamic forces, ie, lift or drag, to produce a net positive torque on a rotating shaft, resulting in the production of mechanical power, which can then be used directly or converted to electrical power. 

Use a torque wrench to tighten the fasteners to ensure correct surface-to-surface contact of the current-carrying parts (Figure 29.2(c)). The recommended values of bolt torque are given in Table 29.1. A pressure that is too high may eause relaxation of the joint by cold flow and must be avoided. 

Textile motors Crane motors Determining the size of motor Sugar centrifuge motors Motors for deep-well pumps Motors for agricultural application Surface-cooled motors Torque motors or actuator motors Vibration and noise level Service factors Motors for hazardous locations Specification of motors for Zone 0 locations Specification of motors for Zone I locations Motors for Zone 2 locations Motors for mines, collieries and quarries Intrinsically safe circuits, type Ex. f Testing and certifying authorities Additional requirements for ciritical installations Motors for thermal power station auxiliaries Selection of a special-purpose motor... 

The torque that can be transmitted over the length of the hub without slipping, called the holding torque, is a function of the friction and the radial pressure between the hub and shaft, the contact surface area and the radius of the shaft itself. The holding torque, Mh, is given by ... 

Disc friction loss. This loss results from frictional torque on the back surface of the rotor as seen in Figure 6-32. This loss is the same for a given... 

In a toroidal traction drive, toroidal input and output disks face one another, separated by a number of rollers that contact the toroid surfaces. The rollers are mounted so that they can he tilted to vaiy the radius from the centerline of the disks where they contact the toroids, and therefore determine the input/output speed ratio of the rotating disks. A substantial axial force must be applied to the disks to prevent the rollers from slipping on the disk surfaces. To avoid excessive losses when the torque transmitted is low, this force needs to he modulated in proportion to the torque transmitted. 

A V-belt greatly increases the deliverable torque, since the wedging of the belt in the sheave groove increases the force of contact between the surfaces (N) far above the tension force (P). The driving... 

Unless a measure while drilling instrument is used, there is no way to ascertain whether the turbine motor is operating efficiently since rotation speed and/or torque cannot be measured using normal surface data (i.e., standpipe pressure, weight on bit, etc.). 

Rotary speed of the positive displacement motor is directly proportional to flowrate. Torque is directly proportional to pressure. Thus, normal surface instruments can be used to monitor the operation of the motor downhole. 

As the positive displacement motor is lowered and weight is placed on the motor and thus the bit, the motor speed continues but the differential pressure increases, resulting in an increase in torque and horsepower. As more weight is added to the positive displacement motor and bit, the torque and horsepower will continue to increase with increasing differentiated pressure (i.e., standpipe pressure). The amount of torque and power can be determined by the pressure change at the standpipe at the surface between the unloaded condition and the loaded condition. If too much weight is placed on the motor, the differential pressure limit for the motor will be reached and there will be leakage or a mechanical failure in the motor. 

Planning for a positive displacement motor run and actually drilling with such a motor is easier than with a turbine motor. This is mainly due to the fact that when a positive displacement motor is being operated, the operator can know the operating torque and rotation speed via surface data. The standpipe pressure will yield the pressure drop through the motor, thus the torque. The circulation flowrate will yield the rotational speed. 

Total Pressure Loss. Since bit life is not an issue in a short deviation control motor run operation, it is desirable to operate the positive displacement motor at as high a power level as possible during the run. The motor has a maximum pressure loss with which it can operate. This is 580 psi (see Table 4-114). It will be assumed that the motor will be operated at the 580 psi pressure loss in order to maximize the torque output of the motor. To obtain the highest horsepower for the motor, the highest circulation flowrate possible while operating within the constraints of the surface mud pump should be obtained. To obtain this highest possible, or optimal, circulation flowrate, the total pressure losses for the circulation system must be obtained for various circulation flowrates. These total pressure losses tabulated in the lower row of Table 4-117 represent the surface standpipe pressure when operating at the various circulation flowrates. 

The surface measured torque is 2 kft-lb and the downhole torque is 1 kft-lb. Assuming the heat generated is entirely transferred to the descending mud stream, what is the temperature rise due to the pipe friction ... 

The F, Fj, T, are not known for each element of the drillstring. Average friction factors are calculated for the whole string using the surface measurements of WOB and torque and the downhole measurements of WOB and torque. Consequently, DRAG and FRIC are calculated using the following equations ... 

ATOR = surface torque minus downhole torque W = weight of drillstring in the mud... 

Torsional vibrations are due to the stick-slip effect of the stabilizers in deviated boreholes. They can be seen at surface as large torque oscillations with a period of 3 to 10 s. Figure 4-308 shows a near-bit stabilizer in a deviated borehole. The stick-slip effect increases with WOB and RPM. 

A torque feedback system has been developed to dampen the surface torque oscillations and consequently the stick-slip motion at the bit. The system consists of (see Figure 4-309)... 

Only surface WOB and torque are available. Borehole inclination is 40 . 

Drilling surface data such as weight-on-bit and torque were difficult to interpret because they were loosely related to downhole values. MWD for the first time in the history of drilling gives values of parameters measured at the bit or close by. Rock strength, bit wear, drag and friction can be calculated in real time. Shocks, temperature and pressure can also be measured. 

Lubrication plugs must be clean (to prevent the introduction of contaminants to the lubricant and machine surfaces) before being installed and must be torqued to the manufacturer s specifications. 

Shear stress-strain data can be generated by twisting (applying torque) a material specimen at a specified rate while measuring the angle of twist between the ends of the specimen and the torque load exerted by the specimen on the testing machine. Maximum shear stress at the surface of the specimen can be computed from the measured torque that is the maximum shear strain from the measured angle of twist. 

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