Pull-out

Most rigs are now fitted with a system whereby the drill string is rotated by a drive mechanism in the mast rather than by the rotary table at rig floor level. Thus 90 foot sections can be drilled before connections need to be made, and the drill string can be rotated while pulling out of the hole in 90 foot sections. This improved system, which speeds up the operation and allows better reaming of the hole is known as top drive. 

Coring is performed in between drilling operations. Once the formation for which a core is required has been identified on the mud log, the drilling assembly is pulled out of hole. For coring operations a special assembly is run on drill pipe (Fig. 5.33) comprising a core bit and a core barrel. 

Substituting p = -ill V, dx = r2dr SinOdO dej), and pulling out constants gives ... 

The beater additive process starts with a very dilute aqueous slurry of fibrous nitrocellulose, kraft process woodpulp, and a stabilizer such as diphenylamine in a felting tank. A solution of resin such as poly(vinyl acetate) is added to the slurry of these components. The next step, felting, involves use of a fine metal screen in the shape of the inner dimensions of the final molded part. The screen is lowered into the slurry. A vacuum is appHed which causes the fibrous materials to be deposited on the form. The form is pulled out after a required thickness of felt is deposited, and the wet, low density felt removed from the form. The felt is then molded in a matched metal mold by the appHcation of heat and pressure which serves to remove moisture, set the resin, and press the fibers into near final shape (180—182). 

Other elastomeric-type fibers iaclude the biconstituents, which usually combine a polyamide or polyester with a segmented polyurethane-based fiber. These two constituents ate melt-extmded simultaneously through the same spinneret hole and may be arranged either side by side or ia an eccentric sheath—cote configuration. As these fibers ate drawn, a differential shrinkage of the two components develops to produce a hehcal fiber configuration with elastic properties. An appHed tensile force pulls out the helix and is resisted by the elastomeric component. Kanebo Ltd. has iatroduced a nylon—spandex sheath—cote biconstituent fiber for hosiery with the trade name Sidetia (6). 

Even when crimp is fiiUy developed it is easy to pull out (low energy) and difficult to translate into noticeably bulkier woven and knitted fabrics. It does however improve the absorbency and the cohesion of the staple (important in spun-yam and nonwoven making) and gives a subtiy different texture... 

Natural Deposits. Natural deposits, eg, minerals and fossil fuels, are located by drilling operations. An auger, eg, a screw or worm, is turned in the earth and pulled out, and material is scraped from the auger for analysis. Alternatively, samples can be taken by hoUow core drills which, when withdrawn, enclose a core of the earth that is representative of the strata through which the drill has passed. Such core samples are used in geological surveys for fossil fuels. As the drill drives deeper into the strata, each core is extracted and placed in a shallow box and coded so that a complete cross section of the geological strata can be reconstmcted. From this, the relative thickness of coal and mineral seams can be directly measured. 

The pullout regime assumes a linearly decreasing constitutive relationship as the crack opens up, and the whiskers pull out of the matrix with increasing ease. One solution (52) for frictional pullout alone is... 

Field current is an important control element. It controls not only the power factor but also the pullout torque (the load at which the motor pulls out of synchronism). For example, field forcing can prevent pullout on anticipated high transient loads or voltage dips. Loads with known high transient torques are driven freqiiently with 80 percent power-factor synchronous motors. The needed additional field supplies both additional pullout torque and power-factor correc tion for the power system. When high pullout torque is required, the leading power-factor machine is often less expensive than a unity-power-factor motor with the same torque capabihty. 

Reduced-Voltage Starting Reduced-voltage starting is used to reduce system voltage dip. Voltage dips must be limited otherwise, they may drop other motors off the line, cause synchronous motors on the system to pull out of step, or cause objectionable lamp flicker. 

To ensure that the motor does not stall or lock-up during pick-up under such a condition, it should have an adequately high pull-out torque (Tpo). 

Judicious electrical design will ensure a pull-out torque slip as close to the full-load slip as possible and minimize the additional slip losses in such a condition. See Figure 1.8. A motor with a pull-out torque as close to full load slip as possible would also be able to meet a momentarily enhanced load torque during a contingency without any injurious heat or a stalling condition. 

The maximum value of the output and torque of the motor can be obtained by dropping perpendiculars CC and CC3 on the output and torque lines respectively from the centre C.CjCi and C C4 indicate the magnitude of the maximum output and torque, respectively, that the motor can develop. This torque is the pull-out torque Tpp. In slip-ring motors it can be obtained at any speed on the normal speed-torque curve by inserting a suitable resistance into the rotor circuit to vary the slip. 

Pull-out or breakdown torque (maximum torque) Rated torque... 

The nearest standard rating to this is 7.5 kW, and a motor of this rating will suit the duty cycle. To ensure that it can also meet the torque requirement of 10.5 kW, it should have a minimum pull-out torque of 10.5/7.5 or 140% with the slip at this point as low as possible so that when operating at 140%... 

These are required to make threads, i.e. the final drawing, twisting and winding of cotton. Such motors must possess very smooth acceleration to eliminate breakage of threads. They are recommended to have a starting torque of 150-200% of T, and a pull-out torque of 200-275% of with a mean acceleration torque ol 150-175%. A normal acceleration time of 5-10 seconds is recommended. Faster acceleration may cause more breakages, while a slower acceleration may result in snarls and knots in the yarn as a result of insufficient tension. 

For all the applications discussed above, which may require special starting and/or pull-out torques or speed variations, the use of static drives is more appropriate today. With the use of this technology, a standard motor can be made to perform any required duty, except the constructional features and the applicable deratings as discussed in Chapter 1. See also Example 7.1. 

The minimum value of pull-out torque at the rated voltage should be 150% of the rated torque according to IS 9283. 

With the s inie pull-out torque as above, if we select a slip-ring motor and arrange the starter to develop an average pick-up torque of 200%. the avaihible accelerating torque will be (200-68) = 142%... 

A claw-type puller, as shown in Figure 10.2, with adjustable jaws must be used when pulling out the bearing or the pulley from its seat. The claws are so set that they do not bear against the outer ring of the bearing while... 

Torque characteristics, i.e. starting torque, pull-out torque ind pull-in torque, in the entire speed range to ensure that the motor will develop adequate torque at all speeds to meet the load requirement. See Section 2..5 for more details. 

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