Roller Drill Bits

In August 1908, Howard R. Hughes, an American, patented the first tine bit. The initial idea was to transform the rotary motion of the drill column into the impact and crushing action of the teeth on the bottom of the well, so that the rotary drill could also achieve the breaking up of hard strata in a similar way to the tonnage drill. Subsequently, the two-tooth wheel bit and three-tooth wheel bit were invented successively. Since the three-tooth wheel bit has greater advantages than the other tooth wheel bits, it is still in use since its invention until now, therefore, it is mainly introduced here with the three-tooth wheel bit. First, the structure and working principle of the tooth wheel drill bit 1.Structure of the tooth wheel drill bit 1) the overall structure of the tooth wheel drill bit is composed of the shell, tooth claw, tooth wheel, bearings, water eyes and oil storage sealing compensation system and other parts.

The upper part of the casing is threaded to connect with the drilling column. The lower part of the shell is welded with a tooth claw (also known as palm), the tooth claw with a tooth wheel shaft, the tooth wheel is mounted on the tooth wheel shaft, the tooth wheel with teeth, used to break the rock. Between the tooth wheel and tooth wheel shaft is equipped with bearings to lock the tooth wheel and bear the load. The water eye (also known as the nozzle) is the channel for the drilling fluid. The reservoir seal compensation system is used to store and replenish grease into the bearing cavity to prevent drilling fluid from entering the bearing cavity and to prevent grease leakage.

(1) Toothed wheel. The tooth wheel is a cone made of alloy steel by die forging, with teeth milled on the taper of the tooth wheel (called a milled tooth bit) or set with carbide teeth (called a set-tooth bit), and with bearing runway shoulders inside the tooth wheel. Dental wheel taper with two or more kinds of taper, single cone dental wheel by the main cone and back cone; compound cone dental wheel by the main cone, vice cone and back cone, some have two vice cone.

(2) Tooth. At present, the domestic and foreign production of the tooth wheel drill according to the tooth material is divided into milled teeth (also known as steel teeth) and set teeth (also known as tungsten carbide teeth) two categories. The teeth of milled tooth wheel drill are milled and processed from the tooth wheel blank, mainly wedge-shaped teeth.

In order to improve the wear resistance of the teeth, in the teeth of the surface of a layer of tungsten carbide welding powder; in order to prevent the drill bit drilling when the drill bit diameter is overly small, the outer row of teeth required to be made into a L-type T-type or mouth type.

In order to trim the well wall and prevent the back cone from wearing out, tungsten carbide powder is surfaced on the back cone of the tooth wheel or flat-top shaped teeth are mounted. Inlaid teeth dental wheel cobalt head is drilled holes in the taper of the dental wheel, after the teeth made of carbide material set into the holes. There are roughly six shapes of tungsten carbide teeth.

(3) The bearing structure of the tooth wheel drill bit consists of the inner cavity of the tooth wheel, the bearing raceway, the tooth palm journal, and the locking element. There are four bearing subs: large, medium, small and thrust bearing. According to the sealing or not of the bearing vice, it is divided into two categories: sealed and non-sealed. According to the structure of the bearing sub, divided into two categories of rolling bearings and plain bearings.

(4) Drill bit water eye The drill bit water eye is the channel through which the drilling fluid flows out of the drill bit and shoots to the bottom of the well. In the drilling process, in order to make full use of the water power of the drill bit, so that the high-speed liquid directly to the bottom of the well, in order to fully remove the rock debris at the bottom of the well, to improve the drilling efficiency, this drilling technology is called jet drilling, suitable for jet drilling needs of the drilling bit is called the jet bit. Jet drill bits are equipped with removable and reusable carbide nozzles at the waterhole.

(5) Oil lubrication sealing systemThe oil lubrication sealing system of the tooth wheel drill bit can effectively prevent the drilling fluid from entering into the bearings of the drill bit, and ensure that the bearings are lubricated, which greatly improves the service life of the bearings.

Working Principle of Toothed Wheel Drill Bit

1. Rotation and rotation of teethWhen the tooth wheel drill bit is working, the teeth fixed on the tooth wheel rotate clockwise around the drill bit axis together with the drill bit, which is called rotation; and the teeth rotate anti-clockwise around the tooth wheel axis, which is called rotation. The rotation speed of the tooth wheel is related to the rotation speed of the drill bit and the role of the teeth on the bottom of the well, and the rotation of the tooth wheel is the result of the interaction force between the teeth and the ground rock when breaking the rock.

2. The longitudinal vibration of the drill bit and the impact on the formation, the crushing effect of the drill bit work, the drilling pressure through the teeth on the rock, the tooth wheel rolling so that the teeth and the bottom of the contact is a single tooth, double-tooth staggered, single-tooth contact with the bottom of the well, the centre of the wheel is in the highest position; double-tooth contact with the bottom of the well, the centre of the wheel down. The rolling of the tooth wheel makes the centre of the tooth wheel exchange up and down constantly, so that the drill bit does up and down reciprocating motion along the axis, i.e. the longitudinal vibration of the drill bit. The longitudinal vibration of the drill bit at the bottom of the well makes the drill column continuously compressed and stretched, generating an impact load, which is transformed into an impact force on the formation through the teeth of the drill bit to break the rock, and the static load indentation force generated by the drilling pressure forms the impact and crushing effect of the drill bit on the formation rock, which is the main way to break the rock by the tine wheel drill bit. Although the impact load is favourable to rock crushing, it will cause premature damage to the drill bit bearing and make the teeth, especially the carbide teeth, crumble.

3. The shearing effect of teeth on strata In addition to the impact and crushing effect on strata rock, the tooth wheel drill bit also produces shearing effect on strata rock. Shear effect is mainly through the tooth wheel rolling in the bottom of the well also produces teeth on the bottom of the well sliding to achieve the reason for sliding is caused by the drill bit over the top of the compound cone and shift the axis of the three structural features. The sliding caused by overtopping and compound cone can not only break the rock in the tangential direction together with impact and crushing, but also shear off the rock between the crushing pits of neighbouring teeth in the same tooth circle. In addition to axial sliding and cutting stratigraphy, the axial shift can also shear off the rock between the teeth. Although the sliding of the teeth can shear the rock at the bottom of the well to improve the crushing efficiency, but accordingly, the teeth damage is aggravated. The axial sliding caused by shifting the shaft makes the inner face of the tooth partially worn, while the tangential sliding caused by over-topping and re-cone makes the side of the tooth worn.

4. Self-cleaning tooth wheel drill bit When the tooth wheel drill bit is working, especially when drilling in soft stratum, it is easy to accumulate rock chips between the teeth to produce mud packs, which affects the drilling effect. Self-cleaning drill bit through the tooth wheel arrangement so that the teeth of each tooth wheel meshes with each other, a tooth wheel of the teeth of the rock debris accumulated between the teeth of the other tooth wheel by the teeth of another tooth wheel to remove, this way is called the self-cleaning of the tooth wheel drill bit. The tooth wheel arrangement of self-cleaning tooth wheel drill bit is divided into self-cleaning without shifting shaft and self-cleaning shifting shaft two kinds of programmes.

Second, the manufacture and rational use of the tooth wheel drill bit 1.Manufacture of the tooth wheel drill bit 1)Material and performance of parts

(1) Toothed wheel and claw. According to the special situation of the tooth wheel drill bit working downhole, the material is required to have high strength, impact toughness, wear-resistant, corrosion-resistant and other comprehensive mechanical properties, milling teeth and tooth-set drill bit commonly used materials are: 20CriMo, 15Ni3Mo, 20Ni4Mo and so on.

(2) Carbide teeth. Cemented carbide is a kind of powder metallurgy products, which is made of tungsten carbide powder, titanium carbide powder and cobalt powder pressed and moulded according to different proportions and requirements, and sintered at high temperature to become a mechanical mixture, which is characterized by high hardness, high wear resistance and so on. The tungsten carbide teeth of the tooth wheel drill bit generally adopt _yG8, _yG11, _yG13 and other models, which also need to be processed by grinding machine to improve their surface finish and dimensional accuracy when assembled to the tooth wheel.

(3) Balls. Bearing in the ball is generally used 55SiMoV and 55SiMoA two kinds, crushing the destructive load is not less than ^20x104N, tempering hardness is HRC55~58.

(4) Seal ring. In addition to wear-resistant, corrosion-resistant, oil-proof sealing ring, the rubber hardness of Shore degree between 78~82 tearing strength is greater than 20MPa, the surface is smooth without scars, no internal slag and defects.

(5) Bushing. Requirements for the material _Cr17, carburising, quenching, tempering hardness of HRC59 ~ 62.

(6) Pressure compensation membrane. Its rubber hardness Shore degree is 63~67, tearing strength is more than 18MPa, bonding strength with metal is more than 4MPa, and the surface is smooth without scars.

Before assembling and assembling, each part of the drill needs to be repeatedly cleaned and divided, paired, and then sent in pairs to the assembly line.

(1) Installation of the three-valve tooth claw to make the drill bit into a whole. When assembling the drill bit, use the locating pins on the three-flap jaws to combine the three flaps into a whole, and then use the clamp to clamp and roughly measure the outside diameter to ensure that the outside diameter of the drill bit is within the permissible tolerance.

(2) Welding. Welding time is interrupted, three times welded. Pay attention to the tip of the tooth claw and plug pin at the welding temperature should be controlled below 80 ℃ so as not to affect the life of the sealing pike rubber parts.

(3) Clear the weld and residual spatter slag. The purpose of removing the weld is to check the quality of the weld, do not allow the weld to have cracks, fusion, porosity and other defects.

(4) Turn tapered threads. In the die or imitation lathe will be connected to the drill bit taper thread according to the regular thread processing out, pay attention to the taper thread centre line and the drill bit centre line of the coaxiality and the drill bit centre line and the three tooth wheel in a horizontal plane of perpendicularity.

(5) Test pressure. After drilling the connection cone thread processing, install the nozzle test pressure. After pressurising with water to 50~60MPa, keep it for 1min without leakage as qualified.

(6) Oil injection. Vacuum quantitative oil injection, oil storage and compensation device installed after the vacuum, the required vacuum degree of 0.2 gross, oil injection pressure of 2.5-3.0MPa, quantitative injection after blocking the oil hole. So that the drill is assembled, the overall inspection.