CA1256423A - Rotary drill bits and methods of manufacture thereof - Google Patents
Rotary drill bits and methods of manufacture thereofInfo
- Publication number
- CA1256423A CA1256423A CA000505588A CA505588A CA1256423A CA 1256423 A CA1256423 A CA 1256423A CA 000505588 A CA000505588 A CA 000505588A CA 505588 A CA505588 A CA 505588A CA 1256423 A CA1256423 A CA 1256423A
- Authority
- CA
- Canada
- Prior art keywords
- cast iron
- mould
- bit
- bit body
- iron
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims abstract description 24
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 19
- 229910001018 Cast iron Inorganic materials 0.000 claims abstract description 65
- 239000000654 additive Substances 0.000 claims abstract description 18
- 229910001567 cementite Inorganic materials 0.000 claims abstract description 18
- 230000000996 additive effect Effects 0.000 claims abstract description 17
- 238000001816 cooling Methods 0.000 claims abstract description 11
- 238000007711 solidification Methods 0.000 claims abstract description 11
- 230000008023 solidification Effects 0.000 claims abstract description 11
- 229910052714 tellurium Inorganic materials 0.000 claims abstract description 8
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 claims abstract description 8
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 7
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims abstract description 5
- 229910052796 boron Inorganic materials 0.000 claims abstract description 5
- 238000005520 cutting process Methods 0.000 claims description 25
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 claims description 14
- 238000005553 drilling Methods 0.000 claims description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 6
- 239000012530 fluid Substances 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 239000000463 material Substances 0.000 abstract description 13
- 238000005266 casting Methods 0.000 abstract description 6
- 230000000694 effects Effects 0.000 abstract description 5
- 239000011248 coating agent Substances 0.000 abstract description 4
- 238000000576 coating method Methods 0.000 abstract description 4
- 229910000734 martensite Inorganic materials 0.000 abstract description 3
- 239000011159 matrix material Substances 0.000 description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 6
- 230000003628 erosive effect Effects 0.000 description 6
- 229910002804 graphite Inorganic materials 0.000 description 6
- 239000010439 graphite Substances 0.000 description 6
- UONOETXJSWQNOL-UHFFFAOYSA-N tungsten carbide Chemical compound [W+]#[C-] UONOETXJSWQNOL-UHFFFAOYSA-N 0.000 description 6
- 238000005755 formation reaction Methods 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
- 229910000831 Steel Inorganic materials 0.000 description 3
- 229910003460 diamond Inorganic materials 0.000 description 3
- 239000010432 diamond Substances 0.000 description 3
- 239000010959 steel Substances 0.000 description 3
- 238000005219 brazing Methods 0.000 description 2
- 239000000969 carrier Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000012254 powdered material Substances 0.000 description 2
- 229910001141 Ductile iron Inorganic materials 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 229910001092 metal group alloy Inorganic materials 0.000 description 1
- 238000004663 powder metallurgy Methods 0.000 description 1
- 239000011435 rock Substances 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B10/00—Drill bits
- E21B10/46—Drill bits characterised by wear resisting parts, e.g. diamond inserts
- E21B10/56—Button-type inserts
- E21B10/567—Button-type inserts with preformed cutting elements mounted on a distinct support, e.g. polycrystalline inserts
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D15/00—Casting using a mould or core of which a part significant to the process is of high thermal conductivity, e.g. chill casting; Moulds or accessories specially adapted therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
- B22D27/20—Measures not previously mentioned for influencing the grain structure or texture; Selection of compositions therefor
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B10/00—Drill bits
- E21B10/46—Drill bits characterised by wear resisting parts, e.g. diamond inserts
Landscapes
- Engineering & Computer Science (AREA)
- Geology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Mechanical Engineering (AREA)
- Mining & Mineral Resources (AREA)
- Physics & Mathematics (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Earth Drilling (AREA)
- Heat Treatment Of Articles (AREA)
Abstract
S P E C I F I C A T I O N
"Improvements in or relating to rotary drill bits and methods of manufacture thereof"
ABSTRACT OF THE DISCLOSURE
A method of manufacturing a rotary drill bit at least partly from cast iron comprises forming a hollow mould in the configuration of at least a portion of the bit body, and casting said portion of the bit body in the mould by a casting process which includes the steps of pouring molten cast iron into the mould and then cooling in the mould so that the cast iron solidifies to form said portion of the bit body. The method includes the further step of subjecting the cast iron to treatment, during the casting process, which results in at least one surface portion of the cast iron bit body becoming hardened. The hardening treatment may comprise adding an iron carbide forming additive, such as boron or tellurium, to the cast iron before it is poured, or by chill hardening during solidification, or by coating the interior of the mould, before pouring, with a wash of iron carbide forming material, such as tellurium, or by controlling the rate of cooling after solidification so as to effect the formation of martensite.
"Improvements in or relating to rotary drill bits and methods of manufacture thereof"
ABSTRACT OF THE DISCLOSURE
A method of manufacturing a rotary drill bit at least partly from cast iron comprises forming a hollow mould in the configuration of at least a portion of the bit body, and casting said portion of the bit body in the mould by a casting process which includes the steps of pouring molten cast iron into the mould and then cooling in the mould so that the cast iron solidifies to form said portion of the bit body. The method includes the further step of subjecting the cast iron to treatment, during the casting process, which results in at least one surface portion of the cast iron bit body becoming hardened. The hardening treatment may comprise adding an iron carbide forming additive, such as boron or tellurium, to the cast iron before it is poured, or by chill hardening during solidification, or by coating the interior of the mould, before pouring, with a wash of iron carbide forming material, such as tellurium, or by controlling the rate of cooling after solidification so as to effect the formation of martensite.
Description
The invention relates to rotary drill bits for use in drilling or coring deep holes in subsurface formations. In particular, the invention is applicable to 5 rotary drill bits of the klnd comprising a bit body having an external surface on which are mounted a plurality of cutting elements for cutting or abrading the formation, and an inner passage for supplying drilling fluid to one or more nozzles at the -external surface of the bit. The nozzles are so located at the surface of the bit body that drilling fluid emerging from the nozzles flows past the cutting elements, during drilling, so as to cool and/or clean them.
Although not essential to the present invention, the cutting elements may be in the form of so-called "preform" cutting elements in the shape of a tablet, often circular, having a superhard cutting face formed of polycrystalline diamond or other superhard material.
Conventionally there are two main methods of manufacturing such drill bits. In one common type of drill bit the bit body is machined from steel and the surface of the bit body is formed with sockets which receive pegs or studs on which the cutting elements are mounted. In the second common type of bit the-bit body is formed by a powder metallurgy process in which a hollow mould is first formed, for example from graphite, in the configuration of the bit body. The mould is packed with powdered material such as tungsten carbide, usually around 3~
~2~
-~ -2-a s~eel blank, and the powdered material is then infiltrated with a metal alloy in a furnace so as to form a hard matrix. If the cu~ting elements are of a kind which are not thermally stable at the infiltration -temperature, formers are mounted on the interior surf-ace of the mould so as to define in the finished bit body sockets or other locations where cutting elements may be subsequently mounted.
Steel bodied bits are generally simpler and cheaper to manufacture than matrix bodied bits. However, they are more susceptible to erosion during drilling and, for this reason, they are sometimes provided with a hard surface coating, for example of tungsten carbide, which adds to the complexity and cost of production.
On the other hand, although matrix ~odied bits are more resistant to erosion, their manufacture is complex and costly due largely to the high material cost and to the additional processes involved. Matrix bodied bits also may be made with the matrix at the surface more erosion resistant than that inside the bit body.
The present invention sets out to provide a new method of manufacturing a rotary drill bit using cast iron, in which at least some of the disadvantages of the known steel-bodied and matrix-bodied bits may be overcome.
British Paten~ Specification No. 1,574,884 discloses the use of cast iron in the manufacture of cutting bodies suitable for working or cutting material, such as cutting tips or inserts in rock drilling or chip ~ 3 ~ ~ r,~
forming machines. In such products it is necessary for surface portions of the product to be sufficiently hard to be resistant to erosion and damage during use of the product. Specification No. 1,574,884 describes a method - 5 of providing a hard surface which requires the encasting of a hard metal, such as a sintered hard carbide, e.g.
tungsten carbide, in the cast iron. Such methods have not, however, proved satisfactory in practice due to the high cost of the process and the difficulties of ensuring that the carbide is securely bonded within the cast iron.
~.S. Patent Specification No. 4,499,795 describes the use of cast iron in the manufacture of a rotary drill bit. In this case the inner surface of a mould is packed or coated over selected portions with paiticles of sintered tungsten carbide or similar sintered refractory hard metal and then cast iron is melted and poured into the mould. In this case, also, therefore, the hard surface of the finished bit is provided by tungsten carbide.
The present invention provides methods of manufacturing a rotary drill bit using cast iron where the cast iron itself forms the necessary hardened surface portions of the drill bit, the steps of the method being such as to effect the necessary hardening of the cast iron during the casting process.
According to the invention there is provided a method of manufacturing a rotary drill bit comprising a m~th~ of m~nu~ctur~n~ ~ ro~ry ~rlll ~1 having a bi~ body, ~omp~lgl~g ~he ~tep~ o~:
(a) ~ormln~ a hollow mould ln he ~o~lr~
con~iguration of ~t lea~t ~ ~or~ion o~ th~ blt bo~y5 (b) addlng to ~ ~ir~t body of molt~n ~t ron an lron carblde-~orming Add1tlve;
~ c) pourin~ the ~lrst bo~y o~ molt~n ~t ir~n into the lowermo~t p~rt o~ ~he ~ouldl (d~ coolln~ ~he mould 60 that said ~rst ~ody of cast ~ron ~olld1fl~s and, upon solidificAtlon, ~orm#
maB~ive lnclu~ion~ of cement~te;
~ e) pourin~ a ~econd body of molt~n o~st lron, without ~i~nificant amounts of 6uch lron carb~e-formlng additlve, into the mould on top of th~
~olidif1 ed flrst ~ody oP cast iron; and ~ ) aoolin~ the mould ~o th~t said secon~
~ody of cast iron ~olidifle~.
Said hardening treatment ~ay comprise adding to at least part of the molten cast iron, before it is poured into the mould, an ixon carbide-forming additive, whereby said part of the cast iron, upon solidification, contains massive inclusions of cementite. Said additive may comprise boron or tel1uri~m. Approximately 1/2% of additive may be added t~ the molten cast iron.
If reguired the molten cast iron may be poured int~ the mould in two successive pourings, said additive being added only to the cast iron in ~he first pouring ~o as to harden only the portion of the bit b~dy which is lowermost in the mould.
~ ~.5~ ~ 2~
In an altern~tive methDd according ~o the invention said hardening treatment comprises the ~tep of chill hardening a portion of the surface of ~he bi~ body by accelerated cooling of said surface portion during the solidification part of ~he casting process, said accelerated cooling being at a rate to produce massivP
~nclusions uf cementite in the ~olidified surf~ce p~rtion.
Said chill hardening may be effe~t~d by lDcating a metal heat sink in the mould adjacent said ~urface portion of the bit b~dy which is to be hardened.
There may be mounted on the interiDr of the mould, prior to pouring the cast iron into the mould, formers which project into the mould cavity so as to form sockets in the solidified cast iron bit body, said formers being in close thermal contact with said metal heat sink, whereby ~he interior of each socket i5 chill hardened.
In a further method according to the invention said hardening treatment comprises the step, before pouring the cast iron int~ the mould, of coating at least part of the interior surface of the mould with a material which rea ts with ~he cast iron, during solidification thereof, to form massive inclusions of cementite in at least one surface portion of the bit body. Said coating material may be tellurium.
In a still further method according to the inventi~n said hardening treatment comprises controlling the rate of cooling of the bit b~dy, after solidification `~' ~;~5~
of the cast iron and during ~che ~ubsesluent cooling portion of the casting process, in such manner as to ef f ect the formation of martensite in at least one surace porkion of the bi t ~ody .
~he invention includes within its ~cope a rc~t~Lry ~rlll bl'c comprl~ L b~t bo~y havin~ an external Ecur~ce on which ~Lre mour,Lted ~L
plurality of cu~cting elemant~ for eu~ct~ng or abrtL~lln~
the fonnatl~n belng drilled, a number o~ nozzle~ ~t ~clle external sl;r~ace o~ the bit, and an ln~Ler pa6s~L~e ~or 6upplylng ~rillin~ f lui~l to the nozzle~;, at lea~t ~ ma~n port ~ on of the ~lt body belng f ormed ~rom C~Lst ~ro~ ~n~
at lea~t a p~Lr~ of the ~urface of the ceL~t iron comprlsing a 6eparat~1y c~Lst outer layer of aaet lron c~ontaining n a6sive lnclusion~ of cementito Pormed by the addition of a c~r~de-formlng additive ~o ~he molt~n cast ~ron, ~uch masfii~re lnclusion~ of cem~n~ite l~lng absent from said malrL portion of the bit bo~y.
In a drill bit manufactured according to the me~hods of the invention, it is preferably those parts of the bit body which are particularly subject to erosi~n durin~ drilling, for examples the areas around the nozzles and cutting elements, which are hardened to increase their resistance to such erosion. At the same time, provided a sui~able form of cast iro~ is used, the rest of the bit bGdy may be accurately machined or otherwise worked after it has been cast. Thus the present invention may combine R~3~
6~ ~5~ ,23 the simplicity o~ m~nufqc~ure of ~eel bodied ~its wi~h the er~sion resistance of matrix bodied bit~ and, indeed, the erosion resi~tance of B drill bit according to the inventi~n will be ~uperivr to that of a ~teel b~died ~it and may also be ~uperior ~o tha~ of ~ matrix b~died bit.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:
Figure 1 is a ~ide elevation ~f a typical drill bit of ~he kind to which ~he invention is applicable, Figure 2 is an end elevation ~f ~he drill bit shown in Figure 1, Figure 3 is a vertical section ~hrough a mould showing the manufacture of a drill bit by one method according to the invention, and ~;~`
~ Z5 ~h2~'~
-7~
Figure 4 is a vertical section through a mould showing the manufacture of a drill bit by ano'cher method according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referrirlg to Figures 1 and 2, the body 10 of the drill bit is formed of cast iron by the method to be described, and has a threaded shank 11 at one end for connection to the drill string.
The operative end face 12 of the bit body is formed with a number of blades 13 radiating from the central area of the bit, and the blades carry cutting structures 14 spaced apart along the length thereof.
The bit has a gauge section including kickers 16 which contact the wall of the borehole to stabilise the bit in the borehole. A central passage (not shown~ in the bit body and shank delivers drilling fluid through nozzles 17 in the end face 12 in known manner to clean and/or cool the cutting elements.
In the particular arrangement shown each cutting structure 14 comprises a preform cutting element mounted on a carrier in the form of a stud which is located in a socket in the bit body. Normally, each preform cutting element is circular and comprises a thin facing layer of polycrystalline diamond bonded to a backing layer of tungsten carbide. ~owever, it will be appreciated that this is only one example of the many possible variations of the type of bit to which the invention is applicable, including bits where each preform cutting element ~5~Z~
comprises a unitary layer of thermally stable polycrystalline diamond material.
Figure 3 illustrates a method of manufacturing a bit body of the kind shown in Figures 1 and 2.
Referring to Figure 3, a two-part mould 19 is-formed from suitable material, such as sand. The two-part mould comprises an upper part 20 and a lower part 21 which between them define a mould cavity 22. The mould cavity has an internal configuration corresponding generally to the required surface shape of the bit body or a portion thereof. A passage 23 is formed in the upper mould part 20 and leads to the mould cavity 22 from a pouring chamber 24 at the upper surface of the mould part 20.
To produce the cutting face confiyuration of the drill bit shown in Figures 1 and 2, the mould may be formed with elongate recesses corresponding to the blades 13 of the drill bit. Spaced apart along each blade forming recess will be a plurality of sockets each of which receives a cylindrical former (not shown), the object of the formers being to define in the bit body sockets to receive the studs on which the cutting elements are mounted. Accordingly, the formers will be of the same cross-sectional shape as the ~studs, for example circular or rectangular.
There is also provided in the mould 19, at each desired location for a nozzle 17, a socket (not shown) which receives one end of an elongate former (not shown) which extends into the mould space so as to form in the _9 bit body a socket in which a nozzle may be subsequently inserted.
In one method according to the invention cast iron is melted and poured into the mould via ~he chamber -5 24 and passage 23. While ~he cast iron is molten and before it is is poured into the mould, there is added to the molten cast iron an additive having the property of causing iron carbide (cementite) to be formed in the cast iron during solidification. Suitable additives are boron and tellurium and approximately 1/2% of additive may be added to the molten cast iron.
After the mould cavity 22 has been filled with the molten cast iron with the additive, the mould is allowed to cool and by the time solidification of the cast iron h~s occurred, the additive will have caused the inclusion of massive bodies of cementite in the cast iron, thus substantially hardening the cast iron.
As previously mentioned, it may be desirable for only the lower surface portion of the bit body to be hardened, the upper portion of the bit body being softer so as to be machinable. To achieve this, the cast iron is poured into the mould in two portions. The first portion contains the boron or tellurium additive and i5 sufficient to fill only the bottom of the mould up to a certain level, as indicated for example by the line 25 in Figure 3. The remainder of the mould cavity is then filled with cast iron without the additive. As a resu:Lt, only the lower surface portion of the body will be hardened by the -10- ~ 2 inclusion of massive cementite.
In another method in accordance with the invention the internal surface of the mould cavity is coated, before introduction of the molten cast iron into the mould, with a material which reacts with the cast iron, during solidification, to effect surface hardening thereof by the production of massive inclusions of cementite. A suitable material is a wash of tellurium over the interior surface of the mould or a part thereof.
Thus, where it is only required that the lower portion of the bit body be hardened, the tellurium wash is coated over only the lower part of the mould cavity, that is to say up to the level of the line 25 in Figure 3.
In a further method according to the invention, the hardening of the cast iron is effected by controlling the rate of cooling of the bit body after solidification has occurred. Thus, after the cast iron in the mould has solidified suitable controlling of the rate of cooling of the mould will result in the production of martensite which has the effect of hardening the cast iron.
A still further method in accordance with the invention is illustrated with respect to Figure 4.
In this case the lower part 21 of the mould is provided with a heat sink in the form of a chill plate 26.
The size and initial temperature of the chill plate 26, which may comprise a body of graphite, machined steel or cast iron, is selected so as to accelerate the rate of cooling of the cast iron in the lower part of the mould y~
cavity and thus effect hardening of the cast iron in that locality by ~he process as known "chill hardening". As is well known, in chill hardening the production of massive inclusions of cementite in the cast iron occurs.
Preferably the chilling at the surface of the bit body effected by the chill plate 26 is at a rate sufficient to cause the formation of cementite ~iron carbide) so that at the surface itself, the material is almost entirely composed of cementite, the proportion of cementite decreasing with distance inwardly from the chilled surface.
As previously mentioned, normally cutting elements, or carriers for cutting elements such as studs or pegs, are secured within sockets in the surface of the lS finished bit body by brazing. Cast iron is normally difficult to braze due to the presence of surface graphite and, accordingly, it is advantageous to chill harden the surface of the body within sockets being formed in the bit body during its formation to receive cutting elements or their carriers, since the hardening reduces the amount of graphite present at the surface of each socket, thus facilitating brazing. Thus the aforementioned formers may be of metal and in close thermal contact with the chill plate 26 so as to chill harden the cast iron defining the sockets.
Although any form of cast iron may be employed in the methods according to the invention, it preferably comprises a spheroidal graphite cast iron in which, in known manner, graphite is precipitated in nodular forrn by the addition of magnesiurn or some other suitable material.
Al~ernatively the cast iron may be of the type known as "grey" cast iron, or may be compacted graphite cast iron ~ontaining titaniurn or some other material.
Although not essential to the present invention, the cutting elements may be in the form of so-called "preform" cutting elements in the shape of a tablet, often circular, having a superhard cutting face formed of polycrystalline diamond or other superhard material.
Conventionally there are two main methods of manufacturing such drill bits. In one common type of drill bit the bit body is machined from steel and the surface of the bit body is formed with sockets which receive pegs or studs on which the cutting elements are mounted. In the second common type of bit the-bit body is formed by a powder metallurgy process in which a hollow mould is first formed, for example from graphite, in the configuration of the bit body. The mould is packed with powdered material such as tungsten carbide, usually around 3~
~2~
-~ -2-a s~eel blank, and the powdered material is then infiltrated with a metal alloy in a furnace so as to form a hard matrix. If the cu~ting elements are of a kind which are not thermally stable at the infiltration -temperature, formers are mounted on the interior surf-ace of the mould so as to define in the finished bit body sockets or other locations where cutting elements may be subsequently mounted.
Steel bodied bits are generally simpler and cheaper to manufacture than matrix bodied bits. However, they are more susceptible to erosion during drilling and, for this reason, they are sometimes provided with a hard surface coating, for example of tungsten carbide, which adds to the complexity and cost of production.
On the other hand, although matrix ~odied bits are more resistant to erosion, their manufacture is complex and costly due largely to the high material cost and to the additional processes involved. Matrix bodied bits also may be made with the matrix at the surface more erosion resistant than that inside the bit body.
The present invention sets out to provide a new method of manufacturing a rotary drill bit using cast iron, in which at least some of the disadvantages of the known steel-bodied and matrix-bodied bits may be overcome.
British Paten~ Specification No. 1,574,884 discloses the use of cast iron in the manufacture of cutting bodies suitable for working or cutting material, such as cutting tips or inserts in rock drilling or chip ~ 3 ~ ~ r,~
forming machines. In such products it is necessary for surface portions of the product to be sufficiently hard to be resistant to erosion and damage during use of the product. Specification No. 1,574,884 describes a method - 5 of providing a hard surface which requires the encasting of a hard metal, such as a sintered hard carbide, e.g.
tungsten carbide, in the cast iron. Such methods have not, however, proved satisfactory in practice due to the high cost of the process and the difficulties of ensuring that the carbide is securely bonded within the cast iron.
~.S. Patent Specification No. 4,499,795 describes the use of cast iron in the manufacture of a rotary drill bit. In this case the inner surface of a mould is packed or coated over selected portions with paiticles of sintered tungsten carbide or similar sintered refractory hard metal and then cast iron is melted and poured into the mould. In this case, also, therefore, the hard surface of the finished bit is provided by tungsten carbide.
The present invention provides methods of manufacturing a rotary drill bit using cast iron where the cast iron itself forms the necessary hardened surface portions of the drill bit, the steps of the method being such as to effect the necessary hardening of the cast iron during the casting process.
According to the invention there is provided a method of manufacturing a rotary drill bit comprising a m~th~ of m~nu~ctur~n~ ~ ro~ry ~rlll ~1 having a bi~ body, ~omp~lgl~g ~he ~tep~ o~:
(a) ~ormln~ a hollow mould ln he ~o~lr~
con~iguration of ~t lea~t ~ ~or~ion o~ th~ blt bo~y5 (b) addlng to ~ ~ir~t body of molt~n ~t ron an lron carblde-~orming Add1tlve;
~ c) pourin~ the ~lrst bo~y o~ molt~n ~t ir~n into the lowermo~t p~rt o~ ~he ~ouldl (d~ coolln~ ~he mould 60 that said ~rst ~ody of cast ~ron ~olld1fl~s and, upon solidificAtlon, ~orm#
maB~ive lnclu~ion~ of cement~te;
~ e) pourin~ a ~econd body of molt~n o~st lron, without ~i~nificant amounts of 6uch lron carb~e-formlng additlve, into the mould on top of th~
~olidif1 ed flrst ~ody oP cast iron; and ~ ) aoolin~ the mould ~o th~t said secon~
~ody of cast iron ~olidifle~.
Said hardening treatment ~ay comprise adding to at least part of the molten cast iron, before it is poured into the mould, an ixon carbide-forming additive, whereby said part of the cast iron, upon solidification, contains massive inclusions of cementite. Said additive may comprise boron or tel1uri~m. Approximately 1/2% of additive may be added t~ the molten cast iron.
If reguired the molten cast iron may be poured int~ the mould in two successive pourings, said additive being added only to the cast iron in ~he first pouring ~o as to harden only the portion of the bit b~dy which is lowermost in the mould.
~ ~.5~ ~ 2~
In an altern~tive methDd according ~o the invention said hardening treatment comprises the ~tep of chill hardening a portion of the surface of ~he bi~ body by accelerated cooling of said surface portion during the solidification part of ~he casting process, said accelerated cooling being at a rate to produce massivP
~nclusions uf cementite in the ~olidified surf~ce p~rtion.
Said chill hardening may be effe~t~d by lDcating a metal heat sink in the mould adjacent said ~urface portion of the bit b~dy which is to be hardened.
There may be mounted on the interiDr of the mould, prior to pouring the cast iron into the mould, formers which project into the mould cavity so as to form sockets in the solidified cast iron bit body, said formers being in close thermal contact with said metal heat sink, whereby ~he interior of each socket i5 chill hardened.
In a further method according to the invention said hardening treatment comprises the step, before pouring the cast iron int~ the mould, of coating at least part of the interior surface of the mould with a material which rea ts with ~he cast iron, during solidification thereof, to form massive inclusions of cementite in at least one surface portion of the bit body. Said coating material may be tellurium.
In a still further method according to the inventi~n said hardening treatment comprises controlling the rate of cooling of the bit b~dy, after solidification `~' ~;~5~
of the cast iron and during ~che ~ubsesluent cooling portion of the casting process, in such manner as to ef f ect the formation of martensite in at least one surace porkion of the bi t ~ody .
~he invention includes within its ~cope a rc~t~Lry ~rlll bl'c comprl~ L b~t bo~y havin~ an external Ecur~ce on which ~Lre mour,Lted ~L
plurality of cu~cting elemant~ for eu~ct~ng or abrtL~lln~
the fonnatl~n belng drilled, a number o~ nozzle~ ~t ~clle external sl;r~ace o~ the bit, and an ln~Ler pa6s~L~e ~or 6upplylng ~rillin~ f lui~l to the nozzle~;, at lea~t ~ ma~n port ~ on of the ~lt body belng f ormed ~rom C~Lst ~ro~ ~n~
at lea~t a p~Lr~ of the ~urface of the ceL~t iron comprlsing a 6eparat~1y c~Lst outer layer of aaet lron c~ontaining n a6sive lnclusion~ of cementito Pormed by the addition of a c~r~de-formlng additive ~o ~he molt~n cast ~ron, ~uch masfii~re lnclusion~ of cem~n~ite l~lng absent from said malrL portion of the bit bo~y.
In a drill bit manufactured according to the me~hods of the invention, it is preferably those parts of the bit body which are particularly subject to erosi~n durin~ drilling, for examples the areas around the nozzles and cutting elements, which are hardened to increase their resistance to such erosion. At the same time, provided a sui~able form of cast iro~ is used, the rest of the bit bGdy may be accurately machined or otherwise worked after it has been cast. Thus the present invention may combine R~3~
6~ ~5~ ,23 the simplicity o~ m~nufqc~ure of ~eel bodied ~its wi~h the er~sion resistance of matrix bodied bit~ and, indeed, the erosion resi~tance of B drill bit according to the inventi~n will be ~uperivr to that of a ~teel b~died ~it and may also be ~uperior ~o tha~ of ~ matrix b~died bit.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:
Figure 1 is a ~ide elevation ~f a typical drill bit of ~he kind to which ~he invention is applicable, Figure 2 is an end elevation ~f ~he drill bit shown in Figure 1, Figure 3 is a vertical section ~hrough a mould showing the manufacture of a drill bit by one method according to the invention, and ~;~`
~ Z5 ~h2~'~
-7~
Figure 4 is a vertical section through a mould showing the manufacture of a drill bit by ano'cher method according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referrirlg to Figures 1 and 2, the body 10 of the drill bit is formed of cast iron by the method to be described, and has a threaded shank 11 at one end for connection to the drill string.
The operative end face 12 of the bit body is formed with a number of blades 13 radiating from the central area of the bit, and the blades carry cutting structures 14 spaced apart along the length thereof.
The bit has a gauge section including kickers 16 which contact the wall of the borehole to stabilise the bit in the borehole. A central passage (not shown~ in the bit body and shank delivers drilling fluid through nozzles 17 in the end face 12 in known manner to clean and/or cool the cutting elements.
In the particular arrangement shown each cutting structure 14 comprises a preform cutting element mounted on a carrier in the form of a stud which is located in a socket in the bit body. Normally, each preform cutting element is circular and comprises a thin facing layer of polycrystalline diamond bonded to a backing layer of tungsten carbide. ~owever, it will be appreciated that this is only one example of the many possible variations of the type of bit to which the invention is applicable, including bits where each preform cutting element ~5~Z~
comprises a unitary layer of thermally stable polycrystalline diamond material.
Figure 3 illustrates a method of manufacturing a bit body of the kind shown in Figures 1 and 2.
Referring to Figure 3, a two-part mould 19 is-formed from suitable material, such as sand. The two-part mould comprises an upper part 20 and a lower part 21 which between them define a mould cavity 22. The mould cavity has an internal configuration corresponding generally to the required surface shape of the bit body or a portion thereof. A passage 23 is formed in the upper mould part 20 and leads to the mould cavity 22 from a pouring chamber 24 at the upper surface of the mould part 20.
To produce the cutting face confiyuration of the drill bit shown in Figures 1 and 2, the mould may be formed with elongate recesses corresponding to the blades 13 of the drill bit. Spaced apart along each blade forming recess will be a plurality of sockets each of which receives a cylindrical former (not shown), the object of the formers being to define in the bit body sockets to receive the studs on which the cutting elements are mounted. Accordingly, the formers will be of the same cross-sectional shape as the ~studs, for example circular or rectangular.
There is also provided in the mould 19, at each desired location for a nozzle 17, a socket (not shown) which receives one end of an elongate former (not shown) which extends into the mould space so as to form in the _9 bit body a socket in which a nozzle may be subsequently inserted.
In one method according to the invention cast iron is melted and poured into the mould via ~he chamber -5 24 and passage 23. While ~he cast iron is molten and before it is is poured into the mould, there is added to the molten cast iron an additive having the property of causing iron carbide (cementite) to be formed in the cast iron during solidification. Suitable additives are boron and tellurium and approximately 1/2% of additive may be added to the molten cast iron.
After the mould cavity 22 has been filled with the molten cast iron with the additive, the mould is allowed to cool and by the time solidification of the cast iron h~s occurred, the additive will have caused the inclusion of massive bodies of cementite in the cast iron, thus substantially hardening the cast iron.
As previously mentioned, it may be desirable for only the lower surface portion of the bit body to be hardened, the upper portion of the bit body being softer so as to be machinable. To achieve this, the cast iron is poured into the mould in two portions. The first portion contains the boron or tellurium additive and i5 sufficient to fill only the bottom of the mould up to a certain level, as indicated for example by the line 25 in Figure 3. The remainder of the mould cavity is then filled with cast iron without the additive. As a resu:Lt, only the lower surface portion of the body will be hardened by the -10- ~ 2 inclusion of massive cementite.
In another method in accordance with the invention the internal surface of the mould cavity is coated, before introduction of the molten cast iron into the mould, with a material which reacts with the cast iron, during solidification, to effect surface hardening thereof by the production of massive inclusions of cementite. A suitable material is a wash of tellurium over the interior surface of the mould or a part thereof.
Thus, where it is only required that the lower portion of the bit body be hardened, the tellurium wash is coated over only the lower part of the mould cavity, that is to say up to the level of the line 25 in Figure 3.
In a further method according to the invention, the hardening of the cast iron is effected by controlling the rate of cooling of the bit body after solidification has occurred. Thus, after the cast iron in the mould has solidified suitable controlling of the rate of cooling of the mould will result in the production of martensite which has the effect of hardening the cast iron.
A still further method in accordance with the invention is illustrated with respect to Figure 4.
In this case the lower part 21 of the mould is provided with a heat sink in the form of a chill plate 26.
The size and initial temperature of the chill plate 26, which may comprise a body of graphite, machined steel or cast iron, is selected so as to accelerate the rate of cooling of the cast iron in the lower part of the mould y~
cavity and thus effect hardening of the cast iron in that locality by ~he process as known "chill hardening". As is well known, in chill hardening the production of massive inclusions of cementite in the cast iron occurs.
Preferably the chilling at the surface of the bit body effected by the chill plate 26 is at a rate sufficient to cause the formation of cementite ~iron carbide) so that at the surface itself, the material is almost entirely composed of cementite, the proportion of cementite decreasing with distance inwardly from the chilled surface.
As previously mentioned, normally cutting elements, or carriers for cutting elements such as studs or pegs, are secured within sockets in the surface of the lS finished bit body by brazing. Cast iron is normally difficult to braze due to the presence of surface graphite and, accordingly, it is advantageous to chill harden the surface of the body within sockets being formed in the bit body during its formation to receive cutting elements or their carriers, since the hardening reduces the amount of graphite present at the surface of each socket, thus facilitating brazing. Thus the aforementioned formers may be of metal and in close thermal contact with the chill plate 26 so as to chill harden the cast iron defining the sockets.
Although any form of cast iron may be employed in the methods according to the invention, it preferably comprises a spheroidal graphite cast iron in which, in known manner, graphite is precipitated in nodular forrn by the addition of magnesiurn or some other suitable material.
Al~ernatively the cast iron may be of the type known as "grey" cast iron, or may be compacted graphite cast iron ~ontaining titaniurn or some other material.
Claims (4)
1. A method of manufacturing a rotary drill bit having a bit body, comprising the steps of:
(a) forming a hollow mould in the desired configuration of at least a portion of the bit body;
(b) adding to a first body of molten cast iron an iron carbide-forming additive;
(c) pouring the first body of molten cast iron into the lowermost part of the mould;
(d) cooling the mould so that said first body of cast iron solidifies and, upon solidification, forms massive inclusions of cementite;
(e) pouring a second body of molten cast iron, without significant amounts of such iron carbide-forming additive, into the mould on top of the solidified first body of cast iron; and (f) cooling the mould so that said second body of cast iron solidifies.
(a) forming a hollow mould in the desired configuration of at least a portion of the bit body;
(b) adding to a first body of molten cast iron an iron carbide-forming additive;
(c) pouring the first body of molten cast iron into the lowermost part of the mould;
(d) cooling the mould so that said first body of cast iron solidifies and, upon solidification, forms massive inclusions of cementite;
(e) pouring a second body of molten cast iron, without significant amounts of such iron carbide-forming additive, into the mould on top of the solidified first body of cast iron; and (f) cooling the mould so that said second body of cast iron solidifies.
2. A method according to Claim 1, wherein said additive is selected from boron and tellurium.
3. A method according to Claim 1, wherein approximately ? % additive is added to the first body of molten cast iron.
4. A rotary drill bit comprising a bit body having an external surface on which are mounted a plurality of cutting elements for cutting or abrading the formation being drilled, a number of nozzles at the external surface of the bit, and an inner passage for supplying drilling fluid to the nozzles, at least a main portion of the bit body being formed from cast iron and at least a part of the surface of the cast iron comprising a separately cast outer layer of cast iron containing massive inclusions of cementite formed by the addition of a carbide-forming additive to the molton cast iron, such massive inclusions of cementite being absent from said main portion of the bit body.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8508622 | 1985-04-02 | ||
| GB858508622A GB8508622D0 (en) | 1985-04-02 | 1985-04-02 | Rotary drill bits |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1256423A true CA1256423A (en) | 1989-06-27 |
Family
ID=10577095
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000505588A Expired CA1256423A (en) | 1985-04-02 | 1986-04-01 | Rotary drill bits and methods of manufacture thereof |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0197741A3 (en) |
| CA (1) | CA1256423A (en) |
| GB (1) | GB8508622D0 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2793174B1 (en) * | 1999-05-07 | 2001-06-29 | Renault | METHOD AND DEVICE FOR MOLDING A CYLINDER HEAD OF AN INTERNAL COMBUSTION ENGINE |
| AU2001280541A1 (en) * | 2000-07-17 | 2002-01-30 | Consolidated Engineering Company, Inc. | Methods and apparatus for utilization of chills for castings |
| CN103273042B (en) * | 2013-05-24 | 2015-04-15 | 成都工业学院 | Method of preparing vanadium-titanium cemented-carbide drilling bit |
| CN108588768B (en) * | 2018-05-29 | 2019-03-01 | 广州市华番盛化工科技有限公司 | Steel and iron parts alkalinity deep hole nickel-plating additive, pre-plating solution and pre-plating process |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4029140A (en) * | 1975-04-01 | 1977-06-14 | The British Cast Iron Research Association | Method of and means for obtaining white cast iron |
| JPS5575874A (en) * | 1978-11-30 | 1980-06-07 | Yanmar Diesel Engine Co Ltd | Production of tough cast iron casting |
| GB2134542B (en) * | 1982-07-19 | 1987-06-03 | Giw Ind Inc | Abrasive resistant white cast iron |
| US4499795A (en) * | 1983-09-23 | 1985-02-19 | Strata Bit Corporation | Method of drill bit manufacture |
-
1985
- 1985-04-02 GB GB858508622A patent/GB8508622D0/en active Pending
-
1986
- 1986-04-01 EP EP86302375A patent/EP0197741A3/en not_active Withdrawn
- 1986-04-01 CA CA000505588A patent/CA1256423A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0197741A2 (en) | 1986-10-15 |
| EP0197741A3 (en) | 1988-03-16 |
| GB8508622D0 (en) | 1985-05-09 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |