GB2081174A

GB2081174A - Button Bit Grinding Tool Head

Info

Publication number: GB2081174A
Application number: GB8123496A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-08-02
Filing date: 1981-07-31
Publication date: 1982-02-17

Abstract

A button-bit-grinding-tool head (1) is made by compacting a grinding material (8) in a female mould part before the mould part is machined to form the body of the tool head (2A). A male mould part is shaped to form a part-spherical, concave grinding surface (20) with a diametral slot (21) and a third mould part, comprising a generally-cylindrical pin housed in cooperating axial bores in the male and female parts in the closed mould, forms a throughbore in the grinding element. The diametral slot does not extend through the tool body (2A) so that cooling fluid fed through the tool body throughbore (3A) into the grinding element throughbore to the diametral slot (21) is concentrated at the grinding interface. <IMAGE>

Description

SPECIFICATION Button Bit Grinding Tool Head The present invention relates to a button-bit grinding tool head for reprofiling a part-spherical grinding elements of "button-bit" type drill heads once these havo become worn in use, and to a method for the manufacture of grinding-tool heads.

The grinding elements of button-bit drill heads comprise part-spherical projections of a hardmetal material, such as tungsten carbide, set into a flat-faced steel matrix comprising the drill head.

When worn, these grinding elements lose their sphericity and must be reground, or 'reprofiled' with a tool provided with a specially-adapted tool head having a part-spherical grinding surface of the same radius as the element to be reground. The tool head may be driven by, for example, a hand-held or bench-mounted pneumatic drill operated at speeds generally between 5,000 and 20,000 r.p.m.

As in all grinding operations, a considerable degree of heat is generated during reprofiling of a button-bit grinding element and this heat is normally dissipated with the aid of a cooling fluid fed to the grinding zone through a bore in the reprofiling tool head. In tools currently in use, this bore opens into a diametral slot in the partspherical grinding surface which is constituted by a very hard abrasive, such as diamond or cubic boron nitride, set in a bonding material. In these known tools the slot also extends through the surrounding steel of the tool head shell, allowing the coolant to escape from the periphery of the tool head rather than concentrating it on the grinding interface.

A further disadvantage of the reprofiling tool heads currently in use is that the slot for the cooling fluid is cut in the grinding surface by means of a hack-saw: it will be appreciated that, given the extremely hard nature of the grinding material, this is a very laborious process and is expensive, not only in the time involved, but also because of the number of new hack-saw blades required merely to form a single slot.

The object of the present invention is to provide a tool head for reprofiling button-bit grinding tools which can concentrate the coolant more effectively on the grinding interface than tool heads currently available and, in addition, to provide a cheaper and less laborious process for manufacturing a grinding tool head.

According to one aspect of the present invention, there is provided a button-bit-grindingtool head comprising a support adapted for connection to a rotary drive for rotating the tool head about a grinding axis, in use, and a compacted grinding material contained in the support and having a part-spherical, concave grinding surface coaxial with the grinding axis and surrounded by a fully-annular surface of the support, the grinding surface having at least one radially-extending slot communicating with an axial bore in the support for feeding cooling fluid to the grinding interface in use.

Preferably the support has an axially-projecting stem for connection to the rotary drive, the stem having a bore continuous with the axial bore of the support.

The grinding tool head of the invention thus has a radial slot, in practice preferably two diametrally-opposed slots, for receiving cooling fluid but, unlike the slots in the known tool heads, these radial slots are not continued through the surrounding support, normally of steel, and provide for better concentration of the coolant on the interface. As with known heads for buttonbit grinding tools the coolant employed may be air, water, oil or any other suitable fluid.

In order to facilitate the coolant flow to the grinding interface, each slot preferably narrows in transverse section, being widest at the grinding surface.

The grinding material used in the present invention may be of any suitable type but would usually comprise diamond or cubic boron nitride chips as the abrasive, set in a metal-alloy binding agent: the metal-alloys currently in use are perfectly suitable and usually comprise combinations of iron, cobalt, bronze, silver, tin, copper and carbon (amorphous or graphite) in various ratios by weight according to the tool hardness required for grinding a particular button bit.

According to a further aspect of the invention there is provided a method for manufacturing a grinding tool head comprising a grinding element of abrasive particles in a bonding material carried by a support which is adapted for connection to a rotary drive for rotating the tool head about a grinding axis, the method including compacting a grinding material in a mould formed in part by the support simultaneously to form the grinding element and to attach it to the support.

The above method is particularly suitable for manufacturing the button-bit grinding tool head described above in which the support of the tool head is hollow and can form part of the female part of the mould: in this case, the cooperating male part would have a part-spherical protuberance for forming the concave grinding surface of the tool head and at least one additional, radially-elongate, axial projection for forming the radial slot in the grinding surface.

Clearly, by this method, any desired arrangement of radial slots may easily be formed. The projection may also have a bevelled or tapered edge to form a slot which narrows towards its bottom surface.

The hollow, female mould part which subsequently forms the support of the tool head is preferably used, in the moulding, in the form of a blank which is machined to its final form after diamantling of the mould.

The button-bit grinding tool head of the invention must also have a bore for coolant, which opens into the radial slot or slots. In general, this can be formed by location in the mould of a suitable mould part, whether separate or carried by the male or female part; if the female part is formed with its axial throughbore prior to moulding, the mould part for forming the grinding element throughbore preferably projects into, and cooperates with the said throughbore in the female part. In a preferred embodiment of the invention use is made of a three-part mould comprising the male and female parts mentioned above and a pin which is a cooperating fit in coaxial bores in the male and female parts. It is also convenient to form the male mould parts itself in several sections because of the complex nature of the end which forms the slotted, concave grinding surface of the tool head.

The mould part which serves as the support of the tool head is preferably formed with a retaining element, for example a groove or projection, for keying the compacted grinding material thereto although, with some materials and compacting processes, the bonding alloy of the grinding material may bond sufficiently well to the support for this to be unnecessary.

The compacting process employed depends on the materials used and the required hardness of the finished product. Preferably, once the mould has been closed, it is subjected to an initial cold compaction under pressure.

Subsequently it may be heated, for example to temperatures of from 2500C to 9000C, and subjected to further pressure, either simultaneously or in stages, as required. The heating may be effected in a furnace or with an induction or resistance type heater and with or without a non-oxidizing atmosphere according to the bonding agent employed.

It will be appreciated that although the above method is particularly suitable for forming a button-bit-grinding-tool head, it may also be used to form other grinding tool heads when the body, or support, for the grinding element can be employed as, or as part of, either a male or female mould part; a cooperating mould part would then be formed with the appropriate shape for forming a desired grinding surface on the compacted grinding material.

One embodiment of the invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an axial-sectional view of a female mould part for forming a button-bit grinding tool head according to the invention; Figure 2 is a side elevational view of a male mould part for cooperating with the female mould part of Figure 1, showing two mould portions separated; Figure 3 is an axial-sectional view of the mould part of Figure 2, showing the two portions joined together, taken on a line corresponding to line Ill-Ill of Figure 2; Figure 4 is an axial-sectional view of the mould parts of Figures 1 and 3 brought together to close the mould, on a line corresponding to line IV--IV of Figure 3;; Figure 5 is an axial-sectional view of the finished button-bit grinding tool of the invention, taken on line V-V of Figure 6; and Figure 6 is a plan view of the tool taken inthe direction of arrow VI of Figure 5.

Referring to the drawings, Figures 1 to 3 show mould parts for use in the process of the invention for making the button-bit grinding-tool head 1 shown in Figures 5 and 6. Figure 1 shows a female mould part, generally indicated 2, made from steel, which will subsequently form the body section, or support, 2A (see Figures 5 and 6) of the tool head 1.

The mould part 2 has an outer cylindrical surface and an axial throughbore including a narrow cylindrical bore 3A extending from one end face thereof and opening into a wider cavity 4 having a cylindrical portion 5 which opens into the opposite end face of the part 2. The bore 3A opens into the cylindrical cavity 5 through an enlarged portion 6 of the cavity 4 of slightly greater diameter than the cylindrical portion 5, and having an end surface 7 concavely-curved towards the cavity 4: the surface 7 forms a seat for a grinding material 8 (see Figure 4) in use of the mould.

Referring to Figures 2 and 3 of the drawings, a male mould part is shown generally indicated 9 which is formed in two mating portions 10, 11.

The portion 10 is generally cylindrical, being formed to fit into the cylindrical cavity portion 5 of the female mould part 2. At one end the portion 10 is formed with a coaxial, part-spherical protuberance 12 surrounded by a flat, annular shoulder 13, the axial height of the protuberance 1 2 being approximately one third its diameter.

The mould portion 10 is further formed with a slot 14 extending axially from the end with the protuberance 12, for approximately two-thirds of the length of the portion 10, for receiving the generally planar mould-portion 11. When the portion 11 is fitted into the slot 14 and fixed by means of a rivet 1 5 (see Figure 3) passed through cooperating apertures in the two portions, a free end 1 6 of the portion 11 projects beyond the protruberance 12 and is formed with a rounded end surface which cooperates with the curved end wall 7 of the cavity 4 in the female mould part 2. The edges of the end 16 of the portion 11 are bevelled as shown at 17 in Figure 2.

The two male mould portions 10, 11 are also formed with an axial bore 3B, of the same diameter as the bore 3A of the female part 2. In the assembled condition of the mould (see Figure 4) the bores 3A and 3B are coaxial and a cooperating pin 1 8 is located therein.

The pin 18, like the female part 2, is of steel.

The male mould portions 10, 11 may be of steel or carbon.

In use of the mould parts 2, 9 and 18 to make the tool head 1 , the grinding mixture 8 is first made by mixing measured quantities by weight of diamond or cubic boron nitride powder with å metal-alloy bonding agent, the materials and particle sizes being chosen according to the required hardness of grinding actlon of the finished tool head. The pin 1 8 is then located in the bore 3A of the female mould part 2 and a predetermined weight of the grinding mixture 8 is placed in the cavity 4 and compacted and levelled around the pin 18 against the wall 7. The mould is then closed by insertion of the male part 9 into the female cavity 4 to shape the grinding material as shown in Figure 4 and the closed mould is placed under a press for cold compaction.

After cold compaction, if further treatment is needed for the materials employed, the mould is heated to a temperature of between 2500C and 9000C and subjected to pressure as necessary.

The mould is finally air-cooled and dismantled and the female part 2 is machined to form the tool head 1 shown in Figures 5 and 6.

Referring to Figures 5 and 6, it will be seen that the female part 2 has been machined to remove the metal projecting beyond the compacted grinding material 8, and around part of the bore 3A to form a shank 19 which can be gripped by a rotary tool, in use, to provide rotary drive. The grinding material 8 has been moulded to display a concave, part-spherical grinding surface 20, which is suitable for reprofiling button-bit grinding elements, the depth of the surface 20 being approximately one-third its radius to allow the tool head 1 to be moved over the surface of the element during grinding.

The bore 3A of the tool head 1 is intended, in use, to feed a cooling fluid to the grinding surface 20 and opens into a generally V-section diametral slot 21 in the surface 20, the slot 21 having been formed during the moulding operation by the presence of the end 16 of the male mould portion 11. It will be seen that this diametral slot 21 is located solely in the grinding material itself and does not extend through the surrounding rim of the steel body 2A. In use of the tool head 1 to reprofile a button bit grinding element, the coolant is thus concentrated at the interface between the grinding material and the bit element rather than escaping freely from this area as occurs in use of previously known grinding heads.

The actual size of the head 1 and radius of the face 20 may be varied according to the size of the button bit grinding element to be reprofiled by the tool head 1. The grinding material 8 and its moulding process may also be varied; A particular example of a grinding material is as follows: Binding Agent Composition parts by Ingredient weight Bronze (85/1 5-copper/tin) 1000 Silver powder (200 mesh) 50 Copper powder (400 mesh) 50 Tin powder (600 mesh) 50 Graphite powder 10 Abrasive--diamond powder.

The mould is first subjected to pressure at ambient temperature and then heated to 6500C and simultaneously subjected to a pressure of approximately 95 kg/sq.cm.

Claims

1. A method for manufacturing a grinding tool head comprising a grinding element of abrasive particies in a bonding material carried by a support which is adapted for connection to a rotary drive for rotating the tool head about a grinding axis, the method including compacting a grinding material in a mould formed in part by the support simultaneously to form the grinding element and to attach it to the support.

2. A method as claimed in Claim 1, in which the mould includes a part for forming a throughbore in the grinding element coaxial with the grinding axis.

3. A method as claimed in Claim 2, in which the support has a throughbore coaxial with the grinding axis and the part for forming'the throughbore in the grinding element extends into and cooperates with the throughbore in the support when the mould is closed so that the grinding element throughbore communicates with the support throughbore in the finished tool head.

4. A method as claimed in Claim 3, in which the mould part which forms the grinding surface of the grinding element has a bore and the part which forms the grinding element throughbore comprises a generally-cylindrical pin which is a cooperating fit in the said bore and extends into the support throughbore when the mould is closed.

5. A method as claimed in Claim 2, Claim 3 or Claim 4, in which the mould part for forming the grinding surface of the grinding element has at least one projection arranged to form a radiallyextending slot in the grinding surface, which slot communicates with the throughbore of the grinding element.

6. A method as claimed in Claim 5, in which the or each projection for forming a slot in the grinding surface is tapered or bevelled so as to form a slot which narrows in transverse section towards its bottom surface.

7. A method as claimed in Claim 5 or Claim 6, in which the or each slot-fornting projection comprises a projecting end portion of a plate which is a cooperating fit and is captive in a slot in the mould part for forming the grinding surface.

8. A method as claimed in any one of the preceding claims, in which the tool-head support comprises or is part of a female mould part and a cooperating male part of the mould has a partspherical end surface for forming a concave grinding surface in the grinding element.

9. A method as claimed in any one of the preceding claims, in which the surface of the support which receives the grinding material is formed with a retaining groove or projection for keying the compacted grinding element to the support.

10. A method as claimed in any one of the preceding claims, in which the support is part of a metal blank constituting one of the mould parts, which blank is machined to form the support itself after compaction of the grinding material and dismantling of the mould.

11. A method as claimed in any one of the preceding claims, in which the grinding material comprises diamond or cubic boron chips as the abrasive mixed with a bonding material.

12. A method as claimed in Claim 11, in which the bonding material comprises a mixture of powdered metals.

13. A method for manufacturing a grinding tool head substantially as herein described with reference to the accompanying drawings.

14. A grinding tool head made by the method of any one of the preceding claims.

1 5. A button-bit-grinding-tool head comprising a support adapted for connection to a rotary drive for rotating the tool head about a grinding axis, in use, and a compacted grinding material contained in the support and having a part-spherical, concave grinding surface coaxial with the grinding axis and surrounded by a fully-annular surface of the support, the grinding surface having at least one radially-extending slot communicating with an axial bore in the support for feeding cooling fluid to the grinding interface in use.

1 6. A button-bit-grinding-tool head as claimed in Claim 15, in which the support has an axially- projecting stem for connection to the rotary drive, the stem having a bore continuous with the axial bore of the support.

1 7. A button-grinding-bit-tool head as claimed in Claim 1 5 or Claim 16, in which the grinding surface has two diametrally-aligned, radiallyextending slots.

1 8. A button-bit-grinding-tool head as claimed in Claim 1 5, Claim 1 6 or Claim 17, in which the or each slot narrows in transverse section, being widest at the grinding surface.

1 9. A button-bit-grinding-tool head as claimed in any one of claims 1 5 to 18, in which the grinding material comprises diamond or cubic boron nitride chips as the abrasive in a bonding matrix.

20. A button-bit-grinding tool head as claimed in Claim 19, in which the bonding matrix is a metal alloy.

21. A button-bit-grinding tool head substantialiy as herein described with reference to, and as shown in Figures 5 and 6 of the accompanying drawings.