GB2291369A - Forming holes - Google Patents

Abstract

A tool is used to shape a parallel sided hole into one having an upper frustoconical portion. The tool D2 has an upper part having arms 30 with cutting segments 35 on the outside surface, the arms being pivotally mounted on the tool. The tool is inserted into the hole with the arms retracted, they are moved apart and the tool rotated to shape the hole; they are then retracted and the tool removed. <IMAGE>

Description

FORMING HOLES The invention relates to the formation of holes in preformed articles. A specific use of the invention is in the formation of shaped holes through refractory blocks used to line heat chambers such as furnaces, hearths or kilns or the like, the hole being shaped to receive an anchoring or like device by which the block is held to a support wall.

It is usual to form the required hole using a plastics or similar expendable pattern that is inserted into the mould in which the block is cast of refractory concrete or the like. When the block is heated initially to a sintering temperature the pattern is burnt away and because the pattern and the concrete have different rates of expansion cracks are generated by the stresses created. It is an object of this invention to provide a method and tool for forming a hole in a block in such a way that the risk of such damage is avoided or eliminated.

In one aspect the invention provides a method of forming a generally frustoconical portion in a preformed generally parallel sided hole in an article, the method comprising inserting a tool to the intended depth in the hole, the hole having cutting elements which are carried on arms which are pivotably mounted on the tool, the arms being moveable between a retracted condition in which the arms are close together and an extended condition in which the arms are spaced apart in a generally conical shape, the tool being inserted into the hole with the arms in the retracted condition and the arms then being moved to the extended condition; rotating the tool to cause the cutting elements to remove wall material from the hole thereby to define the frustoconical portion; and then removing the tool.

The cutting elements may be secured to the outer faces of the arms. The elements are preferably formed of abrasive material and are in block, strip or segmental form.

They are secured to the arms in known manner.

The preformed hole will typically have a major diameter portion and an axially aligned minor diameter portion with a shoulder being formed at the union of the two portions. In such a case the arms of the tool preferably have cutting elements towards their free ends arranged so as to cut away and shape the shoulder while the frustoconical portion is being formed.

Preferably the tool includes means to flush through a flushing medium to clear away debris.

Preferably the article has been precast of refractory concrete but it can be formed of other materials in which shaped holes are difficult to form, such as wallboard, composites such as metal matrix composites, or the like.

In another aspect the invention provides a tool for the purpose specified comprising a spindle to engage rotary drive; the spindle having a forward end on which is received a nut; the arms being pivotably mounted on the nut, the arms having cutting elements on their outer surfaces; and means for moving the arms from a retracted condition in which they are close together to an extended condition in which the free ends of the arms are spaced apart in a generally conical array Preferably the arms have additional cutting elements adjacent their free ends i.e. at the leading whereby to form the shoulder.

Preferably the cutting elements are made of abrasive material.

Preferably the spindle has a socket on its forward end to receive a shaft the free end of which is placed between the arms. The shaft is moveable axially and in a forward position urges the arms to the second condition where they are spaced apart. Preferably the spindle includes an assembly arranged so as to advance the shaft while keeping the spindle stationery.

The invention also includes a block which has been preformed as a solid and then has had a generally parallel sided hole drilled therein; and such a block in which a generally frustoconical portion has been formed in the hole.

In order that the invention may be well understood it will now be described by way of example only with reference to the accompanying diagrammatic drawings in which Figure 1 is a vertical sectional view through a refractory block showing a formed anchor bolt hole; Figure 2 is a vertical sectional view of a tool for forming the parallel sided hole profile (the upper part of which is shown in ghost outline in Figure 1) Figure 3 is a vertical sectional view of the tool for forming the conical part of the hole as shown in Figure 1 Figure 4 is a detail of the spindle of the tool of Figure 3; and Figure 5 shows the shaft thereof; Figure 6 is an exploded sectional view of the parts for moving the shaft shown in Figure 5; and Figure 7 is a plan view of tongs used to hold the spindle stationary.

A block 1 shown in Figure 1 is cast of a refractory concrete or like material. The block is of a shape suitable for lining a heat chamber such as a furnace hearth, kiln or the like. The block has opposite surfaces 2, 3 between which extends a hole 4, the hole having an upper generally frustoconical portion 5 and a concentric lower parallel sided narrower diameter portion 6. The hole 4 is to receive an anchor bolt, not shown, following which it will be backfilled with a refractory setting material.

Because of the difference in diameter between the portions a horizontal shoulder 8 is formed. It will be noted that the top end 9 of the portion 5 is straight sided. The hole 4 is first formed as a parallel sided hole 4A shown by ghost lines 7 using the rotary drill bit D1 shown in Figure 2. That tool has a spindle 10 connectable to a power drill, not shown, comprising a leading drill tube 11 having spaced apart end abrasive segments 12 and a trailing wider diameter short tube 13 having abrasive segments 14 on its lower face. In a first operation, the drill bit D1 is used to drill the hole 4A and the hole 6, the bit being flushed through with flushing liquid to clear away debris, etc.

The second rotary drill bit D2 shown in Figure 3 comprises a spindle 20 connectable to a power drill, not shown. The forward end of the spindle 20 has a socket 21 which receives the end of a dolly shaft 22 having an enlarged head 23. The forward end of the spindle 20 has an externally threaded portion 24 and a relatively wider forward ring 25. An enclosed slot 26 is present in the forward portion in communication with the socket 21 and the shaft 23 has a pin 27 which travels in that slot; by adjusting the position of the dolly shaft, as explained below, one can adjust the extent to which the dolly projects forward of the spindle. The ring 25 has sockets 28 which receive the pins 29 by which a number of arms 30 are pivotally mounted on the ring 25. Each arm 30 is generally of L shape, being pivoted by the pin 29 at upper end of the longer limb or upright 31.The arms are joined together by a band 32 received in a notch 33 at the upper end of the shorter limb 34 of L.

Strips or blocks of abrasive material 35 are secured, e.g. welded to the outer surface of the limbs; as shown three such strips are secured to the upright limb 31 and one to the shorter limb 34. At rest, the lower portions of the shorter limb 34 lie in a retracted condition and abut the head 23 of the shaft 22, and as shown in Figure 3. The outside walls of the shorter limbs 34 are angled so that the foot of the L shaped limb is at about 100 to the horizontal and the upper inner corner 36 at about 260 with respect to the adjacent wall. When the drill bit is in use the arms 30 are urged outwardly by advancement of the dolly shaft 22 and these angles determine the position of the abrasive segments 35 and thus where they will cut into the wall of the upper hole portion 4A.The abrasive blocks on the longer limbs form the cone and those on the shorter limbs will form a flat floor on the shoulder 8.

Figure 6 shows an assembly by which the dolly shaft 22 is caused to move forward to move the arms 30 to the extended condition. The assembly comprises a nut 37 on which is imposed a disc 38 followed by a washer 39 and a cap 40. The disc and washer fit on to the nut 37 adjacent its lower end and a gap is present between the washer 39 and the cap 40 to receive the head of tongs 41 (Figure 7). The parts are held together by screws received in the holes shown. The nut 37 is engaged with the threaded portion 24 of the spindle 20. The parts are arranged so that clockwise rotation of the nut 32 will cause the dolly shaft 22 to reciprocate.

In use, the tool D1 shown in Figure 2 is used to form the major and minor diameter parallel sided holes. The tool D2 is then inserted into the upper major diameter portion with the arms 30 in the retracted condition and the nut assembly 37 is held by the tongs 41 while the arms 30 are extended to predetermined frustoconical configuration. The tool D2 is then rotated to abrade the wall of the hole to form the desired shape. In both cases swarf or like material is removed via the smaller diameter portion using a flushing liquid. The block is then subjected to the appropriate heat treatment to condition the block for use in the refractory environment. The anchor bolt is then inserted in the usual way and the block secured to the support wall. Settable material is then used to backfill the hole.

By virtue of the invention a preformed block consisting wholly of the required concrete has been made to a uniform degree of strength as a result of which there is no cracking. The required holes have then been drilled in the block by a machining action in a controlled way.

The dimensions of the hole may vary. For example, the frustoconical portion may make up a higher or lower proportion of the overall length of the hole from that shown; the cross-sectional area of the frustoconical portion may vary; and a parallel side portion may be present between the frustoconical portion and the parallel sided portion. The thickness of the blocks may also vary from say 102mm to say 305mm thick.

The block will usually be cast of a refractory concrete but it may instead be preformed of any material in which formation of the hole during manufacture of the block will lead to problems, e.g. shrinkage.

Claims (7)

1. A method of forming a generally frustoconical portion in a preformed generally parallel sided hole in an article, the method comprising inserting a tool to the intended depth in the hole, the hole having cutting elements which are carried on arms which are pivotably mounted on the tool, the arms being moveable between a retracted condition in which the arms are close together and an extended condition in which the arms are spaced apart in a generally conical shape, the tool being inserted into the hole with the arms in the retracted condition and the arms then being moved to the extended condition; rotating the tool to cause the cutting elements to remove wall material from the hole thereby to define the frustoconical portion; and then removing the tool.

2. A method according to Claim 1, wherein the preformed hole has a major diameter portion and an axially aligned minor diameter portion with a shoulder being formed at the union of the two portions and wherein the arms of the tool have cutting elements towards their free ends arranged so as to cut away and shape the shoulder while the frustoconical portion is being formed.

3. A tool for forming a generally frustoconical portion in a preformed generally parallel sided hole in an article, the tool comprising a spindle to engage a rotary drive; the spindle having a forward end on which is received a nut; the arms being pivotably mounted on the nut, the arms having cutting elements on their outer surfaces; and means for moving the arms from a retracted condition in which they are close together to an extended condition in which the free ends of the arms are spaced apart in a generally conical array.

4. A tool according to Claim 3, wherein the arms have additional cutting elements adjacent their free ends.

5. A tool according to Claim 3 or 4, wherein the cutting elements are made of abrasive material.

6. A tool according to any of Claims 3 to 5, wherein the spindle has a socket at its forward end to receive a shaft the free end of which is placed between the arms whereby the shaft is moveable axially and in a forward position urges the arms to the second condition where they are spaced apart.

7. A tool according to Claim 6, wherein the spindle includes an assembly arranged so as to advance the shaft while keeping the spindle stationary.