GB2236704A - Extruding polygonal clay pavior section having discontinuous spacing nibs - Google Patents

Abstract

The apparatus comprises an extruder die (1) that in cross-section has flat faces (2 to 5, Fig 1) corresponding to the side faces of the pavior and that has a groove (7 to 10) formed in at least one of the flat faces, and extending the full length of that face parallel to the axis of extrusion. A wheel (11 to 14) associated with each groove upstream or downstream of its outlet, has a periphery formed with a plurality of circumferentially spaced teeth (24) each having a radial height substantially equal to the depth of the groove, and is mounted for rotation, preferably freely, so that the teeth periodically occlude the groove or the projection of the groove parallel to the axis of extrusion, to form the discontinuous spacing nibs (55, 56, 57) along sides of the paviours (51), formed by cutting transversely of the extruded paviour section, and optionally chamfering of the pavior upper edges. <IMAGE>

Description

APPARATUS FOR MANUFACTURINC CLAY PAVIORS This invention relates to apparatus for manufacturing polygonal clay paviors. Such paviors may be laid in irregular array to from a ground surface such as, for example, a pavement. When so laid they are usually spaced apart by a small distance during laying, and vibration is applied to settle and bed the paviors in place. Adjacent paviors have flat side faces, and it is known to provide nibs on those side faces to assist in proper spacing of the paviors and also to avoid damage to the body of each pavior during the vibration operation.

GB-2187130A discloses paviors having spacing nibs on side faces thereof, the nibs extending for less that the full height of the side face, together with a method and apparatus for manufacturing such paviors. The preseent invention is concerned with an improved apparatus fot--use in the method of this earlier application.

According to the invention apparatus for use in the manufacture of polygonal clay paviors, each pavior having a plurality of side faces at least one of which has a spacing nib thereon, comprises an extruder having a die that in cross-section has flat faces corresponding to the side faces of the pavior and that has a groove formed in at least one of the flat faces, the groove extending the full length of that face parallel to the axis of extrusion, a wheel having a periphery formed with a plurality of circumferencially spaced teeth each having a radial height substantially equal to the depth of the groove in the die, and mounting means externally of the die mounting the wheel for rotation so that the teeth periodically occlude the groove or the projection of the groove parallel to the axis of extrusion.

It will be seen that as a column of clay emerges from the extruder the teeth of the wheel intermittently interrupt the flow of clay from the groove, with the result that intermittent nibs are formed along the edge of the column. Individual paviors are then cut from the extruded column by cutting substantially transversely of the column, the frequency of cutting being related to the frequency of occurence of nibs on the column, so that each individual pavior has at least one spacing nib on a side face thereof, the nib extending for less that the full height of the side face.

It is, of course, necessary that the groove extends the full axial length of the die face in order that the nibs, once formed, are not thereafter destroyed. Those regions of the clay strip where nibs are excluded due to the action of the teeth of the wheel will tend to recover, and accordingly it is preferred that the wheel be positioned close to the downstream end of the die in order to limit the amount of recovery that can occur.

Preferably the wheel is freely rotatable about its axis, so that it is simply caused to rotate by movement of the extruded column of clay. It would be possible to provide positive drive means for the wheel, but this would be significantly more complicated.

Preferably the cross-section of the groove in a plane perpendicular to the axis of extrusion comprises a base wall parallel to the flat face of the die in which the groove is formed and two spaced side walls each substantially perpendicular to the base wall, and the axis of rotation of the wheel is substantially perpendicular to the axis of extrusion and to the side walls of the groove.

Other groove configurations and wheel positions are possible, but the preferred arrangement produces nibs of an ideal substantially rectangular form.

In one embodiment of the invention the teeth of the wheel occlude the groove upstream of the end of the groove, and the width of each tooth is substantially equal to the width of the groove. As already stated, however, the occlusion should occur not too far upstream of the end of the groove, in order to prevent significant recovery of the clay.

In an alternative embodiment the teeth of the wheel occlude the projection of the groove downstream of the end of the groove along the axis of extrusion, and the width of each tooth is greater than the width of the groove. This arrangement may result in cleaner definition of the individual nibs.

Preferably the facing flanks of two adjacent teeth converge radically inwardly of the wheel. This results in substantially trapezoidal nibs, but it does improve clean release of the wheel from the surface of the clay.

Usually a plurality of side faces of the pavior will be provided with nibs, and for such manufacture a plurality of flat faces of the die will each be formed with at least one groove, a toothed wheel being associated with each groove. The wheels may be the same or different, so that similar or different nib arrangements may be present on different faces of the pavior.

A embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig 1 is a transverse cross-section through an extrusion die; Fig 2 is a partial section on the line II of Fig 1; Fig 3 is a schematic representation of an extruded column of clay; Fig 4 shows a finished pavior cut from the column.

Referring to Fig 1 this shows a die head 1, for fitting to an extruder, and designed for the manufacture of rectangular clay paviors. The die head defines a clay passage having opposed upper and lower faces 2, 3 and opposed side faces 4, 5, each opening into the downstream face 6 of the die. The upper face 2 of the die is formed with two grooves 7, 8, each extending substantially the full length of the die. Similarly, each end face 4 and 5 has a groove 9, 10 respectively. The axes of all four grooves 7 to 10 are parallel to the axis of extrusion.

Each groove has associated therewith a wheel 11 to 14 respectively. Each wheel, and the mounting thereof, is identical, and only wheel 11 will be described in detail.

Wheel 11 is mounted for rotation by a bearing 15 mounted on a shaft 16 supported by brackets 17 and 18 secured to the external face of the die. The shaft extends through sleeves 19, 20 welded to the brackets, and is held in position by a pin inserted through a transverse hole 21.

Part of the end of the die is cut away to form an arcuate section 22 which intercepts the groove 7, and part of the circumference of the wheel 11 is received in the cut away section. The wheel has a periphery 23 that is formed with a plurality of circumferentially spaced teeth 24, spaced apart My any suitable angle. Angles of 100 and 200 have been found suitable, although other angles may, of course, be used. Each tooth has a radial height r that is substantially equal to the depth d of the groove. The facing flanks 25, 26 of each pair of adjacent teeth converge radially inwardly of the wheel, so that the groove formed between those teeth is substantially trapezoidal.

The junctions 27, 28 between the flanks of teeth and the base of the groove are desirably slightly radiused.

The wheels may be made of any suitable material, for example mild steel. However, it is preferred that at least the outer periphery and the teeth of the wheel are formed from a more wear-resistant material, such as tungsten carbide. When a wheel does become worn, replacement is effected very simply by removing the pin 21 and shaft 16 and lifting the wheel and its bearing out of position, substituting a fresh wheel and bearing therefor.

Operation of the apparatus will be evident. As a column of clay is extruded from the die the clay engages the wheel and causes this to rotate. As the wheel rotates the teeth periodically occlude the projection of the groove parallel to the axis of extrusion, so excluding rib formation. The result is to form a series of spaced nibs 30 on the extruded column 31. The lengths of the nibs formed on the column of clay, and the frequency of those nibs is ditated by the arrangement of the teeth on the wheel.

Fig 3 shows a column of clay as extruded. The column 31 has two axial rows of nibs 30, 32 on its upper surface, and single rows of similar nibs such as 33, on each of its two side surfaces. The lower surface 34 by way of which the strip rests on a conveyor moving it from the extruder is smooth. It will readily be seen that by cutting the strip along planes indicated by broken lines in Fig 3 sections are formed that may be fired to form individual paviors. In addition to cutting the individual paviors from the column a chamfering step may also be performed, either simultaneously with the cutting step, or in advance of the cutting step. The chamfering will desirably be on all four side of the strip. Fig 4 shows a pavior that has been formed by cutting and chamfering the strip shown in Fig 3. The pavior has an upper face 51, end faces 52a, 52b, side faces 53a, 53b and a lower face 54.Nibs such as 55 are provided on each end face 52 and nibs 56, 57 are provided on side face 53a. The nibs are arranged so that when a number of identical paviors are placed in an array, the nibs will space adjacent paviors apart but cannot coincide. The nibs form regions at which abrasive load is taken during vibratory bedding of the pavior, but the fact that the nibs do not extend the full height of the pavior neans that they will not significantly prevent sideways vibration of keying material between the paviors.

The foregoing description has been only of one particular type of apparatus which may be used in carrying our the invention. The brackets 17, 18 are illustrated as being welded to the external face of the die, but it may be preferable to bolt these brackets to that external face.

When there is a bolted connection shims may be inserted between the brackets and the die in order to ensure the correct relationship of the wheel to the die. The wheel shown in the drawings is slightly narrower than the groove 7, the width of the cutout section 22 being equal to the width of the groove. However, it is possible to make the cutout 22 wider than the groove, and also to make at least the teeth of the wheel wider than the groove. This will help to flatten any slightly raised edges of the clay column that may extend between adjacent nibs.

The wheels are shown located at the ends of the grooves in the die, but it is possible to continue the die (with the grooves) for a short distance beyond the wheel.

If required, a cleaning device may. be associated with each wheel, although in practice it is found that the tapered flanks /25, 26 and radiused junctions 28, 29 promote a clean release of the teeth from the clay column.

Other modifications will be apparent.

Claims (8)

1. Apparatus for use in the manufacture of polygonal qlay pavers, each paver having a plurality of side faces at least one of which has a spacing nib thereon, the apparatus comprising an extruder having a die that in cross-sectionKhas flat faces corresponding to the side faces of the paver and that has a groove formed in at least one of the flat faces, the groove extending the full length of that face parallel to the axis of extrusion, a wheel mounted externally of the dif, the wheel having a periphery formed with a plurality of circumferentially spaced teeth each having a radial height substantially equal to the depth of the groove in the die, and means mounting the wheel for rotation so that the teeth periodically occlude the groove or the projection of the groove parallel to the axis of extrusion.

2. Apparatus according todaim 1 in which the wheel is freely rotatable about its axis.

3. Apparatus according tp claim 1 or claim 2 in which the cross-section of the groove in a plane perpendicular to the axis of extrusion comprises a base wall parallel to the flat face of the die -in which the groove is formed and two spaced side walls each substantially perpesdicular to the base wall, and the axis of rotation of the wheel is substantially perpendicular to the axis of extrusion and to the side walls of the groove.

4. Apparatus according to any one of the preceding claims in which the teeth of the wheel occlude the groove upstream of the end of the groove, and the width of each tooth is substantially equal to the width of the groove.

5. Apparatus according to any one of claim 1 to 4 in which the teeth of the wheel occlude the projection of the groove downstream of the end of the groove along the axis of extrusion, and the width of each tooth is greater than the width of the groove.

6. Apparatus according to any one of the preceding claims in which the facing flanks of two adjacent teeth converge radially inwardly of the wheel.

7. Apparatus according to any one of the preceding claims in which a plurality of flat faces of the die are each formed with at least one groove, and a toothed wheel is associated with each groove.

8. Apparatus for use in the manufacture of polygonal clay pavers, substantially as herein described with reference to the accompanying drawings.