GB2190733A

GB2190733A - Clayware pipe manufacture

Info

Publication number: GB2190733A
Application number: GB08709085A
Authority: GB
Inventors: Peter Lindop Moulding; George Holdsworth Naylor
Original assignee: NAYLOR BROS
Current assignee: NAYLOR BROS
Priority date: 1986-05-19
Filing date: 1987-04-15
Publication date: 1987-11-25
Anticipated expiration: 2007-04-15
Also published as: GB8709085D0; GB2190733B; GB8612083D0

Abstract

Clayware pipes to be fired are conveyed longitudinally through the kiln on a series of driven rollers (12) extending transversely of the kiln, there being an induced draught passing through the kiln from the pipe outlet end to an extractor duct near its inlet end. The pipes are located by spacers 14 on the rollers. The spacers 14 may be angled or mutually offset on adjacent rollers to cause the pipes to rotate. Alternatively the axis of rotation of the rollers can be shown to make the pipes rotate. <IMAGE>

Description

SPECIFICATION Clayware pipe manufacture The invention relates to clayware pipe manufacture, and in particular to the manufacture of clayware pipes of the kind used as drainage or sewer pipes, cable ducts and the like, which are to be connected end to end by means of connecting sleeves. Such connecting sleeves commonly have resilient seals at their opposite ends which are adapted to embrace the ends of the clayware pipes and form watertight joints thereon. Consequently, so that leakage does not take place, and so that the connection of the sleeves can be effected quickly and easily, it is essential that the surfaces of the end portions of the pipes should be as smooth as possible and should be of the required circumference within close dimensional limits. It is also important that such pipes should be as straight as possible.

Heretofore, it has been known to manufacture clayware pipes by a process including the firing of groups of pipes carried through a tunnel kiln standing vertically on respective carriers. Small bore pipes have an inherent lack of stability in firing and when pyroplastic they often deform slightly and emerge as bent pipes. This method has also resulted in high energy costs because the carriers absorb heat which is subsequently wasted. Also because of the difficulty in maintaining consistent firing conditions at all places within the groups of pipes the strengths and dimensions of the finished pipes show substantial variability.

It has also been known to progress clayware pipes through a kiln on an endless conveyor and to cause the pipes to roll along a surface, so as to progress along the kiln, over at least that part of the length of the kiln in which the pipes are at their greatest temperature. However, this can cause scuffing of the surfaces of the pipes, coupled with the fact that the endless conveyor has again been the cause of substantial heat loss by carrying heat out of the kiln system and cooling down in an area where this lost energy cannot be recovered. In addition, the heat treatment of the pipes has not been consistent along the length of each pipe.

The object of the present invention is to provide a method of and means for the manufacture of clayware pipes, enabling the pipes to be fired consistently and economically whilst maintaining good straightness together with good surface finish and the required dimensional accuracy.

According to one aspect of the invention, there is provided a method of manufacture of clayware pipes, the method including the step of conveying the pipes longitudinally through a kiln on a series of driven rollers mounted for rotation about fixed axes which extend transversely of the direction of travel of the pipes so that an induced draught passing through the kiln to an extractor duct near its inlet end passes through and around the pipes whereby the pipes approaching the zone of highest temperature are heated partly by heat recovered from the fired pipes.The method may include the step of entering pre-heated unfired clayware pipes into the inlet end of the kiln in spaced groups of pipes and in this case each group of pipes will preferably be offset from the immediately preceding group by half the spacing of adjacent pipes in each group whereby the tendency for some of the pipes to progress faster than others along the rotating rollers of the kiln is limited by abutment of the leading ends of such pipes against the ends of a pair of pipes of the preceding group of pipes and the free circulation of the induced draught through and around the pipes is not significantly impaired. The step of maintaining the lateral spacing of the pipes in each group of pipes may be taken by providing spacers or guides on at least some of the driven rollers on which the groups of pipes are conveyed.The method may include the step of supporting the pipes on the spacers by means of which the spacing of the pipes in each group of pipes is maintained, each pipe being supported between inclined surfaces of successive pairs of spacers so that the dimensional accuracy of the pipes during their passage through the hottest zone of the kiln is maintained. The method may also include the step of causing the pipes to rotate through at least part of one turn about their longitudinal axes in at least part of the kiln to ensure consistency of heat treatment.

According to a further aspect of the invention, there is provided apparatus for the manufacture of clayware pipes, the apparatus including a kiln through which the pipes can be conveyed longitudinally on a series of driven rollers mounted for rotation about fixed axes which extend transversely of the direction of travel of the pipes through the kiln, at least some of the driven rollers having spacers by means of which the lateral spacing of the pipes can be maintained, there being provided means for inducing a draught passing through the kiln, in contraflow to the direction of travel of the pipes, to an extractor duct near its inlet end.Means may be provided for introducing the pipes into the kiln in spaced groups of pipes, and in this case may include means whereby the groups of pipes can be located in alternately offset positions so that during their passage through the kiln any tendency for some of the pipes to progress faster than others along the rotating rollers of the kiln is limited by abutment of the leading ends of such pipes against the ends of a pair of pipes of the preceding group of pipes. The apparatus may include a pre-heater for the pipes, external to the kiln, and a vestibule arrangement at the inlet end of the kiln, the vestibule having close coupled doors at its opposite ends, the arrangement being such that as one door opens the other closes so that the entry of the groups of pre-heated unfired pipes into the inlet end of the kiln does not interfere with the induced draught.Means may be provided for causing the pipes to rotate, through at least part of one turn, about their longitudinal axes, in at least a part of the kiln. In this case, such means may be constituted by the spacers which are provided on at least some of the driven rollers being progressively staggered longitudinally of the kiln so that the pipes are caused to roll sideways along parallel portions of the driven rollers as said pipes contact successive spacers.Alternatively, such means for causing the pipes to rotate about their longitudinal axes may be constituted by refractory fingers which act on the pipes and cause them to roll sideways along parallel portions of the driven rollers, or may be constituted by the driven rollers, in the at least part of the kiln in which rotation is to take place, being angled relative to the direction of travel of the pipes through the kiln, the spacers by means of which the lateral spacing of the pipes can be maintained then being arranged in rows extending along the length of the kiln and being large enough and sufficient in numbers to ensure that the pipes will progress in a direction longitudinal of the kiln.

in order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a semi-diagrammatic perspective view of apparatus embodying the invention for the manufacture of clayware pipes.

Figure 2 is a sectionai view on the line 2-2 in Figure 1, Figure 3 is a schematic plan view showing how the clayware pipes are conveyed through the apparatus, Figure 4 is a diagrammatic view of a vestibule arrangement and associated mechanism forming part of the apparatus in Figure 1, Figure 5 is a sectional view on the line 5-5 in Figure 4, Figure 6 is a view similar to Figure 2 which illustrates a possible modification which will be referred to, and Figures 7, 8 and 9 are views which illustrate further possible modifications.

Referring now in particular to Figure 1 of the drawings, the apparatus there illustrated for the manufacture of clayware pipes includes a kiln generally indicated 10 through which the pipes, arranged in spaced groups, can be conveyed longitudinally on a series of driven rollers 12. The driven rollers, which are relatively closely spaced (i.e. spaced only a few centimetres apart) are mounted for rotation about fixed axes which extend transversely of the direction of travel of the pipes through the kiln, and every fourth roller is provided with spacers 14 (see Figure 2) by means of which the lateral spacing of the pipes in each group of pipes can be maintained.

Burners (not shown) are provided within a firing zone of the kiln and means (not shown) which constantly monitor the temperature at closely spaced points along the length of the kiln control the operation of the burners so that the pipes are subjected to a temperature variation somewhat as shown diagrammatically above the kiln in Figure 1. Any deviation from the ideal temperature 'curve' results in an almost immediate response from the control system for the burners. Since the kiln is very well insulated and is of very low mass, and since the groups of pipes being fired are not conveyed on travelling carriers which would absorb heat, the burners are quickly able to correct any deviation from the ideal temperature 'curve'.

An extractor duct 16 is connected to the kiln very near its inlet end, as shown, and this produces an induced draught which passes through the kiln and out through the extractor duct as indicated by the arrows in Figure 1.

The induced draught passes through and around the pipes whereby the pipes approaching the zone of the highest temperature are heated partly by heat recovered from the fired pipes. The apparatus is therefore of good thermal efficiency. Also shown in Figure 1 is a socalled vestibule arrangement 'V' which communicates with the inlet end of the kiln and which will presently be described.

Referring now to Figure 3, it will be seen that the clayware pipes are conveyed through the kiln in spaced groups of pipes, each group of pipes being offset from the immediately preceding group by half the spacing of adjacent pipes in each group. In this way, the peculiar tendency for some of the pipes to progress slightly faster than others along the rotating rollers of the kiln is limited by the abutment of the leading ends of such pipes against the ends of a pair of pipes of the preceding group of pipes and the free circulation of the induced draught through and around the pipes is not significantly impaired.

This is important because fine control of the temperature to which the pipes are raised is vital for the maintenance of good surface finish and dimensional accuracy of the finished pipes. It will be understood that the open end portions of each pipe are, in effect, subjected to slightly different firing conditions than its intermediate length. Consequently, it would significantly affect the finished products if the pipes were able to abut end to end, and axially in line, because the firing conditions of the abutting end portions would be different from those of other pipes moving freely along the kiln.

Referring now in particular to Figures 4 and 5, these illustrate the vestibule arrangement and associated mechanism at the inlet end of the kiln, the vestibule, generally indicated 15, having close coupled doors 16 and 18 at its opposite ends. The doors are pivotally connected, as shown, to the opposite ends of a rocker member 20. The rocker member is pivotally mounted at 22 on a mounting bracket 24, and a lever 26 which is connected to the rocker member is powered by a pneumatic ram 28 pivotally mounted at 30.

The arrangement is such that as one door opens the other closes so that the entry of the groups of pre-heated unfired pipes into the vestibule 15, and their subsequent entry into the inlet end of the kiln does not interfere with the induced draught flowing through the kiln. The pipes are pre-heated before entering the vestibule to a temperature in excess of 100"C to ensure that virtually all the water in the clay mix of which the pipes have been extruded (in apparatus not shown) has been driven off. This is essential to guard against the pipes disintegrating when meeting the hot gases in the kiln.

It will be seen that, as drawn, there is a group of pre-heated unfired pipes in the vestibule 15, these being mounted on a set of rollers 32 similar to the driven rollers 12 on which the pipes progress through the kiln. At this time the door 16 is open and the door 18 is closed; the rollers 32 are driven at the same speed as the rollers 12 of the kiln so that the pre-heated pipes in the vestibule are advanced into the kiln at a rate which maintains their spacing from the immediately preceding group of pipes. When the trailing ends of the group of pipes being transferred from the vestibule has cleared the door 16, this is detected by means not shown and the pneumatic ram 28 is triggered into operation, closing the door 16 and opening the door 18.

When the door 18 has opened, this signals the need for a further group of pipes waiting outside the vestibule to be lifted on a dolly 34 and to be pushed into the vestibule. Means for lifting the dolly with the further group of pipes mounted on it are generally indicated 36. A pusher device 38 is shown to move from the position in which it is shown in full lines in Figure 4 to the position in which it is shown in chain-dotted lines to push said further group of pipes into the vestibule. The pusher device is located beneath a track 40 along which it is guided by rollers 42. The means by which it is powered are not shown.

The drive arrangement to the rollers 32 within the vestibule includes an overrunning clutch device (not shown) so that the further group of pipes can be entered quickly into the vestibule, that is to say at a rate substantially faster than the rate of travel at which they will presently be driven forwards by the rollers into the kiln. When the pusher device has then been retracted clear of the door 18, the pneumatic ram 28 is once more triggered into operation to cause the door 18 to close and the door 16 to open, and another feeding sequence commences. Because the pipes already in the kiln have moved away during the feeding sequence, the rollers in the vestibule turn faster for a short period of time (governed by a timer) and then revert to the same speed as the kiln rollers. Thus the timer determines the spacings between successive groups of pipes.

The means whereby the groups of unfired pipes can be entered into the vestibule arrangement, and subsequently into the kiln, in alternately offset positions are illustrated in Figure 5. These means are constituted by a hydraulic ram 44 which can move an upstanding guide track 46 between alternative positions, as shown. A guide roller 48 which engages the guide track thus positions the dolly 34, on which the groups of unfired pipes are mounted, at an appropriate location on a carrier 50. As shown, the dolly is mounted on the carrier by pairs of rollers 52 for lateral adjustment thereon. The means 36 previously referred to for lifting the dolly with the further group of pipes mounted on it are constituted by pairs of bell crank levers 54 mounted for pivotal movement about respective shafts 56.

The bell crank levers are operated simultaneously by means of a hydraulic ram 58 acting against a push rod 60 and lever 62. The bell crank levers are linked together for simultaneous movement by further push rods 64.

Upstanding arms of the bell crank levers are pivotally connected, as shown, beneath the carried on which the dolly is mounted.

Thus there is provided a method of and means for the manufacture of clayware pipes which enables the pipes to be fired consistently and economically whilst maintaining straightness, good surface finish and the required dimensional accuracy. However, various modifications may be made. For example, it may be found advantageous to provide every one of the driven rollers which extend transversely of the direction of travel of the pipes through the kiln with spacers 14 by means of which the lateral spacing of the pipes in each group of pipes can be maintained. Furthermore, in this case it may also be found advantageous to increase the diameters of the spacers so that, as shown in Figures 6, each pipe is supported between inclined surfaces of successive pairs of spacers.

In this way the dimensional accuracy of the pipes during their passage through the hottest zone of the kiln will be maintained. It will also be understood that the optimum spacing of the driven rollers may be determined by trial and experiment.

The optimum spacing between successive groups of pipes being entered into the kiln may also be determined by trial and experiment. Indeed it may be found that provided each group of pipes is offset from the imme diately preceding group, as described, it is not essential to space the successive groups of pipes. Conversely, if the group of pipes were sufficiently spaced to ensure that individual pipes could never catch up with the pipes preceding them, there may be no need to laterally offset the groups of pipes in the manner described.

Referring now to Figure 7 of the drawings, this illustrates a possible modification which may be made in an attempt to ensure even better consistency of heat treatment. The modification involves the spacers 14 (which are of a diameter and spacing such that the pipes are supported by the parallel portions of the driven rollers 12 between them) being progressively staggered, as viewed longitudinally of the kiln, so that the pipes are caused to roll sideways along the parallel portions of the driven rollers as said pipes contact successive spacers. Such staggering of the spacers may extend along only part of the length of the kiln, for example along the firing zone only.

Due to space limitations, the amount of lateral rolling of the pipes as they progress longitudinally along the kiln may be very limited, but nevertheiess be sufficient to avoid uneven heat treatment. Each pipe may roll in only one direction. On the other hand, each pipe may be arranged to roll towards one side and then back again.

In Figure 8 there is illustrated a further possible modification which may be made to obtain the same end result of lateral rolling of the pipes to effect even better consistency of heat treatment, this involving the provision of refractory fingers 66 within at least the firing zone of the kiln, said fingers being arranged to act on the pipes to cause them to roll sideways. This again requires a sufficient length of parallel guide roller between each co-operating pair of spacers to enable the pipes to roll sideways.

In Figure 9 (which is a purely diagrammatic plan view illustrating an arrangement of driven rollers 12 closely spaced apart along at least the firing zone of the kiln) the rollers are shown to be slightly angled relative to the direction of travel of the pipes through the kiln. However, the spacers 14 by means of which the lateral spacing of the pipes can be maintained are arranged in rows extending along the length of the kiln and they are large enough and sufficient in numbers along the length of the kiln to ensure that the pipes will progress in a direction longitudinal of the kiln.

The result is that throughout their movement along the length of the kiln in which the driven rollers are inclined, the pipes will undergo a rotational movement as they progress axially.

Claims

1. A method of manufacture of clayware pipes, the method including the step of conveying the pipes longitudinally through a kiln on a series of driven rollers mounted for rotation about fixed axes which extend transversely of the direction of travel of the pipes so that an induced draught passing through the kiln to an extractor duct near its inlet end passes through and around the pipes whereby approaching the zone of highest temperature are heated partly by heat recovered from the fired pipes.

2. The method according to claim 1, including the step of entering pre-heated unfired clayware pipes into the inlet end of the kiln in spaced groups of pipes.

3. The method according to claim 2, in which each group of pipes is offset from the immediately preceding group by half the spacing of adjacent pipes in each group whereby the tendency for some of the pipes to progress faster than others along the rotating rollers of the kiln is limited by abutment of the leading ends of such pipes against the ends of a pair of pipes of the preceding group of pipes and the free circulation of the induced draught through and around the pipes is not significantly impaired.

4. The method according to either one of claims 2 and 3, in which the step of maintaining the lateral spacing of the pipes in each group of pipes is taken by providing spacers or guides on at least some of the driven rollers on which the groups of pipes are conveyed.

5. The method according to claim 4, including the step of supporting the pipes on the spacers by means of which the spacing of the pipes in each group of pipes is maintained, each pipe being supported between inclined surfaces of successive pairs of spacers so that the dimensional accuracy of the pipes during their passage through the hottest zone of the kiln will be maintained.

6. The method according to any one of the preceding claims, including the step of causing the pipes to rotate through at least part of one turn about their longitudinal axes in at least part of the kiln to ensure consistency of heat treatment.

7. Apparatus for the manufacture of clayware pipes, the apparatus including a kiln through which the pipes can be conveyed longitudinally on a series of driven rollers mounted for rotation about fixed axes which extend transversely of the direction of travel of the pipes through the kiln, at least some of the driven rollers having spacers by means of which the lateral spacing of the pipes can be maintained, there being provided means for inducing a draught passing through the kiln, in contraflow to the direction of travel of the pipes, to an extractor duct near its inlet end.

8. Apparatus according to claim 7, in which means are provided for introducing the pipes into the kiln in spaced groups of pipes.

9. Apparatus according to claim 8, in which the means provided for introducing the pipes into the kiln in spaced groups of pipes include means whereby the groups of pipes can be located in alternately offset positions so that during their passage through the kiln any tendency for some of the pipes to progress faster than others along the rotating rollers of the kiln is limited by abutment of the leading ends of such pipes against the ends of a pair of pipes of the preceding group of pipes.

10. Apparatus according to either one of claims 8 and 9, including a pre-heater for the pipes, external to the kiln, and a vestibule arrangement at the inlet end of the kiln, the vestibule having close coupled doors at its opposite ends, the arrangement being such that as one door opens the other closes so that the entry of the groups of pre-heated unfired pipes into the inlet end of the kiln does not interfere with the induced draught.

11. Apparatus according to any one of claims 7 to 10, in which means are provided for causing the pipes to rotate, through at least part of one turn, about their longitudinal axes, in at least a part of the kiln.

12. Apparatus according to claim 11, in which the means provided for causing the pipes to rotate about their longitudinal axes are constituted by the spacers which are provided on at least some of the driven rollers, said spacers being progressively staggered longitudinally of the kiln so that the pipes are caused to roll sideways along parallel portions of the driven rollers as said pipes contact successive spacers.

13. Apparatus according to claim 11, in which the means provided for causing the pipes to rotate about their longitudinal axes are constituted by refractory fingers which act on the pipes and cause them to roll sideways along parallel portions of the driven rollers.

14. Apparatus according to claim 11, in which the means provided for causing the pipes to rotate about their longitudinal axes are constituted by the driven rollers, in the at least part of the kiln in which rotation is to take place, being angled relative to the direction of travel of the pipes through the kiln, the spacers by means of which the lateral spacing of the pipes can be maintained being arranged in rows extending along the length of the kiln and being large enough and sufficient in numbers to ensure that the pipes will progress in a direction longitudinal of the kiln.

15. Apparatus for the manufacture of clayware pipes, the apparatus being constructed, arranged and adapted to operate with reference to Figures 1 to 5 or Figure 7 or Figure 8 or Figure 9 of the accompanying drawings.