GB2181209A - Drive gear particularly for conveying systems used in chemical processing - Google Patents

Abstract

In a parallel roller conveying system intended for use in chemical processing carried out at an elevated temperature, wherein the rollers are driven by a layshaft (9) via mating pinions provided respectively at the end (10) of each roller and on the layshaft, each pinion is made of a ceramic material (e.g. of 95% Aluminium), preferably by moulding. In a preferred form, the pinions are each formed with teeth (1) having straight driving faces (2) which taper towards each other, the roots and tips of the teeth being rounded off, the rear face (3) of the teeth is substantially perpendicular to the pinion axis, and the front face (4) is angled with respect to said axis so as to taper inwardly towards the tips of the pinion teeth. In use, a pair of such pinions are set normal to each other and intermesh on their driving faces (2) at a point near to their respective tips and with the angled front faces (4) facing towards each other. <IMAGE>

Description

SPECIFICATION Drive gears particularly for conveying systems used in chemical processing This invention relates two drive gears for conveying systems, particularly for use in chemical processing carried out at an elevated temperature, e.g. an etching process used in the manufacture of printed circuit boards.

In the manufacture of printed circuit boards, it is normal practice to feed the boards through a series of processing machines via a conveyor system, the process steps including resist stripping, precleaning, etching, neutralising, water rinsing and drying. The conveying system is generally oftheform of a series of rollers spaced through the machines, arranged parallel to each other, normal to the conveying direction. The rollers are driven bya layshaftvia a bevel gearcomprisingapinion provided atone common driven end of each roller arranged to mesh with a mating pinion appropriately located on the layshaft which extends in the conveying direction.Where the conveyor crosses between adjacent processing machines, each machine is provided with a layshaft and these are either appropriately coupled together so thatthey are all driven by a single drive motor, or each is provided with its own drive motor, in which case the motors must be arranged to be driven at substantially the same speeds.

Problems have arisen for manyyearswith such conveying systems, particularly where they pass through the etching process. This is because etching is carried out at elevated temperatures, e.g. 120 1300F.,which can cause the etching machinetowarp along its length with continued use. Also, the abrasive nature ofthe etchants, e.g. ferric chloride, alkaline ammonia and cupric chloride, cause rapid wear of the pinions, which latter up to present have been of a thermo-setting plastics.Furthermore, due to sludge build-up, caused by the dissolving action ofthe etchant on the copper ofthe printed circuit boards passing therethrough, with bevel gear pinions of normal design there is a tendencyforthe sludge to be compressed into the roots between the gearteeth, which eventually can force the meshing pinions apart.Asa result ofthis latter problem, pinionswith teeth in the form of individual, radially extending pins have been used, the pins being arranged so that they intermesh normal to each other with large root clearances so that there is no tendency to compress sludge into the root spaces between the pins.

An object of the invention is to provide an improved pinionforsuch bevel gears which is notaffected by chemically abrasive fluids, or elevated temperatures, and also to provide a layshaft drive arran gementfora conveyor system utilising such pinions, where the drive is unaffected by misalignments due to warping, etc.

According to this invention, such a pinion is characterised by being made of a ceramic material, preferably by moulding.

A particularly suitable material is that known by the trade reference ULSOl ,this ceramic of 95% Alumina is manufactured by Wade (Advanced Ceramics) Ltd.

To obtain efficient meshing, the teeth of the pinions are each formed with straight driving faces which taper towards each other, the roots and tips of the teeth being rounded off. One, rearface ofthe pinion teeth issubstantiallyperpendiculartothe pinion axis, whilst the other, frontface is angled with respect to said axis so as to taper inwardlytowards the tips of the pinion teeth. With such a pinion form, when used in bevel gear, a pair of such pinions are set normal to each other and arranged to intermesh on their driving faces art a point neartotheirrespect- ivetips and with the angled front faces ofthe pinions facing towards each other.

According to a feature of the invention, when used in a layshaftdrivearrangementforconveyorrollers, the pinions each are provided with a hub having a bore shaped to be non-rotatably mounted on the drive layshaftand each common driven shaft end of the conveyor rollers, the pinionsthus being interchangeable between the drive and driven shafts.

Preferably, the layshaft is of stock size hexagon bar and the driven shaft ends ofthe conveyor rollers are machined to suit.

In orderthatthe invention may be readily understood, one embodiment of layshaft drive shaft, bevel geararrangementforthe conveying system of an etching machine will now be described with refer encetotheaccompanying drawings, in which Figure 1 is an elevation ofthe pinion forthe bevel gear in accordance with the invention.

Figure la is a cross-section through a pinion tooth on the line la-ia, Figure2 is a plan view showing the layshaftgear arrangement using two pin ions in accordance with Figure 1 arranged as a bevel gear, and Figure 3 is a fragmentary view showing a flexible supportsforthe layshaft, and, Figure4isan elevation ofthearrangementshown by Figure 2.

Referring to Figure 1, the pinion is moulded from ceramic material, such as that sold byWade mentioned hereinbefore, and comprises teeth 1 which have straight driving faces 2. These faces taper tow ards each other and are radiussed at the tips and roots as shown. Referring now also to Figure 2, one rear face 3 of the pinion is normal to the pinion axis, whilstthe otherfrontface 4 is at an angle to the axis and tapers towards the teeth tips. Atypical crosssection through a tooth 1 is shown in Figure 1 a. The pinion has a hub 5 having rear and front faces 6,7 normal to the pinion axis and defining a central hexagonal bore 8. The dimension ofthe bore 8 is chosen to be a sliding fit over a hexagonal bar of appropriate stock size, which is conveniently used as the layshaft 9 (see also Figure 3) and the common driven ends 10 ofthe conveyor rollers 11 are machined to the same size so that the pinions are interchangeable.

As evident from Figure 2, when arranged as a bevel gear, the pinions mesh towards the tips of theirteeth.

Furthermore, the angled front faces 4 of the pinions, in use, tend to urgethepinionsawayfromeach other. Because ofthis, it is not essential to directlyfix the pinions onto the layshaft 9. Instead, they can be slidably mounted on their respective shafts and be axially set in their meshing positions by suitably loc atedpins(orcirclips) 12.Thisenablesthepinionsto tiltwithin thetolerance oftheir bores 8 on the layshaft 9 and thereby axially corrector any small changes in positional relationship between the driving and driven pinions due, for example, to warping or bowing ofthe etching machine in use.Furthermore, to accommodate for any misalignment along the length ofthe machine due to such warping or bowing, the layshaft 9 is supported in flexible supports comprising bearing blocks 13 which allow a de- gree of lateral movement of the layshaft. Thus, refer ingalsoto Figure 3, each bearing block has a journal bore 14to accommodate a bearing race 15, the bore 16 of which accommodates the layshaft via resilient packing 17.

In accordance with the invention, the Applicants have found, unexpectedly, that a moulding of ceramic material particularly when in the form described above, can provide sufficient strength to be used in a conveying system for an etching machine. Thus, the excellent characteristics of ceramic in resisting temperature and corrosive attack enable such pinions to be used with considerable advantage since, by such use, long standing problems have been overcome.

Claims (6)

1. Drive Gearfor a conveying system intended for use in chemical processing carried out at an elevated temperature, the conveying system being generally oftheform of a series of spaced rollers arranged parallel to each other, normal to the conveying direction, the rollers being arranged to be driven by a layshaft which extends in the conveying direction via a bevel gear comprising a pinion provided atone common driven end of each roller which meshes with a mating pinion appropriately located on the layshaft, characterised in that each pinion is made of a ceramic material, preferably by moulding.

2. Drive Gear according to Claim 1, characterised in that said ceramic material comprises 95% Alumina.

3. Drive Gearaccordingto Claim 1, characterised in thatthe pinions are each formed with teeth having straight driving faces which taper towards each other, the roots and tips oftheteeth being rounded off, and in that one rearface ofthe pinion teeth is substantially perpendicularto the pinion axis, whilst the otherfrontface is angled with respect to said axis so as to taper inwardly towards the tips of the pinion teeth, the arrangement being such that when used in said bevel gear, a pair of such pinions are set normal to each other and arranged to intermesh on their driving faces at a point near to their respective tips and with the angled front faces of the pinionsfacing towards each other.

4. Drive Gear according to Claim 3, characterised in thatthe pinions are each provided with a hub hav ing a bore shaped so that it can be non-rotatably mounted on said layshaft and each common driven shaft end ofthe conveyor rollers, the pinionsthus being interchangeable between the drive and driven shafts.

5. Drive Gear according to Claim 4, characterised in that the layshaft is of stock size hexagon bar and the driven shaft ends of the conveyor rollers are machined to suit.

6. Drive gear for a conveying system intended for use in chemical processing carried out at elevated temperature constructed arranged and adapted for use substantially as herein before described with re ference to, and as such in, the accompanying drawing.