WO2017069625A1

WO2017069625A1 - Method for manufacturing at least a part of a ring gear, and ring gear

Info

Publication number: WO2017069625A1
Application number: PCT/NL2016/050723
Authority: WO
Inventors: Dirk Hubert Petrus VAN DER WEGEN
Original assignee: Holwegen Tilburg B.V.
Priority date: 2015-10-23
Filing date: 2016-10-21
Publication date: 2017-04-27
Also published as: NL2015647B1

Abstract

The invention relates to a method for manufacturing a ring gear (2). The invention also relates to a ring gear (2) obtained by applying the method according to the invention. In addition, the invention relates to a gearbox comprising a ring gear (2) according to the invention. The invention moreover relates to a rotatable drum (23), preferably for use as rotatable oven or rotatable grinding mill, comprising: a frame, an axially rotatable drum housing (23) supported by the frame, at least one ring gear (2) according to the invention, connected to the drum housing (23) and at least one drive (24) co-acting with the at least one ring gear (2) for axially rotating the drum housing (23).

Description

Method for manufacturing at least a part of a ring gear, and ring gear

The invention relates to a method for manufacturing at least a part of a ring gear. The invention also relates to a ring gear component obtained by applying the method according to the invention. The invention further relates to a ring gear obtained by applying the method according to the invention. In addition, the invention relates to an assembly of a ring gear according to the invention and at least one pinion configured to co-act with the ring gear. The invention moreover relates to a rotatable drum comprising a ring gear according to the invention. The invention subsequently relates to a device for manufacturing a part of a ring gear according to the invention.

In heavy industry, such as the mining industry and the cement industry, heavy rotatable drum-shaped installations, referred to in short as rotatable drums, are used among other things to make (mined) materials suitable for further processing. The rotatable drums can for instance serve here as oven, dryer and/or as grinding mill. Each rotatable drum comprises here a housing which can be driven by applying a so-called open gear drive. The open gear drive comprises here at least one ring gear, formed by an annular gear with an external toothing which is mounted on the housing, and a pinion co-acting with the ring gear. The pinion is directly or indirectly coupled to a motor here. Motor driving of the pinion results in rotation of the ring gear and thereby of the housing. In such mills the ring gears which are used have a typical diameter of several metres.

Open gear drives are usually explained according to the applicable AGMA standards (American Gear Manufacturers Association) or DIN standards. The AGMA standards in particular stress the hardness of the material of the ring gear. Increasingly greater hardness is aimed for.

The ring gears were in the past usually manufactured from cast steel (such as

G.35CrMo4 or G.35CrNiMo6.6). Later, the use of nodular cast iron (such as EN-GJS- 700) increasingly superseded traditional cast steel in various applications. Examples hereof are semi-autogenous and autogenous grinding mills, also referred to as SAG and AG mills, which are typically used in the mining industry. Nodular cast iron however has little elongation and is not resistant to impact loads, so that it is still necessary to fall back on (cast) steel in a great number of applications. The casting of ring gears from cast steel is a difficult process. Expensive (wood or Styropor) models need first be made, while the products are often cast only once. The casting of cast steel is accompanied by many quality problems. The relatively heavy toothing part thus cools much more slowly than the relatively light inner side, often resulting in (shrinkage) cracks. Large risers, which are later removed from the casting, are cast in order to avoid impurities in the final product. This means a great loss of material and energy. Despite all experience and technology, blowholes, (shrinkage) cracks and other imperfections often result in the final casting, which have to be ground out and welded following written permission from the client. A new heat treatment then has to take place. All in all, the process is very time-consuming, and stable production is not possible. Higher Brinell hardnesses (H_B) in the order of magnitude of 300-310 can moreover only be achieved by means of additional heat treatments and cooling in liquid. This however causes a greatly increased risk of cracking. Manufacturing (heavy) ring gears from cast steel is therefore expensive, time-consuming, and the final quality is often mediocre.

Compared to cast steel, nodular cast iron is considerably simpler to use. The casting process in use of nodular cast iron is more predictable and easier to control. Cracks are almost always cut off very quickly, and cannot continue, as a result of the graphite particles present in nodular cast iron. It is therefore readily possible to cast a high- quality casting with reasonably great certainty. Expensive models however also need to be made in the case of nodular cast iron. Large risers, which have to be removed from the casting later by machine, are additionally also cast, this resulting in additional costs. A further drawback of nodular cast iron is that a great hardness is not compatible with the elongation. The loss of elongation with greater hardness ensures that impact loads can lead directly to cracking of the material, making nodular cast iron unsuitable for some applications. A first object of the invention is to provide an improved production process for manufacturing at least a part of a ring gear.

A second object of the invention is to provide an improved production process for manufacturing at least a part of a ring gear without using casting materials. At least one of the above stated objects can be achieved by providing a method of the type stated in the preamble, comprising the steps of: A) providing at least one annular and/or arcuate forged basic component with a first diameter, and B) bending outward each basic component into an arcuate ring gear segment with a second diameter, wherein the second diameter is greater than the first diameter. Steps A) and B) of the method according to the invention are aimed at manufacturing one or more ring gear segments by bending outward one or more forged basic components. The ring gear segments formed by means of steps A) and B) of the method according to the invention can then be processed further and be mutually coupled, thus forming a ring gear, which is further described in the following. The method according to the invention has a number of advantages. Because the basic components provided during step A) are forged instead of cast, these basic components can be provided in relatively simple and inexpensive manner, wherein the forged basic components are moreover practically always completely solid and thus comprise no (core) cavities, this having a beneficial effect on a desired constant and high quality, defined inter alia by the material hardness. A further advantage of using a forged starting material compared to a cast starting material is that a forged material is better suited to being welded. In addition to the starting material being more advantageous than cast steel or cast iron, the method according to the invention has the additional advantages that the forged basic components used have a sharper curvature than the ring gear segments to be formed on the basis of these basic components. This has on the one hand the logistical and economic advantage that the basic components can be transported and stored more easily. This has on the other hand the technical advantage that bending outward of the basic components to form the ring gear segments results in a thickening of material on an outer peripheral edge (outer periphery) of the ring gear segments, and thereby of the ring gear as such, this resulting in a further improvement of the good mechanical properties of the outer periphery of the formed ring gear segments in particular, and thereby of the ring gear to be finally formed as such. The toothing of the ring gear will otherwise generally be arranged in the above stated outer peripheral edge, this resulting in a relatively high load-bearing capacity of the toothing and thereby of the ring gear as such. Forming the ring gear segments with a relatively large second diameter on the basis of basic components with a relatively small first diameter, typically between 1 and 10 metres, has the additional advantage that use is made of annular (or arcuate) (standard) basic components, which are generally particularly widely available on the market at a relatively low cost price and which are moreover of relatively compact nature, which has a beneficial effect on transport and storage. Ring gears with different diameters can be manufactured in relatively simple manner on the basis of the

(standard) basic components. A plurality of forged basic components will generally be provided during step A). Providing can be understood to mean both purchasing and/or manufacturing. The applied basic components are preferably identical, which is most efficient from a practical viewpoint. It is however possible to envisage different kinds or types of basic component being provided during step A) of the method according to the invention, wherein the (first) diameters of the different basic components can differ from each other. In this latter case the applied - mutually differing - first diameters of the different basic components are however smaller than the second diameter of the ring gear (with external toothing) to be manufactured, so that the above stated technical advantage associated with the bending outward of the basic components remains guaranteed. As stated, a basic component can be arcuate or annular. An annular basic component has a closed (continuous) annular or circular body and, from a three- dimensional viewpoint, generally a (flat) hollow cylindrical body, while an arcuate basic component has a finite circle segment-shaped geometry and, from a three- dimensional viewpoint, generally has a (flat) hollow cylinder segment- shaped body. The height of the basic components generally lies between 10 and 150 centimetres. The wall thickness of the basic component generally lies between 2 and 25 centimetres. The diameters (and associated curvatures) of an annular basic component and an (other) arcuate basic component can be identical herein. It is however also possible to envisage oval, elliptical or other non-circular ring gears being desired for determined

applications, whereby such varying forms can also be taken into consideration during the bending outward of basic components as according to step B). The basic

components preferably have a rectangular and optionally square geometry in cross- section (section along a longitudinal plane), which considerably facilitates the processing of the basic components into a ring gear as compared to the situation in which the basic components were to have a round cross-section.

The ring gear manufactured by means of the method according to the invention is intended particularly, though not exclusively, to be applied in heavy industry, such as the cement industry and the mining industry, as part of a drive of an axially rotatable mill housing, as already noted in the preamble of this patent publication. For application of the ring gear in such heavy equipment the diameter of the ring gear is advantageously sufficiently large, and it is moreover advantageous that use is preferably made of a limited number of basic components to manufacture the ring gear, which generally enhances the strength and other mechanical properties of the ring gear. It is therefore preferred that during step B) n ring gear segments are formed for forming a ring, wherein n equals an even number, n will generally equal 2 or 4. An even number of ring gear segments is generally easier to mount on a rotatable drum. The ring gear segments are here arranged on the drum in uncoupled state and then mutually coupled in situ - on location - so that a closed ring gear results.

The second diameter of the ring gear segments is greater than the first diameter of the basic components. This means that the (first) curvature of the basic components is greater than the (second) curvature of the ring gear segments. The first diameter is otherwise interpreted as the maximum distance between two points on a (real or virtual) circle defined by an outer peripheral edge of the arcuate or annular basic component. The second diameter is interpreted as the maximum distance between two points on a virtual circle defined by an outer peripheral edge of an arcuate ring gear segment or as the maximum distance between two points on a real circle defined by an outer peripheral edge of the ring gear to be finally formed.

The basic components will generally be manufactured from (high-grade) forged steel, whereby the final ring gear will generally also be manufactured at least partially from forged steel. Forged steel generally has a particularly good strength to weight ratio, which is particularly advantageous for the primarily intended application in heavy equipment. The ring gear segments (obtained from the basic components) - which are finally provided with a toothing - will be loaded most heavily during use, whereby it is preferred that precisely these relatively heavily loaded parts of the final ring gear are manufactured from (high-grade) forged steel. Other parts of the ring gear, such as for instance web plates optionally used as inner band (inner web), which are loaded less heavily during use, are generally of (rolled) steel plate.

The basic components provided during step A) are more preferably manufactured from a rolled forged material, preferably a seamless rolled forged material, and each basic component is more preferably formed by a seamless rolled ring manufactured from forged steel. Seamless rolled rings with diameters of up to about 8 metres are (currently) relatively readily obtainable on the market. These seamless rolled rings are generally manufactured from a solid block of cast steel, also referred to as ingot, which is compressed (flattened) at high temperature - typically about 1100 °C - by means of a hydraulic press, wherein the steel is forged (compacted), this resulting in a higher material quality because imperfections (seams, cracks, cavities and so on) can in this way be obviated almost wholly. After forging of the steel a hole will be arranged in the forging, after which the then resulting ring is further formed by rolling the rough ring into the correct general shape by means of a rotating movement, thus forming the seamless rolled forged steel ring. The formed ring will generally subsequently be cooled rapidly to about 600 degrees Celsius, whereby the material structure is more or less fixed (frozen), which enhances the final material hardness. The advantage of a seamless rolled forged steel ring is that the material is relatively homogenous and solid, with a high material density, wherein the material fibres are moreover oriented in the same direction, which significantly enhances the (uniform) strength of the annular basic component.

The method preferably also comprises step C), which comprises, following provision of at least one annular basic component as according to step A) and before bending outward of the at least one annular basic component as according to step B), of opening, preferably sawing open, the at least one annular basic component. In contrast to alternative techniques, such as opening the annular basic component by means of cutting or severing, interrupting of the preferably seamless rolled annular basic component by means of sawing will have no or practically no influence on the material properties of the annular basic component, whereby a high-grade material quality can be maintained, which also enhances the quality of the final ring gear.

It is preferred for the method to comprise step D), which comprises, before bending outward of the at least one basic component as according to step B), of mechanically processing the inner periphery of the basic component, thus forming a radially protruding longitudinal nose. The longitudinal nose is in fact a (small) upright ridge which forms an integral part of the inner peripheral edge but which protrudes, typically about 10-40 millimetres, relative to a remaining part of the inner peripheral edge. The longitudinal nose is configured to enable easier connection, particularly by means of welding, of one or more reinforcing radially protruding web plates, as will be elucidated hereinbelow. The longitudinal nose is preferably though not necessarily arranged on a central part of the inner peripheral edge. The longitudinal nose preferably lies at a distance here from the end surfaces of the ring gear segment in question, as seen from a cross-section of the ring gear segment. This gives the ring gear segment a -I -like form.

Bending outward of a basic component, thus forming a ring gear segment, as according to step B) preferably takes place by applying a device for outward bending. The device for outward bending generally comprises at least one inner pressing element configured to realize at least two inner pressure points on an inner peripheral edge of the basic component, and at least one outer pressing element configured to realize an outer pressure point on an outer peripheral edge of the basic component, wherein the outer pressure point lies between at least inner pressure points and wherein the at least one inner pressing element and the at least one outer pressing element are mutually displaceable. During clamping and bending outward of the basic component as according to step B) the basic component is retained by the pressing elements by displacing the at least one inner pressing element and the at least one outer pressing element toward each other. The basic component is subsequently carried through a space formed between the pressing elements, whereby at least a large part of the basic component is bent outward by means of pressing. Each pressing element can here comprise one or more axially rotatable roller straightening machines. At least one roller straightening machine will generally be actively driven (in motorized manner) here to displace a basic component in a space formed between the pressing elements. The end surfaces of the basic component generally cannot be deformed by the device for outward bending, whereby the end surfaces generally retain the original curvature. It is therefore advantageous for the method also to comprise step E), which comprises, following forming of the at least one ring gear segment as according to step B), of shortening at least one end surface, preferably two opposite end surfaces of the ring gear segment, preferably by means of sawing. By shortening a ring gear segment on two sides the ring gear segment acquires a uniform curvature (uniform second diameter), this facilitating the subsequent manufacture of an annular ring gear. The shortening of the ring gear segments results in some reduction of the circumference of the ring gear. This must be taken into consideration during bending outward as according to step B). The circumference of the final ring gear is generally equal to or smaller than the sum of the circumferences (or arc lengths) of the applied basic components for manufacturing the above stated ring gear, particularly if the ring gear segments formed from the basic components are shortened as according to step E). In other words, the (second) diameter of the ring gear will generally be equal to or smaller than the sum of the (first) diameters of the applied (annular) basic components of the above stated ring gear, since the circumference and the diameter of an annular body are directly proportional to each other. The second diameter is already determined during step B) of the method according to the invention.

Since the longitudinal nose, if applied, also deforms during bending outward, which generally influences the dimensioning (measurements) of the longitudinal nose, it is preferred for the method to comprise step F), which comprises, following forming of the at least one ring gear segment as according to step B), of adjusting the measurements and optionally forming the longitudinal nose. Adjusting of the longitudinal nose as according to step F) preferably takes place by means of milling. The longitudinal nose can in this way be provided with the (most constant possible) radius, which allows one or more curved web plates to be positioned against the longitudinal nose as tightly as possible (preferred step G) of the method according to the invention; see below). The radius formed by an inner peripheral edge of the longitudinal nose will here correspond substantially wholly to the radius of an outer peripheral edge of the one or more web plates.

Step F) preferably takes place after step E) has been performed in order to be able to prevent new damage to or degradation of the longitudinal nose while step E) is being performed.

In a preferred embodiment the method also comprises step G), which comprises, following bending outward of the at least one basic component into an arcuate ring gear segment as according to step B), of connecting at least one radially protruding web plate to an inner peripheral edge of the at least one ring gear segment by means of welding. The at least one web plate is preferably welded here to the longitudinal nose (if applied). The overall length of an outer peripheral edge of the at least one web plate welded to a ring gear segment during step G) preferably substantially corresponds to the length of the inner peripheral edge of the ring gear segment. This results in the situation where the whole inner peripheral edge is provided with one or more (reinforcing) web plates. The total number of web plates is usually referred to jointly as the web or inner band. In this respect a ring gear segment can be deemed an outer tyre. The at least one web plate is generally welded during step G) to the longitudinal nose forming part of the inner peripheral edge of the ring gear segment. This welding usually takes place in two steps, wherein the at least one web plate is initially connected to the inner peripheral edge of the ring gear segment by means of spot welds during step G). These spot welds are relatively weak, but serve particularly to initially hold the web plates in position relative to the ring gear segment. The at least one web plate is subsequently fully connected to an inner peripheral edge of the ring gear segment, preferably by means of electron beam welding (EBW). Substantially fully connecting the applied web plates to the inner peripheral edge of the ring gear segments is understood to mean connecting the applied web plates to the inner peripheral edge of the ring gear segments more firmly (relative to the spot weld connections). The whole (peripheral) seam enclosed by the web plates and the inner peripheral edge of the ring gear segments is preferably welded here. Electrons are moved from an electron gun in the direction of the welded seam at very high speed during the electron beam welding (EBW). When these electrons collide with and in a surface of a seam at high speed, a significant amount of heat is developed locally, which is concentrated substantially only in a (particularly) small area, whereby the metal, particularly the steel, of the web plates and the ring gear segments not only melts but even partially vaporizes at the position of the welded seam. This creates a slot whereby welding can take place through and through, to a very great depth - 120 mm in steel is no problem. By moving the electron gun and thereby the electron beam the molten metal, particularly steel, of the ring gear segments fuses with the molten metal, particularly steel, of the web plates so that a particularly strong welded connection is created over the whole thickness of the web plates. EBW takes place in a vacuum. Without vacuum, the atmosphere would comprise too many spurious particles, which impedes the electron beam and would cause a diffuse beam. The ring gear components to be welded are therefore preferably welded in a vacuum chamber. An EBW weld is much narrower and more homogeneous, and therefore stronger, compared to a conventional submerged arc weld (SAW weld), which is characterized by a double bell- shaped form. An EBW weld is generally about 20% stronger than a conventional SAW weld. An additional advantage of an EBW weld relative to a SAW weld is that the EBW weld is realized in only one movement and welding need only be done from one side, while a so-called fully welded (full penetration) SAW weld can only be realized by welding from two (or more) sides. The energy supply (heat input) is moreover much smaller per cm² in the case of EBW - typically about 30-35 times smaller - than in all other welding techniques, including SAW welding, whereby no or hardly any deformation of material occurs. In addition, SAW welding requires the use of a welding electrode, generally of a different material than the materials which are mutually connected by means of the welding electrode, which results by definition in a relatively weaker welded connection. Even more important is that hardly any stresses result owing to the low energy supply, whereby it is expected that stress-free annealing and subsequent sandblasting are no longer necessary after the welding. Omission of this further processing step (annealing and sandblasting) results in significant energy, time and cost savings. Stress-free annealing will moreover result in a reduced hardness of the final product; no longer applying the stress-free annealing therefore results in a final product with a relatively great hardness, which thus also entails a technical advantage.

A plurality of web plates which mutually define a plane are preferably welded during step G) to an inner peripheral edge of a ring gear segment, wherein end surfaces of connecting web plates are also welded to each other. The mutual welding can be realized by means of the same two-stage process (spot welding followed by EBW). It is preferred that connecting web plates are finally welded to each other by means of a (continuous) EBW weld for the above stated reasons.

The method preferably also comprises step H), which comprises of connecting at least one joint-surface, generally extending in axial (longitudinal) direction, to an end surface of the inner peripheral edge of the ring gear segment by means of welding, wherein the at least one joint- surface is configured to be connected to a joint- surface of another ring gear segment. Step H) is preferably performed after step G) has been performed, wherein the at least one joint-surface is also welded to a web plate during step H). The above stated weld can also be formed by means of EBW, optionally preceded by one or more spot welds. Each end surface of the inner peripheral edge of the ring gear segment is preferably welded to at least one joint-surface during step H). This enables joint- surfaces of adjacent ring gear segments to connect closely to each other and to subsequently be mutually connected, generally by making use of mechanical attaching elements. It is preferred here that the joint-surfaces connected to an end surface of an inner peripheral edge of a ring gear segment mutually enclose a web plate and are welded to said web plate. It is also possible to envisage only a single joint-surface being welded to an end surface of an inner peripheral edge of the ring gear segment, wherein a front side of the joint-surface also lies against an end surface of a web plate. The web plate does not extend here to an end surface of the inner peripheral edge of the ring gear segment, but allows some space for placing of the joint-surface. The at least one joint- surface is here welded during step H) to the inner peripheral edge of the ring gear segment, and preferably also to a connecting web plate, preferably by means of electron beam welding (EBW). Each joint-surface is generally provided with a plurality of passage openings for bolts for enabling mutual mechanical attachment of joint-surfaces of different ring gear segments. The passage opening is usually adapted here to the type of bolt which will finally be inserted into the passage opening, wherein use is generally made of reamed bolts configured particularly to fix mutually coupled joint-surfaces, and thereby mutually coupled ring gear segments, to each other, as well as of connecting bolts configured particularly to transmit and absorb exerted forces.

The method preferably also comprises step J), which comprises of mutually connecting the ring gear segments, thus forming a ring. As already indicated above, the mutual coupling preferably takes place by mechanically connecting adjoining joint-surfaces of different ring gear segments. Mutual coupling of the ring gear segments usually, though not necessarily, takes place while forming a ring, and a toothing is subsequently arranged on a peripheral edge of each ring gear segment during step K) of the method according to the invention. Arranging a toothing on an outer (or inner) peripheral edge of the ring gear segments as according to step K) will generally take place by milling away material from the above stated peripheral edge. The toothing therefore preferably forms an integral part of the assembly of coupled ring gear segments, this considerably enhancing the strength of the toothing and therefore of the ring gear as such. The orientation of the toothing arranged during step K) and a longitudinal axis of the ring gear as such can mutually enclose an angle, this generally enhancing the absorption and transmission of greater forces during later application. The above stated angle preferably lies here between 0 and 45 degrees. The method according to the invention preferably also comprises step L), which comprises, preferably following mutual connection of the ring gear segments, thus forming a ring, as according to step J), of arranging mounting holes in the web plates for subsequent mounting of the ring gear on a rotatable drum.

The ring gear is usually disassembled after arranging of the toothing (step K)) and optionally the mounting holes (step L)) for transport to a location where a rotatable drum is disposed on which the ring gear is then once again assembled and in fact formed, wherein the ring gear components are connected to the drum as well as mutually connected. A ring gear component is defined here as an assembly comprising: an arcuate ring gear segment provided on an outer peripheral edge with a toothing, at least one radially protruding web plate connected to an inner peripheral edge of the ring gear segment by means of welding, and at least one upright joint-surface positioned on at least one end surface of the inner peripheral edge of the ring gear segment and connected to the ring gear segment by means of welding.

The invention also relates to a ring gear component manufactured by applying the method according to the invention, comprising: an arcuate ring gear segment provided on an outer peripheral edge with a toothing, at least one radially protruding web plate connected to an inner peripheral edge of the ring gear segment by means of welding, and at least one joint-surface which is positioned on at least one end surface of the inner peripheral edge of the ring gear segment, extends in axial direction and is connected to the ring gear segment by means of welding. The ring gear component is deemed here to be a semi-manufacture for manufacturing a final ring gear.

The invention also relates to a ring gear manufactured by applying the method according to the invention.

The invention further relates to an assembly of a ring gear according to the invention and at least one pinion configured to co-act with the ring gear.

The invention then relates to a rotatable drum, preferably for use as rotatable oven, rotatable dryer or rotatable grinding mill, comprising: a frame, an axially rotatable drum housing supported by the frame, at least one ring gear according to the invention connected to the drum housing and at least one drive co-acting with the at least one ring gear for axially rotating the drum housing.

The invention moreover relates to a device (for outward bending) for manufacturing a part of a ring gear, comprising: at least one inner pressing element configured to realize at least two inner pressure points on an inner peripheral edge of an annular or arcuate basic component to be bent outward, at least one outer pressing element configured to realize an outer pressure point on an outer peripheral edge of the above stated basic component, wherein the outer pressure point lies between at least inner pressure points, wherein the at least one inner pressing element and the at least one outer pressing element are mutually displaceable in order to determine the degree of outward bending of the basic component. The pressing elements are configured here to mutually retain and preferably guide a basic component to be bent outward. The pressing elements can be configured here to retain a basic component such that the basic component extends in a horizontal or vertical plane when being retained, which is generally most

advantageous from a practical viewpoint.

A plurality of inner pressing elements is preferably applied, wherein each inner pressing element is configured to realize one pressure point on the inner peripheral edge of the basic component to be bent outward. It is possible to envisage at least one or even each pressing element being formed by an axially rotatable roller. In a preferred embodiment at least one axially rotatable roller is coupled to a motorized drive for motorized axial rotation of the axially rotatable roller. The outer pressing element is preferably formed by an axially rotatable roller driven in motorized manner. Since the basic component to be bent outward extends during the process of outward bending in a direction remote from the outer pressing element, it is precisely in this direction that there is generally the most space for positioning a drive for axially rotating the roller which functions as outer pressing element, and optionally also space for displacing the outer pressing element from and toward the at least one inner pressing element. The at least one inner pressing element can be disposed here in substantially stationary position. It is however also possible to envisage also giving the at least one inner pressing element a mobile (displaceable) configuration. All pressing elements are generally supported by a, preferably shared, support structure. It is noted for the sake of clarity that it is not necessary to apply axially rotatable rollers. It is also very well possible to envisage non- rotatable pressing elements being applied instead of rotatable rollers to press the basic components into a desired outward bent orientation. The three (or more) pressure points realized by the pressing elements press the forged steel of the basic components beyond the yield point, whereby the forged steel is plastically deformed to have a desired second diameter.

The invention will be elucidated on the basis of non-limitative exemplary embodiments shown in the following figures. Herein:

figures 1-14 show successive method steps for manufacturing a ring gear according to the invention,

figure 15 shows a perspective view of an assembly of a pinion and a ring gear manufactured by means of the method according to the invention, figures 16a- 16f are successive method steps for manufacturing an annular basic component for use in the method for manufacturing a ring gear as shown in figures 1-14,

figure 17 shows a comparative image of a conventional SAW weld and an EBW weld, and

figure 18 shows a perspective view of a rotatable oven comprising a ring gear according to the invention.

An example of the method according to the invention will be described step by step hereinbelow, wherein reference is also made to the figures.

Step 1: Providing basic components (figure 1)

Step 1, also referred to as step A) in the claims, consists of providing annular basic components 1 for manufacturing a ring gear 2 according to the invention. For manufacturing the ring gear use can be made of 2 or 4 seamless rolled forged rings (seamless rolled rings), depending on whether a two-part or a four-part ring gear 2 is desired. In order to achieve a ring gear circumference of 8 metres, rings 1 in principle have to have a diameter of + 4 metres. A ring gear with a diameter of 8 metres has a circumference of 25.13 metres, this requiring a circumference of 12.56 per ring gear component in the case of a ring gear constructed from two equal parts (ring gear components). Since each end surface of each ring gear component is shortened by about 50 centimetres during the production process due to rolling loss (pressing loss), which is described in further detail hereinbelow, a starting circumference of about 13.5 meters is necessary, which can be realized with seamless rolled rings with a diameter of 4 meters which function as basic components. The general rule of thumb is that a ring gear 2 with an external diameter smaller than or equal to 8 meters is constructed from two parts and that a ring gear 2 with an external diameter greater than 8 metres is constructed from four parts.

In the case of a seamless rolled ring 1 the starting point is cast material 3, which is heated and is compacted by means of pressing. This process step is also referred to as the forging of material 3. A hole 4 is subsequently pressed into material 3. Forging 5 is then rolled out to the desired diameter from this hole 4. This process is also shown in figures 16a-16f. Directly after the rolling there follows a thermal treatment (refining) and quenching in liquid in order to bring the material to the desired hardness. The quality of this type of ring is normally very high. Seamless rolled rings in this order of magnitude are readily available. These rings can moreover be supplied preprocessed, so that extensive and comprehensive NDT research (Non-Destructive Testing research) can already be carried out by the supplier in order to guarantee the initial quality.

Step 2: Preprocessing the basic components (figure 2)

In order to enable the subsequent welding process to be performed, a (longitudinal) nose 6 preferably has to be formed on the inner side of these seamless rolled rings 1 by turning. As shown, the inner side of each ring 1 is hollowed out on two sides, whereby a ridge protruding inward about 30 mm remains on the inner side, which ridge is referred to as nose 6. The width of nose 6 substantially corresponds to the thickness of web plates 7 to be attached to nose 6 later (see figure 8).

Step 3: Opening the basic components (figure 3)

The basic components formed by rings 1 are then sawn through by means of a sawing machine so that an opening (interruption) is created.

Step 4: Bending the basic components outward (figures 4a-4f)

Each interrupted ring 1 is then arranged in a device for outward bending 8 comprising plurality of roller straightening machines 9 (or non-rotatable pressing elements

(pressure points)) displaceable relative to each other (and in vertical direction) for bending outward (bending open) the interrupted ring 1 into a ring gear segment 10 with a greater diameter (see figures 4a-4f). The original radius of r=2.25m (04.5m) will be bent outward here to achieve the desired radius of the ring gear, for instance a radius of r=4m (on the basis of a two-part ring gear with a diameter of 08m). The shells or shell parts (arches) formed during this outward bending function as ring gear segment 10 for manufacturing the final ring gear 2. In this exemplary embodiment ring gear segments 10 each cover an angle of 180 degrees for manufacturing a two-part ring gear 2. If a four-part ring gear were for instance desired, ring gear segments 10 can be configured as quarter segments (90-degree segments). It is noted for the sake of completeness that the ring gear segments can differ from each other in a ring gear with a toothing with an odd number of teeth. In the case of for instance a two-part ring gear with 201 teeth a first ring gear segment can be provided on a peripheral side with 100 teeth, while the other, second ring gear segment is provided on a peripheral side with 101 teeth. In practice the first ring gear segment covers in that case a first angle at the centre smaller than 180°, while the second ring gear segment covers an angle at the centre greater than 180°. The total of the first and second angle at the centre forms 360°, this enabling a closed annular ring gear to be formed. The same can generally apply to each n-part ring gear if the number of teeth of the toothing cannot be divided by n. Material on an outer side of rings 1 is compressed and compacted during deformation by the outward bending of original rings 1, which will result in improved mechanical properties and thereby a higher load-bearing capacity of final ring gear 2.

Step 5: Removing end surfaces (figure 5)

During the bending outward of rings 1, thus forming ring gear segments 10, as shown in figures 4a-4f, it will generally not be possible to bend the outer ends of the ring fully into the correct radius (run-in and run-out of device for outward bending 8). These insufficiently deformed end surfaces 10a, 10b are removed by means of milling or sawing.

Step 6: Precisely milling longitudinal nose (figure 6)

Design and dimensioning of longitudinal nose 6 can then be milled to achieve exactly the desired radius. This milling operation generally takes place on a "Computerized Numerical Control"-controlled (CNC-controlled) milling machine, whereby the radius can be followed precisely. For the subsequent welding process it is important that the welded seam is preprocessed very precisely.

Step 7: Processing web plates (web) (figure 7)

In order to reinforce the final ring gear 2 diverse web plates 7 are applied, which are attached to an inner side of ring gear segments 10, as will be discussed hereinbelow. The assembly of web plates 7 is also referred to as web. Each web plate 7 is here burnt as cutting piece from steel plate. These segments are preprocessed on a CNC processing machine such that all welded seams are prepared as well as possible and fit onto the inner peripheral edge of the ring gear segments 10 functioning as outer tyre.

Step 8: Placing of the web plates (web) (figure 8)

Web plates 7 (web) are then placed in the formed ring gear segments 10. Several small spot welds 11 can be arranged for fixing purposes, so that the components are temporarily fixed to each other.

Step 9: Manufacturing the main weld (figure 9)

Electrons are moved from a gun 12 in the direction of the welded seam at very high speed by means of electron beam welding (EBW). Enormous heat is created when these electrons collide with the surface (welded seam) at very high speed. This heat development is concentrated in a very small area, whereby a high temperature results such that the steel not only melts at the location of the welded seams, but even partially vaporizes. This creates a slot, whereby welding can take place through and through, to a very great depth (120 mm in steel is no problem). By moving the electron beam the molten steel of the outer tyre fuses with the molten steel of the web, and a very strong connection results over the whole thickness of the web. The previously formed spot welds 11 will vaporize during the electron beam welding.

This process must take place in a vacuum. Without vacuum, the atmosphere would comprise too many spurious particles, which impedes the electron beam and causes a diffuse beam. The ring gear to be welded therefore preferably has to be welded in a vacuum chamber. The temporarily fixed ring gear parts 7, 10 are placed in a vacuum chamber, after which the door of the vacuum chamber is closed and a vacuum is created by means of pumps in about 20-30 minutes, depending on the volume of vacuum chamber 13 and the power of the pumps.

Figure 17 shows a cross-section of a normal SAW weld on the left-hand side, wherein it is clearly visible that a bell-shaped weld is generated from many different layers from both sides. Shown on the right-hand side is an EBW weld which is obtained by means of electron beam welding (EBW). The EBW weld is much narrower in comparison to the SAW weld. The SAW weld is generated in one movement and need only be welded from one side. The energy supply (heat input) is much smaller per cm² in electron beam welding than in all other welding techniques, whereby hardly any deformation occurs. Even more important is that hardly any stresses result owing to the low energy supply, whereby stress-free annealing after the welding is probably no longer necessary.

Omission thereof results in large energy, time and cost savings. Even more important however is the fact that a final product with a much greater hardness can be produced because of the omission of the stress-free annealing.

As shown in figure 9, the main weld is welded in the vacuum chamber fully

automatically from one side. Figure 9 shows only one ring gear half, although it is of course possible to weld a plurality of halves or quarters (simultaneously) in one vacuum operation, depending on the dimensioning of the vacuum chamber and the size of ring gear segments 10, which can considerably enhance efficiency.

The main weld can thus be welded fully automatically and under vacuum. The result is a very high-quality weld. The chance of errors is practically negligible as a result of the degree of automation and the absence of atmospheric influence. The strength of the weld is about 20% greater than the conventional SAW weld.

It is moreover not necessary to use an electrode or welding wire because the types of steel of outer tyre 10 and web 11 simply fuse together. External preheating (preheating is done by the electron beam) is not necessary.

Step 10: Placing the joint-surfaces (figure 10)

After web plates 7 have been connected to ring gear segments 10 by means of EBW welds the vacuum is released and coupling flanges 14 are temporarily attached to web plates 11 and ring gear segments 10 by means of spot welds 15. Each end surface of each ring gear segment 10 is provided here with two coupling flanges 14 which mutually enclose a web plate 11. Step 11: Welding coupling flanges 14 (figure 11)

After a new vacuum has been created the coupling flanges 14 can be fully connected to ring gear segments 10 and web plates 11 by means of EBW welds. The same electron gun 12 can be applied for this purpose, although gun 12 will generally be rotated over 90° or a similar angle here so that the welded seam is perfectly accessible to gun 12. The use of EBW will significantly reduce the chance of errors and will greatly improve the quality of these heavily loaded welds.

Step 12: Perforating coupling flanges 14 (figure 12)

Each coupling flange 14 is then provided with a plurality of holes 15, for instance by means of drilling. Holes 15 serve to guide bolts 16 (see figure 13).

Step 13: Forming ring gear 10 (figure 13)

Ring gear segments 10 are mutually connected by means of bolts 16 and nuts 17. Step 14: Arranging toothing (figure 14)

Web plates 11 are then provided with holes 18, which facilitates subsequent mounting of ring gear 2. A toothing 19 is furthermore arranged on an outer peripheral edge of the assembly of ring gear segments 10 by means of milling (removing material from) the outer peripheral edge.

Ring gear 2 is then ready for use and can subsequently be received in a (gear wheel) housing 20, of which only ring gear 2 and a pinion 21 are shown in figure 15. Housing 20 can then for instance be applied in a rotatable oven 22 (see figure 18), wherein an oven housing 23 is enclosed by the ring gear 2 which is connected to oven housing 23 in fixed manner, and wherein housing 20 is configured to rotate housing 23. Housing 20 is driven here by a motor 24.

It will be apparent that the invention is not limited to the exemplary embodiments shown and described here, but that within the scope of the appended claims numerous variants are possible which will be self-evident for the skilled person in this field. It is possible here to envisage that different inventive concepts and/or technical measures of the above described embodiment variants can be wholly or partially combined without departing from the inventive concept described in the appended claims.

The verb "comprise" and conjugations thereof used in this patent publication are understood to mean not only "comprise", but are also understood to mean the phrases "contain", "substantially consist of, "formed by" and conjugations thereof.

Claims

1. Method for manufacturing at least a part of a ring gear, comprising the steps of:

A) providing at least one annular and/or arcuate forged basic component with a first diameter, and

B) bending outward each basic component into an arcuate ring gear segment with a second diameter, wherein the second diameter is greater than the first diameter.

2. Method as claimed in claim 1, wherein the first diameter lies between 1 and 10 metres.

3. Method as claimed in claim 1 or 2, wherein a plurality of forged basic components are provided during step A) and wherein the forged basic components are bent outward during step B) into arcuate ring gear segments configured to be mutually coupled, thus forming a ring.

4. Method as claimed in claim 3, wherein a plurality of basic components are bent outward during step B) into arcuate ring gear segments with a substantially identical, preferably wholly identical, second diameter.

5. Method as claimed in claim 3 or 4, wherein the arc length of the ring gear segments formed during step B) is substantially identical.

6. Method as claimed in any of the claims 3-5, wherein n ring gear segments are formed during step B) for forming a ring, wherein n equals an even number.

7. Method as claimed in any of the foregoing claims, wherein the basic components are manufactured from forged steel.

8. Method as claimed in any of the foregoing claims, wherein the basic components provided during step A) are formed by a seamless rolled forged steel ring.

9. Method as claimed in any of the foregoing claims, wherein the method also comprises step C), which comprises, following provision of at least one annular basic component as according to step A) and before bending outward of the at least one annular basic component as according to step B), of opening, preferably sawing open, the at least one annular basic component.

10. Method as claimed in any of the foregoing claims, wherein the second diameter is smaller than the sum of the first diameter.

11. Method as claimed in any of the foregoing claims, wherein bending outward of a basic component, thus forming a ring gear segment, as according to step B) takes place by applying a device for outward bending.

12. Method as claimed in claim 11, wherein the device for outward bending comprises at least one inner pressing element configured to realize at least two inner pressure points on an inner peripheral edge of the basic component and wherein the device for outward bending comprises at least one outer pressing element configured to realize an outer pressure point on an outer peripheral edge of the basic component, wherein the outer pressure point lies between at least inner pressure points and wherein the at least one inner pressing element and the at least one outer pressing element are mutually displaceable, wherein the bending outward of the basic component as according to step B) takes place by displacing the at least one inner pressing element and the at least one outer pressing element toward each other, and preferably subsequently carrying at least a part of the basic component through a space formed between the pressing elements.

13. Method as claimed in any of the foregoing claims, wherein the method comprises step D), which comprises, before bending outward of the at least one basic component as according to step B), of mechanically processing the inner periphery of the basic component, thus forming a radially protruding longitudinal nose.

14. Method as claimed in any of the foregoing claims, wherein the method also comprises step E), which comprises, following forming of the at least one ring gear segment as according to step B), of shortening at least one end surface, preferably two opposite end surfaces of the ring gear segment.

15. Method as claimed in claim 13, wherein the method comprises step F), which comprises, following forming of the at least one ring gear segment as according to step B), of adjusting the form of the longitudinal nose.

16. Method as claimed in claim 14 and 15, wherein step F) is performed after step E) has been performed.

17. Method as claimed in any of the foregoing claims, wherein the method also comprises step G), which comprises, following bending outward of the at least one basic component into an arcuate ring gear segment as according to step B), of connecting at least one radially protruding web plate to an inner peripheral edge of the at least one ring gear segment by means of welding.

18. Method as claimed in claim 17, wherein the overall length of an outer peripheral edge of the at least one web plate welded to a ring gear segment during step G) substantially corresponds to the length of the inner peripheral edge of the ring gear segment.

19. Method as claimed in claim 13, 15 or 16 and claim 17 or 18, wherein the at least one web plate is welded during step G) to the longitudinal nose forming part of the inner peripheral edge of the ring gear segment.

20. Method as claimed in any of the claims 17-19, wherein the at least one web plate is initially connected to the inner peripheral edge of the ring gear segment by means of spot welds during step G).

21. Method as claimed in claim 20, wherein the at least one web plate is fully connected to an inner peripheral edge of the ring gear segment by means of electron beam welding (EBW) during step G), following connection of the at least one web plate to the inner peripheral edge of the ring gear segment by means of spot welds.

22. Method as claimed in any of the claims 17-21, wherein a plurality of web plates which mutually define a plane are welded during step G) to an inner peripheral edge of a ring gear segment, wherein end surfaces of connecting web plates are also welded to each other.

23. Method as claimed in any of the foregoing claims, wherein the method also comprises step H), which comprises of connecting at least one axially extending joint- surface to an end surface of the inner peripheral edge of the ring gear segment by means of welding, wherein the at least one joint-surface is configured to be connected to a joint-surface of another ring gear segment.

24. Method as claimed in any of the claims 17-22 and claim 23, wherein step H) is performed after step G) has been performed, wherein the at least one joint-surface is also welded to a web plate during step H).

25. Method as claimed in claim 24, wherein each end surface of the inner peripheral edge of the ring gear segment is welded to at least one joint-surface during step H).

26. Method as claimed in claim 25, wherein the joint-surfaces connected to an end surface of an inner peripheral edge of a ring gear segment mutually enclose a web plate and are welded to said web plate.

27. Method as claimed in any of the claims 23-26, wherein the at least one joint- surface is welded to the inner peripheral edge of the ring gear segment, and preferably also to a connecting web plate, by means of electron beam welding (EBW) during step H).

28. Method as claimed in any of the claims 23-27, wherein each joint-surface is provided with a plurality of passage openings for bolts for enabling mutual mechanical attachment of joint-surfaces of different ring gear segments.

29. Method as claimed in any of the foregoing claims, wherein the method also comprises step J), which comprises of mutually connecting the ring gear segments, thus forming a ring.

30. Method as claimed in any of the foregoing claims, wherein the method also comprises step K), which comprises of arranging a toothing on a peripheral edge of each ring gear segment.

31. Method as claimed in claim 30, wherein arranging a toothing on a peripheral edge of each ring gear segment as according to step K) takes place by milling away material from said peripheral edge.

32. Method as claimed in claim 30 or 31, wherein the orientation of the toothing arranged in each ring gear segment during step K) and a longitudinal axis of the ring gear which has been formed or is to be formed as such mutually enclose an angle.

33. Method as claimed in claim 29 and any of the claims 30-32, wherein step K) is performed after step J) has been performed.

34. Method as claimed in claim 29 and any of the claims 30-32, wherein step K) is performed before step J) is performed.

35. Method as claimed in any of the claims 17-22, 24-28, wherein the method also comprises step L), which comprises of arranging mounting holes in the at least one web plate for mounting of the ring gear on a rotatable drum.

36. Method as claimed in claim 29 or 33 and claim 35, wherein step L) is performed after step J) has been performed.

37. Ring gear component manufactured by applying the method as claimed in any of the claims 23-28 and any of the claims 30-32, comprising:

an arcuate ring gear segment provided on an outer peripheral edge with a toothing,

at least one radially protruding web plate connected to an inner peripheral edge of the ring gear segment by means of welding, and at least one axially extending joint-surface positioned on at least one end surface of the inner peripheral edge of the ring gear segment and connected to the ring gear segment by means of welding.

38. Ring gear manufactured by applying the method as claimed in any of the claims 33, 34, 36.

39. Assembly of a ring gear as claimed in claim 38 and at least one pinion configured to co-act with the ring gear.

40. Rotatable drum, preferably for use as rotatable oven, rotatable dryer or rotatable grinding mill, comprising:

a frame,

an axially rotatable drum housing supported by the frame,

- at least one ring gear as claimed in claim 38 connected to the drum housing, and

at least one drive co-acting with the at least one ring gear for axially rotating the drum housing.

41. Device for manufacturing a part of a ring gear, comprising:

at least one inner pressing element configured to realize at least two inner pressure points on an inner peripheral edge of an annular or arcuate basic component to be bent outward,

at least one outer pressing element configured to realize an outer pressure point on an outer peripheral edge of said basic component, wherein the outer pressure point lies between at least inner pressure points,

wherein the at least one inner pressing element and the at least one outer pressing element are mutually displaceable in order to determine the degree of outward bending of the basic component.

42. Device as claimed in claim 41, wherein a plurality of inner pressing elements is applied, wherein each inner pressing element is configured to realize one pressure point on the inner peripheral edge of the basic component to be bent outward.

43. Device as claimed in claim 41 or 42, wherein at least one pressing element is formed by an axially rotatable roller.

44. Device as claimed in claim 43, wherein at least one axially rotatable roller is coupled to a motorized drive for motorized axial rotation of the axially rotatable roller.

45. Device as claimed in claim 44, wherein the outer pressing element is formed by an axially rotatable roller driven in motorized manner.