WO1996036572A1

WO1996036572A1 - Apparatus for the formation of man-made vitreous fibres

Info

Publication number: WO1996036572A1
Application number: PCT/EP1996/002066
Authority: WO
Inventors: Flemming Weiss Tonder
Original assignee: Rockwool International A/S
Priority date: 1995-05-15
Filing date: 1996-05-14
Publication date: 1996-11-21
Also published as: AU5896796A; GB9509781D0

Abstract

The invention provides an apparatus for the formation of man-made vitreous fibres which comprises a housing, a non-rotatable sleeve (3) mounted in the housing, a rotor (1) by which mineral melt can be thrown radially as fibres, a drive shaft (2) within the sleeve and coaxial with the rotor and sleeve, an associated motor (4) for driving the drive shaft, at least one set (5, 6) of roller bearings between the non-rotatable sleeve on the one hand and the drive shaft or rotor or both on the other hand and in the apparatus at least one set of roller bearings is made of a ceramic material. Such materials are advantageous in that they can withstand especially high temperatures and are capable of being lubricated with water.

Description

Apparatus for the Formation of Man-Made Vitreous Fibres

The present invention relates to an apparatus for the formation of man-made vitreous fibres by the use of one or more rotors which are required to rotate at very high speed.

It is known to provide ball bearings and roller bearings made of various materials. For instance, roller bearings having cylindrical rolling elements made of hard ceramic material have been used in off-shore oil drilling apparatus. These bearings were large, rather heavy slowly rotating roller bearings.

EP-A-258845 describes a ceramic roller bearing for general use in high temperature environments. In this publication it is stated that they can be used at very high temperatures at which it is not possible to use a lubricant with the bearings.

In EP-A-158901 roller bearings are described in which the cylindrical rollers may be made entirely of ceramic materials. It is suggested that the bearings may be components of apparatus for electroplating, alloy casting and furnaces for melting metal. EP-A-477755 describes a ball bearing which is made entirely of ceramic material for exposure to temperatures above 500°C. US-A-4770549 describes a ceramic ball bearing for long load life. None of these are lubricated.

Steel ball and roller bearings are more usual. It is well known to produce various types of man-made vitreous fibres (MMVF) such as glass wool and stone wool, by the use of an apparatus comprising one or more rotors which are arranged so as to be capable of rotating at high speed and throwing off radially in the form of fibres mineral melt poured on to the rotor. Various types of apparatus are known. These include the spinning cup type of apparatus, often used for the formation of glass fibres. Mineral or stone fibres may be produced using a single rotor system, where the rotor is rotatable about a substantially horizontal axis. Systems are also known which comprise more than one rotor. These may be arranged in a cascade formation so that melt poured on to the top rotor is thrown from this rotor on to the subsequent rotor and on to each subsequent rotor in turn so as to form fibres. These multiple rotor cascade arrangements are particularly useful for the production of mineral or stone fibres.

In all of the known forms of apparatus the rotor or rotors are exposed to very high temperatures (the melt is usually above 1100°C) and are each required to rotate at very high speed. Each rotor is attached to a drive shaft which is driven by an associated motor and which also must rotate at high speed. It is therefore necessary to provide bearings in the apparatus to take the rotating load and to reduce as far as possible friction between the drive shaft and/or the rotor and components of the housing in which the rotor is mounted. Steel roller bearings have been used for this purpose.

Unfortunately this type of bearing generally gives a very high friction loss, too high to be lubricated adequately.

Generally then it is conventional to use steel ball bearings for this purpose. Conventionally these bearings are made of hardened steel. They give some friction loss, although this is lower than with steel roller bearings, and must be lubricated. This is generally achieved with the use of grease or oil. A disadvantage of the requirement to use grease or oil as lubricant is the temperature limitation imposed thereby on the bearings. Grease or oil lubricant can usually only survive an environment having a temperature of up to around 120°C. At temperatures greater than this, evaporation and/or decomposition of the lubricant become problematic. The region of the rotor itself will necessarily be at a very high temperature, therefore oil-lubricated steel ball bearings must be situated at a great enough distance from the rotor itself to allow the bearing temperature to be low enough that lubrication remains effective.

Steel bearings tend to be rather large if they are to take the load effectively. They may also be required to be a considerable distance apart in order to bear the load effectively. These requirements, coupled with the necessity for keeping the bearings an adequate distance from the rotor itself, result in a rather large, heavy set of bearings and drive shaft. Steel bearings are also rather sensitive to the presence of contaminant abrasive particles in the oil lubricant. If such contaminants are present friction may increase significantly and the bearings may become susceptible to wearing. It would be desirable to provide an improved bearing system for spinners for making MMV fibres.

The invention provides an apparatus for the formation of man-made vitreous fibres which comprises a housing, a non-rotatable sleeve mounted in the housing, a rotor by which mineral melt can be thrown radially as fibres, a drive shaft within the sleeve and coaxial with the rotor and sleeve, an associated motor for driving the drive shaft, at least one set of roller bearings between the non- rotatable sleeve on the one hand and the drive shaft or rotor or both on the other hand characterised in that at least one set of the roller bearings is made of a ceramic material.

Preferably the apparatus also comprises water supply means which are arranged to supply water as lubricant to the roller bearings. In this specification when we refer to a roller bearing we mean a rolling bearing in which the rolling elements are substantially cylindrical (rather than spherical) .

The provision in the invention of roller bearings made of ceramic material has various advantages. Ceramic roller bearings are capable of bearing very large rapidly rotating loads. In particular they are capable of bearing greater loads than are equivalent steel bearings. Furthermore, they are also generally lighter than steel bearings for bearing the same load. The great strength of ceramic roller bearings means that it is possible to position them closer together on the drive shaft than is usually possible with conventional steel bearings. This allows for the provision of smaller, lighter drive shafts. Ceramic materials can be considerably harder and more resilient than even hardened steel. Steel roller bearings can be sensitive to particulate contaminants in the lubricant and can be worn down by these contaminants. Ceramic bearings are less sensitive and more wear resistant than conventional steel bearings. Thus ceramic roller bearings may have a considerably longer life than steel bearings. This can result in greater economy in the long term.

According to the invention at least one set of roller bearings in the apparatus is made of the ceramic material. The or each drive shaft and rotor may be supported by a single set of roller bearings. In such a case, at least one set of roller bearings in the apparatus is made of ceramic material, and preferably all sets of roller bearings are made of ceramic materials.

More usually, in particular if the rotors are rotatable about a substantially horizontal axis, the or each drive shaft and rotor is supported by two sets of roller bearings. In such a case at least one set of bearings in the apparatus is made of ceramic material. Preferably each drive shaft and rotor is supported by at least one set of ceramic bearings. Most preferably all sets of roller bearings are made of ceramic material.

Where two sets of roller bearings are used for a single drive shaft rotor, the set nearer to the rotor is known as the axial bearing and the set further from the rotor is known as the radial bearing.

When the or each rotor and its associated drive shaft are supported by two sets of roller bearings, one set of bearings may be situated between the rotor and the non- rotatable sleeve, for instance surrounding the sleeve. Preferably however at least one set of the roller bearings, and preferably each set of the roller bearings, is situated between the drive shaft and the non-rotatable sleeve, i.e. internal of the sleeve. The set of bearings at the rotor end of the shaft (axial bearing) can be positioned within the volume prescribed by rotation of the rotor. Thus the rotor may be cup shaped with the open end of the cup facing towards the motor and with the shaft and sleeve passing through the open end of the cup, with the ceramic bearing between the sleeve and the cup walls or between the sleeve and the shaft at a position between the base of the cup and the end of the cup facing the motor. Such a location of conventional bearings is shown in EP-A-347418. Preferably the ceramic bearing adjacent the rotor is positioned wholly on the motor side of the rotor, so that if the rotor is cup shaped the bearing is preferably located wholly on the motor side of the cup.

Usually a further set (radial bearing) of ceramic roller bearings is situated between the drive shaft and the non-rotatable sleeve at a position distant from the rotor and is generally positioned adjacent the motor.

The roller bearings may be supplied in any shape conventional for such bearings. They usually have an external substantially annular race fixed relative to the non-rotatable sleeve, a series of cylindrical rollers which contact the external race and a further internal substantially annular race fixed with respect to the drive shaft or rotor. The bearings may also include one or more flanges attached to either or both races. Where an axial and a radial set of bearings are used, the axial bearing preferably comprises two cylindrical flanges, one attached to each of the external and internal races.

The ceramic roller bearings in the apparatus of the invention usefully have an axial length of between 25 and 100mm, often between 30 and 70mm, preferably 30 to 50mm. Their diameter may be between 60 and 200mm, often between 70 and 160mm, preferably 80 to 140mm. Such a size is particularly appropriate where the apparatus is a multi- rotor cascade spinner apparatus.

We find that as a result of the greater heat- resistance and load-bearing capacity of ceramic bearings in comparison with conventionally used steel bearings, the length of a single rotor unit (comprising a rotor, drive shaft and non-rotatable sleeve) may be reduced by up to half where the bearings are ceramic roller bearings, in comparison with an equivalent rotor unit in which the bearings are steel bearings. The length of a rotor unit in a multiple rotor cascade spinner apparatus according to the invention may be for instance below 1 metre, often below 70cm. In the invention the roller bearings made of ceramic material are preferably lubricated with water. We find that amounts of water generally equivalent to (or less than) the amounts which are conventionally used for cooling rotors can act effectively as a lubricant at temperatures higher than those which can be withstood by oil lubricant. Lubrication with water is particularly compatible with positioning the ceramic roller bearings close to or within the volume defined by the or each rotor and thus exposed to very high temperatures. Water as lubricant tends to evaporate less slowly than oil lubricants. If some evaporation of water does occur it may be replaced easily and economically. Water lubricant is not susceptible to the problems of degradation of lubricant which are encountered with oil lubricant.

The apparatus of the invention preferably includes means for supplying water as lubricant to the bearings. More preferably these water supply means include means for supplying cooling water to the or each rotor and means for diverting some or all of this to the ceramic roller bearings for use as lubricant.

Preferably the drive shaft and rotor each have a hollow centre through which water may be caused to flow during use of the apparatus so as to cool the drive shaft and rotor. Water may be diverted from this flow and caused to pass through the bearings and subsequently rejoin the flow of cooling water. A single set of ceramic roller bearings may be lubricated with amounts of water of from 50 to 500 1/hr, preferably 100 to 300 1/hr, more preferably 110 to 220 1/hr.

Generally the lubricating water is supplied in bulk liquid form. It is also possible to supply lubricating water in atomised form. Use of atomised lubricating water can allow use of much lower amounts of lubricant, for instance from 0.5 to 2 1/hr, often 0.5 to 11/hr lubricant.

The supply of water to be atomised may include an aqueous phase'only. Alternatively it may be a water-in-oil emulsion which is atomised and subsequently supplied to the ceramic roller bearings.

It is known to supply atomised oil lubricant to steel bearings and equipment is available for this. Equipment of this type may be used to supply atomised water, in particular atomised water-in-oil emulsions.

The apparatus of the invention may be any apparatus having at least one rotor which is used for the production of MMVF fibre. The shaft may be vertical or horizontal. The rotor can be mounted on a substantially vertical shaft and can be a spinning cup, for instance for the production of glass or stone wool. In vertical-shaft rotors the invention has the advantage that the bearings may be placed closer to the rotor than has been usual in the past. This is particularly advantageous for the production of stone wool using a vertical-shaft rotor such as a spinning cup, since stone wool melts tend to be spun at a temperature of around 1,400°C. Ceramic bearings are especially useful at temperatures approaching this.

It may alternatively be an apparatus suitable for the production of stone wool fibres which includes a single rotor which is rotatable about a substantially horizontal axis. Preferably it comprises a series of rotors arranged in cascade formation, for instance for the production of stone wool. Thus preferably the apparatus comprises a first rotor rotatable about a substantially horizontal axis and at least 1, usually 2 or 3 subsequent rotors. Preferably at least 1 rotor, and preferably all, of the rotors, are as defined in the invention.

The motor associated with the drive shaft may be connected to the drive shaft by a belt system. In such a case the motor itself is placed to the side of the drive shaft such as described in US-A-2678466. Preferably however the motor is provided co-axial with the drive shaft and rotor, as described in EP-A-347418.

Ceramic materials suitable for production of the at least one roϊler bearing in the apparatus of the invention include those based on silicon nitride, silicon carbide, Sialon, alumina, partially stabilised zirconia (PSZ) , tetragonial zirconia polycrystal (TZP) and any other material from the class known as "construction ceramics". These materials are sintered, preferably under pressure at high temperature. Alternatively they may be sintered at ambient pressure. Suitable materials may be added as sintering aids, for instance alumina or any aluminium compound which converts to the oxide on heating, for instance aluminium nitride. Other sintering aids include magnesia, spinel, garnet, titania, zirconia, molybdenum carbide and rare earth metal oxides such as yttria. These are particularly preferred as sintering aids where the ceramic is based on silicon nitride. Other sintering aids include elemental boron, carbon and aluminium, which are particularly preferred where the ceramic is based on silicon carbide. In the present apparatus preferred ceramics are based on zirconia stabilised with yttria or silicon nitride.

The bearings may be formed from previously formed and sintered material. Alternatively they may be formed and sintered directly into the shape required for the bearings. Formation of the ceramic material is done in any conventional manner.

Preferably the ceramic bearings are made of a material having a Vickers hardness of at least 7 GPa, more preferably at least 10 GPa, most preferably at least 12 GPa.

The ceramic material should be able to withstand extended exposure to high temperatures, for instance 500°C or higher, often 1,000°C or 1,400°C or higher. In some cases, for instance for certain materials, it is desirable to use a low-oxygen atmosphere when the ceramic bearings are subjected to particularly high temperatures, such as approaching 1,400°C.

Preferably the material has a 3-point bend strength of at least 170' MPa, more preferably at least 300 MPa. 3- point bend strength is a standard parameter of ceramic material and may be tested using conventional apparatus, for instance as described by David W Richerson in "Modern Ceramic Engineering:Properties, Processing and Use in Design" (Marcel Dekker, Inc, 1992) in Chapter 5 at pages 179-183.

An embodiment of the invention will now be illustrated with reference to the accompanying drawing which illustrates a cross-sectional side view of a single drive shaft and rotor of a mineral fibre forming apparatus according to the invention. In an exemplary apparatus according to the invention there are provided four rotors arranged in a cascade formation so as to be able to form mineral fibre by the pouring of mineral melt on to the top rotor. The melt is then thrown on to the first subsequent rotor and on to each subsequent rotor in turn resulting in the formation of mineral fibres.

A single rotor and drive shaft is illustrated in the figure. The rotor 1 is attached to a drive shaft 2. Both are housed within a housing (not shown) . This housing contains a non-rotatable sleeve 3. The drive shaft is driven by a coaxial motor 4. The drive shaft and rotor are supported by two sets 5 and 6 of roller bearings made of ceramic material placed between the drive shaft and the non-rotatable sleeve 3. The axial set 5 of roller bearings is positioned between the non-rotatable sleeve and the drive shaft adjacent to the rotor on the motor side of the rotor. The second, radial set 6 of roller bearings is placed between the drive shaft and the non-rotatable sleeve a distance from the rotor between the rotor and the motor.

The ceramic material is Zyazirk Z105, a ceramic based on zirconium oxide containing 10.5% Y₂0₃. It has Vickers hardness 17 GPa and a 3-point bend strength 276 MPa. It is available from Dukadan, a Danish Company.

Claims

1. An apparatus for the formation of man-made vitreous fibres which comprises a housing, a non-rotatable sleeve (3) mounted in the housing, a rotor (1) by which mineral melt can be thrown radially as fibres, a drive shaft (2) within the sleeve and coaxial with the rotor and sleeve, an associated motor (4) for driving the drive shaft, at least one set (5, 6) of roller bearings between the non-rotatable sleeve on the one hand and the drive shaft or rotor or both on the other hand characterised in that at least one set of the roller bearings is made of a ceramic material.

2. An apparatus according to claim 1 additionally comprising water supply means which are arranged to supply water, as lubricant, to the roller bearings (5, 6) .

3. An apparatus according to claim 2 in which the water supply means are arranged to supply water at a rate of from 50 to 500 1/hr preferably 110 to 220 1/hr.

4. An apparatus according to any preceding claim in which at least one set (5) of said roller bearings is between the rotor (1) and'the sleeve (3) or between the sleeve and the shaft (2) adjacent to the rotor.

5. An apparatus according to any preceding claim in which at least one set (5) of roller bearings is between the non- rotatable sleeve (3) and the drive shaft (2) at a position adjacent to the rotor (1) on the motor side of the rotor.

6. An apparatus according to claim 5 in which there is a further set (6) of roller bearings between the non- rotatable sleeve (3) and the drive shaft (2) at position adjacent to the motor (4) on the rotor side of the motor.

7. An apparatus according to any preceding claim which comprises a set of rotors comprising a top rotor and one or more subsequent rotors each mounted in the housing for 12 rotation about a different substantially horizontal axis and arranged such that melt poured on to the top rotor is thrown from this rotor on to the subsequent rotor, or on to each subsequent rotor in turn, so as to form man-made vitreous fibre.

8. An apparatus according to claim 2 in which the water supply means are arranged to supply water to the at least one set (5, 6) of roller bearings at a rate and temperature effective to cool the roller bearings during use of the apparatus.

9. An apparatus according to claim 2 in which the or each drive shaft (2) or rotor (1) has a hollow centre and in which the water supply means are arranged to supply water through this hollow centre at a rate and temperature effective to cool the drive shaft and rotor during use of the apparatus.

10. An apparatus according to any preceding claim in which the motor (4) associated with the or each rotor (1) is provided coaxial with that rotor.