GB1568303A

GB1568303A - Duplex copying transfer system

Info

Publication number: GB1568303A
Application number: GB9210/77A
Authority: GB
Original assignee: Foseco International Ltd
Current assignee: Foseco International Ltd
Priority date: 1977-03-04
Filing date: 1977-03-04
Publication date: 1980-05-29
Also published as: JPS53110712A; DE2809325A1; SE7802258L; ZA781249B; BR7801258A; FR2382582A1; IT7867450A0; ES467531A1; AU3383178A

Description

(54) CATALYTIC CONVERTER (71) We, FOSECO INTERNATIONAL LIMITED, a British Company of 285 Long Adre, Nachells, Birminghana. B7 5JR, England, do hereby declare the invention, for which we pray that a pat@nt may be granted to us, and the method by which it is to be pe@formed, to be particularly described in and by the following statement: This invention relates to catalytic converters, and in particular catalytic converters of the type used in exhaust systems of interhal combtistion engines.

Such catalyst converters comprise a cata lyser body held in a metallic casing by means of some form of mounting. L@ use the catalytic converter is subject to vibration @@@@@@@@ed by the chgine and failure of the converter can result due to the fact that the mounting cannot withstand the vibration.

British Patent Specification No. 1,412,142 describes a reactor, suitable for treat@ng ex haust gases, consisting of a body of porous foam-structured ceramic material mounted in a metal casing by means of a sleeve of @brous co@an@@@@ i@sulating material. The sleeve, which has internal dimensions cof responding to the external dimensions of the ceramic body, is smicared inferna@y with a suitable ceranific bonding agent and the ceramic body is pushed into the sleeve. In practice it has been found difficult to pro duce a sufficiently tight fit of the body in the casing by means of such a mounting, and in use reactors made in this way may fail due to their inabifity to withstand v@bration.

British Patent Specification No. 1,418,912 describes a catalytic converter in which a catalyser body is held in a metalfic casing by means of a vacuum-formed ring of flo rous material. The fibrous ring is impregnated with an adhesive such as cofloidal silica sol and the adhesive is then dried so as to adhere the ring to the body and to the casing.

It has now been found that a catalytic converter can be assemb@ed more readily, and that the need to treat the mounting with an adnesive can be obviated using a partieu lar type of sleeve.

According to the invention there is provided a catalytic converter comprising an outer casing. an inner catalyser body and a sleeve of fibre-containing refractory heatinsulating material located radially cor pressed between the body and the casing, the sleeve being formed at least partly of polycrystalline inorganic fibres.

The sleeve is located between the body and the casing to reduce the flow of heat from the catalyser body to the casing. The sleeve preferably has a longitudinal open seam and is held in compression such as to resist any tendency of the sleeve to separate from the casing ar body under vibration.

Typically the catalyser body will be of cylindrical form and may be formed of a ceramic material having cells or pores coated internally with a suitable metal, the body being permeable from end to end. The casing will typically be made of a relatively strong metal such as nickel steel.

As indicated above the sleeve is made of a composition comprising high duty ceramic fibres i.e. inorganic fibres which are polycrystalline. Examples of polycrystalline inorganic fibres are polycrystalline metal oxide fibres of metals such as aluminium, zir conium, magnesium, silicon or thorium.

such a compostion may also contain a proportion of vitreous fibres such as alumina fibre or aluminosilicate fibre, and a preferred sleeve comprises polycrystalline refractory fibre, vitreous aluminosilicate fibre and the residue of colloidal silica sol as binder.

Polycrystalline fibres are characteristically more stable to thermal cycling than vitreous fibres and hence retain the desired property of resilience in such converters better than vitreous ones. This is because polycrystalline fibres such as of alumina have an extremely small crystallite size, typically 50500 Angstrom units. Crystal growth does not readily occur at the temperature to which the sleeve is normally exposed, i.e.

up to 1000 C, and the brittleness of the fibre is therefore not markedly increased.

In contrast, devitrification of vitreous fibres takes place readily at these temperatures, whereby relatively large crystals grow uncontrollably from widely separated nucleation sites. This consequently causes an embrittlement of the fibres and resilience is reduced to an intolerable level.

Polycrystalline refractory metal oxide fibres and methods for their manufacture are described in British Patent Specifications Nos. 1,237,288, 1,313,677, 1,360,-197 1,360, 198, 1,360,199, .1,360,200, 1,425,934 and 1,445,331 and in United States Patent Specification No. 3,975,565.

After manufacture of the sleeve the preferred seam is formed by cutting a slit through the wall of the sleeve longitudinally and moving the walls of the slit apart or by cutting out a narrow section of the wall of the sleeve along the whole length of the sleeve. Preferably the side walls of the seam of the sleeve are not in a radial plane relative to the longitudinal axis-of the sleeve.

When the metal casing is also of a form having a longitudinal seam it is preferable to assembly the catalyser body, sleeve and casing in such a way that the seam of the sleeve underlies the closed seam of the casing. The seam may be made by welding the two ends of a metal blank together around the sleeve, by a butt or lap joint.

An embodiment of the invention is illus--- trated in the accompanying diagrammatic drawing which shows a perspective view taken from one end of a catalytic converter.

The converter comprises a catalyser body 1 of the so-called monolithic type which is a cylinder of ceramic material permeable from end to end. Mesh walls 2 are arranged at the ends of the cylinder in between which there is a matrix suitably coated with a metal such as palladium. The body 1 is housed in a protective metal casing 3 formed by rolling up a blank of metal and temporarily holding the ends together by clips 4, after which the ends of the blank are seam welded together or joined by some other means.

Between the body 1 and the casing- 3 is located, according to the invention, a radially compressed sleeve 5 of a resiliently deformable refractory heat insulating material comprising polycrystalline alumina fibre, vitreous aluminosilicate fibre and the dried residue of colloidal silica sol as binder. The proportions of these ingredients are most preferably substantially 35% by weight polycrystalline alumina fibre, 35% by weight aluminosilicate fibre and the balance - the colloidal silica sol residue, the sleeve having an open longitudinal seam 6. The sleeve 5 prior to assembly of the catalytic converter is of wall thickness greater than the annular clearance between -the body 1 and the casing 3 in the assembled condition.

To assemble the converter, the catalyser body 1 is held in a suitable frame following which the sleeve 5 of refractory material is - slid about the catalyser body. The outer casing 3 is then located about the sleeve and the opposite ends of the blank of the casing are urged together under compression to engage the clips 4, whereafter the ends of the blank are seam welded together. This compression fitting of the casing 3 onto the catalyser body 1 compresses the resiliently deform able refractory heat insulating ma terial of the sleeve 5 so as to take up any irregularities caused by the crude tolerances to which the catalyser body has been made, the material of the sleeve deforming to close up the open seam of the sleeve. The degree of compression should not be so great that the material of the sleeve 5 loses its re silience.It is believed that by virtue of the presence of the open seam, the sleeve can be compressed and the material of the sleeve flow to reduce the space defined by the open seam resulting in improved locking of the catalyser body in the casing.

The cased catalyser body of the invention may be secured in an exhaust - manifold or exhaust pipe of a car where it may be -used to clean exhaust gases. Because of the re siliently deformable nature of the sleeve, the casing is securely held to the catalyser body despite vibration, as a result of which the parts have a reduced tendency to separ ate. The -sleeve also assists in compensating the differential thermal expansion between body and casing in use.

In order to prevent erosion of the material of the sleeve by exhaust gases it may be desirable to protect the end or ends of the sleeves.

This can be done by impregnating the ends of the sleeve with colloidal silica sol, followed by drying, so as to produce a hard core erosion resistant skin at the surface of the ends, or by providing annular flanges of metal extending from the casing or from the walls of the pipework to which the converter is fitted across the ends of the sleeve.

A catalytic converter according to the invention made as described above was fit ted into the exhaust system of a 4 cylinder internal combustion engine driven car. The car was run for SO,000 miles and the cata lytic converter was inspected periodically.

Despite the engine vibrations and exhaust pulsations associated with the engine there was no deterioration of the fibre-containing sleeve or separation of the components of the catalytic converter Although the invention has been des cribed in connection with catalytic con verters which are of circular cross-section the invention is equally applicable to. con verters of other cross-sectional shape, such as elliptical.

Claims

WHAT WE CLAIM IS:-

1. A catalytic converter comprising an outer casing, an inner catalyser body and a sleeve of fibre-containing refractory heatinsulating material located radially compressed between the body and the casing.

the sleeve being formed at least partly of polycrystalline inorganic fibres.

2. A catalytic converter according to claim 1, wherein the sleeve has a longitudinal open seam and is held in compression such as to resist any tendency of the sleeve to separate from the casing or body under vibration.

3. A converter according to claim 2, in which the side walls of the seam are not in a radial plane with respect to the longitudinal axis of the sleeve.

4. A converter according to claim 2 or claim 3, in which the casing is formed by rolling up a blank of metal and welding or otherwise joining the ends of the blank together, and the sleeve is arranged relative to the casing such that the open seam of the sleeve underlies the closed seam of the casing.

5. A converter according to any one of the preceding claims, in which the sleeve is vacuum formed from a composition com- prising a polycrystalline refractory fibre.

6. A converter according to claim 5, wherein the sleeve comprises polycrystalline refractory fibre, vitreous aluminosilicate fibre and the residue of colloidal silica sol as binder.

7. A catalytic converter substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.