EP0397231A1

EP0397231A1 - Roller for transporting hot objects

Info

Publication number: EP0397231A1
Application number: EP90201022A
Authority: EP
Inventors: Cornelis Franciscus Jacobus De Haan; Ferdinand Albert Schuurmans
Original assignee: Hoogovens Industrial Ceramics BV
Current assignee: Hoogovens Industrial Ceramics BV
Priority date: 1989-05-08
Filing date: 1990-04-24
Publication date: 1990-11-14
Also published as: NL8901148A

Abstract

A roller for transporting hot objects, comprises a cylindrical steel core (2) and on the core a plurality of annular elements (3) for contacting the hot objects which elements are slidable axially along the core and each comprise a refractory filling (10) and an outer hard surface material (9). To prevent tensile stresses and provide long life, the outer hard surface material is a jacket (4) of an industrial ceramic material and between each adjacent pair of the annular elements (3) there are means on the core (2) for maintaining the elements spaced apart in the form of at least one annular disc (12) of diameter less than the elements (3).

Description

The invention relates to a roller for transporting hot objects which the roller contacts and to a conveyor for hot objects comprising a plurality of the rollers.
One known form of roller for transporting hot objects has a cylindrical steel core and a plurality of cylindrical elements with central holes which slide onto the core with a slight clearance. A roller of this type is shown in FR-A-793 942. The cylindrical elements are discs made of material containing asbestos and are pressed together at their outer peripheries to reduce wear. Such a roller in practice is used for example in a furnace at a temperature of about 1200°C for transporting stainless material with a width of about 1500 mm and a thickness of about 12.7 mm. The known roller wears rather badly and also presents health hazards.
Another roller for hot objects is disclosed in DE-C-996 177. The surface of the roller is provided by an outer sleeve of ceramic material, specifically SiC, and between the sleeve and the steel core is a filling of cement. The roller is thus a unitary body. The defect of such a roller is that the bending caused by the weight of the supported object is liable to introduce tensile stresses in the ceramic sleeve, which may crack.
FR-A-1462 443 describes a roller in which annular elements are mounted on a metal shaft. The elements are of low density refractory material in the form of asbestos fibers and diatomaceous earth, and have a very thin enamel surface at their periphery. This construction is unsuitable for heavy loads or high temperatures, being intended for the handling of glass ampules containing liquids for pharmaceutical use. If heavy loads are applied, the resultant bending of the roller would cause stress between the elements, resulting in cracking of the enamel.
The purpose of the invention is to create a roller suitable for high temperatures and heavy loads which need not have any asbestos in it, but which compares well in price and service life with the known high temperature roller first mentioned. above.
The present invention provides a roller as set out in claim 1.
A roller in accordance with the invention with an outer jacket of industrial ceramic material, such as for example Si₃N₄ or SiC or a combination of the two, such as for example Si₃N₄ with about 4-8% SiC, is resistant to use at very high temperature, such as for example 1200°C, and is very resistant to wear. The use of annular spacing discs between the load-contacting elements achieves correct spacing and avoids stresses due to bending of the roller.
Preferably the spacing discs are circular with a diameter less than the outside diameter of the annular elements, preferably less than half the latter diameter, and a central hole with a diameter larger than the external diameter of the core. This helps reduce tensile stresses in the industrial ceramic material as the roller bends under the effect of the weight of the hot objects to be transported.
The annular elements preferably have preformed inner sleeves defining their contact holes. Anchoring projections may extend outwardly from the inner sleeve into the filling. This means on the one hand that the component has a pre-determined dimension, while on the other there is a fixed connection between the inner sleeve and the refractory material.
Using for example plasma spraying or a similar technique the outer jacket of the industrial ceramic material may be attached to the refractory material which forms the filling. However, it is preferable for the outer jacket to be of a pre-formed sleeve of industrial ceramic material which is subsequently filled with a filling of refractory material in thick liquid form or in the form of a mass. The filling may then take a solid form through the action of a binder such as a chemical or hydraulic binder.
The refractory filling material is preferably a refractory concrete. The combination of an outer jacket of wear resistant industrial ceramic material and a filling of a relatively inexpensive material is very attractive in price.
The outer jacket is preferably provided on its inside with keying projections and/or recesses extending axially and/or circumferentially. This prevents the sleeve from rotating and/or displacing axially relative to the refractory filling material.
An embodiment of the invention will be illustrated by way of example, with reference to the drawings, in which:-

Fig. 1 shows a longitudinal section of the roller embodying the invention;
Fig. 2 shows a longitudinal section and a cross-section of an outer sleeve of an annular element of the roller; and
Fig. 3 shows a longitudinal section and a cross-section of an inter sleeve of an annular element of the roller.

Fig. 1 shows a roller 1 comprising a cylindrical steel core 2 with a plurality of cylindrical load-contacting annular elements 3 which slide axially onto the core and which are retained by the end discs 4 and 5. The furnace wall is schematically indicated at 6. At the end discs 4 and 5, the roller is taken through the furnace wall 6 with the aid of a seal, for example a labyrinth seal (not shown in the drawing). The drawing shows the core 2 as hollow; it is cooled by means of air flowing through it in the direction of arrow 7.
Fig. 2 shows in detail that each annular element 3 has an outer jacket 8 in the form of a preformed sleeve 9 of industrial ceramic material i.e. engineering quality ceramic such as Si₃N₄ containing 4-8% SiC, and a filling 10 of refractory material such as refractory concrete. The element 3 slides onto the core 2 with a slight clearance. Retaining the filling 10 at the inner side is a preformed sleeve made e.g. of steel, which is provided externally with anchors 15 which extend into the filling 10. Spacing means in the form of annular discs 12, 13, e.g. of metal, are fitted between the neighboring components. These discs 12, 13 have an outside diameter which is much less than that of the outer jacket 8 and a hole with a diameter which is a little larger than the core 2.
Each annular element 3 has for example a length/diameter ratio lying between 0.5 and 2. This means that, generally speaking, the tensile stresses in the industrial ceramic material resulting form the weight of the objects transported are acceptable.
As shown in Fig. 3, the external sleeve 9 is provided internally with axially and circumferentially extending projections 14 for preventing the sleeve from rotating or displacing on the filling 10.

Claims

1. Roller for transporting hot objects, comprising a cylindrical steel core (2) and on the core a plurality of annular elements (3) for contacting the hot objects which elements are slidable axially along the core and each comprise a refractory filling (10) and an outer hard surface material (9) characterized in that said outer hard surface material is a jacket (4) of an industrial ceramic material and in that between each adjacent pair of said annular elements (3) there are means on the core (2) for maintaining the elements spaced apart in the form of at least one annular disc (12) whose periphery is radially spaced from the core less than the outer surface of the roller.

2. Roller according to claim 1 wherein the radial thickness of each said disc (12) is less than half the radial thickness of the annular elements (3).

3. Roller according to claim 1 or claim 2 wherein the annular elements (3) have preformed inner sleeves (11) defining their central holes.

4. Roller according to claim 3 wherein anchoring projections (15) extend outwardly from the inner sleeve (11) into the filling (10).

5. Roller according to any one of claims 1 to 4 wherein said industrial ceramic material is Si₃N₄ or SiC or a combination of the two.

6. Roller according to any one of claims 1 to 5 wherein the refractory filling (10) is a refractory concrete.

7. Roller according to any one of claims 1 to 6 wherein said outer jacket (4) is a pre-formed sleeve.

8. Roller according to claim 7 wherein said sleeve has axially and/or circumferentially extending projections (14) and/or recesses, for keying to the refractory filling (10).

9. A conveyor for hot objects comprising a plurality of rollers according to any one of the preceding claims.