WO1995033965A1

WO1995033965A1 - Reinforced ceramic rollers for ovens

Info

Publication number: WO1995033965A1
Application number: PCT/FR1995/000733
Authority: WO
Inventors: Jacques Paul Raymond Schoennahl
Original assignee: Nuova Sirma S.P.A.
Priority date: 1994-06-08
Filing date: 1995-06-07
Publication date: 1995-12-14
Also published as: TW296424B; EP0769126B1; CN1150474A; DE69504080D1; EP0769126A1; FR2721098B1; FR2721098A1

Abstract

The invention relates to a composite roller for a roller oven comprising an external hollow roller (1) made of refractory material based on oxide and a reinforcement element (2) made of refractory material having a high hot elasticity modulus and arranged inside the external roller, the larger dimension of the cross-section of the reinforcement element being slightly smaller than the inside diameter of the external roller. Utilisation particularly in ovens for baking ceramic tiles.

Description

Reinforced ceramic rolls for ovens.

The invention relates to ceramic rollers for roller ovens.

A roller oven is a passage oven whose bottom is made up of ceramic rollers arranged parallel to each other and rotated around their central axis by means of a drive system. All the rollers rotate in the same direction and at substantially the same speed. This movement causes the load to be cooked through the oven. These ovens are mainly used for firing ceramic tiles used for coating floors and walls. The cooking tiles are placed directly on the rollers at the entrance to the oven. However, roller ovens are also used to cook complex shaped items: tableware, sanitary fittings, electronics substrates. In this case, the products to be cooked are loaded onto slabs forming supports, these then being placed on the rollers.

Current rollers have a length of 1200 to 4000 mm and their outside diameter is between 25 and 55 mm for a wall thickness of 5 to 6 mm.

They ^s' are subjected to various types of stress: D Mechanical Stresses:

"dead weight and loads from the products to be cooked;

• dynamic fatigue (rotation). D Chemical attacks:

"by the alkaline vapors given off by the products to be cooked; • by oxidation (in the case of SiC rolls). α Thermal gradients: between the part located inside the oven and the ends passing through the walls of the oven. π Thermal shocks: m when a cold new roller is introduced into an operating oven to replace a faulty roller;

"during standby or maintenance shutdowns. There are three types of rollers on the market:

- rollers formed of refractory materials based on oxides baked at moderate temperature (<1500 ° C), such as alumina-mullite-cordierite materials (such as the Siroll LP material sold by the company Nuova Sirma, Italy); - rolls based on alumina, alumina-mullite or mullite baked at very high temperature (> 1500 ° C);

- rollers formed of refractory materials based on silicon carbide and / or silicon nitride and / or silicon oxynitride and / or sialon (hereinafter called materials based on at least one silicon compound) , such as materials formed from Sic grains bound by a silicon nitride binder (such as the Advancer material sold by the company Norton), recrystallized silicon carbide (such as the Norton Crystar product), or materials based of silicon carbide impregnated with silicon.

Rollers based on oxide baked at moderate temperature have the disadvantage of only supporting modest loads: thus, the best rolls based on alumina-mullite-cordierite are limited to maximum loads such as the total bending stress (load + self-weight), i.e. less than 50 kg / cm ² for a maximum working temperature less than or equal to 1250 ° C. This greatly limits their usefulness for certain applications. Rolls based on alumina, alumina-mullite or mullite baked at very high temperatures withstand bending stresses of up to 80 kg / cm ² for maximum working temperatures less than or equal to 1300-1350 ° C, but their cost is much higher than that of rolls baked at low temperature.

On the other hand, the rollers formed from a material based on at least one silicon compound withstand bending stresses of 200 to 500 kg / cm ² , for a limit temperature of use which can reach 1600 ° C., but their cost is 7 to 20 times that of the oxide-based rollers.

It would therefore be very useful for industry to have rollers having improved properties compared to rollers based on conventional oxides, while being less expensive than rollers based on alumina, alumina-mullite or mullite. very high temperature frits or based on at least one silicon compound currently sold.

The invention aims to satisfy this need. More specifically, the invention relates to a composite roller for roller ovens comprising a hollow outer roller made of a refractory ceramic material based on oxides and a reinforcing element made of a refractory material having a higher modulus of elasticity at 1200 ° C. than that of the material of the outer roller, arranged inside the outer roller, the largest dimension of the cross section of the reinforcing element being slightly less than the inner diameter of the outer roller.

Advantageously, the modulus of elasticity at 1200 ° C. of the material of the reinforcing element is equal to at least 2 times that of the outer roller and, preferably, to at least 3 times. The modulus of the reinforcing element can be up to 20 times, and even more, than that of the material of the external element.

The outer roller will usually be made of an inexpensive oxide material suitable for the manufacture of oven rolls, for example an oxide material baked at moderate temperature, such as the aforementioned alumina-mullite cordierite material. . Such a material typically has a modulus of elasticity at 1200 ° C of 10 to 25 GPa. The wall thickness of the outer roller is typically of the order of 5-6 mm, without these values being of critical importance. The internal reinforcement element can have various shapes, for example that of a hollow cylinder or that of a hollow bar with hexagonal, square, triangular section or an X-shaped profile.

Preferably, for reasons of economy of material, mechanical strength and ease of manufacture, use will be made of a hollow cylindrical reinforcing element, that is to say in the form of a tube, having a wall thickness of the 1.5 to 4 mm.

The reinforcing element can be made, for example, of a material based on oxides baked at high temperature, such as a material based on alumina, alumina-mullite or mullite or a material based on at least one silicon compound such as those mentioned above, among others. Materials based on alumina, alumina-mullite or mullite baked at high temperature typically have a modulus of elasticity at 1200 ° C of 50 to 200 GPa, while materials based on at least one compound of silicon typically have a modulus of elasticity at 1200 ° C from 150 to 400 GPa. The internal reinforcement element advantageously has a length less than or equal to 0.9 times that of the external roller to be reinforced. For reasons of economy of material, it is preferred to use a reinforcing element of length substantially less than that of the outer roller, for example of a length representing 0.15 to 0.65 times that of the outer roller. For example, for an external roller 3 m long, the reinforcing element preferably has a length of approximately 0.5 to 2 m. The maximum dimension of the cross section of the reinforcing element should be slightly less than that of the inside diameter of the outside roller to allow the reinforcing element to be put in place and exert its action as soon as the outer roller bends a little under a load. For example, a clearance of 0.1 to 0.5 mm is usually satisfactory without these values being critical.

The reinforcing element will advantageously be centered with respect to the supports of the roller on the bearings of the oven supporting the roller, or also with respect to the loads supported by the roller in service, so that the external oxide-based roller is reinforced. mechanically in the area where the maximum bending stress prevails in service.

Experience has shown that it is not necessary to interpose ceramic felt or a layer of glue or cement between the reinforcing element and the outer roller. During assembly, the reinforcing element can be held in place with a little organic glue. During commissioning, it burns and the reinforcing element will be held in place in the position chosen by the arrow effect.

In the drawing, the single figure is a view, in longitudinal section, of a composite roller according to the invention.

In the figure, the reference 1 designates the exterior oxide-based roller, the reference 2 a reinforcing element in the form of a tube and of length shorter than that of the exterior roller, the reference 3 designates the areas where the roller will be, in service, supported on bearings, and the reference 4 designates the part of the roller which will project from the oven and will receive means for driving the roller, for example a toothed wheel (not shown).

The following nonlimiting example is given for the purpose of illustrating the invention. EXAMPLE Composite rollers of the type shown in the figure were produced, the roller 1 of which was produced from SIROLL LP (material of the Alumina-Mullite-Cordierite type) marketed by the Nuova Sirma Company) and had the following characteristics:

- outside radius 20 mm

- internal radius 15 mm - length 3 m

- Young's modulus at 1200 ° C 22000 Mpa

- coefficient of expansion 5.2 x ÎO ^"6 -. ^{" 1}

- density 2360 kg / m ³ The reinforcing element 2 was made of ADVANCER (Sic grains bound by a silicon nitride binder sold by the company Norton) and had the following characteristics:

- outer radius 14.5 mm

- internal radius 12.5 mm - length 0.5 m

- Young's modulus at 1200 ° C 225000 Mpa

- coefficient of expansion 4.8 x ÎO ^ K ^'1

- density 2820 kg / m ³ The rollers thus produced were mounted in a roller oven intended for firing ceramic tiles at a temperature of the order of 1200 ° C.

The distance between the supports of each roller on the bearings of the oven was 2.91 m and the loaded length was 1.83 m. First experience

The deflection taken by these composite rollers was compared with that of identical rollers in SIROLL LP unreinforced and that of Advancer rollers of identical geometry having a wall thickness of 5-6 mm. It can be seen that the weight of the Advancer reinforcement elements results in an increase in deflection of the composite rolls of about 1 mm when empty, compared to that of the rolls made of unreinforced Siroll LP. On the other hand, by circulating a load in the oven, corresponding to a load of 1.25 kg per roll distributed over the central portion of the roll, length 1.83 m, it is noted that the composite rollers of the invention have a arrow about 3 times lower than that of unreinforced rollers: 3.4 mm instead of 11.1 mm, while the deflection of the Advancer rollers is 2 mm. Second experiment The rolls were loaded with Siroll LP with a load of 3 kg per roll distributed over a length of 1.83 m. The deflection measured is 12 mm and the rupture occurs very quickly, after a few hours of operation.

On the other hand, the deflection measured is 6.0 mm for the composite rollers of the invention supporting the same load.

The present invention therefore makes it possible to obtain performance in service much higher than that of rolls based on standard oxides at a cost lower than that of rolls made of material baked at high temperature and much lower than that of rollers based on minus a silicon compound. Indeed, the reinforcing element used in the invention has a volume much lower than that of a roller made entirely of high performance material, because its diameter, its wall thickness and its length can be much less.

The invention also makes it possible to use the good hot stiffness of materials based on alumina, alumina-mullite or mullite baked at high temperature (overcooked), without risking rupture by thermal shock, when they are introduced into an oven on. Indeed, the outer roller, very resistant to thermal shock, constitutes a protective envelope for the internal reinforcement element, sensitive to thermal shock. It goes without saying that the embodiment described is only an example and it could be modified, in particular by substitution of technical equivalents, without departing from the scope of the invention.

Claims

1. A composite roller for roller ovens comprising a hollow outer roller made of a refractory ceramic material based on oxides and a reinforcing element made of a refractory material having a modulus of elasticity at 1200 ° C higher than that of the material of the outer roller, arranged inside the outer roller, the largest dimension of the cross section of the reinforcing element being slightly less than the inner diameter of the outer roller.

2. A roller according to claim 1, characterized in that the internal reinforcing element has the form of a tube.

3. A roller according to claim 2, characterized in that the reinforcing element has a wall thickness of 1.5 to 4 mm.

4. A roller according to any one of claims 1 to 3, characterized in that the reinforcing element is shorter than the outer roller.

5. A roller according to claim 4, characterized in that the length of the reinforcing element represents 0.15 to 0.65 times that of the outer roller.

6. A roller according to claim 1, 4 or 5, characterized in that the reinforcing element is centered relative to the supports of the roller on the bearings of the oven supporting the roller.

7. A roller according to claim 1, 4 or 5, characterized in that the reinforcing element is centered with respect to the loads supported by the roller in service.

8. Roller according to claims 2 to 7, characterized in that the modulus of elasticity at 1200 ° C of the material constituting the reinforcing element is at least 2 times greater than that of the outer part.

9. Roller according to claims 2 to 7, characterized in that the modulus of elasticity at 1200 ° C of the material constituting the reinforcing element is at least 3 times higher than that of the external part.

10. Roller according to any one of claims 1 to 9, characterized in that the outer roller is made of alumina-mullite-cordierite and the reinforcing element is made of a material chosen from the group formed by materials based on alumina, alumina-mullite or mullite, materials based on at least one silicon compound chosen from the group formed by silicon carbon, silicon nitride, silicon oxynitride and sialons.