Manufacturing method of magnesium-aluminium spinel brick and magnesium-aluminium spinel brick manufactured by the method

Abstract

A manufacturing method of a low heat-conducting magnesium-aluminium spinel brick includes: (1) evenly mixing sintered magnesia, fused magnesia, magnesium-aluminium spinel and corundum to prepare flame retardant coating raw material mixed powder, adding naphthalene binder to the flame retardant coating raw material mixed powder to prepare the flame retardant coating raw materials after evenly mixing; (2) evenly mixing forsterite, fayalite and magnesia, adding the naphthalene binder to the mixed powder, moulding, drying, and then burning to obtain aggregate composite hortonolite raw materials; adding the naphthalene binder to the aggregate composite hortonolite having granularity ≤5 mm to prepare the thermal insulating layer raw materials after evenly mixing; (3) spacing and loading the flame retardant coating raw materials and the thermal insulating layer raw materials in a mold, pressing into green bricks, keeping the green bricks at a temperature of 110° C. for 24 hours, drying, and burning into magnesium-aluminium spinel bricks.

Claims

1. A manufacturing method of a magnesium-aluminium spinel brick, wherein the magnesium-aluminium spinel brick comprises a flame retardant coating and a thermal insulating layer, the manufacturing method of the magnesium-aluminium spinel brick comprises specific manufacturing steps as follows: step (1) preparing flame retardant coating raw materials using the following components by mass percent, evenly mixing 40%-70% of sintered magnesia having a granularity ≤5 mm, 10%-40% of fused magnesia having a granularity ≤3 mm, 10%-20% of magnesium-aluminium spinel having a granularity ≤4 mm, and 0%-10% (excluding 0%) of corundum having a granularity ≤2 mm to prepare flame retardant coating raw material mixed powder, then additionally adding 1%-5% of naphthalene binder by taking the flame retardant coating raw material mixed powder as a basis, for an even mixing to prepare the flame retardant coating raw materials; step (2) preparing thermal insulating layer raw materials using the following components by mass percent, evenly mixing 40%-60% of forsterite, 10%-40% of fayalite, and 10%-50% of magnesia to obtain mixed powder, adding 1%-5% of naphthalene binder by taking the mixed powder as a basis to obtain a mixed material, moulding the mixed material by a frictional press, drying the mixed material at 110° C.-150° C., and then burning the mixed material at a temperature of above 1000° C. to obtain aggregate composite hortonolite raw materials; taking aggregate composite hortonolite having a granularity ≤5 mm from the aggregate composite hortonolite raw materials as a single raw material, adding 1%-5% of naphthalene binder to the aggregate composite hortonolite having the granularity ≤5 mm for an even mixing to prepare the thermal insulating layer raw materials; and step (3) spacing and loading the flame retardant coating raw materials and the thermal insulating layer raw materials in a mold by using corrugated thin iron sheets, pressing the flame retardant coating raw materials and the thermal insulating layer raw materials into green bricks by a press machine, keeping the green bricks at a temperature of 110° C. for 24 hours, drying the green bricks, and burning the green bricks into the magnesium-aluminium spinel brick at a temperature of 1550° C.-1750° C. in a tunnel kiln; wherein a sequence of the step (1) and the step (2) are allowed to be inversed.

2. The manufacturing method of the magnesium-aluminium spinel brick according to claim 1, wherein: step (1) the preparation of the flame retardant coating raw materials using the following components by mass percent, evenly mixing 45%-70% of sintered magnesia having the granularity ≤5 mm, 15%-40% of fused magnesia having the granularity ≤3 mm, 10%-20% of magnesium-aluminium spinel having the granularity ≤4 mm, and 0%-40% (excluding 0%) of corundum having the granularity ≤2 mm to prepare the flame retardant coating raw material mixed powder, then additionally adding 2%-5% of naphthalene binder by taking the flame retardant coating raw material mixed powder as a basis for an even mixing to prepare the flame retardant coating raw materials; step (2) the preparation of the thermal insulating layer raw materials using the following components by mass percent, evenly mixing 50%-60% of forsterite, 20%-30% of fayalite, and 20%-30% of magnesia to obtain the mixed powder, adding 2%-5% of naphthalene binder by taking the mixed powder as a basis to obtain the mixed material, moulding the mixed material by the frictional press, drying the mixed material at 110° C.-150° C., burning the mixed material at the high temperature of above 1000° C. to obtain the aggregate composite hortonolite raw materials; and taking the aggregate composite hortonolite having the granularity ≤5 mm from the aggregate composite hortonolite raw materials as a single raw material, adding 2%-5% of naphthalene binder to the aggregate composite hortonolite having the granularity ≤5 mm for an even mixing to prepare the thermal insulating layer raw materials.

3. The manufacturing method of the magnesium-aluminium spinel brick according to claim 1, wherein: in the step (2), the step of taking the aggregate composite hortonolite having the granularity ≤5 mm from the aggregate composite hortonolite raw materials as a single raw material comprises: taking 65%-75% (mass percent content) of a first aggregate composite hortonolite having the granularity ≤5 mm and 25-35% (mass percent content) of a second aggregate composite hortonolite having a granularity ≤0.088 mm as the single raw material.

4. The manufacturing method of the magnesium-aluminium spinel brick according to claim 3, wherein: a mass percent content of the aggregate composite hortonolite having the granularity ≤5 mm is 67%-70%, and a mass percent content of the aggregate composite hortonolite having the granularity ≤0.088 mm is 30%-33%.

5. The manufacturing method of the magnesium-aluminium spinel brick according to claim 4, wherein: the mass percent content of the aggregate composite hortonolite having the granularity ≤5 mm is 67%, accordingly the mass percent content of the aggregate composite hortonolite having the granularity ≤0.088 mm is 33%; or the mass percent content of the aggregate composite hortonolite having the granularity ≤5 mm is 68%, accordingly the mass percent content of the aggregate composite hortonolite having the granularity ≤0.088 mm is 32%; or the mass percent content of the aggregate composite hortonolite having the granularity ≤5 mm is 70%, accordingly the mass percent content of the aggregate composite hortonolite having the granularity ≤0.088 mm is 30%.

6. The manufacturing method of the magnesium-aluminium spinel brick according to claim 1, wherein the naphthalene binder is naphthalene sulfonate formaldehyde condensate.

7. The manufacturing method of the magnesium-aluminium spinel brick according to claim 1, wherein in the flame retardant coating raw materials: a mass percent content of MgO in the sintered magnesia is above 96.5%; a mass percent content of MgO in the fused magnesia is above 97%; the magnesium-aluminium spinel is sintered magnesium-aluminium spinel or fused magnesium-aluminium spinel, a mass percent content of Al.sub.2O.sub.3 in the sintered magnesium-aluminium spinel is 66%-73%, a mass percent content of Al.sub.2O.sub.3 in the fused magnesium-aluminium spinel is 70%-75%; a mass percent content of Al.sub.2O.sub.3 in the corundum is above 99%; in the thermal insulating layer raw materials: a mass percent content of MgO in the forsterite is 62%-67% and a mass percent content of SiO.sub.2 in the forsterite is 25%-30%; a mass percent content of FeO in the fayalite is 48%-53% and a mass percent content of SiO.sub.2 in the fayalite is 41%-46%; the magnesia is sintered magnesia or fused magnesia, a mass percent content of MgO in the sintered magnesia is above 96.5%, a mass percent content of MgO in the fused magnesia is above 97%.

8. A magnesium-aluminium spinel brick, wherein the magnesium-aluminium spinel brick is manufactured by the manufacturing method according to claim 1.

9. The manufacturing method of the magnesium-aluminium spinel brick according to claim 2, wherein in the flame retardant coating raw materials: a mass percent content of MgO in the sintered magnesia is above 96.5%; a mass percent content of MgO in the fused magnesia is above 97%; the magnesium-aluminium spinel is sintered magnesium-aluminium spinel or fused magnesium-aluminium spinel, a mass percent content of Al.sub.2O.sub.3 in the sintered magnesium-aluminium spinel is 66%-73%, a mass percent content of Al.sub.2O.sub.3 in the fused magnesium-aluminium spinel is 70%-75%; a mass percent content of Al.sub.2O.sub.3 in the corundum is above 99%; in the thermal insulating layer raw materials: a mass percent content of MgO in the forsterite is 62%-67% and a mass percent content of SiO.sub.2 in the forsterite is 25%-30%; a mass percent content of FeO in the fayalite is 48%-53% and a mass percent content of SiO.sub.2 in the fayalite is 41%-46%; the magnesia is sintered magnesia or fused magnesia, a mass percent content of MgO in the sintered magnesia is above 96.5%, a mass percent content of MgO in the fused magnesia is above 97%.

10. The manufacturing method of the magnesium-aluminium spinel brick according to claim 3, wherein in the flame retardant coating raw materials: a mass percent content of MgO in the sintered magnesia is above 96.5%; a mass percent content of MgO in the fused magnesia is above 97%; the magnesium-aluminium spinel is sintered magnesium-aluminium spinel or fused magnesium-aluminium spinel, a mass percent content of Al.sub.2O.sub.3 in the sintered magnesium-aluminium spinel is 66%-73%, a mass percent content of Al.sub.2O.sub.3 in the fused magnesium-aluminium spinel is 70%-75%; a mass percent content of Al.sub.2O.sub.3 in the corundum is above 99%; in the thermal insulating layer raw materials: a mass percent content of MgO in the forsterite is 62%-67% and a mass percent content of SiO.sub.2 in the forsterite is 25%-30%; a mass percent content of FeO in the fayalite is 48%-53% and a mass percent content of SiO.sub.2 in the fayalite is 41%-46%; the magnesia is sintered magnesia or fused magnesia, a mass percent content of MgO in the sintered magnesia is above 96.5%, a mass percent content of MgO in the fused magnesia is above 97%.

11. The manufacturing method of the magnesium-aluminium spinel brick according to claim 4, wherein in the flame retardant coating raw materials: a mass percent content of MgO in the sintered magnesia is above 96.5%; a mass percent content of MgO in the fused magnesia is above 97%; the magnesium-aluminium spinel is sintered magnesium-aluminium spinel or fused magnesium-aluminium spinel, a mass percent content of Al.sub.2O.sub.3 in the sintered magnesium-aluminium spinel is 66%-73%, a mass percent content of Al.sub.2O.sub.3 in the fused magnesium-aluminium spinel is 70%-75%; a mass percent content of Al.sub.2O.sub.3 in the corundum is above 99%; in the thermal insulating layer raw materials: a mass percent content of MgO in the forsterite is 62%-67% and a mass percent content of SiO.sub.2 in the forsterite is 25%-30%; a mass percent content of FeO in the fayalite is 48%-53% and a mass percent content of SiO.sub.2 in the fayalite is 41%-46%; the magnesia is sintered magnesia or fused magnesia, a mass percent content of MgO in the sintered magnesia is above 96.5%, a mass percent content of MgO in the fused magnesia is above 97%.

12. The manufacturing method of the magnesium-aluminium spinel brick according to claim 5, wherein in the flame retardant coating raw materials: a mass percent content of MgO in the sintered magnesia is above 96.5%; a mass percent content of MgO in the fused magnesia is above 97%; the magnesium-aluminium spinel is sintered magnesium-aluminium spinel or fused magnesium-aluminium spinel, a mass percent content of Al.sub.2O.sub.3 in the sintered magnesium-aluminium spinel is 66%-73%, a mass percent content of Al.sub.2O.sub.3 in the fused magnesium-aluminium spinel is 70%-75%; a mass percent content of Al.sub.2O.sub.3 in the corundum is above 99%; in the thermal insulating layer raw materials: a mass percent content of MgO in the forsterite is 62%-67% and a mass percent content of SiO.sub.2 in the forsterite is 25%-30%; a mass percent content of FeO in the fayalite is 48%-53% and a mass percent content of SiO.sub.2 in the fayalite is 41%-46%; the magnesia is sintered magnesia or fused magnesia, a mass percent content of MgO in the sintered magnesia is above 96.5%, a mass percent content of MgO in the fused magnesia is above 97%.

13. The magnesium-aluminium spinel brick according to claim 8, wherein: step (1) preparing the flame retardant coating raw materials using the following components by mass percent, evenly mixing 45%-70% of sintered magnesia having the granularity ≤5 mm, 15%-40% of fused magnesia having the granularity ≤3 mm, 10%-20% of magnesium-aluminium spinel having the granularity ≤4 mm, and 0%-40% (excluding 0%) of corundum having the granularity ≤2 mm to prepare the flame retardant coating raw material mixed powder, then additionally adding 2%-5% of naphthalene binder by taking the flame retardant coating raw material mixed powder as a basis for an even mixing to prepare the flame retardant coating raw materials; step (2) preparing the thermal insulating layer raw materials using the following components by mass percent, evenly mixing 50%-60% of forsterite, 20%-30% of fayalite, and 20%-30% of magnesia to obtain the mixed powder, adding 2%-5% of naphthalene binder by taking the mixed powder as a basis to obtain the mixed material, moulding the mixed material by the frictional press, drying the mixed material at 110° C.-150° C., burning the mixed material at the high temperature of above 1000° C. to obtain the aggregate composite hortonolite raw materials; and taking the aggregate composite hortonolite having the granularity ≤5 mm from the aggregate composite hortonolite raw materials as a single raw material, adding 2%-5% of naphthalene binder to the aggregate composite hortonolite having the granularity ≤5 mm for an even mixing to prepare the thermal insulating layer raw materials.

14. The magnesium-aluminium spinel brick according to claim 8, wherein: in the step (2), the step of taking the aggregate composite hortonolite having the granularity ≤5 mm from the aggregate composite hortonolite raw materials as a single raw material comprises: taking 65%-75% (mass percent content) of a first aggregate composite hortonolite having the granularity ≤5 mm and a mass percent content of 25-35% of a second aggregate composite hortonolite having a granularity ≤0.088 mm as the single raw material.

15. The magnesium-aluminium spinel brick according to claim 14, wherein: a mass percent content of the aggregate composite hortonolite having the granularity ≤5 mm is 67%-70%, and a mass percent content of the aggregate composite hortonolite having the granularity ≤0.088 mm is 30%-33%.

16. The magnesium-aluminium spinel brick according to claim 15, wherein: the mass percent content of the aggregate composite hortonolite having the granularity ≤5 mm is 67%, accordingly the mass percent content of the aggregate composite hortonolite having the granularity ≤0.088 mm is 33%; or the mass percent content of the aggregate composite hortonolite having the granularity ≤5 mm is 68%, accordingly the mass percent content of the aggregate composite hortonolite having the granularity ≤0.088 mm is 32%; or the mass percent content of the aggregate composite hortonolite having the granularity ≤5 mm is 70%, accordingly the mass percent content of the aggregate composite hortonolite having the granularity ≤0.088 mm is 30%.

17. The magnesium-aluminium spinel brick according to claim 8, wherein the naphthalene binder is naphthalene sulfonate formaldehyde condensate.

18. The magnesium-aluminium spinel brick according to claim 8, wherein in the flame retardant coating raw materials: a mass percent content of MgO in the sintered magnesia is above 96.5%; a mass percent content of MgO in the fused magnesia is above 97%; the magnesium-aluminium spinel is sintered magnesium-aluminium spinel or fused magnesium-aluminium spinel, a mass percent content of Al.sub.2O.sub.3 in the sintered magnesium-aluminium spinel is 66%-73%, a mass percent content of Al.sub.2O.sub.3 in the fused magnesium-aluminium spinel is 70%-75%; a mass percent content of Al.sub.2O.sub.3 in the corundum is above 99%; in the thermal insulating layer raw materials: a mass percent content of MgO in the forsterite is 62%-67% and a mass percent content of SiO.sub.2 in the forsterite is 25%-30%; a mass percent content of FeO in the fayalite is 48%-53% and a mass percent content of SiO.sub.2 in the fayalite is 41%-46%; the magnesia is sintered magnesia or fused magnesia, a mass percent content of MgO in the sintered magnesia is above 96.5%, a mass percent content of MgO in the fused magnesia is above 97%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is the configuration of refractory materials of a domestic cement rotary kiln.

(2) FIG. 2 is an Al.sub.2O.sub.3—SiO.sub.2—CaO system phase diagram.

(3) FIG. 3 is a MgO—Al.sub.2O.sub.3—CaO system phase diagram.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) In the following embodiments, a naphthalene binder employs naphthalene sulfonate formaldehyde condensate. The use of naphthalene binder improves the dispersion effect of the binder, does not introduce air, has a small effect on the setting time of materials, has a high semifinished product moulding strength. The most important characteristic is that it is alkalinous and does not react with alkalinous refractory materials.

(5) In the following embodiments, in the flame retardant coating raw materials:

(6) the mass percent content of MgO in adopted sintered magnesia is above 96.5%; the mass percent content of MgO in adopted fused magnesia is above 97%; magnesium-aluminium spinel may adopt sintered magnesium-aluminium spinel or fused magnesium-aluminium spinel, and if the sintered magnesium-aluminium spinel is adopted, the mass percent content of Al.sub.2O.sub.3 in sintered magnesium-aluminium spinel is 66%-73%, and if the fused magnesium-aluminium spinel is adopted, the mass percent content of Al.sub.2O.sub.3 in fused magnesium-aluminium spinel is 70%-75%; the mass percent content of Al.sub.2O.sub.3 in adopted corundum is above 99%;

(7) in the thermal insulating layer raw materials:

(8) the mass percent content of MgO in adopted forsterite is 62%-67% and the mass percent content of SiO.sub.2 is 25%-30%; the mass percent content of FeO in adopted fayalite is 48%-53% and the mass percent content of SiO.sub.2 is 41%-46%; magnesia may adopt sintered magnesia or fused magnesia, and if the sintered magnesia is adopted, the mass percent content of MgO in sintered magnesia is above 96.5%, and if the fused magnesia is adopted, the mass percent content of MgO in fused magnesia is above 97%.

Embodiment 1

(9) The present embodiment provides a manufacturing method of a magnesium-aluminium spinel brick and a magnesium-aluminium spinel brick manufactured by employing the method. The magnesium-aluminium spinel brick includes a flame retardant coating and a thermal insulating layer. Specific manufacturing steps are as follows:

(10) (1) preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent,

(11) sintered magnesia, granularity is ≤5 mm, accounts for 45% of total amount;

(12) magnesium-aluminium spinel, granularity is ≤4 mm, accounts for 10% of total amount

(13) fused magnesia, granularity is ≤3 mm, accounts for 40% of total amount;

(14) corundum, granularity is ≤2 mm, accounts for 5% of total amount.

(15) The above mentioned raw materials are weighted, mixed, and compounded by the naphthalene binder to manufacture flame retardant coating raw materials of the low heat-conducting magnesium-aluminium spinel brick. The amount of the added naphthalene binder is 1%-5% (mass percent) by taking the above mentioned mixed powder as a basis. Preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis. In the present embodiment, the amount of the added naphthalene binder is 2% by taking the above mentioned mixed powder as a basis.

(16) (2) preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent,

(17) forsterite which accounts of 40%-60% of the total amount, fayalite which accounts of 10%-40% of the total amount, magnesia which accounts of 10%-50% of the total amount are selected to be evenly mixed, additional 1%-5% naphthalene binder is added by taking mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; specifically, in the present embodiment, forsterite which accounts of 50% of the total amount, fayalite which accounts of 20% of the total amount, magnesia which accounts of 30% of the total amount are evenly mixed, 1%-5% naphthalene binder is added by taking mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; wherein the amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis; preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis; in the present embodiment, the amount of the added naphthalene binder is 2% by taking the above mentioned mixed powder as a basis.

(18) Mass of a portion, which has granularity ≤5 mm, of the above mentioned manufactured aggregate composite hortonolite raw material is made account for 67% of the total amount, mass of a portion which has granularity ≤0.088 mm is made account for 33% of the total amount, then 1%-5% naphthalene binder is additionally added by taking the aggregate composite hortonolite raw material as a basis, thermal insulating layer raw materials are prepared after evenly mixing; preferably, here, the amount of the added naphthalene binder is 2%-5% by taking the aggregate composite hortonolite raw material as a basis; in the present embodiment, the amount of the added naphthalene binder is 2% by taking the aggregate composite hortonolite raw material as a basis.

(19) (3) the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine after the thin iron sheets are removed, kept at a temperature of 110° C. for 24 hours, dried, and burned into low heat-conducting magnesium-aluminium spinel bricks at a temperature of 1710° C. in a tunnel kiln.

(20) wherein the sequence of step (1) and step (2) is irrelevant.

(21) After the above mentioned three steps, the low heat-conducting magnesium-aluminium spinel brick is obtained.

Embodiment 2

(22) The present embodiment provides a manufacturing method of a magnesium-aluminium spinel brick and a magnesium-aluminium spinel brick manufactured by employing the method, which may be used for a transition zone of a cement kiln. The magnesium-aluminium spinel brick includes a flame retardant coating and a thermal insulating layer. Specific manufacturing steps are as follows:

(23) (1) preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent,

(24) sintered magnesia, granularity is ≤5 mm, accounts for 60% of total amount;

(25) magnesium-aluminium spinel, granularity is ≤4 mm, accounts for 10% of total amount;

(26) fused magnesia, granularity is ≤3 mm, accounts for 25% of total amount;

(27) corundum, granularity is ≤2 mm, accounts for 5% of total amount.

(28) The above mentioned raw materials are weighted, mixed, and compounded by the naphthalene binder to manufacture flame retardant coating raw materials of the low heat-conducting magnesium-aluminium spinel brick. The amount of the added naphthalene binder is extra 1%-5% by taking the above mentioned mixed powder as a basis. Preferably, here, the amount of the added naphthalene binder is extra 2%-5% by taking the above mentioned mixed powder as a basis; in the present embodiment, the amount of the added naphthalene binder is 3% by taking the above mentioned mixed powder as a basis.

(29) (2) preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent,

(30) forsterite 40%-60%, fayalite 10%-40%, magnesia 10%-50% are selected to be evenly mixed, 1%-5% naphthalene binder is added by taking mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; specifically, in the present embodiment, forsterite which accounts of 55% of the total amount, fayalite which accounts of 25% of the total amount, magnesia which accounts of 20% of the total amount are evenly mixed, 1%-5% naphthalene binder is added by taking the mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; wherein the amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis; preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis; in the present embodiment, the amount of the added naphthalene binder is 3% by taking the above mentioned mixed powder as a basis.

(31) A portion, which has granularity ≤5 mm, of the above mentioned manufactured aggregate composite hortonolite raw material is made account for 70% (mass percent) of the total amount, a portion which has granularity ≤0.088 mm is made account for 30% (mass percent) of the total amount, then 1%-5% (mass percent) naphthalene binder is additionally added by taking the aggregate composite hortonolite raw material as a basis, thermal insulating layer raw materials are prepared after evenly mixing; preferably, here, the amount of the added naphthalene binder is 2%-5% by taking the aggregate composite hortonolite raw material as a basis; in the present embodiment, the amount of the added naphthalene binder is 3% by taking the aggregate composite hortonolite raw material as a basis.

(32) (3) the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine after the thin iron sheets are removed, kept at a temperature of 110° C. for 24 hours, dried, and burned into low heat-conducting magnesium-aluminium spinel bricks at a temperature of 1630° C. in a tunnel kiln.

(33) wherein the sequence of step (1) and step (2) is irrelevant.

(34) After the above mentioned three steps, the low heat-conducting magnesium-aluminium spinel brick is obtained.

Embodiment 3

(35) The present embodiment provides a manufacturing method of a magnesium-aluminium spinel brick and a magnesium-aluminium spinel brick manufactured by employing the method, which may be used for a transition zone of a cement kiln. The magnesium-aluminium spinel brick includes a flame retardant coating and a thermal insulating layer. Specific manufacturing steps are as follows:

(36) (1) preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent,

(37) sintered magnesia, granularity is ≤5 mm, accounts for 68% of total amount;

(38) magnesium-aluminium spinel, granularity is ≤4 mm, accounts for 10% of total amount;

(39) fused magnesia, granularity is ≤3 mm, accounts for 19% of total amount;

(40) corundum, granularity is ≤2 mm, accounts for 3% of total amount.

(41) The above mentioned raw materials are weighted, mixed, and compounded by the naphthalene binder to manufacture flame retardant coating raw materials of the low heat-conducting magnesium-aluminium spinel brick. The amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis. Preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis, in the present embodiment, the amount of the added naphthalene binder is 3% by taking the above mentioned mixed powder as a basis.

(42) (2) preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent,

(43) forsterite 40%-60%, fayalite 10%-40%, magnesia 10%-50% are selected to be evenly mixed, 1%-5% naphthalene binder is added by taking the mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; specifically, in the present embodiment, forsterite which accounts of 40% of the total amount, fayalite which accounts of 40% of the total amount, magnesia which accounts of 20% of the total amount are evenly mixed, 1%-5% naphthalene binder is added by taking the mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; wherein the amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis; preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis; in the present embodiment, the amount of the added naphthalene binder is 4% by taking the above mentioned mixed powder as a basis.

(44) Mass of a portion, which has granularity ≤5 mm, of the above mentioned manufactured aggregate composite hortonolite raw material is made account for 68% of the total amount, mass of a portion which has granularity ≤0.088 mm is made account for 32% of the total amount, then 1%-5% naphthalene binder is additionally added by taking the aggregate composite hortonolite raw material as a basis, thermal insulating layer raw materials are prepared after evenly mixing; preferably, here, the amount of the added naphthalene binder is 2%-5% by taking the aggregate composite hortonolite raw material as a basis; in the present embodiment, the amount of the added naphthalene binder is 5% by taking the aggregate composite hortonolite raw material as a basis.

(45) (3) the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine after the thin iron sheets are removed, kept at a temperature of 110° C. for 24 hours, dried, and burned into low heat-conducting magnesium-aluminium spinel bricks at a temperature of 1580° C. in a tunnel kiln.

(46) wherein the sequence of step (1) and step (2) is irrelevant.

(47) After the above mentioned three steps, the low heat-conducting magnesium-aluminium spinel brick is obtained.

Embodiment 4

(48) The present embodiment provides a manufacturing method of a magnesium-aluminium spinel brick and a magnesium-aluminium spinel brick manufactured by employing the method, which may be used for a transition zone of a cement kiln. The magnesium-aluminium spinel brick includes a flame retardant coating and a thermal insulating layer. Specific manufacturing steps are as follows:

(49) (1) preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent,

(50) sintered magnesia, granularity is ≤5 mm, accounts for 40% of total amount;

(51) magnesium-aluminium spinel, granularity is ≤4 mm, accounts for 20% of total amount;

(52) fused magnesia, granularity is ≤3 mm, accounts for 30% of total amount;

(53) corundum, granularity is ≤2 mm, accounts for 10% of total amount.

(54) The above mentioned raw materials are weighted, mixed, and compounded by the naphthalene binder to manufacture flame retardant coating raw materials of the low heat-conducting magnesium-aluminium spinel brick. The amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis. Preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis. In the present embodiment, the amount of the added naphthalene binder is 5% by taking the above mentioned mixed powder as a basis.

(55) (2) preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent,

(56) forsterite which accounts of 40% of the total amount, fayalite which accounts of 10% of the total amount, magnesia which accounts of 50% of the total amount are evenly mixed, 1%-5% naphthalene binder is added by taking mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; wherein the amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis; in the present embodiment, the amount of the added naphthalene binder is 1% by taking the above mentioned mixed powder as a basis.

(57) A portion, which has granularity ≤5 mm, of the above mentioned manufactured aggregate composite hortonolite raw material is made account for 65% (mass percent) of the total amount, a portion which has granularity ≤0.088 mm is made account for 35% (mass percent) of the total amount, then 1%-5% (mass percent) naphthalene binder is additionally added by taking the aggregate composite hortonolite raw material as a basis, thermal insulating layer raw materials are prepared after evenly mixing; preferably, here, the amount of the added naphthalene binder is 2%-5% by taking the aggregate composite hortonolite raw material as a basis; in the present embodiment, the amount of the added naphthalene binder is 5% by taking the aggregate composite hortonolite raw material as a basis.

(58) (3) the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine after the thin iron sheets are removed, kept at a temperature of 110° C. for 24 hours, dried, and burned into low heat-conducting magnesium-aluminium spinel bricks at a temperature of 1550° C. in a tunnel kiln.

(59) wherein the sequence of step (1) and step (2) is irrelevant.

(60) After the above mentioned three steps, the low heat-conducting magnesium-aluminium spinel brick is obtained.

Embodiment 5

(61) The present embodiment provides a manufacturing method of a magnesium-aluminium spinel brick and a magnesium-aluminium spinel brick manufactured by employing the method, which may be used for a transition zone of a cement kiln. The magnesium-aluminium spinel brick includes a flame retardant coating and a thermal insulating layer. Specific manufacturing steps are as follows:

(62) (1) preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent,

(63) sintered magnesia, granularity is ≤5 mm, accounts for 50% of total amount;

(64) magnesium-aluminium spinel, granularity is ≤4 mm, accounts for 18% of total amount;

(65) fused magnesia, granularity is ≤3 mm, accounts for 30% of total amount;

(66) corundum, granularity is ≤2 mm, accounts for 2% of total amount.

(67) The above mentioned raw materials are weighted, mixed, and compounded by the naphthalene binder to manufacture flame retardant coating raw materials of the low heat-conducting magnesium-aluminium spinel brick. The amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis. Preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis, in the present embodiment, the amount of the added naphthalene binder is 3% by taking the above mentioned mixed powder as a basis.

(68) (2) preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent,

(69) forsterite which accounts of 60% of the total amount, fayalite which accounts of 20% of the total amount, magnesia which accounts of 20% of the total amount are evenly mixed, 1%-5% naphthalene binder is added by taking mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; wherein the amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis; preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis; in the present embodiment, the amount of the added naphthalene binder is 3% by taking the above mentioned mixed powder as a basis.

(70) A portion, which has granularity ≤5 mm, of the above mentioned manufactured aggregate composite hortonolite raw material is made account for 70% (mass percent) of the total amount, a portion which has granularity ≤0.088 mm is made account for 30% (mass percent) of the total amount, then 1%-5% (mass percent) naphthalene binder is additionally added by taking the aggregate composite hortonolite raw material as a basis, thermal insulating layer raw materials are prepared after evenly mixing; preferably, here, the amount of the added naphthalene binder is 2%-5% by taking the aggregate composite hortonolite raw material as a basis; in the present embodiment, the amount of the added naphthalene binder is 4% by taking the aggregate composite hortonolite raw material as a basis.

(71) (3) the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine after the thin iron sheets are removed, kept at a temperature of 110° C. for 24 hours, dried, and burned into low heat-conducting magnesium-aluminium spinel bricks at a temperature of 1750° C. in a tunnel kiln.

(72) wherein the sequence of step (1) and step (2) is irrelevant.

(73) After the above mentioned three steps, the low heat-conducting magnesium-aluminium spinel brick is obtained.

Embodiment 6

(74) The present embodiment provides a manufacturing method of a magnesium-aluminium spinel brick and a magnesium-aluminium spinel brick manufactured by employing the method, which may be used for a transition zone of a cement kiln. The magnesium-aluminium spinel brick includes a flame retardant coating and a thermal insulating layer. Specific manufacturing steps are as follows:

(75) (1) preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent,

(76) sintered magnesia, granularity is ≤5 mm, accounts for 70% of total amount;

(77) magnesium-aluminium spinel, granularity is ≤4 mm, accounts for 10% of total amount;

(78) fused magnesia, granularity is ≤3 mm, accounts for 15% of total amount;

(79) corundum, granularity is ≤2 mm, accounts for 5% of total amount.

(80) The above mentioned raw materials are weighted, mixed, and compounded by the naphthalene binder to manufacture flame retardant coating raw materials of the low heat-conducting magnesium-aluminium spinel brick. The amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis. Preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis. In the present embodiment, the amount of the added naphthalene binder is 2% by taking the above mentioned mixed powder as a basis.

(81) (2) preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent,

(82) forsterite which accounts of 50% of the total amount, fayalite which accounts of 30% of the total amount, magnesia which accounts of 20% of the total amount are evenly mixed, 1%-5% naphthalene binder is added by taking the mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; wherein the amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis; preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis; in the present embodiment, the amount of the added naphthalene binder is 5% by taking the above mentioned mixed powder as a basis.

(83) A portion, which has granularity ≤5 mm, of the above mentioned manufactured aggregate composite hortonolite raw material is made account for 69% (mass percent) of the total amount, a portion which has granularity ≤0.088 mm is made account for 31% (mass percent) of the total amount, then 1%-5% (mass percent) naphthalene binder is additionally added by taking the aggregate composite hortonolite raw material as a basis, thermal insulating layer raw materials are prepared after evenly mixing; preferably, here, the amount of the added naphthalene binder is 2%-5% by taking the aggregate composite hortonolite raw material as a basis; in the present embodiment, the amount of the added naphthalene binder is 3% by taking the aggregate composite hortonolite raw material as a basis.

(84) (3) the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine after the thin iron sheets are removed, kept at a temperature of 110° C. for 24 hours, dried, and burned into low heat-conducting magnesium-aluminium spinel bricks at a temperature of 1600° C. in a tunnel kiln.

(85) wherein the sequence of step (1) and step (2) is irrelevant.

(86) After the above mentioned three steps, the low heat-conducting magnesium-aluminium spinel brick is obtained.

Embodiment 7

(87) The present embodiment provides a manufacturing method of a magnesium-aluminium spinel brick and a magnesium-aluminium spinel brick manufactured by employing the method, which may be used for a transition zone of a cement kiln. The magnesium-aluminium spinel brick includes a flame retardant coating and a thermal insulating layer. Specific manufacturing steps are as follows:

(88) (1) preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent,

(89) sintered magnesia, granularity is ≤5 mm, accounts for 70% of total amount;

(90) magnesium-aluminium spinel, granularity is ≤4 mm, accounts for 10% of total amount;

(91) fused magnesia, granularity is ≤3 mm, accounts for 10% of total amount;

(92) corundum, granularity is ≤2 mm, accounts for 10% of total amount.

(93) The above mentioned raw materials are weighted, mixed, and compounded by the naphthalene binder to manufacture flame retardant coating raw materials of the low heat-conducting magnesium-aluminium spinel brick. The amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis. In the present embodiment, the amount of the added naphthalene binder is 1% by taking the above mentioned mixed powder as a basis.

(94) (2) preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent,

(95) forsterite which accounts of 55% of the total amount, fayalite which accounts of 35% of the total amount, magnesia which accounts of 10% of the total amount are evenly mixed, 1%-5% naphthalene binder is added by taking the mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; wherein the amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis; preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis; in the present embodiment, the amount of the added naphthalene binder is 3% by taking the above mentioned mixed powder as a basis.

(96) A portion, which has granularity ≤5 mm, of the above mentioned manufactured aggregate composite hortonolite raw material is made account for 75% (mass percent) of the total amount, a portion which has granularity ≤0.088 mm is made account for 25% (mass percent) of the total amount, then 1%-5% (mass percent) naphthalene binder is additionally added by taking the aggregate composite hortonolite raw material as a basis, thermal insulating layer raw materials are prepared after evenly mixing; in the present embodiment, the amount of the added naphthalene binder is 1% by taking the aggregate composite hortonolite raw material as a basis.

(97) (3) the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine after the thin iron sheets are removed, kept at a temperature of 110° C. for 24 hours, dried, and burned into low heat-conducting magnesium-aluminium spinel bricks at a temperature of 1580° C. in a tunnel kiln.

(98) wherein the sequence of step (1) and step (2) is irrelevant.

(99) After the above mentioned three steps, the low heat-conducting magnesium-aluminium spinel brick is obtained.

Embodiment 8

(100) The present embodiment provides a manufacturing method of a magnesium-aluminium spinel brick and a magnesium-aluminium spinel brick manufactured by employing the method, which may be used for a transition zone of a cement kiln. The magnesium-aluminium spinel brick includes a flame retardant coating and a thermal insulating layer. Specific manufacturing steps are as follows:

(101) (1) preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent,

(102) sintered magnesia, granularity is ≤5 mm, accounts for 50% of total amount;

(103) magnesium-aluminium spinel, granularity is ≤4 mm, accounts for 20% of total amount;

(104) fused magnesia, granularity is ≤3 mm, accounts for 20% of total amount;

(105) corundum, granularity is ≤2 mm, accounts for 10% of total amount.

(106) The above mentioned raw materials are weighted, mixed, and compounded by the naphthalene binder to manufacture flame retardant coating raw materials of the low heat-conducting magnesium-aluminium spinel brick. The amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis. Preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis, in the present embodiment, the amount of the added naphthalene binder is 4% by taking the above mentioned mixed powder as a basis.

(107) (2) preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent,

(108) forsterite which accounts of 55% of the total amount, fayalite which accounts of 20% of the total amount, magnesia which accounts of 25% of the total amount are evenly mixed, 1%-5% naphthalene binder is added by taking the mixed powder as a basis, they are moulded by a frictional press, dried at 110° C.-150° C., burned at a high temperature above 1000° C. to obtain aggregate composite hortonolite raw materials; wherein the amount of the added naphthalene binder is 1%-5% by taking the above mentioned mixed powder as a basis; preferably, the amount of the added naphthalene binder is 2%-5% by taking the above mentioned mixed powder as a basis; in the present embodiment, the amount of the added naphthalene binder is 4% by taking the above mentioned mixed powder as a basis.

(109) A portion, which has granularity ≤5 mm, of the above mentioned manufactured aggregate composite hortonolite raw material is made account for 68% (mass percent) of the total amount, a portion which has granularity ≤0.088 mm is made account for 32% (mass percent) of the total amount, then 1%-5% (mass percent) naphthalene binder is additionally added by taking the aggregate composite hortonolite raw material as a basis, thermal insulating layer raw materials are prepared after evenly mixing; in the present embodiment, the amount of the added naphthalene binder is 3% by taking the aggregate composite hortonolite raw material as a basis.

(110) (3) the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine after the thin iron sheets are removed, kept at a temperature of 110° C. for 24 hours, dried, and burned into low heat-conducting magnesium-aluminium spinel bricks at a temperature of 1650° C. in a tunnel kiln.

(111) wherein the sequence of step (1) and step (2) is irrelevant.

(112) After the above mentioned three steps, the low heat-conducting magnesium-aluminium spinel brick is obtained.

(113) In the following, a performance test is performed on magnesium-aluminium spinel bricks obtained by the above mentioned 8 embodiments as follows.

(114) TABLE-US-00003 TABLE 3 comparison of high temperature antiflex strength of the magnesium-aluminium spinel brick of the present invention and the magnesium-aluminium spinel brick of the prior art high high temperature antiflex temperature antiflex strength/MPa (keep the strength/MPa (keep the temperature at 1100° C. temperature at 1400° C. item for 0.5 hours) for 0.5 hours) prior magnesium-aluminium spinel brick 4.73 1.12 Embodiment 1 flame retardant coating 4.67 1.04 thermal insulating layer 4.34 1.21 bonding spot between 4.12 1.13 flame retardant coating and thermal insulating layer Embodiment 2 flame retardant coating 4.13 0.91 thermal insulating layer 4.15 0.98 bonding spot between 4.06 0.95 flame retardant coating and thermal insulating layer Embodiment 3 flame retardant coating 3.70 0.84 thermal insulating layer 3.68 0.88 bonding spot between 3.73 0.86 flame retardant coating and thermal insulating layer Embodiment 4 flame retardant coating 3.51 0.56 thermal insulating layer 3.24 0.51 bonding spot between 3.17 0.58 flame retardant coating and thermal insulating layer Embodiment 5 flame retardant coating 4.11 0.85 thermal insulating layer 4.23 0.90 bonding spot between 4.06 0.88 flame retardant coating and thermal insulating layer Embodiment 6 flame retardant coating 4.18 0.77 thermal insulating layer 4.06 0.74 bonding spot between 4.00 0.71 flame retardant coating and thermal insulating layer Embodiment 7 flame retardant coating 3.66 0.73 thermal insulating layer 3.57 0.69 bonding spot between 3.60 0.75 flame retardant coating and thermal insulating layer Embodiment 8 flame retardant coating 4.20 0.81 thermal insulating layer 4.01 0.86 bonding spot between 3.94 0.83 flame retardant coating and thermal insulating layer

(115) TABLE-US-00004 TABLE 4 physicochemical indices of magnesium-aluminium spinel brick of the present invention room thermal shock coefficient temperature 0.2 MPa stability of thermal coefficient of volume compressive refractoriness apparent (1100° C. conductivity at expansion at item density resistance underload porosity water-cooling) 700° C. 1450° C. unit g/cm.sup.3 MPa ° C. % times W/m .Math. k W/m .Math. k Embodiment 1 flame 2.96 65 >1700 15.5 >10 3.713 1.77 retardant coating thermal 2.63 42 1684.5 23.1 / 2.508 1.58 insulating layer Embodiment 2 flame 2.94 58 >1700 16.1 >10 3.735 1.78 retardant coating thermal 2.65 39 1651.2 22.6 / 2.539 1.61 insulating layer Embodiment 3 flame 2.93 54 1675.1 17.2 >10 3.746 1.88 retardant coating thermal 2.68 23 1590.6 21.1 / 2.711 1.60 insulating layer Embodiment 4 flame 2.90 49 1683.5 17.8 >10 3.725 1.96 retardant coating thermal 2.71 25 1610 20.7 / 2.763 1.69 insulating layer Embodiment 5 flame 2.95 60 >1700 15.7 >10 3.715 1.75 retardant coating thermal 2.60 33 1637 22.8 / 2.515 1.57 insulating layer Embodiment 6 flame 2.94 55 >1700 16.3 >10 3.741 1.82 retardant coating thermal 2.66 35 1655 23.3 / 2.522 1.63 insulating layer Embodiment 7 flame 2.93 49 1692.5 16.9 >10 3.746 1.90 retardant coating thermal 2.66 29 1617 21.5 / 2.526 1.66 insulating layer Embodiment 8 flame 2.94 59 >1700 15.9 >10 3.737 1.79 retardant coating thermal 2.64 42 1670.5 22.6 / 2.551 1.62 insulating layer

(116) As may be seen from Tables 3 and 4, the flame retardant coating of the magnesium-aluminium spinel brick reserves good high temperature mechanical behavior such as erosion resistance, scour resistance, thermal shock resistance, mechanical stress resistance, which the magnesium-aluminium spinel brick has, but the coefficient of thermal conductivity is comparatively high, thermal loss is comparatively large; whereas the thermal insulating layer has a coefficient of thermal conductivity lower than that of the flame retardant coating, while reserving good high temperature mechanical behavior of the flame retardant coating. Two kinds of materials of different properties of the flame retardant coating and the thermal insulating layer can be bonded firmly. Strengths of the magnesium-aluminium spinel, the hortonolite as well as their bonding spot are very close to each other. The formula of the thermal insulating layer can increase the sintering temperature of the thermal insulating layer, make it match the flame retardant coating, such that consistency of linear expansivity of the flame retardant coating and the thermal insulating layer is guaranteed. As such, on the premise that service performance is guaranteed, reduction in the coefficient of thermal conductivity is achieved.

(117) Preferably, compared to other embodiments, for embodiments 1, 2, 5, 6 and 8: (1) coefficients of expansion of the flame retardant coating and the thermal insulating layer are more consistent; (2) mechanical behavior is better; (3) bonding of the flame retardant coating and the thermal insulating layer is more firm.

(118) Finally, it is to be explained that, the above embodiments are only used to explain the technical solutions of the present invention, but not to limit the present invention. Although the present invention is explained in detail with reference to embodiments, those ordinary skilled in the art should understand that, without departing from the spirit and the scope of the technical solutions of the present invention, modifications or equivalent substitutions are made to the technical solutions of the present invention, which are to be covered by the scope of the claims of the present invention.