GB2106494A

GB2106494A - Refractory ramming mix

Info

Publication number: GB2106494A
Application number: GB08222344A
Authority: GB
Inventors: Philip Leslie Smith
Original assignee: STEIN REFRACTORIES; Gr Stein Refractories Ltd
Current assignee: STEIN REFRACTORIES; Gr Stein Refractories Ltd
Priority date: 1981-08-08
Filing date: 1982-08-03
Publication date: 1983-04-13

Abstract

In linings of aluminium electrolysis cells, the gap between pre-fired carbon bottom blocks and either monolithic or pre-fired side walls is conventionally rammed with a mass comprising carbonaceous aggregates and a tar/pitch binder. Such mass is inevitably installed hot, a labour- intensive lengthy procedure with considerable emission of fume during installation and during burning-in. In addition the areas where ramming is to be effected need to be pre-heated for lengthy periods. The invention is to provide a ramming mix which avoids those disadvantages, the mix being a refractory material comprising 55- 90 wt% calcined anthracite grains, up to 40% graphite, 3-25 wt% of a thermo-setting resin and 4-15 wt% of an alcoholic wetting agent e.g. monoethylene glycol.

Description

SPECIFICATION Refractory materials This invention relates to refractory materials, and is particularly concerned with a refractory ramming mass for use in linings of aluminium electrolysis cells.

In aluminium electrolysis cells, the linings are generally formed from a) carbon as a monolithic structure, b) pre-fired carbon bottom blocks with monolithic side walls, or c) pre-fired bottom blocks with pre-fired side walls. With pre-fired bottom blocks and side walls of both types, considerable quantities of carbonaceous ramming materials are utilised, in the areas between the sides and ends of the blocks and the side walls, The present procedure is to fill such areas with a ramming mass comprising carbonaceous aggregates and tar/pitch binder having a softening point high enough to dictate that such a mixture is installed hot. As this ramming procedure is usually labour-intensive and lengthy, the quality of the installation is dependent to a significant extent on the environment in the area, which is worsened by a hot fuming mixture.Ramming tools must be heated and attention paid to the mix temperature as densification is poor at low temperatures with such mixes. It is not unusual for areas to be pre-heated by gas flame for lengthy periods prior to ramming to lessen the "heat sink" effect of the previously installed pre-fired carbon block.

Failure to co-ordinate the various stages of the process leading to production and installation of such mixes in the smelter can lead directly to the costly premature failure of the electrolytic cell.

Furthermore, the cost of equipment to produce such hot mixes, transport them to the lining area, preheat the areas to be rammed, provide the additional man-power required and purchase the additional material required for each pot, is very high.

The object of the present invention is to provide a refractory material suitable for use as a ramming mix in linings of aluminium electrolysis cells, which avoids the disadvantages referred to above.

According to the present invention, a refractory material comprises calcined anthracite grains, graphite, a thermo-setting resin and a wetting agent.

Thus, the refractory material may comprise from 55wt% to 90wt% calcined anthracite grains, it being preferred that electrocalcined anthracite grains are used. It is further preferred that the graphite is in the form of grains, natural flake or powdered residue from machining graphite electrodes, and is in the amount up to 40wt%. The thermosetting resin binder may be a novolak-type phenolic resin containing a formaldehyde generator capable of hardening the mix, or may be a mixture of novolaktype phenolic resin and a thermosetting resin such as a resol-type phenolic resin which serves as a hardener. In either instance, it is preferred that the binder is present in the amount 3wt% to 25wt%.It is further preferred that the wetting agent is monoethylene glycol and present in the amount 4wt% to 1 5wt%. However other suitable wetting agents such as methanol, ethanol, diethylene glycol, and other high alcohols can be used.

Thus, the invention provides a refractory material that constitutes a superior ramming mix, which has the advantage that it can be prepacked and used directly from the package and it has good storage properties and hence reasonably long shelf life. Of great significance is the fact that there are substantially no fume emissions during installation and very low fume emissions during burning-in. In addition, there is increased low temperature strength and increased thermal conductivity, and no capital investment is required in equipment for producing hot mixes, their transport and their effective installation.

The invention will now be illustrated in the following example.

Example A mix containing: 87.7 wt.% Calcined Anthracite grains 4.4 wt.% Powdered Resin 7.9 wt.% Monoethylene Glycol was blended in a cold mixer with the dry ingredients being mixed alone for 3 minutes. The liquid addition or additions are then made and mixing continued for 10 minutes more. The mix was then in a condition to be packed in appropriate impervious bags for storage and transport.

The mix, straight from the bag was installed at ambient temperature in the aluminium electrolytic cell by compacting successive layers of the loose packed mix using unheated pneumatically powered ramming tools and using practices common in the industry to avoid laminations within the mass.

Such a mix gave the following test results Bulk Density as Rammed 1.55 gm cc- Room Temperature Crushing Strength after baking at 11 OOC 2700 psi % Wt. loss after firing to 1 0000C 7% Thermal Conductivity 25-8000C 38-46 BTU jn-1 hr-' ft-' OF' For comparison purposes the following are typical properties for pitch/tar containing mixes available to the aluminium industry:: Bulk Density as Rammed 1.45-1.50 gm cc-l Room Temperature Strength after baking to 11 0cm 500-1000 psi % Wt. loss after firing to 1 0000C 1017% Thermal Conductivity 25-8000C 14-28 BTU in-' hr-1 ft-' OF' In addition to providing properties significantly better than those of conventional available materials, the installation of the mix in the aluminium electrolytic cell, by being at ambient temperature, resulted in substantially no fume emissions in installation and very low fume emissions during burning-in. There was, in addition, the avoidance of the need to pre-heat the ramming tools and the avoidance of the need to provide means to heat the mix and maintain it hot until it was actually used.

By avoiding such measures considerably reduced installation costs were realised with considerably better environmental conditions for the operatives.

Claims

1. A refractory material comprising calcined anthracite grains, graphite, a thermo-setting resin and a wetting agent.

2. A refractory material as in Claim 1, wherein calcined anthracite grains are present in the amount 55 wt.% to 90 wt.%.

3. A refractory material as in Claim 1 or Claim 2, wherein the calcined anthracite grains are electro-calcined anthracite grains.

4. A refractory material as in any of Claims 1 to 3, wherein the graphite is in the form of grains, natural flake or powdered residue from machining graphite electrodes.

5. A refractory material as in any of Claims 1 to 4, wherein the graphite is in the amount up to 40 wt.%.

6. A refractory material as in any of Claims 1 to 5, wherein the thermo-setting resin is a novalaktype phenolic resin containing a formaldehyde generator capable of hardening the mix.

7. A refractory material as in any of Claims 1 to 5, wherein the thermo-setting resin is a mixture of novolak-type phenolic resin and a thermo-setting resin such as a resol-type phenolic resin which serves as a hardener.

8. A refractory material as in any of Claims 1 to 7, wherein the thermo-setting resin is present in the amount 3 wt.% to 25 wt.%.

9. A refractory material as in any of Claims 1 to 8, wherein the wetting agent is monoethylene glycol.

10. A refractory material as in any of Claims 1 to 9, wherein the wetting agent is present in the amount 4 wt.% to 1 5 wt.%.

11. A refractory material substantially as hereinbefore exemplified.