Keith Ceramic Materials produces a range of bonds designed for use with high quality refractory aggregates.
The performance of refractories at service temperatures is strongly influenced by the amount of glassy phase present in the mix. Traditional bonds, like clay, phosphates and silicates, form significant amounts of glassy phase which may detract from the refractory properties of the aggregates being bonded. KCM High Purity Bonds dissociate during heating up to 500oC, leaving only high purity alumina as the sintering bond.
Their use gives:
The major constituents are (1) a complex aluminium oxychloride solution, designed to give an optimum strength dry film; (2) a fine alpha alumina which acts as an activator. This reinforces the dry oxychloride film so that refractory shapes have maximum dry green strength. It also influences the way in which the oxychloride film decomposes, so that maximum intermediate and final strengths are obtained. Very small amounts of organic materials are included which help to maintain the alumina in suspension and improve the flow characteristics of the final mix.
5035 5038/5050 Ignition Residue 64% 58% Soluble Chloride 6.2% 6% Alumina 63% 57% Silica 0.4% 0.4% Soda 0.2% 0.2% Iron Oxide 0.02% 0.02% Calcium Oxide 0.06% 0.05% Magnesium Oxide 0.02% 0.02% 5025 Alumina 11.5% Chloride 10.0% S G at 20oC 1.33
All bonds other than 5025, are white pastes, 5025 being a clear liquid. They are mildly acidic and will react with both basic refractory aggregates and metallic contaminants such as free iron in refractory mixes. The pH of all bonds is between 2 and 3 and the Bulk Density is 2 gm/cubic centimetre.
It is important to use correct grain size distribution of aggregate for the particular application, to optimise final refractory properties. KCM Bonds become fully effective when each grain of aggregate is coated with a film of the bond. Mixing techniques are therefore extremely important and should be carried out in high speed intensive mixers, or pan mills with rollers.
Mixing technique is dependent on equipment available. We have found the
following system satisfactory in most cases:
(a) Put fines fraction into mill
(b) Add bond and mix to homogeneity
(c) Add coarse grain and mix to
homogeneity
(d) Add G.C.
Powder and mix to homogeneity
(e) Add any extra water required for
specific pressing requirements, very sparingly -- possibly 0.5% by weight
(f) Aging the mix overnight, under damp covers, has been known to improve
plasticity.
In general an addition of 10% of KCM Bonds will give a mix with
good dry pressing characteristics. The mix will appear to be 'dry' and great
care should be taken in adding water. Increments of not more than 0.1% should be
used. This is most important.
The principal difference between the grades is simply water content. 5035 contains the least water and is designed for use with low porosity aggregate such as Fused Alumina, Fused Mullite and Silicon Carbide. 5038 has a slightly higher water content and should be used with the more porous aggregates, for example, sintered mullite and tabular alumina. 5050 is designed with special flow characteristics for use in rams and mouldable. 5025 is used when the application calls for no additions or the customer wishes to use his own.
Drying should be carried out as for normal clay bonded ware at a minimum temperature of 80oC. It is important that all free moisture is driven off before firing.
Firing. Dry strength is substantially retained in the early stages of firing and, as ceramic bond formation begins, the strength properties improve. Final firing temperature can be in the range 1250 - 1800oC depending on the aggregate bonded and the final service application.
KCM High Purity Bonds 5035, 5038 and 5050 are packed in 25 Kg plastic pails, stretch-wrapped onto pallets in 675 Kg modules. KCM High Purity Bond 5025 is packed in 250 Kg drums, 4 drums per pallet or 55Kg kegs, 5 per pallet.
No. KCM High Purity Bonds are water based thick pastes except 5025. The constituents are non-toxic in circumstances where spillage or splashing may occur, we advise the use of face shields as the material could irritate the eyes. Any spillage may be cleaned up by the liberal use of clean water. All materials are safe if properly used and are supplied in accordance with the Health and Safety at Work Act 1974.
All technical data published by the company are indicative only and all business is undertaken strictly in accordance with the company's Conditions of Sale. Material Safety Data Sheets are available on request.