News Letter 03
News Letter 04
When I started Keramicalia I wanted it to become the place where all the interesting enquiries end up. After 20 years it has got there, and I am very happy, Keramicalia may be a commercial disaster, but we sure have a lot of fun. This is the way I wanted it.
My wife, Judy just looked over my shoulder and pointed out that my title is her saying. Yes she is the master of “Making it Happen.” She has a Range Guide troop, and one day she announced that we were all going to Switzerland for a skiing holiday. The parents thought she had “lost it”; I personally thought she had finally bitten off more than she could chew, but sure enough she got us there. Eleven girls, my whole family and a few other parents. It was the most awesome holiday. Yes it was a lot of work, some inventive fundraising, but it was unwavering, focused effort for a couple of years, and nobody regretted it. If you focus on your goal you get there. You lose it when you take the line of least resistance.
We have brought up our children in this culture of making it happen. Gina is now a trauma nurse, working on a ship doing a world cruise. John is going to China in May to film driving a convoy through China, India, Pakistan the Middle East to Djibouti, Ethiopia, through Africa ending back in Northcliff. Christopher has just come back from the USA where he spent his varsity holiday working in a shop, then checking out Washington and New York with his earnings. Nikki is having a ball with her gap year at a school in Southampton. I am so proud of all of them.
One of my most irritating saying is “Why put off for tomorrow what you can just as easily do today?” I am not good at that one, but at least I try a bit to strive towards it.
So think about what YOU really want, not what society expects of you, and go for it NOW.
Kerasic is our alumina bonded silicon carbide material. The “sic” comes from SiC, the chemical abbreviation for Silicon carbide. The” Kera” is because I am not very imaginative and call most of the things I make Kerasomething or other. (None of my kids are Keraanthing) kerasic is a fine pourable material and lends itself to very complex and intricate castings. It is used mainly for thin walled castings, for example, sintering trays, thermocouple sheaths, elements sleeves lances and fluxing tubes, thin walled crucibles, furnaces muffles, heat radiators, element cages and distillation columns it is also extremely strong. The items above are all small sophisticated expensive pieces and the cost of the material; R45/kg is no problem.
Gideon Kriel of Gee Kay Industrial Ceramics was a pioneer in the use of Kerasic and made some remarkable items. Hennie van der Bank of Quarlcor got rapid casting down to a fine art, and could turn around moulds in 20minutes!
Jay Lloyd of Fornax pioneered Kerasic as a die-casting material. He was casting items in a R10 000 steel die of 2 cavities. With Kerasic he made 24 spin casting moulds at a cost of R6 each. The high thermal conductivity of kersic is good for die casting, also the fine surface finish and thermal shock resistance. Jay then started making thin walled crucibles. Because of the high strength, they do not have to be as thick as graphite crucibles, so you get faster heat transfer. Jay’s sidekick, Peter has invented an ingenious machine for moulding and stripping them. The three wise men of the gold industry have been doing ground-breaking work on composite castings using strange bedfellows such as kerasic and cellular insulation materials, also Zirconiaflow and Kerabrade C and Keratab Ultrafine. They have had some magnificent results. Of course I always want to cut them up to see the interface. Some of them don’t work at all on paper, but work brilliantly in practice. Now they can have their cake and eat it, a single component can be pyroplastic at one end, strong in the middle and insulating at the end.
Currently the crowning glory of Kerasic is Jay’s Element Cages. These are the most intricate castings I have ever seen. When he conceived the idea I told him it was impossible. But as Gideon says, anything is impossible until someone has done it. Element cages are shaped like squirrel cage and hold elements in place while hardly impairing radiation, and with almost no thermal mass. Take an element cage, wind an element into it, wrap it with fibre blanket, clad it, insert a kerasic crucible, connect it to 220 volts and you can melt 2kg of aluminium in 20 minutes . I have been working on a Kerasic pump for molten aluminium. I had problems in some areas. I believed it would be impossible to machine Kerasic, but Danie Wilkins of the CSIR proved me wrong! He has made some components of unbelievable precision.
We have got the volume stability remarkably good, and we can now cast 2 metre rods at 19mm thick. We have one 4 metres long now, still in the mould. I need to build a kiln to fire it as it passes through vertically.
Silicon carbide is a remarkable material. Diamond is the hardest natural mineral, 10 on the Moh scale of hardness. And corundum comes second at 9. ( That’s where the company “Moh 9 got its name. Silicon carbide has a hardness of 9.5. It is therefore the first choice for abrasives, not being as expensive as Diamond.
The other superior it has is its cleavage. It breaks with sharp edges. I am having difficulty getting facts and figures for this article, because silicon carbide does not occur naturally, and is therefore not found in any of my mineral reference books. It is not likely to be found in nature, as its synthesis requires the equivalent of long standing bolts of lightning. *Silica and carbon are placed in a long pile and an enormous electrical current is run through it for days on end. The result is a fused but porous mass of large silicon carbide crystals. The electricity consumed would make even a submerged arc furnace operator cry. The lump gets sorted into green silicon carbide from the centre and black from the outside of the pile. Next the material gets crushed. In the process, the silicon carbide removes a lot of the metal content of the machinery! Now it gets screened these sharp particles are difficult to screen, and abrasive manufacturers always use single sized particles, so that there are gaps between the grains, otherwise grinding wheels would not work. This gives the producers a major headache, because they may have 20 customers wanting 50 to 60 mesh and nobody wanting 60 to 70 mesh. It all adds up to make silicon carbide rather expensive. For sub micron material I have paid as much as R80/kg. Silicon carbide has an enormously high thermal conductivity. Pure crystals have a conductivity of 84 Watts per metre Kelvin. The highest of common Refractories is magnesite, with a measly 4W/mK. Yet fused magnesia is used as the isolator in stove and kettle elements. Why not silicon carbide? Well it is also electrically conductive. This makes it suitable for globar elements. Wonderful things, but pricey. The other property of silicon carbide is its high surface tension. It is not easily wetted by liquids. This makes it difficult to formulate pourable refractories, but makes it perform superbly in molten metal contact situations.
*Frans Nyikos recently gave me a book on silicon carbide which records a few small natural occurrences
For sale 5 cubic metre kiln belongs to Grob ceramics, now retiring R100 000
I want second hand and scrap kilns to repair and sell
3 000 insulation bricks, 1400°C @ R20ea
Sorry this newsletter is such a mess, I want to put a place for you to unsubscribe but haven’t got that right yet.
News Letter 04
This newsletter was written on 2.5. 1997! Then my photocopier broke. Colin Coomer lent me his old machine. We were both bidding on this machine at an auction, but I backed down. Anyway, thanks, Colin.
As you can see we are now on e-mail and have a web site. The web site, when it works, contains most of our data sheets. You can download it or we can give you all our data sheets on a disc.
I have had a lifelong assosciation with the medical profession. My father was a doctor, my daughter is a nurse, my wife and my mother have both been medical receptionists and my mother in law is a matron. South Africans tend to regard doctors as omniscient and infallible beings. If a doctor lets on to a patient that he does not know everything and can possibly make a mistake, he will probably never see that patient again. If he keeps up the image of being infallible, he may feel terribly guilty about it, but at least he will stay in business.
So what can you do about it? My advice is this; When you meet your doctor, tell him that you don't expect him to diagnose your ailment. I tell my doctor that I don't know what's wrong with my body even though I live in it, so I really can't expect him to find the problem. I would, however, gladly pay him to listen to my layman's description of what I feel in the hope that he may have some suggestions. You will probably see your doctor visibly relax, and I am sure he will be totally honest with you.
Another thing I believe about medicine is that half of healing is psychological. Sangomas successfully kill people just by convincing them they are going to die. Conversely, people have been seen to survive extreme injuries if they have a strong will to live. I believe my wife saved my life when I was dying from malaria and failed to respond to treatment. She stayed at my side and fuelled my will to live. She even invented stories about cute things my daughter had done. My running friend Mervyn Niland has some fascinating stories about mind power. I went to one of his seminars recently, and he got us all, everyone in the whole group, walking over red hot coals! Nobody even felt any heat on their feet or showed any sign of burning. As a refractories technologist I find that fascinating. Go on, try it, Mervyn's number is 083 286 1936.
Product Feature - KERAPUMP
Since I first joined the Ceramic Society, Dr Richard Kruger was dead keen on cenospheres. He introduced me to them, and opened up a whole new world of possibilities. After many years of toil and maneuvering, Richard realised a dream and commercially produced cenospheres. We worked together closely and Richard gave me immense support to create a whole new generation of refractories.
Cenospheres are tiny hollow ceramic spheres which impart amazing properties. They flow almost like water and impart brilliant thermal insulation properties. I call the new generation of refractories "Cellular Insulation". The materials made from cenospheres appear to be solid, but are full of microscopic sealed cavities. Many readers will have seen the demonstration or the advertisements of me holding in my bare hands a crucible with 2000øC molten steel in it.
Kerapump is a series of pourable or injectable refractories. Kerapump 1 stood around in the lab for a while. Colin Coomer asked me if I could meet the stringent spec. for an insulation material for Mossgas. I said I think I have just the right thing. I had tests done on Kerapump 1 and it exceeded the strength requirements so far that Mosgas rejected it!
Iscor Newcastle were pumping an imported insulation foam on their hot blast stoves on hot spots. They had to repeat the procedure every few months on exactly the same spots. They agreed to try Kerapump 1, and it worked permanently. Some years later Mike Kuys 'phoned me at 2am on a Monday morning. A section of the roof of the hot blast stove had fallen in, just after they had spent R20million on relining the blast furnace. If they did not get the stove going soon, the whole blast furnace would solidify and have to be rebuilt. Kerapump was the only hope. Everyone pitched in to help. We even had two ex bank managers driving bakkies up and down from Newcastle. Four days later the stove was back on line.
We didn't have a party, we all went off to sleep for a long time. Some months later Mike Kuys 'phoned again. Slight problem; somebody pumped Kerapump into the compensators, a sort of expansion bellows, and they jammed solid as a rock. Could I make something compressible?
And so Kerapump 2 was born.
Billy Wolmarans and I repaired cracks behind the buckstays at Vanderbijl's coke ovens. The cracks were totally inaccessible behind the buckstays, we we plugged up all the openings around the buckstays with Versimould Plug, leaving a pipe protruding from the gap. Into this we pumped Kerapump 1. It was most dramatic. Smoke and flames were billowing out from the roof over the regenerators, and about thirty seconds after we started pumping, the smoke and flames would suddenly vanish. Working conditions were apallingly hot. Everything got hot.
The floor was so hot that at times when we picked up plastic bags of Kerapump the bottom of the bag stayed stuck on the floor. Kerapump kept setting in the pump because the water was too hot. Back to the lab.
Kerapump 3 was invented; more fluid, with a longer setting time, or rather more of a heat set. Now it can travel far around a furnace shell, then penetrate cracks and set on its way to the hot face. Martin le Roux discovered Kerapump 3 for glass bending moulds. Previously glass benders had to make clay moulds, prefire them to ñ1100øC and then bend their glass over them. They used to break after about three bendings. Now they can make them with Kerapump 3, fire to 400øC or use them straight away. They seem to last indefinitely. This was such a revolution in Martin's business that he spread the news far and wide. He couldn't do enough for me. He gave me his whole pipe collection, including beautiful hand-carved meerschaum pipes.
I find Kerapump 3 ideal for modelling, because it takes up very fine detail, is volume stable and easily workable to a fine finish, due to its very fine homogeneous microstucture.
Kerapump 4 is still slower setting and softer. Kerapump 5 is lower density, designed to replace Marinite, an asbestos based material used in the aluminium industry. We made some superb Marinite replacement parts for a customer, but he was reluctant to change. It turned out that if he changed, four of his colleagues would be out of their full-time jobs machining Marinite! Our latest development is floats for continuous casting of aluminium. Gideon Kriel is doing the development. The floats control the flow in the same way as a needle and seat mechanism in a car's carburettor. Gideon's samples look stunning compared to the calcium silicate components which have replaced Marinite.
Kerapump 6 is a dense pumpable material with a high zirconia content which has been used in blast furnace repairs.
Kerapump 7 has largely replaced Kerapump 3. It has a very high tolerance for "abuse" on site, and can be used over a wide range of water contents. It is very fine and we make thin walled insulating coffee mugs from it just to demonstrate how good it is.
Ladles are very large refractory lined pots for transporting molten metals. In steel plants they carry in the region of 70 tons of molten steel. They are mostly transported by overhead cranes. Imagine one of them springing a leak! Well, it happens. It happens frequently.
Every time it happens, there is an investigation, and I am always very sceptical of the conclusions. The conclusions always strike me as being the only possible theoretical explanation anybody could come up with, even though it seems rather far fetched.
If molten steel finds a crack leading to the steel shell of a ladle, it will run through and freeze almost instantly. The only breakout explanations that hold any water are those in which the steel continues to flow against the shell. This necessitates a cavity or labyrinth of cracks in contact with the shell. Mike Moore of Richards Bay Minerals discovered that when he increased the capacity of his ladles, the pressure against the shell increased, as evidenced by the insulation being crushed. This had me puzzled for some time. The explanation is as follows; The total outward movement of the refractory lining is determined by the highest expansion. The highest expansion is on the hot face. The larger the diameter of the hot face, the greater the movement outwards of the lining. The hot face of the bricks on the working face expands and the bricks push each other away. The colder bricks are in turn pushed outwards, but they do not expand as much. It follows that the colder bricks are no longer in contact with each other, but are separated by small gaps.
The chances of steel getting into this labyrinth of gaps is small, but it does happen. Note that the pressure forcing it in is enormous. 2" metres of molten steel has a pressure equal to 20 metres of water.
From my explanation, it follows that you can build a ladle lining absolutely perfectly free of cavities, but once you heat the hot face, it will contain a labyrinth of gaps in contact with the shell. The solution is dead easy. As soon as the ladle is hot for the first time, pump some Kerapump 3 through nipples in the shell, and it will fill all the gaps. No gaps in contact with the shell means no possibility of a breakout. There we have the solution to saving countless lives worldwide and millions of rands of equipment. I wonder if anyone will ever listen? If I were a mason building ladles I would certainly latch onto an explanation of how my perfectly solid linings can leak. Would't you?
Our business still revolves mainly around solving problems. We get far more enquiries nowadays than we can handle. We try to attend to them according the following priories.
1. Firm orders
2. Established customers
3. Cash customers
4. Those who pester us the most.
5. Those problems which are technically the most interesting.
Usually we can supply materials off the shelf that are more appropriate than anything made by the bulk manufacturers. We are getting the bulk of our sales today through agents, other refractories manufacturers, suppliers and installers. We like it that way, as we do not have our own salesman.
My landlord, Hennie Maree, has a 35 cubic foot pottery kiln to sell. It opens both sides, and has never been over fired. Tel. 692 1657.
I want to praise our local truck drivers. I find them considerate and friendly. Their practice of pulling over onto the verge of the road to let cars pass is not a legal requirement, in fact I understand it is illegal. Of course there are some nasty ones and some idiots, but I think the standard is generally high. I hear so many people complaining about trucks in the fast lanes of highways. They are merely obeying the overhead lane markings. Sure it is annoying that they do not keep to the left lane, but look at the overhead signs next time you get annoyed, and you will see that the truck drivers are merely obeying the signs. It is the idiots who planned the signs who are causing the obstruction, not the truck drivers.
We have all seen the extent to which truck drivers are harassed by traffic officers, yet they put up with it. It makes me wonder how badly the cops harass township dwellers to earn such hatred. Jerry once had a puncture on our old Toyota Stout 1« tonner on the way to Rustenburg with a full load. Believe me it is a hell of a job changing one of those tyres with a full load. A traffic cop pulled over, and instead of offering help, gave Jerry a ticket because the tyre he was removing was now damaged. I had a flat on the highway with that same old Stout once, and found the spare was flat too. I had no difficulty getting to a garage and back with my two gynormous tyres, thanks to, you guessed it; truck drivers.
Kurt is back from Germany. We had a record turnover in his absence. Perhaps he should go more often! John Onderstall has just won the Art in Magic junior championship in Gauteng. He is available at R30/show for kid's parties. Tel 660 1606
The Onderstalls have moved to 289 Jorissen str., Krugersdorp. The photocopier has just acquired a new drum, and it apologises for the poor quality of the last newsletter. Karbochem has just cancelled a large order for Multimould industrial gaskets. The reason; When they opened the sulphur tank for the reline, they found the old Multimould gaskets still fit for re-use. Previously no gaskets had ever lasted one campaign successfully.
We have a few letters from prison from irate readers, the rest of you keep up the fight against the evil toll-lords. Doug says he doesn't pay toll at all anymore, just drives through, and invites us all to join him. John Weston says he used to wait patiently in toll queues, but now that he is aware of how unneccessary they are, he finds it irritating. Sorry, John.
Anyone want a second-hand Carbolite kiln? Make an offer.
Frik van der Berg is selling his bus, and wants R45 000.
Versimould is our product range of "Cold setting phosphates". Phosphate bonded materials are normally heat-setting. "Cold-setting"means that they set by themselves, but it is a bit confusing because they can get very hot from their exothermic setting reactions.
They set rather rapidly. We have achieved 20 MPa in 20 minutes! The strength of Versimould products can be rather deceptive. Some of them can be thrown onto concrete without breaking. They give the impression of being extremely strong, but if you measure their cold crushing strength, they give values around 20MPa. Some of them do not break at all in the cold crushing test; they simply carry on deforming. What makes them different from normal ceramics and refractories, is the fact that they are not brittle. You can hit them with a hammer, and leave a slight dent instead of shattering them.
Another valuable characteristic is the fact that they are impermeable. One of applications for this property is casings for porous plugs. "Porous plugs" or bubbling plugs are refractory cones built into the bottom of ladles or furnaces to blow gases into molten metal. Traditionally they have metal casings, and it is notoriously difficult to get a gas-tight seal between the "can" and the refractory. In induction furnaces, a steel can cannot be used, as it is within the induction field of the furnace and would melt. We make special bubbling plugs with a Versimould casing for this application.
Versimould is supplied as a powder plus liquid. In many applications it is recomended to refrigerate the liquid before mixing. In some cases this is absolutely essential. One such case is repair of rotary kilns. Rotary kilns have to keep turning, otherwise the top gets too hot and the shell buckles. Repairing them is a major operation involving a lengthy shutdown. With Versimould, a small patch can be repaired from the outside by injection. The kiln is stopped for a few minutes with the hot spot on top. A nipple is welded onto the hot spot, a hole lanced through it and a cap fitted. The kiln is then rotated a few more times, and stopped with the nipple at the bottom.
Versimould or "Versiject" is then pumped through the nipple and the missing lining is replaced. 15 minutes after stopping, the kiln must be rotated again. The total downtime is only about half an hour. Another characteristic of Versimould is that it expands during setting. This is a result of the impermeable nature of the bond plus the heat of reaction, which causes trapped bubbles of gas to expand. This property makes it ideal for sealing applications. It is particularly useful when doing pumping repair of cracks. All cracks are sealed superficially with "Versimould Plug", leaving only one orifice with a pipe sticking out. The pump nozzle is attached to the pipe and the material injected. Any other material applied to a hot crack would fail to seal it.
There are certain applications where normal refractories would fail due to impact. We have done quick repairs on hot boiler panels with "Versimould Panel". These heavy panels get unavoidably bumped against the superstructure during installation, and only Versimould can survive the impact. Versimould is also useful for applications where high thermal gradients are involved and cracking is undesirable. The last application is hot repair of small areas of furnaces. It is possible to repair minor damage very quickly with Versimould, and once installed, the furnace can be switched on immediately. This can save many hours to days of downtime.
Versimould is so named because of its versatility. Each of its properties gives it certain niche applications. It bonds well to steel, and the phosphate also inhibits corrosion of steel. Another obscure application is "Welding Aid". Have you ever battled to hold several pieces of metal in position simultaneously while welding them? Stick them together with welding aid. It can also be used to make a bath of weld material, or to protect cetain areas from the arc. About 10 years ago I made a Versimould concoction to patch my Kombi's silencer. The patch outlasted the rest of the silencer. I spilled a few blobs on my tarred driveway, and they are still there today!
Many chemical reactions give off heat, and I want to point out some of the consequences. The first and most important thing to remember is that the heat is dissipated through the material. Therefore a thin layer of exothermic setting material will show very little rise in temperature. A large mass on the other hand will get very hot. The inside of the mass will get even hotter than the surface. Large castings of Keraset (Magnesium oxychloride) generate enough heat to explode. Explosion occurs as soon as the steam pressure exceeds the tensile strength of the bond. Cornelia de Villiers invented a remarkable material by accident. She made a batch of "Corkalium", a magnesium oxychloride bonded cork-chip flooring mix, in a nappy bucket. The mix started getting very hot and eventually boiling. She sent her assistant out into the street with it, where it started erupting and exploding. The resulting pieces of product were remarkably light but very hard. I tried in vain to reproduce it in the lab. I pestered Cornelia about her formulation, but she consistently gave the same details. Eventually it dawned on me that the material cannot be made on a small scale without insulation or heat input.
Trapped gases in an exothermic material will expand with the heat, and cause the casting to bloat. The best way to combat this is to start with cool materials, keep the castings small and cool them as far as possible during setting. Use metal oulds in preference to wood.
Pyromould is an exothermic material of a different nature. It is a concoction of pyrotechnic and refractory materials. The installation is ignited at one point, and the reaction proceeds in a wave through the body. Any given point in the body rises suddenly from ambient temperature to about 500øC and then gradually cools. The temperature reached is not related to the size of the installation. Pyromould's main application is ramming the joint between the furnace and a precast and dried launder.
News Letter 03
I have just driven to Salt Rock for a long weekend. The road was busy and there were queues at the toll gates. The army taught me to hate queues, and I have already spent far too much of my life in them. I noticed that there were on average two unmanned toll booths per toll gate. The queues were therefore totally unnecessary.
I experimented with driving through the empty ones with the red crosses above them. At worst I had to drive over a road cone or two. At best I got a toll collector going hysterical, which I found quite gratifying.
South Africans are world renowned for their apathy and complacency, which is why we always get such bad service. Let's start doing something about it. Call it "affirmative toll paying". When you arrive at a toll gate and there are queues and some of the toll booths are unmanned, drive through. If enough people do it, the toll operators will be forced to spend that tiny bit more to pay enough staff to prevent queues.
This is the New South Africa, let's be positive in everything we do and make it a better place to live in.
Keramicalia have become the West Rand agents for Alusil gold pots. Alusil Refractories in Springs have a reputation for being the most innovative furnace builders in South Africa. Amongst their achievements is char plant built and comissioned in their factory, then dismantled and shipped overseas. Eddie Fullard invented the monolithic gold pot. He started with a brick lining in sections, and developed the technology step by step until the present complete unit with a prefired lime-free lining. Naas van Heerden, previously of Elgin and later Tugela Alumina, handles sales.
Product feature - KERAPOUR
Kerapour is a most unusual material. It combines most of what one wants from a refractory lining. It can resist molten metal contact, which is the downfall of most insulation materials. This can be demonstrated by making steel in a crucible of Kerapour. We use the "thermit" process, a dramatic chemical reaction between iron oxide and aluminium.
Incidentally, we repair slag pots by this process. Maybe we will use the subject for another newsletter.
Kerapour is a viscousbut free flowing, self-leveling material. Just add water, mix and pour.
Kerapour is frequently called on to do miracles. At Sappi's Enstra mill, a brick lining in their furnace had come loose. Here Kerapour was called on to fill the cavity and cement the lining, otherwise it would have to be re-bricked, and the shutdown would cost a fortune. I built a "swallow's nest" funnel out of Versimould Plug in the rather restricted doorway which was my only access to the crack leading to the cavity. I call this funnel structure a "swallows nest", because it is built up in layers similar to a swallows nest. It looks more like a swft's nest. Into this cup we poured Kerapour, and we poured and poured. Eventually we got half a ton in. The Kerapour leaked out of a few small holes which we plugged with Versimould Plug as they appeared. When the furnace was eventually rebuilt, we were able to determine how far the Kerapour had flowed; it had flowed for ten metres horizontally!
Some time later the same plant had a crack in the brickwork of a boiler arch. The air leaking through was causing premature ignition on the chain grate and destroying the breast plate and guillotine. A shutdown was already programmed to rebuild the arch at a cost of R30 000. I asked the engineer to give me just one day to try blocking the crack with Kerapour. We studied the drawings and found the appropriate points to introduce the Kerapour. We poured some in and sure enough it emerged through the crack over the whole length of the arch and sealed it. The boiler worked perfectly again.
Lance Pretorius of Natal Foundry Suppliers also did a neat "Red Adair" style repair on a gas leak at Sapref with Kerapour. A number of options were considered, and eventually Kerapour was chosen as the only safe option. It worked perfectly; a tribute to the properties of "cellular" insulation.
Cellular insulation is the answer to heat conservation in ladles. A backlining of Kerapour ensures a steel tight seal, as can easily be demonstrated in the thermit crucible test. Installation requires a casting former, which is not always available, so tiles are also made, for installation with Kerasil mortar. (Kerasil mortar is used because it is important to leave no gaps.) Tiles have proved themselves at Siltek and Scaw metals, and are now being offered for large ladles.
A basic version of Kerapour has now been developed at the request of some customers. Incidentally, we also have a basic insulating water-free mortar for use in contact with dolomite brick. It is particularly useful for preventing steel from getting behind the dolomite bricks, and helps to make breaking out easier.
Some readers want to know what a "contirution" is. Isn't it something to do with tying your body in a knot? Somebody reckoned it was either a printer's gremlin or the word processor reminding us to pay the installment.
Several readers want to know why we didn't tell them years ago about Multimould. Sorry, but that's the purpose of this newsletter. Two products down, about 50 to go.
Selling insulation by the kilogram has always been a hazardous occupation. Customers usually get the impression that good insulation materials are expensive. Furnace builders usually have more insight and immediately recognise a good insulation material as a bargain. To help evaluate new materials, I have developed a comparison which I call the "Heat containment cost factor". By definition it is the cost per square metre of a large furnace wall to reduce the temperature from 1000øC to 115øC. The average castable or brick has a thermal conductivity of around 1,3W/mK and a density of around 2,4g/cmþ. To reduce a furnace temperature from 1000 to 115øC we need 130cm of castable,to give us a K value of 100. One therefore requires 312kg per square metre, and say it costs R1 400/ton, the heat containment cost factor is R436.80. Heat containment cost factors for working linings are around this figure of 450 for aluminosilicate materials, and around for basic materials. Kerapour has a thermal conductivity of around 0,3W/mK, a density of 1,1g/cmþ and cost of R3 500/ton. This gives a heat containment cost of R25.41 i.e. it costs one tenth as much as normal materials to do the job of keeping the heat inside the furnace.
Let us take a simple example: Say we have a small furnace of 100mm square. We want a temperature of 1000øC inside the furnace and a cold face temperature of 115øC. To achieve this with a conventional castable or brick with a thermal conductivity of 1,3W/mK we would need a thickness of 130mm The total volume of material would therefore be 45 litres, weigh 108kg and cost R151. In Kerapour, we would need a thickness of 30mm, use 3,1 litres, weigh 3,4kg and cost R12, i.e. less than a twelfth of the price of normal dense materials. If you built the same out of basic brick, which would be daft, it would weigh 6 tons and cost 1000 times as much as Kerapour!
Note that the energy consumption drops drastically with good insulation and the speed of heating up increases drastically. Please let us do an exercise on your furnace to see if we can help. Fax us your dimensions, operating temperature and present lining design.