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.