Freeze linings are made of thick, high conductivity refractories, cooled by water copper coolers. The principle is sound, and works as long as there is good thermal contact between the refractory lining and the cooler. Unfortunately this thermal contact is frequently lost, mainly because nearly all refractories fail to adhere to copper. In this situation, the thermocouples in the affected coolers show a drop in temperature, while the temperature in the neighbouring refractories is actually rising. With no cooling, the temperature continues to rise, melting frozen metal fins in the refractory, and the metal melting point isotherm reaches the gap between refractory and coolers. Molten metal runs through into the gap and keeps on running until the exposed cooler explodes and a run out follows.
The discontinuity of thermal contact cannot be prevented, but it can be relocated. Keramicalia worked with Anglo Vaal pilot plant to develop a refractory with excellent adhesion to copper. (See report) This material is virtually impervious, and is called Phospatch. It clings to the cooler, and the discontinuity now opens between the Phospatch and the freeze lining. As before, metal eventually enters this gap and fills it. But it does not touch the copper. The thermocouple shows a sudden rise in temperature, and then drops back to normal, once the metal has frozen and the thermal continuity is restored. No damage results and operation continues.
Phospatch is used to coat waffle coolers to prevent contact by molten metal. (Ask for more details.)
The installation can be done at the foundry, on site or installed in the furnace. Outside the furnace, it is easiest to apply the lining with the with the waffle cooler lying on its back, level. It requires short shuttering around the edges, either level with the top of the copper or 40mm above it, at the customer's discretion. If the cooler is upright a sturdy shuttering is required. Build a box frame to fit around the edges. Tilt the cooler backwards and fit the frame. Cut a filling hole in the top and a "riser" hole on the opposite end. Close all gaps and holes. Cover the front. Tie the shuttering securely around the back of the cooler. You can use strapping. If you leave out this step the pressure will push the shuttering off the face. Build a crude funnel around the filling hole, enough to hold 10kg. Do not use oil or grease on the shutterboards.
Weigh out a few batches of 10kg Phospatch powder and 1,8kg liquid binder. Put on latex gloves and mix powder and liquid in plastic bowls. The latex gloves are so you can rip them off and start with clean hands frequently. Phospatch is very sticky and difficult to wash off. Don't wash the plastic bowls, Leave them dirty and break the hard Phospatch off the next day just by bending the bowls. Mix for one minute and dump the mix into the funnel. The material flows slowly into the void. After the first few mixes you can add materials without weighing, judging by consistency. Phospatch is very forgiving. It will work over a wide range of powder to liquid ratios. Add all the material through one filling funnel. The continuity of flow avoids all defects. It is best to have two people mixing, and keep a constant flow of fresh material. Never interrupt the installation. Stop when the riser is full. Now you can prod the material a bit to remove air trapped under the top shuttering. (If you leave the top surface open instead of closed with the two holes, you will need to grind the whole surface flat, as the Phospatch will rise as it sets.) Do not at any point try to vibrate the Phospatch.
Strip the next day or wait until the material gets quite hot, after 2 to 4 hours.
If you follow these instructions you will be amazed at the quality of the installation. There will be no joints, no cracks, no bubbles, no laitance, no bleeding and no sign of any defect or irregularity. Penetration into gaps will be down to 1mm at half metre head and 3mm near the top surface.
Fig 1 Installing Phospatch on water cooled taphole at chambishi in Zambia
Fig 2 Copper cooler at Polokwane Smelter
Fig 3 Framing It
Fig 4 Shuttering completed
Fig 5.Casting Completed
Fig 6. Shuttering stripped
Fig 7. Note Penetration
Fig 8. Detail of casting surface showing the extreme perfection of the structure.
Say goodbye to runouts!!!!!!!
Dave Onderstall 082 808 4757
A patching material for hot surfaces and surfaces difficult to bond to. Phospatch is virtually impervious. It is totally silica free and immune to thermit reactions. It is very sticky and sets in 10 minutes.
Chemical analysis; Al2O3 88%
Maximum service temperature; 1780°C
Max. particle size; 3mm
Mechanical properties; Phospatch has an exothermic setting reaction and expands slightly while setting. It sets in 10 minutes, and grips onto nearly all surfaces, even copper. Phospatch is not brittle; a hammer blow will make a slight dent rather than shatter it. Test cubes on cold crushing strength deform without breaking. The impervious structure gives immunity to chemical attack except on the surface. Strength increases with temperature, but the malleability changes to a more brittle rigid ceramic structure.
APPLICATIONS; Protection of waffle coolers from molten metal contact.
Patching of launders, flues, any hot repairs of furnaces.
Patching of surface contact line in aluminium furnaces to prevent thermit reaction.
Colour; Pure white.
Mixing; Mix 100 weight parts powder to 22 weight parts liquid gives a gives a good workability, but can be used from pourable to rammable without any problem. A lot of gas is evolved during mixing. Do not make large batches, as the exothermic reaction is self accelerating. Setting can be retarded by refrigerating the liquid binder.
Patches and castings can be heated up 20 minutes after mixing.
Packaging; 5kg box repair kit, with mixing bowl and gloves.
10kg combined weight packs.
25kg packs, combined weight of powder and liquid.
25kg plastic bags of powder and 45kg polycans of liquid.
Shelf life; 3 years.
Development no. 39107
Claimer; This information had better be correct, because Dave Onderstall stakes his reputation on it.
(Reg No: 1993/034692/23
P O Box 55705 ARCADIA 0007 Tel/Fax 012 343 5429 Cell: 082 403 3615
ADHESION OF PHOSPATCH REFRACTORY TO COPPER.
Bonding between refractories and metal substrates is problematic because of the lack of chemical interaction between any of the constituents of the refractory with the substrate. Specifically, the hydration products of dry cement have no affinity for clean metal surfaces. This means that bonding is primarily dependent on mechanical keying and weak, short range forces.
Phospatch is a phosphate bonded high alumina refractory. Phospatch is supplied as a two-pack product: a dry powder consisting of refractory with cement, and an activating solution.
In Phospatch, the activating solution causes a chemical reaction on the metal surface, and this provides a measure of chemical bonding.
Trials were conducted to ascertain the relationship between surface preparation and effectiveness of bonding. These trials were conducted on copper blocks with machined tapered channels, as would be found on the surface of a water-cooled panel operating in a furnace sidewall. The dimensions of the copper blocks were 250mm x 150mm.
All the surfaces were degreased. One had no further treatment, one was washed with phosphoric acid to convert residual oxides to phosphate and one was treated with a commercial silane primer. The blocks were encased in a brick-shaped mould that gave final product dimensions 250mm x 150mm x100mm after Phospatch had been cast into it. Phospatch was mixed and poured into the mould. After setting, the copper-refractory composite was sectioned and examined. The surface detail was examined in a Jeol 840A microprobe analyser. The degree of adhesion was evaluated by the amount of observable chemical interaction between refractory and metal.
There was little adhesion between phosphoric acid-treated copper or the silane-primed copper and the refractory. The copper surface with the degreasing treatment only exhibited a chemical reaction that resulted in the formation of mixed copper-aluminium phosphates. These were visible in the refractory at depths of up to 50μm and were usually less than 1μm in diameter. A typical area is shown in Figure 1. The mixed phosphate particles always bridged neighbouring aggregate grains when found in the refractory; they were not found as discrete particles in the matrix. Accommodation between the refractory and asperities on the metal surface was good, especially in areas where there was most copper aluminium phosphate, as shown in Figure 2. In areas where the surface asperities were too small to accommodate the smallest aggregate particles, the surface was covered with impervious aluminium phosphate.
The main body of the refractory contained numerous spherical closed pores, as shown in Figure 3. These pores were absent from the refractory in the immediate vicinity of the metal. This absence of porosity next to the metal surface contributes to better fracture strength in this area.
The activating solution contains a soluble aluminium salt. There is an insoluble salt on the surface after the refractory has set. This means that the aluminium salt has either decomposed on drying to produce aluminum phosphate or there has been a reaction between that salt and the copper. Whatever reaction occurs between the activator solution and the substrate occurs most readily on a surface containing residual oxides. It occurs less readily on a chemically clean copper surface or a surface on which the residual oxides are converted to phosphates. It may be postulated that the best degree of adhesion is obtained on a surface that is cleaned and subjected to a controlled chemical oxidation treatment before application of the refractory.
My colleague Clive Woodford involved me in a project for an explosives manufacturer. He was asked to make detonator coolers to prevent premature explosions in hot blastholes. His solution was too expensive. I did a lot of basic R& D and eventually solved the problem. Our goal was to keep the detonator below 137°C for half an hour with the temperature at 1000°C in the hole.
We have achieved it and want to demonstrate it. The client did not buy the technology and we are looking for new clients.
Sometimes coal seams ignite underground, and smoulder very slowly because it takes very long for oxygen to get down there. If you drill blast holes into such a seam, you suddenly let fresh air in and the temperature goes screaming up to 1000°C. Then they put a detonator down, and pump dynamite down the hole. The detonator overheats and explodes when it reaches about 137°C. I devised a super insulation capsule to delay the heat transfer. I cannot find a case of this actually happening, but if it does happen while dynamite is being pumped from a tanker, the destruction will be devastating. I think it unlikely that I will sell lots of insulators, but am hoping that an explosives manufacturer will buy the technology and some insulators and offer it to his coal mining customers, just to cover his arse. If they don’t buy it, and the shit hits the fan, he can show that he has done everything he can to prevent this catastrophe, and is therefore blameless. I can’t guess what the implications would be in SA, but in the USA this could be viewed as a very handy “insurance policy.”
If I could find the right guy in the USA to sell it, he could possibly sell it to several manufacturers, perhaps some mines too. Maybe he could get several million US$ for it, give a cut to everyone along the chain, including me and you. Do you have contacts who could perhaps get the ball rolling?
Dave Onderstall of Keramicalia and Clive Woodford of Mirja ceramics.
Below I have attached some background information. I have patented the technology and would like to sell the patent. Otherwise Clive and I can manufacture the product for you.
Tests are going well. I left the file at work, but here are some results;
I found many products with high porosity and high strength. Kerafire is one of the best, about 50% porosity by volume, and it absorbs 50% water.
Here is my little Heraeus furnace at 1100C. I put soaked specimens in at between 1100 and1200C to check if they explode.
Kerafire at the back and ceiling board in front after 10 minutes.
The little one at the back is Plaster of Paris, The curved one is Insulag boiler plaster, the square one is calcium aluminate bonded board and Harmonite in front, before firing
After firing, Insulag is melting, PoP a bit buggered.
Darling mix right, a blob of sorel cement behind it and microporous insulation on left.
After cooling; Calcium aluminate board looks best. Kerafire got damaged during handling while hot.
The Heraeus burned an element, busy repairing the brickwork. Next I would like to clad detonator containers with Kerafire and return them for testing.
Subject: Hot hole simulation
Our test rig took a long time to perfect. The biggest problem is that when you place the cold capsule in the furnace at 1000°C, the temperature drops. The solution is to place high thermal mass sleeves in the kiln to stabilize the temperature.
Fig 1. Heat stabilizing sleeve on left, capsule on right.
Fig 2. Sleeves in the kiln.
The next problem is heat loss on opening the kiln. We now have built a dedicated kiln with holes through which to insert the capsules.
Fig 3. Kiln with holes plugged by bungs. The one on the right has a thermocouple inserted. The instruments above it record the kiln temperature and the temperature inside the capsule.
Fig 4. A thermocouple is inserted through a bung.
Fig. 5 The false lid for the thermocouple.
Fig. 6 The real lid with thread and groove for the cable.
It seems that we now have a real simulation of a hot hole. We start the test at 1050°C, and it drops but recovers, giving roughly an average temperature of 1000°c over the test.
We have now achieved the goal of 30 minutes below 137°C inside the capsule.