PACKAGING
Harbison-Walker packages rammed plastic refractories in 55-lb (25 kg) or 100-lb (44 kg) cartons. The refractory mass is divided into four to six slabs, or more, depending on product or cus-tomer preference. Plastics are made to specified workability and moisture levels. Harbison-Walker will manufac-ture to individual customer requirements as needed. This can be important when thick walls, overhead installation, or immediate installation is anticipated.
Please discuss your special workability needs with your H-W representative.
Plastic is sealed in polyethylene to minimize moisture loss and preserve the plastic's workability.
Gunned plastics are packaged in 1500, 2500, and 3000-lb. bulk containers.
Storage HEAT-UP
It is necessary to begin heat-up as soon as possible after completion of the structure. If this cannot be done, all refractory surfaces should be covered with a resin-based curing compound to slow drying and reduce shrinkage cracks. The use of a colored curing compound is helpful when performing a visual inspection of surface coverage.
Shrinkage cracks should be resprayed with curing compound to keep them from getting larger, although they normally close during heat-up. If desired, cracks can be sealed with a slurry of PHOXBOND® mortar. (Do not use an air-setting mortar.) Remove forms; do not permit wood forms to burn out. If forms cannot be removed, then expanded metal forms are often a better choice because they allow the heat to penetrate the plastic better.
Schedule I:
Heat-Setting and Air-Setting Plastics 1. From ambient temperature, heat to 500°F (260°C) at the hot face of the lining at a rate not exceeding 50°F (10°C) per hour.
2. Hold at 500°F (260°C) for one hour per inch plastic thickness.
3. Heat to 1000°F (538°C) at a rate of 50°F–75°F (10°C–24°C) per hour.
4. Hold at 1000°F (538°C) for one hour per inch plastic thickness.
5. Heat to operating temperature at a rate not exceeding 100°F (38°C) per hour.
6. Hold for steaming (see note).
PLUS® DESIGNATION
Plastics that include the word PLUS® in the product name contain non-metallic fiber additions to facilitate moisture removal during the dry-out. These plastics have passed a very severe spalling test indicating that under specific conditions they can be heated more quickly. For specific heat-up requirements, contact your Harbison-Walker Sales Representative.
Note: If steaming of the lining is evident at any time during heat-up, hold the temperature until steaming subsides.
STORAGE
Even though Harbison-Walker plastic refractories are carefully packaged to retain moisture, dry-out is possible if plastics are stored too long, especially in warm places. Unopened packages of plastic materials should be stored in cool, shaded areas under roof and away from sources of heat. The optimum temperature for storage of plastics is 55-60°F (13-16°C) . If plastics must be stored outdoors, the packages should be covered with a tarpaulin or similar covering. In hot outdoor areas, the tarp or covering should be raised to provide an 8–12 inch space for air circulation. In winter, plastics should be prevented from freezing. As a rule of thumb, use plastics as soon after receipt as possible, on a first-in, first-out basis. Check all plastic carefully before use. During installation, unwrap only as much plastic as is immediately needed. Pre-opened plastic may lose moisture and workability, resulting in improper knitting of slabs and a less than satisfactory installation.
WINTERIZING
For heat-set and air-set plastics, Harbison-Walker offers a winterized version. This lowers the freezing point to below 15°F (- 9°C) and permits storage of the products at lower temperatures. The winterizing process has no effect on refractory properties.
Phosphate-bonded plastics already have a similar freezing point and do not require winterizing. All plastic materi-als, even those winterized, should be kept above freezing before installation and, equally important, after installation until heat-up.
Schedule II:
Phosphate-Bonded Plastics
1. From ambient temperature, heat at a rate not exceeding 50°F (10°C) per hour to 250°F (121°C) at the hot face of the lining.
2. Hold at 250°F (121°C) for one hour per inch plastic thickness.
3. Heat to 500°F (260°C) at a rate of 50°F (10°C) per hour.
4. Hold at 500°F (260°C) for one hour per inch plastic thickness.
5. Heat to 1000°F (538°C) at a rate of 50°F–75°F (10°C–24°C) per hour.
6. Hold at 1000°F (538°C) for one hour per inch plastic thickness.
7. Heat to operating temperature at a rate not exceeding 100°F (38°C) per hour.
8. Hold for steaming (see note).
UR - 18 Harbison-Walker
Overview
Rigid forms are required when ramming vertical walls, roofs, or arches and care must be taken to prevent deflection of the forms during the ramming operation. Ram at the most acute angle possible to the hot face.
RAMMING
An anvil-type or reciprocating air rammer having a metal ramming head should be used to install Harbison-Walker ramming mixes. Metal ramming heads are of various shapes and sizes.
The type of installation involved determines which is appropriate.
Serrated ramming heads have been used for some installations.
Continuous feeding of the mix during ramming is preferable to batch feeding.
When batch feeding the material, the smooth surface formed by the rammer should be roughened with a small trowel or small rake to eliminate laminations and provide a continuous bond from batch to batch. Score each layer to approximately ¼-inch depth to assure knitting of the subsequent layer. The blows of the rammer should be directed in such a manner that lamination planes are not parallel to the hot face of the ramming mix.
Proper installation of Harbison-Walker ramming mixes will provide a dense, lamination-free structure. A good
indication that the material has been rammed sufficiently, is when the rammer head leaves noticeable tracks in the top face of the layer. The surface should then be scored and additional material rammed. The installation should be finished in one continuous operation, if possible. If it is necessary to interrupt the ramming operation for more than one hour, cover the unfinished area with a damp cloth so that the face will remain moist and new material will bond to it properly.
HEAT-UP
Bring temperature up slowly, at a rate of no more than 75oF (40oC) per hour and hold at 500oF (260oC) for at least one hour for every inch of thickness.
Temperatures then can be increased at a rate of no more than 100oF (55oC) per hour until operating temperatures are reached.
Installing ramming mix in top cap of coreless induction furnace.
Harbison-Walker UR - 19
Overview
Sound furnace refractory lining and construction — whether carried out by
experienced masonry specialists working on a high production furnace or a contractor building a municipal incinerator — begins with a few fundamental ideas required to produce satisfactory performance.
FOUNDATION
The foundation must function at the temperature produced by the furnace.
For many industrial furnaces, contrac-tors build foundations of concrete, consisting of a crushed stone aggregate, sand and binder of hydrated Portland cement. Under normal conditions, Portland cement concrete has been safely used for furnace foundations up to 700°F (371°C). When the tempera-ture reaches 900°F (483°C), dehydration of the cement reaches a point where the concrete retains little mechanical strength.
Ordinary aggregates include quartz pebbles, silica gravel, crushed silica rock and/or crushed limestone. An aggregate of silica rock in any form will expand sufficiently at temperatures up to 1000°F (538°C) to set up stresses in the concrete and weaken the foundation.
Limestone or dolomite rock in an aggregate will calcine at somewhat higher temperatures and weaken considerably. For temperatures above 700°F (371°C), good practice points to the choice of a castable refractory for the foundation. Calcined fireclay, in sizes up to 1 inch, can be substituted for conventional aggregate. Its thermal expansion is low, and it will not shrink at the highest temperature to which concrete can be subjected.
High temperature furnace operation also calls for ventilation in the lower courses of brickwork or the upper part of the foundation. Good furnace design often requires placement of the furnace on plates, girders or low brick piers, so that air circulates under the vessel.
Sometimes, cross flues are formed in the top of the concrete foundation. At others, pipes, 3 inches in diameter or larger, are embedded in the foundation.
Building furnaces is a specialized branch of masonry, best placed in the
hands of bricklayers experienced in furnace construction. Walls, arches and other furnace details should be de-signed and constructed to assure structural stability. Otherwise, a return on your refractory investment may not be realized.