ZIRALCAST-95 Mixing and Casting Guidelines

ZIRCAR Alumina Castable Type ZIRALCAST-95 mixes are handled and placed in the same manner as concrete. The best mixer is a paddle type concrete mixer. However mortar boxes, wheelbarrows and other stationary containers can be used.  Be sure the mixer used is clean of all foreign products.

Steel, acrylic and other plastic forms are best for casting shapes, but plaster, wood and cardboard forms can be used if coated with a product to make them impervious to moisture. Aluminum forms should no be used, due to reaction with the castable. Clean all forms and coat them with a release to prevent sticking. Suggested release agents are oil, oil and graphite, silicone oils or paraffin.

Vibration casting and pouring are the preferred installation methods. Mechanical vibrators allow for the use of a mix with lower water content which can give the best results. However, care should be taken to avoid excessive vibration which brings the water, fine particles and bond to the surface, and forms films which can cause layering, spalling and low strength. 

Vibration casting requires a closer control of the water content to insure removal of air pockets and proper placement. When pouring shapes be sure that you do not use an excessive amount of water to get the desired consistency.  Higher water content will reduce the strength and increase shrinkage of the cast product. 

When mixing, weigh both the castable and water to be sure the exact water content is obtained. Clean water in a temperature range of 65-80⁰F (18-27⁰C) should be used.  Colder water retards the set times and warmer water accelerates them. Add part of the water to the concrete mixer before adding dry mix, then add the balance of the water while mixing. When mixing in stationary mixers, add water slowly to the dry castable while mixing with a hoe or paddle by hand.  Keep the concrete mixer turning while placing the mix, or keep turning the mix over by hand with a hoe or paddle to keep it in the same consistency for placement.

After casting, all exposed surfaces should be covered with damp cloths or plastic to keep them moist. Initial set will take place in one-half to four hours, depending on the water content, method of placement and temperature.  Final set will occur in three to six hours.  Forms may be removed anytime after final set has taken place, but all exposed surfaces should be kept moist for 24 hours after casting to allow for maximum strength development.

Air drying at room temperature is recommended for as long as practical after uncovering the cast refractory, with a minimum of 24 hours before application of heat.  Attaching thermocouples to the refractory surface is an excellent way to monitor its temperature. Bring the temperature on the cast refractory up to 250⁰F (121⁰C) at the rate of 25⁰F/hour (14⁰C).  Hold at 250⁰F (121⁰C) for 24 hours per inch of refractory thickness.  The casting should then be heated at a rate of 25⁰F (14⁰C) per hour to a minimum of 2000⁰F (1093⁰C).  If there are any indications of forced steam evolving from it, then a slower rate should be used.  After holding at this temperature, the cast refractory is ready for service.

Copyright © 2004  ZIRCAR Ceramics, Inc.