Historically, it was common refractory practice to build brick walls 9 to 18 inches thick. Today, the customers are designing walls of combinations of meterials such as: brick, castables, plastic, ceramic blanket board and modules, along with supporting steel anchors to increase the efficiency of their furnace and reduce refractory waste. An excellent way of reducing installation costs of refractory castables is the gun method.
First, select the gunning case table best suited to meet the service conditions are: peak temperature, strength requirement , thermal conductivity and , abrasion resistance. Thereafter, estimate the quantity required for the job. Upon receiving your wesco Refractories gunning castable, it should be stored in a cool but not cold, dry area.
Applying a refractory lining by gunning is generally accepted because it results in a controlled density, uniform mixing time and labor saving. Gunning permits an even and gradual build-up of the lining achieving a well-bonded texture and strong, homogeneous structure. It is also possible to install two or more several inch layers of different material, such as a lightweight insulating castable layer, protected by a dense abrasion-resistant layer.
Procedure
Gunning a refractory lining requires close control of the amount of water, material feed rate and , gun air pressure to prevent excessive rebound and achieve maximum strength. Pre-dampening is important to achieve lower rebound, less dusting and, lining uniformity, Using a consistent and even nozzle motion and consistent water content minimizes planes of weakness and trapping rebound ( lamination).
Building a Wall
When gunning a wall 2 inches or greater, begin from the bottom and work your way up. Usually the nozzle man will use a quick circular motion to build to almost full thickness in a somewhat localized area. This area will have a diameter of about 12 to 18 inches. When full thickness is achieved, the nozzle man will move over a little and begin the process again. This localized wall building procedure is to insure that the castable hits the wall with a consistent force and water content. This consistent force and water content will reduce laminations and rebound.
Rebound and Lamination
The nozzle man must be mindful of the rebound. Rebound is the material that does not stick to the wall. Wescolis Tex Kast HS G is formulated to be fast wetting and have a very low rebound. Another way the nozzle man reduces the danger of trapped rebound is by creating a slope on the top of each localized wall area. This slope will cause the loose rebound to roll off the top of the wall and fall to the floor rather than resting on top of the wall section where it can become trapped when a nearby section is shot.