Why Colloidal Silica Bonded Monolithic Instead of Brick?
For many years the term refractories generally only referred to bricks or shapes intended for exposure to aggressive environments. Recent advances in unshaped, colloidal silica bonded monolithic refractories have lead to a substantial reduction in refractory brick usage. The advantages of colloidal silica bonded monolithic refractories over bricks include the following:
1) Availability and Lead-time
- The manufacture of bricks requires that individual pieces be pressed, cast or extruded to specific sizes and shapes and then be fired according to a specific heat-treating schedule. This is a laborious and time-consuming process that can require many weeks to produce a single truckload of bricks. Since different applications may require different sizes or shapes it is not always possible to substitute refractory bricks intended for one customer or order with that of another order or from product available in inventory. In some cases, short lead-time orders are simply not possible.
- Colloidal silica bonded monolithic refractories are generally shipped unshaped and unfired. Manufacturing is primarily a blending and bagging process of raw materials generally stored on-site. Since no specific shaping or firing is required, many truckloads of refractory can be produced daily. Also, since no in-house shaping is required a product of given composition can easily be routed to any of several awaiting customers or applications. Short lead-time orders are generally possible as long as the raw materials are on hand.
2) Exact Fit with No Required Cutting or Back-filling
- Vessels requiring refractory lining are seldom flat or without irregularities. As a result, flat-sided bricks rarely can be installed without voids which must be back-filled or which will result in a permanent weakness in the refractory lining. The cutting of bricks can reduce the amount of voids but cannot eliminate them and involves more labor in the installation.
- Pumped or cast linings allow for all void space to be filled. This minimizes any channeling of liquids or gases behind the refractory that might otherwise reduce lining life.
3) Labor and Time Savings
- The installation of brick linings requires skilled laborers and is very time consuming. Each laborer can only install a limited number of bricks per hour.
- Pumped or cast refractory can be installed at installation rates of up to 20 tons per hour using a single refractory pump and mixer. Installation of several hundred tons of refractory per day is easily attainable.
4) Brick Joints are a Weakness
- All bricked linings contain joints that are often the performance limiting area of the lining. Even if the refractory brick is of outstanding characteristics the joint is often preferentially attacked.
- Channeling of gases or liquids into the lining through joints can cause damage behind the refractory lining.
- Since colloidal silica bonded monolithic refractories have limited refractory joints these potential weak areas are minimized.
5) Excellent Colloidal Silica Bonded Monolithic Properties
- Recent advances in colloidal silica bonded monolithics have resulted in refractory properties superior to many existing brick compositions. New colloidal silica bonded monolithic binders and aggregates have resulted in refractories with improved high temperature properties such as hot strength, creep resistance, abrasion resistance, thermal shock resistance, oxidation resistance and corrosion resistance as well as improved installation characteristics through placement techniques such as shotcreting and faster, safer dryout characteristics. Magneco/Metrel colloidal silica bonded Metpump refractories provide cement-free options with outstanding high temperature properties that are very forgiving with regard to water removal and dryout.
6) Disposal and endless lining philosophy
- Replacing spent brick linings involves replacing many undamaged bricks as well as many partially damaged bricks. Although only a small portion of a brick may be damaged, it is typically required to replace the entire brick. These spent bricks must be disposed of in environmentally safe landfills.
- Colloidal silica bonded monolithics allow for easier adaptation of an endless lining philosophy. Cleaning the lining surface and replenishing or replacing only the worn material minimizes the quantity of spent refractory disposed of. Furthermore, since a significant portion of the existing lining is reused, the quantity of refractory required for making a repair is greatly reduced.
7) Lower overall costs
- Since less refractory and less labor is generally required for colloidal silica bonded monolithic refractory linings, the installed lining cost may be lower. Furthermore, since vessel turn-around time can be greatly shortened production downtime will be minimized resulting in greater production efficiencies.