GENERAL

Generally classified as mouldable refractories, this group of products represents a significant contribution to the concept of monolithic linings by widening the scope of appliances in which monolithics can be used and give excellent service.

Mouldable materials consist of a mixture of graded refractory aggregates, mouldable bond clays and water. They are packed in watertight containers and are ready for immediate use by the purchaser. When they rely on heat to set and harden, they are known as 'heat setting' materials. When chemical binders are added, the setting and hardening takes place as moisture is removed at low temperatures. These materials are called 'chemically bonded'.

Mouldable are usually presented in the form of extruded blocks cut into slabs approximately 300 x 300 x 50 mm (or 300 x 150 x 50mm) that can be laid and rammed very quickly. Mouldables differ from castables in their bonding mechanisms. Whereas the latter rely on the hydraulic setting of a cement bond, mouldables use refractory clay or chemical bonds, or a combination of both. They can be classified as being heat-setting or air-setting depending on their patterns of strength development.

Some of the features that determine their selection are as follows:

Mouldables can be installed in vertical walls without the need for formwork. In horizontal roofs and sloping or angled walls the formwork required is less costly than for castables.

The clay or chemical bonds of mouldables will generally resist erosive slags better than cement bonded castables.

Mouldables have every high resistance to thermal shock spalling in cyclic conditions and also tend to absorb mechanical shock better than the more brittle, rigid castables.

With the use of ceramic anchors, mouldable linings can be designed for thermal efficiency with the use of considerable amounts of back-up insulation. This is because the metal support components for ceramic anchors are generally buried well back from the hot working face.

PRE-INSTALLATION

Storage.

Mouldables should be stored in a cool, dry, well ventilated area and held off the floor on pallets. If stored outside, the cartons must be protected from rain or dripping water by a fixed cover. If they are further protected by plastic sheeting, ensure that there is sufficient ventilation underneath the plastic sheet to prevent water condensing on the boxes.

Pallets should not be stacked more than 3 pallets (6 tonnes) high when in storage. This is to prevent compression of the cartons on the bottom rows of the pallet.

Most Thermal Ceramics Australia mouldables have a finite shelf life called a "nominal shelf life". The nominal shelf life is half of the maximum expected shelf life of the material. When quoting shelf life, a nominal shelf life of 3 months is used. Product that is older than the nominal shelf life should be checked for workability prior to use.

Signs of aging are increased stiffness of the material (low workability) and reduced strengths. All cartons have the date of manufacture printed on them to aid in determining the age of the material. Always use the oldest materials first and if aged beyond the nominal shelf life, have the material tested for workability before commencing use.

Preparation Prior to Refractory Placement

The work surface shall be substantially free of dust, scale, oil, water, dirt and loose foreign material and shall be cleaned by sandblasting if necessary.

Anchors.

Both ceramic and metallic anchors are appropriate for use with mouldable refractories. This subject is treated in a separate procedure (IP/008).

INSTALLATION

Temperature

The workability of mouldables is particularly affected by temperature but provided the material is above 5(C and a pneumatic rammer is used, most materials can be adequately placed. If the material has frozen in storage however, it must be gently thawed out before use. If done slowly, no harm will come to the material of finished installation. In the event of a placed installation freezing in-situ before initial firing, it must be thawed out slowly at a low temperature and brought up to between 25-40(C before beginning the normal firing schedule.

Joints

There are two types of joints used in casting:

Construction Joints

These joints are designed to break the job up into conveniently sized panels. Adjoining panels are rammed against each other without leaving any gaps using the set face of previously cast sections as the formwork edge. Panels are generally 1.0 - 1.5 m². This size can generally absorb stresses without cracking. Larger panels can be made if required, with scoring of the lining completed between anchors as a point for controlled expansion cracking. The construction joint can be regarded as placing a crack where you require it, rather than leaving the castable to stress relieve itself in a random crack pattern.

Expansion Joints

For these joints adjacent panels are separated during installation by materials such as cardboard or plastic that will burn out during firing and leave a gap, or by high temperature materials such as ceramic fibre which remain in the gap, but have some degree of recovery after compression.

Equipment

Pneumatic rammers for mouldables are preferable to hand rammers. Such a unit would be fitted with a steel or cast iron butt for ramming of approximately 60 mm in diameter. Rubber butts are preferred where ramming is taking place around and near ceramic anchors due to the nature of the anchor to break if struck with a metal rammer. For small cavities, smaller rammers are available with a shorter stroke and butt size.

When a number of rammers are being used a manifold is generally used with an oil dispenser and water trap fitted to the inlet side of the manifold.

Use of Forms

Support forms are used where there may be danger of slumping e.g. installing roofs, bullnoses, arches and sloping walls etc. When using phosphate bonded mouldables such as MORAL( MOULD 85P, the forms must be left in place during the initial heat-up. Phosphate-bonded mouldables are very dense and require forms to prevent deformation before and during initial heating until the material has strengthened. Support forms must be well constructed and braced so that they are capable of bearing the full weight of the refractory mass without bending or buckling. Formwork should be well treated with oil or, in the case of phosphate bonded mouldables, a parting medium such as ROCOL SWITCH PLATE LUBRICANT, should be used to coat the forms. The material parts at elevated temperature and allows easy removal of formwork after initial heating.

Ramming

The mouldable material is extruded with most of the final required density as supplied. Therefore the amount of ramming required needs only be enough to knit the edges and layers together into a homogenous lining.

Typically, the edges are well rammed and the surface of the slab receives only about three passes of the rammer. Over ramming should be avoided. This is noticed when the material bulge's at a point away from the ramming area.

Begin by laying the mouldable slabs tightly together along the base of the wall, similar to brickwork stretcher course, with the outer edge parallel to the line of the intended wall face. If there is any gap between the back of the pieces and the face of the insulation or shell, it should be filled with broken pieces, offcuts and trimmings. With the succeeding layer, again as in brick laying.

The direction of the rammer should be parallel to the hot face of the material and vessel wall, roof or floor. The entire mass should be rammed thoroughly, without over-ramming, to assure its integrity.

Holding the rammer vertically, begin by ramming all the joints of each mouldable slab. Then, beginning in the centre of the slab of mouldable, move the rammer slowly back and forth between the centre line of the wall and the cold face parallel to the working face. Progress slowly along the wall, ensuring that each impact of the ramming head covers half of the preceding contact area. When all of the back portion of the wall is consolidated, ramming should proceed in a similar manner in the hot face region. The entire thickness of the wall is then rammed, moving the rammer in a pattern perpendicular to the working face keeping it vertical at all times. Now lightly ram the front portion of the wall again. Each layer should finish 10-15 mm beyond the intended face lining thickness to allow for trimming. Excessive bulging should be avoided, but if it occurs, it should be trimmed rather than forced back with the rammer.

When seating anchors into the mouldable, build the layer to slightly above half the anchor height, then place the anchor and tap into the mass with a leather or rubber mallet. Ensure ceramic anchors are pulled to the front of the C-Clip to give the correct wall thickness and support to the anchor. Never use the steel head of the rammer to place the ceramic anchor as the anchor may break! Place slices of mouldable on either side and at the rear of the anchor and gently ram these to equalise the pressure around the anchor until it is firmly in place.

When the complete line of anchors is in place, ramming can proceed as previously outlined up to the next anchor line. When using ceramic anchors, the space between the back of the ceramic anchor and the metal C-Clip should be filled with a material such as ceramic fibre or cardboard which allows the ceramic anchor to expand and move as the wall heats up. The hot face of the ceramic anchor is the limit of thickness of the wall.

At regular periods in the build up of the monolithic wall, the mouldable should be trimmed back to the correct thickness as given by the position of the ceramic anchor. This is generally done with spades and/or trowels. The trimmed material can then be re-used in the wall by placing on top of the mouldable and ramming into place.

Finishing

The as rammed finish of the refractory is quite acceptable, but if a smoother surface is required, it can be scraped with the edge of a trowel or wooden board as soon as possible after the completion of ramming. The rough open texture should be left; smooth trowelling or floating to slick the surface is unacceptable.

Before firing, venting of the mouldable structure should be done. This involves the use of a welding rod pushed at least three quarters of the way into the wall on 150mm centres (on conical, horizontal and other shapes, vent on 50-75 mm centres). Exposed mouldable surfaces should be covered with polythene sheet prior to firing to prevent surface drying.

FIRING

Detailed firing schedules are separate from this procedure. They are available from any Thermal Ceramics Australia office or representative.

BACK

TABLE OF CONTENTS

Combustion & Chemical Engineering.
Copyright © 1998 [CCE]. All rights reserved.
Information in this document is subject to change without notice.
Other products and companies referred to herein are trademarks
or registered trademarks of their respective companies or mark
holders.