Refractory Anchor Systems Part 2 of 2

Refractory Anchor Systems Part 2 of 2

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Metal anchors are most commonly utilised, some typical maximum operating temperatures are shown in the table below:

TYPICAL MAXIMUM TEMPERATURE. GRADE OF STEEL.

450°C Carbon Steel
900°C 304 Stainless Steel
°C 310 & 310S Stainless Steel
°C Incalloy 601

Other materials are available on request and would be imported as required.

Anchor lengths should be a minimum of 25mm below the hot face lining and tests have shown that the anchor tip may be 150°C to 350°C below the hot face refractory temperature, however in general it is accepted to use the higher grade anchor material to that of the hot face temperature.

Another consideration is the coefficient of thermal expansion of the anchor material, which will be higher that the refractory material, thus the stresses produced can result in lining cracking and eventual failure of the refractory material and also the anchor. It is suggested that all anchors be coated with a material (bitumen) that will burn out at low temperature and allow very small movement between the anchor and castable lining to accommodate the differential expansion.

Plastic caps only cover the anchor tips and are not adequate, the whole anchor should be coated. It is also said that the plastic caps help with the longitudinal expansion were most of the damage is done to the refractory material, full anchor coating helps with the radial expansion. It is good manufacturing practice to not produce anchors with the legs being the same length, this cause a shear plain across the anchor tips and results in the hot face of the refractory lining breaking off exposing the anchor tips to the hot face and shortening the life of the refractory lining.

Anchor Spacing tables should be used as a guide only as each application should be considered according to the type of unit being lined, the temperature, the high stress areas, the formation of cracking, side wall or roof application. On large side walls support plates (wall seats) should be used to take the load off the anchors, this must also be used to separate monolithic and brickwork applications, it also makes it easier for future repairs.

Typical Anchor Spacing Table:

LINING THICKNESS ANCHOR CENTRES

50 to 75mm 150mm = 44/m²
100 to 125mm 250mm = 16/m²
150 to 350mm 300mm = 11/m²

Remember this is just a guide and you should contact your anchor supplier for more experienced and detailed placement of the anchors, the pattern is also important, anchors must never be placed in straight lines, this will cause severe cracking, were possible, and should be placed at 90° to each other.

Common anchor shapes include Y and V types which are used in single or double refractory linings, anchors are also used for triple linings, care should be taken not to us anchors with threaded sections, the threaded sections do not handle the high heat and will oxidise much faster causing premature failure.

To eliminate threaded anchors a &#;split pin&#; type anchor is recommended for use in double linings, once the cold face lining has been installed a washer is placed over the anchor and the two legs are opened out to form a vee.

Other anchoring systems include Brick anchoring (brick ties), Ceramic Fibre Linings (fibre pins and modules), Petro-Chemical FCC linings etc. (hex metal, flex metal, speed cells, s-bars and corner tabs). For additional and experienced knowledge in this field please contact your anchor provider for advice. Floating anchors are preferred for shells that are moving, like a rotary kiln were the shell moves and the anchor pull the refractory lining with it, an anchor welded direct to the shell in this case would be subject to continuous movement and could break off within a short period.

With a floating anchor a solid block is welded to the shell and the anchor passed through a hole which allows the slight movement during operation.  The block can be manufactured in various lengths for single or double linings and different grades of steel. Another anchor design includes a 8 to 10mm diameter stud which is attached to the shell, the anchor is then bolted to the studs with a plastic spacer, the plastic spacer then melts away at low temperature and allows movement in the anchor.

Attachment of anchors can be done in four ways, hand welding, and stud welding, bolting and hook method. Always make sure the surface is clean and free of rust, scale or paint.

Hand welding being the most common method, again attention must be given to the base of the anchor, does it have sufficient area to weld onto, an anchor should have a long flat base or 90° bent foot for attaching to the shell. The recommended length of the foot is +- 4 x the diameter of the anchor material. (e.g. 8dia. = 32mm long) The choice of electrode is very important due to the anchor mostly being stainless steel and the shell in mild steel, in past experience we have found that E312-16 electrodes work very well for welding dissimilar metals, they cost more but do the job providing your welding operator is qualified in the procedure.

Stud welding is very fast and saves time and cost of the electrodes, less labour is required to attach the anchors, however it is recommended that only qualified personnel trained to operate stud welding equipment be used. The most common applications are refractory linings like ducting&#;s and thinner linings upto 150mm thick, in certain application large diameter anchors can be stud welded, but you should consult a company experienced to carry out these welds and offer the best design to suit the application.

Bolting can be done by having a hole in the furnace shell, hand or stud welding a stud and then bolting the anchor down, the plastic spacer can also be used in this application as explained with floating anchors, the plastic spacer is designed to melt at a low temperature and allow the movement of the anchors. However if you choose the stud method proper care must be given to the size of the stud and the fixing method, as this will be the weakest point if done incorrectly.

Hooked anchors are used on side walls and roof applications.

Ceramic Anchors are often utilised in roof applications/ bullnose or in very hot areas with minimal heat transfer is required to the cold face, these require a stainless steel &#;C&#; Clip or Scissor Clip type anchor, the &#;C&#; Clip can be attached to the shell in many ways please contact your anchor supplier for recommendations, the Scissor clip basically hooks over the I beam attached to the roof structure.

ME steel Fibre (Melt Extract steel fibre) ME Fibres used as an addition to the castable mixing to improve its thermal shock and its mechanical shock resistance, to extend and enhance refractory lifetimes. ME fibres control the crack development, improve cohesion and strength of the refractory castable. Added at 2.5 to 3.5% of the castable, as designed by the refractory engineering company.

ME steel fibres are supplied in 20kg boxes and manufactured in 430, 446, 304 and 310 stainless steel, for castable applications a common 25mm long fibre is used, for shotcrete 19mm is used.

The design of high performance, reliable furnaces and pyrometallurgical vessels is incomplete without inclusion of monolithic refractory linings and anchoring.

Anchors and monolithic refractories are an integral part of any successful vessel design, insulation, heat transfer management and installation. Despite anchors playing an integral part in the performance of a furnace, they are not always given due consideration when designing a refractory lining. It is important for a plant manager or engineer to fully understand the use and selection of refractory anchors in their plants. Below are a few critical things to note about Monolithic Refractory Anchors.

ALLOY GRADE

Low grade anchors will lead to premature failure and will cost thousands in repairs as such cheap or inferior quality anchors should never be considered, the anchors are a fraction of the cost of your refractory materials and you need the best support possible. Correct choice of monolithic refractory material is also vitally important in optimizing the process and expected life campaign of the refractory material. Typical maximum operating temperatures of different steel grades are shown in the table below:

Typical Maximum Temperature Grade of Steel

450°C                                               Carbon Steel

900°C                                                     304 Stainless Steel

°C                                                    310 & 310S Stainless Steel

°C                                                    Incalloy 601

MECHANICAL PROPERTIES

For more Refractory Anchors Manufacturerinformation, please contact us. We will provide professional answers.

Bending can affect the mechanical structure of on anchor. A good practice is to &#;soft form&#; the anchor in a CNC wire bending machine rather than the old method of hammering out the desired shape in a press, furthermore when using a CNC machine many different designs can be done without having to manufacture costly dies used in a press. Anchors can be custom manufactured to suit any application.

ANCHOR LENGTHS

Anchor lengths should be a minimum of 25mm below the hot face lining, tests have shown that the anchor tip may be 150°C to 350°C below the hot face refractory temperature, however in general it is accepted to use the higher grade anchor material to that of the hot face temperature.

ANCHOR SPACING

Anchor Spacing tables should be used only as a guide. Each application should be considered according to the vessel being lined, the operating temperatures involved, the anticipated stress on different areas and the position (side wall or roof application). On large side walls support plates (wall seats) should be used to take the load off the anchors, this must also be used to separate monolithic and brickwork applications, it also makes it easier for future repairs. Typical Anchor Spacing Table:

Lining Thickness                                     Anchor Centres

50 to 75mm                                              150mm = 44/m²

100 to 125mm                                           250mm = 16/m²

150 to 350mm                                           300mm = 11/m²

The pattern is also important, anchors must never be placed in straight lines as this will cause severe cracking, were possible they should be placed at 90° to each other.

THERMAL EXPANSION

The coefficient of thermal expansion of the anchor material should always be considered as it is always higher than that the refractory material, thus the resulting stresses can lead to lining cracking and eventual failure of the refractory material and the anchor. It is suggested that all anchors be coated with a material (bitumen) that will burn out at low temperature and allow very small movement between the anchor and castable lining to accommodate the differential expansion. Plastic caps only cover the anchor tips and are not adequate, the whole anchor should be coated. It is also said that the plastic caps help with the longitudinal expansion were most of the damage is done to the refractory material, full anchor coating helps with the radial expansion. It is good manufacturing practice to not produce anchors with the legs being the same length, this cause a shear plain across the anchor tips and results in the hot face of the refractory lining breaking off exposing the anchor tips to the hot face and shortening the life of the refractory lining.

COMMON FAILURES

The most common refractory anchor failures are the interface between the hot face and insulation layers, wrong alloy choice, incorrect welding methods and anchor spacing. The anchors used to retain refractory materials on roofs and vertical walls are more critical as they must remain able to support the weight of refractory even at the elevated temperatures and operating conditions.

The Anchor Division at Dickinson Group has been designing, manufacturing, delivering and welding standard and custom-made high-quality refractory anchors for almost 30 years. It manufactures and distributes a comprehensive range of products for standard industrial use, through to specialty applications in the mining, metals smelting and mineral processing industries. The product range includes Refractory Anchors, Hex Mesh and Tabs, Reinforcing Fibers, Stud welding equipment, CD Pins and Clips, Arc Studs, Wear Studs & Shear Connectors.

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