Hindustan composites Ltd. has been in the field of manufacture of insulating and sealing materials for over 45 years now. Compressed asbestos fibre jointings developed and manufactured with overseas technical backup by Hindustan composites Ltd has been more than satisfying the needs of the industry domestically as well as overseas.
To avoid the necessity of producing perfect finish on the contact faces of a mechanical assembly, which is not only costly but quite often impracticable, a gasket from compressed asbestos fibre jointings enables a tight seal to be created and maintained between separable members. The seal is effected by the yielding, or the flow of the jointing material into the imperfections of the joint contact faces. In this way the gasket provides an unbroken barrier of homogenous structure through which no pathways exist for escape of the confined media.
Highly specialized knowledge and technical skill is necessary to manufacture adequate grades of compressed asbestos fibre jointings to various service parameters, such as resistance to contained fluid and pulsating loads if necessary.
The engineers and technicians involved in design, production and maintenance are quite familiar with the wide range of compressed asbestos fibre jointings manufactured by Hindustan composites and hitherto marketed under the brand names of 'permanite' and 'firefly' CAF. These jointings after upgradation, wherever necessary are now being offered under our export brand name 'FYSAX'.
Our R&D center with its highly specialized and experienced staff continues to provide all the backup services for upgradation of technology and products to meet the highest quality and performance standards while keeping pace with the accelerated rate of technological advancement and demand for excellence from the industry.
This catalogue contains the comprehensive data in the from of guidelines for engineers and technicians to enable them to select the appropriate grade of jointing materials for application from the wide range available. However the numerous parameters under which the jointing is expected to meet manifold demands may make the selection difficult. Our Technical cell would be most delighted to help solve your problems promptly.
CHOICE OF JOINTING GRADE
The choice of the grade of jointing material for any and given condition is of paramount importance. A number of factors need to be taken into consideration, while the choice of the correct grade and thickness is finally made for a particular application.
TYPE OF CONFINED MEDIA
Resistance to attack by the confined media on the jointing material forms the sole basis of selection. Please refer to the Fibre jointings Recommendation chart given at the end. Though other factors also play an important role in the selection procedure these guidelines serve the purpose adequately.
FLANGE SURFACE FINISH
Too smooth a surface would be detrimental. The gasket and flange surface must provide suitable friction to reduce the chances of the gasket bursting under pressure.
Concentric grooves, particularly the standard gramophone record or spiral type are most ideal, though. Commercial machine finish would do in most cases. However the jointing material itself should have a high surface co-efficient of friction, so that it may be firmly gripped between the flange faces. This characteristic of the jointing though appears to be insignificant for consideration, plays an important role in reducing the possibilities of gasket burst. Hindustan Composites pays special attention to technology of surface compounds to meet this requirement.
GASKET AND BOLT CONFIGURATION
For a given gasket stress, the possibilities of leakages will increase as the width of the gasket decreases. Placement of bolts to even out the stress is also an important consideration while designing the flange.
Actual initial compression needed on a gasket to reduce leakage to zero or to an acceptable level, also known as minimum gasket sealing stress depends upon the following:
Design of the flange and bolt configuration
Internal pressure of the fluid
Viscosity of the contained fluid and its temperature which has an effect on the viscosity
Generally the actual clamping pressure is increased over the minimum gasket sealing stress by multiplying internal pressure by a factor known as the 'Gasket Factor'. As a thumb rule, the gasket factor for liquids is 1 and that for gases is 2.5.
CHOICE OF THICKNESS
Though there are no hard and fast rules governing the choice of gasket thickness, the gasket should be as thin as possible to minimize the stress relaxation. The considerations are, dimensions and conditions of the flange. As a guideline the following choices can be made, depending upon the condition of the flange surface:
Finely machine finished
Well forged or die-cast
0.25 to 0.4 mm
0.5 to 1.00 mm
1.2 to 1.5 mm
1.5 to 3.0 mm
3.0 mm and above
IMPORTANT CHARACTERISTICS OF JOINTING MATERIALS
Specifications covering the physical properties basically help in classifying the grades of jointing materials. For example, in recent years there has been an increasing tendency to take tensile strength as being the total measure of the quality and likely performance, but in reality it is by any means, not the sole criterion to judge its possible behavior in service. The following characteristics also play an important role in determining how efficiently the jointing material performs under varying operating parameters.
COMPRESSIBILITY - A jointing material should possess compressive characteristics so that it allows the material to flow and conform to the flange surface with an ability to 'bed-in' and offer necessary friction.
RECOVERY - As the jointing material should get compressed under pressure, it should also offer resilience to recover and maintain its sealing effect by not allowing any 'Permanent Set' due to changes in pressure of the confined fluid and effects of its temperature, or due to flange deflection or bolt expansion.
STRESS RELAXATION - This determines the dimensional stability of the jointing material under combined effects of pressure and temperature. There should be a minimum tendency of the gasket to relax its stresses under high pressure/temperature conditions to reduce the torque loss and maintain an effective seal.
Hindustan Composites Limited strive to maintain these important characteristics in its jointing material, through well formulated furnished, controlled manufacturing process, stringent checks and balances at every stage.
GUIDELINES ON THE USE OF FYSAX AMJ JOINTINGS
The FYSAX AMJ series of jointings are carefully designed to perform excellently under normal fitment. However, certain preparatory precautions would help in achieving the best results:
The flange faces must be clean and devoid of any projections, dents, burrs, distortion, etc.
The OD, ID and the bolt clearances should be cut with a sharp cutter to avoid folds and burrs.
Ensure that the flange surfaces are fully covered by the gasket to avoid possible corrosion, with adequate clearance around bolt holes to avoid folds, bulge or shear during bolt tightening.
Avoid contamination of the gasket with oil, grease, adhesives, etc.
Insert the gasket in between the flanges, slip one bolt and position the gasket and place other bolts.
Lightly tighten in the following order and repeat the order with full spanner pressure.
Range of Nominal Thicknesses in mm
Thickness Range (mm)
All(except AMJ545 Ultra Metallic)
1.5 & above
1550(±50) x 1550(±50)
All (except AMJ 493 ACID
and AMJ545 ultra metallic)
1850(±50) x 1250(±50)
AMJ 493 ACID AND AMJ 545 Ultra-Metallic
0.6 & above
1850(±50) x 1250(±50)
1500(±50) x 1500(±50)
NOTE: Sheet Sizes of 3200(±50)x3200(±50) ,1500(±50)x4500(±50) ,3200(±50)x 1600(±50) can also be supplied on mutual consent.