High Tensile Fasteners


Big bolt nut is the biggest manufacturer for larger diameter high tensile fasteners & nuts in India, we have a monthly production of over 300 tons in bigger sizes from M-24 to M-64 in 8.8 and 10.9 grade. These high tensile fasteners are used in energy sector like wind, solar, thermal and hydro energy. These are also used widely in all other kind of sectors namely, transportation, railways, heavy engineering, Valves and pump Industry, Bridges and road constructions, cross country pipe lines, flange joints and other critical applications. We are the pioneers in manufacturing critical fasteners for the wind energy sector in India. These Fasteners are manufactured only by hot forging process and we have the complete list of machines in our factory to manufacture these bolts & nuts.


These bolts are forged on heavy upsetting machines and are then machined on latest CNC machines in our factory, we also do the heat treatment in our factory using an advanced SQF sealed quench heat treatment furnace from DOWA Japan, the heat treatment furnace is SCADA controlled and provides 100% repeatability batch after batch. The heat treatment result is a perfect marten site after hardening and gives perfect results after tempering as per standard requirement.

These high tensile fasteners in bigger diameters can also be thread rolled after heat treatment to get better fatigue life for these bolts. Thread rolling after heat treatment results in a better life of the bolting and removes any concern of carburising or decarburising in heat treatment process.

High tensile Fasteners Grades

We offer High tensile fasteners in 8.8 and 10.9 grade, the choice of the grade depends upon the application and requirement of the customer. The grades 8.8 or 10.9 have separate mechanical characteristics which are defined in the above sheet.

High tensile Fasteners characteristics:

From the perspective of the force characteristics: high tensile bolts apply pre-tension and transmit external forces by friction. The ordinary bolt connection relies on the shear strength of the bolt and the bearing wall pressure to transmit the shear force.

Finish

We can offer surface finishing as per customer requirement in hot dip galvanising, we take special care to ensure there is no hydrogen embrittlement in 10.9 grade with our special curing system which ensures that 10.9 grade bolts are not damaged by hydrogen embrittlement post galvanising process. We also do zinc electroplated in blue, yellow or black colour as per customer requirements.

Special coatings in specific industries require zinc flake coatings, these coatings are done as per ISO 10683, depending upon customers requirement for salt spray life we offer coating systems from NOF Japan and Doerken from Germany, these coatings are provided with the help and support of our partners who have the required licence and have successfully done validations with our existing customers. Salt spray life can vary from 500 to 1500 hours.

Black Oxide or black coating is a general type of coating offered on bolts & nuts & stud bolts to give a pleasant appearance and to prevent any rusting during transportation or storage, the normal salt spray life for the fasteners applied with such coatings is often less than 100 hours

Xylan is a brand name of With fort USA and is a special coating applied on fasteners / stud bolts where extreme temperatures and harsh condition exist. The Highlights of this coating is that it gives

High tensile Fasteners characteristics:
  • Low friction CoF as low as 0.02.
  • High corrosion and chemical resistance in most environments including marine and Oil & Gas
  • "Wide temperature operating range: from -420° to +550°F (-250° to 285°C)"
  • "Wide color range: color-code your product"
  • Machinability: apply multiple coats of Xylan coating (most formulations) and mill to specification
  • Wear resistance is very high, even under extreme pressures.
  • Weather resistance: against sunlight, salt water and road chemicals
  • Flexible curing schedule: ambient to 750°F (400°C).
  • Pliability: Many Xylan coatings will bend freely and repeatedly without breaking.
  • "Salt spray SST life: above 1000 hrs."
Applications

Our High Tensile Fasteners are used in the heavy industry, marine, ship building, oil and wind energy.

Manufacturing

We manufacture High tensile Bolts in bigger diameters from M-20 to M-64 in diameter in class 8.8 and 10.9, stocks are readily available and we are manufacturing bolts diameter from M-20 to M-64 diameter, we also offer ISO threads and nominal thread fitments. The biggest advantage of our manufacturing is that we do thread rolling after heat treatment, this provides for extra torque and extra fatigue strength by more than 50% and also ensures stronger unbroken fibre lines and a very fine marten site in core and in the threads of the bolts

Torque method

The torque method is a two-stage operation, bedding in following by tightening. Tightening is always done in two steps, ‘Initial Torque’ and ‘Final torque’ using a calibrated torque wrench. This can be either a manual wrench or power tool fitted with a torque cut-out that must first be calibrated on a bolt from the job batch using a bolt load meter or similar device for determining bolt tension.