Multi-jackbolt tensioner
Encyclopedia
Multi-jackbolt tensioners (MJT) provide an alternative to traditional bolted joints Rather than needing to tighten one large bolt, MJTs use several smaller jackbolts to drastically reduce the torque
required to attain a certain preload. MJTs range in thread
sizes from 3/4” to 32” and can achieve up to 20 million pounds of force
and greater. MJTs only require hand-held tools, such as torque wrench
es or air/electric impacts, for loading and unloading bolted joints.
Superbolt or Supernut, are designed to decrease the torque required to tighten large bolted joints. One of the major problems associated with traditional bolt tightening methods is as the diameter of the bolt increases, the amount of torque required to tighten it increases in the third power of the diameter. Because of this, the largest size bolt a person can typically tighten by hand is 1".
Multi-jackbolt tensioners reduce the amount of torque required to clamp the joint by using multiple jackbolts threaded through the nut or bolt head.
The jackbolts, which are small enough to be tightened by simple hand tools, thrust
against a hardened washer
and generate clamping force on the joint. Loads
up to 20,000,000 pounds and greater are attainable using only hand tool
s. MJTs and related products are produced by Superbolt, Inc. in Carnegie, PA.
for tightening large nuts. To calculate mechanical advantage over standard hex nuts, the following formula is used:
Where:
tightening, crane
wrenching, hydraulic wrenches
and sledgehammer
s, can cause serious worker injuries due to heat, electricity, highly pressurized hydraulic fluid and brute force. Back and other injuries can also be avoided because no heavy tightening equipment needs to be lifted onto the bolt. Safety is also increased because MJTs prevent parts from becoming loose.
, which reduces downtime caused by needing to replace damaged components.
applications, and in plants where the number of studs/bolts to retrofit is difficult to justify versus prior investment in existing tightening equipment.
, bearing blocks, high-pressure piping, die cushions, cylinder ram bolting, and anchor bolt
s.
motors, drag lines, pinion
gears, split gears, and excavator
bearing caps, because the joint is loaded in pure tension without twisting. Some applications, such as toothed rims, require short bolts – MJTs can be useful in these applications because they greatly improve the elasticity of the joint.
coupling
s, blade bolts, turbine wheel to shaft bolting, pelton turbine nozzles, servo piston nuts, bearing
housings, and ball valve
s. Multi-jackbolt expansion bolts provide additional benefit for shaft couplings, because they generate both radial and axial forces, creating the interference fit necessary. MJTs can also easily achieve the high preloads required on Kaplan turbine crossheads and servo piston rods.
s, and feedwater heater
s. MJTs can save a lot of time during scheduled downtime or maintenance because they require less time to install and remove than other bolting methods.
industry, multi-jackbolt tensioners have been used on reactor
vessels, heat exchanger
heads, turbine control valves
, turbine joints, pipe flanges, anchor bolts, couplings, compressors
, and pumps.
end nuts and crosshead jamnuts are used to ease the installation of piston rods, especially considering space limitations. Other applications include anchor bolts, flexible disk couplings, dehydration towers, compressor cylinders, compressor doghouse bolting, end plates, and gas compression engines.
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
required to attain a certain preload. MJTs range in thread
Screw thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...
sizes from 3/4” to 32” and can achieve up to 20 million pounds of force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
and greater. MJTs only require hand-held tools, such as torque wrench
Torque wrench
A torque wrench is a tool used to precisely apply a specific torque to a fastener such as a nut or bolt. It is usually in the form of a socket wrench with special internal mechanisms. It was invented by Conrad Bahr in 1918 while working for the New York City Water Department...
es or air/electric impacts, for loading and unloading bolted joints.
Basics of multi-jackbolt tensioners
Multi-jackbolt tensioners (MJTs), registered under the trademarkTrademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...
Superbolt or Supernut, are designed to decrease the torque required to tighten large bolted joints. One of the major problems associated with traditional bolt tightening methods is as the diameter of the bolt increases, the amount of torque required to tighten it increases in the third power of the diameter. Because of this, the largest size bolt a person can typically tighten by hand is 1".
Multi-jackbolt tensioners reduce the amount of torque required to clamp the joint by using multiple jackbolts threaded through the nut or bolt head.
The jackbolts, which are small enough to be tightened by simple hand tools, thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
against a hardened washer
Washer (hardware)
A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. Other uses are as a spacer, spring , wear pad, preload indicating device, locking device, and to reduce vibration...
and generate clamping force on the joint. Loads
Structural load
Structural loads or actions are forces, deformations or accelerations applied to a structure or its components.Loads cause stresses, deformations and displacements in structures. Assessment of their effects is carried out by the methods of structural analysis...
up to 20,000,000 pounds and greater are attainable using only hand tool
Hand tool
A hand tool is a device for performing work on a material or a physical system using only hands. The hand tools can be manually used employing force, or electrically powered, using electrical current...
s. MJTs and related products are produced by Superbolt, Inc. in Carnegie, PA.
Carnegie, Pennsylvania
Carnegie is a borough in Allegheny County, Pennsylvania, United States and is part of the Pittsburgh Metro Area. The population was 7,972 at the 2010 census.-Geography:Carnegie is located at . It is approximately southwest of Pittsburgh...
Types of tensioners
- Nut type
- NutNut (hardware)A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...
type MJTs, otherwise known as Torquenuts, can be retrofitRetrofitRetrofitting refers to the addition of new technology or features to older systems.* power plant retrofit, improving power plant efficiency / increasing output / reducing emissions...
ted onto existing bolts or studsScrewA screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...
. Because of this, they are the most common type of MJT.
- Nut
- Bolt type
- Bolt type MJTs, otherwise known as Torquebolts, have a ring of jackbolts almost touching the bolt shank. They typically have a smaller outside diameter than Torquenuts. With Torquebolts, it is possible to have very close spacing even at high preloads.
- Thrust-collar type
- Thrust-collar type MJTs are used in applications where it is difficult to use threaded tensioners, such as on rolling mills where the joint would typically need to be tightened by craneCrane (machine)A crane is a type of machine, generally equipped with a hoist, wire ropes or chains, and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of...
wrenching. Jackbolts push a threadless nut against a retainer ringRetaining ringA retaining ring is a fastener that holds components or assemblies onto a shaft or in a housing/bore when installed in a groove. Once installed, the exposed portion acts as a shoulder which retains the specific component or assembly....
, which is fitted into a groove and transfers the jacking force to the main bolt or stud. Because there are no threads, they can also be used in pressMachine pressA machine press, commonly shortened to press, is a machine tool that changes the shape of a workpiece.-Servomechanism:A servomechanism press, also known as a servo press or a electro press, is a press driven by an AC servo motor. The torque produced is converted to a linear force via a ball screw....
column applications, eliminating the problems and hassles associated with large nut threads.
- Thrust-collar type MJTs are used in applications where it is difficult to use threaded tensioners, such as on rolling mills where the joint would typically need to be tightened by crane
Mechanical advantage
MJTs have a high mechanical advantageMechanical advantage
Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Ideally, the device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force...
for tightening large nuts. To calculate mechanical advantage over standard hex nuts, the following formula is used:
Where:
| MA | = overall mechanical advantage |
| T | = main thread torque |
| Tj | = jackbolt torque |
| n | = number of jackbolts |
| D | = main thread pitch diameter Diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle... |
| d | = jackbolt pitch diameter |
| A | = torque advantage of jackbolts over tension bolts (with graphite Graphite The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal... lube A=1.37) |
Safety
MJTs are a relatively safe bolting method because only small hand or air tools are required for tightening. Other methods, including thermalThermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....
tightening, crane
Overhead crane
An overhead crane, commonly called a bridge crane, is a type of crane found in industrial environments. An overhead crane consists of parallel runways with a traveling bridge spanning the gap...
wrenching, hydraulic wrenches
Hydraulic torque wrench
A hydraulic torque wrench is a tool designed to exert torque on a fastener to achieve proper tightening or loosening of a connection through the use of hydraulics. A torque wrench is applied to the nut either directly or in conjunction with an impact socket. Hydraulic torque wrenches apply a...
and sledgehammer
Sledgehammer
A sledgehammer is a tool consisting of a large, flat head attached to a lever . The head is typically made of metal. The sledgehammer can apply more impulse than other hammers, due to its large size. Along with the mallet, it shares the ability to distribute force over a wide area...
s, can cause serious worker injuries due to heat, electricity, highly pressurized hydraulic fluid and brute force. Back and other injuries can also be avoided because no heavy tightening equipment needs to be lifted onto the bolt. Safety is also increased because MJTs prevent parts from becoming loose.
Downtime
Due to dynamic loads, bolted joints have a tendency to loosen. Downtime is significantly reduced because MJTs are able to easily achieve the large clamping forces required to prevent bolted components from vibrating loose. Therefore, less time is spent tightening joints repeatedly and fixing problems caused by loose joints. MJTs also reduce the likelihood the bolted joint will failStructural failure
Structural failure refers to loss of the load-carrying capacity of a component or member within a structure or of the structure itself. Structural failure is initiated when the material is stressed to its strength limit, thus causing fracture or excessive deformations...
, which reduces downtime caused by needing to replace damaged components.
Installation time
Even though more individual jackbolts must be tightened, installation is still fast in comparison to other methods. Because the torque required to tighten each small jackbolt is exponentially less than the torque required to tighten one large nut, it takes less time and effort overall to tighten the larger number of jackbolts. Also, no additional time is spent moving around heavy equipment to tighten each nut. Installation processes have been developed using air tools, which also greatly reduces installation time. Additionally, multiple workers can work on a joint simultaneously since the tooling required is inexpensive. Another common method, thermal tightening, can take a long time because the stud must be heated, and clamping force is not obtained and cannot be checked until it is cooled since it depends on shrinkage. If the stud is not at proper stretch, the heating process must be repeated.Versatility
- MJTs can be used in tight spaces because no bulky equipment is required to tighten the bolts.
- MJTs can also be engineered to specifications for almost any application. There are few size limitations, and they can be used with extremely large thread sizes (as high as 32" thread diameter). They can also be used effectively in high temperature applications, given proper materials are used. Overall, the unique properties of MJTs created by the use of jackbolts can simplify complicated applications, especially for large thread sizes.
Joint integrity
- Thread gallingGallingGalling usually refers to the adhesive wear and transfer of material between metallic surfaces in relative converging contact during sheet metal forming and other industrial operations....
and seizing is significantly reduced because mating bolts/studs are loaded in pure tension without twistingTorsion (mechanics)In solid mechanics, torsion is the twisting of an object due to an applied torque. In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius....
. - In many applications, elasticityElasticity (physics)In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....
in a bolt significantly helps to keep a joint held together. Tests have shown turbine-type MJTs increase the elasticity of the average bolting system by the equivalent of four stud diameters, and nut-type MJTs increase the elasticity by 4 to 12 diameter equivalents, which would triple or quadruple the elasticity of the bolting system. In other words, MJTs increase elasticity by adding up to 2 to 4 equivalent bolt effective lengths. This is particularly advantageous in high-temperature bolting applications where bolts are subject to creepCreep (deformation)In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material....
, because elastic bolting systems will take longer to reach a given relaxation stress than in a rigid system. Elastic bolting systems can also improve the integrity of gasketGasketthumb|sright|250px|Some seals and gaskets1. [[o-ring]]2. fiber [[Washer |washer]]3. paper gaskets4. [[cylinder head]] [[head gasket|gasket]]...
ed joints by compensating for temperature changes, joint movement and changes in internal pressure. - Stress relief—Most bolts fail at the bottom of the nut in the first two or three threads. Hoop stressHoop stressCircumferential stress is a type of mechanical stress of a cylindrically shaped part as a result of internal or external pressure.The classic example of circumferential stress is the tension applied to the iron bands, or hoops, of a wooden barrel...
es on the nut in MJTs cause an increase in diameter at the bottom and decrease at the top, distributing thread stress more evenly and reducing the likelihood the stud or bolt will fail.
Disadvantages
MJTs may not be cost effective for bolts smaller than 1" diameter, low-stressStress (physics)
In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...
applications, and in plants where the number of studs/bolts to retrofit is difficult to justify versus prior investment in existing tightening equipment.
Presses
Multi-jackbolt tensioners can be used on many press column applications, especially where large thread sizes are required. Thrust collars ease assembly and disassembly on large press columns, while greatly reducing critical problems such as thread galling and seizing. Multi-jackbolt tensioners are also used on tie-rodsTie rod
A tie rod is a slender structural unit used as a tie and capable of carrying tensile loads only.- Subtypes and examples of applications :* In airplane structures, tie rods are sometimes used in the fuselage or wings....
, bearing blocks, high-pressure piping, die cushions, cylinder ram bolting, and anchor bolt
Anchor bolt
An anchor bolt is used to attach objects or structures to concrete. There are many types of anchor bolts, consisting of designs that are mostly proprietary to the manufacturing companies. All consist of a threaded end, to which a nut and washer can be attached for the external load...
s.
Mining
Mining applications often require high preloads, and joints encounter high dynamic forces, which can cause joints to loosen. MJTs can keep joints tight on boom points, ring gears, side frames, hoistHoist (device)
A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting medium. The load is attached to the hoist by means of a...
motors, drag lines, pinion
Pinion
A pinion is a round gear used in several applications:*usually the smallest gear in a gear drive train, although in the case of John Blenkinsop's Salamanca, the pinion was rather large...
gears, split gears, and excavator
Excavator
Excavators are heavy construction equipment consisting of a boom, stick, bucket and cab on a rotating platform . The house sits atop an undercarriage with tracks or wheels. A cable-operated excavator uses winches and steel ropes to accomplish the movements. They are a natural progression from the...
bearing caps, because the joint is loaded in pure tension without twisting. Some applications, such as toothed rims, require short bolts – MJTs can be useful in these applications because they greatly improve the elasticity of the joint.
Hydro Power
Multi-jackbolt tensioners are used in several hydro applications, including turbineTurbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
coupling
Coupling
A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded.The...
s, blade bolts, turbine wheel to shaft bolting, pelton turbine nozzles, servo piston nuts, bearing
Bearing (mechanical)
A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...
housings, and ball valve
Ball valve
A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends...
s. Multi-jackbolt expansion bolts provide additional benefit for shaft couplings, because they generate both radial and axial forces, creating the interference fit necessary. MJTs can also easily achieve the high preloads required on Kaplan turbine crossheads and servo piston rods.
Steam Power
In steam power plants, MJTs are used on boiler feed pump head and barrel casings, boiler circ pump main flanges, stop valves, control valves, turbine couplings, stay rods, manway doors, inlet flangeFlange
A flange is an external or internal ridge, or rim , for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera; or for a flange of a rail car or tram wheel...
s, and feedwater heater
Feedwater heater
A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system...
s. MJTs can save a lot of time during scheduled downtime or maintenance because they require less time to install and remove than other bolting methods.
Steel Mill
Multi-jackbolt tensioners have a number of uses in the Steel industry. Thrust collars can be used on rolling mills, which makes changing the rolls much easier than other methods, and frees up crane time because only hand tools are required. Other MJTs are used on mill motors, bearings, shaft mounts, anchor bolts, and slitter knives.Petrochemical
In the petrochemicalPetrochemical
Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....
industry, multi-jackbolt tensioners have been used on reactor
Chemical reactor
In chemical engineering, chemical reactors are vessels designed to contain chemical reactions. The design of a chemical reactor deals with multiple aspects of chemical engineering. Chemical engineers design reactors to maximize net present value for the given reaction...
vessels, heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
heads, turbine control valves
Control valves
Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor...
, turbine joints, pipe flanges, anchor bolts, couplings, compressors
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...
, and pumps.
Gas Compression
Special multi-jackbolt pistonPiston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
end nuts and crosshead jamnuts are used to ease the installation of piston rods, especially considering space limitations. Other applications include anchor bolts, flexible disk couplings, dehydration towers, compressor cylinders, compressor doghouse bolting, end plates, and gas compression engines.