Spring washer tightening torque

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Spring washer tightening torque

An ordinary nut with an ordinary washer, used to fasten a bolt on something that is subject to repetitive vibration -- say, a wheel axle or engine accessory -- would eventually vibrate loose.

Lock washers and lock nuts prevent this from happening. Lock washers, when tightened to the required torque beneath an ordinary fastener, will exert a spring tension against the fastener to keep it from vibrating loose.

Most projects will call for either locking washers or locking nuts -- not both -- to be used on a given fastener. Place the lock washer between the nut and the work surface if using a nut-and-bolt configuration, or between the fastener head and the work surface if using a tapped hole configuration. In other words, the bolt goes straight into the hole and doesn't poke out the other end, so no nut is used.

Verify that the teeth of the locking washer engage completely with both the fastener -- or nut -- head and the work surface. Tighten the nut or bolt to the torque specified in your project manual. Use a torque wrench to ensure that the appropriate torque is achieved.

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Inspect the locking washer to, once again, verify that the teeth are completely hidden by the fastener head and the work surface. If the required torque flattens the split washer into the shape of a standard washer, it will no longer function as a locking washer; use a toothed locking washer instead. Place the lock nut against the threaded end of the bolt, just as you would place an ordinary nut.

Make sure that if the nut has a raised center portion this faces out; the flat surface of the locking nut should sit flush against the work surface once tightened.

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Tighten the lock nut with a torque wrench until it reaches the specified torque. Step 1 Place the lock washer between the nut and the work surface if using a nut-and-bolt configuration, or between the fastener head and the work surface if using a tapped hole configuration.

Step 2 Verify that the teeth of the locking washer engage completely with both the fastener -- or nut -- head and the work surface.

Step 3 Tighten the nut or bolt to the torque specified in your project manual.

Torque Information

Step 1 Place the lock nut against the threaded end of the bolt, just as you would place an ordinary nut. Items you will need Locking nuts or locking washers Torque wrench. Photo Credits torque wrench and accessories image by Christopher Dodge from Fotolia.Threaded fasteners bolts, screws, etc.

In these situations, a "locking" fastener may be required. A locking fastener is designed to resist loosening and can be externally threaded, such as a screw, or internally threaded, like a nut. In this section we'll look at some of the more common non-permanent locking schemes an example of permanent locking uses a chemical reaction to form an adhesive that bonds with the mating threads.

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Basically, there are two types of locking fasteners: free-running and prevailing torque. Regardless of the type, the objective is to increase the "break-loose" torque, which is the amount of torque required to loosen the fastener once it is installed.

Free-running types often rely upon an additional component, such as a lock washer or jam nut. Once initially loosened, however, they offer no further resistance to loosening, which is their main disadvantage.

Still, in some applications, that may not be a problem. Prevailing torque types, however, are designed to create friction. Even after slight loosening, friction continues to resist further loosening. However, that generally means there is substantial friction during assembly. There are a variety of different free-running styles to choose from and, often, the application will dictate which is the most appropriate. Said to be one of the first locking schemes, a thin "jam" nut is first installed and tightened, then the normal thick nut is installed and tightened against the jam nut.

Although effective, extra bolt length is needed to accommodate the additional nut, and installation time is increased because assembly involves two nuts that must be individually tightened. Slotted nuts are used with bolts or studs that have a hole drilled in their threaded section. Once the nut is installed, a cotter pin or safety wire is inserted through opposing slots in the nut and the bolt's hole to prevent the nut from loosening. Unless the cotter pin or safety wire shears breaksthe nut remains in position.

This system does require that the hole be drilled in the correct place. And because the nut slots are spaced at degree intervals, it may not be possible to tighten the nut precisely—it may have to be over- or under-tightened for the hole and a slot to align. Additional time is also required for assembly. Slotted nuts have a flat top; castle nuts have a higher profile because of their slotted cylindrical top.

Lock washers are a very popular locking choice especially with smaller-sized fasteners. Essentially, there are two types: spring action and tooth. Spring action washers include split, conical Belleville and wave. These washers, placed under the nut or screw head, compress as the fastener is tightened and the spring-back tension deters loosening.

A tooth lock washer—internal, external, internal-external and countersunk external—creates a ratchet action by biting into the nut or screw head and the surface it contacts. Despite their widespread usage, tooth lock washers can scratch mating surfaces.They enhance the security of general industrial assemblies in the following ways:.

Helical washers are trapezoidal in section. This further deformation is caused by a complex twisting of the trapezoidal section and a slight increase in the diameter of the washer under load.

spring washer tightening torque

See Figure 1. The spring rate which is developed by the final deformation is very high and provides a reactive load that is equivalent to a significant increase in effective bolt length.

Bolts stretch under load. The longer the effective length of the bolt, the more it can stretch. A long bolt can, therefore, be a very effective spring and, like a spring when stretched, it attempts to return to its original length. This applies a clamping or tightening force to the assembly. The clamped components are compressed and, in their inherent effort to expand to their original form, they set up an opposing force.

It is these two forces that create the dynamics of a tight assembly. Two terms are used to define and measure these described forces. One is Spring Rate. The other is equivalent bolt length. Spring Rate is the ratio of load to deflection in the loaded part; it is deflection related to load and is expressed in terms of the amount of load required to achieve specific levels of deflection.

spring washer tightening torque

The optimum joint performance is obtained when the spring elements in the fastening system have a spring rate which is low enough to assure that any yielding of the joint members in compression will not significantly reduce the designed tensile stress in the fastener. To obtain this optimal condition, the conventional solution is to utilize the spring characteristics of very long bolts.

An auxiliary spring element, such as helical spring lock washer, is a very effective alternative. What this means to the design engineer is that the effective bolt length in the joint is increased by the thickness of the flattened helical spring lock washer, plus the equivalent length provided by the spring rate derived from the visually flattened washer.

The significant contribution of the helical spring lock washer to the overall tightness of an assembly is best shown in the test results for an assembly without a washer and an assembly that includes a helical spring washer.

Finishes When carbon steel helical spring washers are required for galvanizing, this must be indicated on the order or inquiry. ASME standards call for such washers to be coiled to limits 0. Other materials and finishes are available on special request. Mechanical Finish will limit exposure to hydrogen embrittlement unless otherwise specified.Log In.

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spring washer tightening torque

Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. I am looking into the proper use of spring lock washers.

5 Causes of Loose Bolts – and 5 Ways to Prevent Them

We have a few applications where we use them, but are having them split open while tightening. One concern is that lock washers are basically useless when torqued down until it becomes flat. Does anyone have any information on this? The most frequently used lockwasher is the helical spring split type.

The helical spring lockwasher Figure is flattened when the bolt is torqued down. Once compressed, it acts as a flat washer, contributing normal friction between the nut or bolt and the bearing surface during tightening.

If the fastener clamping load relaxes, the spring action of the lockwasher will maintain some load between the threads of the fastener, reducing the tendency of the fastener to rotate. Some helical spring lockwashers have a sharp tooth on each end that bites into each bearing surface and prevents rotation.To obtain a leak-free flange connection, a proper gasket installation is needed, the bolts must be assign on the correct bolt tension, and the total bolt strength must be evenly divided over the whole flange face.

With Torque Tightening the application of preload to a fastener by the turning of the fastener's nut the correct bolt tension can be realized. Correct tightening of a bolt means making the best use of the bolt's elastic properties.

To work well, a bolt must behave just like a spring. In operation, the tightening process exerts an axial pre-load tension on the bolt. This tension load is of course equal and opposite to the compression force applied on the assembled components. It can be referred to as the "tightening load" or "tension load". Torque Wrench is the general name for a hand-guided screwing tool, and used to precisely set the force of a fastening such as a nut or bolt. It allows the operator to measure the rotational force torque applied to the bolt so it can be matched to the specifications.

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The selection of the proper flange bolt tigtening technique requires experience. The successful application of any technique also requires qualification of both the tools that will be used and the crew who will do the work. The following summarizes the most commonly used flange bolt tightening techniques.

Torque loss is inherent in any bolted joint. When torque loss reaches an extreme, the internal pressure exceeds the compressive force holding the gasket in place and a leak or blow-out occurs. A key to reducing these effects is proper gasket installation.

By bringing the flanges together slowly and parallel when installing a gasket and taking a minimum of four bolt tightening passes, following the correct bolt tightening sequence, there is a payoff in reduced maintenance costs and increased safety. Proper gasket thickness is also important. The thicker the gasket, the higher the gasket creep which in turn can result in torque loss.

On standard ASME raised face flanges a 1. Thinner gasket materials can take a higher gasket load and therefore higher internal pressures. Lubrication reduces the friction during tightening, decreases bolt failure during installation and increases bolt life. Variation in friction coefficients affect the amount of preload achieved at a specific torque.

Higher friction results in less conversion of torque to preload. The value for the friction coefficient provided by the lubricant manufacturer must be known to accurately establish the required torque value.

Lubricant or anti-seizure compounds should be applied to both the nut bearing surface and the male threads. Continue this sequence until all bolts are tightened. When tightening a four-bolt flange, use a criss-cross pattern. In a flanged connection, all components must be correct to achieve a seal. The most common cause of leaky gasketed joints is improper installation procedures.A pressurized bolted flange joint assembly begins to leak, creating a safety hazard.

A rotor with its blades separates from the nacelle and spins off a wind turbine, crashing to the ground. Under constant vibration from the engine of an ocean freighter, loose bolts on a large piece of mining equipment work their way off the bolted joints and roll around the hull, inflicting further damage to the equipment. Bolted joints are critical to the safe operation of many types of equipment in a wide range of applications, including power generation, manufacturing, mining, and transportation.

In a bolted joint, tightening the nut actually stretches the bolt a small amount, like pulling on a stiff spring. This stretching, or tension, results in an opposing clamp force that holds the two sections of the joint together. If the bolt comes loose, this clamp force weakens.

Loose bolts are not just an irritating nuisance. If the joint is not quickly retightened, the application may begin to leak fluid or gas, the bolt may break, equipment may become damaged, or catastrophic accidents may occur. By definition, an under-tightened bolt is already loose and the joint does not have enough clamp force to hold the individual sections together.

This can lead to sideways slippage between sections, placing unwanted shear stress on the bolt that could eventually cause it to break. These repeated movements work against the friction between the bolt and joint threads that is holding the joint together. The design engineers who specify the tension on a bolt allow for a break-in period, during which bolt tightness relaxes to a certain degree. If the joint has not been designed properly, or if the specified tension was not achieved on the bolt at the start, this embedment of the joint can lead to a loss of clamp force.

Gasket creep.

Torque Loss

Many bolted joints include a thin, flexible gasket between the bolt head and the surface of the joint to seal the joint completely against gas or liquid leaks. The gasket itself acts as a spring, pushing back against the pressure of the bolt and the joint face. This can also happen if the gasket area directly next the bolts is crushed, or if the bolts are not tightened evenly across the entire face of the joint.

Differential Thermal Expansion. If the material of the bolt and the joint are different, large differences in temperature due to rapid environmental changes or cycling industrial processes can cause bolt material to expand or contract rapidly, possibly loosening the bolt.

Dynamic or alternating loads from machinery, generators, wind turbines, etc. Just as with vibration, this slippage can ultimately lead to loosening of the bolts. Because loose bolts are so common, an astonishing array of devices has been invented to prevent them from occurring.

Here are five basic types of prevention methods:. Washers are typically wider than the bolt head, with the additional surface area adding extra friction to the joint to maintain the clamp force. However, simple split washers, sometimes called helical spring washers, have been found to actually loosen the bolt under vibration even faster than a joint with no washer.

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Conical, or Belleville washers, are cup-shaped washers that perform little better than spring washers in vibration tests. Several types of locking washers have been developed, with flutings, ribs or teeth that dig into the surface of the joint during the tightening process, in order to prevent loosening. This may cause permanent damage to the joint finish or surface, which may be unacceptable, such as in critical aerospace applications where surface indentations may cause fatigue stresses.

It may also prevent re-tightening of the joint to the proper tension. Wedge-locking washers work in sets of two, with each washer having opposite facing wedges that interact with each other and with the joint and nut surfaces to prevent self-turning of the bolt.

The wedges are designed to add tension stretch to the bolted joint if the bolt begins turning due to vibration or shock, preventing a loss of clamp force. Mechanical devices. Numerous clever gimmicks have been developed to lock a tightened nut into place on a bolted joint. Castellated nuts have a slotted end and are used with a cotter pin or wire that fits through a hole drilled in the bolt.

Locking fastener systems have a shaped flat retainer, similar to a washer, and a clip that fits into a groove on the bolt head. Tab washers have two tabs on opposite sides, which fold up to secure the bolt head or nut after installation, and may have teeth that can penetrate the surface of the joint to hold it in place. While these devices do prevent the nut from falling off the bolt, they generally do not help the joint maintain the specified clamp force.

Prevailing torque nuts. A related idea is to fit a spring inside the nut, which firmly grasps the bolt threads and is designed to move in the opposite direction of the nut if vibration or other forces cause it to unwind.Several factors will play a large part in how much torque is required, such as gasket load requirements, bolt condition, coatings or lubrication on the bolt, and user preference.

Ultimately though, the answer comes from the sealing load needed on the gasket, not from the belleville washer. To better understand this, we need to understand torque and its relationship to a bolted system. Torque is a rotational force which, when applied to a bolt, is converted to an axial load, stretching the bolt like a spring. As additional torque is applied to the nut, the bolt continues to stretch.

Meanwhile, this spring-like stretch of the bolt pulls the flanges together and applies a clamping force on the gasket. So how does a belleville washer affect the above scenario? As a type of spring, the belleville acts similar to the bolt and stretches while the nut is being torqued. However, the belleville will not affect the torque required to provide proper clamping load on the gasket.

Instead, the belleville only increases the available stretch in the system, which will require more turns of the torque wrench to reach to correct torque value. In summary, each gasket and flanged connection has its own unique properties, and therefore it is best to consult with the supplier of the gasket for their recommended torque value.

The belleville washer can then be added seamlessly and no modification to this torque value is needed. Should you have any additional questions, our engineering team here at Belleville International is available for your convenience and can be reached by calling Fluid Sealing AssociationJune. Name require. Mail require.

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How to prevent screws from loosening: Loctite, Safety Wire, Jam nuts & More Part 1 of 2

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