shock loading wire rope for sale

The load which a new wire rope may handle under given operating conditions and at an assumed design factor. A design factor of five is chosen most frequently for wire rope. (Operating loads not to exceed 20% of catalog breaking strength). Operating loads may have to be reduced when life, limb, or valuable property are at risk, or other than new wire rope is used. A design factor of 10 is usually chosen when wire rope is used to carry personnel. (Operating loads not to exceed 10% of catalog breaking strength). Responsibility for choosing a design factor with the user.

Rope sockets, thimbles, sleeves, hooks, links, shackles, sheaves, blocks, etc., must match in size, materials and strength, to provide adequate safety protection. Proper installation is crucial for maximum efficiency and safety.

Shock loading can occur in any situation where the load on the crane suddenly increases. The crane and accessories are designed to take up the weight of loads gradually and steadily. They are not designed to withstand sudden increases or decreases in the apparent weight of the load.  Some examples of how shock loading can occur are shown below.

Operators and equipment owners should be aware of the causes and potential dangers of shock loading. Because the equipment is being used in a way that it is not designed for, shock loading can lead to damaging the equipment, the facility, or injuring personnel. Understanding the causes of shock loading will help to prepare operators to safely and accurately operate the equipment.

Skilled operators are a company"s first defense against shock loading. Lifting and lowering should always be done in slow speed until all slack has been taken out of the wire rope and any below the hook devices. Additionally, operators should be aware of their surroundings, making sure that the load they are lifting is not likely to snag on other pieces of machinery or the building itself. When lifting or lowering the load, operators should be careful to make sure the load is not bouncing as they operate the hoist. Additionally, operators should ensure that their loads are secure and well balanced.

Beyond operator training and best practices, features such as the HoistMonitor®assist operators in preventing shock loads. The HoistMonitor ensures that starting and stopping is initiated in slow speed, which helps prevent a jumping motion of the load. Sudden load supervision, also a standard feature of the HoistMonitor, prevents the hoist from continuing the hoisting motion when a load increase is suddenly detected, like if the load snagged on another item.

1. Turn back the specified amount of rope from the thimble. Apply the first clip one base width from the dead end of the wire rope. Place the U-bolt over the dead end; the live end rests in the clip saddle. Tighten the nuts evenly to the recommended torque.

3. Space additional clips, if required, equally between the first two. Turn on nuts, take up any rope slack, and tighten all nuts evenly to the recommended torque.

4. Apply the initial load and retighten the nuts to recommended torque. The rope will stretch and shrink in diameter when loads are applied. Inspect the clips periodically and retighten. Recommended torque values are based on the threads being clean, dry and free of lubrication.

Loads may slip or fall if proper eye bolt assembly and lifting procedures are not used. Always inspect eye bolts before use and never use eye bolts that show signs of wear or damage. Never use eye bolts if eye or shank is elongated or bent. Be sure all threads are clean. Do not exceed the following working load li

Fibrous and synthetic rope, wire rope and cable must be inspected regularly. No product, even when used in the proscribed manner, can function forever at its rated capacity. The end user must inspect the product frequently for any condition (abrasion, abuse, negligence, normal wear and tear, etc.) which, should the product be left in use, might result in its failure.

Working load is based upon static or moderately dynamic lifting/pulling operations. Instantaneous changes in load, up or down, in excess of 10% of the sling"s rated working load constitutes hazardous shock load, and would void normal working load recommendations.

These products are not designed or recommended for use in the entertainment rigging business, but are offered as a service to our customers who indulge in climbing or similar recreational activities. It is the responsibility of the end user to be properly trained in the inspection, maintenance and use of these products.

Before we address shock loading let us take the time to understand the difference between static and dynamic forces. Static force is stationary. Static force usually refers to an object not in motion. Whereas dynamic force refers to an object that has unequal forces acting upon it. Rapid acceleration in lifting and rapid deceleration in lowering of a small or large load can result in what is often referred to as dynamic load.

Remember Newton"s second law? F = ma Force equals mass times acceleration. Acceleration refers to a change in the rate of velocity. Assuming we are referring to the same mass (size of the object), we see that the force exerted on an object is proportional to the acceleration it is given. This is the basis of the phenomena known as shock loading.

Generally speaking shock force or shock loading occurs when an operator takes up sling slack rapidly or suddenly releases the load creating a sudden jerk. Both rapid acceleration and deceleration of a load can create a shock force that far exceeds the working load limit of the wire rope. Always remember that the sudden release of a load can cause internal and external damage to a wire rope. Why is the safe working load limit of rigging slings and crane lines significantly lower than their minimum breaking strength? A safety factor must always exist. Remember that minimum breaking strengths are stated for static, straight lifts or pulls.

The four pictures in this post clearly illustrate what shock force or shock loading will do to a wire rope. Note the one strand has become unraveled from the other strands in forming the wire rope. Look closer and you will note broken wires at different points of the strand. Remember a series of individual wires make up each strand on a wire rope.

To understand shock forces you must know that there exists static (not in motion) forces, and dynamic (in motion) forces. In the real world we rarely have just simply static forces occurring during lifts. Even small amounts of speeding up or slowing down of the load result in dynamic loads. The very act of even slow lifting often results in some forces caused by movement such as swinging and drifting.

However, the force we are talking about it the one that occurs rapidly as opposed to slow dynamic forces. Shock force is more commonly referred to as shock load. This derives from the fact that engineers routinely refer to forces occurring in and on structural members as loads. In rigging a load is an object to be lifted or flown from one point to another point, hence the use of the phrase shock force in this article.

Shock forces can occur for any number of reasons, most notably; an operator taking up sling slack with a sudden jerk, the rapid acceleration or deceleration of the load, failure of fair leads or sheave guides to prevent the rolling out of a slack line.

The magnitude of a shock force can be many times that of the weight of the load be lifted. This is why the safe working load of rigging equipment is substantially lower than the minimum breaking strength. Minimum breaking strengths are stated for static, straight pulls. A factor of safety must therefore exist.

The amount of force created in a shock situation is dependent on, among other things, the weight of the load and the distance of travel. The exact determination can be quite complicated because the value of the load"s stopping distance is based on the amount of elastic stretch.

In order to precisely calculate the stopping distance we would need to know the exact composition of the wire rope, the equivalent cross sectional area, and the apparent modulus of elasticity of the wire rope composite, and then use a complicated formula to calculate the exact amount of elastic stretch*.

Many manufacturer"s websites state that there exists no practical method to estimate shock force. Gelrum** provides an example of a 75 foot long (L) 1⁄4 inch diameter galvanized cable sling subjected to a shock force by the sudden dropping of a 500 pound load 6 inches. The resulting shock force is 2,296 pounds, a value over 4 times the weight of the load!

*A free applet, or automated calculator, for wire rope elastic stretch is located online at:http://www.macwhyte.com/Technical/Metallic-Area-Elastic-Stretch-Calculator

Even with experienced crane operators, it can be challenging to lift a load without incurring stress to the crane, the load or the building’s structure. That’s because, before a load lifts off the ground, the rigging gear is loose and any upward hoisting would first move the rigging gear, not the load. Once the rigging gear is taut and the load is engaged, however, the hoist must be operated very slowly so as not to jerk the load into the air. Excess speed during the critical time of lifting the load off the ground can “shock” the crane system, causing high stress.

Konecranes has the answer: Shock Load Protection. With Shock Load Protection, the hoist drive monitors the load. If it is picked up too fast, the hoisting speed is automatically reduced until the load is in the air. This protects the crane, lifting load and the whole building from extra stress. This, in turn, provides lower maintenance costs for the crane and maximizes cycle times by reducing hoisting speed only during the critical moment of lift off.

Shock Load Protection is designed for smooth load pickups and works to prevent shocks to the load and the crane, extending the lifetime of the crane’s steel structure and mechanical parts. Shock Load Prevention is a feature of Konecranes Variable Frequency Drives for hoist control, and it works to eliminate shock loads automatically. With this automated feature, the operator can focus on controlling the load, monitoring his or her environment and ensuring that the load remains secure. Without the operator needing to purposely slow down operation as the hoist is raised, the crane can operate efficiently, speeding up operation while decreasing the mechanical wear and tear on the overhead crane.

Shock Load Protection is available for overhead cranes with, or with the capability of having, Variable Frequency Drives. Contact a Konecranes Representative to see if Shock Load Protection or any of our other Smart Features, can help your business.

Even with experienced crane operators, it can be challenging to lift a load without incurring stress to the crane, the load or the building’s structure. That’s because, before a load lifts off the ground, the rigging gear is loose and any upward hoisting would first move the rigging gear, not the load. Once the rigging gear is taut and the load is engaged, however, the hoist must be operated very slowly so as not to jerk the load into the air. Excess speed during the critical time of lifting the load off the ground can “shock” the crane system, causing high stress.

Konecranes has the answer: Shock Load Protection. With Shock Load Protection, the hoist drive monitors the load. If it is picked up too fast, the hoisting speed is automatically reduced until the load is in the air. This protects the crane, lifting load and the whole building from extra stress. This, in turn, provides lower maintenance costs for the crane and maximizes cycle times by reducing hoisting speed only during the critical moment of lift off.

Shock Load Protection is designed for smooth load pickups and works to prevent shocks to the load and the crane, extending the lifetime of the crane’s steel structure and mechanical parts. Shock Load Prevention is a feature of Konecranes Variable Frequency Drives for hoist control, and it works to eliminate shock loads automatically. With this automated feature, the operator can focus on controlling the load, monitoring his or her environment and ensuring that the load remains secure. Without the operator needing to purposely slow down operation as the hoist is raised, the crane can operate efficiently, speeding up operation while decreasing the mechanical wear and tear on the overhead crane.

Shock Load Protection is available for overhead cranes with, or with the capability of having, Variable Frequency Drives. Contact a Konecranes Representative to see if Shock Load Protection or any of our other Smart Features, can help your business.

When choosing the right type of Wire Rope, you need to consider a number of factors to ensure optimal performance and safety, as well as extend the life of the rope. For example, there are 7 characteristics of wire rope, design characteristics to help you select the wire rope to give you the optimum safety and service life for your wire rope:Strength

No one wire rope will have all of these attributes. In fact, when a wire rope ranks high in one particular category, it typically scores lower in another category. Therefore, you need to be extremely careful when making an assessment about wire rope. Ultimately, you want select one that sacrifices the least important benefits as opposed to the most important ones.

Considering strength, note the potential workload. Will you experience dynamic loads caused by abrupt acceleration, shock loads, sudden stops, dead weight, and high speeds.

Vibration fatigue is caused by anything that can send a shockwave through the rope. Because this energy must be absorbed and since absorption takes place at different points along the rope, choose the right product based on the shockwave type. When a wire rope is repeatedly bent, it begins to fatigue to the point of eventual failure preceded by telltale broken wires. For that reason, consider the diameter of the rope wires, smaller wires tend to give longer bending fatigue life. Fatigue can also be reduced by using larger diameter sheaves and drums.

With crushing, external pressure applied to the rope, causing distortion to the cross-section. At that point, the rope can no longer move and adjust as it should. Larger outer wires and strand & rope compacting make for a more crush resistant, stable wire rope.

Think about resistance to metal loss and deformation when selecting a wire rope. Of the conditions deemed destructive to wire rope, this is the very common. Although this often happens at the sheaves and drums, it can also occur when the rope rubs against itself or an object. Eventually, the rope wears, making it inoperable and unsafe. Larger outside wires and compaction of rope or strands will last longer than smaller, non-compacted wire ropes & strands when resisting metal loss and deformation.

A wire rope used as a crane hoist line, single part or multi part, where rotation resistance is important, there are many rotation resistant wire ropes to choose from. Ranking from the least Resistant to Rotation, 19x7 or 19x19. If these don’t satisfy your rotation issue, 35x7 class wire ropes are the most Rotation Resistant commonly available and should solve most any Rotation problems.

Should your application require the wire rope to go around some relatively small sheaves and drums, you will need a wire rope that is more bendable. Not flexible, bendable. A wire rope with small outer diameter wire will be more bendable than one with larger outer wire.

Standard Bright wire ropes are not very resistant to corrosion. The only protection that they have is a fairly thin layer of lubricant/corrosion preventative to keep them from corroding. If additional protection is required, you can first try heavy, often applied lubrication. Next to reduce corrosion, Drawn Galvanized wire rope is available in most sizes and constructions. Drawn Galvanizing allows the wire rope be equal in strength to a Non Galvanized wire rope of the same construction and diameter. Should greater corrosion resistance be required, Stainless Steel wire rope is available, at a lower strength for equal size and construction. Most common choice is Type 302/304 SS. For additional Corrosion Resistance consider Type 316 Stainless Steel. For extreme conditions other exotics are available in limited sizes – Monel & Inconel are two.

When overloads and shock loads occur in a rigging operation, the results can be deadly. A failure of gear or equipment can take place at the time the over/shock load happens or in many cases weeks, months or years later.

Most of us are familiar with the statistics used in rigging books and charts on the effects of shock loading. When a load of “X” pounds is allowed to free-fall or is popped off the ground, it introduces a load to the lifting device which can be two times or more its static weight.

This compounding of weight takes its toll on the load’s internal and external structure, rigging attachment points, all rigging hardware, slings, hoist hook, running ropes, drum and entire hoisting system whether overhead or mobile crane.

A typical method of shock loading results from turning or flopping a load over from one plane to another. (Actual case) A coal-fired steam plant uses pulverizer journal assemblies to crush the coal into a fine talc – like powder for burning. The journals are awkward and difficult to handle with no available lifting lugs. After a journal is pulled from service and it has received maintenance, it is transported back to the pulverizer unit. A bridge crane picks up the journal from its vertical carrying cradle and sets the base on the floor. The crane then trolleys to pull or “flop” the journal over to a 45 degree angle. A special sling assembly is then used to hoist the journal into the pulverizer cavity.

During the “trolley and flop” movement, the slamming of the journal arms into their chain slings sends dust and dirt flying off the overhead bridge crane. How much weight in real pounds was introduced to the crane? Has anything happened to the crane’s structure? Does anyone suspect a broken weld, metal fatigue fracture or that damage has possibly occurred to the hoist system or wire rope? What if this happens twice a month for four years? Your imagination can provide many unwelcome answers to these questions.

Have you ever heard an employee say, “We were only lifting 2 tons on our 5 ton bridge crane and the whole thing came down on top of us!” Was it the 2 ton lift that caused the accident? Certainly not! It was the four years of repeated abuse, shock loading and structural damage which turned a fine bridge crane into a life threatening bucket of bolts.

If you have these situations in your operation, do everything possible to develop alternative rigging methods. Make a comprehensive inspection of all hoisting and rigging components. Using the proper procedures for each type of equipment perform load tests and make another inspection to ensure reliability. (Always check with the equipment manufacturer for testing procedures and limitations.)

Choker hitches reduce lifting capacity of a sling, since this method of rigging affects the ability of the wire rope components to adjust during the lift, places angular loading on the body of the sling, and creates a small diameter bend in the sling at the choke point.

RATED CAPACITY (Rated Load, WLL) of a wire rope sling is based upon the Nominal Breaking Strength of the wire rope used in the sling, AND FACTORS which affect the overall strength of a sling. These factors include ATTACHMENT or SPLICING EFFICIENCY, the number of parts of rope in the sling, type of hitch (see above), DIAMETER AROUND WHICH THE BODY OF THE SLING IS BENT, and the diameter of pin (or hook) over which the eye of the sling is rigged.

RATED CAPACITY of a sling is different for each of the three basic methods of rigging (see above). These rated loads are listed in this catalogue. The RATED CAPACITIES apply to UNIROPE slings ONLY and may be indicated on optional tags (if requested).

NEVER “SHOCK LOAD” a sling. There is no practical way to estimate the actual force applied by shock loading. The rated capacity of a wire rope sling can easily be exceeded by a sudden application of force, and damage can occur to the sling. The sudden release of a load can also damage a sling.

The BODY of a wire rope sling should be protected with corner protectors, blocking or padding against damage by sharp edges or corners of a load being lifted. Sharp bends that distort the sling body damage the wire rope and reduce its strength.

A SLING EYE hould never be used over a hook or pin with a body diameter larger than the natural width of the eye. NEVER FORCE AN EYE ONTO A HOOK. The eye should always be used on a hook or pin with AT LEAST THE DIAMETER OF THE ROPE.

SLING ANGLE (also called Angle of Loading) is the angle measured between a horizontal line and the sling leg or body. This angle is very important and can have a dramatic effect on the rated load of a sling. As illustrated here, when this angle DECREASES, the LOAD ON EACH LEG INCREASES. This principle applies whether one sling is used with legs at an angle in a basket hitch, or for multi-leg bridle slings. Angles less than 30 degrees should not be used.