More from: Lifting and Rigging

Rigging Basics: The Snatch Block

A typical rigging set up includes any number of components including blocks, hooks, chains, ropes, and slings. The snatch block is but one of those parts. Snatch blocks are usually manufactured with either shackles or hooks for connecting them with other parts of the rigging set up.

This post will discuss the basics of the snatch block. You will learn what snatch blocks are used for, how to use them safely, and so forth. We hope you will take a few minutes after reading this post to check out our entire inventory of rigging supplies.

Snatch Blocks and Winches

A snatch block is a very simple piece of equipment. Generally used with either a winch or boom, the snatch block is essentially a pulley with an accessible side plate that alleviates the need to thread rope or cable through the pulley. You may think this is not a big deal until you are presented with a piece of cable with a loop on the end; a loop you cannot thread through the pulley.

There are two purposes for including snatch blocks in a rigging set up. The first is to increase pulling power by distributing the weight of a load over more area. The second is to change the direction of the pull if necessary. A direction change can be accomplished by offsetting the anchor point of the snatch block in question.

Increasing Pulling Power

The first use of the snatch block is something you have probably observed more than once in your lifetime. Snatch blocks are added to a rigging set up in order to increase pulling power. The more blocks in the setup, the less power required to lift the load. However, the downside is that more blocks require more rope or chain.

The science behind this principle is actually quite simple. Introducing a block evenly distributes the force of the load being lifted. Rather than lifting dead weight, you are applying just enough force to carry the load along the pulley of the block. The block takes the remainder of the load on the other side. Adding additional blocks further reduces the needed lifting power by further distributing the load.

Changing Load Direction

A less common use of the snatch block is to change the direction of a pull. Let’s say you are a toll operator trying to recover a vehicle on the side of a busy highway. You might use a single block along with two chains to pull the vehicle up. But what if you also wanted to pull it out?

You could use a second snatch block with an offset position to accomplish just that. By carefully placing your snatch blocks in the right position, you can lift the car both up and out at the same time.

Using Blocks Matches Safely

As with all things rigging, safety is a top priority with snatch blocks. The first thing is knowing where to place them within the rigging set up to ensure maximum efficiency with the least amount of risk. Suffice it to say that it does matter where blocks are placed.

Second is knowing the working load limits of each block in your configuration. Blocks have to be capable of sustaining the load being placed on them, so it’s not good enough to merely guess.

Finally safety requires understanding the direction a load will be pulled in based on block configuration. It is a lot like understanding the direction a tree will fall as you cut it. Safely using snatch blocks means planning ahead of time so that your load moves in its intended direction.


5 Interesting Things You Might Not Know About Wire Rope

Anyone looking for rigging supplies here on our website will find several varieties of wire rope to choose from. Wire rope is one of the primary materials for managing complicated lifts. It is preferred by experienced lift masters because of its strength and reliability.

As with most things in the Mytee inventory, there is more to wire rope than meets the eye. How it’s constructed, where it comes from, and many other aspects of wire rope remain hidden for the simple fact that there is really no need to know. We want to change that for our readers. To that end, there are five interesting things about wire rope you might not know, listed below.

1. It Was Preceded by Wrought Iron Chains

Before there was wire rope, lift masters and engineers relied on wrought iron chains to do the work. But as you might imagine, failure was a common problem with said chains. All it took was one bad link to create a disaster. So engineers had to find a replacement that was both up to the task and would greatly reduce the risk of catastrophic failure. They looked to the engineering of spiderwebs to eventually come up with the design we now know as wire rope.

2. A Helix Design Provides the Strength

One of the things engineers learned by studying spiderwebs is that a helix design offers incredible strength. The helix design starts with a single wire that acts as the core of the rope. Additional wires are then twisted around the core and fastened together. This design spreads the force of a load across multiple wires instead of a single link of chain.

3. The Helix Also Limits Failure

If there is one flaw to the helix design, it is the fact that the individual wires that make up a rope can wear out over time due to friction. But it is not a big deal for the most part. Why? Because individual wire strands rarely fail at the same time. Initial failure is generally limited to one, in which case the remaining wires are more than capable of carrying the load.

4. The First Wire Ropes Appeared in the 1830s

Historically speaking, the first wire ropes were manufactured to support mining operations in the 1830s. Lift masters in Germany used them to replace metal chains and hemp ropes. The first wire rope produced in the U.S. appeared in the early 1840s. Its purpose was to provide support for suspension bridges.

By the late 1840s wire rope was used heavily in the railroad industry for a variety of different purposes. That led to a number of manufacturing plants opening across United States producing wire rope in ever increasing volumes.

5. Wire Ropes Are Classified According to Use

Just like there is more than one way to construct a wire rope, said ropes are classified according to their use. There are four generally recognized classifications as follows:

1. Running Ropes – Stranded ropes used over sheaves and drums that will bend them.
2. Stationary Ropes – Spiral ropes capable of carrying fluctuating tensile forces.
3. Track Ropes – Fully locked ropes capable of handling the kinds of forces typical of crane lifting.
4. Wire Rope Slings – Stranded ropes used as harnesses for lifting.

So, how did you do? If you knew all five things mentioned in this post, you know more about wire rope than the average person. One last thing to know is that you can get the wire rope you need for your rigging jobs here at Mytee Products.


Rigging 101: 3 Fundamental Questions about Shackles

Mytee Products carries a complete range of shackles as part of our rigging inventory. Customers use them to perform heavy lifts, particularly when loading unusual cargo onto flatbed trailers. We know how dangerous such lifts can be, which is why we do our best to encourage customers to adopt a safety-first mindset.

Where shackles are concerned, an important part of safety is thoroughly understanding what they are and how they work. There is not enough space in a single blog post to talk about shackles in detail, but we can offer a few basics. We have done so by way of three fundamental questions that we often hear from customers purchasing shackles for the first time.

 

What are the different kinds of shackles?

Shackles are defined by their shape and the pins they utilize. The purpose in classifying them this way stems from the fact that the shackle has two main paths through which energy travels: the main body and the pin.

In terms of shape, you are looking at anchor-style and chain-style shackles. The former is more circular in shape with the legs tapering toward the center of the shackle’s main body. The latter looks just like a chain link. For purposes of description, these kinds of shackles are sometimes referred to as D-shape shackles.

Pins can be either screw or bolt-type pins. A screw-type pin is just as its name suggests. It has a threaded end that is screwed into the opposite leg of the shackle after insertion. A bolt-type pin slips through both legs and is then secured by either a nut or cotter pin.

What are the biggest concerns when using shackles?

This question is usually born out of inexperience. It is a fair enough question and getting the right answers could mean the difference between a safe lift and an unnecessarily dangerous situation. From our perspective, here are the biggest concerns:

• Replacing manufacturer pins with generic bolts or unidentified pins. A replacement pin that is not strong enough can bend under load.
• Allowing shackles to be pulled at odd angles, thus allowing the legs to open. This could lead to a broken shackle.
• Mistakenly using deformed shackles or those with bent pins. Disaster awaits.
• Purposely forcing pins, or the shackles themselves, into position. This puts unnecessary stress on a shackle.
• Exceeding a 120° angle between multiple sling legs. This puts too much stress on sling and shackle alike.

Most of the concern over lifting with shackles relates to creating unsafe conditions by not using lifting equipment properly. The best way to avoid accidents is to thoroughly understand lifting principles and abide by all generally accepted safe lifting rules.

How often should shackles be inspected?

General guidelines say shackles should be inspected regularly. We prefer a more defined answer: inspect shackles prior to and after each lift. Shackles should be inspected for:

• pin hole elongation and wear
• any bending in the shackle body
• distortion, wear, fractures, or blemishes on pins
• pin straightness and seating
• any distortion in excess of 10% of a shackle’s original body shape.

It is always better to be safe than sorry where shackle inspections are concerned. Some normal wear and tear is expected over the life of a shackle, but wear and tear should not be enough to significantly alter the appearance or function of a shackle. The presence of any significant distortion is reason to discard a shackle.

We carry a variety of rigging equipment and supplies for your convenience. Please do not hesitate to ask if you have questions about our shackles, slings, etc.


How to Use Outrigger Pads the Safe Way

Outrigger pads are tools used to keep cranes and other pieces of heavy equipment from sinking into the ground during lifting. Anyone experienced with rigging is probably familiar with the pads to at least some extent. We sell outrigger pads as part of our inventory of rigging supplies.

We cannot stress enough the need for safety when deploying outrigger pads. As with everything related to rigging, there are safe and unsafe ways to deploy them. Relying on general rules of thumb or intuition doesn’t cut it. To be safe, you have to do things the right way.

Government Regulations

The place to begin here is with government regulations. According to OSHA, safety is always a requirement. OSHA 1926.1402 states that, in all instances in which a crane or other lifting equipment is used, the ground on which the equipment is placed must be firm, sufficiently drained, properly graded, and able to support blocking, cribbing, and outrigger pads.

OSHA regulations relate mainly to construction and industrial work. So for jobs outside their scope we look to ASME B30.5 code. This code has been approved by the U.S. government, making it legally binding. It states that any blocking or pads used to support heavy equipment must be sufficiently strong. They must be able to safely support floating and transmission of the load without excessive settlement, shifting, or toppling.

This is just a general outline of OSHA and ASME rules. For details, consult both documents online. They offer all the information you need for a safe lifting experience.

Working Load Limits

Next, it is important to know and understand the working load limits of your outrigger pads, blocking, or cribbing. The three models of outrigger pads that we sell have working load limits of 45,000, 55,000, and 60,000 pounds. All have a crush rating of 200 PSI.

These working load limits apply just to the pads themselves. They have nothing to do with the strength or support of the ground underneath. So just because you have an outrigger pad strong enough to handle the load you’re lifting doesn’t necessarily mean you’re good to go.

Making Some Calculations

Lifting safely requires a few basic calculations, beginning with the total amount of force the operation represents. Total force is really just the sum of all the ‘moving parts’, so to speak. Add together the weight of the crane, load, rigging equipment, and any accessories. The total weight equals the force of the load.

Next, you must calculate the amount of area needed to safely distribute the load across your outrigger system. For that, you’ll need to know ground (soil) pressure. The lift supervisor should provide you with that number measured as pounds per square inch (psi).

To determine area, divide the total force by the ground pressure. The resulting number will be the total area over which the weight will be distributed. Calculate the square root of that number and you’ll know how much area each of the four corners of your rigging system should cover.

In some cases, you may find your outrigger pads are sufficient in and of themselves to carry the load. Other cases might require additional blocking or cribbing underneath the pads. Just make sure you get it right one way or another.

Feel free to contact us if you have questions about our outrigger pads. Also remember that we carry a full line of rigging supplies. Whether you need slings, straps, blocks or hooks, Mytee Products probably carries it. And if we don’t, contact us anyway. We might be able to procure what you’re after.


Rigging Science: The Physics Behind the Block and Tackle

Mytee Products carries a full inventory of rigging supplies covering everything from blocks to turnbuckles and shackles. All of that is well and good, but sometimes it is helpful to understand the physics behind rigging principals. Understanding makes for safer lifts.

In light of that, we thought it might be interesting to discuss the physics behind the block and tackle principal. The block and tackle represents one of the easiest ways to lift extremely heavy loads with very little force. Block and tackle setups have been used for centuries by cultures all over the world.

The Block and Tackle Defined

A block and tackle isn’t a single piece of equipment. Instead, it is a particular kind of rigging set-up that includes multiple pulleys and some sort of means to lift the load – be it rope, wire, chain, etc. The most basic setup utilizes at least two pulleys with a rope or wire running between them.

The pulleys in a block and tackle system can be located close together or at a distance. Locations are chosen based on the nature of the lift. The pulleys on a crane might be close together while those in the warehouse rigging system are farther apart.

The Principle of Lifting Force

Physics dictates that a certain amount of force is required to lift a load off the ground. The heavier the load, the more force required. The lifting force has to be either equal to or greater than the weight of the load.

For example, imagine you are lifting a 200-pound load using a single pulley and a 200 ft. rope. You have to apply a minimum of 200 pounds of force in order to get the load off the ground. All 200 pounds will be carried by that single pulley. Also note that the amount of force you need is inversely related to the length of your rope.

If your rope is 100 feet long, more force will be required. The opposite is true if your rope is longer than 200 feet. What does this tell you? It tells you that a longer rope and more pulleys should require less lifting force from you.

Sharing the Load among Blocks

Remember that a block and tackle system utilizes multiple pulleys (or blocks) for lifting. Each of those blocks takes some of the weight of the load. So once again, let us assume a 200-pound load and two blocks in your system. Each block carries half the weight, or 100 pounds. Using the same 200-foot rope now means you only have to apply 100 pounds of lifting force instead of 200.

Introduce a third block into the system and you reduce the total weight carried by each block yet again. Instead of 100 pounds per block, you are now in the neighborhood of 70 pounds.

In theory, you can continue adding blocks and lengthening the rope to make your load even easier to lift. In practice though, there is a tipping point. Additional blocks and longer rope create resistance. Make your block and tackle system too big and the amount of resistance in the system could make it impossible to lift the load anyway. So there is a balance between distributing the weight and minimizing resistance.

Distributing the Load

The simplest way to understand the physics of a block and tackle system is to understand that each block in the system takes part of the load. It is all about load distribution. Greater distribution means less lifting force to get a load off the ground. That’s about it in a nutshell.