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Deep Field & Shallow Field Lifting Magnets

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Are you aware there are deep field and shallow field Lifting Magnets available?

Deep field (Passive Shunting) Lifting Magnets have been used for many decades in Australia. In the last ten years shallow field (Active Shunting) Lifting Magnets have been gaining in Popularity.

To understand why we need to look at the differences and what that means in the workplace.

Deep field magnets are generally durable robust pieces of equipment, but many people are not aware that they will only lift their advertised capacity at the depth of their magnetic field.

This depth varies between sizes. An average PML 500kg magnet has a 40mm deep field. This means it is only rated to lift 500kg if the material you are handling is 40mm thick. If the material is 20mm thick this 500kg magnet is rated to lift 350kg.  A 1-tonne deep field magnet typically has a 60mm deep field, so on 20mm material thickness, it is rated to lift 350kg which is the same as a PML 500kg magnet.

A shallow field magnet rated to lift 400kg has a 12.7mm deep field so it can lift 400kg of 12.7mm material. When you are handling 20mm plate it is still rated to lift 400kg.

Interestingly, most deep field magnets are not rated to lift material less than 10mm thick while many shallow field magnets are rated on material as thin as 0.5mm thick.

So, what that means in the workplace when you are using deep field magnets, is there is more potential to mismatch the magnet to the load.

A mismatch like using a 1-tonne PML with a 60mm field to lift 15mm plate will result in the lever being very hard to actuate and very hard to turn off. The lever will be very forceful on release resulting in a risk of wrist injuries.

Furthermore, a calculation is required by the operator to ensure the magnet is rated to lift the material at the given thickness.

Using a shallow field magnet on material from 0.5mm to 25mm thick will ensure that the levers actuate in a gentle manner, reducing potential wrist injuries while reducing the risk of operator error due to misunderstanding their magnets capacity on various thickness’s.

At MSA we supply both types and are looking forward to offering advice on which type suits your requirements.

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Selecting Between Deep Field Passive Shunting And Shallow Field Active Shunting Lifting Magnets

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Hand Injuries

Many Australian companies have a strong focus on reducing hand and wrist injuries. They may be interested in an Active Shunting Magnet due to it’s more gentle actuation. Deep Field Magnets can be quite forceful when being turned on and off, particularly when it is operating too far from its maximum magnetic saturation thickness. For example, a 3-tonne Passive Shunting Lifting Magnet is not rated for use below 30mm and is a happier operation in the 50mm-80mm range.

The other reason Active Shunting Magnets are good at preventing hand injuries is to have no residual magnetism. This eliminates the requirement to remove swarf and grit from the bottom of the magnets between lifts thus reducing the risk of laceration type hand injuries.

Do you intend to lift material less than 10mm thick?

If so, be aware that many Passive Shunting Magnets are not rated for it. The two main reasons are that you have to apply so much force to the handle that the magnet can be damaged and once the magnet is actuated, so much of the flux is wasted below the sheet metal.

De-stacking

If you’re using the magnet to lift sheet or plate off a stack, you’re most likely better off with a Shallow Field to reduce the chance of picking up multiple pieces.

Preventing damage to Materials

Does the material have to be handled carefully to reduce the risk of scratching it? If so an Active Shunting Magnet with zero Residual Magnetism is the way to go. See our video on Residual Magnetism for more detail on this.

Handling billet or very thick steel 40-80 mm plus

A Passive Shunting Magnet is usually a good choice and really come into their own here. Just ensure that the magnet has a two-action control that prevents accidental discharge as per the Australian standard. We see many for sale in Australia that doesn’t.

 

We are not playing favourites here, we highly recommend our Passive Shunting Prolift range, they are robust and dependable. We also really like the Active Shunting Magswitch products for their technology and all the solutions they offer.

At MSA we want to see the right magnets used for the job, safely and at the best price whether it’s a Prolift or Magswitch MLAY.

Contact MSA today for advice on selecting the right Lifting Magnet for your application.

 

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Achieving Different Hold Forces Using Lifting Magnets

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Lifting magnets will achieve different hold forces depending on the thickness of the steel it is in contact with.

Some magnets are geared towards lifting thin material (Active shunting) and some thicker material (Passive Shunting).

Let’s look at how the two compare at the midrange thicknesses we commonly handle in Australia:

The active shunting Magnets are more likely to lift the number on the side of the magnet as they waste less flux due to the more efficient circuit. This reduces the risk of operator error.

Contact MSA today for advice on selecting the right Lifting Magnet for your application.

 

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Understanding The Hold Force Of Lifting Magnets

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Passive shunting Magnets achieve their full hold force between 30mm – 80mm thick while most Active Shunting Magnets are achieving their full hold force between 9mm and 20mm. This is the range of thicknesses that are most commonly handled.

What that means is that at some thicknesses of an enormous Passive Shunting Magnet has less hold force than a small Active Shunting Magnet.

With that in mind, let’s compare some costs of the two types based on lifting material from 10-40mm thick.

Note: We are not including material thickness less than 10mm as most Passive Shunting Deep Field Magnets are not rated for it.

Some takeaways from this are that using a powerful Passive Shunting Magnet on thin material is expensive and that using smaller Shallow Field Magnets on 10mm and 20mm material can be an economical option.

It’s important to consider that selecting the magnet best suited to the thickness of materials you intend to handle, reduces the risk of operator error.

Contact MSA today for advice on selecting the right Lifting Magnet for your application.

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How Well Do You Know Lifting Magnets?

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Ever heard of Residual Magnetism? What is it, and how does it affect your Lifting Magnets?

Residual Magnetism occurs when a magnet fails to turn completely off. The magnetic flux is a result of a circuit being created between the rare earth magnets inside and the steel body of the magnet. The level of Residual Magnetism depends on the Shunting Technology and the overall design of the magnet.

These next 3 magnets are a good example of Residual Magnetism found in lifting magnets and why magnets with no Residual Magnetism are the safest option:

 

Extreme Residual Magnetism

  • The 1st magnet has quite extreme Residual Magnetism, which will cause the magnet to collect ferrous particles and debris even after it has been turned off
  • Debris will likely cause an air gap on subsequent lifts and may permanently score the magnet. This can significantly de-rate the magnets SWL (Safe Working Load) and the magnet could fail a pull test
  • High risks of hand injuries if the operator uses their hands to separate the magnet from the load
  • The material being handled will also be damaged by any debris stuck to the magnet

 

 

 

 

 

 

 

 

Low Residual Magnetism

  • This magnet is a good quality Passive Shunting magnet. It has a small amount of Residual Magnetism, although not enough to risk hand injuries
  • Will still require regular inspection for debris, however, you can expect it to collect much less than the first magnet

 

 

 

 

 

 

 

 

No Residual Magnetism

  • The 3rd magnet uses Active Shunting Technology which allows it to be turned 100% of the way off
  • It is the safest type of magnet and is also unlikely to collect any ferrous debris after being turned off
  • In the event of damage to the working surface, replacement pole shoes can be fitted safely and easily using basic tools in your workshop

 

 

 

 

 

 

 

MSA Pro-Lift and Magswitch Lifting Magnets are designed to have a clean break of magnetic flux at the OFF position. We ensure the highest industry safety standard of our industrial Lifting Magnets while making sure they are easy to use!

Click here to watch the video now!

Need a better understanding? Contact our magnet experts today.

 

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