Magnetic Separator Audit for Jordans Dorset Ryvita

Inspecting Magnet Strength

Bunting engineers have conducted a thorough review of all the Magnetic Separators installed at the Jordans Dorset Ryvita plant in Poole, Dorset.  The audit was completed over three days, including attending site on Saturday to prevent any loss in production.

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Master Magnets Grate Magnet

Jordans Dorset Ryvita has a strong heritage of making whole grain foods and working with farmers to protect the countryside.  Ever since the brands first came together, they have continued to act on these values.

A Magnetic Separator Audit involves the inspection and test of Magnetic Separators to confirm their magnetic and physical integrity.  Commonly, such tests are conducted annually, with the final report forming part of the company’s quality audit process.

The tests in a Magnetic Separator Audit are conducted in two stages.  Stage one involved the inspection of the physical integrity of the Magnetic Separator.  This includes checking welds, and assessing any wear and damage to the surface.

Bunting Magnetics Pull Test Kit
The Spring Balance

Stage two involves testing the magnetic strength of the Magnetic Separator.  These tests are conducted by placed a magnetic ball or plate into the magnetic field and then measuring the force (in kgs) needed to remove that object from the surface of the magnetic separator.  The actual ‘gauss’ reading of a Magnetic Separator is not checked as measurement is difficult and often inaccurate.  Gauss is the is the cgs unit of measurement of magnetic flux density (or “magnetic induction”, but can be difficult to measure accurately.

Bunting Magnetics Pull Test Kit
The Magnetic Test Piece

The metal test piece is attached to the end of the Spring Balance and then placed into the magnetic field, being attracted to the magnetic pole.  The metal test piece is then pulled off the surface of the magnetic separator whilst holding the other end of the spring balance.  The amount of force needed to remove the metal test piece from the surface is recorded (in kgs).  The test is repeated three times and an average reading taken.  Similar techniques are used to test other designs of Magnetic Separators such as Plate Magnets.

Bunting Magnetics Pull Test Kit
The magnetic test piece on the surface of the Magnetic Separator

There were a wide range of designs, strengths and ages of Magnetic Separators in the production process at Jordans Dorset Ryvita.  The company had not experienced any problems due to metal contamination and requested the audit as part of their continued improvement plan.

Day one was spent assessing the location and recording the customer identity numbers of all the Magnetic Separators.  Checking the location also highlighted any health and safety issues that needed to be considered for the audit, such as working at heights.  The review identified 52 Magnetic Separators.

The physical checks of the Magnetic Separators were conducted on day two and three, on the weekend to minimise any production downtime.  Each Magnetic Separator was removed from its location and visually inspected.  Then the magnetic strength was checked using the pull test technique.  The data was recorded and presented in a detailed report with recommendations following the audit.  This report can then be used as part of the quality management system.  It also provides base data for comparison on future audits.

 

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Master Magnets Grate Magnet

Following the audit, the engineering team at Jordans Dorset Ryvita have made several changes to improve the removal of metal during the production process.

“Having an external review of the Magnetic Separators really helps the client,” explained Mark Harris, Bunting’s Engineer.  “We conducted the audit without any assumptions and this freedom enabled us to highlight the areas where protection was good and also focus attention where they could be improvements.  We are looking forward to working with the team at Jordans Dorset Ryvita for the long-term and providing our technical support when needed.”

For further information on measuring the strength of a Magnetic Separator, please visit our website or contact us on:

Phone: +44 (0) 1442 875081
Email: press@buntingeurope.com
Via the website

Photographs taken and videos produced by Paul Fears Photography

Practically Measuring Magnetic Separator Strength

Technically Assessing Magnetic Separator Power

A Magnetic Separator is designed to attract, capture and hold magnetic particles.  The magnetic strength needed to successfully achieve that design objective is commonly stated in a magnetic separator supplier’s quotation or specified in the tender.  This ‘Magnetic Strength’ is usually referenced in terms of ‘gauss’, a unit of measurement.  However, the ‘gauss’ value can be very difficult to accurately measure.

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Fine iron contamination captured on Tube Magnets

There is a more practical method of assessing the magnetic strength.  This removes any ambiguity whilst providing simple, repeatable, and comparable data to assess most Magnetic Separators.

Measuring Magnetic Strength

The magnetic strength of a Magnetic Separator is often referenced in terms of ‘gauss’.  Gauss (symbolized G) is the centimetre-gram-second (cgs) unit of magnetic flux density. A flux density of 1 G represents one maxwell per centimetre squared (1 Mx ­ cm -2 ).  It is named after the German scientist Carl Friedrich Gauss.

Gauss can be measured using a Gaussmeter.  However, it is important to note that the Gauss rating on its own does not fully indicate the strength of a magnet.  Additionally, gaussmeters can give a range of readings dependent upon the orientation of the probe and several other variable parameters.

Proposals for Tube Magnets often include details of length, diameter and the gauss reading.  With the gauss reading being so difficult to test and prove, purchasers and users are unable to check that the Tube Magnets supplied actually meet the specification of the quote and the order.

However, in terms of Magnetic Separation the objective for the user is simple; the magnetic force must enable the attraction and capture of any magnetically susceptible metal.  That ability can be measured as a function of the effort needed to remove a specific steel item from the surface.

The Method

Measuring the effort needed to remove a steel item from the face or surface of a Magnetic Separator is achieved using a spring balance and is commonly called a ‘Pull Test’.  The magnetic test piece (e.g. a 6mm ball bearing welded onto a non-magnetic attachment ring) is clipped onto the end of the spring balance.

Bunting Magnetics Pull Test Kit
A Pull Test Kit ‘Spring Balance’

The magnetic test piece is placed on the surface of the Magnetic Separator and force applied at the other end of the spring balance until it is detached.  The force required to remove the magnetic test piece (measured in kgs) is recorded on the measurement scale of the spring balance.

Measurements are taken in the centre of the Tube Magnet and on the end poles.  They are repeated three times and the average recorded as the force required to remove the magnetic test piece at each point.

The following video explains the Pull Test technique.

This simple but effective method does not record or provide any indication of the gauss, but accurately provides data that can be used to compare the condition of a Magnetic Separator over time and compare the performance with other similar designs.

Pull Test Experiments

Magnetic Separator designs vary considerably depending on the application.  The Pull Test technique is suitable for measuring the magnetic strength of smaller Magnetic Separators such as Tube or Cartridge Magnets and Plate Magnets.

Tube or Cartridge Magnets are often used stand alone or as part of a Magnetic Separator configuration (e.g. Drawer Filter or Liquid Trap).

Bunting Magnetics Pull Test Kit
Magnetic Test Piece

A small steel ball is used as the magnetic test piece when measuring the magnetic strength of a Tube or Cartridge Magnet (the photograph shows a 6mm diameter ball)

The metal test piece is attached to the end of the Spring Balance and then placed into the magnetic field, being attracted to the magnetic pole.

Bunting Magnetics Pull Test Kit
Magnetically Attracted Metal Test Piece

In a series of experiments, we used the Pull Test technique to assess the magnetic strength of Tube Magnets with Ceramic (Ferrite), Standard Neodymium Rare Earth, and High Strength Neodymium Rare Earth Magnets.

The tests were undertaken using three different sizes of steel ball in the magnetic test piece (6mm, 12mm and 25mm) and introduced non-magnetic spacer to assess the magnetic strength at specific distances away from the surface (3mm and 6mm).  All the recorded measurements are in kilograms (kg)

Ceramic (Ferrite)

Gap 6mm Ball 12mm Ball 25mm Ball
None 1.25 1.75 2.5
3mm NR NR 1.2
6mm NR NR NR

Graph - Ceramic Tube Magnet

Note:  all measurements are recorded in kilogrammes.

Standard Neodymium Rare Earth

Gap 6mm Ball 12mm Ball 25mm Ball
None 2 4.25 9
3mm 1.2 1.6 2.45
6mm NR 1.25 1.5

Graph - Std Neo Tube Magnet

Note:  all measurements are recorded in kilogrammes.

High Strength Neodymium Rare Earth

Gap 6mm Ball 12mm Ball 25mm Ball
None 3.75 9 14.5
3mm 1.5 2.5 4.6
6mm 1.1 1.5 2.25

Graph - High Strength Neo Tube Magnet

Note:  all measurements are recorded in kilogrammes.

In all cases, the drop off in magnetic strength as you move away from the surface of the Tube Magnet is significant and this highlights the need for metal contamination to come into contact with the surface.  Arrangements where the Tube Magnets are configured as a Grate (i.e. are lined up and equally spaced) commonly have a deflector above the gap between the Tubes that directs material in the area of maximum magnetic strength.

Comparison

The tests highlight the difference in magnetic strength on the surface, with high strength Rare Earth magnets producing nearly 3 times as much pull as Ceramic magnets.

Findings During Magnetic Separator Audits

Magnetic Separator Audits often highlight issues that had previously gone undetected.  The first check focuses on the physical integrity of the Magnetic Separator, inspecting welds, and assessing wear and damage.  Once these have been completed, the measurements are taken.

The most common findings when undertaking magnetic separator audits are:

Weld Failure

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Consequence of weld failure on a Liquid Magnetic Filter

Magnetic Liquid Filters, fitted into pipelines, have Tube Magnets that are welded to a lid and project down into the product flow.  Metal is attracted and captured on the surface of the Tube Magnet.

In cases where the welds have failed (e.g. poor manufacture, eaten away by acidic or alkaline liquids), liquid will seep into the tube and onto the magnets.  The magnets then swell and lose magnetic strength, ultimately splitting the outer stainless-steel casing.

Tube Magnet Wear

When material falls directly onto the surface of a Tube Magnet, over time the surface can be worn.  Wear usually occurs on the poles where magnetic particles have been captured.  Once the outer stainless-steel casing has been breached, the Tube Magnet should be replaced.

Weak Tube Magnets

Magnetic separation audits highlight the variance in magnetic strength of Tube Magnets.  Often, the Tube Magnets have been installed for some time and details of the original specification have been lost.  When testing the magnetic strength, some Tube Magnets are found to have very poor strength and provide little if no metal separation protection.  This is of great concern when the Tube Magnet is positioned to protect a particular item of processing plant where metal contamination damage could result in production downtime and costly repairs.

Conclusion

The Pull Test Experiments highlights the importance of physically checking the real magnetic strength of a Tube Magnet and not only replying on the stated gauss.  Including details of the force needed to detach a 6mm steel ball from the surface of the Tube Magnet in the request for quotation and the order, protects the user and ensures that the supplied equipment is as exactly as stated.

This ‘Pull Test’ measurement technique also enables a regular comparative test that will immediately highlight any drop in magnetic strength.  This can be used in annual audits or inspections as part of a plant’s quality management system.  A change in ‘pull’ strength may be the result of physical (e.g. failed weld, broken magnets from being dropped) or excessive heat.  The reduced magnetic force may result in the magnetic separator no longer being fit for purpose.

For further information on measuring the strength of a Magnetic Separator, please visit our website or contact us on:

Phone: +44 (0) 1442 875081
Email: press@buntingeurope.com
Via the website

Photographs taken and videos produced by Paul Fears Photography