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Magnet Grades
Magnet Grading
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Magnet Grades
Magnet Grading
BJ Magnets is expert in bespoke industrial process magnet design, manufacture and support
Our technical knowledge and capability have been built over 15 years experience, delivering high-quality magnet solutions to thousands of applications, meeting our customers’ specific process requirements.
Design categories
Our process and mechanical engineering design professionals use their expertise and experience to provide our customer with the optimal solution for their needs.
As a bespoke manufacturer, we custom-tailor your magnet-solution to your own specifications. We use the very latest sophisticated inverter software and will send you a CAD drawing of our design for your approval prior to manufacturing; however strictly ONLY upon receipt of your Purchase Order.
This allows us to always ensure that the customer is given the best possible system solution.
MAGNET MATERIALS & APPLICATIONS
We have wide experience of both more traditional Ferrite magnets and more powerful Rare-Earth Magnets. We will specify the correct magnetic material according to the application.
A great example is the Hinged Plate magnet we designed recently for a customer:
CAD Drawing confirming design specification:
BJ Magnets has 15 years experience in magnet manufacture. Our expertise can also be seen in the high-quality finish of our products. All our products are bespoke, designed specifically to meet your application needs. Our comprehensive in-house capabilities and materials stock-holding allow us to deliver competitive lead times.
We manufacture using a range of magnetic materials, both ferrite and rare-earth.
We combine reliable equipment operation with durability and carefully finished construction in all our products.
“The type, location and strength of magnets shall be fully documented, in which cased the documented procedures shall be in place for inspection, cleaning, strength testing and integrity checks. Records of all magnet testing shall be maintained.”
BJ Magnets offers magnet testing services to both new and existing customers. We provide full documentation which can be used together with existing HACCP procedures. We use a certified gauss meter to test the gauss strength of the magnets. The gauss meter is calibrated on an annual basis, and we can supply a copy of the calibration certificate. The report identifies the strength of the magnets required in a particular location, the type of magnet, the actual reading, and whether the magnets have passed or failed.
The report also assesses the general state of the magnets and the housing and identifies where remedial action is required. We also supply accompanying photographs which are emailed to you for ease of identification
Magnets do not lose their strength if they are left in their natural state. However if they are exposed to excessive heat, vibration or shock, then they will lose some strength. For example, does the product flowing over the magnets sometimes exceed 80 degrees? Are the magnets are in a vibrating sieve or chute? Do the operatives bang the magnets when they clean them to remove excess product?
There is no specific frequency for magnet testing. It depends on the customer, what other protection is in the process (eg metal detectors) the level of contamination that may be present, and the production environment. As a general rule, it is recommended to always have your magnets checked annually.
Magnets and magnetic separators can fail for a number of reasons. Most common are physical damage and loss of performance.
Magnets are inherently brittle so any knock or shock can damage or even shatter a magnet.
Excessive heat is a common cause of magnets losing strength and performance.
A LOGICAL APPROACH TO REPAIR
We use an analytical approach to our magnet repair services.
Our aim is to deliver the best solution for you and your requirements.
As bespoke industrial magnet specialists, we can advise whether it makes more sense to repair or replace your magnets.
Given the wide range of approaches to industrial magnet manufacture and our commitment to delivering the best service to you, we can only repair magnets originally supplied by us. We also offer comprehensive maintenance & magnet testing services to help you ensure your magnets are delivering the right performance.
BJ Magnets guarantees its products for 12 months subject to wear and tear.
RECOMMENDATIONS
Magnet Inspection, Cleaning, Checking for Strength and Contamination Removal advice.
INSPECTION AND CLEANING
Processes, products and levels of contamination vary from industry. Therefore, there is no set timescale for inspecting and cleaning of the magnets. However, magnets operate more effectively when they are clean. It is thereof up to each company, given their expected levels of contamination, to decide when they should be cleaned. A regular rotation should be set up for personnel to inspect and clean the magnets. Ideally this will be at least after each different process. This will help in identifying problems up the process line, if some processes show more collection of contamination than others.
STRENGTH TESTING
We supply magnets according to strength required. We can also issue a certificate for this if required. There is no set time when the strength of magnets should be checked. It is up to the company to decide. The magnets are permanent and should not lose their strength unless exposed to heat, shock or vibration. Magnets should not be heated above their heat resistance. The heat resistance of the magnets will have been specified when ordered. As a general rule, however, an annual inspection should suffice.
To test the strength, you will require a gaussmeter that ideally shows maximum readings. Using the probe on the surface, the magnet strength varies along the tube, so it is important to find the highest reading, which can sometimes take 10-15 minutes.
CONTAMINATION REMOVAL CAPABILITIES
In terms of collection, powerful magnets can collect contamination particles as small as 30 microns. However it is important to bear in mind that not all 100% contamination will be removed for various reasons, such as shear rates, flow dynamics, or the possibility that small particles can be trapped within the product, thus preventing removal. However the higher the strength of the magnets, which we can manufacture up to 12000 gauss, the more likely it is that the particles will be attracted and held to the magnets in the product stream.
Rare earth magnets are 10 x more powerful than traditional magnets.
They are fitted with keepers for your protection.
Hence, handle with great care as they are extremely dangerous.
They must be stored in their packaging and kept at least 300 mm apart.
Only unpack one magnet at a time. Once you have removed the packaging and handle only one magnet at a time.
We strongly recommend that the magnets are fitted with their keepers on, and then remove the keepers when the magnets are firmly secured into place.
When the magnets are removed from the machinery, replace the keepers immediately.
Always keep unpackaged magnets at least 1m apart.
During assembly, fix each magnet into place one at a time.
Do not place on steel bench or near other steel objects. Keep away (Min 1m) from computers, watches, CDs, heart pacemakers and other magnetic sensitive equipment.
Ensure suitable PPE is worn when handling magnets.
Rare Earth magnetic material will maintain its properties indefinitely if the following guidelines are followed:
DO NOT subject to temperatures above 90 degrees C
DO NOT impact or shock load the magnetic material
DO NOT subject to excessive vibration.
PLEASE ASK OUR ADVICE IF YOU ARE UNSURE.
Please note : Once you have taken delivery of these magnets, you are responsible for any injury arising from the use, assembly or handling of these magnets.
Magnetic and non-Magnetic Stainless Steel
There are several families of stainless steels with different physical properties. The magnetic properties of stainless steel are very dependent on the elements added into the alloy. A basic stainless steel has a ‘ferritic’ structure and is magnetic, formed from the addition of chromium – it can be hardened through the addition of carbon, making it ‘martensitic’. However, the most common stainless steels are ‘austenitic’ – these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the steel and makes it theoretically non-magnetic.
304 stainless steel contains chromium (min. 18%), and nickel (min. 8%). It is an austenite steel and is only slightly responsive to magnetic fields. It also contains 18 – 20% chromium and 8-10.50% nickel, and lesser quantities of some other elements.
316 stainless steel is a molybdenum-alloyed steel. The fact that it is also negligibly responsive to magnetic fields means that it can be used in applications where a non-magnetic metal is required. It also contains a number of other elements in varying concentrations.
Transformation from non-magnetic to magnetic phases
As both 316 and 304 stainless steels are austenitic, when they cool, the iron remains in the form of austenite (gamma iron), a phase of iron which is nonmagnetic. The different phases of solid iron correspond to different crystal structures. In other alloys of steel, this high-temperature phase of iron transforms to a magnetic phase when the metal cools. The presence of nickel in the stainless steel alloys stabilizes austenite against this phase transition as the alloy cools to room temperature. This corresponds to a somewhat larger magnetic susceptibility than we might expect for other nonmagnetic materials, but is still well below what might be considered magnetic.
However, this does not mean that you should expect to measure such a low susceptibility on any item of 304 or 316 stainless steel that you encounter. Any process which can change the crystal structure of stainless steel can cause austenite to be converted to the ferromagnetic martensite or ferrite forms of iron. These processes include cold working and welding. It is also possible for austenite to spontaneously convert to martensite at low temperatures. To complicate matters further, the magnetic properties of these alloys depend on the alloy composition. Within the allowed ranges of variation of Ni and Cr, significant differences in magnetic properties may be observed for a given alloy.
Practical implications for removal of stainless steel particles
Both 304 and 316 stainless steel possess paramagnetic characteristics. As a result of these properties, small particles (approx < 0.5mm dia sphere for example) can be attracted to powerful magnetic separators positioned in the product stream. Depending upon their weight and specifically their weight ratio to magnetic attraction, these small particles will be held to the magnets during the production process.
These can then be removed during the magnet cleaning operation. From our experience 304SS small particles are more likely to be held in the flow than 316 SS particles due to its slightly more magnetic nature.
Paramagnetic materials have a small, positive susceptibility to magnetic fields, and are very weakly attracted by an externally applied magnetic field.
These materials do not retain the magnetic properties when the external field is removed. Paramagnetic materials include magnesium, molybdenum, lithium, and tantalum.
Paramagnetic properties are due to the presence of some unpaired electrons, and from the realignment of the electron paths caused by the external magnetic field.
Small stainless steel particles can become paramagnetic, which means that they can be picked up by strong magnets.