In Focus

Brushless DC Motors: The Bonded Neo Advantage

The trend to have lighter, smaller and more efficient motor is the need of the day for automotive accessory and home appliance motors. The recent surge in rare earth raw material prices and the continuous decline in the price of the power electronics devices open a new era of permanent magnet brushless DC (PM BLDC) motors as a replacement for brushed permanent magnet DC (PMDC) motors.

The major drawback of PMDC motors is the need for the brush and the commutator, resulting in low efficiency, additional maintenance, an increase in the overall length, and generation of magnetic interference signals. The maximum number of poles possible in practical design of PMDC motors is four due to the number of brushes and the space required to accommodate them. On the other hand the PM BLDC motor can have a higher number of poles therefore resulting in smaller and lighter motors. The absence of a commutator and brushes also increases overall system efficiency and life.

Bonded neo magnets offer the following distinct advantages compared to sintered ferrite or sintered neo. These advantages are useful for designers in achieving smaller, lighter, more efficient and quieter PM BLDC motors.

  • Ease in achieving tailored magnetization profiles (e.g. Radial, Halbach, Skew) offering advantages such as low noise and vibration, elimination of physical skewing of the magnet or stator, and the possibility to use a non-magnetic rotor back-iron
  • Ease of assembly for higher pole machines and the possibility for different pole numbers from the same ring-shaped magnet design
  • Always dysprosium free resulting in reduced cost and more price stability compared to sintered neo magnets.

To demonstrate the advantages of PM BLDC motors over brushed PMDC motors an automotive HVAC Blower was designed using the bonded neo magnet to achieve the same performance in each motor type. The PM BLDC motor was designed with a Halbach magnetized magnet and 10 poles while the PMDC was designed with four poles. As the magnet for the PM BLDC motor was magnetized in a Halbach orientation there was no need for soft magnetic material in the rotor to complete the flux path. The rotor backing material used in the design is made of non-magnetic material, such as plastic, resulting in a much lighter rotor and a faster response. Figure 1 shows the cross section and the no-load flux distribution. From this figure it can be observed that the magnet is Halbach magnetized and there is very little flux in the rotor behind the magnet. Figure 2 shows the back-emf and phase current for the motor at a load of 250 mN-m. Figure 3 shows the cogging and the developed torque. The Halbach magnetization of the magnet with the sinusoidal current results in negligible cogging torque and torque ripple, which can be observed from Fig. 3. Figure 4 shows the comparison of the performances for both brushed PMDC and PM BLDC motors. Table 1 gives the key physical parameters and the weight of the key raw materials (Copper, soft iron and magnet) for both motor types. From the table it can be observed that the raw material required for the PM BLDC motor is significantly lower compared to the PMDC motor. Also the PM BLDC motor is much lighter and smaller compared to the corresponding PMDC counterpart.


Fig. 1 PM BLDC motor cross section and no-load flux distribution


Fig. 2 PM BLDC motor back-emf and phase current at load of 250 mN-m at 4436 rpm


Fig. 3 Cogging and developed torque of the PM BLDC motor


Fig. 4 Motor performance


Table 1: Comparision of key physical parameters of the designed PM BLDC and PMDC motors


The effect of epoxy loading on density and mechanical strength

The selection and usage of binder is very important for bonded magnets to achieve desired magnetic properties as well as mechanical properties. For compression molded rare earth magnets, epoxy is the most popular binder. It is widely accepted that there is a balance between magnetic property (magnetic powder loading) and mechanical property (ring crush strength): higher loading of epoxy binder will increase the ring crush strength at the cost of lower magnetic powder loading, hence, results in lower magnetic property.

Challenge arises in achieving in both high magnetic property and mechanical property. Generally, at least 1.5wt% of epoxy has to be employed into the magnet to offer acceptable mechanical strength for further processes and applications. On the other hand, if more than 4wt% of epoxy loading is employed, it will not only lead to much lower density of the magnet, but also tend to deform and generate defects within the magnet during curing.

How to maintain magnetic powder loading while increasing the binder loading from 1.5wt% towards 4wt% so that greater mechanical strength could be obtained without sacrificing the magnetic property?   A closer look at a typical compression molded MQP magnet with a density of 6.0g/cm3 might give some clue. Within the magnet body, around 98.5wt% is magnetic powders while the remaining 1.5wt% is binders and lubes. However, the volume contribution to the magnet in total is less than 86vol% of the magnet. The remaining 14vol% is simply pores filled with air. If these pores can be filled with epoxy binders, the binder loading could in total reach to more than 4wt% without reducing magnetic powder loading.

Raising compaction temperature and pressure can help to reduce the porosity but would increase the processing cost. Using epoxies with lower molecular weight would be a more economical way to achieve such purpose since such epoxies have a much lower glass transition temperature. The heat generated during compaction process alone might be enough to soften the epoxies and the softened epoxy can be squeezed to the pores.

However, there is still another challenge to use higher epoxy loading in magnets making. It becomes more difficult to obtain a uniformly coated compound with increasing epoxy loading. Lower molecular weight epoxy will make the process even more difficult since these epoxies will become soft or even viscous throughout the coating process. Advanced coating technology has to be applied to achieve this. In Magnequench, our unique MQEP coating technology makes it possible to coat as high as 3.5wt% epoxy onto MQP powders uniformly. With such compound, greater mechanical strength can be obtained without losing magnetic properties.

Dysprosium-free Rare Earth Permanent Magnet Motors

The unprecedented rise in REE prices have resulted in the increase of Nd-Fe-B magnet prices by 300% or more in some cases. Sintered Nd-Fe-B magnets prices not only have been impacted by both Nd and Pr prices, but also by the soaring prices for dysprosium (Dy). The dollar value of Dy in a standard Nd-Fe-B magnet is 50% greater than that of Nd and Pr even though the weight of Nd and Pr is 8 times that of Dy.

Dysprosium-free Rare Earth Permanent Magnet Motors

The rate of Dy consumption is expected to increase as relatively Dy rich sintered Nd-Fe-B applications continue to proliferate. The demand for sintered Nd-Fe-B magnets is estimated to reach over 100,000 MT, translating to about 4,000MT of Dy. While the demand for Dy is growing, the supply of Dy is not because Dy concentrations found in typical heavy rare earth deposits range from only 3% to 8% with merely 500MT being recovered per year. Many companies have embarked upon new mining projects outside of China, the vast preponderance of these projects contains light rare earths.

This fundamental supply-demand imbalance for Dy will result in long-term rising prices. Given the likely rising costs of sintered Nd-Fe-B magnets, many consumers of sintered Nd-Fe-B magnets are considering utilizing alternative materials which do not rely on Dy.

In most cases, it is difficult or impractical to implement sintered Nd-Fe-B without Dy. However, bonded Nd-Fe-B magnets do not rely on Dy and offer equivalent performance to sintered Nd-Fe-B magnets for certain applications operating up to 180oC. Since all MQP™ grades are Dy free, bonded Nd-Fe-B magnets will not be impacted by the impending supply-demand constraints and the resulting price increase. This will make an MQP™ based solution will be ideal and less expensive in many applications.

» Why Dysprosium is used in rare earth magnets
» Motor Design (Dy-Free Solution): Power Tool Motor (MQP-14-12 vs. N35SH)
» Motor Design (Dy-Free Solution): HVAC Blower Motor (MQP-B+-20056)
» Motor Design (Dy-Free Solution): Power Tool Motor (MQP-14-12 vs. N27SH/N30SH)
» Motor Design (Dy-Free Solution): Engine Cooling Fan Motor (MQP-14-12)

Award Achievements in Magnequench Korat

At Magnequench Korat (MQK), we not only ensure that we produce quality products, we are also committed to our facility's excellence.

Green Industry Award 2011
Increasing worldwide environmental consciousness has been driving attention to the number of green industries, while traditional industries are contesting with this public's attention. Officially launched by the Industry Minister on 4th May 2011, the Thailand's Ministry of Industry announced a Green Industry Project. This was followed up by a Memorandum of Understanding signed at the end of last year with BOI, IEAT and several industrial institutes. The aim of this project is to support small and medium sized enterprises (SMEs) to develop a sustainable approach by achieving the 5 classified levels in the Green Industry development.

Under this project, MQK achieved the Green System level, Level 3, to verify that we have systems in place for environmental management which comprise of follow-up, assessment and review for continued development.

Green Industry Award 2011

Outstanding EH&S Management Award 2011
This award is presented by the Labor Welfare Department, Ministry of Labor in Thailand to companies that demonstrate outstanding safety management and performance in each year.

MQK participated in this program this year for the first time and has achieved the provincial complimentary award as a company that performs outstanding management for Safety, Occupational Health and Environment.

Outstanding EH&S Management Award 2011

Zero Accident Campaign Award 2011
This award, verified by the Social Security Record, is presented by the Labor Welfare Department, Ministry of Labor in Thailand to the companies that can demonstrate a zero accident record over the past year.

MQK participated this year, for the first time as well. We had no accidents with a record at 100,000 man hours from December 2009 to December 2010. We are now recognized as a company that maintains zero accident levels. Moreover, MQK still maintains a zero accident record and we are reaching our new record for 200,000 man hours in near future.

Zero Accident Campaign Award 2011

Upcoming awards in 2011
MQK has participated in Safety Management for SMEs and we are expected to receive the certificate at the end of this year. In addition MQK has also achieved the national award in Outstanding Management for Employee Relation and Welfare last year. We have participated again this year and are expecting to be awarded for our second year soon.

Upcoming awards in 2011

Lastly, along with the above achievements in this year, we are also participating in the Corporate Social Responsibility Project. We have completed the basic assessment and we will expect to achieve this project award at the end of this year too.

The State of Magnetic Materials Development

Thirty years on from the discovery of Nd2Fe14B, development of rare earth permanent magnet materials has reached a state of maturity. However, research continues to address the requirements of magnet users; namely to provide stronger, more stable and lower cost magnet solutions.

The search for "stronger" permanent magnets covers a range of activities from the blue-skies research into nano-scale particles [1], through to the introduction of high energy anisotropic bonded magnets [2].

"More stable" magnet materials are required for those devices that operate in the challenging environments of heat and humidity. Metallurgical alloy additions like Dy and Co can be used to reduce the thermal coefficients of magnetic performance (α and β) and improve corrosion resistance, respectively. Advanced powder coating techniques can be applied with great effect to impart a physical barrier between the magnetic particles and their environment [3].

"Lower cost" is a very topical issue with the current price of rare earth metals. Using rare earth magnets has traditionally brought a cost saving to electric motor devices as they enable a net reduction in device size and the material requirement [4]. MQP powders are available with a range of rare earth contents and costs. Where cost is critical, magnetic alloy compositions can be tailored accordingly.

Magnequench and the research community continue to search for superior magnetic materials for the next generation of permanent magnet applications.

[1] J.P. Liu. Journal of Metals Vol. 62 No. 4 April 2010, p.56
[2] http://www.mqitechnology.com/downloads/brochures_PDF/MQA-Overview.pdf
[3] http://www.mqitechnology.com/anti-aging-developments.jsp
[4]http://www.mqitechnology.com/downloads/articles/Bonded neodymium magnets.pdf

Magnequench's ongoing effort to optimize cost and performance

The rare earth magnet industry has been experiencing an unprecedented rise in the price of neodymium metal, the Nd in NdFeB and the Neo in Neo magnets. Since the beginning of this year the price of Nd oxide has increased by a factor of 6 and is up by a factor of 10 since January 2010. Higher prices for MQP powders are the unavoidable result.

Magnequench is meeting this challenge by systematically redesigning our product portfolio to include lower cost rare earth metals such as Pr and Ce. Our flagship MQP-B powder series is now available with new alloy composition based on Nd and Pr that can lower the final powder price by 10% or more while maintaining the same high magnetic performance. In a new series of products, Ce metal has substituted up to 80% of the Nd and Pr content creating powders ranging from MQP-8-5 to MQP-14-9 performance offering alternatives to the popular MQP-13-9 series and providing new cost effective opportunities where ferrite magnets are short of performance.

Finally, our R&D team is exploring the use of metals such as Zr. The effort is producing powders with unique compaction properties enabling higher density bonded magnets, which will open new markets and will make better, more cost effective use of our materials. Samples of the first of these products, MQP-16-9-HD and MQP-15-9-HD, are now available.

Magnequench's expanded and more functional technical resource website

The Magnequench Technical Resource Website (www.mqitechnology.com) is an online representation of the Magnequench Technology Center in Singapore, showcasing all of our technical resources, products, services, and capabilities, throughout the world. Nd-Fe-B magnetic powder used in the manufacture of bonded magnets has been commercially available for over 20 years; however, this material is unique in many ways, and as such, we endeavor to work with our customers — magnet manufacturers and magnet users — to fully harness and exploit the advantages of "bonded Neo powders" and magnets.

By working with motor companies, for example, during initial design stages, we are able to jointly identify an application's required magnetic and mechanical properties, select the most cost effective powder grade, tailor the magnet's magnetization pattern, and finally supply a bespoke magnet. All of these efforts, which are illustrated on this site, are undertaken in order to match magnetic performance to a specific, unique application and thereby creating value for our customers.

In addition to our work within the magnetics field, we also leverage our vast experience of rapidly solidifying Nd-Fe-B magnetic material and work with partner companies to develop new markets or enhance the cost-performance of other non-magnetic materials. Our Advanced Rapid Solidification efforts are also outlined on this site.

As we continue to develop new materials or enhance our technical services, we will be updating this site. We hope you will check the site frequently for updates. Contact us at your convenience at research@magnequench.com or visit our corporate site www.magnequench.com for additional information about Magnequench.

How to improve the parallelism when pressing magnets

The height tolerance for magnets is typically ± 0.05mm, but some products might require ± 0.03mm. If the parallelism of the magnetic powder is not properly controlled, it might be difficult to maintain the height tolerance and affect the conformance of the magnets produced. Some methods we have identified to improve parallelism when pressing magnets include:

  1. Ensuring that the tools are completely de-magnetized, as magnetized tools prevent uniform powder dispersion when filling the die
  2. Rotating the core rod for better powder dispersion in the die
  3. Adjusting the height of the core rod to make it a little higher or lower than the die (not exceeding 0.3mm)
  4. Adjusting the gap between the powder feed shoe and die by adjusting the air pressure

The preceding tips are based on our manufacturing experience and are provided as reference only. Please contact Magnequench directly if you have any queries.

Source and remedies for noise and vibration in PM motors

The Applications group of the Magnequench Technology Center has prepared a presentation highlighting various causes of noise and vibration in a PM motor. Included in this presentation are the guidelines for preventing excessive noise and vibrations during motor design.

Issues addressed in this presentation include:

  1. Vibrating frequency generated due to various mechanical causes
  2. Electromagnetic causes and the remedial steps for the same
  3. Effect of slot/pole combination on the dominant vibrating mode frequency

A case study demonstrating how a proper selection of slot/pole combination with an appropriate skew angle helps in reducing the noise and vibration due to substantially reduced cogging torque as well as unbalanced magnetic pull is also presented.

The flexibility of generating the desired airgap flux profile (including the skew magnetization) from the same magnet by appropriate design of the magnetizing fixture offered by an isotropic bonded neo magnets is very useful in tuning the airgap flux profile to match the requirement of drive and hence reducing the torque ripple and corresponding vibrating frequencies.

» Noise and Vibration in PM Motors – Sources and Remedies

Capacity planning

Magnequench, as the leading global producer of Neo powders for bonded magnets, has an obligation to our customers and the market in general to ensure our production facilities have sufficient capacity to meet our customers demand today and in the future. We have 13 fully operational jet casters currently, with 10 jet casters in Tianjin, China (MQTJ) and 3 jet casters in Korat, Thailand (MQK) respectively. With our installed capacity, we are able to serve 85% of the market. Committed to ensure sufficient supply to the market, we are expanding MQTJ's jet caster capacity by 15%. This capacity expansion, which will be completed by early 2012, will ensure that we will have sufficient capacity for the industry's dynamic growth well into the future.

However adding jet casting capacity is only part of the expansion currently ongoing at MQTJ. Both upstream and downstream processes have to be expanded to encompass the increased jet casting capacity. The alloy expansion plan for MQTJ will result in an additional 160% capacity by the end of 2011 compared to 2008. Additional crushing and annealing lines are being added for powder processing and will be operational in Q3 2011. In addition, to offer customers a more tailored 'Neo powder solution' additional milling and compounding capacities have been added at MQTJ to provide smaller particle size products and 'ready to press' compound products.