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Injection Molded Magnets

Polymer bonded magnets opened a new world of application opportunities. The processing temperatures to blend and mold the material mixture is low enough to allow many different magnet powders to be used alone or in combination in the polymer binder to achieve an unprecedented range of properties.

Another benefit of the injection molding process is that magnet material can be directly molded into, onto, or against other assembly components eliminating subsequent assembly steps. This is called insert injection molding.

Injection molded magnets can be formed from very simple shapes to very complex shapes. All or only part of the device may be magnetized. Often, it is cost advantageous to make an entire part out of the magnet material and magnetize only the portion requiring magnetic output.

Materials

Magnetic powders include ferrite, neodymium-iron-boron (NdFeB), and samarium cobalt (SmCo). There are several alloy compositions available of ferrite and NdFeB providing many different magnetic properties. Magnets using combinations of the powders were introduced by Arnold in 1995 and are called "hybrid magnets."

Polymer binders utilized by Flexmag's Plastiform product include nylons 6 and 12 and PPS (polyphenylene sulfide). Binder evaluations are a continuous activity in the Development Laboratory, in an effort to improve physical strength, maximum recommended use temperature, improved corrosion resistance for the rare earth magnetic materials, improved dimensional stability in the presence of water and solvents, and greater ease of processing.

Temperature Characteristics

Maximum use temperature is a function of both the magnetic alloy powder and of the binder. For example, ferrite powders in nylon 6 or PPS have tested satisfactorily at 180°C. On the other hand, nylon 12 melts above 170°C and is not recommended for use above 150°C. Magnetic material such as the highest energy NdFeB grade, with intrinsic coercivity of 9,500 Oersteds (760 kA/m), suffers significant irreversible magnetic loss above 120°C, regardless of which binder is used. Maximum use temperatures are listed on each product's specification sheet.

Tolerances

An important characteristic of injection molded magnets is that they conform dimensionally to the mold cavity which is precisely machined, the result being close tolerances in the finished product. What little dimensional variability there is results from shrinkage of the polymer during cooling. This depends upon part thickness and shape. Typical tolerances are +/-0.003 in/in. Closer tolerances on critical dimensions can be negotiated.

Product Availability Guide

Part No. Magnetic Material Polymer Density (g/cc) Max. Br (Gauss) Max. Hc (Oe) Max. Hci (Oe) Max. Bhmax (MGOe) Max. Temp (ºC)
2039 SrFerrite Nylon 6 3.80 3,070 2,570 3,070 2.35 160
2040 SrFerrite Nylon 12 3.75 3,060 2,540 3,190 2.34 150
2046 SrFerrite Nylon 6 3.58 2,890 2,550 3,150 2.11 160
2048 SrFerrite Nylon 6 3.55 2,880 2,510 3,210 1.99 160
2049 SrFerrite Nylon 12 3.21 2,460 2,340 3,600 1.52 150
2051 SrFerrite Nylon 6 3.76 3,130 2,590 3,140 2.41 160
2052 SrFerrite PPS 3.65 2,880 2,530 3,320 2.05 180
2070 SrFerrite Nylon 12 3.63 2,940 2,520 3,190 2.17 150
2071 SrFerrite Nylon 12 3.53 2,810 2,680 4,020 2.05 150
2101 SmCo Nylon 12 5.60 6,880 6,000 11,600 11.28 150
2103 SmCo Nylon 6 5.50 6,380 6,000 28,000 9.72 160
2202 NdFeB Polyamide 4.85 5,800 4,320 10,000 7.15 125
2204 NdFeB Nylon 12 5.20 5,390 4,920 13,200 5.94 150
2206 NdFeB PPS 4.40 4,400 4,000 10,500 4.26 150
2212 NdFeB Nylon 12 4.90 5,720 4,320 9,000 6.63 150
2213 NdFeB Nylon 12 5.20 5,890 5,000 10,000 7.44 150
2214 NdFeB Nylon 12/Polyamide 4.65 4,800 4,200 9,840 5.56 125
2216 NdFeB Nylon 12 5.16 6,110 4,800 9,000 6.63 125
2217 NdFeB PPS 4.90 4,820 4,800 18,000 5.17 180
2218 NdFeB Nylon 12 5.20 5,890 4,800 9,600 7.44 150
2225 NdFeB Special plastic 5.70 6,800 5,800 10,200 9.4 150
2409 SrFerrite/NdFeB Nylon 12/Polyamide 4.15 4,620 2,880 4,320 3.43 125
2413 SrFerrite/NdFeB Nylon 12/Polyamide 4.72 5,200 2,640 4,400 4.77 125
2414 SrFerrite/NdFeB Nylon 12 4.85 5,300 4,100 9,100 5.95 150
2415 SrFerrite/NdFeB Nylon 12 4.00 3,870 2,830 4,220 3.03 150
2416 SrFerrite/NdFeB Nylon 12 4.97 5,400 4,310 9,400 6.31 150
2417 SrFerrite/NdFeB Nylon 6 3.85 2,200 1,740 2,640 1.01 150
2521 SrFerrite Nylon 12 3.65 2,810 2,680 4,020 2.05 150
2534 SrFerrite Nylon 6 3.53 2,730 2,250 3,300 1.89 150
2535 SrFerrite Nylon12/Polyamide 3.65 2,840 2,650 4,000 1.96 125
2560 SrFerrite Polyamide 3.65 2,840 2,650 4,000 1.96 125