Page 37 - MetalForming May 2011

Demystifying Demagnetization
Information compiled by the staff of MetalForming magazine
One of the hidden affects in the manufacturing of metallic parts is magnetism. Transforming parts from raw material to finished, formed products can cause parts or assemblies (particularly welded assemblies) to become magnetized.
Materials that interact with magnetic fields fall into one of three general categories: ferromagnetic (most steels), paramagnetic and diamagnetic. Of the three, ferromagnet- ism (according to Wikipedia) is the strongest type and is the only type that can pro- duce forces strong enough to be felt, and is responsible for the common phenomena of magnetism encountered in everyday life. Paramagnetism is a form of magnetism that occurs only in the presence of an externally applied magnetic field.
Depending on the application of newly formed and/or welded parts, the magnetism built up in the parts may need to be removed by an industrial demagnetizer. The pro- cedure for demagnetizing steel workpieces, according to an article on www.gauss- busters.com, to remove its residual magnetism consists of repeatedly applying a reversing and gradually reduced imposed magnetic force. Industrial demagnetizers can be a flat-plate or aperture type. One manufacturer, Walker Magnetics Group (www.walkermagnet.com), recommends plate-type demagnetizers for toolroom use to demagnetize drills, cutters and even small welded assemblies. The part is demagnet- ized by sliding the workpiece slowly over the top of the energized plate. Walker sells units with plates measuring 8 by 10 or 10 by 10 in.
Aperture-type demagnetizers allow the workpiece/assembly to pass through the energized aperture and then removed from the demagnetizing field. For production-line applications (similar to the application at Buhrke), according to Walker, a nonmetallic conveying system can be used to move parts through the aperture. These units are available in tabletop and floor-stand models.
Walker literature warns that when running parts through a demagnetizer, take care not to pile them on top of one another. This can lead to inconsistent results.
conveyor, the belt would become too slick to provide enough grip to keep them moving onto the table.
“We needed a more aggressive belt, a belt with more grip to provide enough friction to keep the assembly housings moving onto the table and off of the conveyor,” Amaro says. “When three or four of our housings back up into each other, half of which may already be on the table, that’s extra weight that the belt needs to keep moving to ensure all four move off the conveyor and provide enough space for the demagnetizer.
“Since the belt had a smooth sur- face, required for its previous applica- tion in our facility,” adds Amaro, “it would slip under the weight of the parts.”
Dorner provided Amaro with a selection of belt swatches to try out. He settled on a new high-friction Type 64 belt, 0.17 in. thick with a rough PVC top surface.
“The conveyor runs great and we’re pleased with the new processing line,” Amaro says. “And, our customer is happy because we’re able to confidently
Buhrke end-of-line technician Veljko Sisarica inspects airbag-housing assem- blies exiting the demagnetizer, and files down any remaining rough edges before sending the housings to the customer for e-coating.
supply them with more than 350,000 demagnetized housing assemblies per year.” MF
Article provided by Dorner Mfg. Corp., Hartland, WI: 262/367-7600; www.dornerconveyors.com.
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