Abrasive Belt, Demagnetizer Prove Key to New Conveying Solution

May 1, 2011

Imagine trying to paint a surface sprinkled in saw dust. Obviously, before completing your first swipe of the brush you’ll need to clean the surface so it’s smooth and free of debris.

Buhrke Industries, an Arlington Heights, IL, a stamper/assembler and Tier One supplier to the automotive industry, experienced a similar challenge when manufacturing a custom part for an automotive-airbag assembly. Throughout the manufacturing process, the stamped assembly housing was becoming magnetized. As a result, the housing would attract small metallic dust and other particles, affecting overall appearance.

“When our customer would apply an e-coating to the part, these foreign particles often would result in a rough, substandard finish,” says Steve Amaro, a process engineer at Buhrke. “Clearly, we needed to demagnetize the parts to leave them with a smooth finish for the coating process, to make our customer happy.”

Magnetics—Cause and Effect

Amaro blames the magnetization issue on the company’s robotic-welding process used to assemble the airbag housing. To solve the problem, Amaro added a demagnetizer to the housing’s production line, and a conveyor to help improve product flow.

Buhrke end-of-line technician Veljko Sisarica inspects airbag-housing assemblies exiting the demagnetizer, and files down any remaining rough edges before sending the housings to the customer for e-coating.

The solution: Install a conveyor into the table that collects the housing assemblies as they slide down the chute, moving them a from the demagnetizer. To do so, Buhrke technicians cut out a space on the table to make room for a repurposed, spare conveyor the firm had inhouse (a Dorner 2200 Series center-drive model). The conveyor belt sits flush with the table. Two tall guide strips mount on the table alongside the 3-ft.-long, 6-in.-wide conveyor to keep housing assemblies positioned straight on the belt as they discharge onto the table.

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, ferromagnetism (according to Wikipedia) is the strongest type and is the only type that can produce 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 procedure for demagnetizing steel workpieces, according to an article on www.gaussbusters.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 demagnetized 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.

Getting a Better Grip

The conveyor worked as anticipated, but Amaro soon noticed that parts still would back up on the conveyor and fail to travel the proper distance a from the demagnetizer. As assembly housings began backing up on the 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 surface, required for its previous application 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 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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See also: Dorner Manufacturing Corporation