Tuesday, August 28, 2012

Frequently Asked Questions An In-Depth Look: Magnetic Parts

The sPINner deburring system uses a magnetic field, so there are several factors to bear in mind when processing parts with a magnetic property. This document will help explain the variables to factor in when processing or evaluating magnetic parts.

The parts will “stick” to the bottom of the container:
When magnetic parts are introduced in the sPINner, they will be attracted to the magnetic field. As the magnetic field is concentrated to the bottom of the container, the parts will tend to “stick” to the bottom and the media will move around the part. Non-magnetic parts will tend to tumble with the media in a circular motion. Magnetic parts (depending on size and material) will tend to move slowly along the bottom of the container during machine operation in the opposite direction of the flow of media. This is caused by the parts trying to keep up with a very fast moving magnetic field. Heavy part or parts with very sharp edges that are pulled along the bottom of the container by the magnets may score the container and may wear through the container over time. If this happens the container will need replaced. Also fixturing the parts can limit their movement and decrease the wear on the container. See below the Fixturing section for more details.

The parts will stay in the magnetic field:
Parts with a magnetic property will be attracted to the magnetic field at the bottom of the container. The parts will stay in the strongest parts of the field during operation. The parts will tend to “line-up” with each other during processing. As the parts are responding to the magnetic field, they will attract other magnetic items in the container. This includes the magnetic media and other magnetic parts. The result is the parts developing a layer of media around them during processing and parts sticking to each other during processing.

Picture of fixture used with magnetic parts. Shown here with a few parts, each part is placed on an arm. The angle of the arms allows the parts to sit in the flow of the media while preventing the parts for damaging each other. Parts are free to rotate insuring that all areas are exposed to the action of the media.
Single layer of parts:
As parts with a magnetic property will tend to attract other magnetic items in the container including other parts, only a single layer of parts should be added to the container at a time. If parts are allowed to stack on top of each other, they will “stick” to each other and may prevent areas from being exposed to the media. 

Again, a fixture may be required to insure the parts do not damage each other during processing.

Sometimes it helps to fixture the parts in the processing container. This can provide some benefits and eliminate some issues that can arise when processing magnetic parts. Fixturing parts can keep them in the flow of the media to insure the parts are being subjected to the action of the media. Also, fixturing the parts will help keep them separated preventing any damage from other parts and eliminating any void areas (areas where the media cannot get to) from parts ”sticking” to each other.

Types of Fixtures: There are as many different types of fixtures as there are different parts.  Below are some common fixture types that can either provide a station for each part or simply “cage” of “harness” the parts.

These fixtures are placed in the processing container. Since the parts can no longer contact each other during processing, the potential to damage each other is eliminated. The associated batch size is limited to the number of stations on the fixture. Please note, many different designs of fixtures are possible and the design is dependent on the specific application. Precision Finishing can help design and build a fixture for any application. Call us for details.

Machine Speed: In order to minimize the cushioning effect of a layer of media around the part, the spin rate of the magnetic field may need to be slowed to about 30-40 Hz.

ID burrs are difficult with magnetic parts:
Because the sPINner uses a magnetic field to impart energy to the media as opposed to gravity or vibration, one advantage of the system is the ability to deburr ID areas. This benefit is primarily limited to non-magnetic parts. For a 

Heat build-up:
During processing the friction of the media and the parts will produce heat. For non-magnetic parts the amount of heat is less than that of magnetic parts. The reason is that the magnetic parts create vibration that generates heat. Processing times of 30 minutes and longer in the sPINner on magnetic parts will generate heat and the contents of the container should be allowed to cool prior to handling.

There are several materials that magnetic parts may be made of that will need a compound other than the soap and water solution typically used in the sPINner. When rust of other corrosion is a concern, a compound should be chosen that has an inhibitor. The results from using various compounds may vary greatly and should be carefully tested prior to mass usage. When using a compound other than the compounds provided by Precision Finishing, make sure to use a compound that has a flash point above 180° F. Also, make sure to try the compound in a little media first to help determine the effects on the media.

Please contact us at 317-842-8934 to discuss any specific application or if we can help provide any additional information on processing magnetic parts.

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