Magnetic rods are widely used magnetic devices that generate strong magnetic fields to remove metal impurities and other magnetic substances from processed materials. Magnetic rods are a product with widespread applications.
Structure of Magnetic Rods
A magnetic rod consists of four parts: a stainless steel tube, permanent magnets, spacers, and stainless steel plugs. The magnetic rod ends are sealed with double-layer riveting and welding for better water resistance and durability.
The permanent magnets can be made of ferrite, neodymium iron boron (NdFeB), or samarium cobalt (SmCo). The choice of magnet depends on the required magnetic performance and the operating temperature of the product. Due to the protection of the outer stainless steel layer, the magnets inside the rod do not need surface coating.
Magnetic rods are mainly classified by their diameter and surface magnetic strength. The diameter range is generally 10mm to 100mm, and the surface magnetic strength range is typically 4000Gs to 12000Gs.
Buyers can choose based on their actual needs. Using magnets of the same grade, larger diameters result in stronger surface magnetism. The two ends of the rods can also be made in different shapes according to customer requirements.
Magnet Selection for Magnetic Rods
Generally, N35 NdFeB magnets are used in magnetic rods. To achieve a surface magnetic strength of over 12000 Gauss on a 1-inch diameter magnetic rod, N40 or higher grade neodymium magnets are required.
When temperatures exceed 150°C, high-temperature resistant samarium cobalt magnetic rods are usually chosen. However, SmCo magnetic rods are not selected for large-diameter rods.
Selecting Magnetic Rods
Different magnetic strengths can attract different types and sizes of metal impurities. Selection should be based on the user’s actual needs.
| Surface Magnetic Field Strength | Minimum Adsorbable Metal Particle Size |
| 1500 Gauss | >50um iron filings |
| 2500 Gauss | 20~50um iron filings |
| 5000 Gauss | Submicron iron filings, weak magnetic particles, such as 304 stainless steel |
| 10000~20000 Gauss | Fine weak magnetic particles, rust, etc. |
| In battery and pharmaceutical industries, even small iron impurities can have a significant impact, so magnetic rods with around 12,000 Gauss should be chosen.
| For attracting 304 stainless steel, which is austenitic stainless steel with weak magnetism, magnetic rods with a strength of 12000 Gauss or higher are required.
| For materials with a high content of metal impurities, such as agricultural products, the stronger the magnetic properties, the more difficult it becomes to remove the metal impurities. A reasonable approach is to use lower-strength rods in the early stages of processing to attract larger metal objects, and higher-strength rods in later stages to attract smaller metal objects or weakly magnetic substances.
Demagnetization Rate of Magnetic Rods
The price difference in magnetic rods is mainly due to their demagnetization rates. Some high-quality manufacturers have an annual demagnetization rate of about 1%. Better-quality rods have better permanent magnetism, while lower-quality rods demagnetize quickly.
The main factors causing demagnetization are:
| High temperature: Below 80°C, temperature has limited impact to the magnetic properties; above 80°C, high-temperature resistant magnets should be chosen.
| Material quality: More impurities in the magnet result in weaker magnetic retention.
| Strong external magnetic fields: External fields stronger than the rod’s strength can easily cause demagnetization.
| Impact: Frequent high-frequency impacts can affect magnetic properties. Avoid installing near vibration sources.
| Humidity: Humid environments can affect the magnetic force of the rod.
Frequency of Checking Magnetic Rods
Surface magnetic strength is normally checked using a Gauss meter, with records kept. Under normal usage conditions, magnetism weakens slowly; the typical checking frequency is once every 1 to 3 months. In harsh environments like high temperature or vibration, more frequent checks are recommended.
Magnetic rods should be replaced when their magnetic field strength decreases by more than 30% of the initial strength.
Cleaning Metal Impurities from Magnetic Rods
Metal impurities on magnetic rods should not accumulate too much. Generally, when the attached metal impurities exceed 2mm in thickness, it significantly affects the attraction effect and cleaning is necessary.
Before cleaning, the attached metal impurities should be inspected. Prepare standard photo cards of different metal impurities and compare the objects on the magnetic rods with these cards to determine if the metal impurities level is normal. If screws or nuts are attracted, cause analysis for such unusual objects is needed.
Cleaning Methods
| Automatic cleaning: Automatic cleaning designs include an outer sleeve on the magnetic rod. When the rod is withdrawn, the magnetism in the sleeve disappears, and the attached metal impurities automatically fall off.
| Manual cleaning: Use disposable non-woven fabric for wiping and discarding after use.
Image Source: Goudsmitmagnets & Filtrasupply & Hsmagnets & Leyuangroup & Sinoneo & Web
