Magnet Patterns


Absolute Permeability

The permeability of a magnetic material expressed in actual physical units, not relative to permeability of free space. The permeability of magnetic materials is rarely expressed in terms of absolute permeability. The usual mode is in terms of relative permeability.

Air Gap

A non-magnetic discontinuity in a ferro-magnetic circuit. For example, the space between the poles of a magnet, although filled with brass, wood or any other non-magnetic material, is nevertheless called an air gap.


Refers to magnetic materials that are metallurgically non-crystalline in nature.


Having properties which are dependent upon direction within the material. See also, “Isotropic.”


A high-temperature conditioning of magnetic material to relieve the stresses introduced when the material was formed. To prevent oxidation, the annealing process is usually performed in a vacuum or inert-gas atmosphere.

AWG American Wire Gauge

A gauging system used to size magnet wire.

B – Magnetic Induction

The magnetic field induced by a field strength, H. It is the vector sum of each point within the substance, of the magnetic-field strength and resultant intrinsic induction. Magnetic induction is the flux-per-unit area normal to the direction of the magnetic path.

Bd – Remanent Induction

Any magnetic induction that remains in a magnetic material after removal of an applied saturating magnetic field, Hs. (Bd is the magnetic induction at any point on the demagnetization curve; measured in gauss or tesla.)

Bd/Hd – Slope of the Operating Line

The ratio of the remanent induction, Bd, to a demagnetizing force, Hd. It is also referred to as the permeance coefficient, shear line, load line or unit permeance.

Bd x Hd – Energy Product

Indicates the energy that a magnetic material can supply to an external magnetic circuit when operating at the Bd, Hd point on its demagnetization curve; measured in megagauss-oersteds (MGOe) or kilojoules per cubic meter (kJ/m3).

BHmax – Maximum Energy Product

The maximum product of (Bd x Hd) which can be obtained on the demagnetization curve, i.e. in the second quadrant of the hysteresis loop.

Bis (or Js) – Saturation Intrinsic Induction

The maximum intrinsic induction possible in a material.

Bg – Magnetic Induction in the Air Gap

The average value of magnetic induction over the area of the air gap, Ag; or the magnetic induction measured at a specific point within the air gap; measured in gauss.

Bi (or J) – Intrinsic Induction

The contribution of the magnetic material to the total magnetic induction, B. It is the vector difference between the magnetic induction in the material and the magnetic induction that would exist in a vacuum under the same field strength, H. This relation is expressed by the equation: Bi = B – Hem where; Bi = intrinsic induction in gauss (or tesla); B = magnetic induction in gauss (or tesla); Hem = field strength in oersteds (or kA/m).

Br – Residual Induction (or Flux Density)

The magnetic induction corresponding to zero magnetizing force in a magnetic material after saturation in a closed circuit; measured in gauss or tesla.

BH Loop

A hysteresis loop of four quadrants. In practice, usually only the first and second or, more typically, only the second quadrant is shown.

CGS System

Centimeter-gram-second system, the oldest system of units and the one used for presenting powder core data. Only the units for magnetizing force, magnetic-flux density, length, mass and time are utilized.

Closed-Circuit Condition

Exists when the external flux path of a permanent magnet is confined within high permeability material.

Coercive Force, Hc

The value of demagnetizing force that reduces residual induction to zero. The maximum coercive force, as measured on a saturated magnet, is proportional to the remanent flux density. See “flux density.” It is expressed in oersteds or kiloamps per meter (kA/m).

Coercivity, Hci or iHc

The resistance of a magnetic material to demagnetization. It is equal to the value of H where the intrinsic curve intersects the H axis in the second quadrant of the hysteresis loop. It is expressed in oersteds or kiloamps per meter (kA/m).

Curie Temperature, Tc

The temperatures above which ferromagnetic materials become paramagnetic, losing substantially all of their permanent magnetic properties. Some references state that materials become nonmagnetic above the Curie temperature.

Demagnetization Curve

That portion of the hysteresis loop which lies between the residual induction point, Br, and the coercive-force point, Hc (normal curve) or Hci (intrinsic curve). The coordinates Bd and Hd designate points on the normal curve.


A material condition where a ringing AC field has reduced the remanent induction to or near zero. A ringing AC field is a continually decreasing sinusoidal field. A pulsed DC field can be used to achieve gross demagnetization, but with much effort and with residual local magnetization.


A magnet formed by current flowing through a conductor. The electrical conductor may be wire, copper plate or strips of foil and may exist with a permeable material such as steel to conduct the field to desired areas. The magnetic field exists only so long as current flows through the coil.

Energy Product

The energy that a magnetic material can supply to an external magnetic circuit when operating at a point on its demagnetization curve; measured in megagauss-oersteds (MGOe). See also BHmax.


A soft ferrite material that has lower permeability with very low eddy-current loss. The common ferrites are nickel-zinc, manganese-zinc and magnesium-zinc ferrite.


Ferromagnetic materials have atomic fields that align themselves parallel with externally-applied fields creating a total magnetic field much greater than the applied field. Ferromagnetic materials have permeabilities much greater than one. Above the Curie temperature, the ferromagnetic materials become paramagnetic.

Flux in magnetics, the Magnetic Field

Flux implies flow, which is not the case in magnetics. That is, no one has measured a magnetic “flow.” Flux is represented conceptually as “magnetic lines of force.” Flux density is measured in gauss or tesla.


An instrument that measures the change of flux linkage with a search coil. The current in the search coil caused by relative motion with the magnet is integrated (totalized). Using a calibrated coil allows calculation of field and magnet properties.


The unit of magnetic induction, B, in the CGS (centimeter-gram-second) electromagnetic system. One gauss is equal to one maxwell per square centimeter or 10-4 tesla.


An instrument that measures the instantaneous value of magnetic induction, B. Its principle of operation is usually based on one of the following: the Hall effect, nuclear magnetic resonance (NMR), or the rotating-coil principle.

Hc – Coercive Force

Equal to the demagnetizing force required to reduce residual induction, Br, to zero; measured in oersteds (or kA/m). The material characteristic of coercivity is taken as the maximum coercivity — that value of H required to reduce the residual induction to zero after the material has been saturated (fully magnetized).

Hci – Intrinsic Coercive Force

Indicates a material’s resistance to demagnetization. It is equal to the demagnetizing force which reduces the intrinsic induction, Bi, in the material to zero; measured in oersteds (or kA/m). As for coercivity, the maximum value of intrinsic coercivity is obtained after the material has been saturated (fully magnetized).


The value of H corresponding to the remanent induction, Bd; measured in oersteds (or kA/m).

Hs – Net Effective Magnetizing Force

The magnetizing force required in the material, to magnetize to saturation; measured in oersteds (or kA/m).


Common symbol for maximum applied magnetizing force.

Hysteresis and Hysteresis Loss

Hysteresis is the tendency of a magnetic material to retain its magnetization. Hysteresis causes the graph of magnetic flux density versus magnetizing force to form a loop rather than a line. The area of the loop represents the difference between energy stored and energy released per unit volume of material per cycle. This difference is called hysteresis loss. It is one of two major loss mechanisms in inductor cores; the other is eddy current loss. Hysteresis loss is measured at low frequency to distinguish it from eddy current loss.

Hysteresis Loop

A closed curve obtained for a material by plotting (usually to rectangular coordinates) corresponding values of magnetic induction, B, for ordinate and magnetizing force, H, for abscissa when the material is passing through a complete cycle between definite limits of either magnetizing force, H or magnetic induction, B. If the material is not “driven” to saturation, it is said to be on a minor loop.

Hysteresis, Magnetic

The property of a magnetic material by virtue of which the magnetic induction for a given magnetizing force depends upon the previous conditions of magnetization.


An instrument that draws hysteresis loops. Also called permeameter.


Having magnetic properties that are independent of magnet orientation. Most magnetic materials are anisotropic as cast or powdered: each crystallite has a preferred direction of magnetic orientation. If the particles are not physically oriented during manufacture of the magnet, this results in a random arrangement of the particles and magnetic domains and produces isotropic magnet properties. Conversely, orienting the material during processing results in an anisotropic magnet.


1 kilogauss is equal to 1,000 gauss.

Knee (of the demagnetization curve)

In the second and fourth quadrants of the hysteresis loop, some materials such as ferrite and rare-earth magnets exhibit a distinct “knee” or rapid change in slope of the intrinsic curve. The location of the knee is of interest to designers. If the magnet operates below the knee, irreversible loss of magnetic output occurs.

Magnetic Circuit

The combination of magnet, permeable flux carriers and air gaps through or around which the magnetic flux path passes.

Magnetic Energy

The product of the flux density (B) in a magnetic circuit and the (de)magnetizing force (H) required to reach that flux density.

Magnetic Circuit

The combination of magnet, permeable flux carriers and air gaps through or around which the magnetic flux path passes.

Magnetic Path

The route magnetic flux follows in a magnetic circuit.

Poles, North and South Magnetic

The north pole of a magnet, or compass, is attracted toward the geographic North Pole of the Earth. If you were to use a compass to determine polarity, the south pole of the compass will point towards the north pole of a magnet. The north pole of a compass is more properly called the north-seeking pole because it seeks out the geographical North Pole. Few people take the time to say “north-seeking pole.” If you were to use a gauss meter, using an axial probe, the side of the magnet that gives you a positive reading will be the north pole.

North pole = north-seeking pole = north magnetic pole = positive gauss-meter reading


The magnetic induction remaining in a material when the magnetizing force has been reduced to zero. Also called “remanent induction.”

Residual Flux

The flux that remains in a core when an applied MMF (magnetomotive force) is returned to a value of zero.

Return Path

A magnet typically forms only part of the magnetic circuit. Soft magnetic materials such as steels are used to carry the magnetic flux to the gap or working region for interaction with other components. This conductor of magnetic flux is referred to as the return path. It is usually designed to minimize fringing and leakage flux.


Treatment of a magnetic material, designed to increase the permanency (stability) of its magnetic properties or condition in an application, by causing the loss prior to or during installation or assembly, but prior to testing and use.

Tc – Curie Temperature

The transition temperature above which a material loses its (ferro) magnet properties. Most references state that the ferromagnetic material becomes paramagnetic (weakly magnetic).

Tmax Service Temperature

The maximum temperature to which the magnet may be exposed with no significant long-range instability or structural changes. A proposed magnetic definition is that the hysteresis normal curve is substantially a straight line in the second quadrant up to the Tmax temperature and becomes curved above Tmax.

Temperature Coefficient

A factor that describes the reversible change in a magnetic property with a change in temperature. The magnetic property spontaneously returns when the temperature is cycled to its original point, so long as a limit condition is not exceeded (see note below). It usually is expressed as the percentage change per unit of temperature over a specified temperature range.

Note: above (or below) a critical temperature, dependent upon the material and its magnetic characteristics and magnetic circuit, an irreversible loss may take place, which is recovered when the magnet is re-saturated.

Temperature Stabilization

After manufacture, many types of hard and soft magnetic materials can be thermally cycled to make them less sensitive to subsequent temperature extremes.


MKSA (SI) unit for magnetic flux density, defined by Faraday’s Law. A tesla represents a volt-second per square meter per turn. One tesla equals 10,000 gauss.


The practical unit of magnetic flux. It is the amount of magnetic flux which, when linked at a uniform rate with a single-turn electric circuit during an interval of one second, will induce in this circuit an electromotive force of one volt. One weber = 108 maxwells.


A process of holding a material at a temperature mean, but below its melting point, the objective being to permit stress relaxation without distortion of shape. It is often used on molded articles to relieve stresses set up by flow into the molds.

Back Pressure

The viscosity resistance of a material to continued flow when a mold is closing. In extrusion, the resistance to the forward flow of molten material.


In a reinforced plastic, the continuous phase which holds together the reinforcement.


A bubble on the outside of the part.


Gas trapped inside the part.


White, brown, or black area in the part. Burns are caused by a dirty mold or vent, no vent, wet material, high temperatures or a fill rate that is too fast.


(v.) To prepare sheets of material with pressure between two or more counter-rotating rolls.
(n.) The machine performing this operation.


Depression in a mold made by casting, machining, hobbing, or a combination of these methods; depending on number of such depressions, molds are designated as single-cavity or multi-cavity.

Clamping Pressure

In injection molding and in transfer molding, the pressure that is applied to the mold to keep it closed, in opposition to the fluid pressure of the compressed molding material.

Coefficient of Expansion

The fractional change in length (sometimes volume, specified) of a material for a unit change in temperature. Values for plastics range from 0.01 to 0.2 mils/in., C.

Cold Look

Frosty appearance on parts. Could be the beginning of underfill.

Cold Slug

The first material to enter an injection mold; so called because in passing through a sprue orifice it is cooled below the effective molding temperature.

Cold-Slug Well

Space provided directly opposite the sprue opening in an injection mold to trap the cold slug.


A thoroughly integrated mixture of (a) polymers(s) with all the materials necessary for the finished product.

Compression Mold

A mold that is open when the material is introduced and which shapes the material by heat and by the pressure of closing.


A foreign substance in the material such as metal, cardboard or other matter.


For a container, the shape in which various cross-sections have a common center.


The subjection of a material to a stipulated treatment so that it will respond in a uniform way to subsequent testing or processing. The term is frequently used to refer to the treatment given to specimens before testing.


See Sink Mark


The dimensional change with time of a material under load, following the initial instantaneous elastic deformation. Creep at room temperature is sometimes called Cold Flow.


A state of molecular structure in some resins which denotes uniformity and compactness of the molecular chains forming the polymer. It normally can be attributed to the formation of solid crystals having a definite geometric form.


To change the properties of a polymeric system into a more stable, usable condition by the use of heat, radiation, or reaction with chemical additives. NOTE: Cure may be accomplished, for example, by removal of solvent or by cross-linking.


The complete, repeating sequence of operations in a process of part of a process. In molding, the cycle time is the period, or elapsed time, between a certain point in one cycle and the same point in the next.


Refers to the shape of a container that has a circular cross section parallel to the minor axis and a rectangular cross section parallel to the major axis.


Weight per unit volume of a substance, expressed in grams per cubic centimeter, pounds per cubic foot, etc.

Dimensional Stability

Ability of a plastic part to retain the precise shape in which it was molded, fabricated, or cast.


The degree of taper of a side wall or the angle of clearance designed to facilitate removal of parts from a mold.

Drag Marks

Scratch-type marks caused by foreign objects present during the molding process.

Double Cycle

A part that has been cycled twice. Part may have flash, appear top heavy, flat, etc.

Ejector Pin

A pin or thin plate that is driven into a mold cavity from the rear as the mold opens, forcing out the finished pieces. Also Knockout Pin.


A material which at room temperature stretches under low stress to at least twice its length and snaps back to the original length upon release of stress.


The fractional increase in length of a material stressed in tension.


Enclosing an article (usually an electronic component or the like) in a closed envelope of plastic, by immersing the object in a casting resin and allowing the resin to polymerize or, if hot, to cool.


The compacting of a plastic material and the forcing of it through an orifice in more or less continuous fashion.


To work a material into a finished form by machining, forming, or other operation or to make flexible film or sheeting into end products by sewing, cutting, sealing, or other operation.

Family Mold

A multi-cavity mold where each of the cavities forms one of the component parts of the assembled finished object.


The plastic forming the opening of a container shaped to accommodate a specific closure. Also, the ultimate surface of an article.


Extra plastic attached to a molding along the parting line; it must be removed before the part can be considered finished.

Flexural Modulus

A measure of the strain imposed in the outermost fibers of a bent specimen.

Flexural Strength

The strength of a material in blending, expressed as the tensile stress of the outermost fibers of a bent test sample at the instant of failure. With plastics, this value is usually higher than the straight tensile strength.

Flow Line

A mark on a molded piece made by the meeting of two flow fronts during molding.

Flow Mark

Wavy surface appearance of an object molded from thermoplastic resins caused by improper flow of the resin into the mold.


In injection and transfer molding, the orifice through which the melt enters the cavity. Sometimes the gate has the same cross-section as the runner leading to it; often, it is severely restricted.

Guide Pins

Devices that maintain proper alignment of force plug and cavity as mold closes.


The resistance of a plastic material to compression and indentation. Among the most important methods of testing this property are Brinell hardness, Rockwell hardness and Shore hardness.


Conical feed reservoir into which molding powder is loaded and from which it falls into a molding machine or extruder, sometimes through a metering device.

Hot-Runner Mold

A mold in which the runners are insulated from the chilled cavities and are kept hot. Parting line is at gate of cavity, runners are in separate plate(s), so they are not, as is the case usually, ejected with the piece.

Injection Mold

A mold into which a plasticated material is introduced from an exterior heating cylinder.

Injection Molding

A molding procedure whereby a heat-softened plastic material is forced from a cylinder into a relatively cool cavity which gives the article the desired shape.

Injection-Molding Pressure

The pressure on the face of the injection ram at which molding material is injected into a mold. It is usually expressed in psi.


An integral part of a plastics molding consisting of metal or other material which may be molded into position or may be pressed into the molding after the molding is completed.

Knit Lines

A mark on a molded plastic piece made by the meeting of two flow fronts during the molding operation.

Melt Flow

The flow rate obtained from extrusion of a molten resin through a die of specified length and diameter under prescribed conditions of time, temperature and load as set forth in ASTM D1238.

Melt Temperature

The temperature of the molten plastic just prior to entering the mold or extruded through the die.

Melting Point

The temperature at which solid and liquid forms of a substance are in equilibrium. In common usage the melting point is taken as the temperature at which the liquid first forms in a small sample as its temperature is increased gradually.

Molding Pressure

The pressure applied to the ram of an injection machine or press to force the softened plastic completely to fill the mold cavities.

Movable Platen

The large back platen of an injection-molding machine to which the back half of the mold is secured during operation. This platen is moved either by a hydraulic ram or a toggle mechanism.

Multi-Cavity Mold

A mold with two or more mold impressions, i.e., a mold which produces more than one molding per molding cycle.


The hollow-cored metal nose screwed into the extrusion end of (a) the heating cylinder of an injection machine or (b) a transfer chamber where this is a separate structure. A nozzle is designed to form under pressure a seal between the heating cylinder or the transfer chamber and the mold. The front end of a nozzle may be either flat or spherical in shape.


The generic name for all synthetic fiber-forming polyamides; they can be formed into monofilaments and yarns characterized by great toughness, strength and elasticity, high melt point, and good resistance to water and chemicals. The material is widely used for bristles in industrial and domestic brushes, and for many textile applications; it is also used in injection molding gears, bearings, combs, etc.


The alignment of the crystalline structure in polymeric materials so as to produce a highly uniform structure. Can be accomplished by cold drawing or stretching during fabrication.

Parting Line

Mark on a molding or casting, where the halves of its mold met during the manufacturing process.


To soften a material and make it plastic or moldable, either by means of a plasticizer or the application of heat.


A polymer in which the structural units are linked by amide or thioamide groupings. Many polyamides are fiber forming.


A polymer prepared by the polymerization of butene as the sole monomer.


A resin formed by the reaction between a dibasic acid and a dihydroxy alcohol, both organic. Modification with multi-functional acids and/or bases and some unsaturated reactants permit cross-linking to thermosetting resins. Polyesters modified with fatty acids are called alkyds.


A thermoplastic material composed by polymers of ethylene. It is normally a translucent, tough, waxy solid which is unaffected by water and by a large range of chemicals.


A high-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the mer; e.g., polyethylene, rubber, cellulose. Synthetic polymers are formed by addition or condensation polymerization of monomers. If two or more monomers are involved, a copolymer is obtained. Some polymers are elastomers, some plastics.


A tough, lightweight rigid plastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst at relatively low pressures and temperatures.


A water-white thermoplastic produced by the polymerization of styrene (vinyl benzene). The electrical insulating properties of polystyrene are outstandingly good and the material is relatively unaffected by moisture.


A family of resins produced by reacting diisocyanate with organic compounds containing two or more active hydrogen to form polymers having free isocyanate groups. These groups, under the influence of heat or certain catalysts, will react with each other, or with water, glycols, etc., to form a thermosetting material.


Cleaning one color or type of material from the cylinder of an injection-molding machine or extruder, by forcing it out with the new color or material to be used in subsequent production. Purging materials are also available.


Irregular indentation or distortion when parts resist being ejected from the cavity.


Plastic that is re-introduced into the production stream.

Reinforced Plastics

A plastic with high-strength fillers embedded in the composition, resulting in some mechanical properties superior to those of the base resin.


A strong inert material bound into a plastic to improve its strength, stiffness, and impact resistance. Reinforcements are usually long fibers of glass, sisal, cotton, etc. in woven or non-woven form. To be effective, the reinforcing material must form a strong adhesive bond with the resin.

Relative Humidity

Ratio of the quantity of water vapor present in the air to the quantity which would saturate it at any given temperature.


Any of a class of solid or semi-solid organic products of natural or synthetic origin, generally of high molecular weight with no definite melting point. Most resins are polymers.

Rockwell Hardness

A common method of testing a plastic material for resistance to indentation in which a diamond or steel ball, under pressure, is used to pierce the test specimen. The load used is expressed in kilograms; a 10-kilogram weight is first applied and the degree of penetration noted. The so-called major load (60 to 150 kilograms) is next applied and a second reading obtained. The hardness is then calculated as the difference between the two loads and expressed with nine different prefix letters to denote the type of penetrator used and the weight applied as the major load.


Any product of a molding operation that is not part of the primary product. In compression molding, this includes flash, culls, runners, and is not reusable as a molding compound. Injection molding and extrusion scrap (runners, rejected parts, sprues, etc.) can usually be reground and remolded.


The yield from one complete molding cycle, including scrap.


Contraction of a container upon cooling.

SI Units

The International System of Units (Systems International) is a modernized version of the metric system established by international agreement. It provides a logical and interconnected framework for all measurements in science, industry and commerce. Officially abbreviated SI, the system is built upon a foundation of seven base units.

Sink Mark

An imperfection, a depression in the surface of a molded material where it has retracted from the mold. A shallow depression or dimple on the surface of an injection-molded part due to collapsing of the surface following local internal shrinkage after the gate seals. May also be an incipient short shot.

Specific Gravity

The density (mass per unit volume) of any material divided by that of water at a standard temperature, usually 4 degrees C. Since water’s density is nearly 1.00 g./cc., density in g./cc. and specific gravity are numerically nearly equal.


Silver streaks appearing on the part due to wet material, heat or too much mold release spray.

Stress Crack

An external or internal crack in a plastic caused by tensile stresses less than its short-time mechanical strength.

Stripper Plate Mold

A plate that strips a molded piece from core pins or force plugs. The stripper plate is set into operation by the opening of the mold.

Thermal Conductivity

Ability of a material to conduct heat; physical constant for quantity of heat that passes through a unit cube of a substance in a unit of time when difference in temperature of two faces is one degree.


Capable of being repeatedly softened by heat and hardened by cooling (n.) A material that will repeatedly soften when heated and harden when cooled. Typical of the thermoplastics family are the styrene polymers and copolymers, acrylic, cellulosic, polyethylene, vinyl, nylon, and the various fluorocarbon materials.

Tie Bars

Bars which provide structural rigidity to the clamping mechanism often used to guide platen movement.


A specified allowance for deviations in weighing, measuring, etc., or for deviations from the standard dimensions or weight.


In injection molding, failure to fill the mold completely.


In a mold, a shallow channel or minute hole cut in the cavity to allow air to escape as the material enters.

Virgin Material

A plastic material in the form of pellets, granules, powder, flock, or liquid that has not been subjected to use or processing other than that required for its initial manufacture.


Internal friction or resistance to flow of a liquid. The constant ratio of shearing stress to rate of shear. In liquids for which this ratio is a function of stress, the term “apparent viscosity” is defined as the ratio.


(1) In a solid plastic, an unfilled space of such size that it scatters radiant energy such as light. (2) A cavity unintentionally formed in a cellular material and substantially larger than the individual cells.


Dimensional distortion in a plastic object after molding.