Industrial Solenoid Basics
Industrial Work Solenoid Construction and Basic Operation
A typical industrial work solenoid consists of the following main elements: a cylindrical coil, a steel or iron frame or shell, a steel or iron plunger and optionally, a stationary magnetic pole/travel stop. A magnetic field is generated within the industrial work solenoid by passing electrical current through the coil. The frame or shell surrounds the coil, providing a flux path. In effect, it focuses the magnetic field produced by the coil. The plunger, being made of highly magnetic material, reacts to the magnetic field by attempting to move to the center of the coil. The plunger will travel to the centered position unless stopped by a load which exceeds the industrial work solenoid's force capability or the plunger contacts the stationary pole/travel stop.
Industrial Work Solenoid Operation Specifics
The force generated by an industrial work solenoid is dependent upon the current flowing though the coil windings. The average current in the coil of a DC industrial work solenoid is the simple result of average source voltage divided by the resistance of the coil. DC industrial work solenoids may be powered from pure DC sources such as batteries or electronic power supplies, or from time varying sources so long as the source is single polarity. The most common time varying sources are rectified AC and Pulse Width Modulation (PWM) type electronic controls. When powered from a time varying source, current flows in proportion to the average value of the source voltage. The force developed by the industrial work solenoid is thus dependent upon the average value of the source voltage.
Because the current in the coil of a DC industrial work solenoid never reverses, the magnetic field never reverses either. In most cases the current and therefore the magnetic field is nearly constant. This is a significant factor in the design and construction of DC industrial work solenoids. The contrasting situation is an AC industrial work solenoid in which the current and resultant magnetic field are constantly reversing direction. This field reversal results in significant losses in the metal structure unless stringent precautionary steps are taken during design and fabrication. Without getting into details, it is sufficient to say that the design of AC industrial work solenoids requires dealing with significant constraints on the configuration of the metal components. DC industrial work solenoids avoid these constraints, allowing use of common wrought steels in their construction.
Because the metal components of a DC industrial work solenoid can be fabricated from wrought steel, standard machining and metal forming processes can shape individual components. The basic performance of the industrial work solenoid force developed versus plunger position, can be influenced dramatically by shaping the plunger and stationary pole face in particular. By using advanced analysis tools like magnetic finite element analysis (FEA) coupled with industrial work solenoid design experience the shape of the metal components of the solenoid can be developed to yield optimum performance for any specified application.
Industrial Work Solenoid Application Considerations
Industrial work solenoids can be designed to accept attachment of the load to the pulling or pushing end of the plunger. For some applications the plunger assembly is designed to accept load attachments at both ends. Properly designed and applied, a linear industrial work solenoid will generate forces sufficient to move the applied load through the specified stroke and in the specified period of time. It must do so under all specified operating conditions.
There are several issues that must be considered when any customer application is being reviewed:
• The method of connecting the load to the industrial work solenoid must be developed with consideration in mind that side loads will be detrimental to industrial work solenoid life if not properly accounted for. Furthermore, if the installation causes a binding condition anywhere within the required operating stroke, excessive wear and reduced operating life will result.
• Industrial work solenoid holding force typically suffers dramatically if the plunger is not allowed to come into contact with the stationary pole piece. If the industrial work solenoid will be required to generate a sustained holding force after it has moved the load through its working stroke, then, it most likely will be a requirement that the plunger seat itself is at the end of travel as opposed to being stopped by the load. There are exceptions to this general rule. They must be dealt with through detail application and design analysis.
• Excessive force can cause its own set of problems. If under any operating conditions, the industrial work solenoid generates forces far in excess of what is required to move the load, then there will be excess kinetic energy developed in the plunger as it accelerates through its stroke. This excess kinetic energy needs to be dissipated in a manner that is not harmful to the industrial work solenoid or the mechanism it is driving.
• Electronic controls often make practical what otherwise may not be a practical application. In other cases they can serve to optimize the design of the total system through shaping or stabilizing the performance of the industrial work solenoid, reducing its size or a combination of these factors. While controls are an added cost item, they can often offset other costs by reducing the size and cost of the industrial work solenoid required for the task and/or by simplifying the entire mechanism of which the industrial work solenoid is a component.