Effect of the variation of the gating system on the magnetic properties of injection molded pole-oriented rings

Abstract

<jats:title>Abstract</jats:title> <jats:p>The demand for contactless and wear-free sensor systems for the measurement of different physical values, such as angle, position, or speed has increased over the past years and opened up new application areas for magnetically sensitive sensors. Polymer bonded magnets can be used as signal transmitters in these sensor applications. In general, a high precision and good repeatability of the magnetic field is required, whereas in particular, a high peak flux density and accurate pole length of each pole is demanded for precise measurement. These polymer bonded magnets can be produced economically using the injection molding process with an integrated magnetization of the particles, such that a second magnetization step is unnecessary. This article addresses the influences of the gating system on the magnetic properties of multipolar bonded rings. Further, the particle orientation as well as filler content at different locations, and along the pathway are investigated. It was evaluated that the gating system significantly influences the pole length accuracy, as well as the peak flux density. However, differences in the filler orientation and content cannot be analyzed quantitatively.</jats:p>

Variation of the Pole Length in Pole-Oriented Bonded Rings due to the Location and Number of Injection Points

“…particle distribution remains constant over the whole cross section and at different locations of the flow path [28]. For the gating system with two injection points, short shots with five different changeover points without holding pressure are produced additionally in order to identify the pole length accuracy during the filling phase.…”

“…However, defining the degree of orientation of the particles is not possible due to the irregular particle shape. The filler particle orientation of multipolar bonded rings is discussed in more detail in [28]. Figures 10 and 11 show the magnetooptic analysis of the multipolar rings with a gating system with two injection points for different characteristic positions at the ring; Figure 12 shows the analysis for a ring with film gate.…”

“…Further, the influence of the process parameters, such as melt or mold temperature on the magnetic properties, was investigated [23][24][25]. For multipolar rings the influences of different processing parameters, different filler content, and different gating systems on the major quality criteria for encoder wheels, such as maximum flux density as well as pole length, are analyzed [26][27][28]. In particular, the melt and mold temperature lead to an improvement of the pole length accuracy, due to the lower viscosity or lower cooling rate at the surface area and resulting improvement of the orientation of the filler particles [27].…”

“…In particular, the melt and mold temperature lead to an improvement of the pole length accuracy, due to the lower viscosity or lower cooling rate at the surface area and resulting improvement of the orientation of the filler particles [27]. Furthermore, the pole length accuracy is highly influenced by the used gating system, in particular the number of injection points [28]. It was shown that a general deviation of smaller pole length in the pole with centrally located injection point and wider pole length in the pole with centrally located weld line can be detected [28].…”

“…Furthermore, the pole length accuracy is highly influenced by the used gating system, in particular the number of injection points [28]. It was shown that a general deviation of smaller pole length in the pole with centrally located injection point and wider pole length in the pole with centrally located weld line can be detected [28]. Generally, higher melt and mold temperature lead to a lower pole length deviation [27].…”