The issue you raised regarding fixed-point configurations-specifically in the context of preventing common-mode interference in hot runner systems-indeed touches upon a critical detail in practical engineering implementation. I fully understand the desire to translate theoretical designs into reliable installation practices; a well-conceived fixed-point design can effectively suppress vibration and stress transmission, thereby indirectly enhancing the system's stability against interference.
In the context of preventing common-mode interference in hot runner systems, the primary function of fixed-point configuration is to ensure the reliability and consistency of single-point grounding for shielded cables. This prevents the formation of ground loops caused by loose connections, miswiring, or multiple contact points. A typical example involves consolidating the outer shielding layers of all temperature control signal cables at a single, designated grounding point (the PG busbar) located within the temperature control cabinet, where they are secured via crimped connections.
I. Key Principles for Fixed-Point Configuration
1. Single-Point Grounding for Shielding Layers
The outer shielding layers of all hot runner temperature control signal cables must be terminated at the temperature control cabinet side. After being crimped using copper lugs, they are collectively connected to the chassis ground (PG) busbar.
Grounding at the mold end or at any intermediate point along the cable run is strictly prohibited to prevent the formation of ground loops.
Example: A specific production line for automotive lamp covers mandates the following: the braided shielding layers of all 16 thermocouple cables must be crimped using Φ6 copper lugs and secured with M6 bolts to a yellow-and-green PG copper busbar* located in the bottom-right corner of the temperature control cabinet. This busbar is directly connected to the facility's main grounding electrode via a 10 mm² cable.
2. Independent Grounding for Functional Ground (SG)
The Signal Ground (SG) is routed out via isolation modules and connected separately to a dedicated Signal Ground busbar. This SG busbar is then connected to the PG busbar at a single point within the cabinet, thereby achieving physical separation between the FG (Functional Ground) and PG (Protective Ground) circuits.
II. Examples of Physical Mounting Structures
1. Standardized Mounting for Terminal Blocks
A dedicated shielding ground terminal zon should be established within the temperature control cabinet. This zone should utilize spring-clamp-style grounding terminals (e.g., the Weidmüller LG series) to ensure that the contact resistance of the shielding layer remains below 0.1 Ω. Each grounding point is assigned a unique identifier that corresponds one-to-one with the associated cable number, facilitating traceability.
2. Equipotential Bonding of Metal Conduits and Shielding Cable Trays
Signal cables running from the temperature control cabinet to the mold are routed through galvanized steel conduits. Each section of conduit is no longer than 2 meters and is connected to the equipment frame via a grounding clamp.
Conduit joints are bridged using braided copper straps (with a cross-sectional area of ≥ 4 mm²) to ensure equipotentiality throughout the entire run.
Practical Case Study: At a new energy battery housing injection molding line in Zhejiang, a circular equipotential bonding ring (30 × 3 mm red copper strip) was installed around the mold. All heating element junction boxes, sensor shields, and metal conduits were connected to this ring as a single reference point; this configuration reduced system common-mode interference noise by over 90%.
III. Key Control Points for Installation Procedures
|
Item |
Standard Requirement |
Inspection Method |
|
Shield Termination Crimping |
Copper lugs must be crimped securely with no loose strands |
Visual inspection + Tensile strength test |
|
Grounding Bolt Torque |
M6 bolts must be tightened to a torque of ≥ 5.5 N·m |
Verification using a torque wrench |
|
Contact Resistance |
Single-point ground resistance must be ≤ 0.2 Ω |
Measurement using a micro-ohmmeter |
|
Grounding Point Labeling |
Use yellow-and-green labels marked "PG Single-Point Ground" |
Process inspection |
Risk Warning: If the cable shield accidentally makes contact with the metal housing of a junction box at the mold end (e.g., due to a screw penetrating the cable jacket and touching the shield), a second grounding point will be created. This will significantly amplify common-mode currents and must be thoroughly diagnosed using an insulation resistance tester during the commissioning phase.
