Procedure for Replacing the Barrel and Screw
Replacing the barrel and screw is a delicate and high-risk operation. The core principles are: "Disassemble while hot," "Strictly forbid forceful hammering," and "Align with reference marks." The main screw assembly must be extracted before the residual material has completely cooled and solidified. Furthermore, one must strictly adhere to procedures regarding power disconnection and lockout/tagout, the use of specialized tools for assembly and disassembly, and post-installation testing. Any forceful or violent manipulation could result in a bent screw or scratches on the inner wall of the barrel, causing irreversible damage to the equipment.
Pre-Disassembly Preparation: Safety and Barrel Purging
Prior to commencing disassembly, thorough preparation can prevent 80% of potential accidental damage.
Power Disconnection and Lockout/Tagout: Cut off the main power supply to the machine as well as the heating power supply. Affix a "Do Not Energize" warning sign to the control panel to ensure absolute safety.
Purging and Cleaning:
Stop the material feeding process and extrude as much of the residual material remaining in the barrel as possible.
If processing highly viscous or heat-sensitive materials-such as PC or PVC-it is imperative to feed a purging material (e.g., PS or PE) into the machine before shutting down. This "purging" process prevents residual material from solidifying and adhering firmly to the screw after cooling, which would make it extremely difficult to remove.
Tool Staging: Prepare the necessary tools: a specialized screw puller (extraction tool), a copper rod, a wooden mallet, heat-resistant gloves (asbestos gloves), wrenches, and hoisting equipment.
Strictly forbid the use of hard striking tools, such as iron hammers.
Temperature Control: Maintain the barrel in a heated state, or slightly increase the temperature in the front section of the barrel. This utilizes residual heat to soften the remaining material, thereby facilitating a smoother disassembly process.
Disassembly Steps: Core Operational Procedures
Depending on the type of equipment (single-screw or twin-screw), specific operational details may vary slightly; however, the underlying logic and sequence remain consistent.
Disassembling the Die Head and Connecting Components
Remove the pressure sensors, temperature sensors, and heating bands located at the die head section.
Loosen and remove the flange bolts securing the die head, then detach the entire die head assembly.
Clean While Hot: Immediately use a copper scraper to remove residual material from the die head orifice and the tip of the screw before it cools and hardens.
Separating the Drive Connection
Loosen the coupling set screws that connect the output shaft of the gearbox to the tail end of the screw. **Key Markings:** For twin-screw equipment, it is imperative to carefully observe and record the alignment markings between the splines at the rear of the two screws and the sleeve coupling (e.g., the alignment position of specific characters or symbols); this is critical for ensuring accurate phasing during reassembly.
Disengage the key connection at the rear of the screw to separate the screw from the drive shaft.
