Mechanical Transmission System Components and Inspection - Tie Bars

Tie bars, also known as tie rods or guide pillars, play a crucial role in the mold-clamping device of injection molding machines. They serve two key functions: first, forming a rigid frame together with the templates; second, acting as guide pillars that restrict the sliding movement of the movable template along the tie bars. Due to the sliding fit between tie bars and templates, tie bars must withstand enormous tensile stress during mold clamping, as well as bending forces that support the templates and molds. Therefore, tie bars should possess the following characteristics:

1. High-quality carbon steel (such as 45# steel) is selected for manufacturing tie bars to ensure sufficient strength, rigidity, and wear resistance.

2. Tie bars are designed in a cylindrical shape, and their manufacturing process involves multiple steps, including blank forging, quenching and tempering, and machining.

3. The surface roughness Ra of the tie bar cylinder should not exceed 0.63μm. To enhance the wear resistance of the cylindrical working surface, surface treatment is required—either quenching, hard chrome plating, or ensuring a surface hardness of ≥45HRC.

4. A sliding fit is adopted between tie bars and templates, with the common fit systems being H7/f7 or H8/f7.

Inspection Content and Procedures for Tie Bars

The inspection of tie bars involves the following content and step-by-step procedures:

1. Pre-inspection Preparation

First, review technical documents such as assembly drawings and structural diagrams to understand and familiarize yourself with the structural components. Then, prepare for disassembly and assembly—this includes preparing the machine station for disassembly, as well as the tools and materials required for the process.

During disassembly, follow the principles outlined in the technical documents or disassembly drawings: disassemble external components first, then internal ones; disassemble upper parts first, then lower parts; and disassemble assemblies or sub-assemblies first, then individual parts or components.

2. Mounting for Measurement

After removing the tie bar, place it on the V-shaped iron pad of the workbench to prepare for measurement.

3. Bending Deformation and Radial Runout Inspection

Place the magnetic base and dial indicator on the workbench, and use them to measure the stress-concentrated points of the tie bar respectively. Adjust the distance between the dial indicator probe and the tie bar surface—ensure the probe is perpendicular to the axis of the tie bar and just makes contact with the surface. Rotate the dial indicator by hand to calibrate it to zero, then rotate the tie bar by hand. Observe the fluctuation of the dial indicator pointer to check for bending deformation or radial runout of the tie bar, and determine the outer diameter roundness tolerance.

4. Outer Diameter Wear and Roundness Inspection

Use a micrometer to measure the diameter of the tie bar. Conduct measurements at three separate sections (Sections A and C are marked in the diagram for reference) to inspect the outer diameter roundness and wear condition of the tie bar.