Self-Lubricating Graphite Bronze Bearings in Rotary Vertical Plastic Injection Molding Machines

Applications, Material Selection, and Engineering Guidelines

Rotary type vertical plastic injection molding machines operate under high clamping forces, intermittent rotation, and repetitive sliding motion. In these environments, conventional grease-lubricated bearings often fail due to contamination, lubricant loss, or maintenance limitations.

For this reason, many machine builders adopt self-lubricating graphite plugged bronze bearings (also called oilless bearings) to ensure stable operation and reduced maintenance.

These bearings combine a high-strength bronze matrix with embedded solid graphite lubricants, allowing them to operate under high load, low speed, and high temperature conditions without external lubrication.

Key Applications of Graphite Bronze Bearings in Rotary Vertical Injection Molding Machines

1. Rotary Table Center Shaft Bearings

The rotary table system is the core feature of vertical injection molding machines. It allows multiple molds to rotate between injection, loading, and unloading stations.

Bearing Function

• Support the weight of the rotary table and molds

• Maintain smooth indexing rotation

• Absorb axial and radial loads

Typical Bearing Types

• Graphite plugged thrust bushings

• Large bronze sliding bearings

• Self-lubricating wear plates

Recommended Materials

• C86300 Manganese Bronze

• CuZn25Al5Mn4Fe3 high-strength brass

Reason for Selection

• Excellent load capacity

• Strong resistance to impact and wear

• Good performance under intermittent motion

2. Tie Bar Guide Bushings (Clamping Unit)

The four-column clamping system ensures precise mold alignment during opening and closing.

Operating Conditions

• Repetitive sliding motion

• Medium-to-high loads

• Low sliding speed

Typical Bearing Design

• Graphite plugged guide bushings

• Flanged bronze bushings

Recommended Materials

• SAE660 / C93200 bearing bronze

• CuSn7Zn4Pb7 leaded tin bronze

Advantages

• Low friction coefficient

• Good anti-seizure performance

• Excellent machinability

3. Mold Slider and Slide Plate Systems

Mold sliders are used for side-core pulling mechanisms in injection molds. These sliding components experience frequent movement and high surface pressure.

Typical Bearing Components

• Graphite bronze wear plates

• Self-lubricating slide blocks

Recommended Materials

• C95400 aluminum bronze

• CuAl10Ni5Fe4 nickel aluminum bronze

Engineering Benefits

• High hardness and wear resistance

• Excellent load carrying capacity

• Superior resistance to shock loads

4. Ejector System Guide Bushings

The ejector system pushes molded parts out of the cavity after cooling. Guide bushings ensure precise linear motion of the ejector plates.

Operating Conditions

• Repetitive reciprocating motion

• Medium loads

• Clean working environment required

Recommended Materials

• CuSn8

• CuSn12

These materials provide excellent wear resistance and dimensional stability while preventing lubrication contamination of molded plastic parts.

5. Injection Unit Sliding Mechanisms

The injection carriage moves forward and backward during injection cycles.

Typical Applications

• Injection unit guide rails

• Carriage sliding blocks

• Machine base wear plates

Recommended Materials

• CuSn12 + graphite

• C86300 graphite bronze

These alloys provide stable operation under heat exposure and intermittent loads.

Bronze Material Selection for Graphite Plugged Bearings

Working Principle of Graphite Plugged Bronze Bearings

Graphite bronze bearings consist of:

• Bronze metal matrix → provides structural strength

• Solid graphite plugs → provide continuous lubrication

During operation, microscopic graphite particles transfer to the sliding surface and form a solid lubricating film, which reduces friction and prevents metal-to-metal contact.

Typical performance parameters:

Why Self-Lubricating Bearings Are Ideal for Injection Molding Machines

Key advantages include:

• Maintenance-free operation (no grease required)

• Resistance to plastic contamination

• High load capacity in low-speed motion

• Long service life in high-temperature environments

• Improved machine reliability

For rotary vertical injection molding machines, these bearings are widely used in rotary tables, clamping systems, mold slides, and ejector assemblies, making them an essential component for modern injection molding equipment.

✅ Conclusion

Self-lubricating graphite bronze bearings play a critical role in ensuring the durability and efficiency of rotary type vertical plastic injection molding machines.

Proper material selection—such as C86300 for heavy loads, SAE660 for guide bushings, and aluminum bronze for sliding plates—significantly improves wear resistance, machine stability, and maintenance intervals.

For manufacturers and maintenance engineers, selecting the right graphite plugged bronze bearing solution can dramatically extend the service life of critical injection molding machine components.