1. Overview

The main production process of an extrusion blow molding machine includes:

1. Extrusion of the parison;
2. Mold closing to clamp the parison;
3. Mold transfer to the blowing position (for certain machine designs);
4. Air inflation to expand the parison;
5. Cooling and shaping of the product;
6. Mold opening;
7. Product removal.

Among these processes, the mold transfer system and mold opening/closing system are two of the most critical mechanical and control systems. They directly affect:

• Production cycle time;
• Product wall thickness uniformity;
• Mold positioning accuracy;
• Flash thickness and trimming requirements;
• Mold locking stability;
• Energy consumption;
• Machine service life.

With the development of blow molding technology toward larger sizes, higher speeds, and higher precision, traditional hydraulic control systems are gradually evolving toward:

• Servo hydraulic systems;
• Electro-hydraulic hybrid systems;
• Fully electric control systems.

2. Mold Transfer Control Methods

The mold transfer system is responsible for moving the mold between different positions during the blow molding process, including:

• Mold closing position;
• Blowing position;
• Cooling position;
• Product ejection position.

The main control methods include:

1. Hydraulic mold transfer system;
2. Servo motor + ball screw drive system;
3. Servo motor + rack and pinion drive system;
4. Servo hydraulic mold transfer system.

2.1 Hydraulic Mold Transfer System

(1) Working Principle

The hydraulic mold transfer system is the most traditional and widely used method in extrusion blow molding machines.

The basic structure is:

Hydraulic tank
      ↓
Hydraulic pump
      ↓
Proportional valve / servo valve
      ↓
Hydraulic cylinder
      ↓
Moving platen

The hydraulic cylinder extends and retracts to move the mold carrier or moving platen.

For large blow molding machines, the moving components may weigh several tons or even more than ten tons. Therefore, hydraulic systems have significant advantages due to their high force output capability.

(2) Advantages

① High Output Force

The greatest advantage of hydraulic systems is:

High force density and excellent load capability.

For large blow molded products such as:

• 50L drums;
• 200L chemical containers;
• Automotive fuel tanks;
• Large pallets;

the mold weight and moving inertia are very high.

Hydraulic cylinders can easily provide the required pushing force, which may reach tens or hundreds of tons.

② Strong Impact Resistance

During blow molding operation, the machine experiences:

• High-speed mold closing;
• Parison clamping impact;
• Mold temperature variation;
• Long continuous operation cycles.

Hydraulic systems have natural damping characteristics and can absorb mechanical impact.

Compared with rigid mechanical transmission systems, hydraulic systems provide:

• Better shock absorption;
• Higher reliability;
• Longer service life.

③ Cost Advantage

Traditional hydraulic systems have:

• Mature technology;
• Wide availability of components;
• Easy maintenance.

For large machines, hydraulic solutions are usually significantly less expensive than fully electric systems.

(3) Disadvantages

① Higher Energy Consumption

Traditional hydraulic systems usually use:

• Fixed displacement pumps;
• Constant pressure circuits.

Even when the machine is waiting for operation, the hydraulic motor may continue running.

Energy losses mainly come from:

• Overflow losses;
• Hydraulic oil heating;
• Pressure losses in pipelines.

Therefore, conventional hydraulic systems have relatively high energy consumption.

② Lower Motion Control Accuracy

Hydraulic systems are affected by:

• Oil temperature changes;
• Compressibility of hydraulic oil;
• Valve response characteristics;
• Internal leakage.

During high-speed mold movement, these factors may cause:

• Positioning deviation;
• Speed fluctuation;
• Mold impact during stopping.

③ Higher Maintenance Requirements

Regular maintenance is required, including:

• Hydraulic oil replacement;
• Filter cleaning;
• Seal inspection;
• Contamination control.

If hydraulic oil becomes contaminated, it may cause:

• Proportional valve sticking;
• Unstable movement;
• Reduced system pressure.

2.2 Servo Motor + Ball Screw Mold Transfer System

(1) Working Principle

This system uses a servo motor as the power source:

Servo motor
      ↓
Gear reducer
      ↓
Ball screw
      ↓
Linear motion
      ↓
Mold movement

A closed-loop control system with encoder feedback is used to achieve precise positioning.

(2) Advantages

① High Positioning Accuracy

Because servo systems provide:

• Position feedback;
• Speed feedback;
• Torque feedback;

the mold position can be accurately controlled.

Typical repeat positioning accuracy:±0.01～0.05 mm

This provides significant advantages for:

• Precision packaging bottles;
• Medical products;
• Multi-cavity molds.

② Flexible Motion Profile Control

The PLC system can define different motion stages:

• High-speed movement;
• Slow mold approach;
• Soft stop;
• Pressure holding.

For example:

Initial stage:

High-speed movement → Improve production efficiency

Approaching mold:

Low-speed movement → Reduce impact

Final stage:

Precise positioning → Ensure mold alignment accuracy

③ Excellent Energy Efficiency

Servo motors consume power mainly during movement.

Compared with conventional hydraulic systems:

Energy savings can reach:30–60%

(3) Disadvantages

① Limited Load Capacity

The main limitation of ball screw systems is load capability.

When mold weight reaches:

• Several tons;
• Tens of tons;

the required screw diameter becomes very large.

This results in:

• Higher cost;
• Increased inertia;
• Reduced speed.

② Lower Impact Resistance

Blow molding machines experience high-speed mold impacts.

If not properly controlled, problems may occur:

• Ball screw damage;
• Nut wear;
• Accuracy degradation.

2.3 Servo Motor + Rack and Pinion Mold Transfer System

(1) Structural Principle

The structure is:

Servo motor
      ↓
Gear reducer
      ↓
Pinion gear
      ↓
Rack
      ↓
Moving platen

(2) Advantages

① Suitable for High-Speed Long-Stroke Movement

Compared with ball screws, rack and pinion systems provide:

• Longer travel distance;
• Higher speed capability;
• Simpler mechanical structure.

They are suitable for:

• Multi-station blow molding machines;
• Rotary blow molding systems.

② Higher Load Capability

Rack and pinion systems can withstand higher:

• Radial loads;
• Impact loads.

They are suitable for medium-size blow molding machines.

(3) Disadvantages

① Lower Accuracy Compared with Ball Screws

The main issue is gear backlash.

After long-term operation:

• Gear surface wear;
• Increased clearance;

may reduce positioning accuracy.

② Higher Operating Noise

At high speed, gear meshing may generate:

• Vibration;
• Mechanical noise.

2.4 Servo Hydraulic Mold Transfer System

(1) Technical Characteristics

Servo hydraulic systems represent one of the development directions for high-end large blow molding machines.

Structure:

Servo motor
      ↓
Variable displacement hydraulic pump
      ↓
Hydraulic cylinder
      ↓
Moving platen

(2) Advantages

① Combines High Force and Energy Efficiency

It retains the advantages of hydraulics:

• Large output force;
• High reliability;

while adding servo advantages:

• Precise control;
• Reduced energy consumption.

② Improved Dynamic Response

Compared with conventional hydraulic systems:

• Faster acceleration;
• Faster speed adjustment;
• Better motion control.

Suitable for high-performance large blow molding machines.

(3) Disadvantages

① Higher Cost

Additional components include:

• Servo motor;
• Servo drive;
• Advanced control system.

② More Complex Control System

Requires:

• Pressure closed-loop control;
• Speed closed-loop control;
• Position closed-loop control.

3. Mold Opening and Closing Control Methods

The mold opening and closing system is responsible for:

• Opening the mold;
• Closing the mold;
• Generating and maintaining mold locking force;
• Ensuring stable clamping during the blowing process.

The main types of mold opening and closing control systems include:

1. Hydraulic direct pressure clamping system;
2. Hydraulic toggle clamping system;
3. Servo electric toggle clamping system;
4. Fully electric direct drive clamping system.

3.1 Hydraulic Direct Pressure Clamping System

(1) Working Principle

The hydraulic direct pressure system uses hydraulic cylinders to directly generate mold closing and locking force.

Basic structure:

Hydraulic cylinder
        ↓
Moving platen
        ↓
Mold closing and locking

The hydraulic cylinder directly pushes the moving platen until the mold is fully closed.

(2) Advantages

① Extremely High Clamping Force

The biggest advantage of hydraulic direct pressure systems is their ability to generate very high locking force.

They are especially suitable for large blow molding products, such as:

• Large industrial containers;
• 200L drums;
• Automotive fuel tanks;
• Large water tanks;
• Heavy-duty pallets.

For large molds with high weight and large projected area, hydraulic direct pressure systems remain one of the most reliable solutions.

② Simple and Reliable Structure

Compared with mechanical toggle systems, hydraulic direct pressure systems have:

• Fewer mechanical components;
• No complex linkage mechanism;
• Lower mechanical wear.

Therefore, they provide:

• High reliability;
• Easy maintenance;
• Long service life.

(3) Disadvantages

① Lower Operating Speed

Because hydraulic cylinders usually have:

• Long stroke distance;
• Large oil flow requirements;
• Hydraulic inertia;

the opening and closing speed is relatively limited.

For high-speed production applications, hydraulic direct pressure systems are less competitive.

② Continuous Pressure Holding Requires Energy

During the mold locking stage, the hydraulic system often needs to maintain pressure continuously.

This results in:

• Higher energy consumption;
• Increased oil temperature;
• Reduced system efficiency.

③ Lower Dynamic Response

Compared with servo-driven systems, traditional hydraulic systems respond more slowly to:

• Speed changes;
• Position adjustments;
• Load variations.

3.2 Hydraulic Toggle Clamping System

(1) Working Principle

The hydraulic toggle system uses a hydraulic cylinder to drive a mechanical toggle mechanism.

Structure:

Hydraulic cylinder
        ↓
Toggle linkage mechanism
        ↓
Moving platen
        ↓
Mold locking

The toggle mechanism amplifies the force generated by the hydraulic cylinder.

(2) Advantages

① High Mold Opening and Closing Speed

The toggle mechanism has two different working stages:

Fast movement stage

The mechanism moves quickly to reduce cycle time.

Locking stage

The toggle mechanism generates mechanical force amplification to achieve high locking force.

This makes it suitable for high-speed production.

② Good Mechanical Rigidity

After reaching the locking position, the toggle mechanism provides strong mechanical support.

Advantages include:

• Stable mold locking;
• Reduced hydraulic pressure requirement;
• Improved repeatability.

③ Lower Energy Consumption Compared with Direct Pressure Systems

Once the toggle mechanism reaches the locked position:

• The hydraulic cylinder requires less holding pressure;
• The hydraulic pump operates less frequently.

Therefore, energy consumption is lower than traditional direct hydraulic locking.

(3) Disadvantages

① More Complex Mechanical Structure

The toggle system contains many moving components:

• Connecting rods;
• Pins;
• Bushings;
• Hinges.

These components require:

• Regular lubrication;
• Wear inspection;
• Periodic adjustment.

② More Complicated Mold Thickness Adjustment

When changing molds with different thicknesses, the toggle mechanism usually requires adjustment of:

• Tie bar position;
• Toggle stroke;
• Mechanical alignment.

This increases setup time.

3.3 Servo Electric Toggle Clamping System

(1) Working Principle

The servo electric toggle system replaces the hydraulic cylinder with a servo motor.

Structure:

Servo motor
        ↓
Ball screw
        ↓
Toggle mechanism
        ↓
Mold locking

The servo motor precisely controls the movement of the toggle mechanism.

(2) Advantages

① Highest Control Accuracy

The servo electric system can accurately control:

• Mold closing speed;
• Mold position;
• Locking force;
• Compression process.

This provides excellent repeatability.

It is especially suitable for:

• Precision packaging;
• Medical containers;
• High-quality cosmetic packaging.

② Excellent Energy Efficiency

Because there is no hydraulic power unit:

• No hydraulic oil losses;
• No pressure holding losses;
• Less heat generation.

Compared with conventional hydraulic systems:

Energy savings can reach:

30–70%

③ Clean and Environmentally Friendly

Since there is no hydraulic oil:

Advantages include:

• No oil leakage risk;
• Cleaner production environment;
• Lower maintenance requirements.

It is suitable for industries requiring high cleanliness, such as:

• Food packaging;
• Medical products;
• Pharmaceutical packaging.

(3) Disadvantages

① Limited Maximum Clamping Force

The main limitation of servo electric systems is the available force output.

For extremely large blow molding machines:

• Large containers;
• Heavy industrial products;

fully electric systems are still difficult to replace hydraulic solutions.

② Higher Initial Investment Cost

The system requires:

• High-power servo motors;
• Servo drives;
• Precision mechanical components;
• Advanced control software.

Therefore, the initial equipment cost is significantly higher.

3.4 Fully Electric Direct Drive Clamping System

(1) Working Principle

A high-power servo motor directly drives the mold movement mechanism without hydraulic components.

Basic structure:

Servo motor
        ↓
Mechanical transmission system
        ↓
Moving platen
        ↓
Mold closing

(2) Advantages

① Excellent Motion Control Performance

The system provides precise control of:

• Position;
• Speed;
• Acceleration;
• Force.

② Fast Response

Because the transmission path is short:

• Acceleration is faster;
• Response time is shorter;
• Motion repeatability is improved.

(3) Disadvantages

① Difficult to Apply to Very Large Machines

For very high clamping force requirements:

• Motor size becomes extremely large;
• Mechanical structure becomes expensive;
• System cost increases significantly.

Therefore, fully electric direct drive systems are currently more common in small and medium-sized machines.

4. Comprehensive Comparison of Different Systems

System Type	Speed	Accuracy	Force Capability	Energy Efficiency	Reliability	Cost
Conventional Hydraulic Mold Transfer	★★★	★★	★★★★★	★★	★★★★★	Low
Servo Ball Screw Mold Transfer	★★★★★	★★★★★	★★	★★★★★	★★★	High
Servo Rack & Pinion Mold Transfer	★★★★★	★★★★	★★★	★★★★	★★★★	Medium
Servo Hydraulic Mold Transfer	★★★★	★★★★	★★★★★	★★★★	★★★★★	High
Hydraulic Direct Pressure Clamping	★★	★★★	★★★★★	★★	★★★★★	Low
Hydraulic Toggle Clamping	★★★★	★★★★	★★★★	★★★	★★★★	Medium
Servo Electric Toggle Clamping	★★★★★	★★★★★	★★★	★★★★★	★★★★	High
Fully Electric Direct Drive	★★★★★	★★★★★	★★～★★★	★★★★★	★★★★	Very High

5. Future Development Trends of Blow Molding Machine Control Systems

With the continuous development of the blow molding industry, equipment requirements are becoming increasingly focused on:

• Higher production efficiency;
• Lower energy consumption;
• Higher precision;
• Better repeatability;
• Improved automation level;
• Reduced maintenance requirements.

The future development direction of mold transfer and mold opening/closing systems can be summarized as:

• Electrification;
• Servo control;
• Intelligent hydraulic systems;
• Electro-hydraulic hybrid technology.

5.1 Small and High-Speed Blow Molding Machines

Development Direction:

Fully Servo-Electric Control

Typical configuration:

Servo mold transfer + Servo electric toggle clamping

Main Characteristics:

① High Production Speed

Servo systems provide:

• Fast acceleration;
• Short response time;
• Accurate motion control.

This significantly reduces:

• Mold opening/closing time;
• Empty movement time;
• Overall cycle time.

② High Positioning Accuracy

Servo systems can precisely control:

• Mold position;
• Closing speed;
• Locking position;
• Motion profile.

This improves:

• Product consistency;
• Flash quality;
• Mold alignment accuracy.

③ Low Energy Consumption

Compared with traditional hydraulic systems:

• No hydraulic pump losses;
• No oil heating losses;
• Lower standby energy consumption.

Energy savings can be significant, especially for long-term continuous production.

④ Cleaner Production Environment

Because there is no hydraulic oil:

Advantages include:

• No oil leakage;
• Lower contamination risk;
• Easier factory management.

Therefore, this technology is suitable for:

• Medical packaging;
• Food containers;
• High-end cosmetic packaging.

5.2 Medium and Large Blow Molding Machines

Development Direction:

Electro-Hydraulic Hybrid Technology

Typical configuration:

Servo hydraulic mold transfer + Hydraulic toggle clamping system

Main Advantages:

① Maintains High Hydraulic Force Capability

Hydraulic systems still provide significant advantages for large equipment:

• High output force;
• Strong impact resistance;
• Excellent reliability.

This is difficult to completely replace with electric systems.

② Improved Energy Efficiency

By using servo-driven hydraulic pumps:

Compared with conventional hydraulic systems:

• Pump output is adjusted according to demand;
• Unnecessary pressure losses are reduced;
• Oil temperature rise is minimized.

Energy savings can typically reach:30–60%

③ Better Motion Control

Servo hydraulic systems provide:

• Closed-loop speed control;
• Closed-loop pressure control;
• Improved positioning accuracy.

This allows large machines to achieve performance closer to electric systems while maintaining hydraulic power advantages.

5.3 Extremely Large Blow Molding Machines

Examples include:

• 500L+ industrial containers;
• Large chemical tanks;
• Automotive structural components;
• Heavy-duty pallets.

Current Mainstream Solution:

Hydraulic direct pressure clamping + Hydraulic mold transfer

Reasons:

① Extremely High Force Requirement

Large products require:

• Heavy molds;
• Large clamping force;
• Strong structural rigidity.

Hydraulic systems remain the most practical solution.

② High Reliability

Large industrial blow molding machines usually operate:

• Continuously;
• Under heavy load;
• In harsh environments.

Hydraulic systems provide proven reliability under these conditions.

③ Better Cost Performance

For very large machines:

A fully electric solution requires:

• Extremely large servo motors;
• High-capacity drives;
• Expensive mechanical structures.

The total investment becomes significantly higher.

6. Overall Comparison and Selection Principles

There is no single optimal control system for all blow molding machines.

The best solution depends on:

• Product size;
• Mold weight;
• Required production speed;
• Accuracy requirements;
• Energy efficiency targets;
• Equipment investment budget.

Recommended Selection Guidelines

Small Precision Blow Molding Machines

Recommended:

Servo electric mold transfer + Servo electric toggle clamping

Suitable for:

• Small bottles;
• Medical containers;
• Cosmetic packaging;
• Precision products.

Advantages:

• Highest accuracy;
• Highest efficiency;
• Lowest energy consumption.

Medium-Sized Blow Molding Machines

Recommended:Servo rack-and-pinion transfer + Hydraulic toggle clamping

Advantages:

• High speed;
• Good reliability;
• Balanced cost and performance.

Suitable for:

• Packaging containers;
• Household products;
• Industrial containers.

Large Blow Molding Machines

Recommended:

Servo hydraulic mold transfer + Hydraulic direct pressure/toggle clamping

Advantages:

• High force capability;
• High reliability;
• Reduced energy consumption compared with conventional hydraulic systems.

Suitable for:

• Large drums;
• Automotive parts;
• Industrial tanks.

Ultra-Large Blow Molding Machines

Recommended:

Conventional hydraulic mold transfer + Hydraulic direct pressure clamping

Advantages:

• Maximum force capability;
• Simple structure;
• Proven reliability.

7. Final Summary

The mold transfer system and mold opening/closing system are two of the most important subsystems in an extrusion blow molding machine.

Different control methods have their own advantages and limitations:

Hydraulic Systems

Advantages:

• Extremely high force output;
• Strong impact resistance;
• High reliability;
• Lower equipment cost.

Disadvantages:

• Higher energy consumption;
• Lower positioning accuracy;
• More maintenance requirements.

Servo Electric Systems

Advantages:

• Excellent precision;
• Fast response;
• High energy efficiency;
• Clean operation environment.

Disadvantages:

• Higher initial investment;
• Limited force capability for very large machines.

Servo Hydraulic Systems

Advantages:

• Combines hydraulic power with servo precision;
• Lower energy consumption;
• Improved dynamic response.

Disadvantages:

• Higher system complexity;
• Higher equipment cost.

Final Engineering Conclusion

For modern blow molding machine design:

Small machines should focus on speed and precision through electrification;
Medium and large machines should focus on the combination of hydraulic power and servo control;
Extremely large machines should continue to utilize hydraulic systems for maximum reliability and force capability.

The future trend is not simply replacing hydraulic systems with fully electric systems. Instead, the optimal engineering approach is to achieve the best balance among:

• Clamping force;
• Motion speed;
• Position accuracy;
• Energy consumption;
• Equipment cost;
• Long-term reliability.

The most advanced blow molding machines will increasingly adopt servo-driven, intelligent, and hybrid control technologies to achieve higher efficiency and better product quality.