Blow Molding Machine
A blow molding machine transforms PET preforms into finished plastic bottles through a heating and high-pressure air process. Preforms are small, test-tube-shaped pieces with pre-formed threaded necks that occupy minimal storage and transport space compared to finished bottles, significantly reducing logistics costs in bottling operations.
How Blow Molding Machines Work
The blow molding process begins when preforms enter the machine's oven system, typically moving upside down on mandrels. Infrared lamps heat the preform body above its glass transition temperature while the pre-formed neck remains unaffected. Once heated, stretch rods extend into the preform while high-pressure air inflates it against the mold walls, creating the final bottle shape. After cooling, bottles transfer to conveyor systems for downstream processing.
Temperature uniformity during heating is critical for consistent wall distribution. Advanced machines address this challenge through:
- Separate blow valve systems for each cavity
- Optimized lamp positioning to compensate for temperature variation
- Return-path heating zones for temperature equalization
Types of Blow Molding Machines
Linear Blow Molding Machines
Linear blowers feature molds mounted in a single body moving with a common cylinder, typically offering 4 to 10 cavities. These machines suit medium production requirements up to 20,000 bottles per hour and require less floor space than rotary alternatives.
Key characteristics of linear blow molding machines:
- Preforms feed through a hopper to an unscrambler
- Transfer to tempered aluminum mandrels matched to specific neck specifications
- Compact footprint ideal for space-constrained facilities
- Lower capital investment compared to rotary systems
Rotary Blow Molding Machines
Rotary blow molding machines deliver high-speed production up to 86,000 bottles per hour with configurations reaching 40 cavities. Each preform travels to an individual blow station mounted on a rotating wheel, ensuring identical timing between heating and blowing for every bottle.
Advantages of rotary blowers include:
- Consistent quality through uniform preform-to-blow timing
- Single electric motor driving all functions via transmission belts
- Cam mechanisms operating stretch rods and mold sequences
- Automatic synchronization when adjusting production speed
- Torque limiters on drive pulleys preventing damage from malformed preforms
Combi-Block Systems
Combi-block configurations integrate blowing, filling, and capping into a single compact system. This design eliminates air conveyors between machines and reduces floor space requirements significantly.
Combi-block technology includes:
- Unified human-machine interface (HMI)
- Single recipe management with archived traceability
- Coordinated maintenance scheduling for the entire system
- Optional integration of labeling, level inspection, and cap detection
- Space for saturators or premix drink systems
Blow Molding Processes
Two-Stage Stretch Blow Molding
The two-stage process separates preform injection and bottle blowing into independent operations. Injection presses produce preforms that can be stored, transported, and blown on separate equipment as needed.
Benefits of two-stage stretch blow molding:
- Independent optimization of injection and blowing processes
- Flexibility to produce different bottle formats from stored preforms
- Enables preform trading between manufacturers
- Suitable for cylindrical, rectangular, or oval bottles
Single-Stage Blow Molding
Single-stage machines perform both preform injection and bottle blowing in one unit. Three-station configurations eliminate separate reheating by utilizing latent heat from injection, reducing energy costs by up to 25% compared to four-station designs.
Ideal applications:
- Small production batches and frequent format changes
- Non-circular and rectangular bottle shapes
- Operations requiring uniform wall thickness control
Injection Blow Molding (IBM)
Injection blow molding produces small containers for pharmaceutical and single-dose applications. The polymer is injection molded onto a center pin, rotated to a blow station, inflated, cooled, and ejected through a three-stage process.
IBM characteristics:
- Precision molded finishes for medical containers
- Typical cavity configurations from 3 to 16 molds
- Limited to small volume bottles
- No biaxial stretching for barrier enhancement
Semi-Automatic Blow Molding Machines
Semi-automatic blowers feature independent oven sections where operators manually load preforms onto mandrels. These machines offer an economical entry point for lower-volume production.
Production capacity ranges:
- 50 bottles/hour for 20-liter containers (single cavity)
- 700 bottles/hour for 0.5-liter bottles (double cavity)
- Up to 1,500 bottles/hour with automatic preform feeding
Safety features include two-button mold closing sequences protecting operators during operation.
Technical Specifications
Standard blow molding machine specifications include:
| Parameter |
Typical Range |
| Mandrel spacing |
38–50mm (wider for large openings) |
| Neck diameter |
28–33mm (water and beverage) |
| Heating zones |
20+ zones plus return-path stations |
| Linear cavities |
4–10 cavities |
| Rotary cavities |
Up to 40 cavities |
Each blow station includes:
- Dedicated mold assemblies
- Stretch rods operated by cam mechanisms
- Water circuit connections for cooling
- Three-valve air systems: pre-blow, blow, and exhaust
Leading Manufacturers
The global blow molding machine market features established manufacturers known for innovation, reliability, and service support:
- Sidel – high-speed rotary systems and combi-blocks
- Krones – integrated bottling line solutions
- Sipa – single-stage and two-stage technologies
- KHS – energy-efficient blowing systems
- Sacmi – compression blow forming innovation
Used equipment from these brands offers proven reliability with available spare parts and worldwide service networks.
Buying Used Blow Molding Equipment
Used blow molding machines typically come configured for specific neck formats. Key considerations when purchasing:
- Neck format modifications – possible subject to machine design analysis
- Thread pattern changes – lower conversion costs within same diameter
- Generation compatibility – later models offer greater customization flexibility
- Capping system verification – required when changing neck specifications
- Hours of operation and maintenance history
Modern patented connection systems allow combining used blow molding machines with filling monoblocks, creating combi-block functionality from existing equipment at reduced investment compared to new or overhauled integrated systems.
