A used blow molding machine creates plastic bottles starting from a preform generally made of PET. The preform is nothing more than a bottle that has not yet been formed or printed. It has the shape of a small test tube where only the threaded mouth for the cap is not changed. The rest of the body, on the other hand, is first heated inside the machine oven and then molded by blowing. Why use a blow molding machine? The reason why we don’t start directly from the finished bottle is due to the space required for storage and transport. The space for transporting the preforms is significantly less than the bottle and of the blow molding machine. This obviously affects the costs associated with the entire bottling production cycle.
Blow molding machine: how does it work
In most blow molding machines, the preforms moves upside down, and the stretch rods operating from below. After blowing, the bottles pass to the pick-up station and placed back vertically on the conveyor belt. Although these blow molding machines provide an economical solution for the production of PET containers, they have some significant disadvantages. The first and most serious is the way in which the preforms pass through the oven system. It is almost impossible to make all the preforms spend the same amount of time inside the ovens, due to how they are indexed. This becomes more problematic as the number of mold cavitations increases. Furthermore, the heat emitted by an infrared lamp is not constant along its length: at the central point of an infrared lamp, at maximum temperature, it emits 15/20% more heat than at the ends.
Solutions to the blowing problem
The consequence is that the oven is unable to heat the preforms evenly, temperature differences are unfortunately recurring. This, in turn, leads to differences in the distribution of the bottle walls (in the mold). Some of these differences can be improved if each cavity has a separate blow valve system, but not all machines have one. Some machines are equipped with paths, in the oven section, where the preforms move parallel to each other, with the lamps in the center. This solution provides overall better performance without reaching the level of that of continuous cycle machines. Most blow molding machines set the distance of the preforms with the same pitch as the cavities of the blow mold. This results in an economically disadvantageous use of the oven since the lamps heat a large volume of air.
Types of used blow molding machine
Like with other types of used machine there are various types of used blower equipment, both linear and rotary and combi-block. A linear machine usually works for medium hourly production speeds, up to 20,000 BPH. Furthermore is preferable in the event that the space inside the bottling plant is limited, as these machines require less space than a rotary blow molding machine.
When workloads require high production speeds, a rotary molding machine is usually used. The rotary blow molding machine can produce up to and above 90 / 100.000 BPH.
That’s why large companies which use plastic containers prefer rotary blowers. Even if this involves having a machine that occupies much more space than a linear one.
Different types of process
Heated stretch-blow molding is a part of the two-stage production process of PET bottles; PET is the most used material in packaging for the water and beverage sector in general. Injection presses are the machines that carry out the first stage of injection molding. The machines produce the preforms in the shape of a vial-finger-tube. The neck of the preforms is complete and meets the customer’s needs-requests however the dimensions are much smaller than the bottle into which they will be transformed during high pressure blowing in the appropriate molds of the blow molding machine.
Blow molding machine: the first step
The part of the creation of the preform is the first step that allows to obtain the liquid stored in an adequate, resistant-transparent material, to do this the equipment called presses is needed that transform the PET granule-powder into a preform. When this is produced it can be immediately heated and blown by the blow molding machine or deposited in large containers called Octabins which serve as containers; these are introduced into the appropriate filters and then conveyed by the loader and oriented towards the blowing unit. As previously written, these can be linear or rotary, with alternating or continuous cycle
Different methods of producing PET bottle
The single-stage process, the integrated two-stage process, or the two-stage process. The latter has many advantages over the other two such as: the injection molding process and the blow molding process are fully independent and can therefore be optimized separately. This means that the preforms can be both stored and shipped where it is required and used when necessary; by doing so it is possible to produce different types of preforms using different molds-matrix. On the single-stage blow molding machine, both the preforms and the bottles arrive from the same machine. On the other hand, the integrated two-stage machines are halfway between the single-stage and the double-stage; in fact, they produce the preforms by injection molding and transfer them into the mold through transfer pliers; this oven has infrared lamps which preheat before blowing.
Semi-automatic blow molding machines
These usually have an independent furnace section built close to the blowgun. The worker manually places preforms on the mandrels that enter the oven; up to 4 preforms can be blown at the same time. These machines close the mold by pressing two buttons in sequence, in order to protect the operator from accidents. The mold then closes and stretch-blows one or more bottles. The operator removes the bottles and adds the other preforms to the mandrels and the process starts all over again. The speed ranges from 50 bp / h 20L in a single cavity to 700 bp / h 0.50L in a double cavity. A variant of this type is a four-cavity machine with automatic feeding of the preforms into the oven system. The positioning of the preforms in the blow mold is manual once it has been opened. The production speed reaches 1500 light bottles/hour.
Linear blow molding machines
Linear blow molding machines have molds mounted in a single body that moves with a common cylinder. The maximum of the cavities are 10 but normally they range from 4 to 8 cavities. These machines fulfill the market needs for low speeds. Thanks to a hopper, the preforms arrive at the unscrambler via an inclined conveyor belt. The preforms are then overturned by means of an appropriate number of grippers operated by pneumatic cylinders. The parts for transporting the preforms into the oven are called mandrels and are all in tempered aluminum; they are made on the type of bottleneck of the preform chosen by the customer. All the cavities for blowing are placed next to each other.
Rotary blow molding machines
Due to the widespread consumption of PET as a liquid containment material, we have pushed towards much more performing solutions. This has resulted in an innovation that has enhanced the capabilities of the blow molding machines themselves. Capacity is generally measured in bottles/hour (bph). On the market are currently available blowers up to 40 cavities and with capacities up to 86000 bph. This enormous progress was made possible thanks to the increasing speeds of the drives and the optimal regulation of the processing time.
One of the main operating barriers at the highest levels is the thickness of the bottle walls which requires cooling times. The nominal speeds, reported by the manufacturers in the technical data sheets of these machines, always relate to the production of light bottles for mineral water; they are characterized by a completely stretch-blown bottom. The bottles for soft drinks, with or without carbon dioxide, require longer processing times: the effective yields of the blow molding machines are thus reduced. The oven sections of the rotary machines are very similar to those of the other types of machines; this is in order to heat the preforms effectively avoiding unnecessary temperature increases in the preform packages.
The main difference between the various blow molding machines lies in the design of the closure of the blowing group. In a rotary machine, the preform moves towards its own blow closure which is in turn disposed on a blow wheel. All the functionalities provided to these closures arrive through the center of the blowing wheel by means of rotary distributors. The need for an appropriate design of all the kinematic couplings is therefore evident, given a mechanism of such complexity.
Why so efficient:
The time that elapses between the end of the kiln section and the beginning of the blowing is identical for each preform. This feature allows rotary blow molding machines to consistently deliver excellent quality. A single electric motor drives all the functions of the machine via transmission belts. Furthermore, cam mechanisms operate the stretching rods and the opening/closing sequences of the molds. Consequently, to vary the processing speed, it is only necessary to change the motor speed and all other functions are automatically synchronized.
How do perform heating and transport work?
The engineering of the spindles that receive the preforms from the feeding section is a very important issue:
The mandrels have various spring-loaded devices with the function of keeping the preform in its place; this to ensure both alignment and safe assembly.
Inside the blow molding machine, most of the spindles move along guides and are equipped with a pinion on the upper part: in oven systems, where the preforms pass upside down, the pinion is located on the lower part.
The pinion meshes with a chain that sets the spindles in rotation and can move them through the furnace section.
How Much Can They Measure?
Spindle spacing varies from 38 to 50mm and can be increased to double the shape for wide opening applications. Most bottles for mineral water and soft drinks use preforms with neck diameters from 28 to 33mm, easily processed with standard spacing. Once rotated thanks to the mandrels, the preforms are exposed to infrared radiation. For example, 28 heating furnaces of which 20 are away from the blowing wheel and 8 are on the return path.
Inside the blow molding machine in the section of the furnace returning to the blowing wheel, the preforms are subjected to balancing; This is the balance of the temperature differences within the walls of the preform.
Composition of a blow mold
At the end of the furnace path, the preforms enter a star wheel or other transfer device: they are moved one by one to the first available position of the blowing wheel. Each cavity has its own blow mold, its ironing rod, its connection to the water circuit, and three blowing valves (pre-blowing, blowing, and discharge). The connections to the air, water, and electrical circuits for sensors and switches come from a power supply unit. In the blow molding machine it is positioned in the center of the blowing wheel. These determine, with the same cavitation, higher purchase costs for rotary machines than linear ones.
The blown bottles leave the molds by means of pliers or star wheels that position them on belts. The design of these grippers can vary from machine to machine, especially when compared to that of linear machines. The pliers carry out the preform transfers between the oven, molds, and unloading. This device saves time and maintenance by requiring the presence of the support ring in the design of the preform neck. To facilitate the interaction between the star wheel and the calipers you need enough space for the gripper to grip the preform above the transfer ring. The main advantage blow moulders is the continuous movement of all their components. A single electric motor drives the entire machine and transmits movement via toothed belts and pulleys.
Safety for possible anomalies:
What happens in case of incorrect closing of the mold, due to a malformed preform? In the case of a rotary machine with a capacity of 20,000 b/c hour, it would be a disaster: this would cause serious damage to the entire kinematic chain if the appropriate protections were not provided.
These protections are realize by mounting a torque limiter on each of the driving pulleys keyed on the rotating components of the machine. When the driving torque on the limiter exceeds a fixed value, the limiter detaches the driving pulley from the rotating part: this allows free rotation without structural damage. It will therefore be up to the operator to reset the limiter and properly rotate the rotating part, restoring synchronization. The following image shows a typical torque limiter, widely used in the field in question.
Combi block solution:
The increasing demands for efficiency and compactness have led to the birth of this particular configuration.
The combiblock system combines blowing, filling, and capping in a single integrated solution; It allows the bottling and filling of water and carbonated and flat drinks with the utmost precision.
By combining different equipment and production steps into one system, the efficiency of the line is improved.
The market for used bottling equipment offers occasional buying opportunities.
Like the used blow moulders, the used combiblock is usually offered with a particular type of bottleneck: this neck can however always be modified according to one’s production needs.
It is obvious that customization of the neck may affect the purchase price but it is certainly recommended; the price of used equipment depends on both the hours of work and the year, make, and model.
Combi block technology includes:
A single human-machine interface
Single report and single recipe management, with archived traceability and long-lasting memory.
Combined automated operation of blowing, filling and capping.
Standardized operating procedures for lubrication, cleaning and auditing: with this protocol there is a lot of time and safety savings in interventions and planning.
Maintenance plans aligned for the entire system.
When you see the combined system in production, you understand how much this helps to keep production under control; the operator in a single position can control up to the labeler.
In this hypothesis, we have blowing, filling, capping, level, and cap control, labeling, labeling control.
Long belts used to divide the spaces between one machine and another, both for the air and for the transport of full bottles, now it condenses in very little space.
This space also includes saturators or premixed drinks.
Maintenance and customization work:
In these combiblocks it is possible to intervene with a specific-programmed work plan for each section concerned.
In the hypothesis of making the package change, some things must be taken into consideration:
It is possible to make all the desired preform packages but subject to an analysis of the conformation of the blow molding machine.
This is true on the latest versions on the market, on the first types the feasibility must ALWAYS be checked first.
If you stay on the same neck diameter but with a different thread, the changes are less expensive.
The capping will always be checked as well.
These systems are made with neck grip only by the latest versions: previously the conveyance was partially carried out from the neck and combined with that from the bottom / bottle diameter.
Solutions on used blow moulders:
Today it is also possible to combine used bottling equipment with a new patented connection system: this allows the elimination of air belts even in used bottling lines already installed.
You take a blow molding machine and a filling monoblock and you can make a combiblock using your own equipment; this allows you to save money compared to the purchase of new machinery or used / overhauled combiblock.
How to save energy
This heated air is a disadvantage compared to the consistent heating provided for the preform. Many blow molding machines offer dedicated systems for controlling the total capacity of the furnace (with respect to the measured temperature of the preform), but they do not detect all the variations of the ambient temperature in a typical day/night thermal cycle. Another disadvantage of these machines is given by the rotary movement first of the preforms (overturned), then of the bottles (straight upwards). The installed drive devices, consisting of three cylinders (each for up / down, forward / reverse, feed/eject movements), can be a major maintenance problem, which has affected many companies in the sector.
For this technology, large companies are studying to increase the efficiency/space ratio more and more.
Here are the systems that allow you to have:
Labeling machine integrated into the combi block after the capping machine
High precision internal inspection systems for both the level and the presence of the cap.
Inspectors for the presence of labels
Systems for monitoring the quality of the preform produced with storage of negative events: eventually help the specialists to modulate and correct any production defects of the preforms.
The blow molding machines most famous brands to date are Sidel, Krones, Sipa, KHS, Sacmi and they all battle it out:
level of assistance
value for money
by the value of spare parts.
by the speed of intervention