Which molding machine is used to make bottles?

In the world of manufacturing, especially bottle manufacturing, blow molding machines are essential &#; but which is better for you: a single-stage process or a two-stage process?

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Blow molding machines employed in PET (polyethylene terephthalate) bottle manufacturing are of various types, and that is why manufacturers need to ascertain the actual injection stretch blow molding process to use in producing plastic bottles.

The ability to choose the right method comes with the perks of increasing productivity, reducing cost, and also minimizing the cycles required to produce these materials.

However, the significant differences between single-stage and two-stage molding processes require you to make a decision.

What are Blow Molding Machines?

Blow molding machines are an equipment that is used in manufacturing plastic and glass bottles.

It takes advantage of several processes to form hollow parts in plastics before these parts are joined together to form a bottle.

In a bid to make this possible, there are three major processes:

• Injection stretch blow molding
• Injection blow molding
• Extrusion blow molding

While each of these will lead to the production of a bottle, the injection stretch blow molding process is what is required to create PET or plastic bottles.

What is the Single-Stage Blow Molding Process?

A single-stage process gains its name from the fact that it creates preforms, stretches, and blows them on the same machine before cooling.

Therefore, single stage PET blow molding machines can also be said to employ a direct method.

This level of functionality can be attributed to the injection molding system and blow molding station being built into one machine.

Likewise, the machine can either be a 3-station or 4-station system.

A 3-station single-stage machine has three stages which are injection, stretch blow, and ejection. It also uses latent heat which saves the cost of having to reheat, thereby reducing 25% of heat in tooling.

The 4-station, on the other hand, comprises of these three stages and an additional reheating stage.

Processes Involved in the Single-Stage Method

The transformation of the raw materials into a bottle using the single-stage follows the procedures outlined below:

1. Dehumidifying and drying of PET materials
2. Melting and injecting of the raw materials into the preform mold through the injection nozzle
3. Cooling of the molten material in the preform mold to 120 ° Celsius
4. Transfer of the hot preform mold to a bottle mold to begin the stretch molding

Advantages of Single-Stage Blow Molding Process

There are several advantages of a single-stage molding process and they include:

• Compact and flexible
• Transfer ring is optional
• Creates blemish-free bottles
• More suitable for low volumes
• Control over preform production
• Control over thread start to align with bottle&#;s shape
• Less expensive in comparison to two-stage machines
• Suitable for blowing rectangular and non-circular shapes

Disadvantages of Single-Stage Blow Molding Process

The disadvantages of employing this method include:

• Long cycle times
• Long changeover times
• Restriction in the bottle design
• Wall distribution may be uneven
• Great expertise is required in mastering both processes and PET drying
• Inefficient blow station due to injection station having more precedent over cycle time

Let&#;s take a look at some of these scenarios:

&#; Wall Distribution May be Uneven:

Generally, PET material can level by itself, but there are cases where an uneven wall distribution will still be evident in the final product.

What happens here is, the movement of the melt material along the barrel and hot-runner channels which exerts some amount of heat on it.

Despite this, the melt still retains some amount of thickness or viscosity and the warmer part tends to flow to the back of the new channel.

The result is a thicker design at the back of most bottles that employ this method, even though its manufacturer or brand may sometimes disguise it using labels.

&#; Inefficient Blow Station:

The issue of inefficient blow station has been combated with the creation of another category of single-stage machines which can be considered as integrated two-stage machines.

They are those featuring multiple pairs or triple injection cavities in each blow cavity. Their blow sections also complete two to three cycles for every injection cycle.

Consequently, this saves blow cavities while also reducing the tooling cost; a reason that makes the single-stage method more suitable for companies that are out to produce bottles in low or medium volumes.

What is a Two-Stage Blow Molding Process?

The technique used in two-stage injection stretch blow molding machines involves two machines. These are the injection molding system and stretch blow molding machine.

Here, the plastic is molded into a fully-cooled preform in the first machine before being shipped to the second machine.

The preform will usually feature the neck of the bottle as well as its thread, and it can be sold to a third party even before it is blown using the second machine.

When received by the latter, they are then unscrambled, reheated using infrared radiation, and conditioned before molding.

The need to cool the preform before reheating and stretching also gives this process its name, the &#;cool preform method&#;.

Processes Involved in the Two-Stage Method

• Dehumidifying and drying of PET materials
• Injecting of molten raw materials into the preform mold by the injection machine
• Cooling of molten PET to room temperature
• Processing of preform by a finishing machine
• Transferring of the preform to reheating stretch blow molding machines
• Blowing high-pressure air into bottles with the use of metal blow molds

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Advantages of Two-Stage Blow Molding Process

Some advantages of the two-stage molding process include:

• Flexibility
• Fast cycle times
• Fast changeovers
• Less restriction to bottle design
• The process can be stopped at anytime
• Good wall distribution for round bottles
• Preforms can be sold before being blown
• Handles high volumes of to 72,000 bottles/hr

Disadvantages Two-Stage Blowing  Molding Process

The disadvantages of this process include:

• High capital to maintain
• Floor space required is high
• Scratches may occur on bottles
• Potential damage to the preforms

Single-Stage vs. Two- Stage Process, Which is Better?

Having made comparisons between single-stage vs. two-stage process of blow molding machines, it is evident that where one fails, the other makes up for it.

That being the case, great care must be taken before settling for one.

Single-Stage

Let&#;s take for instance the single-stage method, consideration must be given to the inability to inspect the preform before molding in the direct stage.

In this aspect, operators must have good knowledge about injection and blow molding in order to determine if there are any defects while the preform was formed.

Two-Stage

Many think the same of the cool preform method which comes with its own limitation of making bottles susceptible to scratches. The latter is as a result of the need to store, align, and transfer the preform from one machine to the other.

An instance of this is where the preform tumbles onto the conveyor belt before entering the storage containers. Preforms may also be in the blow molding machines which can create blemishes on the bottle.

It is worthy to note that these scratches might not very noticeable given that some brands take the extra time of placing labels on their bottles in order to conceal such marks.

On the other hand, scratches may the least to worry about because if these preforms are purchased by a third party or vendor, they may not be in the right size,

As such, problems like finding the right neck and weight for the bottle may arise.

Conclusion

Having accessed the pros and cons of single-stage and two-stage blow molding machines, the choice of which to settle for will be dependent on what&#;s your priority.

Do you want a blemish-free bottle, in a precise oblong shape, a fixed thread, at a low capital cost? Then the single-thread is a better choice.

Alternatively, if you&#;re out to get something more economical, productive, and without any technical difficulty, then it would be the two-stage method due to its high scalability per hour.

There are four distinct blow molding processes that use heated liquid plastic to create hollow objects, like bottles or other packaging. Pressure forces the material into a mold cavity, which gives the object its hollow shape. At Drug Plastics, we use all four distinct blow molding processes to manufacture our products: Extrusion Blow Molding (EBM), Compression Blow Molding (CBM), Injection Blow Molding (IBM), and Injection Stretch Blow Molding (ISBM).

In general, the size and geometry of the bottle and the type of plastic resin being used determine the best manufacturing process. We leverage our knowledge acquired from over 60 years of bottle making to choose the optimal blow molding process for every product we produce. Drug Plastics commits to deliver perfect bottles each and every time.

We believe it&#;s important for our customers to understand the primary differences between molding processes. Why? Because understanding how we manufacture our products will help you make more informed decisions about your plastic packaging. Let&#;s review the differences between the four distinct blow molding processes. Read further or watch our video to learn more. Each process starts the same way &#; with pellets of plastic resin.

Extrusion Blow Molding

In the EBM process, we extrude the heated resin to form a parison. The parison is a vertical tube-like piece of plastic through which compressed air can pass. A two-part mold closes on the parison from both sides. A blow pin is inserted into the neck area of the bottle that blows air into it when sealing the mold. The air pressure makes the parison conform to the shape of the mold, including the threads in the neck portion of the mold.

The mold is cooled, and the bottom of the parison is trimmed. The mold opens and the bottle is placed on a conveyor belt, the top (typically dome-shaped) is trimmed, leaving the finished bottle. The EBM process is used to manufacture large-size, High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), and Polypropylene (PP) bottles with large necks.

Compression Blow Molding

CBM is a specialized form of extrusion molding. In CBM, the blow pin not only blows air into the parison so the plastic conforms to the shape of the bottle, but it also uses physical pressure to force the plastic into the neck area of the mold. This results in increased thread definition and precise bore tolerance.

Bottles with medium to large blow-up ratios are produced using CBM. The blow-up ratio is the comparison between the diameter of the neck of the bottle and the diameter of the body of the bottle. Bottles with large blowup ratios typically have large bodies and relatively small necks. The CBM process can be used to manufacture bottles that are made with HDPE, LDPE, and PP resin, and can achieve very tight critical neck dimensions.

The EBM and CBM processes also allow the weight of the bottle to be adjusted. This is done by controlling the amount of plastic in the parison. This is ideal when the contents of the filled bottle require a thicker wall, or as a conscious effort to conserve raw materials by reducing the amount of plastic. The EBM and CBM processes are also used when a bottle has multiple plastic layers (outside and inside); and when a transparent window stripe is needed to allow for determining the amount of product remaining in the bottle.

Injection Blow Molding

During the IBM process, the heated resin is injected into the mold using a long screw. This injected plastic is molded into a preform, then air is used to blow the preform into the shape of the mold. The mold is cooled and the bottle is placed on a conveyor belt after being ejected from the mold.

This process is ideal for the production of HDPE, LDPE, and PP bottles with a small to medium blowup ratio. Bottles with small blow-up ratios typically have small bodies and relatively small necks. IBM is used when manufacturing bottles with very tight neck tolerances.

Injection Stretch Blow Molding

During the ISBM process, the heated resin is injected into the machine using a long screw. This injected plastic is then molded into a preform.

Next, the preform is conditioned and prepared for stretching. The preform is stretched as air is used to blow it into the shape of the mold. The stretching of the preform increases the barrier properties of the PET bottle. The mold is cooled and the bottle is placed on a conveyor belt after being ejected from the mold. ISBM is typically used for bottles with small to medium blow-up ratios. We use ISBM to manufacture all of our Polyethylene Terephthalate (PET) bottles.

Summary

Manufacturing Customized Packaging Molds

We are also proud to have our own mold-making facility. There are instances when a customer wants custom designed packaging for their brand &#; that&#;s our specialty. Our team can design, fabricate, maintain, and repair our own molds.  From unit-cavity prototype molds through multi-cavity production molds, we build the highest precision tools using high-grade materials and proprietary technologies developed in-house. This ensures that our molds produce a consistent product, perform exceedingly well under high production demands, and work on all of the relevant blow molding machines. Our team will take the time to work with you to determine the best solution for your packaging challenges. For those times when quick production-ready solutions are needed, Drug Plastics offers a large selection of stock bottles in our inventory.

We Can Help

Whether you are looking for plastic packaging for a new product, or if you want to enhance your brands&#; existing packaging, we can help. Our plastic bottles are used worldwide to package prescription drugs, over-the-counter medications, vitamins, supplements, and cannabis products. When you work with us, we will recommend the best blow molding process to make your bottle. Our goal is to manufacture defect-free packaging every time, no exceptions. Ready to discuss your packaging? Call 610-367- to get in touch with a knowledgeable team member.

Contact Us

If you want to learn more, please visit our website Blow Molding Systems.