Blow molding ( blow moulding ), or plastic blow molding, is a fabricating process that manufacturers use to create hollow plastic parts and products. It is named blow molding because it involves blowing compressed air into molten plastic so that it expands like a balloon and takes a particular shape.
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Blow molding ( blow moulding ), or plastic blow molding, is a fabricating process that companies use to create hollow plastic parts and products. It is named blow molding because it involves blowing compressed air into molten plastic so that it expands like a balloon and takes a particular shape. Read More&#;
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Manufacturers use the blow molding process in order to form a smooth, airtight, uniform product that does not need to be assembled. Also, blow molded products are capable of holding a variety of substances such as herbicides, pesticides, cosmetics, and automotive oil. Some of the many industries that use blow molded plastics include: automotive manufacturing, food and beverage, lawn and garden, waste collection and recycling, storage and transportation, organization, office, healthcare and more.
Products Produced
Manufacturers use blow molding to make numerous products. Examples include: automotive ducting, water bottles, food storage containers, plastic totes, recycling cans, garbage cans, 55-gallon drums, hoses, planters and watering cans. Also, manufacturers blow mold cases and any other hollow consumer item that has a three-dimensional shape.
History
The concept of blow molding originated in 1st century BC Syria and was improved upon in Egypt between BC and BC.
The first modern blow molding machine was designed by Americans William Kopitke and Enoch Ferngren. After they sold the rights to their invention in to the Hartford Empire Company, a select number of manufacturers across the country began using the blow molding process for their purposes. One of the first items American manufacturers mass produced was the plastic bottle. While the method had incredible potential, prior to World War II, manufacturers did not have access to many types of plastic. In WWII, the need for synthetic plastics increased, and engineers responded by designing many new varieties. This trend continued after WWII, when manufacturers began producing plastic containers for the home.
Blow Moulding &#; R&D Molders, Inc.
Blow Moulding &#; R&D Molders, Inc.
One of the first items American manufacturers mass produced was the plastic bottles in . By , 60 years later, the US was producing upwards of ten billion plastic soft drink containers. While plastic and plastic injection is as popular and present as ever, there is now a movement to use materials that create less potential waste and litter. One way that plastics manufacturers are seeking to keep up with the green movement is by creating new products from recycled products.
Materials Process
The plastic utilized for these processes are all thermoplastic resins. They include acetal, polysulfone, polyamide, polystyrene, butadiene styrene, polyvinyl chloride (PVC), polycarbonate and high-density polyethylene (HDPE).
Acetal, or more technically Polyoxymethylene (POM) features: high dimensional stability, low friction, high rigidity, high strength and hardness. Most often, manufacturers employ it for engineering applications like fasteners, gear wheels, ball bearings and lock system fabrication.
Polysulfone thermoplastics are durable, strong, rigid and thermally stable polymers. These high-performance plastics are highly resistant to a variety of chemicals with pH levels between 2 and 13, including: bleaches, electrolytes, alkalis and mineral acids. They are reasonably resistant to hydrocarbon oils and surfactants. They have above average compaction resistance, so they work well in high pressure applications.
Polyamides are characterized by their durability and strength. They can occur naturally or be made synthetically. Most often, they&#;re used in automotive manufacturing.
Polystyrene is an inexpensive polymer used for a variety of purposes that do not require sealing from water or air. It is available as a solid material or a foamed material (think Styrofoam). Manufacturers use it to blow mold plastic containers and bottles of all sorts. However, polystyrene takes a very long time to biodegrade, and has been found in alarming quantities in the Pacific Ocean and along shorelines.
Butadiene styrene, not to be confused with styrene-butadiene rubber (SBR), is a thermoplastic elastomer made from styrene and butadiene. It is more commonly known as acrylonitrile butadiene styrene, or ABS. ABS is strong, shiny, heat resistant and impact resistant.
PVC, also known as vinyl, is one of the most widely used polymers in the world. It is available as a flexible or rigid material. Some of its many blow molding applications include: bottles, plumbing components and non-food packaging.
Polycarbonates are thermoplastic polymers that feature carbonate groups in their makeup. They are strong, durable and impact resistant. However, they have poor scratch resistance and poor chemical resistance.
HDPE is a thermoplastic known for its high tensile strength and high strength-to-weight ratio. It is also water resistant and solvent resistant. This recyclable thermoplastic material works well as: potable water storage, bottles, piping, food storage, plumbing boxes, electrical boxes, bags and more.
Process Details
There are three methods in which blow molded plastic products can be produced: extrusion blow molding, injection blow molding, and stretch blow molding. All of these processes consist of just a few main steps, which vary the most in the early stages. All blow molding processes share the steps of 1) melting and forming the plastic, and 2) introducing air pressure.
Below, in more detail, are the steps of blow molding:
1. The first step in the blow molding process involves melting the plastic, and then using injection molding to form it into a preform, or parison.
A parison is a piece of plastic shaped like a tube with a hole on one end which allows compressed air to pass through.
The preform, which is soft and moldable, is pushed by a metal ram and expanded to the designated height of the product.
2. The parison or preform is then clamped into a mold cavity. The ultimate shape of the blow molded plastic depends on the shape of the mold cavity.
3. Air pressure is introduced to the inside of the parison via a blow pin. The air pressure causes the parison to expand like a balloon and fully take the shape of the mold cavity.
4. The final product can be cooled either by running cold water through the mold, by conduction, or by evaporating inconsistent fluids within the container. The blow molding process takes a few seconds; blow molding machines are capable of producing up to 20,000 containers in an hour.
5. Once the plastic part has been cooled and hardened, the mold opens up and allows the part to be ejected.
Design
When preparing a custom blow molding procedure, manufacturers must decide on a few different things, mainly: the material they will use, the blow molding process they will use and the shape of the mold cavity. The decisions they make depend entirely on the client application specifications and requirements. For example, if the product requires strong compaction resistance, they will likely consider a material like polysulfone.
While blow molded products come in an assortment of standard shapes and sizes, there are some products that are used for special applications and must be made via custom blow molding. Blow molding service providers routinely craft custom molds so that you can receive the most well-tailored product possible. To make sure you are on the same page, they will first create a prototype to share with you. If there is something you don&#;t like, you can discuss it before they&#;ve gone into full production.
Custom blow molding takes longer but yields great results. However, if you are short on time or your budget is small, your manufacturer can also blow mold your products with a standard mold. They typically have a wide variety of standard molds with which they make commonly shaped and sized containers, jars and the like.
Variations and Similar Processes
Extrusion blow molding is the simplest of the three blow molding methods. Extrusion blow molding involves melting plastic extruding it into a parison, then expanding the parison with compressed air. Extrusion blow molding allows for a wide range of sizes, shapes, handle ware, and openings for containers. Notably, extrusion blow molding only makes hollow products. When creating the containers, the extrusion blow molding process utilizes two mirror molds, which result in a seam running down the middle of the product.
Injection blow molding hybridizes the processes of blow molding and injection molding. During the injection molding process, the plastic preform is injection molded before being blown into a mold inside the injection blow molding machine. The injection blow molding process is not suitable for manufacturing any kind of handle ware but is permissible for small containers.
Stretch blow molding is divided into two different methods: injection stretch blow molding (ISBM) and reheat and blow molding (RHB). These processes are often used to manufacture bottles for beverages such as water and juice.
ISBM (injection stretch blow molding) involves injection molding a preform, and then moving it to the next station to be blow-molded. ISBM is a costly process, and is used to manufacture liquor bottles, water bottles, and peanut butter jars.
RHB (reheat and blow molding) involves purchasing a preform from another vendor who has already injection-molded the material. The preform is reheated to prepare it for the blow-molding process. RHB is much more cost-effective than ISBM, because it eliminates the need for injection molding equipment and provides access to various pre-made preforms.
Benefits
The blow molding process has many advantages, especially when compared to other methods of plastic manufacturing. First, blow molding is cheaper than injection molding. In part, this is because it requires so few tools. Second, unlike many others, blow molding is suitable for fabricating plastic parts that are hollow. Third, blow molding has a faster cycle time than other processes, such as rotational molding. Another benefit of blow molding is its ability to perform high volume production runs. On top of this, it can be used to mold complex parts.
Things to Consider
Blow molding has a few disadvantages that you should keep in mind. First, blow molding can struggle to yield even wall thickness. If even wall thickness if one of the most important things for you, then we recommend checking out rotational molding instead. Also, from time to time during this process, the plastic can spring leaks or develop holes.
If you have decided that blow molding is the right process for you, your next logical step is locating the right manufacturer. Who is the right manufacturer? The right manufacturer is the one who will not only manufacture blow-molded plastic parts to your satisfaction within your timeline and budget, but who will consult with you and provide high quality customer service from beginning to end. To find a blow molder like that, check out those we have listed on this page. We&#;ve put together a comprehensive directory of those blow molding companies that we have found to be the most experienced, reliable and service-oriented. To choose from them, start by putting together a list of your specifications. Then, with it right next to you, check out the profiles of the companies on this page. Pick out three or four you believe hold the most promise, then reach out to each of them individually. Discuss your application at length, making sure to address all your questions and concerns. Once you&#;ve done that, compare and contrast your conversations. Pick the manufacturer that will best serve you and get started.
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Blow Molding Informational Video
HDPE blow molding is a highly efficient manufacturing process for producing hollow products like milk drinking bottles, beverage containers, edible oil bottles,engine oil bottles,lubrication oil bottles,plastic jerry cans, chemical drums,chemical or pharmaceutical bottles...Despite its potential to create high-quality containers, challenges can arise during the blow molding process. Identifying the root causes of these issues and knowing how to address them is crucial.In this article, we will explore the 6 top common defects and problems encountered in the production of HDPE blow molding products, along with their potential causes and effective solutions:
1.Rocker Bottoms in HDPE Blow Molding Bottles
Rocker bottoms in blow-molded bottles are a common issue caused by various factors, and addressing them is vital to ensure product quality. Rocker bottoms refer to the instability or rocking motion of the base of a bottle. Below, we delve into the causes of this problem and suggest effective solutions:
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1)Insufficient Cooling
One primary cause of rocker bottoms is insufficient cooling of the blown bottle before it is removed from the mold. To remedy this, consider increasing the water flow in your cooling system. If this adjustment doesn't yield the desired results, inspect the cooling channels of the blow molding machine for any blockages and clean them thoroughly.
2)Excessive Parison Thickness in the Flasher Area
Another potential culprit for rocker bottoms is excessive thickness of the parison in the flasher area at the bottom of the bottle. This excess thickness prevents the mold from fully closing at that point and results in incomplete contact between the material and the mold. To address this issue, ensure that the parison thickness in this area is appropriate to allow the mold to close fully.
3)Poor Air Exhaust
In some instances, rocker bottoms can be traced back to inadequate air exhaust from the product's neck after the blowing cycle has concluded but before the mold opens. During the forming process, constant air pressure pushes the parison walls against the mold. When this process concludes, the blow pin nozzle should retract slightly to release any excess pressure. Failure to do so can lead to pressure expansion at the bottom of the bottle, causing instability. Therefore, it's essential to ensure proper air exhaust mechanisms are in place.
2.Leakage
There are various factors problem cause the leakage from HDPE bottles.It might result from a tear in the bottle's wall, inadequate welding of molten plastic in critical areas like the bottom, sides, or top handles. Another culprit could be the contamination of melted resin by dirt or impurities originating from recycled materials, leading to non-leakproof walls.For plastic products with narrow necks, such as bottles, jerry cans, and narrow-mouth drums, pinpointing the source of leakage can be challenging. When designing the tooling for your product, it's essential for the blow molding manufacturer to ensure a precise match between the blow pin nozzle and the mold. Depending on the parison wall thickness, the gap between these components should be narrow enough to allow the blow pin to push the material inside the mold, ensuring that the plastic adequately fills the space between the mold and the blow pin. This prevents the top of the neck from developing irregularities that can cause leakage when sealing the container. If this gap is too large, the material won't be pushed inwards effectively, resulting in an uneven top surface and potential leakage issues.
3.Tearing of Joint Line During Deflashing in HDPE Blow Molding
The occurrence of tearing in a container during the deflashing process, particularly at the joint lines of the product such as handle parts and the bottom parts, can pose significant challenges in HDPE blow molding.One of the most prevalent causes of this issue is the speed of the mold closes, specifically the slow-speed phase of the clamping unit's operation. Let's delve into this issue and its possible solutions:
1)Slow Mold Close Speed
To understand this issue, it's essential to recognize that the clamping unit closes the blow mold in two steps: the first mold close (fast speed) and the second mold close (slow speed). The purpose of the slow-speed mold close is to ensure that the material is pushed inward into the mold, creating robust welding lines. This process is critical for preventing tearing at these areas when removing the excess flash material. If your bottle, drum, or jerry can is experiencing tearing at the welding lines during deflashing, consider reducing the speed of the slow mold close. This adjustment can help alleviate the problem.
2)Insufficient Parison Thickness
If reducing the slow mold close speed doesn't resolve the tearing issue, it may be due to insufficient parison thickness at the handle area of the jerry can or in the bottom flasher area. To address this, increase the thickness profile at these specific points in the parison. By ensuring that an ample amount of material is present when the mold closes, you can provide adequate support for the welding process, minimizing the risk of tearing.
3)Cooling System Design
If tearing continues to be a problem despite the aforementioned adjustments, the issue may stem from an inadequately designed cooling system for the mold. Proper cooling is essential to ensure that the material sets correctly and forms strong welding lines. Review and optimize your mold's cooling system design to ensure that it adequately cools the product during the blow molding process.
4.Addressing Uneven Radial Wall Thickness in HDPE Blow Molding
Achieving a uniform radial wall thickness in your jerry cans, bottles, or drums is crucial for maintaining product quality and preventing excessive shrinkage. But why does uneven thickness occur? A product with an uneven radial thickness will exhibit a thinner side that cools down faster than the thicker side, necessitating extended cooling time to prevent excessive shrinkage.
To rectify this issue, consider the following solutions:
1)Alignment of Die Mandrel and Die
Ensure that the die mandrel (pin) and the die are properly aligned. This alignment is essential for producing an extruded parison that appears straight. Correct alignment minimizes the chances of thickness variations along the radial wall.
2)Adjust Die Mouth Diameter
Parisons with larger diameters are inherently easier to control than narrower ones. Increasing the die mouth diameter can help promote a more consistent radial wall thickness. This adjustment contributes to better control over the distribution of material and, consequently, minimizes variations.
3.)Reduce Pre-Blow
Another strategy to address uneven radial wall thickness is to decrease the pre-blow of the parison. Reducing the pre-blow helps create a more uniform starting shape for the parison, which can lead to improved consistency in wall thickness as it expands during the blow molding process.
5.Finish Trim Imperfections
Efficiently trimming the flasher from jerry cans and bottles requires minimal effort from the operator, or if using an automated deflashing unit, a seamless process. When the deflashing process falls short of expectations, it often indicates inadequate clamping force in the flasher area of the mold. This frequently occurs when a smaller mold is utilized in a blow molding machine designed for higher-volume ranges, such as using a 1L or 5L jerry can mold in a machine tailored for 10L &#; 25L jerry cans. This approach is neither ideal nor recommended because the clamping force becomes misaligned, leading to improper cutting around the flasher area. Consequently, the optimal solution is to avoid using a mold that does not match the specific blow molding machine.If you are indeed using molds that are compatible with the machine but still encounter this issue, it may be attributed to inadequate cooling of the flasher. This can result from suboptimal mold cooling system design or insufficient cooling water flow. Alternatively, it may occur because the parison thickness is excessive in the flasher area, preventing the mold from closing completely and impeding sufficient flasher cooling for trimming. To rectify this, consider reducing the thickness in the flasher areas of your bottles, drums, or jerry cans.
6.Addressing Surface Wall Defects in HDPE Blow Molding
In HDPE blow molding, surface wall defects can manifest in various forms, from subtle imperfections like tiny black spots to more noticeable issues like horizontal ring-like lines, vertical streaking lines, wall bubbles, and rough, rippled surfaces resembling "orange peel." Each of these defects can impact the quality of your bottles or containers and may arise due to different factors. Here, we explore these common defects, their causes, and effective solutions:
1)Black Spots
Black spots on your HDPE jerry cans or bottles often result from foreign matter or degraded old resin inside the extruder die head. These contaminants mix with the molten plastic, leading to differently colored spots on the final product. In some cases, foreign matter or old resin can become lodged inside the die bushing, causing distortion or vertical lines in the extruded parison and resulting in streaking lines on the product. To address this issue, it's essential to identify the location of contamination within the die head and thoroughly clean it.
2)Wall Bubbles
Wall bubbles occur when moisture or water particles condense in the cold resin, typically in warm and high-humidity climates. To prevent this defect, consider installing a hopper dryer or maintaining the resin's warmth to evaporate condensed water before it enters the extruder hopper. Additionally, ensure that the cooling water flow in the extruder feed opening is not excessive.
3)Horizontal Ring-Like Lines
Horizontal ring-like lines encircling your drums or jerry cans are a result of significant variations in parison thickness between two consecutive points. This discrepancy causes the parison thickness controller to adjust the die or die mandrel rapidly, leading to the formation of ring-like lines on the product. To prevent this issue, gradually adjust the thickness between profile points and maintain consistency between the thickness of the first and last profile points.
4)Rippled Surface or "Orange Peel" Effect
A rough surface resembling ripples or orange peel texture can occur when the parison wall makes contact with the cold mold surface twice intermittently rather than just once. This premature solidification and subsequent stretching of the wall disrupt the smoothness of the parison. This problem is more common with oval-shaped jerry cans and bottles, where the parison is narrow, and a high pre-blow is used to achieve an oval shape before the cycle blow. To resolve this, consider using a larger die mouth to reduce the pre-blow. The oval shape required for the bottle will be achieved during the cutting and sealing phase of the blow molding process.
What to Consider?
Defects can significantly impact your production output and your relationship with valuable clients, which is undesirable for a blow molding plastic products manufacturer. Likewise, as a purchaser of blow molding plastic products, accepting subpar quality is simply not acceptable according to the required standards.
Therefore, it is imperative to conduct thorough inspections of your bottles, jerry cans, or drums. Should you encounter any of the previously mentioned defects, it is essential to pinpoint their origins and determine how to prevent or rectify them. While some rejected pieces may occasionally emerge, the goal is to keep these instances below 1% or at an absolute minimum.
Choosing the Right Blow Molding Machine
Selecting high-quality machinery is the foremost preventive measure to avoid issues. When acquiring an Extrusion Blow Molding Machine, ensuring consistent quality in the containers it produces is paramount. High output is of little value if a significant percentage of jerry cans or bottles are rejected during production.Hence, choose a good extrusion blow molding machine manufacturer is very important.These include guaranteed quality consistency, high production efficiency, reliable after-sales service, cutting-edge technology, and competitive pricing.
When procuring a blow molding machine from EVERWIN, you can be confident that our high-performance machines will operate with maximum efficiency, meeting all your specifications. Additionally, as customer, you will enjoy our lifetime after-sales support and within 24 hours online customer service.
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