Welcome to our comprehensive guide on how to choose the perfect blow molding machine! If you are in the market for this essential manufacturing equipment, you've come to the right place. Whether you are a seasoned professional or a newcomer to the industry, selecting the right blow molding machine can be a daunting task. With our expert tips, detailed insights, and years of experience, we aim to provide you with the information you need to make an informed decision. Discover the factors that matter, understand the various types and technologies available, and gain the confidence to invest wisely. Join us as we delve into the world of blow molding machines, promising to equip you with the knowledge necessary to find the ideal solution for your specific needs.

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Understanding the basics of blow molding machines

Understanding the Basics of Blow Molding Machines

Blow molding machines play an essential role in the manufacturing industry, particularly in the production of plastic products. These machines are utilized to produce a wide range of plastic containers, such as bottles, jars, and containers for various industries, including food and beverage, personal care, pharmaceutical, and household goods. As a leading manufacturer of blow molding machines, TECH-LONG is committed to providing high-quality, efficient, and reliable machines to meet the demands of different industries.

At its core, blow molding is a manufacturing process used to create hollow plastic products by inflating a heated plastic tube, also known as a parison, inside a mold until it takes the desired shape. Understanding the basics of blow molding machines is crucial for making an informed decision when choosing a machine that best suits your production needs.

1. Types of Blow Molding Machines:

There are three main types of blow molding machines: extrusion blow molding, injection blow molding, and stretch blow molding. Each of these types has its unique advantages and is suited for different applications. TECH-LONG offers a comprehensive range of blow molding machines that cater to all these types, ensuring that customers have an extensive selection to choose from.

2. Extrusion Blow Molding:

Extrusion blow molding is the most common and versatile type of blow molding used for producing plastic bottles and containers. It involves melting plastic resin and extruding it into a hollow tube, which is then inflated and cooled to obtain the desired shape. TECH-LONG's extrusion blow molding machines utilize advanced technology to ensure precise control and efficient production.

3. Injection Blow Molding:

Injection blow molding combines the injection molding and blow molding processes to create complex and intricate plastic products. It starts with the injection of molten plastic into a mold cavity, followed by the inflation and cooling stages. TECH-LONG's injection blow molding machines incorporate state-of-the-art features to deliver superior quality and efficiency.

4. Stretch Blow Molding:

Stretch blow molding is a process used to produce bottles with precise neck and thread finishes. It involves heating a preform and stretching it in both length and diameter to achieve the desired bottle shape. TECH-LONG offers high-performance stretch blow molding machines that ensure consistent and reliable production.

5. Key Factors to Consider:

When choosing a blow molding machine, several factors need to be taken into account. These include production capacity, product specifications, material compatibility, energy efficiency, and maintenance requirements. TECH-LONG understands the importance of these factors and strives to provide customized solutions to meet specific production needs.

In conclusion, understanding the basics of blow molding machines is crucial in selecting the right machine that suits your production requirements. TECH-LONG, as a reputable manufacturer of blow molding machines, offers a wide range of high-quality and efficient machines for various applications. By considering factors such as machine type, production capacity, and product specifications, you can make an informed decision when choosing a blow molding machine that fits your needs. With TECH-LONG's cutting-edge technology and commitment to customer satisfaction, you can trust them to provide reliable and innovative solutions for your blow molding needs.

Evaluating your specific production requirements

Evaluating your specific production requirements is a crucial step in choosing the right Blow Molding Machine for your business. As the market is flooded with numerous options, it becomes essential to assess your individual needs and make an informed decision. In this article, we will guide you through the process of selecting the perfect Blow Molding Machine, keeping in mind the keyword "Blow Molding Machine," and introducing our brand, TECH-LONG, as a reliable and renowned choice in the industry.

When it comes to Blow Molding Machines, each manufacturing facility has unique production requirements. These requirements depend on factors such as the type of products you intend to produce, production output, size, and technical specifications. Understanding these needs is crucial in evaluating various machine options and finding the one that best suits your business.

TECH-LONG, a reputable brand in the Blow Molding Machine industry, offers a wide range of machines carefully designed to cater to diverse production requirements. As a trusted name, TECH-LONG has gained recognition for its cutting-edge technology, reliability, and excellent customer support. Therefore, considering TECH-LONG as your choice is a step towards ensuring a production line that meets your specific needs efficiently.

To begin evaluating your production requirements, you need to identify the type of products you plan to manufacture. Blow Molding Machines are used in various industries, including packaging, automotive, and medical, to produce items such as bottles, containers, and even automotive parts. Determining the specific products you intend to manufacture will help narrow down your options and choose a machine tailored to your industry's demands.

Another crucial aspect to consider is production output. The quantity of products you need to manufacture within a given timeframe will influence the type of Blow Molding Machine best suited for your business. TECH-LONG offers machines designed for both high-volume production lines and smaller-scale operations, enabling you to find the most suitable solution for your production demands.

In addition to production output, the size of the products also plays a pivotal role in choosing the right Blow Molding Machine. Different machines have varying capacities for producing products of different sizes. TECH-LONG provides a range of machine options, ensuring compatibility with various product dimensions. Whether you require small bottles or large containers, TECH-LONG has a machine to meet your specific size requirements.

Technical specifications are equally important when selecting a Blow Molding Machine. Factors such as the type of resin, machine cycle time, and extrusion capacity need to be considered. TECH-LONG's extensive range of machines covers a wide spectrum of technical requirements, allowing you to choose a machine that aligns perfectly with your production needs.

By carefully evaluating your specific production requirements, considering factors such as product type, production output, size, and technical specifications, you can make an informed decision about which Blow Molding Machine to choose. The commitment to quality and reliability offered by TECH-LONG makes it a brand you can trust to deliver exceptional results.

In conclusion, when searching for the perfect Blow Molding Machine, it is vital to evaluate your individual production requirements thoroughly. TECH-LONG, a trusted name in the industry, offers a diverse range of machines suitable for various industries and production demands. By considering TECH-LONG's advanced technology, reputation, and commitment to customer satisfaction, you can ensure a successful and efficient production line tailored to your specific needs. Choose TECH-LONG for a reliable and superior Blow Molding Machine that meets all your business requirements.

Key factors to consider when selecting a blow molding machine

Blow molding machines have become an essential tool in many industries, including packaging, automotive, and consumer goods. With their ability to create hollow plastic parts with precision and efficiency, these machines are revolutionizing the manufacturing process. However, with the market flooded with various options, it becomes challenging for businesses to select the most suitable blow molding machine. In this article, we will discuss the key factors to consider when selecting a blow molding machine, helping you make an informed decision for your manufacturing needs.

1. Machine Type: There are three main types of blow molding machines - extrusion blow molding, injection blow molding, and stretch blow molding. Each type has its own advantages and limitations. Extrusion blow molding is ideal for large-scale production and produces containers with a continuous parison. Injection blow molding is suitable for producing complex shapes and tight tolerances. Stretch blow molding is commonly used for producing bottles with intricate details. Consider your specific requirements and choose the machine type that best fits your production needs.

2. Machine Size and Capacity: The size and capacity of the machine directly impact your production capabilities. Consider the size of the products you intend to manufacture and choose a machine that can accommodate the desired dimensions. Additionally, assess the production volume and select a machine with the appropriate capacity to meet your demands. It is crucial to strike a balance between the machine's capabilities and your production requirements to maximize efficiency and minimize downtime.

3. Machine Quality and Durability: Investing in a high-quality blow molding machine is essential to ensure optimal performance and longevity. Consider the reputation and credibility of the manufacturer before making a decision. Look for machines that are made from durable materials and feature robust construction. Check for certifications and warranties that guarantee the reliability and longevity of the machine. Investing in a reliable and durable machine from a reputable manufacturer like TECH-LONG ensures that you get the best value for your money.

4. Automation and Integration: In today's fast-paced manufacturing environment, automation and integration play a crucial role in improving efficiency and productivity. Consider machines that offer automation features such as robotic handling, quick mold change systems, and advanced control systems. These features not only enhance production speed but also reduce human error. Moreover, choose a machine that can seamlessly integrate with your existing production line. This ensures smooth operations and minimizes disruptions during the integration process.

5. Energy Efficiency: As sustainability becomes a top priority for many businesses, it is crucial to choose a blow molding machine that is energy-efficient. Look for machines that incorporate energy-saving technologies such as servo-driven systems and efficient heating methods. These features not only reduce energy consumption but also result in cost savings in the long run. A TECH-LONG blow molding machine is known for its energy-efficient design, helping businesses minimize their carbon footprint while optimizing production.

In conclusion, selecting the right blow molding machine is a critical decision that can significantly impact your production capabilities and profitability. Consider the machine type, size, capacity, quality, automation, integration, and energy efficiency when making your decision. By carefully evaluating these factors and choosing a reliable and reputable manufacturer like TECH-LONG, you can ensure that your blow molding machine meets your specific requirements and contributes to the success of your manufacturing operations.

Comparing different types and models of blow molding machines

Comparing Different Types and Models of Blow Molding Machines

Blow molding machines have become an essential tool in the manufacturing industry, particularly for producing hollow plastic products such as bottles, containers, and tanks. With the advancement of technology, different types and models of blow molding machines have emerged, offering manufacturers a wide range of options to choose from. In this article, we will delve into the intricacies of blow molding machines, highlighting the various types and models available in the market.

One of the leading names in the blow molding machine industry is TECH-LONG. With a focus on innovation and quality, TECH-LONG has gained a reputable position as a renowned manufacturer and supplier. Let's explore the different types of blow molding machines offered by TECH-LONG as we aim to educate manufacturers on how to choose the most suitable machine for their production requirements.

1. Extrusion Blow Molding Machines:

Extrusion blow molding machines are widely used in the industry due to their versatility in manufacturing products of various shapes and sizes. TECH-LONG offers a range of extrusion blow molding machines that utilize the extrusion process to produce hollow plastic products. These machines efficiently melt the plastic material and shape it into a parison, which is then inflated to form the desired product.

2. Injection Blow Molding Machines:

TECH-LONG also offers injection blow molding machines, which are ideal for producing high-quality, intricate products. These machines combine the processes of injection molding and blow molding to create seamless and precise hollow products. Injection blow molding machines are commonly used for manufacturing medical bottles, pharmaceutical containers, and other small-sized products requiring intricate designs.

3. Stretch Blow Molding Machines:

For manufacturers looking to produce PET bottles or containers, TECH-LONG's range of stretch blow molding machines comes to the rescue. These machines employ the stretch blow molding process to create clear, strong, and lightweight bottles commonly used in the beverage, cosmetics, and household products industry. With their advanced technology, TECH-LONG's stretch blow molding machines ensure exceptional product quality and high production efficiency.

In addition to different types, blow molding machines also come in various models, each offering unique features and capabilities to suit specific production requirements. TECH-LONG provides a range of models, including the TL-Series, BM-Series, and EV-Series, all designed to meet different production demands while maintaining the highest standards of quality and efficiency.

The TL-Series models are known for their excellent energy-saving performance and compact design, making them the ideal choice for small to medium-sized manufacturing operations. The BM-Series machines, on the other hand, are renowned for their high-speed production capabilities, ensuring optimal efficiency for large-scale production facilities. The EV-Series models combine the strengths of both energy-saving and high-speed production, striking the perfect balance for manufacturers looking to maximize productivity without compromising on energy consumption.

Considering the investment required to acquire a blow molding machine, it is crucial for manufacturers to carefully evaluate their production needs and budget constraints. When choosing a blow molding machine, factors such as the type of products to be manufactured, production volume, desired quality, and efficiency must be taken into account. By partnering with a trusted manufacturer like TECH-LONG, manufacturers can ensure they find the most suitable blow molding machine that aligns with their requirements.

In conclusion, comparing different types and models of blow molding machines is essential for manufacturers seeking to optimize their production processes. TECH-LONG, a leading brand in the industry, offers a wide range of blow molding machines, including extrusion, injection, and stretch blow molding machines. With their advanced features and capabilities, TECH-LONG machines cater to various production demands, ensuring exceptional quality and efficiency. By carefully analyzing their production needs and partnering with TECH-LONG, manufacturers can make an informed decision and choose the perfect blow molding machine for their manufacturing operations.

Making the final decision: Factors beyond just the machine itself

Choosing the right blow molding machine is a critical decision that can greatly impact the success of a business. With numerous options available in the market, it can be overwhelming to determine which machine will best suit your needs. While considering the specifications and features of the machine is important, there are several other factors that go beyond just the machine itself. In this article, we will explore these factors and provide guidance on how to make an informed decision when choosing a blow molding machine.

When it comes to blow molding machines, TECH-LONG is a trusted brand known for its high-quality and reliable equipment. TECH-LONG has been an industry leader and has established a strong reputation for delivering top-notch blow molding machines. With their extensive experience and expertise, TECH-LONG understands the importance of considering factors beyond just the machine specifications.

First and foremost, it is crucial to assess the specific requirements of your business. Consider the type of products you will be manufacturing, the desired production capacity, and any specific customization or special features you may require. Understanding your unique needs will help you narrow down the options and choose a machine that is the best fit for your business.

Another important factor to consider is the machine's energy efficiency. Energy costs can significantly impact the overall production costs, and it is essential to choose a machine that is designed to minimize energy consumption. TECH-LONG blow molding machines are known for their energy efficiency, ensuring optimal production while minimizing energy expenditure.

In addition to energy efficiency, it is also important to consider the machine's maintenance requirements. A machine that requires frequent repairs or extensive maintenance can lead to unexpected downtime and increased costs. TECH-LONG blow molding machines are built with durability and longevity in mind, minimizing maintenance needs and maximizing uptime.

Furthermore, it is crucial to consider the level of technical support and customer service provided by the manufacturer. Timely and effective technical support can be pivotal in resolving any issues that may arise during the machine's operation. TECH-LONG, with its strong commitment to customer satisfaction, provides excellent technical support and customer service, ensuring that any concerns or problems are promptly addressed.

Additionally, it is beneficial to evaluate the reputation and track record of the manufacturer. A brand with a long-standing history of delivering high-quality machines speaks volumes about their expertise and reliability. TECH-LONG has a proven track record of manufacturing top-of-the-line blow molding machines and has gained the trust and loyalty of numerous satisfied customers worldwide.

Lastly, it is vital to consider the long-term partnership potential with the manufacturer. A blow molding machine is a significant investment, and it is important to choose a manufacturer that is dedicated to building a lasting relationship with their customers. TECH-LONG not only provides high-quality machines but also strives to establish strong partnerships with its clients, offering ongoing support and maintenance services.

Choosing a blow molding machine goes beyond just the technical specifications. It is a decision that requires careful consideration of multiple factors, including the specific requirements of your business, energy efficiency, maintenance needs, technical support, manufacturer reputation, and long-term partnership potential. By keeping these factors in mind and choosing a trusted brand like TECH-LONG, you can make an informed decision and ensure the success of your blow molding operations.

Conclusion

1. The importance of considering the specific needs of your industry: When choosing a blow molding machine, it is crucial to understand the unique requirements of your industry. Whether you are in the packaging, automotive, or healthcare sector, selecting a machine that aligns with your production goals and quality standards is essential. By considering the specific needs of your industry, you can ensure that the chosen machine will optimize your production processes and deliver superior results.

2. The significance of evaluating machine features and capabilities: In the process of choosing a blow molding machine, it is vital to thoroughly evaluate the features and capabilities offered by different models. Factors such as mold size, capacity, energy efficiency, versatility, and automation options should be carefully considered. By selecting a machine with the right set of features, you can enhance the efficiency, productivity, and profitability of your manufacturing operations.

3. The role of technology advancements in blow molding machines: As technology continues to advance, blow molding machines are becoming more sophisticated and efficient. From advancements in material distribution systems to precise controls and monitoring capabilities, these technological innovations are revolutionizing the industry. It is crucial for manufacturers to stay updated with the latest trends and choose machines that incorporate the most recent technological advancements to stay competitive in the market.

For more information, please visit tailored blow molder.

4. The significance of considering long-term costs and maintenance: When choosing a blow molding machine, it is essential to not only consider the initial purchase cost but also the long-term expenses. Factors such as energy consumption, maintenance requirements, and spare parts availability should be evaluated. Opting for a machine that offers low ongoing costs and easy maintenance can contribute to a higher return on investment and prolonged equipment lifespan.

In conclusion, selecting the right blow molding machine involves understanding the specific needs of your industry, evaluating machine features, keeping up with technology advancements, and considering long-term costs and maintenance. By taking these perspectives into account, manufacturers can make an informed decision and choose a machine that will best suit their production requirements, optimize productivity, and ensure the longevity of their manufacturing operations.

The Custom-Pak blow molding design guide provides you with basic design tools for making engineered blow molded parts. This guide focuses on the extrusion blow molding process. No two designs are alike, so the mold and process must be adjusted to optimize each design. Software products can help predict molding characteristics and our engineers are here to help make your product great. Our design assistance is confidential and free.

A. Blow-Molding Process
B. Materials
C. Capturing the Parison
D. Exterior Cavity-Mold Design
E. Interior Core-Mold Design
F. Air Space
G. Creating Structure
H. Finishing

Blow molding is a simple five-step sequence.

A. Blow Molding Process 

1. The first step involves mixing, melting and pushing plastic (extrusion) to form it into a tube called a parison that will be used to make the part.
2. A mold is used to make the part shape you desire. The mold has two halves that are closed around the molten parison.
3. Air is blown into the inside of the parison to expand the molten plastic against the mold surface.
4. The mold is cooled to set the plastic to the new shape of the mold.
5. The molded plastic part is removed from the mold, separated from excess parison material called flash, and finished. (Most finishing steps can be completed in-mold but some involve secondary operations.)

B. Materials

Material selection is a critical aspect of design and should involve serious study of:

1. the plastic resin properties
2. the material cost
3. the processing properties
4. your finished-part objectives

Although there are thousands of plastic materials available, most won't meet the needs of your product. Experience with blow molding grade materials is essential and we have practical molding experience using every blow moldable material

Commodity Materials 

Some of the least expensive materials are also the easiest to process. Polyethylene (PE) and polypropylene (PP) are the most popular blow molding resins. PE is currently less expensive but PP tends to be stiffer which sometimes offsets the cost difference. These materials are resistant to most chemicals. One difference is temperature performance with PE performing better at -75 to +160 degrees F and PP performing well from -0 to +170 degrees F. These materials usually form parts matching the principles discussed in this design guide.

Engineering Resins 

Many engineering-grade resins can be blow molded. Some of the acronyms include PPO, PC, PETG, ABS, TPE ' you get the idea. These resins require special consideration prior to molding. Most require drying before processing, specially designed extruder screws and specific processing conditions. The design criteria in this guide may not apply to parts molded from some engineering resins. Please obtain the correct design information for your specific project directly from our engineering personnel.

C. Capturing the Parison 

In order to design a blow molded product, you must understand the interaction between the molten plastic parison and the mold. If you've blown a bubble from bubble gum you can understand blow molding. The plastic material stretches like the gum and if it gets too thin it ruptures. Since the parison is extruded as a tube, it is easy to make a tube or bottle shaped part, not much stretching occurs. The two mold halves open, the parison is inserted,the mold halves close and the part is blown.  The split between mold halves is known as the parting line. There is often a knife like edge on the parting line around the part shape known as pinch-off.

If the part shape to be molded is changed from a tube into a flat panel type part, the
parison tube must be flattened to make the panel. When this happens the circumference of the parison becomes the surface that needs to cover the width of the panel. So we try to have a large enough parison diameter that as it flattens, it can be captured by the entire perimeter of the panel at the  pinch-off. If the parison does not extend to all areas of the pinch-off, it must stretch the rest of the way.

The soft plastic can stretch only a short distance before it begins thinning. Like the bubble gum, the first thin spot is weakest and it gets thinner fastest until it pops. If the plastic parison pops it is called a 'blow-out' and results in no part formation at all.

As the complexity of the part progresses to double-wall shapes with side walls and inner contours, the parison must not only be captured at all points along the parting line, but it must also meet the material thickness needs for the variety of molding conditions specific to each area of the part. Many of the design criteria used to make a tray with molded inner shapes will be the same for designing a complex industrial part.

D. Exterior Surface (Mold Cavity) Design

The inner and outer walls of the part are formed simultaneously and integrally, but interior and exterior designs are essentially independent so we review them separately. As the design develops, the designer should begin thinking about the interaction of the plastic and the mold that will produce the part. The visual exterior of many products is formed in one half of the mold called a cavity. Following are some of the features of mold cavities the designer will want to consider.

Cavity ' Cavity Blow Ratio = W>D 

A bottle is a typical example of a blow molded part formed using 2 cavity mold halves. A round bottle has a blow ratio that is comprised of a width=diameter and a depth=radius (2:1). The result is excellent material distribution in a round bottle. But, not all parts will be round. As designers start to push the limits of draw down into cavities, how far should they go? The answer depends on the elongation elasticity of the material and how thin a wall you are willing to accept. But as a rule of thumb, the material won't stretch much further down into a cavity (Depth=D) than than the width of material available to fit into the cavity (Width=W). So, try not to design your cavity-cavity part to be deeper than the width.

Cavity ' Core Blow Ratio = W>2D 

Many industrial parts are formed using a combination of cavity and core mold elements where the core forms interior shapes. The core changes the blow ratio parameters.

The diameter of the cylindrical parison that forms a double wall part must allow enough material to enter the mold to adequately form each half of the part. Half of the cylindrical parison is used to form the exterior half (cavity) of the part and the other half of the cylindrical parison forms the interior half (core) of the part. Since there is no flow of material along the mold walls (only stretching), it follows that the depth of the cavity (D) should be no more than one-half the length or width of the cavity(W). A part design utilizing cavity depths that exceed this relationship will be subject to severe thinning or blow-out. So like the relationship between diameter and radius, cavity-core parts should have overall blow ratios of W>2D.

With multiple or divided cavities each cavity should meet this W>2D requirement.

The design of certain complex parts will require changes in the parting-line location in order to stay within this relationship. These steps in the parting line must include clearance for repeated opening and closing of the mold halves and be positioned so they do not shear the parison during mold-close. A parting line angle of 10° draft or greater is generally designed into mold parting line steps. When 10° draft is not possible, options like angling the mold in the machine so that the parting lines form a positive draft relative to one another or moving mold sections can be used.

Sidewalls & Draft 

The plastic parison sticks and begins to solidify as soon as it hits the mold. The material then stretches to fill the cavity as blowing progresses. There is no flow of material along the mold walls. There are three aspects of thinning to consider.

1. The thinning caused by stretching results in weakness. Any thin, weak location is susceptible to further thinning because it has become thin & weak. The thinning progresses rapidly in these locations.
2. The apparent rigidity (or strength) of any area on the part varies proportionately with the square of the wall thickness.
3. Variation in wall thickness can result in warpage.

The thinning along sidewalls and in corners is the reason that parts should have outside draft angles. Exterior draft is not critical to part removal from cavities since the plastic shrinks away from the outer mold walls as it cools. Draft is recommended when exterior walls are to be textured.

Plastic contouring of heavy parison sections to match these critical areas can improve 
the condition but not eliminate it.  Because of this, cavity design must avoid features that contribute to thinning. Designs that utilize sharp 90° corners will result in parts with extremely thin, weak corners. There are a variety of corner configurations that improve or alleviate this problem. The most common approach is angling the sidewall and putting a radius or an chamfer-angle at the corner.

Part removal may be a problem with back-draft sections. Back-drafted areas can lock the part in the mold. If possible, a part with back draft on one side should have an equal positive draft on the opposite side. Thus, a part with a 15° back draft on one side and a 15° positive draft on the other side can be removed like a part with no draft. Otherwise, molds may need moving sections to remove the back drafted feature.

Shrinkage & Warpage 

Shrinkage varies by material, the rate of temperature change and the thickness of the material. For PP and PE materials, the material thickness is the best predictor. Thin wall parts may shrink as little as 1% and thick parts in excess of 10%. A .060' thick  part will shrink approximately 1.65% as it cools and a .125' thick part will shrink about 1.85%. The shrinkage expectation must be taken into consideration when setting the mold  size.

Designs that allow wall thinning variation to occur in the part may result in warped parts. The thin areas will shrink less before cooling than the thick areas. The variation in shrinkage rates and distances can cause the part to warp. Some wall thickness & shrinkage variation occurs in every molded product because the cooling rate of the plastic will vary. The skin of the material against the mold metal will cool and take a set before the material not actually touching the mold metal. The result is a tendency for outer walls to warp inward and is offset by the tendency of the inner wall to warp outward. The use of structural ribs, welds between walls, arcs or steps can create a structure that helps reduce warpage.

Cooling 

To control dimensions, surface appearance and warpage, it is important to have as much control over the cooling of the part as possible. Flow rate is a major factor in heat removal and cycle time. By creating turbulent flow, heat extraction and cycle times can be improved. To control warpage in many designs, it is essential that the mold cooling be targeted to provide extra heat extraction in the heavier wall portions of the part. The overall flow pattern also affects the part quality. Water warms as it flows through the mold.

The mold should contain several inlets and outlets in an oscillating cooling pattern.
A cold mold surface can also cause problems in reproducing surface details such as texture. Tooling engineers can target water lines near each critical section of the mold to provide the dimensional control and appearance you need.

Venting

When the mold closes the parison is captured at the pinch-off. A certain amount of air is trapped between the outside of the parison and the mold cavity. When air is blown to
expand the parison, the trapped air becomes compressed by the expanding parison until an interior ' exterior pressure equilibrium is reached. When this occurs, the parison will not completely touch the mold wall. The results are visible surface abnormalities, loss of texture & engraving detail, the appearance of creases and drag-lines, and longer cycles from poor mold cooling.

Venting can be easily located at the edge of any insert in the cavity. Slotted vent inserts or porous metals can be purchased and fit into nearly any location. Some venting methods will produce visible markings on the finished part. Texture, inserts and other techniques can be employed to mask the markings made at the vent location.

E. Interior Surface (Mold Core) ' Design

The interior surface of double-wall blow molded parts is normally formed by a mold core. Since the mold core must fit inside the cavity, there should be no question it meets the same W>2D overall size requirement as the cavity.

The half of the parison that is draping over the mold core is already beginning to set as the air is injected into the parison. As in the cavity, the plastic begins to stretch to fit the mold contour. Almost no flow occurs. Unlike the cavity, some different rules apply.

Blow Ratio ' W>D 

As the mold halves close on the parison, the core presses against the parison and forces it into the cavity until the pinch-off is sealed around the perimeter of the part. The highest point on the core forms the deepest depression inside the part.

If the double-wall part design has a dividing wall between two compartments, this wall is formed by stretching the plastic into a groove in the mold core. As the plastic begins stretching into a groove, it begins to thin. If the groove is too deep, the plastic quickly reaches the point where it thins until the internal air blows-out through the wall to the outside of the part. No part will form.

Because of this, there is one simple yet absolute rule, which governs the design of the ribs or divisions between compartments. The depth (D) of the groove between core sections must not exceed the width (W) of the rib W>D. This rule also applies to other structural shapes. For example, a 1' tall, round post in the center of a tray would have to be 1' or more in diameter.

If the part design requires a mold parting line which steps to various levels for the part to function properly, then the core must have a positive draft on these steps at the pinch-off to match the pinch-off on the cavity element of tooling. Varying pinch-off levels can change the W-D relationships of nearby pockets or ribs. All of the levels within a part must pass the W>D requirement in each direction.

Sidewalls & Draft 

When the mold closes, half of the parison is draped over the mold core to form the interior of the part. As the plastic cools, it shrinks onto the metal mass of the mold core. Positive draft is needed on all sides of the mold core in order to remove the plastic part after it has shrunk. The more generous the draft, the easier the part can be removed from the mold. A part with 5° positive draft on all sides of the core can be removed with the assistance of ejector pins. Parts with lesser draft can also be removed with ejector pin assistance but as draft on the core decreases, the risk of damaging the part during ejection increases. If a core design requires a no-draft or back-draft section, a positive draft should be provided on the opposite side of the core, if possible.  Snap-fits and small undercuts can be fine-tuned to allow ejection.

With core-cavity molds, the parison becomes fixed at two levels, the top of the core and the pinch-off. When the part is blown, the fixed plastic walls stretch (no flow) to meet the sidewall of the core. A deep core with little draft and a sharp corner will produce a thin, weak-walled part. Draft, corner radii and chamfer-angles can help eliminate thin walls

Shrinkage & Warpage 

Overall the shrinkage of the interior will match the shrinkage of the exterior. But, the shrinkage of an interior shape is restricted by the metal core used to form the shape. Minor mold size adjustments may be needed to meet specific dimensions.

Interior part design must consider the potential for warpage. Warp will be caused by variations in wall thickness and material distribution during cooling. Both W>2D overall sizing and W>D localized draw ratios need to be followed throughout the part design to prevent warpage

Cooling

Frequently, the metal mass of the core is greater than the cavity and will require a greater cooling capacity. Targeting waterlines for optimal heat 
extraction can be critical to the success of the part.

Venting

Any location where air can be trapped between the parison and the mold wall is a location for a vent. Deep cores can trap large volumes of air and the blowing speed can require larger venting capacity for the trapped air to escape. If there is doubt, it is better to include a vent than to discover the problem at production.

F. Air Space 

It is the combination of closing the mold on the parison and the expansion of air inside the parison that forms the part. The designer must leave sufficient space between the inner and outer part surfaces to permit adequate blowing of air into every square inch of the part. If the air passage inside the part is reduced or obstructed, the part will not form.

Distance Between Walls 

There are no clear-cut rules regarding the amount of air space needed between inner and outer walls to form a part. Smaller and lighter gauge parts seem to require less air space than large and heavy-gauge parts. Sidewalls typically require slightly more air space than bottom or top surfaces. Rule-of-thumb minimums for air space in parts up to 1 sq.ft. would be 3/8' on sidewalls and 3/16' on top or bottom surfaces. Parts larger than 1 sq.ft. should form adequately with 5/8' air space between sidewalls and 5/16' on top and bottom surfaces. The more air space you can allow, the better the part will form. It is also interesting to note that thin panels can become stronger by increasing the distance between walls.

Webbing 

There is a molding phenomenon called webbing that can occur when the mold closes. As the core and cavity mold pieces close onto the parison, the parison is rapidly transformed from a tube or bag shape into a functional configuration. As the core is pushing the parison into the cavity it is possible for the opposite sides of the parison to touch before the air is injected to form the part. When this happens, the plastic welds together inside the parison and when the parison is inflated, the weld resists separation. The result is either a part with a very thin, weak section all around the welded web or, if the nearby material tears when the parison is inflated, it blows out and no part forms.

Webbing is more pronounced in deep cavities with corresponding deep cores. However, certain configurations can make the parison collapse or fold back on itself to cause webbing when the mold closes. It is a good idea to ask for a simulation test on deep parts that might produce webbing.

Compression Molding 

Many functional designs are greatly enhanced by the inclusion of compression-molded tabs, locks or mounting surfaces.

Compression molded tabs can be added at any point along the mold parting line on the same plane as the pinch-off. To change the angle of a tab relative to the basic parting plane, you must create a mold parting line at the desired angle. This can be done with angled parting line steps or inserts along the perimeter of the part or moving inserts within the part.

When blow molded parts are to be combined with other parts through the use of mounting screws, bolts or rivets, an exceptionally strong mounting surface can be provided by compressing the inner and outer walls together. The two walls can be compressed together at nearly any angle or location as long as there is ample room surrounding the compression for good airflow and as long as the mold halves can close without interference.

By compression molding inner and outer walls together, the part rigidity and straightness can be improved significantly. It is also an excellent way to provide stacking strength when dealing with heavy loads

G. Creating Structure

The double walls in blow molded parts provide engineers with a tremendous opportunity to create structure within the plastic part. A properly designed double-wall part will be substantially stronger than a ribbed single-wall part of equal weight and can easily outperform metals in many applications. There are several ways to add strength to blow molded part designs.

Weld Cones & Tack-Offs 

By designing the mold to close in specific locations to a distance that is less than the combined thickness of inner and outer walls, a weld is formed. The amount of compression sets the strength of the weld. By adjusting the distance between mold halves to between 60% and 80% of the combined thickness of inner and outer walls, the weld can resist both compression and separation forces.

The location of welds within a part will determine the stiffness and ability to support loads. Designers must remember to pay attention to blow ratios between welds.

Ribs & Curves 

Ribs are very effective at adding strength to parts. Ribs can be designed to support expected forces in nearly any direction. Sidewalls can be ribbed to add stacking strength. Panels can be ribbed to improve stiffness and control sag. For best results, ribs should weld inner and outer walls together in controlled intervals. The rib location and length must also be such that a hinging action won't develop when loads are applied. By alternating rib directions in non-uniform patterns, ribs create excellent stiffness and the ability to support loads.

By combining curvature with ribs and weld cones, lightweight plastic parts can become stronger than steel. Circles and arches create some of the strongest structures on earth. Custom-Pak engineers can help with design evaluation and testing so you can be sure you will achieve the results you are seeking.

H. Finishing 

There are a limitless number of secondary operations that can be performed on a blow molded part to meet the needs of the finished product. Drilling, sawing, milling, cnc routing, die cutting, punching, riveting, screwing, sonic, spin or heat welding, and surface treating are common operations. Nearly any secondary step can be performed economically if the right equipment is available. A surprising number of operations can be done in-mold. Custom-Pak provides a huge variety of secondary operations equipment at no charge.

Decorating molded parts requires planning in the design stage. For heat transfer or hot
stamp decorating, the part design must provide a means to support the tonnage of the stamping process. For in-mold labels, magazines to hold the labels and mold surface locators must be prepared. For embossed plaques, the attachment method should be included in the part design.

Texture is commonly applied to mold surfaces. Blow molding textures are typically etched .008' to .012' deep in the mold surface (much deeper than injection molding). Draft may be needed to allow the texture to form and still release from the mold. There are many ways to get the appearance that you want in your blow molded parts. We can help you make sure your design will look great long after the consumer has made their purchase.

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