Maya Ellison
Plastic pellets need to be dried before they are used for injection moulding or extrusion. This is because they can absorb moisture from the air, which can cause cosmetic defects in the final product, such as streaking or bubbling. There are several ways to dry plastic pellets, including using an oven, dehydrator, vacuum dryer, or hopper dryer. However, one of the most effective methods is to use a drying mixer, which combines the functions of mixing and drying within one unit, removing moisture and ensuring a uniform end product.
Characteristics and Values Table for Drying Plastic Pellets for Filament
| Characteristics | Values |
|---|---|
| Why dry plastic pellets? | To prevent moisture absorption, which can cause cosmetic defects, weaken molecular bonds, and affect the quality of the final product. |
| Types of plastic resins | Hygroscopic (absorbs moisture) and non-hygroscopic (does not absorb moisture). |
| Methods | Oven, dehydrator, vacuum dryer, drybox with silica gel, hopper dryer, industrial mixer, drying mixer. |
| Precautions | Avoid rapid temperature changes, store in airtight containers, maintain consistent temperatures when drying to avoid melting. |
| Measurement | Moisture content is measured in parts per million (PPM) and refers to the moisture level within a pellet. |
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What You'll Learn
Use a self-built drybox with silica gel
Drying plastic pellets for filament is important to ensure the stability, appearance, and mechanical properties of the final product. One effective method is to use a self-built drybox with silica gel, which is a cheap, easy, and energy-efficient way to achieve this. Here are the steps to create and use this setup:
Building the Drybox
Start by sourcing an airtight plastic box that can be upgraded with window seals to make it completely airtight. You can use glue to attach the window seals to the rim of the box. The size of the box will depend on the amount of filament you need to store, with larger boxes accommodating more filament spools.
Preparing the Silica Gel
Silica gel is a desiccant material that absorbs moisture. It is often found in small bags to keep enclosed spaces dry. For this purpose, you can use either silica gel bags or loose silica gel granules. The amount of silica gel needed will depend on the chemical properties of the filament and the humidity levels in your environment. As a general rule, using more silica gel means less frequent drying and replacement. You can estimate the required amount of silica gel by considering that silica can absorb about 40% of its weight in moisture.
Adding the Filament
To add the filament to the drybox, it is recommended to use a microplastic bag to save space and keep everything organized. Place the filament inside the bag and then put it into the drybox. You can also use loose filament granules, but ensure they are contained within the box to avoid spillage.
Monitoring Humidity
To monitor the humidity levels inside the drybox, you can use a hygrometer, which can be purchased for a relatively low cost. Ideally, you want to maintain humidity levels below 20%. You can also periodically weigh the filament to track moisture loss, but this method can be imprecise due to the impact of volatiles on weight.
Regenerating Silica Gel
Over time, the silica gel will reach its maximum capacity for water absorption. To regenerate it, you can place it in an oven at a temperature between 100°C and 120°C for about one to two hours. Alternatively, you can use a hairdryer or heat gun to regenerate the silica gel. Ensure that the water liberated by the heat is removed to prevent re-absorption.
By following these steps, you can effectively dry plastic pellets for filament using a self-built drybox with silica gel. This method helps to prevent issues like bubbling, stringing, and breakage during the 3D printing process.
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Use an oven, dehydrator, or vacuum dryer
Drying plastic pellets before filament production is important to prevent cosmetic defects like splay or silver streaking, and to avoid negative effects on the quality of the end product. Plastic pellets can be dried using an oven, dehydrator, or vacuum dryer.
When using an oven, it is important to ensure that the oven maintains consistent and accurate temperatures to avoid overheating and melting the plastic. A thermometer can be used to corroborate the temperature. The drying time is typically 6-12 hours.
Dehydrators are designed to operate at lower temperatures than ovens, making them an excellent and inexpensive way to dry printing materials. They are easily modified and readily available. The drying time remains the same as for ovens.
Vacuum dryers are another option for drying plastic pellets. Commercial filament dryers are available, some of which are equipped to print directly from the dryer.
It is worth noting that non-polar materials, such as HDPE and PP, usually do not need to be dried as they do not absorb moisture. However, most other commercial polymers have some level of polarity and can absorb moisture from the air, making it necessary to dry them before use.
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Use a drying mixer to mix and dry pellets
If you are looking to dry plastic pellets for filament, a drying mixer is a great option. This is a unique design that combines the functions of mixing and drying within one unit. Drying mixers are designed to efficiently blend plastic pellets while simultaneously removing moisture, ensuring a uniform and dry end product.
The process of drying and mixing is achieved through the rotation of mixing paddles at high speed, which creates significant friction and generates heat within the mixing chamber. This heat serves the purpose of moisture removal, as the rapid evaporation of moisture from the surface of the pellets occurs. An exhaust vent at the top of the mixer allows the evaporated moisture to escape quickly, ensuring the pellets are thoroughly dried.
The Wensui WSQD drying mixer is a compact machine that integrates mixing and drying. It is a leading supplier of auxiliary equipment and conveying systems for plastics processing. The Rollo-Mixer® Mk VII is another industrial mixer that can blend or coat large lots of vinyl and nylon pellets, polyolefin, and polyamides, among other plastic materials.
Drying mixers are beneficial for the plastic processing industry, where maintaining consistent material quality is crucial. They can handle various plastic materials and ensure a uniform mixture, which is essential before further processing and for the final product's appearance and quality.
It is important to note that some mixers offer speed regulation functions, allowing adjustments to be made for different materials and requirements. Additionally, regular maintenance and servicing of the drying mixer are necessary for optimal performance and safety.
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Avoid rapid temperature changes
When drying plastic pellets for filament, it is important to avoid rapid temperature changes. This is because polymers are sensitive to temperature fluctuations, which can lead to surface moisture. For example, if you take plastic from a cold, damp garage into a warm production area, the plastic will start to condense moisture on its surface, leading to bubbles and inconsistencies in the final product.
To avoid this issue, it is recommended to maintain a consistent and controlled temperature environment when drying plastic pellets. This can be achieved by using a drying method that allows for precise temperature control, such as a filament dryer, oven, or food dehydrator. These options offer the ability to set specific temperatures and drying times, ensuring a slow and gradual drying process.
Ovens, for instance, should be preheated to the desired temperature before placing the filament inside. The ideal temperature range for drying filament is generally considered to be between 40°C and 60°C. It is crucial not to exceed the recommended temperatures to prevent the filament from softening, warping, or fusing together.
Additionally, it is important to monitor the temperature throughout the drying process to ensure it remains stable. An oven thermometer can be used for this purpose, helping to avoid any risk of overheating. By maintaining a consistent and controlled temperature, you can effectively dry plastic pellets while avoiding the negative impacts of rapid temperature changes.
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Use a hopper dryer
Using a hopper dryer is an effective way to dry plastic pellets for filament. Hopper dryers use high-temperature hot air to treat moisture on the surface of plastic particles, ensuring they are thoroughly dried. This method is particularly useful when drying pellets for 3D printing filament, as it helps to achieve the desired molding effect and prevents processing problems and defects in the plastic materials.
To use a hopper dryer, plastic pellets are loaded into the hopper and heated by circulating hot air generated by a heater and blower system. As the heated air passes through the pellets, the moisture evaporates, and the dry pellets accumulate at the bottom of the hopper, ready for further processing. This process ensures that the pellets are dry and free-flowing, which is crucial for filling molds smoothly and evenly, reducing the risk of defects, and improving the overall quality of the final product.
Hopper dryers are especially beneficial for moisture-sensitive plastics such as nylon, PET, and polycarbonate, which are susceptible to processing issues caused by excess moisture. By removing moisture from the plastic resin particles before processing, hopper dryers can speed up the drying process, reduce cycle times, and increase production efficiency. They also help maintain the integrity and performance of the plastic material by drying the pellets to an optimal moisture level, ensuring the final product meets the required specifications and performance standards.
It is important to note that rapid changes in temperature can lead to surface moisture on plastic pellets. Therefore, it is crucial to maintain consistent temperatures during the drying process in the hopper dryer to prevent this issue. Additionally, ensuring that the hopper dryer is properly sealed can help optimize the drying conditions and prevent moisture absorption during the drying process.
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Frequently asked questions
Plastic pellets tend to absorb moisture from the air, which can have a negative impact on the quality of the final product.
There are several DIY methods to dry plastic pellets, including using an oven, a dehydrator, or a vacuum dryer. Commercial filament dryers are also available, which are designed exclusively for drying out 3D printing filament.
One DIY method is to use a self-built drybox with silica gel. Another method is to use a drying mixer, which combines the functions of mixing and drying within one unit, using heat generation to rapidly remove moisture.
One way to measure the moisture content of plastic pellets is to weigh them before and after drying. If the weight loss is significant, then the pellets have likely absorbed too much moisture.
To prevent plastic pellets from absorbing moisture, store them in sealed containers or use desiccant packs to absorb any moisture from the air.
