This article will take an in-depth look at plastic crates.
The article will bring more detail on topics such as:
This chapter will cover the definition of plastic crates, their manufacturing process, and their functionality.
Plastic crates are containers designed for the transportation and storage of goods. Made entirely or partially from plastic, these crates are known for their durability. While they tend to be more expensive than wooden or cardboard crates, their longer lifespan and sturdiness justify the higher cost.
Plastic crates are primarily constructed from high-density polyethylene (HDPE) or polypropylene (PP). HDPE offers superior impact resistance and minimal degradation from UV radiation, while polypropylene provides enhanced scratch resistance. To further enhance the durability of these materials, antioxidants and UV protectants can be added.
The method used to form plastic crates depends on their design and shape. Each crate type is suited to a specific fabrication process. Here are some of the common techniques used in the production of plastic crates.
Injection molding is a plastic forming process that involves injecting molten plastic raw materials into a closed chamber or mold. This process has three main processes:
A reciprocating screw extruder is commonly used in the plastic industry for mixing and kneading materials. As the screw moves, it pushes the prepared plastic through the extruder and into a mold.
To achieve the desired shape, a mold is designed with specific features and typically consists of two halves. One half may be stationary while the other can move to release the molded product. The mold includes multiple openings or channels for introducing plastic, venting air, and allowing excess plastic to flow out.
Injection molding is limited when it comes to producing single-sided containers or crates, such as tubs, pails, cups, and bowls. It is not ideal for closed, hollow products like plastic bottles. Instead, gas-assisted injection molding is used for these products. In this process, an inert gas is introduced into a mold partially filled with molten plastic. The gas helps eliminate reactions within the mold and forces the plastic against the mold surface to create a hollow part.
Blow molding is a technique for shaping plastic containers by inflating a heated plastic material within a mold. The primary steps involved in blow molding are:
As the injection molding process occurs in a series of steps, blow molding also makes use of the screw extruders for adding and mixing, and heating the plastic raw materials. In the production of the preform, the process is split into two types:
In this process, a hollow tube is extruded and formed at one end of the mold.
In contrast, this process involves shaping the plastic by injecting it into a mold with an air supply core. Both extrusion and injection blow molding use air to form the plastic against the mold.
When comparing the two methods, injection molding is generally preferred for producing plastic crates, while extrusion molding is more suitable for creating other hollow plastic items such as water jugs, bottles, storage tanks, tube packaging, and intermediate bulk containers.
Rotational molding, often referred to as "roto molding," is a plastic casting technique used to create hollow, seamless plastic containers. Unlike blow molding, which uses pressure to shape the product, rotational molding relies on rotation to distribute the melted plastic evenly across the inner surfaces of the mold. The process involves the following key steps:
Various types of rotational molding machines exist, differing in their mold configurations, the number of molds, and the rotation methods used during heating. Examples of these machines include turret, clamshell, sewing machine, and shuttle types.
Because rotational molding does not involve high pressures, the molds are relatively inexpensive, and the process can accommodate the production of larger items. This technique can also produce double-walled crates without the need for additional processing. Common products made using rotational molding include agricultural and industrial storage tanks, carboys, drums, trash bins, and insulating boxes.
Thermoforming is a process where thin plastic sheets are heated to their forming temperature and then stretched over a mold. This secondary plastic forming method does not use raw plastic resin but rather utilizes plastic sheets or films produced through preliminary processes such as extrusion or calendaring. The main steps involved in thermoforming are:
Thermoforming includes four primary methods: vacuum, mechanical, pressure, and twin sheet forming. Each method differs in how pressure is applied to shape the plastic. Vacuum, pressure, and twin sheet thermoforming use compressed air to press the plastic sheet against the mold. In contrast, mechanical thermoforming involves two dies that press against each other to shape the plastic.
Thermoforming is restricted to making parts with fairly thin walls. However, the procedure is susceptible to problems that include inconsistent thickness, warping, and webbing. It is not quite made for the production of containers requiring rigidity.
Thermoforming is often used to create containers for pharmaceutical and food applications, typically designed for single use. Examples include disposable cups, trays, and clamshell containers.
The compression molding process is designed for shaping plastic resin by pressing it between two molds. This process is typically used for producing large thermosetting plastic products. The steps involved in compression molding are summarized below.
Typically, the compression press process involves downward closing, though upward closing compression presses are also available. The mold is equipped with internal heating elements that soften the plastic, allowing it to flow into the mold's shape. The heat also cures the plastic, during which some of it may release gases. These gases are removed in an additional step known as degassing.
Compression molding is also suitable for creating containers and crates that incorporate fiber components, such as glass or carbon fibers, which are added during the pre-forming stage of the plastic charge.
Similar to injection molding, which uses two mold halves, compression molding is generally limited to producing containers and plastic crates that are open on one side. Examples of items produced by compression molding include large bins, tubs, trays, and plastic caps for bottles.
Crates can be designed in two main configurations: open and closed. Closed plastic crates come with detachable or hinged lids, while open crates lack lids and often feature a grid pattern for easy visibility of their contents. Plastic crates are in high demand from delivery industries and food services, with various food items such as dairy products, bread, beverages, meats, and seafood commonly transported in them.
In general storage settings, such as warehousing facilities, plastic crates are used to organize, store, and transport goods. They typically have handles for easy lifting and are designed to be stackable or nestable to optimize storage space. Available in various shapes, sizes, and colors, plastic crates are engineered to endure different temperatures, weights, and impacts.
The manufacturing of plastic crates involves a process called plastic injection molding. An injection mold machine transforms raw plastic into usable products. The process begins with plastic stock in a hopper, which is then conveyed through a channel. A screw rotates within the channel, heating the plastic to liquefy it for molding.
A mold features a cavity shaped to form the plastic into its final design. The liquefied plastic is injected into this cavity, cooled, and hardened under controlled temperature conditions. Once hardened, the crate is inspected for imperfections and may undergo further processing before being shipped.
Molds can be customized to imprint the name of the customer or the molding company directly onto the finished product by incorporating projecting letters into the mold design. Typically, the plastic used for crate production is High-Density Polyethylene (HDPE), a durable thermoplastic material.
The advent of plastic crates has resolved numerous issues related to the use of wooden and cardboard crates for storing goods. Available in a variety of sizes and shapes, plastic crates offer specific applications and features to meet different needs. Customers can choose the quality of the crate based on their particular requirements.
In this chapter, we will explore the various orientations and types of plastic crates.
Plastic crates come in various stacking orientations, such as stack-nest, stacking, and collapsible designs. These differences are crucial, especially when transporting empty crates, as the volume can impact the transportation costs.
Among plastic crates, collapsible crates are the most expensive to purchase, followed by stack-nest crates, with stacking crates being the least costly.
These crates are designed in a square shape with rounded corners, allowing for efficient use of space by stacking them on top of one another. Depending on the crate's size, stacking can significantly reduce the loss of loading space compared to using loose break bulk.
While stacking crates have a rigid design, space can be saved on return trips by nesting one crate inside two others and overlapping crates during stacking. Allowing for some gaps in the rim of the crates facilitates easier transportation after delivery.
Stack-nest crates are available with various options, including swing bars, covers, or the ability to be stacked at 180°.
The internal volume of a stack-nest crate is less than that of a square-designed crate due to its vertically tapered shape. However, the effective loading space can be higher depending on the crate's size. For example, five nested crates will occupy the same space as two stacked crates of similar size with a swing bar design. The crates can be nested when the bars are swung out. A swing bar is moved from the outside or side over the top of the crate, providing support for the next crate.
The stack crate is somewhat stronger than the stack-nest crate because its bar rests on the corners, whereas in the stack-nest crate, the bar rests along the long side. The swing bar is positioned 1 to 2 cm below the rim of the crate, which facilitates easier stacking. When placing a crate on top, it should align within this rim. Occasionally, provisions are made on the bottom side of the crate to accommodate the swing bar.
In addition to the swing bar, stack-nest crates can be equipped with two cover parts that close the crate and allow another crate to be stacked on top. This cover helps prevent pilferage of the contents. Plastic crates with covers are typically up to 50 percent more expensive than those without covers.
The box can be stacked and nested at a 180-degree rotation by incorporating supports at various points inside the box. These supports require additional space. A collapsible crate features a base with sides connected via plastic or metal hinges.
Although collapsible plastic crates save space when folded and have an appealing design, they are generally not favored in trade, likely due to their higher purchase cost.
Below are some of the most commonly used types of plastic crates.
These crates are designed for various basic storage needs and come in a range of shapes, colors, and sizes. They are commonly used in grocery distribution to protect fragile and delicate items such as produce. These crates ensure smooth handling, excellent ventilation, and stability. In the grocery industry, returnable plastic crates are used: they fold for inbound trips and are rigid for outbound trips. These crates facilitate the transportation of produce between growers and supermarkets worldwide. They feature a standard footprint and six different stack heights to accommodate various types of produce, allowing for stable and efficient unit loads on pallets.
These crates are primarily used for storing food items and vegetables and are available in fully ventilated and nestable designs. They include crates used in the dairy industry, made from durable and resilient polyethylene. Additionally, custom-made plastic crates are available, designed for use throughout the entire material handling process—from farmers to supermarket displays and ultimately to customers' kitchens.
Dairy plastic crates are designed to withstand the rigors of handling and shipping dairy products. They are robust enough to endure automated stacking, sterilization, significant temperature fluctuations, and high-pressure washing. These features make plastic crates more suitable than wooden or cardboard crates, which are sensitive to washing, temperature changes, and cannot be integrated into processing lines.
These high-quality closed crates come in various sizes and shapes and are commonly used for different types of storage, including fish in the fishing industry and other food items. They are especially utilized in the fishing industry for transporting catches to holding tanks for processing. Seafood processors and wholesalers favor these plastic crates over wooden ones due to their ease of handling. Plastic crates offer smooth surfaces that avoid issues like nails and splinters found in wooden crates. They also feature easier opening and closing mechanisms compared to wooden crates, which may suffer from inconsistent craftsmanship.
These crates are designed and manufactured for various uses, available in dimensions of 600L and 400W.
These large-sized crates are primarily used for the storage and transportation of bulky items.
These plastic crates are designed with specific measurements to accommodate applications in poultry, document storage, and bread handling.
Plastic crates can be compared to wooden crates in the following aspects:
Plastic crates offer safer handling compared to wooden crates due to their design, lighter weight, and smooth finish. The reduced weight of plastic crates lessens the risk of back injuries for workers, making them a more ergonomic choice.
Plastic crates are more space-efficient compared to wooden crates, which helps reduce shipping and storage costs. They can be easily stacked on top of one another to optimize storage space.
Plastic crates offer uniformity, a range of designs, and ease of maneuverability, making them simpler to handle.
Plastic crates offer greater versatility compared to wooden crates. They can withstand temperatures ranging from -22°C to +60°C without damage, unlike wooden crates, which are prone to damage from even minor temperature fluctuations. Additionally, plastic crates have a high UV resistance.
Plastic crates are easier to clean and thus more hygienic than wooden crates. Their hygienic advantages are particularly significant in agriculture, pharmaceuticals, and the food industry. Plastic crates can be cleaned effectively with steam, water, or solvents, whereas wooden crates are damaged by steam and moisture.
This chapter will explore the applications and advantages of plastic crates.
The applications of plastic crates include:
In the dairy industry, milk crates serve an extremely important means to supply milk cans and packets across cities and towns. They are also important and efficient in shipping milk across long distances, holding them firmly and avoiding spillage. While compared to wooden and cardboard crates used in the prior years, plastic crates have now become an increasingly gained market due to their lightweight and resilient structures. Typically made of polyethylene (PE), plastic milk crates are resistant to repeated washing and ensure more hygiene in the supply process.
Plastic crates play a crucial role in the agriculture industry, providing a hygienic and efficient method for transporting goods. They are preferred over traditional wooden and cardboard crates due to their resistance to fungal growth. As a result, plastic crates are increasingly chosen for transporting agricultural produce, soil, and seeds on a large scale. Additionally, plastic crates withstand extreme weather conditions, ensuring the secure transport of perishable agricultural products. Their durability and hygiene benefits make plastic crates an essential component in the supply chain for agricultural products, enhancing efficiency and safety.
In the fisheries industry, plastic crates, fish tubs, and ice boxes are essential for preserving fish quality during transport. These crates are poor conductors of heat and are resistant to rain, heat, and harsh weather conditions, effectively protecting the ice within from melting and keeping the fish fresh over long distances. Additionally, plastic crates are easier to clean compared to those made from other materials, ensuring better hygiene. This ease of cleaning is crucial for maintaining hygiene and preventing rust, making plastic containers the preferred choice for storing and transporting fish.
Transporting fruits and vegetables over long distances requires careful handling and hygiene, as these products are perishable and sensitive to harsh weather conditions. Plastic crates are a popular choice for such transport due to their compact design and resistance to external factors. A wide variety of fruits and vegetables are routinely transported in plastic crates from one location to another. During the process, these crates are often stored in built-in pallet storage systems before being further distributed to markets.
Another major domain that utilizes plastic crates is the grocery industry. They are used for storing and transporting grocery items and also assist customers in carrying items easily around supermarkets. These crates help in efficiently supplying packaged grocery items to the markets. The durability and resilience of plastic crates ensure the easy transportation of even bulky grocery items.
Plastic crates are containers used for moving or transporting goods from one point to the other. Plastic crates are found in a variety of configurations including collapsible plastic crates, stack nest plastic crates, etc. Due to their different configurations, each plastic crate has its own unique suitable application, for example the stack crate with cover can be sealed, preventing pilferage of produce. Therefore it is most suitable for use in the food industry where the food needs to be kept clean and safe. Plastic crates also offer many advantages such as being strong, rigid, and easy to clean. They also have disadvantages of damaging the produce with their rough surface. Therefore it is wise to consider the configuration and properties of the plastic material used when opting for a plastic crate.
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