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This article will take an in-depth look at plastic crates.
The article will bring more detail on topics such as:
This chapter will discuss what plastic crates are, their manufacture, and how they function.
Plastic crates are containers used for moving or transporting goods from point A to point B. They are also used for storage and are made of exclusively or partially plastic material. The basic material is plastic; it gives its distinctive character as durability. They are more expensive than wooden or carton crates due to their durability lasting or having a longer life span compared to other crates.
Plastic crates are mostly made of high density polyethylene (HDPE) or polypropylene (PP). Polyethylene has a higher impact strength and a very low degradation by ultraviolet radiation, while polypropylene has a better scratch resistance. To improve the performance of both materials, the addition of antioxidants and UV protectants can be made.
The type of plastic forming process used depends on the form of the plastic crate. Each type of plastic crate has its distinct shape and design that suits one type of fabrication process better than the others. Below are some of the common methods for producing 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 type extruder is used mainly in the industry for plastic making for mixture; there is repeated mixing and kneading of the screw type extruder. When the plastic (raw materials) is ready to be injected, as the screw moves, it pushes the plastic out of the extruder and into the mold.
To make the shape required by the customer, there is a mold designed with specifics that contains a certain shape. Normally it contains two parts or halves with similar features. One does have the ability to move or it remains still while the other part of the mold can move. After molding, the other half can move thus to release the product from the mold in undemented form. The mold contains several or multiple openings or channels. These are used to introduce the plastic into the mold, vent air, and permit some plastic to flow out of the mold.
Injection molding has restricted production when it comes to the production of one sided containers or crates. Tubs, pails, cups, food containers, and bowls are examples. By itself, injection molding is not suited for producing closed, hollow products such as plastic bottles that is why it is suited for the production of open crates. To produce these products, an inert gas is used. This is used because it will eliminate reactions that can incur in the mold when the process is in motion. This is introduced into the mold partially filled with molten plastic. This pushes the plastic onto the surface of the mold producing a hollow part. This process is called gas-assisted injection molding.
Blow molding is a process used for the formation of plastic containers by inflating a softened plastic compound inside a mold. The main steps or processes of 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:
This process extrudes the shape beforehand into a hollow tube dispersed onto one end.
This process, on the other hand, makes use of the production of the shape beforehand by the injection of the plastic into a mold with a core for air supply. Both processes (the extrusion and injection blow molding processes) make use of air to shape the shape beforehand against the mold.
When the two processes are compared, injection molding is considered the best in the production of plastic crates and extrusion molding is considered best in producing other hollow plastic products like water jugs, bottles, storage tanks, tube packaging as well as intermediate bulk containers.
Rotational molding, or commonly known as the "roto molding", is a plastic casting process used in the production of hollow and seamless plastic containers. This process does not use pressure to form its product as does the blow molding process. Rather, it makes use of rotations when forming the crate by spreading the plastic melt on the inner surfaces of the mold. Its operation is has the following steps summarized as follows:
In this process, there are different rotational molding machines. They basically vary on the configuration and the number of the molds and how the molds are rotated while in the heating process. Examples of rotational molding machines are turret, clamshell, sewing machines, and shuttle.
As a result of no high pressures involved in the process, the molds used in the rotational molding technique are cheap. Larger products can also be produced. Rotational molding can also be used to form double-walled crates in the absence of any secondary processing. Multiple products formed using the rotational molding are agricultural and industrial storage tanks, carboys, drums, trash bins, and insulating boxes.
Thermoforming is the procedure of heating thin plastic sheets to their forming temperature and stretching them over a mold. It is a secondary plastic forming process. It does not make use of raw plastic resin for compounding. Instead, it makes use of a plastic sheet or film made from preliminary steps such as extrusion or calendaring. The processes involved in thermoforming are:
There are four main types of thermoforming which are vacuum, mechanical, pressure, and twin sheet forming. Each procedure varies on how pressure is registered to create the thermoform. Vacuum, pressure, and twin sheet thermoforming all make use of the compressed air to bear down on the plastic sheet instead of the mold. Mechanical thermoforming contains two dies that pin against each other to disfigure 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.
Common thermoforming containers are the ones that are used for pharmaceutical and food applications. They are designed for single use. Disposable cups, trays, and clamshell containers are examples.
The compression molding process is meant for shaping the plastic resin by making use of pressing it against two molds. This process is mostly chosen when producing large thermosetting plastics products. The steps involved in compression molding are summarized below.
Generally, the process of compression press is downward closing. But another pressing known as upward closing compression is also accessible. The mold contains internal heating elements that soothe the plastic charge. This makes the plastic flow according to the shape of the mold. The heat also manages to cure the plastic. During the process of curing, some plastic may eliminate or produce gasses that are removed through an additional phase called degassing.
Compression molding can also be used for molding containers and crates with fiber components. Glass or carbon fibers can be joined while pre-forming the plastic charge.
Such as injection molding which makes use of two mold halves, compression molding is restricted to the production of containers and plastic crates that are open on one side. Examples of compression molding containers that can also be produced using this method are large bins, tubs, and trays. The compression molding process can also be used to make plastic caps for bottles.
Designing crates can be in two configurations, the open and closed configurations. Closed plastic crates are designed with detachable or hinged lids, while open crates are designed without lids and can feature a grid pattern for clear visibility of the contents contained. There is high demand for plastic crates from the delivery industries and food services. Most food stuffs such as dairy products, bread, beverages, meats, seafood, and other food items are transported in plastic food crates.
Plastic crates are often found in general storage in places such as warehousing facilities to organize, store, and transport goods. They are made with handles for easy lifting and handling and are designed so that they can be stacked or nested for easy storage and maximize storage in warehouses. There are different shapes, sizes, and colors of the plastic materials used to make crates. They are made to withstand different temperatures, other loaded and stacked crate weights, and impacts.
Plastic crates are manufactured using a process called plastic injection molding. An injection mold is a machine that uses a raw plastic product or stock and processes it into a usable product. The plastic injection molders start with a stock collection in a hopper that is moved directly into a conveyance channel. A screw will turn according to the conveyance channel, coupled with heating, which helps to liquefy the plastic in preparation for the mold.
A mold is a container that has a shaped cavity that, when filled with liquefied plastic raw materials, gives the plastic its shape when cooled. Under strict and regulated temperature control measures, the newly molded plastic will be allowed to cool and harden. Once hardened, the product or crate is cleansed of imperfections if present using other processes. It is then shipped or sent to additional processing.
Every mold can be designed in such a way that imprinting the customer or molding company's name into the finished product is possible; the mold needs only to be designed with projecting letters positioned appropriately. In many cases, the stock used or the raw material for plastic crate production is made of High-Density Polyethylene (HDPE), which is a thermoplastic known for its durability.
The introduction of plastic crates has eliminated many problems associated with storing goods in wooden crates and cardboard crates. Plastic crates are accessible in varying sizes and shapes, and each of them has its distinguished applications and specifications. Customers or clients have the option to determine the quality of the crate according to their usage program.
Plastic crates can be found in different orientations and types. These will be discussed in this chapter.
Plastic crates have different stacking orientations, including a stack-nest, a stacking, or a collapsible design. The differences are particularly important when the crate is transported empty since the volume determines the price to be paid for transport.
These are the most expensive crates to purchase followed by stack-nest plastic crates and then the stacking crates.
They are designed as square and they contain rounded corners, an efficient use of available space is possible as they can be stacked one on top of the other. Depending on the size of the crate, the loss of loading space compared with loose break bulk is much better than stacking.
Although stacking crates have a rigid design, some space during the return trip can be obtained by putting one crate inside two others and overlapping crates during stacking. Some space gaps in the crate's rim are needed, making transportation after delivery also easier.
The stack-nest crates can be found with swing bars or with a cover or be stacked at 180°.
The volume of the inside of a stack-nest crate is less than the inside volume of a crate with a squared design because of its vertically tapered shape. Effective loading space is higher depending on the size of the crate. Five nested crates will use up the space occupied by two stacked crates of similar size with the swing bar design. The crates can be nested if the bars are swung out. A swing bar is swung from the outside or from the side over the top of the crate, forming a support for the following crate.
The stack crate is slightly stronger than the stack-nest crate due to the bar resting on the corners, which is different in the stack nest crate where the bar rests but on the long side of the crate. The placement of the swing bar is made at 1 to 2 cm under the crate’s rim therefore stacking will be easy. The placement of the crate on top should be made within this rim. For the fitting in of the swine bar a provision is made on the crate’s bottom side sometimes.
Besides the swing bar, two cover parts are used for the closing of the crate, on top of which another crate can be stacked. An advantage is that sealing this cover can prevent the pilferage of produce. Plastic crates that consist of a cover are up to 50 percent more expensive than those with no cover.
The box can be stacked and nested in 180 degrees turn position by making supports at multiple places inside the box. Extra space is required for these supports. A collapsible crate consists of a base with sides attached to it by means of plastic or metal hinges.
Despite that these plastic crates save space when folded and they have an attractive design, these crates are generally not accepted in trade, most likely due to their high purchase cost.
The following are some of the most used plastic crate varieties.
These are used for all kinds of basic storage conditions. They are accessible in many various shapes, colors, and sizes. These include plastic crates for grocery distribution. They help by protecting fragile and delicate products such as produce. The use of these crates brings smooth, protective handling, excellent ventilation and good stability. In the grocery industry, there are what are called returnable plastic crates which are folding for inbound trips and rigid for outbound trips used to transport all types of produce between growers and supermarkets around the world. These plastic crates have one common footprint and six different stack heights conforming to the different produce and can be mixed on pallets to make the unit loads more stable and efficient.
These are normally used for the purpose of storage of food items and vegetables. They are accessible in a fully ventilated and nestable design. These include plastic crates used in the dairy industry. They are made from a material called polythene which is strong and resilient. There are also plastic crates that are custom made, that can be made use of from the beginning to the final stage of the process of handling the materials. They can be used for farmers to the display on the shelves of the supermarkets and then to the customer and therefore finally their kitchen.
Dairy plastic crates are strong to handle the process entailed by the handling and shipping of dairy products. These plastic crates are capable of holding automated stacking equipment, sterilization and big temperature changes, high pressure washing. This makes plastic crates better than wooden or cardboard crates that are sensitive to washing, temperature changes and cannot be incorporated into the processing line.
These are high-quality closed crates that can be made in various sizes and shapes. Generally, they are used for all types of storage, including fish in the fishing industry and other food items. These include plastic crates for the fishing industry. The plastic crates are used in the transfer of the catch to the company's holding tank, where they are processed. Seafood processors and wholesalers mostly use these crates. These plastic crates are better than wooden ones in the fish industry because their handling is much easier. Plastic crates support careful handling due to their smooth surface, unlike the nails and splinters found in wooden crates. Their opening is also easier as well as their closing than wooden crates that have craftsmanship that is not accurate.
These crates are designed and made for multiple purposes in 600L and 400 W dimensions.
These are big-sized crates which are mainly utilized in the storage and transportation of large items.
These types of plastic crates are designed using special measurements so that they can suit the application in poultry, document storage, and toast.
Plastic crates can be compared and contrasted to wooden crates in the following aspects:
The handling of plastic crates is safer than that of wooden crates because of their design, low weight, and smooth finishing. The weight of plastic crates is significantly lower than that of wooden crates. The back injuries associated with the worker are reduced through the use of plastic crates
Plastic crates save space relatively to wooden crates and because of that, they reduce the shipping and storage costs. Plastic crates can be easily stacked on the top of each other to save storage space.
Plastic crates are uniform, have a variety of designs, and have ease of maneuverability, therefore are easier to handle.
Plastic crates have a higher versatility than that of wooden crates. They can be used in warm and cold conditions from -22 °C to +60 °C without any damage, unlike wooden crates that can easily damage by even mild temperature changes. Plastic crates have a UV rate that is very high.
Plastic crates are easy to clean and therefore much more hygienic than wooden crates. Their hygienic properties are of importance in agriculture, pharmaceutical industries and food industries. Plastic crates are easy to clean with steam or water or solvents while on the other hand, wooden crates get damaged when they come into contact with steam and water or solvents.
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This chapter will discuss the applications and benefits of plastic crates.
The applications of plastic crates are in:
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 are important and play a very important role in the agriculture industry, facilitating a hygienic and efficient transportation process. These are suitable alternatives to the other ones such as traditional wooden and cardboard counterparts as plastic crates resist the growth of fungi within them. As a result, plastic bins and crates are gaining popularity in the market and are chosen for the transport of agricultural produce, soil, and seeds on a large scale. Moreover, plastic crates are also resistant to extreme weather conditions, which aids in the secure transportation of perishable agricultural products in the industry. The nature of the products to be transported in the agro-industry requires extra care to be taken in terms of hygiene and proper maintenance. Plastic allows for increased efficiency as an element in the supply and transportation of such products.
Fisheries utilize plastic crates and also plastic fish tubs and ice boxes to prevent fish perishing while being transported. As a poor conductor of heat and resistant to rain, heat, and other harsh weather conditions, closed plastic crates protect the ice within the crates and containers from melting and ensure that the fish stored within remains fresh even after being transported across long distances. Moreover, cleaning plastic crates can also be done for the purposes of hygiene. This can be more easily done compared to crates made from other materials. Thus, even in case of spillage, these may be cleaned more easily and hygienically maintained. In this industry rust is not allowed, therefore plastic containers are more suitable when storing and transporting fish.
Transporting fruits and vegetables across long distances requires special care and hygiene to be practiced as these are perishable and easily affected by harsh weather conditions. Plastic crates are popular options for transporting such goods, because they are compact and resist external deterrents. A variety of fruits and vegetables are transported everyday, in plastic crates, from one place to another. In fruit and vegetable transportation, the storage of these crates may be done in in-built systems of pallet storage, before they are further transported to the markets.
Another major domain that utilizes plastic crates is the grocery industry. They utilize plastic crates in the storage and transportation of grocery items and also aid customers to carry them easily around within supermarkets. These crates may be used to carry packaged grocery items that need to be supplied to the markets efficiently. The ease of transportation of even bulky grocery items is ensured by the plastic crates’ durability and resilience of these crates.
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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