What is rotational molding?
What is rotational molding? What are its applications? What processes does it include?
To get the answers to the above questions, stay with us until the end of this article.
If we want to give the answer to the question of ” what is rotational molding ” briefly and usefully, we must say that rotational molding is unique both as a process and as an industry.
Rotational molding is a technology in the field of plastic molds that is ideal for the production of hollow plastics.
This industry by itself has led to the production of a wide range of products that are used by various industries from the past decades until now.
what is rotational molding and what are its applications?
Among these applications, we can mention the manufacture of small parts (such as its use in making doll hands) as well as larger industries (such as gallons with a volume of more than 80,000 liters) that are used to store fuel and water.
As an industry, rotational molding has limited competitors around the world compared to many industries.
You may be wondering what are the advantages of rotolomding and what special techniques craftsmen use in this field.
Like any other industry and specialty, this industry also has its own techniques. But unlike other methods of making plastics, no pressure is involved in this process.
One of the most obvious advantages of this method is that it is very economical to use this method.
Get familiar with the 4 phases of the rotary molding process!
what is rotational molding and how many phases does it include?
The concept of roto-molding is straightforward. The plastic material, usually in powder form, is poured into rotational molding molds which are hollow and made of aluminum or steel.
Then the mold is closed and got into the shuttle rotomolding machine . The plastic sticks to the mold wall by rotating it during the heating process by the furnace. As a result of cooling the mold by airflow or water spray, the final product is taken out of the mold.
As we mentioned, there is no pressure involved in this method. There are many parameters that influence the work output and the production product.
Among these parameters, we can mention temperature, humidity, mold type, material property, and powder quality.
If we want to briefly introduce the phases of this process, the rotational molding process includes 4 stages loading, heating, cooling, and discharging.
In the first step, a mold that has been designed and made in advance (this mold is in the form of the final product) is opened. The plastic material, usually in powder form, is poured into a hollow mold made of aluminum or steel.
In the second stage of the rotational molding process, the mold is closed and then rotates around two vertical and horizontal axes. This mold is placed in a furnace.
The third stage is the cooling stage. The rotating mold enters the cooling chamber.
Cooling is done either by air or by water spray. Sometimes it is done with both of these methods.
By performing the cooling process, the polymer inside the mold is cooled and as a result, the final shape of the final product is obtained.
Now that the final product has been formed after going through the cooling phase, it is time for the fourth stage, which is the discharge stage. At this stage, the product must be unloaded from the mold.
If you are wondering how the thickness of different parts is controlled, we must say that some points of molds that should be thicker are more in contact with the polymer material.
It is very important to note that it is true that increasing the speed of the mold leads to an increase in production efficiency, but there are also limitations in this matter.
It also depends on the complexity of the shape of the product and its size.
Using the most up-to-date machines, Arya Plast Machine Group offers polymer products of the highest quality.
What are the materials used in the rotational molding process?
Low-density polyethylene: This material is the first member of the polyethylene family that has been used in the rotomolding industry and in the rotational molding process.
If you are a bit interested in chemistry, you might be interested to know that this type of polymer is made up of carbon and hydrogen atoms and lots of side branches.
The reason for the presence of these branches is that they prevent the main chains from approaching each other, and as a result, the density of the polymer decreases.
Linear low-density polyethylene: The structure of this type of polymer is the same as the low-density polyethylene. with the difference that its lateral branches are shorter. The same issue leads to maintaining the low density of the polymer.
Medium-density polyethylene: As the name of this type of polymer suggests, it has a series of properties of low-density polyethylene and a series of properties of high-density polyethylene.
In the past, it was mostly used in the rotational molding process .
High-density polyethylene: the obvious difference between this type of polymer and the low-density polymer is that the density of its side branches is ten times lower than the low-density type.
It should be noted that reducing the number of side branches leads to an increase in the density of polymer chains and an increase in the density of the polymer.
crosslinked polyethylene: In this type of polymer, the molecules are connected to each other by chemical bonds. This causes the molecules to be connected to each other in a rigid three-dimensional network.
This property makes the bonds between molecules stronger and these materials retain their physical properties at high temperatures.
Today, since polyethylene is both available and easily formed into a mold, it is widely used in this industry.
Dense polyethylene is needed to go through the rotational molding process.
Usually, linear low-density polyethylene is used in applications such as toys.
One of the most obvious features of polyethylene is its high melting point.
Today, the industry is highly dependent on polyethylene (PE). About 97% of the materials made by rotomolding are of this type.
What are the rotational molding applications
The rotational molding industry is used in the production of various products. The good thing about this method is that different types of products with different shapes can be made.
In addition to the shape, there are no restrictions on the dimensions of the products produced by this method, and therefore any product can be produced with any size and shape.
Among the applications of the products of this industry, we can mention its use in the marine industry (types of buoys), military products, water, and chemical storage tanks, etc.
Currently, the industry of rotational molding is progressing and developing more and more.
In the previous decade, this industry has made significant progress in terms of technology. This technical development includes both the machines that are used for rotational molding and the molds and consumable raw materials.
This industry has attracted the attention of many industrialists and this has led to the competition of specialists in investing in this field.
With the passage of time, the applications of products produced by this method have increased so much that the artisans compete not only in terms of product quality but also in terms of the final price.
Also, more universities have resumed their research on the issue of ” what is rotational molding “, and the attempt is to expand this industry even more in Iran and all over the world.
The application of rotational molding is not only specific to a certain industry and has so many different applications such as medicine, decoration, and cars that you will be surprised to learn about them.
In general, as mentioned, rotomolding is used to make large and hollow plastics, and since different shapes with different sizes can be produced using this method, it has a wide range in the industry.
rotational molding applications in liquid tanks
rotational molding applications in jersey barrier
In the following, we will provide you with a list of the application of rotational molding :
The application of rotary molding in the construction of water and chemical storage tanks (with different volumes and capacities)
Material storage products including pallets and fruit and fish storage containers
Products that are used in the city, such as dustbins, traffic barrels, etc.
Products used in marine industries such as buoys and boats
Parts used in truck bodies, diesel fuel storage tanks, tractor dashboards, etc.
Application of rotary molding in gardening, furniture, and all kinds of sprinklers
Children’s playground equipment and toys
The application of rotational molding in medical applications, including syringes and oxygen masks
rotational molding applications for producing
rotational molding applications for producingfish aerator
One of the most common cases related to rotational molding applications is its use in making different kinds of bags and shelves.
Large shelves, ammunition boxes, and similar equipment can be produced in different thicknesses and sizes.
Also, as mentioned, another application of rotational molding is its use in gardening. As you know, metal tools are more expensive and rust.
Therefore, the plastics we produce with this method do not have these two defects and are considered a good alternative.
These plastics can be used in different temperatures and weather conditions.
Apart from the rotational molding applications for medical purposes, this industry is also used for recreational purposes.
Among these applications, we can mention yachts and ships. It is interesting to know that the light swings are also made with the rotomolding method.
The advantages and disadvantages of rotomolding
The advantages and disadvantages of rotomolding are of concern to artisans who intend to enter this field because knowing them significantly opens the way for them to enter this industry.
Therefore, we suggest reading this part of the article both for craftsmen and for people who intend to increase their knowledge in this field in general.
Rotomolding technology has made significant progress in the last few decades and has been one of the most common technologies in the field of plastic material production.
Arya Plast Machine is one of the pioneers of this industry in the Middle East by using the most up-to-date technology and devices.
From the point of view of the variety of manufactured products, this industry is very interesting. From its application in the marine and military industries to the design and decoration industry.
In the following, we will introduce and explain the advantages and disadvantages of rotomolding.
The advantages of rotomolding
In this section, we are going to introduce you to the advantages of rotational molding. We will introduce them below:
The materials used are flexible and do not get damaged easily:
As you know, the rays emitted by the sun can destroy different materials over time. Unlike metals, rotomolding products do not corrode so easily.
In addition, due to the significant thickness that most rotomolding products have, they are resistant to impact and do not break.
They cause minimal damage to the environment:
During the rotomolding process, harmful chemicals are not released into the environment. Therefore, this industry is considered an environmentally friendly technology.
Also, during the manufacturing process of this product, very few materials are wasted. In addition, these products are recyclable.
A wide range of products with different shapes can be produced:
In rotomoulding, since plastic materials are placed inside the mold, they take the shape of the mold. With rotomolding, almost any product with any shape can be produced.
This makes it possible to use the products of this technology in various industries.
This is one of the most obvious advantages of rotational molding.
A sample of a 200-liter marker buoy that is produced with rotomolding method
Different types of products with different dimensions can be produced:
By using rotomolding technology, all kinds of products with small dimensions, medium dimensions, and large dimensions can be produced.
For example, it is possible to produce all kinds of tanks with different volumes (according to the application).
This, in turn, increases the range of applications in this industry, which is one of the most important advantages of rotational molding.
The possibility of producing two-layer, two-color, or two-material products:
In this process, it is possible to produce two-layer or two-material products without the need for multiple molds or complex machines. Also, by using this method, it is possible to produce double-layer and multi-layer hollow parts with or without foam.
Ability to produce products with low thickness and high volume:
Since the mold inside the furnace rotates around two axes and the plastic sits on the inner wall of the mold, it is possible to produce parts with low thicknesses and high volume.
It should be noted that low thickness means less consumption of raw materials.
Ability to use the primary mold produced for laboratory applications
Ability to use multiple formats simultaneously during the process
Easy opening and closing of templates
The high surface quality of products produced by this method
The controllability of the thickness of different parts of the product
Making molds in a shorter period of time than other methods
Rotational molding disadvantages
In the previous section, you learned about the advantages of rotational molding . In this section, we are going to introduce you to the limitations of the rotational molding industry.
The limitations of rotomolding include the following:
Limitations in the selection of materials used in this process:
The materials used for this industry must have properties such as high-temperature stability. So this makes the choices a bit limited.
Long heating time and high furnace temperature:
This increases the possibility of thermal degradation of the polymer. Some plastic materials cannot withstand the temperature for a long time.
Long production cycle:
The number of production cycles per unit of time is less than in other plastic-forming processes.
In other methods, such as injection molding, the product may be produced in less than a few seconds.
This is one of the most obvious disadvantages of rotational molding .
Difficulty in the separation phase:
As mentioned, the separation of the produced product from the mold is done by shrinking the piece itself.
One of the challenges we face in this case is achieving smooth surfaces.
Also, care should be taken during this step so that plastic materials do not stick to the mold.
High cost of materials:
In this method, the cost of materials is relatively high. Because the raw materials are first made into granules by an extruder and then powdered by a grinder.
The process of pulverization in a certain range of particle sizes increases the cost of materials.
Non-molding of ridges and ribs:
In this method, ridges and ribs are not molded easily. Because the material tends to bridge, the ribs cannot be completely filled.
If we want to compare the rotational molding method with other plastic molding methods in general, we must say that this method is the best method for producing large, thick, hollow, and open products.
Compared to the injection method, the rotomolding method is used in the production of very large, hollow, and more complex products.
In general, the rotomolding method is used in the production of bulky products with low circulation, which is considered an efficient method from an economic point of view.
This is one of the advantages of rotational molding.
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