How to Manufacture Cast Iron Dumbbells?
Among the diverse choices of dumbbells, cast iron dumbbells may be the most welcomed ones as they are easy to start with and offer dumbbells fans a sense of potency. The cast iron dumbbell, mostly belonging to the fixed dumbbells family, is usually composed of a handle and two lumps of fixed weights. Some cast iron dumbbells are made by cast iron inside and rubber outside. The natural rubber, coated to offer a better grip and touching, adds a layer of protection or so-called cushioning. In general, cast iron dumbbells are characterized by incredible durability, great strength performance and cheap prices, and as one of the oldest dumbbells in the world, this type of dumbbells continues to present shining points and is pursued by workout enthusiasts progressively.
Cast iron dumbbells are manufactured by a series of processes:
- Making Dumbbell Patterns
- Molding Sands
1. Designing Dumbbells
Designing dumbbells is the first thing to be considered. This process lays a foundation for future production. You are supposed to take into consideration factors like the shape of both the handle and two ends, weight, surface treatment and the location & design of your logos. So let’s analyze them in turn.
The shape of handle depends on your ideas. Often, the handle narrows down to both ends and is engraved with special stripes to enhance the grip. While, the options for the shape of ends available include round & globe ones and polygonal types like the hex and square ends. The shape of ends plays a vital role in controlling the movement of cast iron dumbbells. If it is a round end, the dumbbell may roll away when placed on the uneven ground/floor, potentially resulting in the damage of floors and household furnishings. On the contrary, cast iron dumbbells with hex ends boast practicality and safety. Such a dumbbell is capable of standing steadily on the ground as long as the angle of the tilt is less than 30 degrees. Therefore, it is advised to have a polygonal design in ends.
When it comes to the weight, you have to consider the adoption of fixed weight and adjustable weight plates. Although the majority of cast iron dumbbells are fixed dumbbells, the presence of adjustable cast iron dumbbells is observed more or less. Fixed dumbbell sets is a great option as weightlifters can pick up dumbbells of different weight levels conveniently. While the shortcomings of dumbbell sets are quite obvious: an entire set costs a lot and takes up too much room for a household gym. Whereas, the economical and space-saving adjustable dumbbells allows dumbbell enthusiasts to increment weights with the increase of training intensity without buying new ones of heavier weight. The disadvantage of adjustable dumbbells comes from its locking system, which is often made by plastics and may wear off as time goes by. Besides, some workout fans also complain about stopping to install or take down new weight plates, which disrupts their concentration on training.
After you choose the weight, you are supposed to think about the application of surface treatments. The most commonly used surface treatment is the rubber coating. By coating a layer of natural rubber on dumbbells, you can improve the touching and provide customers with a better safety. And the surface treatment is also associated with your custom logos & patterns. In order to better promote the cast iron dumbbells as well as your brand, you should decide the position of your brand logos. A great idea paves the way for future selling.
There are two ways to design cast iron dumbbells: the OEM or ODM. If you put the above ideas into real 2D/3D drawings by yourself, you can send them to a manufacturer and move on to the next process. And such a way is called OEM. But if you ask the manufacturer to design the cast iron dumbbells (the ODM order), you can send the design requirements to them who will later offer you 2D/3D drawings accordingly.
2. Making Dumbbell Patterns
The second step is making dumbbell patterns. The pattern is the core and the essence of cast iron dumbbells. In general, the pattern is the reproduction of cast iron dumbbells that undertake a major task to form the mould cavity in the sand flask. The quality of patterns directly affects the final outcomes of cast iron dumbbells. In other words, dumbbell patterns must be made prudently and precisely.
No matter whether you create an OEM order or an ODM request, the pattern design will be delivered to the manufacturer only when the 3D drawing is confirmed. Cast iron dumbbell patterns are normally made by aluminium and are machined by the Computer Numerical Control machine (commonly known as CNC machine). After being processed by the machine, the dumbbell patterns are likely to go through a series of alternative processes based on their processing requirements as well as conditions. For instance, dumbbell patterns may need to suffer from the torture imposed by processes such as drilling, lathe, or welding.
Often, the final cast iron dumbbell pattern is not made by a whole piece, instead, it is assembled by different parts of cast iron dumbbell patterns in the mould cavity. And your customer’s logos as well as lettering are realized in this processing step.
3. Moulding Sands
When it comes to the step of moulding sands, the first thing for a dumbbell manufacturer to do is find the appropriate sands for moulding. Green sands, a versatile industrial material that has been extensively adopted in making construction products such as concrete, features hard texture and natural bonding. The wet green sands are often used as a granular material that acts as a skeleton and filling in concrete and mortar, hence the name of “aggregate” in construction field.
In a word, the outstanding distinctions of green sands perfectly meet the requirements of making the mould. During this step, operators load green sands into a flask before the cast iron pattern is pressed into it. And operators remove the pattern after a certain processing time, leaving a new-born mould cavity for the next process.
In order to make quality cast iron, the raw cast iron material needs to be analyzed by the Spectromax machine to see whether the proportion of components meets corresponding requirements. If the raw material is qualified, it is then transferred to the furnace for melting. The temperature inside of the furnace during melting can reach 1300-1700 degrees Celsius, and the melting point of cast iron is about 1260 degrees Celsius.
After the cast iron is melted, operators then pour the molten iron into the mould cavity made by green sands. For some manufacturers with advanced equipment (like Speck Group), the production line is semi-automatic, which lessens the heavy and dangerous work originally carried out by operators.
The molten iron needs to sit in the mould cavity for 6 to 8 hrs for cooling before the roughcasting is gathered and collected. And the sand-blasting equipment is adopted to sweep and clean the sand left in the mould cavity. The above melting, collecting and cleaning processes all require precise control and management so as to ensure the quality of cast iron piece.
Eventually here comes the last process — machining cast iron dumbbells. After the dumbbell roughcasting has been collected, they are scheduled to go through refining processes like drilling, polishing, smoothing, milling, etc. These processes help to refine the cast iron piece, making it conform to the specifications.
At Speck, before shipping out the products, strict inspections must be performed to assure the high quality of cast iron dumbbells. Such inspections are listed as follows:
- Pinholes Inspection (Liquid Leakage Test)
- Crack Inspection (Liquid Leakage Testing)
- Eddy current Testing
- Magnetic Particle Testing
- Mechanics Performance Testing
- X-ray Testing
- Ultrasonic Testing
- Dropping Test
- Proper Weight Test
- Coating Test
Pack the dumbbells according to customers’ requirement. Click and read more about custom packaging.
Want to know more about the manufacturing process of different kinds of dumbbells? Please follow Speck’s follow-up articles. As the world’s top dumbbell manufacturer, we will share more knowledge of fitness equipment manufacturing for you.