What are cast iron dumbbells?
Cast iron dumbbells have long been the basic go-to dumbbell from the early days of mass production of dumbbells, and in some ways, they will always hold their own when it comes to which dumbbell style to choose from.
Cast iron dumbbells are manufactured from a single piece of metal in a process called casting (which we will discuss later in this article). The heads are predominantly six-sided hexagonal, commonly referred to as hex dumbbells.
This hex shape prevents the dumbbell from rolling when you place it on the floor, and is also convenient when storing the dumbbells on a rack. One of the flat surfaces of the hex head sits securely in place.
Cast iron dumbbells are a very good introduction and entry level set ot free weights which we discuss in our dumbbell buyer's guide, you can read more about that here.
How are cast iron dumbbells made?
Casting metal is a multi-step process that we will break out in this section.
The first stage is to create a design of the dumbbell, this needs to include the shape as well as all the specific details that are required on the outside of each dumbbell. This could include a brand logo, the weight in lb or kg, some texture on the handle, and anything else that the product owner wants to add.
Design work is generally done using 3D computer-aided drawing (CAD) software, which allows the designer to accurately design each size of the dumbbell as well as calculate the actual weight to ensure each finished cast iron dumbbell is accurate to within an allowed tolerance.
Casting is a process which involves pouring molten metal into a mold where it solidifies to create a solid metal shape. The shape of the item being cast is determined by the cavity in the mold and this cavity is created by a pattern.
The pattern is an accurate model of the finished product which is produced from the 3D CAD. The CAD model, which includes all the grinding information and markings, also includes production features that allow for material shrinkage during solidification phase as well as features which allow the solidified metal casting to be removed from the mold.
Patterns are commonly produced from wood or aluminum, which allows the pattern to be used multiple times without being damaged or degraded, thereby providing the accuracy required from the final casting to remain consistent.
Molding sand (often referred to as ‘green sand’) is packed into each half of a mold around the pattern (half of the pattern shape is in each half of the mold). Once the pattern is removed, a cavity remains; this is where the molten iron will be poured and the final dumbbell shape will be produced.
phase of the process is where the approved raw material for the cast iron is heated until it is molten, a temperature in the region of 2200 Degrees F (1204 Degrees C). Once the metal is fully molten, it is poured into the sand mold which fills the cavity in the shape of the dumbbell.
The casting is then left for the molten metal to solidify into a solid cast iron dumbbell, this can take between 6 hours to 24 hours, depending upon the size of the dumbbell being cast. Once the casting is removed from the mold, it is known as a rough casting. This rough casting needs to be cleaned and finished into a product that can be used.
The first part of this phase is to sand blast the rough casting to remove all the sand particles left over from the casting phase. The next step is to remove all the excess metal that is required for the casting process so that a final dumbbell shape is left.
Once the rough casting has been cleaned, it is time for machining. The machining phase includes milling any rough surfaces down to the required finished surface specifications so that the final dumbbell meets the product specifications from the initial design phase.
The dumbbell can then be polished or the desired finish applied such as a paint dip or spray.
The penultimate phase is final inspection where the finished product is subjected to various tests that checks for physical damage, cracks, voids (holes in the casting created during the casting phase), and any other defect that would deem the product a quality failure.
The final inspection point would be to verify the weight of each dumbbell to ensure it is within the allowable tolerance. For cast iron dumbbells this is generally a 5% allowance. If the dumbbell passes the inspection process by meeting all the requirements, it can be released for packing and shipping.
The final phase of the process is packing and shipping. Whether products are sent out individually or in bulk, there should be adequate packing material to protect the products from damage throughout the shipping process, which is how you can be assured to receive undamaged brand new dumbbells at your door a few months after all of this production takes place at the foundry.
Hopefully this gives you a good idea of what it actually is when you buy and use cast iron dumbbells for your exercise routines. But you can rest assured that the material is very strong and sturdy, and a cast iron set of dumbbells should last you a lifetime if treated with care and not dropped. When you consider the benefits of the cost savings realized in buying cast iron rather than more premium materials, it’s hard to beat the value they offer.