GUIDE TO PURCHASING OTK KART GROUP RIMS (FOR TONY KART, KOSMIC KART, LN RACING KART, EXPRIT…)

Based on the characteristics it wants the rim to have, but regardless of the material (magnesium or aluminum), the Italian company uses two distinct production processes:

1. Low pressure casting: is applied to magnesium rims as well as to the aluminum model used for rental karts and has replaced the gravity shell casting, guaranteeing superior production quality. In fact, it’s a process which - precisely due to the low pressure involved in the phase of putting the material into the mold – improves the filling of the mold itself, thereby reducing the forming of porosity, which can be harmful to the structure of the end product, given that it can generate cracks and the consequent breaking of the rim. 
2. Die casting: for aluminum rims and certain magnesium models. It’s a faster casting process compared to low pressure casting, in fact the material is literally injected into the mold. However, this rapid action increases the risk of creating turbulence and blowholes within the structure of the rim itself. That said, the strict quality controls implemented by OTK Kart Group guarantee the structural integrity of each product.

The type of casting used directly influences the behavior of the rim out on the track. In fact, the rims produced by low pressure casting guarantee that the kart slides better in track conditions with hot asphalt and high grip. Those produced by die-casting, on the other hand, are optimal in conditions featuring cold tracks or ones that are not yet perfectly rubberized, as they guarantee the wheel assembly better road holding.

To guarantee the highest quality of its products, the Italian company uses technologically advanced machinery and has automated most of its production processes. Rims produced by low pressure casting require more CNC machining, as they have a lot of excess material. They are easily recognizable because they are processed both internally (meaning the area which is then covered by the tire) and externally (i.e. the part of the flange, meaning the part that’s visible when the tire is mounted). The last step for models produced using the low-pressure casting method is painting. In fact, this production methodology results in raw products that require more processing by robotic machinery. Every single rim made by die casting is checked by an operator and then processed externally, by means of robotic machinery, on the bead part of the tire. In terms of processing, die-cast rims are finished only on the edge since this production technique produces minimal excess material. Once this phase is completed, the rim is painted with a powder coating and is then placed back into the machine to carry out the work necessary to complete the product (such as, for example, centering the hub and making the holes for the anti-loosening screws). 

The last production phase to which OTK Kart Group rims are subjected involves the treatments, which differ based on the casting method used and the construction material of the model.

1. Magnesium rims produced by low pressure casting are subjected to a passivation process, which consists of immersing the rims in a solution. This process cleans the surface of the impurities and iridescence that are typical of magnesium, resulting in the product having better aesthetic qualities. Furthermore, it creates a very thin protective layer on the surface capable of protecting the rim from corrosion. Passivation, however, doesn’t have a sealing function. That’s why each individual rim is subjected to "impregnation" by immersion in special liquids and is then placed in a vacuum. By doing so, the material absorbs the impregnating substances which make the rim watertight. Subsequently, there’s the liquid painting phase, which creates a very fine layer of color ranging from 8 to 12 µm, unlike powder coating, which can reach up to 120 µm. Thinner paint layers guarantee greater heat exchange, meaning the rim can guarantee lower and more consistent operating temperatures. 
2. Die-cast aluminum rims are subjected to a single final treatment called powder coating. In fact, aluminum doesn’t require protective treatment against oxidation, given that, from a chemical point of view, unlike magnesium, it’s less subject to this phenomenon. Furthermore, taking into account that the aluminum models are recommended by OTK Kart Group as being optimal in conditions where there’s "rain/low temperatures/poor levels of grip out on the track", powder coating gives this type of rim low heat exchange and, therefore, a greater ability of the rim to accumulate heat, an aspect that helps tires to reach the correct operating temperature range sooner.

This kind of treatment is not exclusive to aluminum rim models, however. Some magnesium rims, made using die casting, are also powder coated. The reason is also linked to maintaining temperature levels: these specific models are meant for use in cold track conditions, which therefore implies the need for more heat at a tire level.

Quality control, in the OTK Kart Group production cycle, doesn’t represent an actual phase that’s positioned before or after a specific process. It could be said that this task accompanies all the various steps in the construction of a rim, starting from the "initial" phase, i.e. the rigid checks and related quality tests that are carried out on the raw materials (aluminum and magnesium) purchased. Once a rim has completed all the steps in the production process, it is once again examined by the OTK Kart Group quality control department. Here, the engineers verify that each model conforms with certain safety and structural standards. The first step, to which all products are subjected, is the leak test: by immersing the rim in water, "putting it under pressure", it checks that no bubbles escape from the structure. In fact, the appearance of air bubbles indicates that there are cracks or damaged parts. The second step regards the analysis of eddy currents. This phase is carried out on a sample basis and represents a more in-depth test, which checks whether the rim has any micro-fractures or structural imperfections.