AG TIRE TALK KEY TAKEAWAYS
MICHELIN: Tire molds significantly influence both tire longevity and performance through several factors.
ASCENSO: Uniformity will always be better in a segmented mold.
MAXAM: Manufacturers have moved away from traditional “clamshell” molds…toward segmented molds.
YOKOHAMA TWS: A clamshell mold is basically two opposite molds, one fixed to the base of the curing press and one on the top the curing press dome.
BKT: Segmented molds, as the name implies, are molds made in segments that separate outward when the tire is cured- by looking at the tread, you can determine the type of mold that was used.
Ascenso Tires North America
Nick Phillippi: Product Manager / Technical Support North America
Segmented Mold:
- A segmental Mold is an individual part design of sidewall plates and tread segment sets assembled in the actuator container to form the Mold, as called a segmented Mold.
Clamshell Mold (Two-piece Mold):
- A two-piece Mold is a two halves design: Bottom half & Top half to assemble and form the tire cavity.
Uniformity will always be better in Segmented mold. Due to this reason PCR, TBR all are in segmented molds. For high-speed application a segmented mold would need to be used. Generally, when considering speeds over 45 mph.
A segmented molds costs 3-4 times higher than a 2-piece mold. Therefore, the value in cost to the end user must be partially considered in the decision.
Segmented vs Clamshell Mold Applications:
- Bias Rear Tractor—Clamshell Mold
- Radial Rear Tractor —–Clamshell Mold with a very few application sizes that may use segmented
- Bias Implement—–Clamshell Mold
- Radial Implement—–Clamshell Mold with high-speed products move to segmented
- Bias Flotation — Clamshell Mold
- Radial Flotation Clamshell Mold – Segmented molds for critical pattern and high-speed products.
Uniformity can also be gained using steel belts, which Ascenso uses in a great deal of radial ag segment. Therefore, the need for segmented molds to meet the highest standards is reduced.
Maxam Tire International
Greg W. Gilland: Vice President Global Agriculture
In tire manufacturing, vulcanization is the final chemical reaction that turns soft, elastic rubber into a firm, finished product using time, temperature and high pressure. This process takes place inside a heated tire mold, where the exact curing time varies depending on the tire’s size. During vulcanization, the tire’s components – such as nylon or steel cords, belts and layers of rubber – bond into a single finished product.
The mold not only cures the tire but also imprints the final tread design and required markings. As modern tires have become larger or narrower, with greater demands for traction, endurance and fuel efficiency, manufacturers have moved away from traditional “clamshell” molds – once the standard for bias ply tires – toward segmented molds that can more efficiently produce radial tires.
When examining the key differences between the types of tire molds being utilized, the two types can be generally outlined as follows:
Clamshell Molds:
- Commonly used for bias-ply agricultural tires or standard radial tires with an aspect ratio of about 80% or higher.
- Consists of two primary parts (upper and lower shells) that clamp together around the green (uncured) tire.
- Typically, the lower shell remains fixed, and the upper shell raises and lowers for loading and unloading the tire.
- As a rule, we will see smaller ag equipment well below 75 Hp or older Ag equipment using Bias Ply or “standard” size (+80 A/S) Radial tires that can be cured in “Clamshell” molds.
Segmented Molds:
- Typically used for almost all Ag Radial casing tires regardless of tread or aspect ratio.
- Per the below images from MAXAM’s sister company MESNAC, a Segmented Mold allows for significantly more intricate tread designs as well as tire sizes in various aspect ratios (from 35% A/S up to 100% A/S) to be both developed and cured.
- Like a clamshell mold, it closes around the green tire. Multiple segments lock in place concentrically, minimizing tire movement during vulcanization.
- Segmented molds have improved tire uniformity, quality, finish, and overall performance providing the market with better or longer lasting products designed to meet the growing technical challenge of the tire industry.
- As Radial Ag tires continue to evolve in both size and section width with lower aspect ratios and in overall diameters to accommodate larger load carrying air chambers, segmented mold technology is providing the engineering capability to develop the right “tire” solutions.
- In most instances and depending on tire manufacturers, most Ag machinery above +75 HP has evolved to Radial tires that can use both standard and lower aspect ratio tires that will require segmented molds to deliver product solutions that have the performance capability that the market requires for above 100 HP Tractors, Combine Harvesters, Self Propelled Sprayers, Floaters and high-speed implement or tanker platforms.
MAXAM as a division of the Sailun Group Tire Corporation, which is the proprietor and operator of MESNAC, the world’s largest tire building equipment company employs all the available latest technology in every product and tread design being developed for the global tire market to include Agriculture. All our current Radial Ag products from the AgriXtra family of tires to our FlotXtra as well as AgilXtra Flotation high speed radial tires are manufactured using sectional molds to ensure we can deliver the absolute highest quality of finished products.
Yokohama TWS
Norberto Herbener: Senior Technical Service Manager North and Central America
Tire manufacturing involves several processes and the last one, before final quality inspection, is the curing process (vulcanization). During this step the prepared tire – called green tire – is placed in a “curing mold” that will shape and cure the tire and deliver a final product. During this step the mold, with the green tire inside, will be heated at a specific temperature for a specific time depending on the tire size and type. The different tire components, mainly raw rubber, will start to meld together and bond between them at the same time the rubber is hardened. This non-reversable process is called vulcanization and alters the internal chemical structure of the rubber.
This curing step is performed in equipment called curing presses, basically an enclosed sealed chamber where the tire is molded. The external shape of the tire is formed by the shape of the mold and internally an expandable bladder presses the material against these molds. All tires are vulcanized using one of the two types of mold technology available- clamshell or segmented molds.
Clamshell Mold
A clamshell mold is basically two opposite molds, one fixed to the base of the curing press and one on the top the curing press dome. After the green tire is placed inside this mold, the dome closes down and creates a closed chamber where the tire is molded/cured.
This system is mostly used in larger tires and tires with continuous lugs like the R1 tread. This tread allows the tire to slide from the mold during the press opening.
Segmented Mold
In contrast, the segmented mold system involves more moving parts, with two molds for the sidewalls and several molds for the tread area (the quantity of segments depends on the size of the tire). Depending on the tire design and size the segments could also include the sidewall mold area.
During curing these segments are compressed by an outer ring that keeps them aligned. Once the curing is over this ring expands allowing the segments to move outwards releasing the tire. This system is used when the tire tread has long lugs or complex tread designs that could be damaged during mold opening, if using a clamshell system.
The segmented mold system can also be used on R1 tread design tires. Several manufacturers that have segmented mold system presses in their factories use them to increase press usage time.
BKT USA, Inc.
Dave Paulk: Manager Field Technical Services
Tire molds give the tire its final shape. There are two types of molds used in the production of agricultural tires: segmented & clamshell. Both are used, but there are distinct differences in how they work.
Clamshell Molds
Clamshell (2 piece) molds have been used for many years and are still used in both bias ply and some radial ply tire production. They open and close like a clamshell. They are one-piece molds that are solid circumferentially. The green tire is laid in the mold placed over a bladder in the center of the tire. The bladder is inflated (usually by steam) to force the tire outward against the mold where the tread is formed, and the tire is cured under heat. After curing, bias ply tires will shrink. This allows the tire to come out of the mold without tearing the tire and the tread. Most bias ply agricultural tires are cured with this method. Clamshell molds are less costly to make than segmented molds. There are many reasons why bias tires are less expensive than radials, but this is one reason. Uniformity is generally not an issue with bias tires using this type of mold.
Segmented Molds
Segmented molds, as the name implies, are molds made in segments that separate outward when the tire is cured. Pressure to the tire is from the outside, and not from the inside like a clamshell mold. This method doesn’t stress the belt package in the tire when curing. All all-steel radial construction tires and steel belted radial tires are made and cured with segmented molds. The green tires are already pre-shaped. If these are cured in a clamshell mold, there is a chance of “mold scraping” (the mold tread portion touching the green tire before the mold closes). This can disturb the tread mass and cause uneven distribution of tread rubber during curing. These tires have very little shrinkage after curing. If segmented molds are not used, they are very difficult to get out of the molds and can tear the tread bars. The segmented molds open from the tire and allow the tire to easily be taken out. If steel belted tires are cured in clamshell molds, since the pressures is exerted from the inside, stress is placed on the carcass of the tire that can result in tire failures. Segmented molds are more expensive to make but ensure better uniformity when curing all steel or steel belted carcasses.
How to Tell Mold Type- Look at the Tire!
By looking at the tread and finding the leftover mold marks (thin ribbons of rubber), it’s easy to determine which type of mold the tire was made in. If there is only one mold mark and it runs circumferentially around the center of the tire, it was made in a clamshell mold. If the mold marks go across the tread from side to side in a few different spots, the tire is made in a segmented mold.
Although segmented molds are more expensive to make, they are needed for tire production to ensure the integrity of the casing and the uniformity of the tire (especially if it has steel belts or an all-steel casing). As technology changes and more tires are made with steel belts (enhances the resistance against penetration of objects into the tire), segmented molds must be used. Tires have gotten larger in size and are easier to cure in segmented molds. This is a reason that we are seeing more segmented molds used now than in previous past years.
Michelin Ag
David Graden: Global Account Manager – Agriculture
Tire molds significantly influence both tire longevity and performance through several factors:
The design of the mold affects how rubber compounds are distributed throughout the tire, during the manufacturing process. A well-designed mold can ensure even material distribution, reducing weak spots that may lead to premature wear or even failure.
Molds also determine the tread pattern and depth, which impacts tractive capacity of a tire, handling/stability, and the overall performance. More intricate tread patterns from segmented molds can enhance grip and performance in various conditions, while simpler designs from clamshell molds may not perform as well in specialized applications. For example, Michelin Roadbib (Intricate Design) vs MachXbib (Simple R-1W)
Regardless of mold, the quality of each mold can affect how heat is managed within the tire during operation. Proper ventilation and design elements in the mold can help dissipate heat, which is crucial for rubber compound consistency, which could prevent tire blowouts, cause excessive wear and ultimately extend tire life.
Unfortunately, there is a cost associated with a well-designed mold. Some Ag tire molds can cost as little as $25k and higher quality molds could be in excess of $150k. The quality of mold tends to be a one of the few differentiators between a tier 1 brand and a tier 3 brand tire manufacturer.
Overall, in addition to rubber compounds and casing/tread design, tires produced in high-quality molds tend to last longer and perform better than those made in lower-quality molds, despite the mold type.
In radial tire construction, the two main types of molds used are segmented molds and clamshell molds.
Segmented Mold: A segmented mold consists of several individual segments that come together to form the complete circumference and shape of the tire. This allows for more precise control over the tire’s design and enables the creation of complex tread patterns. The visual cue indicating a segmented mold tire is often the presence of a more refined and detailed tread pattern, as well as a potentially smoother sidewall.
Segmented Mold
Clamshell Mold: A clamshell mold is a single, solid mold that opens like a clamshell to form the tire. This type is typically simpler and may not allow for the same level of detail in tread design. Tread patterns on clamshell mold tires may appear more uniform and less intricate compared to those made in segmented molds. Often times, you will find this type of mold is used for typical chevron shaped tread designs.
With the increasing demand for specialized tread patterns and technologies that enhance performance in different agricultural conditions, segmented mold usage is on the rise. These molds can produce tires with specific features and benefits, such as improved tractive capacity in specific conditions, roading wear and fuel efficiency, which are crucial in today’s farming applications.
In terms of recommendations, I would recommend segmented molded tires where you have very specific and high-performance expectations. These applications could include specialty farming, where there is a benefit to using hybrid tread designs for roading, tractive capacity, efficiency, etc. Clamshell molds, on the other hand, are suitable for general purpose applications where cost-effectiveness is the priority of the manufacturer and the need for specialized performance is unnecessary.
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