Brake discs are important part of braking system, which directly impacts driving safety and comfort. In this post, we’ll delve into the world of brake discs, exploring their materials, production standards, types, and manufacturing processes.
1. Brake Disc Materials
The majority of brake discs are made from grey cast iron, particularly the surface that comes into contact with the brake pads. In China, the domestic standard for grey cast iron is HT250, while in Europe it’s GG20 and in the United States, it’s G3000. After-sales markets predominantly adhere to these standards.
The composition of brake disc materials is strictly controlled, with specific requirements for five major elements: carbon, silicon, manganese, sulfur, and phosphorus. Some manufacturers may also have requirements for elements like copper, but most established factories can meet these specifications.
To ensure material quality, manufacturers employ furnace front thermal analysis instruments to measure carbon content, carbon equivalent, as well as liquidus and solidus temperatures. Other elements are analyzed using spectroscopy. Reputable factories conduct these tests on every batch of cast iron, and only after passing the tests is the material allowed to proceed to the casting stage.
There are also special types of brake discs:
* Brembo’s bonded forged brake discs feature different materials for the braking surface and the central part of the disc. The braking surface remains grey cast iron, while the central part is made from an alloy. These components are initially manufactured separately and then combined through pressing or remelting to form a single unit.
* Two-piece brake discs are similar in concept. The braking surface and the central part are made from different materials and connected via bolts.
2. Brake Disc Casting Standards
The casting of brake discs must meet specific material standards:
* Carbon (C): 3.0% – 3.3%
* Silicon (Si): 1.9% – 2.1%
* Manganese (Mn): 0.6% – 0.9%
* Phosphorus (P): Less than 0.1%
* Sulfur (S): Less than 0.1%
In terms of mechanical properties:
* Hardness (Hb): 190 – 220
* Tensile strength: Greater than 220 MPa
* Pearlite content: Greater than 95%
* Graphite requirements: Grade A graphite is mandatory. At a minimum, 60% should be Type A graphite, with higher standards demanding that Type A graphite exceeds 90%. The presence of Type D and E graphite is not allowed.
* Graphite length: Should be between grades 3 and 6.
3. Types of Brake Discs
Brake discs primarily come in two types:
* Vented discs: These discs feature internal vanes that promote heat dissipation during braking, helping to maintain braking performance and prevent brake fade. They are commonly found on the front wheels of passenger vehicles, where braking demands are higher.
* Solid discs: Simpler in design and more cost-effective to produce, solid discs are typically used on vehicles with relatively lower braking requirements, such as some light commercial vehicles and rear wheels of certain passenger cars.
4. Brake Disc Production Method
Brake discs are manufactured through a casting process to obtain a raw shape (blank), which is then machined using equipment like lathes and drills to produce the final product.
The quality of the casting process is crucial as it determines the material composition, microstructure, hardness, and tensile strength of the brake disc, which cannot be fully assessed through subsequent measurements. Factors such as mold making, material selection, inoculation, pouring temperature, and holding time collectively influence the casting quality of brake discs.
Large factories generally employ mechanical molding techniques, which offer better stability and consistency. In contrast, smaller factories often rely on manual molding, which can result in greater variability in quality.
5. Brake Disc Machining
Machining processes, utilizing equipment like lathes and drilling machines, transform the brake disc blank into the final product. Key indicators during machining include:
* Brake surface runout relative to the mounting surface: For OEM (Original Equipment Manufacturer) applications, this is typically required to be within 0.03 millimeters. After-sales markets generally accept a range of 0.05 – 0.1 millimeters. Exceeding 0.1 millimeters can lead to brake judder during braking.
* Brake surface thickness variation (DTV): Measured as the thickness difference on the same radius of the brake surface, OEM requirements are stringent at 0.006 millimeters, while after-sales standards are 0.0127 millimeters. Ideally, this value should not exceed 0.02 millimeters during use. Values between 0.02 – 0.04 millimeters may cause slight judder, while values above 0.04 millimeters can result in severe judder.
Both runout and DTV can contribute to brake judder. Runout is primarily determined during manufacturing but can also be affected by thermal deformation during use. Most brake judder issues stem from excessive runout. DTV, on the other hand, can be influenced by both brake pads and brake discs. Research by DLB (Duo Lian Brake) has shown that brake pads with low metal content formulas are less aggressive towards DTV and can even help repair it to some extent. Ceramic formulas, however, perform poorly in this regard and generally cannot repair DTV.
* Dynamic balance: Like tires, brake discs also require dynamic balancing. Different brands have varying requirements for dynamic balance. For instance, a requirement of 100g·cm means fewer brake discs need balancing, while a stricter requirement of 50g·cm means more brake discs will require balancing, with a higher likelihood of failing to meet the standard. A requirement of 30g·cm is even more demanding.
6. Brake Disc Surface Treatment
Brake discs typically do not undergo heat treatment. Instead, stress relief is achieved through casting and holding processes. Surface treatment of brake discs mainly serves to prevent rust. This is important both before installation and for non-contact surfaces. Common rust prevention methods include:
* Rust preventive oil
* Vapor phase corrosion inhibition using rust-proof paper or bags
* Phosphating (e.g., zinc-iron or manganese-based phosphating)
* Painting with water-based rust-proof paint
* Dacromet or Geomet treatment
* Electrophoretic coating, where the entire disc is coated with electrophoretic paint before machining the brake surface
* FNC (Ferritic Nitro-Carburizing): Currently the latest surface treatment method, FNC primarily enhances rust resistance. The carbonitriding layer is required by General Motors to be between 0.1 – 0.3 millimeters thick.
It’s important to note that rust prevention for brake discs is a challenging issue. While non-contact surfaces can be protected through various methods to delay rusting, the brake surface, which comes into contact with brake pads, cannot undergo rust prevention treatment. Therefore, minor rust on the brake surface is not a cause for concern and can be removed by gently depressing the brake pedal. It’s advisable to avoid emergency braking whenever possible.
7.Brake Discs Manufacturers and Suppliers
When selecting brake discs manufacturers or brake discs suppliers, it’s essential to consider factors such as quality, reputation, and after-sales service. Shandong Sensitive Brake System Co., Ltd is a professional manufacturer of auto parts brake system since 2007, best China Car Brake Pads Factory, brake pad manufacturers & supplier in china. If you want to importing brake pads from China, it will be a best choice for you and your client. Anything you need, just contact us: sales@sensitivebrake.com and +8615666473208, we will providing you professional solution and advice!
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