Ask the Experts

Richard Lynch
Enthone Inc.

Richard Lynch

Automotive Functional Coatings for Brake Systems

Biography | Website | Answer Archive | Ask a question

Q: What is the prevalent finish on pins, and is it changing?

Most modern disc brake systems employ slide pins which allow the caliper frame to move the non-piston side of the brake pads. The pins provide a structural guide which applies equal pressure from both sides of the brake rotor.

Finishing for these pins can be very diverse due to the increasingly highly specialized engineering requirements for each car program and platform. Corrosion can be an issue for these components as the brake must slide freely and free of obstruction to operate effectively. These pins often have a rubber boot at the first line of defense and are coated with special lubricants which aid in corrosion protection.

Traditionally zinc plated, we have seen much of this finish transition to zinc nickel. While this may represent the largest segment of the finish application, there are increasingly fragmented final finishes. Electroless nickel is often applied for corrosion and wear resistance. Stainless steel, even at a premium cost, has seen increasing use, which helps provide some insight to the critical nature the slide pin.

Date asked: 06 August 2013

Q: What can be done to eliminate post-seal discoloration? No baking of the parts, just after time.

Great question and a complex one. The use of sealants for specific applications has proliferated and will continue to do so as industry requires higher levels of application-specific performance.

There are many types of sealants with a wide array of compositions. They may be organic, inorganic, organic/inorganic blends, waxes, polyethylenes, and polyester resins, to name a few. Generally speaking, inorganic-based sealants have less tendency to discolor but there are other drivers such as film thickness and maybe most importantly base material or substrate. The brake caliper substrate is notorious for many issues, largely porosity. Regardless of how much we try to properly dry processed parts, there is inevitably residual moisture trapped in the substrate. The act of drying (heating) parts actually causes the substrate to expand and seal pores, as well as moisture. The trapped moisture can often lead to discoloration, especially when paired with heavy film building sealants. Fasteners may also exhibit these tendencies as a by-product of wire quality and variances in the drawing process. The solution and symptoms are the same. Use of a good-quality acid inhibitor in the pickle tank is critical to prevent exasperating the porosity issue.

When selecting a sealant, we carefully consider the application. Brake calipers often use topical-type sealants, but the highest performance are silane based with a couple unique qualities. Generally we recommend specific high-performance silanes, which are low in viscosity and effectively penetrate the pores. The sealant fills the pore and cures, essentially filling the space. The best choices are often non- film builders, which reduce unintended side effects beyond optimizing corrosion resistance. This means there are only very small amounts of material in the non-porous, non-problem surfaces.

These ultra-thin, high-performance technologies may help solve your problem.

Date asked: 28 June 2013

Q: There is a lot of talk concerning aluminum brake calipers. Does this mean cast iron calipers will be fading away in the coming years?

There has definitely been a transition to aluminum for one very compelling reason – weight. The pending new government CAFE (corporate average fuel economy) standards are applying substantial pressure on OEMs, especially in light of the EV’s (electric vehicle) limited market acceptance thus far.

While calipers vary in size and weight, it is commonplace for cast iron calipers to weigh in excess of ten pounds. This equates to more than 40 pounds per vehicle, which is a real opportunity for engineers looking to eliminate weight, ounces at a time. The pressure on weight is exemplified by the new Cadillac CTS release which touts a 250 pound weight reduction, substantially due to the use of structural aluminum.

So why are calipers still predominately cast iron? The main reason is space. An aluminum caliper needs to be substantially larger in size to maintain acceptable strength when compared to cast iron, which is difficult to accommodate in the tight wheel window. Small cars, due to an even smaller wheel window, have cast iron calipers largely for this reason. We can expect aluminum to play a role but not be a savior any time soon.

Date asked: 21 June 2013

Q: We are a hard chrome plating company and were recently contacted to quote “soft” hard chrome on brake pistons. What is soft hard chrome and what is its purpose?

Brake pistons are the pistons which ride inside the caliper and force the pads against the rotor when receiving hydraulic pressure from the brake fluid system via the master cylinder. Generally, these pistons have only modest corrosion resistance requirements and are plated in electroless nickel or hard chrome. Different brake companies have differing preferences.

Soft hard chrome is unique in application to the brake piston application. It generally is plated as a thinner deposit to avoid the build up of stress in the coating which results in a micro cracked surface. This application requires a crack free surface.

As plated, the deposit is matte to semi bright and processed with subsequent buffing steps to bring out brightness and a smooth deposit. Applied pressure is critical during this buffing stage to avoid liberating stress by the creation of cracks in the surface.

As a hard chrome plating company, you would likely have few issues processing the parts with the assistance of a knowledgeable supplier. The buffing step may be the challenge which will require some investment of time and proper equipment.

Date asked: 05 June 2013

Q: We are a large job shop with historical experience plating cast iron brake calipers. Over the years our business transitioned away from calipers; however we have recently had substantial renewed quoting activity mostly requesting zinc nickel alloy plating. Why zinc nickel and what is happening to bring so much activity to this application?

You are not alone! Plating brake calipers, traditionally with chloride zinc, was big business for many job shops in the 90’s and early 2000’s. These finishes were mostly aesthetic and traditionally used clear, green, and black hexavalent chromates. Prior to this, many calipers were not even plated.

Many Tier one brake manufacturers accelerated their investment to bring plating in house through out the 2000’s to lower their cost per unit. When the automotive recession occurred, the need for outside overflow work subsided as the in-house plating operations absorbed most of the capacity.

With the development of open wheel automotive design, many of today’s brake calipers are clearly visible to the consumer. Many are even a design element. The open visibility has driven the desire for higher levels of corrosion resistance and also milder corrosion products. The voluminous nature of zinc corrosion products is becoming less acceptable especially on premium vehicles.

The trend to zinc nickel is accelerating rapidly and is being largely driven by German OEMs. Europe has been in large scale production for several years and this requirement has now arrived in North America. The North American brake manufacturers are still bringing internal capacity on-line and looking for external sources as a bridge and also for over flow.

Zinc Nickel plating of calipers requires a high degree of applications expertise. The successful and experienced supplier will be a great asset to your business. Ask about successful production installations and check references and you will quickly identify the best system options.

Date asked: 05 June 2013

Back to the list of experts