carbon vs silicon carbide mechanical seal quotation

Carrying on with our series on sanitary mechanical seals, the following will provide a good overview of the mechanical seal face materials we see in sanitary pump applications.

Note that we are only discussing seals and seal material for sanitary pumps.  Sanitary pumps have unique characteristics in that they have to be hygienic or cleanable.  Because of that, many commercial mechanical seals and packing type seals that do an excellent job from a sealing standpoint, are not suitable for sanitary pumps.  So, we are keeping our comparisons to sanitary mechanical seals only.

First, it’s important to think about what makes a good seal face material. Few materials, in fact, are suitable for use in seals. As discussed in our previous blog post, to keep leakage to a minimum, the seal gap must be very small. As a result, the lubricating film is very thin. Consequently, the seal faces need to be able to withstand rubbing together at high speeds. And what also comes when things rub together at high speeds? Friction. Heat. So we also need to select materials that are able to withstand this heat. In sum, the best seal face materials have low friction, high hardness, good corrosion resistance, and high heat conductivity.

Carbon seals. The old standby. Carbon seals offer the greatest economy and lubricity for sealing non-abrasive products. It’s good for clean, abrasive free materials. It self-lubricates to reduce heat and extend service life. It works great with all other seal materials.

Ceramic is much more resistive to abrasive materials than carbon. It’s a great all around seal material. It has good hardness and stiffness. It’s wear resistant, corrosion resistant, and cheap. Despite the material’s stiffness, it struggles in applications with thermal shock. It is most commonly paired with carbon and is Waukesha’s standard seal material in its sanitary positive displacement pumps.  It’s the “can do” seal material in the “can do” sanitary pump.

Silicon carbide, specifically reaction bonded and self-sintered silicon carbide, offers superior strength, abrasion resistance, and thermal conductivity to alumina ceramic.

Reaction bonded silicon carbide is made by infiltrating compacts made of mixtures of SiC and carbon with liquid silicon.  The silicon reacts with the carbon forming silicon carbide.  The reaction product bonds the silicon carbide particles.  Any excess silicon fills the remaining pores in the body and produces a dense SiC-Si composite.

Sintered silicon carbide is a premium version of silicon carbide. It contains no free graphite or silicon. Sintered silicon carbide is Waukesha’s hardest seal face for sanitary pumps.  It contains no silicon that can leach into the process, is excellent in an oxidizing environment, and has good thermal shock resistance due to low thermal expansion coefficient and high thermal conductivity.

In summary, silicon carbide’s combination of hardness, strength, and temperature resistance gives it excellent capabilities for services in a wide range of applications where high speeds, high pressures, and chemical and abrasion resistance are required.

Commonly known as Purebide, siliconized graphite is technically a silicon carbide. It is made from specially formulated graphite whose surface has been converted to silicon carbide.  This provides surface characteristics similar to silicon carbide but is less costly to produce than solid silicon carbide.  Free graphite in the silicon carbide layer serves a dry lubricant, reducing friction and improving performance. Purebide is used exclusively in the Waukesha 200 series sanitary pumps.

There is nothing pure about this material. It is a composite. In order to hold the tungsten carbide particles together, a binder is required. Nickel is common in food applications due to its corrosion resistance and compatibility with food products. The metallic binder provides “toughness” to the seal material, making it perfect for heavy-duty applications where high starting torques or shock loading is present. It’s ideal for products that are sticky or set up, high temperature applications, and high loads. It is not inexpensive and should only be specified when absolutely necessary. Tungsten carbide mates with carbon, silicon carbide or itself.

Chrome oxide is an interesting material because most of the seal is actually machined from stainless steel. The base part’s seal face is then coated with chrome oxide. The stainless steel provides a strong base that resists high starting torques, impact loading, and rough handling.  The chrome oxide coating provides a hard, wear resistant face that provides performance similar to solid ceramic.

To close, we hope is that this gives you a good idea of what seal face materials are available for sanitary pumps and when to consider them. A future post will expound on seal face combinations, focusing on specific applications when they should be applied, but for now, hopefully this table serves as a good recap:

Seal life is determined by a wide variety of factors, many of which are independent of the actual seal design. Installation issues, improper pump operation, and an inadequate seal support system are just a few. Very close attention must be paid to the selection of a mechanical seal and its components—including faces, O-rings, and metallurgy—to ensure maximum life. It’s also critical that the appropriate seal type is chosen for each different application and that the installation procedure is accurately followed. Two of the most common seal failure causes are heat generation and improper installation, both of which have multiple potential root causes.

Today, one of the most commonly used seal face combinations is a softer carbon face against a much harder silicon carbide face. This is a cool-running combination if there is no seal support system, such as a flush plan, in place. Excess heat generation between seal faces will drastically reduce seal life, and must be avoided. The softer carbon face against a silicon carbide face does not generate nearly as much heat as other face combinations, and is therefore a good option for seals without seal support systems.

Seal support systems, such as a plan 11 (flush line from pump discharge), a plan 13 (recirculation to pump suction), or a Plan 53A (pressurized barrier fluid with a seal reservoir), can be simple or highly complex, but they all have the same goal: to keep the seal faces clean, cool, and well-lubricated. If there is a seal support system and abrasives are present, changing the carbon face to either Silicon Carbide or a Tungsten Carbide face is a much better option for extending seal life, as the two hard silicon faces will be much more resistant to abrasion. The piping plan will compensate for the excess heat generated by the two hard faces, increasing seal life. If there are no abrasive solids and there is no chemical issue with the process fluid, then the Carbon versus Silicon Carbide face is the best seal face combination to use.

Improper installation of a mechanical seal is another one of the most common causes of failure. Seal installation should be performed in the steps outlined by the manufacturer, and with great care to avoid damaging the delicate seal faces / O-rings. Forgetting to tighten set screws before removing setting clips, not tightening gland bolts evenly, damaging O-rings, nicking seal faces, and piping connection errors are some of the common installation mistakes made when installing a seal.

Component seal installation is inherently more prone to installation errors when compared to cartridge seals due to the extra steps and measurements needed. This is why, if possible, a cartridge seal design should be chosen over a component design. There is already enough to be meticulous about when installing a mechanical seal; why add additional opportunity for installation mistakes?

The correct seal face combinations, proper installation by a trained technician, a seal support piping plan, and good seal selection will lead to longer MTBF, which is what we are all looking for at the end of the day. There is an understandable cost increase for these improvements, but data suggests that the extra cost is well worth it, as replacing a burned-out seal is much more costly in the end.

Distributor of industrial tools & equipment. Products include abrasives, adhesives, bushings, coolants, boring bars, broaches, hand tools, cutters, tool holders, coatings, cleaners, reamers, lubricants, drills, fasteners & gauges. Positioners, knives, brushes, crimpers, cylinders, adhesive dispensers, drill presses, acutators, seals, bulbs, lamps, lifts, pins, polishers, fittings, pumps, punches, saws, sealants & wrenches are also available. Capabilities include sharpening, kitting, repairing, vending, fabricating, heat treating, outsourced storeroom management, reverse engineering, band saw welding, calibration, hardening, bar coding, inventory & process consulting & outsourced procurement. Kan Ban programs.

Qseals is a specialist in processed (turn/milling/cnc) carbon products and components. We primarily focus on carbon products for use in industry. Naturally, we can also deliver with an FDA and/or EC1935/2004 certification. We also supply semi-manufactured products such as carbon on a bar/tube.

We can provide you with small and large products, from a prototype to an end product. Whether it involves 1 product or 10,000 carbon products. You provide us with your blueprint with a material specification and you will receive a suitable quote for turning and/or milling work. You can outsource the assembly of carbon parts, possibly in combination with other materials, to us. For example, reducing the size of carbon rings or lapping of carbon (rings) for mechanical seals. We can offer you a suitable quote with fast turnaround!

Designing mechanical seals for sealing refrigerants and other low viscosity fluids has been a problem in the industry for many years. It has since been established that mechanical seals with a tread combination of antimony impregnated graphite and silicon carbide are the best solution.

Low viscosity fluids are difficult for mechanical seals because the hydrodynamic film is extremely thin. The sealing surfaces must remain well polished to operate within the specifications. The self-polishing properties of antimony impregnated carbon graphite material and the high dimensional stability of both silicon carbide and antimony impregnated carbon graphite ensure that the seal can function within the specifications.

Our NUTECH cartridge mechanical seals are designed to fit all ANSI pumps for ease of installation and are pressure tested at our Texas manufacturing facility prior to shipping. We can custom design any cartridge style seal to fit your most demanding applications. We use premium grade materials of construction throughout. All seals are made in the USA.

Adding John Crane Diamond to mechanical seal faces helps overcome short seal life and equipment breakdowns caused by harsh operating conditions, including:

Due to its low coefficient of friction, diamond generates less heat, reducing the need for cooling water and, in some cases, auxiliary cooling equipment. In instances where auxiliary equipment is required, the reduction in heat generation can significantly reduce the size of the heat exchanger or sealant system, resulting in decreased water consumption and lower equipment costs.

The face treatment’s low friction also reduces energy loss. Depending on conditions, reducing the motor’s power consumption alone can result in a payback period of fewer than 12 months. This decrease in operating costs continues throughout the life of a seal.

Increased durability: The film of pure diamond delivers unmatched hardness, superior chemical stability and a low coefficient of friction. Seals are more durable, with increased longevity.

Increased reliability: Rigorous controls assure film crystallinity, thickness, consistency and bonding that enhance seal life as well as poor lubricating capabilities, extending MTBF.

Materials used for the manufacture of mechanical seal faces. These materials must meet the tribological demands unique to mechanical seals. Industry has evolved primarily to the use of mechanical carbons and ceramics for these components. A mechanical seal (Fig. 1) is by its very nature a collection of components that are designed to control leakage of a fluid through a sealing interface. These components serve a wide variety of functions and correspondingly require a wide range of material properties. Many of these properties, such as mechanical strength, thermal conductivity, or corrosion resistance, are similar to considerations made for many other devices. Some properties, however, are unique to mechanical seals, such as coefficient of...

S. Chinowsky, Friction and wear of carbon-graphite materials, in ASM Handbook, Friction, Lubrication, and Wear Technology, vol. 18, ed. by P. Blau (1992)

M.B. Huebner, Material selection for mechanical seals, in Proceedings of the 21st International Pump User’s Symposium, Turbomachinery Laboratory, Texas A&M University, College Station, Texas (2005)

Editors and AffiliationsDepartment of Mechanical Engineering and Center for Surface Engineering and Tribology, Northwestern University, Evanston, IL, USA

The PL-Series of seals are pre-engineered single and dual cartridge seals with nonmetallic wetted components for use in highly corrosive chemical services where the alternative cost of high alloy metal ...

The MTM 25_26, manufactured by MICROTEM, is a conical spring mechanical seal that can compensate positioning errors and withstand stresses created by vibrations. The contact surface can be made with silicon ...

... the Type 1 elastomer bellows seal is widely recognized as the industry"s workhorse. Suitable for a wide range of service conditions ranging from water and steam to chemicals and corrosive materials, the Type 1 mechanical ...

The PK Seal features a single spring rubber bellows that will not wear the shaft or sleeve. It fits into shallow stuffing boxes and the flexible rotary face floats to compensate for misalignment.

... fluid containment market. Variations to the seal specification can be accomplished by selecting from many different options. Seal faces are offered in any combination of Silicon Carbide, Tungsten Carbide ...

​​​​​​​The design of the Chesterton 442PR split seal is ideal for hot heater drains and boiler feed pumps where cooling to a single seal must be provided.

... include carbon/ceramic/nbr/ss304,resin carbon/ceramic/nbr/ss304/,sic/sic/nbr/ss304,tc/tc/nbr/ss316 and so on. we also can make changes as customers"requirement or totally design a new type of mechanical ...

The 1030 & 1040 are robust single cartridge mechanical seal with flexible stationary design, and the foundation of the mechanical seal product line. These seals are excellent to use in practically any industry.

The 1040 mechanical seal, in addition to the flush ports, offers quench ports in and out. The 1040 also comes standard with a carbon restriction bushing. Alternate arrangements include lip seal containment system, labyrinth bronze bushing, or die formed packing system.

The Series 1000 seals are available in standard sizes for all ANSI / DIN process pumps. In addition, the 1030+ and the 1040+ are designed to accommodates all big bore, taper bore, and oversized stuffing box arrangements.

Because of our versatility in manufacturing, the Series 1000 cartridge seal line is ideally suited for a variety of equipment types…..these would include:

The use of modular parts for seal face configurations provides for maximum interchangeability. At the same time, the Series 1000 seals can incorporate custom manufactured glands and sleeves to accommodate all types of equipment. This is done without sacrificing seal performance, and in nearly all instances, without requiring equipment modification to accept the seal.