Rotating Face Mechanical Seals

Mechanical seals are engineered for most pumps, mixer and agitator applications in maintenance. In many cases the designs have been proven to be workhorses over years of use. In others seals must be designed for evolving industrial demands.

Mechanical seals deliver a full range or rotary configurations and component materials – to handle virtually and fluid moved by any equipment. When you specify engineered mechanical seals you have the advantage of the most advanced mechanical seal technology, the latest in field proven design and when working with an outside sales force there is hands on technical support.

Rotating face units are the dependable mechanical seal answer for worn equipment when your shaft seals must be replaced. They are ideal for new equipment designs or to improve the usefulness of existing equipment by converting from pump packing to mechanical seals.

Mechanical seals feature:

• Invisible leakage
• Less friction/power loss
• No to little wear on the shafts or sleeves
• Flexibility – to accommodate shaft deflections and “End Play”
• No period maintenance
• Long Life

In practical use, the basic rotating face mechanical seal principle is adaptable to serve a tremendous number of sealing needs: standard mechanical seals can suit most requirements-including temperatures to 500 degrees F and shaft speeds to 3600 RPM through the choice of secondary seal and the combination of seal and seat face materials which are offered. Seals can be ordered in balanced configurations to seal pressures above 200 psi, or used in a multiple for extremely high pressures or especially severe fluid services….Special mechanical seals can be furnished to meet the most demanding of industrial applications considering pressure, temperature, speed or fluid.

Mechanical seal designs range from the work horse “single spring” mechanical seals, to highly engineered double cartridge seals for extreme applications. The basic of each type follows:

Single spring mechanical seals:

Utilize a single spring coiled in a right of left hand design to accommodate left and right hand turning pumps. They have the flexibility to accommodate misalignment, shaft deflection, and break away shock loading. It resists clogging in extremely viscous fluids.

All mechanical seals are constructed of three basic sets of parts:
1) A set of primary seal faces: one that rotates and one that remains stationary.
2) A set of secondary seals known as shaft packings and insert mountings, such as o-rings, rubber boots, PTFE or Grafoil wedges, or V-Rings.
3) Mechanical Seals have hardware including gland rings, collars, compression rings, pins, springs, retaining rings and bellows.

Mechanical Seals can be classified by Arrangement

Mechanical Seals can be classified by Design

A mechanical seal works though the use of two very flat (generally within 3 light bands flat) lapped faces which make it difficult for leakage to occur (beyond a vapor). As mentioned above one face is stationary and one rotates with the shaft. One of the two faces is usually a non-galling material such as carbon-graphite. The other will be a harder material providing dissimilar materials making contact and allowing one to be a sacrificial. The softer mechanical seal face usually has the smaller mating surface and is commonly called the “wear nose” of the mechanical Seal.

The Easiest seal to install as a replacement for pump packing is a cartridge type mechanical seal:

The Beauty of cartridge seals are they are self-contained. Holding all the elements of a mechanical seal set:

*Rotating Face Seal

*Stationary Seal face or faces

*Shaft sleeve

*Gland

Cartridge mechanical seals :

Are the easiest seal for a mechanic to install. Only being required to slide onto the pump shaft and bolt to the pump gland, the cartridge seal cannot be miss installed.

Cartridge seals must fit the stuffing box there is a form on www.americansealandpacking.com under mechanical seals with this and other information on it to help the customer make sure the seal fits there pump.

Installation of single spring, metal bellows or multiple spring seals require much more effort to be sure of an effective long lasting seal. Ask your American Seal & Packing sales representative for installation directions.

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The closure is supplied to the bottler with foil liner already inserted. Although there are various liners to choose from, a typical induction liner is multi-layered. The top layer is a paper pulp that is generally spot-glued to the cap. The next layer is wax that is used to bond a layer of aluminum foil to the pulp. The bottom layer is a polymer film laminated to the foil. After the cap or closure is applied, the container passes under an induction coil, which emits an oscillating electromagnetic field. As the container passes under the induction coil (sealing head) the conductive aluminum foil liner begins to heat. The heat melts the wax, which is absorbed into the pulp backing and releases the foil from the cap. The polymer film also heats and flows onto the lip of the container. When cooled, the polymer creates a bond with the container resulting in a hermetically sealed product. Neither the container nor its contents are affected, and this all happens in a matter of seconds.

It is possible to overheat the foil causing damage to the seal layer and to any protective barriers. This could result in faulty seals, even weeks after the initial sealing process, so proper sizing of the induction sealing is vital to determine the exact system necessary to run a particular product.

Sealing can be done with either a hand held unit or on a conveyor system.

A more recent development (which suits a small number of applications better) allows for induction sealing to be used to apply a foil seal to a container without the need for a closure. In this case, foil is supplied pre-cut or in a reel. Where supplied in a reel, it is die cut and transferred onto the container neck. When the foil is in place, it is pressed down by the seal head, the induction cycle is activated and the seal is bonded to the container. This process is known as direct application or sometimes capless induction sealing.

Leak prevention/protection

Some shipping companies require liquid chemical products to be sealed prior to shipping to prevent hazardous chemicals from spilling on other shipments.

Freshness

Induction sealing keeps unwanted pollutants from seeping into food products, and may assist in extending shelf life of certain products.

Pilferage protection

Induction-sealed containers help prevent the product from being broken into by leaving a noticeable residue from the liner itself. Pharmaceutical companies purchase liners that will purposely leave liner film/foil residue on bottles. Food companies that use induction seals do not want the liner residue as it could potentially interfere with the product itself upon dispensing. They, in turn, put a notice on the product that it has been induction-sealed for their protection; letting the consumer know there was a liner on the plastic bottle prior to purchase.

Sustainability

In some applications, induction sealing can be considered to contribute towards sustainability goals by allowing lower bottle weights as the pack relies on the presence of an induction foil seal for its security, rather than a mechanically strong bottle neck and closure.

Induction heating analysis

Some manufacturers have produced devices which can monitor the magnetic field strength present at the induction head (either directly or indirectly via such mechanisms as pick up coils), dynamically predicting the heating effect in the foil. Such devices provide quantifiable data post-weld in a production environment where uniformity particularly in parameters such as foil peel-off strength, is important. Analysers may be portable or designed to work in conjunction with conveyor belt systems, for example Edge Electronics Ltd (UK) and Relco (UK) ltd. offer a device which will pass and reject individual seal operations automatically in a high speed volume production setting.
High speed power analysis techniques (Voltage and Current measurement in near real time) can be used to intercept power delivery from mains to generator or generator to head in order to calculate energy delivered to the foil and the statistical profile of that process. As the thermal capacity of the foil is typically static, such information as true power, apparent power and power factor may be used to predict foil heating with good relevance to final weld parameters and in a dynamic manner.
Induction sealing without a cap may be achieved through the use of a sealing head that picks and places the foil on the container prior to sealing.
Many other derivative parameters may be calculated for each weld, yielding confidence in a production environment that is notably more difficult to achieve in conduction transfer systems, where analysis, if present is generally post-weld as relatively large thermal mass of heating and conduction elements combined impair rapid temperature change. Inductive heating with quantitative feedback such as that provided by power analysis techniques further allows for the possibility of dynamic adjustments in energy delivery profile to the target. This opens the possibility of feed-forward systems where the induction generator properties are adjusted in near real-time as the heating process proceeds, allowing for a specific heating profile track and subsequent compliance feedback something that is not generally practical for conduction heating processes.

Benefits of induction vs. conduction sealing

Conduction sealing requires a hard metal plate to make perfect contact with the container being sealed. Conduction sealing systems delay production time because of required system warm-up time. They also have complex temperature sensors and heaters.
Unlike conduction sealing systems, induction sealing systems require very little power resources, delivers instant startup time, and its sealing head can conform to out of specification containers when sealing.
Induction sealing also offers advantages when sealing to glass: Using a conduction sealer to seal a simple foil structure to glass gives no tolerance or compressibility to allow for any irregularity in the glass surface finish. With an induction sealer, the contact face can be of a compressible material, ensuring a perfect bond each time

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A mechanical face seal is an important component of variety of pumps used in chemical, petrochemical and process industry. The primary function of a mechanical seal is to prevent leakage of the process fluid from the pump housing and shaft to the environment. The factors that affect the performance of a mechanical seal to leak are friction, wear and its thermal characteristics. Improving upon the thermal characteristics of a mating ring in a mechanical seal would enhance its performance. Implanting a heat exchanger in the mating ring hold great promise for improving the performance of mechanical seals from the viewpoint of reducing heat at the interface and hence enhance the performance of the mechanical seal. To reveal what affect the implanted heat exchangers can have on the thermal characteristics of different seals, in this thesis, three different designs of mating rings were tested in a test rig and the results were compared to a conventional seal in this thesis.

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