How to determine your seal requirements

Here are some inportant factors to take into consideration when you are selecting a seal.

Dimensional Requirements

The size and available space for your seal are significant factors that shape your selection. To select a Ferrofluidic seal from our standard rotary seals, you need to know some information such as:

• Whether you need a solid or a hollow shaft for your seal
• Your spindle size or the size of the hole to be sealed
• Seal mounting characteristics such as external flanges, cartridge seals, or threaded mounting

Ferrotec’s Ferrofluidic products are shown with a representative photograph, dimensional and performance information.

Accompanying the photographs is a dimensional drawing showing the important features of each feedthrough. For hollow shaft products, additional dimensional information pertaining to shaft interface requirements is presented in tabular form.

In the event the feedthrough has a threaded nose mount, appropriate mounting hardware is provided. The mounting hole diameter and nut preloading torque are listed in the tabular information. These values must be adhered to or product damage may result.

Application Environmental Requirements

Depending on the environment where your Ferrofluidic seal will operate, Ferrotec will recommend seal characteristics that help ensure your seal will function reliably and will perform optimally. Factors that need to be considered include:

• Whether you are sealing an environment with aggressive or reactive gas
• What the operating temperature that the seal will be exposed to
• Any other environmental considerations that may shape your Ferrotec solution

Performance information

Your performance requirements will also shape the Ferrofluidic solution that Ferrotec recommends for you. Some of these factors include:

• Shaft speed
• Load specifications
• Torque specifications
• Pressure requirements

General information needed to select a standard feedthrough for a particular application will be found in tables and graphs accompanying each product. The following is a brief description of the information provided. For applications where requirements exceed the referenced data, please contact your nearest field sales engineer.

Shaft Speed. Ferrofluidic feedthroughs are capable of a broad range of speeds due to the their unique non-contact seal design. The catalog lists a maximum no-load speed for each feedthrough. This is the maximum safe speed for that feedthrough with no externally applied loads.

Load carrying capacity. The load carrying capacity of a feedthrough is governed by many factors including shaft speed, mounting orientation, and load attitude. A reference load capacity is given for each feedthrough at an assumed shaft speed of 1,000 rpm. Load capacity is usually defined as the load consistent with a bearing life of 5,000 hours at 1,000 rpm. In some cases the load capacity is limited by a parameter other than rotary speed. Therefore, it is safest to consider the listed load capacities to be maximum safe load for applications not exceeding 1,000 rpm. If your shaft speed is well below 1,000 rpm and you wish to exceed the loads listed in the catalog, or if your shaft speed is above 1,000 rpm but below the maximum no-load speed, consult your nearest field sales engineer for permissible loads at your required speed.

Maximum thrust load is applicable in either direction

Maximum radial load is also a consideration.

Note: Maximum radial and thrust loads should not be combined in the same application. For combined loads, consult with your nearest field sales engineer.

Shaft Torque Capacity. The torque transmission capacity of each feedthrough is provided on the specifications page. The listed values is the maximum safe torque for a feedthrough which is carrying maximum radial load.

Drag Torque. A Ferrofluidic feedthrough presents a modest amount of resistance to rotation. This effect is the result of viscous drag and bearing rolling friction and is usually measured in ounce/inches.

The specification lists approximate drag torque for a shaft speed of 1,000 rpm. Drag torque is proportional to shaft speed. For torque values at different speeds and for particularly torque sensitive applications, consult with your nearest field sales engineer.

When left idle for extended periods, a Ferrofluidic seal may exhibit a somewhat higher break away torque. This is a temporary condition caused by viscous drag and magnetic particle distribution and is alleviated after a few shaft rotations.

* Due to normal production variables, actual drag torque may be up to 30% higher or lower.

Gas Load: Ferrofluidic feedthroughs are commonly used in high vacuum systems. A gas load value is given to assist users in the design of vacuum systems. This is an estimate of the rate of evolution of gas from the feedthrough due to evaporation of ferrofluid.

Note that this is not a leak rate. Atmospheric gas is effectively blocked by the Ferrofluidic seal mechanism. For users who need to understand the nature of the gases which may evlve from a feedthrough, a sample residual gas analysis (RGA) trace of a typical Ferrofluidic Seal is provided.

The values depicted are for feedthroughs equipped with standard ferrofluid. If special process conditions require a nonstandard ferrofluid, these values will change. Contact your representative for a discussion of standard and special ferrofluids.