Determining Your Requirements

How To Determine Your Ferrofluidic Seal Requirements

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

Evaluate Your 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 feedthrough
• 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 vacuum feedthrough products are shown with a representative photograph or drawing, dimensional and performance information.

Individual dimensional drawings show the important features of each feedthrough. For hollow shaft products, additional dimensional information about shaft interfaces is presented.

Appropriate mounting nuts and washers are provided for standard nose-mount styles above 1/4-inch shaft diameter. The mounting hole diameter and nut preloading torque are listed in order to help avoid damage during installation.

Understand Your 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
• Heat exposure and the feedthrough operating temperature
• Any other environmental considerations that may shape your Ferrotec solution

Consider Key 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. Enhancements such as water cooling can extend the operating capacity of some products. 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 their unique non-contacting seal design. The web site lists a limiting 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 limiting speed, consult your nearest field sales engineer for permissible loads at your required speed.

Maximum thrust load is applicable in either direction. For larger products, vacuum creates a significant thrust load proportional to the shaft diameter, that must be added into thrust load calculations. Contact your field sales engineer if you have questions.

Maximum radial load and bending moment are also considerations.

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

Shaft Torque Capacity

The torque transmission capacity of each feedthrough is provided on the specifications tab of the standard product page. The listed value 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 Inch-Ounces or Newton-millimeters.

The specifications list approximate running torque for shaft speeds of 100 and 1,000 rpm. Running 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 days at a time, a Ferrofluidic seal may have somewhat higher initial starting torque. This normal, temporary condition is alleviated after just a few shaft rotations.

The specifications list starting torque for 100 and 1,000 rpm. This is the peak value of drag torque that would be encountered on first startup after a day or more idle. Subsequent startups would not encounter this torque.

Starting torque is proportional to acceleration rate. The tabulated values are for an acceleration rate of 3.33 rev/sec². This rate reaches 100 rpm in 1/2 second or 1,000 rpm in 5 seconds.

Note: 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 can be provided 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 permeation and 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 evolve from a feedthrough, a sample residual gas analysis (RGA) trace of a typical Ferrofluidic Seal can be provided by your field sales engineer.

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.