Series 7500 Formed Metal Bellows
Information at a Glance
Series
7500 Formed Metal Bellows
Material
Steel
Size
1/2 -48 in. / 12-1200 mm
Pressure
≤100, 150 & 300 PSI / 3, 10 & 20 Bar
Motion
unlimited
Product Description
Series 7500 formed bellows can be used in assemblies and for applications that are only limited by your imagination. Hyspan is ready to assist you from preliminary design to final testing. The company maintains extensive engineering capability for the design of metal bellows and related hardware, and has complete facilities for prototype production and development testing. Once developed Hyspan has unparalleled capability for volume production at company owned facilities at five locations.
Vacuum Applications
Series 7500 Bellows can be used for high-vacuum applications requiring leakage rates less than 1 x 10-10 STD ATM CC/SEC at base pressure of 1 x 10-6 TORR.
Since most of these applications require extremely flexible bellows, Hyspan recommends materials thickness of 0.006″ for inside diameters (I.D.) up to 4.5″, 0.008″for I.D. up to 8.0″, and 0.010″ for I.D. up to 14″. Any material Thickness can be used which has a maximum pressure (Column 7 on pages 6-17) exceeding 15 PSIG. Type 321 stainless steel is preferred because of its weldability and availability; however, other alloys can be substituted.
Weld attachments for high-vacuum applications are very critical. Because of the thin bellows material that is normally used, the addition of filler rod is not practical. The illustrations show the Hyspan recommended weld joints for internal and external attachments. The bellows must be a tight fit to the band, and the materials compatible because they are fused together.
Hyspan manufactures standard formed metal bellows configurations that are suitable for most applications. Inside diameters range from 1.0″ through 96.0″ with a wide range of material thicknesses, convoluted lengths and materials. Complete technical information is tabulated including design pressure, spring rates and cycle life.
Beryllium Copper
The beryllium copper alloys have high thermal and electrical conductivity similar to pure copper. It can be readily joined by resistance and fusion welding, brazing and soldering. The material is nonsparking, nonmagnetic; it has high galling resistance, and maintains its strength and ductility at cryogenic temperatures.
Valve Seals
Formed bellows are commonly used for packless valve seals in safety, control and high vacuum valves. Hyspan has a complete library of designs for commonly used valves, and the capability to develop new designs. For high temperature and corrosive service specialty alloys such as Monel 400, Alloy 625, and Hastelloy C-276 are available.
Pressure Restrained
Structural components can be added to react the pressure thrust force of unrestrained bellows. In the photograph to the right, gimbal hardware has been added which restrains the bellows but allows universal angular motion. Two or three joints (depending on the application) of this design will absorb linear motion in all directions.
This photograph is an in-line pressure balanced assembly. There are four small diameter which have a total effective area equal to the larger line bellows, and through the rods and structure the pressure thrust is balanced internally. The only resistance to axial motion is the bellows axial spring rate.
Wave Guides
Formed bellows are used as wave guides. The assemblies in the photograph are made from aluminum. As shown they are easily formed into the required shape. Hyspan also manufactures bellows made from stainless steel and Beryllium copper.
Cryogenics and High Vacuum
Probably the most common applications of formed metal bellows are for cryogenic and ultra-high vacuum service. The assemblies shown in the photograph are for cryogenic service in medical equipment. The copper ring in the center is brazed to the stainless steel bellows. The completed assembly is leak tested to 1×10-10scc/sec. of helium. Hyspan maintains ASNT Level II helium leak testing certifications, and has facilities for liquid nitrogen testing.
Volume Compensation and Pressure Actuators
Bellows can be designed into sealed assemblies that can be pressurized internally or externally to provide large volume changes. The exposed bellows is a “crush formed” bellows assembly that was used in an electrical transformer that was designed for a 3x increase in length. The launch pads at Vandenburg AFB use this concept to raise and lower the launch vehicle. The design pressure for this application was 3000 psig.
Development Testing
Hyspan has facilities and equipment for a wide range of testing that is required for bellows product development. The photographs illustrate two bellows designed into a “tied universal”. It was cycled with a lateral offset of 2″ each side of neutral for 22,000 cycles while pressurized to 280 psig and heated to 900°F. The forces and moments at the end attachments were measured during the test.
Bellows Nomenclature
Bellows Movement
AXIAL
Extension or compression from the manufactured length along the longitudinal centerline with ends parallel.
LATERAL
Displacement perpendicular to the longitudinal centerline with the ends parallel.
ANGULAR
Rotation of the longitudinal centerline about the perpendicular axis.
COMBINED
Axial, lateral, and angular movements can be combined within the rated movements.
TORSION OR TWISTING AROUND THE CENTERLINE
(Not recommended)
Standard Tolerances
| Inside Diameter | Stock Number | Neck I.D. | Convolution I.D./O.D. | Convoluted Length | Trim Length |
| 1″-4″ | 7513-7544 | 0.01 | 0.03 | 0.06 | 0.03 |
| 4.125″-6″ | 7545-7557 | 0.01 | 0.04 | 0.06 | 0.03 |
| 6.25″-12″ | 7558-7577 | 0.02 | 0.06 | 0.09 | 0.06 |
| 12.25″-24″ | 7578-7586 | 0.03 | 0.09 | 0.12 | 0.09 |
| 26″-48″ | 7587-7598 | 0.06 | 0.12 | 0.12 | 0.09 |
| 50″-96″ | 7599-75110 | 0.12 | 0.18 | 0.18 | 0.12 |
Neck Trims
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| STANDARD TRIM I.D. NECK The neck and Convolution I.D. are equal to the nominal I.D |
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STYLE A O.D. NECK The neck O.D. is equal to the convolution O.D. |
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| STYLE B EXPANDED NECK The neck I.D. or O.D. can be specified within the range of the I.D. to the convolution O.D. |
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STYLE C O.D. TRIM The trim line is at the tangent point of the convolution O.D. |
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| STYLE D I.D. TRIM The trim line is at the tangent point of the convolution I.D. |
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INSIDE BAND | |
OUTSIDE BAND |
Series 7500 bellows with Standard, Style A, or Style B neck trims can be specified with inside or outside bands which increase the thickness for welding or added reinforcement. The band thickness is approximately 2.5 times the bellows thickness. The bands are attached by resistance seam welding for sizes 1″ through 48″ and by edge welding (GTAW) for larger sizes.
Caution: The use of bands is not recommended for vacuum applications requiring a mass spectrometer helium leak test.
Multiply or Laminated Bellows
Any standard-size bellows can be fabricated with multiply construction up to four plies of equal thickness. The maximum pressure, spring rate, and stability pressure are increased in direct proportion to the number of plies, but with the same axial deflection as a single ply. Multiply design permits a lower spring rate and a greater cycle life than a single ply configuration for an equivalent pressure. This type of construction is recommended for applications with vibration or rapid cyclic motion because of the inherent damping provided by the relative movement of the plies. Multiply construction in not recommended for vacuum application requiring a mass spectrometer helium leak test because of possible out-gassing from an undetectable leak in an inner ply.
Refer to the individual topics in the Explanation of Tabulated Data for the methods used to calculate multiply bellows parameters.
All dimensional data is applicable to tabulated single and multiply configurations with standard and optional materials. The tabulated performance parameters are for type 321 stainless steel at room temperature; however, they apply to all austenitic stainless steels with minor variations. Variations for other materials are given for each column explanation.
Materials & Properties
The performance data tabulated in Columns 7 through 11 (pages 6-17) was calculated for type 321 stainless steel at 70ºF. These values are a function of the Modulus of Elasticity, strength, and fatigue life. If the service conditions are substantially different or an optional material is used, contact the factory for assistance.
Optional materials can be substituted which include but are not limited to alloys 600, 625, 800, 825, Cb-20 and C-276, Nickel 200, Beryllium Copper and weldable Aluminum alloys.
Use of Tabulation
The data included in this catalog was computed by generally accepted analytical methods and empirical data derived from tests. This data should be used as a design guide only. Consult the factory if you have an application requiring close control of these values.\
The following paragraph numbers refer to the column numbers of the tabulated data on pages 6 through 17.
- Stock Number
A four or five digit number identifies the nominal size (inside diameter), and a letter corresponds to the material thickness. In order to fully specify the desired configuration refer to the Ordering Instructions on page 18. - Inside Diameter
Nominal Inside diameter of the convolutions and the standard neck trim. - Convolution Outside Diameter
Nominal outside diameter of the convolutions and maximum diameter of Style A neck trim. - Effective Area
The cross-sectional area of the bellows based on the mean diameter of convolutions. This area multiplied by the pressure equals the pressure thrust force (Lbs.). - Material Thickness
The values tabulated are representative designs for each diameter. Other thickness may be available – consult the factory. - Maximum Convoluted Length
These values are established by manufacturing limitations. Substantially longer lengths must be obtained by splicing two or more elements. Any shorter length can be specified – refer to the Ordering Instructions. - Maximum Pressure
The highest internal or external pressure recommended with a corresponding test pressure of 1.5 times this value. This pressure is exclusive of the squirm or instability pressure (Column 8).The working pressure for internally pressurized bellows is determined from the pressure tabulated in Column 7, or the squirm pressure calculated from Column 8 – whichever is lowest. For convenience Column 7 and 8 include a test pressure factor of 1.5, i.e., a bellows can be pressurized to 1.5 times the pressure tabulated in Column 7 without permanent set, and the anticipated squirm pressure is greater than 1.5 times the value calculated from Column 8. The working pressure for internally pressurized bellows which are guided or supported to prevent squirm is determined from Column 7.The working pressure for externally pressurized bellows is determined from Column 7 – squirm or instability does not occur. All bellows rated at a pressure (Column 7) exceeding 15 psi are satisfactory for Full Vacuum (internal) applications – Caution – This pressure applies to the convoluted sections only and the standard neck trims. Long unsupported neck trims may collapse. Multiply or Laminated Construction – multiply the values of Columns 7 and 8 times the number of plies. - Squirm or Instability Pressure
Internally pressurized bellows are unstable at the critical or squirm pressure. In most instances this condition is characterized by the centerline of individual convolutions deviating from a common centerline – analogous to buckling of a long column under compression. This condition occurs when the convoluted length is long relative to the inside diameter – over 2 or 2.5 times. There is also a less familiar type of squirm which occurs when the plane of the individual convolutions deviates from parallel planes. Either condition represents a maximum pressure and failure will occur if pressure is increased.The tabulated values (Column 8) are the maximum recommended internal pressure to avoid squirm for one inch of convoluted length. The values are based on a test pressure 1.5 times the tabulated pressure. The pressure for other lengths can be calculated by dividing the tabulated value by the square of the convoluted length.The Column 8 values do not need to be corrected for other materials which have a modulus of elasticity in the range of 28 – 30 x 106 psi. For multiply construction multiply the tabulated value by the number of plies. - Axial Spring Rate
The force (Lbs.) per inch of axial extension or compression resulting from the material and configuration spring constant is tabulated for one inch of convoluted length. The spring rate for other convoluted lengths is determined by dividing the tabulated values by the convoluted length. Multiply this value by the number of plies for multiply construction. - Lateral Spring Rate
The force (Lbs.) per inch of the lateral offset resulting from the material and configuration spring constant is tabulated for one inch of convoluted length. This movement occurs when the ends remain parallel to each other and perpendicular to the longitudinal centerline, but the centerline displaces laterally. The lateral spring rate for bellows other than one inch convoluted length is calculated by dividing the cube of the convoluted length. For multiply construction multiply by the number of plies. Caution – The tabulated values must be multiplied by the 1000 except as noted to obtain the true spring rate. - Axial Deflection
The allowable axial extension or compression for one inch of convoluted length is tabulated for 2000 cycles of movement from the nominal length to the tabulated value. The movement for other convoluted lengths are obtained by multiplying by the required length. Since these values are determined by the metal fatigue due to the bending stress produced by movement it is unchanged for multiply construction.
The tabulated values can be corrected for other numbers of cycles (at 70ºF.) by applying the following factors:
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| 500 | 1.40 |
| 1,000 | 1.20 |
| 2,000 | 1.00 |
| 4,000 | 0.85 |
| 8,000 | 0.75 |
| 10,000 | 0.70 |
Hyspan Series 7500 Formed Bellows may be ordered directly from this catalog by using the stock number selected from the tabulation and adding the appropriate Dash Numbers.
If the neck trim length is deleted from the part number it is assumed to be the standard—0.75″ through 6″ I.D., 1.0″ over 6″ I.D. Optional materials, neck trim configurations, and bands must be specified separately—refer to pages 3 and 4 for options available.
Example
Size: 1.50″ I.D., 1.95″ O.D.
Material: .008″ Thick Type 321Stainless Steel
Convoluted Length: 4.0″
Neck Trim: 0.50″
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