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Bellows Structure
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END
PLATES |
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MACHINE
SLIDEWAY
END
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EXPANSION
TAPES
VENTILATION
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FORMERS
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END PLATES
Metal plates of a suitable thickness are either inserted in the last fold, trapping the fabric to the machine table, or blanking the end of the bellows to enable fixing to the slideway
end. These are normally manufactured in 16 gauge (1.5mm/0.06") mild steel. Any other shape, thickness, or type of metal can be provided to suit your specific requirements. Where suitable, Jubilee
Clips can be supplied and are often used for circular, square or hexagonal collars.
EXPANSION TAPES
Expansion Tapes prevent over expansion of the leading folds and are only necessary with fast operating speeds, when operating vertically, or with large bellows.
The closed size is increased considerably by the addition of tapes - approx. 10%. When tapes are necessary they are fitted internally where possible, three are fitted externally on circular
bellows.
FORMERS
Formers provide a wear surface within the bellows covering slide. In addition to reducing wear on the fabric, they provide stiffness and rigidity to large bellows. They can also be
used to retain a bellows on a slideway or shaft. Formers are made from wear-resistant plastic, from 1mm to 6mm thick. They increase the minimum compressed size of the bellows.
VENTILATION
Ventilation can be provided and is only necessary in a large fast moving bellows but it reduces the protection. This is rarely necessary unless the movement exceeds 2 inches per second or 10
feet (3 mtrs) per minute. Filtered ventilation built into the machine is obviously better.
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Bellows Design
Protection
There are several factors that determine the most suitable style of bellows to use.
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Total enclosure gives the best protection and most robust, rigid shape, and is most suited where operator protection is required.
When deciding on the style of below is required, the type of swarf or contamination should be considered.
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Heavy swarf will cause more bellows wear, but less coverage is needed.
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Dust or light swarf requires more complete coverage to protect slides and shafts.
On new equipment, or when extensive refurbishment is undertaken, complete enclosure bellows are easily incorporated while building.
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| Split for easy fixing |
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However, considerable costs can be incurred in stripping a large machine tool purely to replace a damaged bellows. If this is likely, an open design should be
considered. |
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Joints are glued and sewn and provide a high degree of seal, but they will not contain pressure. Split circular bellows can be made but there is no reliable method of sealing the joint and should only
be considered where there is no alternative. |
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Environment
The ambient conditions are an important consideration when designing a bellow. While temperature, chemicals and swarf need to be considered, other aspects like care, cleaning,
operating speed and frequency, and possible misuse need to be addressed.
Clearances
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INTERNAL CLEARANCES
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Internal
Dimension |
Minimum Clearance
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< 50mm
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3mm
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| 50mm - 200mm |
5mm
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200mm - 600mm
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8mm |
| > 600mm |
10mm |
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Suitable internal running clearances are required to prevent
excessive friction, wear and drag. When total enclosure is
possible the clearances given in the table are the recommended
minimum.
As a general guide for unenclosed shapes, add 50% to these
clearances.
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Fold Size
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Minimum Closed Length
For a given extended length, the fold size will determine the compressed length. The least fold size on any part of the bellows is the one used in the calculation. Formers, end
plates, tapes, and collars add to the closed length.
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OPEN to CLOSED RATIO
for FOLD SIZES
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| FOLD |
RATIO |
| 1/2" |
12mm |
5.5 |
| 3/4" |
19mm |
9 |
| 1" |
25mm |
12 |
| 1¼" |
30mm |
14 |
| 1½" |
37mm |
16 |
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The closed size is estimated using the least fold size on any part of the bellows and applying the open/closed ratio from the table.
Any end fixings, tapes and formers should be added to this size.
These ratios are recommended and may occasionally be exceeded. However, premature failure will obviously result if the ratio is exceeded to a marked degree.
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Fabrics
Polyvinyl Chloride (PVC) coated polyester is our most commonly used fabric. It is economic, tough and wear resistant. It bonds well to formers, tapes and end plates, and is
available in a range of colours. PVC is suitable for use with most chemicals and will operate in temperatures from 0ºC to 100ºC. There is a heavy weight version of the standard black PVC.
Neoprene is a heavy duty fabric which will withstand higher temperatures and is more abrasive resistant. It is one of our heaviest, toughest fabrics.
Neo160 is our most heat resistant fabric. It is a neoprene coated glass cloth which is excellent at withstanding grinding sparks, weld and laser spatter.
Lighter fabrics can be made with fold sizes down to a minimum of 12mm. Heavy fabrics are most suited to fold sizes over 25mm.
Other fabrics are available for use in more extreme circumstances.
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Further Information
The Product Reference page has more details for specific bellows styles. |
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