Banner Fluid Power LTD supply a range of hose assembly equipment in many countries to customers who may use a wide range of hose and fittings. These pages are an attempt to answer some of the more common questions and problems that may be encountered. The various points referred to are intended as a general guide only and are not to be considered as definitive in any respect. In many countries it is the responsibility of the fabricator to ensure hose assemblies are correctly made, so always check with your supplier if you are in any doubt concerning hose assembly componentry or specifications.
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We would like to thank the many people who have offered their time, experience, and advice for the concept and construction of the following document.
Can I mix hose and fittings from different manufacturers?
Generally no. Example-SAE J1273 3:10 and EN856 recommended practice state that: ‘Care must be taken to ensure that proper compatibility exists between the hose and coupling selected based on the manufacturers recommendations and substantiated by testing to industry standards such as SAE J517. End fitting components supplied from one manufacturer are not usually compatible with end fitting components supplied by another manufacturer … and continues, ‘It is the responsibility of the fabricator to consult the manufacturers written instructions or consult the manufacturer directly for proper end fitting componentry’.
Cracking up under pressure
Ferrules that are not ductile enough will usually develop an uneven appearance after assembly with noticeable uneven ferrule ‘ears’ where work hardened material may tend to extrude between the dies. This is usually more pronounced on smaller, light duty ferrules, but all such hard ferrules are at risk of cracking during compression or in some cases many days later.
This work hardening also greatly increases required compression effort, particularly on larger fittings, to such an extent that manually operated presses in particular may stall as the ever increasing effort required to compress the now hardened ferrule overcomes the effort available.
Down to the Wire
During swaging, the ferrule barb form first makes contact with the reinforcement wires before compressing them (and thus the liner) onto the insert. As the operation continues, the rubber liner will reach bulk modulus and cease to flow over the insert. During any further compression the swaging force will now be transferred directly onto the insert and will begin to show as insert bore collapse. The further the barb form tries to compress the reinforcement, the more stress will be placed on the high tensile wire. This will result in a notch being created on the wire, usually at the last ferrule barb nearest the skirt, that will ultimately be the point of premature assembly failure, either short term or long term, depending on pressure, impulse and service conditions.
This practice should be avoided. It is most important that fittings should not be over-swaged.
Ferrules under pressure
The reduction in diameter of a ferrule undergoing assembly tends to cause the material to move in three directions at once. This combination of stresses are called triaxial, and simply put, will encourage the material to flow relatively easily within it’s ductility limits, although strictly speaking work hardening commences directly compression begins.
Although the volume of ferrule material obviously remains the same, as the outside diameter is reduced the ferrule wall, latch collar wall and overall length dimensions will tend to increase, typically by 5 to 10%, to accommodate the displacement of the material that has taken place.
Simply put, if the material is ductile enough a ferrule should reach the required size before the ‘ductility limit’ or fracture point as we could call it, is reached. If the material is not ductile enough to sustain this flow and the fracture point is reached before the ferrule is compressed to required dimension, the ferrule material may work harden to the point of failure.
As the structure of the material fails, it tends to extrude between one or more pairs of dies and is liable to crack in a line along or around the crest of this extrusion. This type of failure is particularly noticeable during the stop-start action of manually operated machines. It may still be present, though less obvious, during the more regulated action of power machine assembly, where heat generated by friction within the material as it quickly changes shape, may to some extent help the material to flow.
How can I check the machine and ferrules?
This method is not foolproof of course, but it provides a useful indicator in most cases. Before proceeding, measure both the latch collar wall thickness (or deduct the collar bore from the outside diameter) and the overall length of the ferrule. Note these measurements for later use. Check the machine first. Place an empty suspect ferrule in the machine, and using the correct dies for that size, reduce the ferrule diameter by 2mm or so, remove and measure the die indentations now visible around the ferrule. These should be evenly spaced on a machine that is in good order. To check ferrules for ductility, replace the empty ferrule in the machine in the same position and complete swage to the normal ‘finished’ diameter and remove from the machine. The ferrule should retain a more or less even appearance, but a slight even ‘dishing’ of the collar face is sometimes present and is usually acceptable.
If excessive work hardening has occurred, or if the material is otherwise unsuitable, the latch collar face will often display pronounced radial corrugations, with evenly spaced high points between the die markings, as well as the extrusion markings mentioned above. The ferrule barb form may also have a ‘folded’ appearance and also show signs of lengthways distortion. Now check the latch collar wall and overall length dimensions, excluding any radial high points, as before and compare. The percentage increases should be similar, typically 5 to 10%. If the latch collar wall shows a much larger percentage increase than the ferrule length, and if the collar and barb form show indications of distortion, the material may be suspect.
If this uneven growth has occurred, it follows that the cross section of the ferrule will now be thicker than if a similar ductile ferrule were used. That is, there can effectively be at least 2 different ‘swage diameters’ possible for the same insert bore collapse due to different ferrule material behaviour. For further componentry checks, measure both the collar bore and the adjacent internal groove in the ferrule, and compare with the matching groove and shoulder diameters on a typical insert as used with this ferrule. These internal diameters of the ‘swaged’ ferrule should not be any smaller than the matching groove and shoulder on the insert. If they are, insert collapse will occur beneath the insert latch collar when used with such ferrules to a standard chart size, weakening the assembly at that point and providing a misleading indicator of apparent general insert collapse.
How do I know if the finished swage is correct?
Swage near to the recommended diameter then check for insert bore collapse. Even in modern tightly controlled hose there can be significant variations on the internal, over the wire and cover diameters, so that swage chart recommendations can only be a guide. There may also be difference in hardness and therefore resistance to compression by the hose liner and cover. The combined effect of all these variables can result in variations in insert collapse by as much as 3mm with apparently similar componentry by using charts alone. It can therefore be argued that recommended size charts usually represent ‘the worst case scenario,’ or minimum swage diameter, if hose liner, wire and cover diameters are towards the lower limits allowed during manufacture of the hose. It is considered to be good practice, particularly when assembling larger multispiral hoses, to check the ‘over the wire’ size by refering to the hose manufactures catalogue limits and adjust the chart size if required. Note however, that some manufacturers may still recommend that chart sizes are to be used at all times.
Any insert bore collapse is generally an important physical indicator that correct compression has been achieved when using validated compatible fittings, unless otherwise specified by the hose and end fitting manufacturer. Note however, that some fitting designs may produce irregular insert bore collapse typical only to that that type of fitting. It is worth noting at this point that inserts of uncertain origin may be produced from very ductile or other unsuitable materials. The insert stem may then offer little resistance to the swaging process and can tend to collapse before bulk modulus of the hose liner is reached, thus encouraging early hose failure. Most, if not all, reputable fitting manufacturers will ‘type’ mark and brand their products for identification purposes, and also to indicate the application they were designed and tested for. It is therefore prudent to view unbranded or untraceable fittings with some suspicion.
So the condition of the steel used is important?
It is of vital importance for the integrity of the finished assembly and certainly helps during the compression process as is described later. The steel used for most ferrules should be in a condition known as ‘isotropic’, that is ‘having the same properties in all directions’. If it is not it may be likened, for example, to wood, where the grain offers strength in one direction – where it may bend under load, but not in the other direction – where it may split under load. Material in this ‘grained’ condition can be typically explained as follows:
‘Bands of stringers, whether made up of inclusions, or differing material structures, will affect the working properties of the material because of directionality and may also act as crack paths when the different bands respond in different ways during the swaging process’.
Why can ferrules crack or extrude between the dies?
Provided the machine and dies are in good working order these two problems may be related to the fittings themselves. Insert and ferrule materials require different properties. As previously shown (see page 2) the insert material is expected to resist deformation during assembly and damage during use when part of a finished assembly. The ferrule, however, will be subjected to considerable deformation during the initial assembly process and yet still be required to be stable after assembly. So one needs to be tough and the other ductile.
However, for commercial reasons both inserts and ferrules may often be produced from either ductile, free machining cold drawn bar, or at the other end of the scale, low grade un-annealed stock bar and this can result in a compromise between the properties required for the two different components. Given the world wide movements of steel and scrap, mixed materials of unknown origin may be combined with newly smelted steels and this may produce materials that contain residual amounts of chromium, nickel, aluminium and copper, for example. These residuals may not appear on material certification documents.
However, if present these residuals may encourage a pronounced drop in the ductility of the material that is so essential if ferrule material is to ‘flow’ during assembly. These same residuals may also inhibit the sub-critical annealing (spherodizing) process that is ideally applied to ferrules after machining. This heat treatment process ideally ensures that the ferrule material is then suitably ductile for the swaging process.