To Crimp or To Swage?

    No matter what application a hose is being used for, the crimping and/or swaging process is a crucial aspect of the hose assembly. The terms ‘crimping’ and ‘swaging’ are both typically used to describe a radial compression process that deforms and shapes roundish objects, reducing their diameter. These terms can easily be confused and are, therefore, sometimes used interchangeably.[1] As there are particular instances where each process should be used, it is important to understand the difference between the two.

    By Angelica Pajkovic

    Figure 1. Hose Assembly.

    Industrial hoses are an assembly comprising of hose, fittings, couplings, a ferrule, and a stem, see Figure 1. To safely secure this assembly to the cut hose length, one of two processes are typically used: swaging or crimping. The basic difference between the two is that the swaging process reduces the ferrule size as it moves towards the fittings, while crimping changes the shape of the entire circumference of the hose.[2] To understand which process should be used, for which application, it is best to look at them in detail.

    Swaging Process

    Swaging consists of a rapid succession of hammer strikes that are used to form and reduce the diameter of metal. In general, it modifies wire or rod; in the hose industry swaging involves pushing a hose and its fittings through a fixed set of dies slowly. The dies open and close rapidly reducing the diameter of the ferrule while compressing the hose into the stem serration which ultimately changes the form of the fitting to permanently attach it to the hose,[3] see Figure 2. The following are the basic swage procedures. For specific instructions for a swager, please refer to the appropriate operator’s manual.

    1. Mark hose for proper insertion depth into coupling.
    2. Use a lightweight oil to lubricate the inside diameter of hose.
    3. See product specific data chart to select specific pusher and die for each coupling and hose combination to be swaged.
    4. Insert the correct die and pusher into the swaging machine.
    5. Lubricate inner bore surfaces of dies with a thin film of lightweight oil.
    6. Feed hose assembly through the dies and hold hose and coupling into the pusher. Start the swage.
    7. Swage is complete when pusher bottoms out on dies.[4]
    Figure 2. Rotary Swaging process diagram. Image is © 2017 EngineeringClicks.

    Fitting retention is very important to mitigating the risk of accident or injuries when dealing with fluid or gas transfer. Proper use of a swaging machine is necessary to ensure uptime is maintained throughout the life cycle of a hose assembly. Effective swaging can also help reduce maintenance issues caused by leaking and other issues related to hose fittings.[3]

    Other benefits of swaging include:

    • Speeds assembly – Fittings can be attached to a variety of other components including wire cable, tubing, hose, flexible tubing, and rod.
    • Less material is used – As the material is hammered, it is displaced longitudinally as opposed to being chipped away.
    • Saves on labor – Several machines incorporating feeders and material handling systems can be tended by a single operator.
    • Control of wall thickness – With the use of a mandrel, swaging allows the operator to have more control of wall thickness throughout the process.[6]

    There are a wide variety of swaging machines available to address different processes. The swaging product selected by fluid power engineers often depends on the machine that is most compatible with the hose manufacturer’s specifications. OEMs will typically suggest using one manufacturer’s swaging machine with their hose and fitting products, as swaging machines are designed for specific product lines. Mixing and matching elements of a hose assembly can cause issues if the swaging process is not configured to the OEM’s specifications.[7]

    Crimping Process

    Figure 3a. Handheld hose crimper diagram.

    Hose crimpers, similarly, are used to join deformable metal fittings with flexible hoses. The crimping process can be done with both powered and un-powered tools which range from simple handheld devices, to freestanding machines that are engineered for precision and high-volume runs. To achieve the connection, crimpers apply force to the outer diameter (OD) with 360° of contact. Typically, this compression is applied once, or at most a few times, with a rotating die that prevents buckling.8 Ultimately, this process changes the shape of the entire length and circumference. As the compression takes place all at once, more force is required to reduce the ferrules, see Figure 3.

    The following are steps to the general crimping process.

    1. Mark the insertion depth of the hose using the hose insertion depth fixture.
    2. Push the hose all the way into the coupling, stopping at the insertion depth mark.
    3. Select the proper die to match the size of hose fittings.
    4. Lubricate the die bowl, then place the die into the base plate.
    5. From beneath, position the hose and fitting into the die.
    6. Rest the bottom of the coupling on the die step and place the die ring on the top of the dies.
    7. Pull the valve handle toward you until the die ring is in full contact with the crimper bowl.
    8. Release the pressure by pushing the valve handle away from you until the die opens and the finished assembly releases.
    9. After crimping, visually inspect the assembly for defects and measure the crimp diameter.

    Depending on the crimper being used, some aspects of the crimping process may vary.[5]

    Figure 3b. Hydraulic hose crimper diagram.

    When using hydraulic hose crimpers, the hose ends must be cut square and the right hose fittings used. Pneumatic hose crimpers are designed for use with pneumatic hoses and custom pneumatic hose assemblies. These hoses also require square ends and fittings but are used in industrial air supply systems.[8]

    Choosing Between Crimping and Swaging

    When considering which process is most appropriate for an application there are a few fundamental questions to ask: Which process fits the application best? What is the media, working pressure, temperature? And what type of fitting is needed for the application?

    For the oil, petroleum, and composite industries, the answers to these questions should lead an operator to choose a swaging process. A rotary hose used at a drill site, for example, has 3-to-4-inch I.D. and withstands up to 5,000 PSI of pressure. This is a very heavy-duty hose and therefore needs swaging to connect its fittings.[2] Industrial applications, on the other hand, seldom use such high pressure rated hoses and therefore can turn to crimping as the most viable option.

    Although crimping machines are expensive, they are automation friendly and can be integrated into any automated line, thus making them a more efficient option, and generally sought after for industrial hoses; swaging alternatively has to be a hands-on operation.[2]

    Figure 4. Depiction of thin-walled tubes react to crimping and swaging. Image courtesy of Blockwise Engineering.[1]
    Final Thoughts

    When choosing which process is best suited to a particular application, it is important to seek advice from a company that can provide a comprehensive understanding of what is required for each assembly. As there are many different kinds of ferrules, fittings and hose I.D.s, and a number of combinations of the three, it is best to have OEMs use their expertise to assess the application specs and suggest a viable option.

    References

    1. “Crimping Versus Swaging.” Blockwise Engineering LLC, blockwise.com/wp-content/uploads/2020/08/MS105-CrimpingVersusSwaging.pdf.
    2. https://www.hoseassemblytips.com/choosing-between-crimping-andswaging/
    3. https://www.hoseassemblytips.com/what-is-a-swaging-machine/
    4. Crimp Data Crimp Data and Dies. Gates, www.coastalhydraulics.net/technical-library/Hydraulic%20Instructional%20information/Gates%20Crimp_Data_and_Dies_Manual.pdf.
    5. http://blog.parker.com/hose-assembly-crimping-use-this-proven-method-to-succeed-every-time
    6. https://www.fenn-torin.com/how-swaging-machines-work/
    7. https://www.hoseassemblytips.com/what-is-a-swaging-machine/
    8. https://www.hidroman.com.tr/icerik/what-is-hose-crimping-howto?dil=en