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    About the heat shrink tubing

    Whether in production, maintenance, service, repair, in the home or also in the hobby sector: Heat shrink tubing is the best solution wherever cables or cable connection points need to be professionally insulated and short circuits reliably avoided. But shrink tubing has far more potential than is expected at the first moment. In order to be able to correctly estimate the various possible uses, one should know was a shrink hose and how it works.

    • What was a shrink hose?

    • What is the purpose of shrink tubing?

    • How do heat shrink tubing work?

    • How are heat-shrink hoses processed?

    • Insulating tubes are not shrink tubes

    What was a shrink hose?

    A heat shrink tube is made of plastic, which contracts (shrinks) when exposed to heat to a previously determined degree. The shrink rates can be 2:1 to 6:1 depending on the shrink tubing. In addition, there are shrink tubes with different diameters and wall thicknesses.
    Depending on the application area, the starting material for shrink tubing is polyolefin (PEX), elastomer (PES), VITON+, fluoropolymer (FPM), polyvinylidene fluoride (PVDF) or fluoroplastics (PTFE, FEP or PFA).

    Heat shrink tubing is available, for example, for use in production as a piece of material on rolls or for household use in practical sets in different sizes and with different colors.

    In addition to the colored versions, there are also transparent shrink tubes with which important cable markings can be permanently attached. But also for shrinking the model-built battery packs a transparent shrink hose is best suitable, since it immediately recognizes which batteries were installed in the pack.

    In double-walled design, the heat-shrink tubes are provided with a melt or adhesive coating on the inside. This completely encapsulates or seals the area over which the heat-shrink tubing has been pulled. The penetration of dirt and moisture is thus reliably prevented.

    Practical heat-shrink tubing set for home use.

    In addition to the hoses, there are still heat shrink caps for secure sealing of cable ends and heat shrink molded parts that take a certain shape after shrinking.

    What is the purpose of shrink tubing?

    Every service technician or hobby electronics engineer who has already connected thin cables and had to isolate had to know that adhesive tape is only partially suitable for isolating the connection points. It does not wrap around the cable in such tight radii and does not hold properly. In the worst case, the adhesive tape will slip on the cable so that the connection points are open and short circuits are the result. A shrink hose of suitable size fits seamlessly even around small cables, without significantly increasing the overall diameter. But this is not the only purpose of heat shrink tubing. That's why we've listed some of the common uses of heat shrink tubing:

    • Electrical insulation of cable connection points.
    • Touch protection of open cable ends.
    • Air- and waterproof insulation of cable connection points.
    • Repair of cables with damaged insulation.
    • Protection of cables from external influences.
    • For increasing the kink protection of cables.
    • For bundling cables.
    • Color coding of individual wires of a cable.
    • Attach warning or labeling.

    Shrink tubing can also be used in other ways. As packaging of bulk goods or as shrink capsules for wine bottles. In the food and pharmaceutical industries, neon tubes are provided with safety shrink tubing as splinter protection. Model makers manufacture ultra-light joints from thin shrink tubes for rudder linkages to their filigree indoor models.

    How do heat shrink tubing work?

    The plastics used for the production of heat shrink tubing are mostly polyolefin-based thermoplastics. During the manufacture of the plastic, certain additives are added to the plastic mixture to obtain the desired color or, for example, flame retardant properties.

    The plastic mixture is heated and sprayed with the aid of an extruder in a hose form. This works in a similar way to the production of injection-molded pastry. At this stage, the molecular chains of the plastic are still unwetted and the diameter of the hose corresponds to the dimensions in the shrunken state.

    In the next production step, the loose-lying molecular chains are networked using electron beams to form a three-dimensional structure. After networking, the heat-shrink tubing is re-heated and expanded or inflated to a defined size. The ratio to which the cross-linked shrink tubing is expanded depends on the material and the wall thickness.

    After cooling down, the shrink tubing retains its widened shape. It is only through the supply of heat that the shrink tubing is drawn together to the original size that it has shown during networking.

    Heat-shrink tubing caps - the preformed heat-shrink tubing

    Shrink-wrap parts or heat-shrink tubing caps function according to the same principle, but are produced differently. In the case of shrink-molded parts, networking is not performed by electron beams, but by chemical additives which are already incorporated in the composition of the plastic formulation. The molded parts are then not produced with the aid of an extruder, but in the injection molding process. Immediately after this, the parts are mechanically expanded to the required extent even when they are warm. After cooling, the shrink-shaped parts retain their widened shape.

    After placing on the workpiece, the molded parts or shrink caps are shrunk with the help of a hot air gun.


    How are heat-shrink hoses processed?

    As already mentioned, the right ratio is important, as there are shrink tubes with different shrink rates. If a shrink hose reduces its size to 50% when it is applied to heat, the shrink rate is 2:1. At a shrink rate of 4:1, the hose pulls together to a maximum of 25% of its original size. The usual shrinkage ratios are 2:1, 3:1, 4:1 and 6:1. For plug mounting or other special applications there are shrink tubes with a shrink ratio of up to 10:1. The higher the shrink ratio, the more cable diameters can be covered with the same heat shrink tubing. 

    The best
    results are obtained when the ratio of the shrink object and the shrink tube is 4:5. Or in other words: The heat shrink tubing should ideally be approx. 25% larger than e.g. the cable. In practice, however, the shrink tubing can also be chosen larger if it is kept to the 20/80-rule. This means that the shrink tubing should shrink by at least 20% and at most 80% of its shrinking capacity.

    The suitable wall thickness
    of heat shrink tubing is divided into three groups, each with different wall thickness. Please note: The thicker the cable and the higher the mechanical load, the greater the wall thickness of the heat-shrink tubing. For this reason, thin-, medium- and thick-walled shrink tubes are offered.

    • To the thin-walled heat-shrink tubing
    • To the medium-walled heat shrink tubing
    • To the thick-walled heat shrink tubing

    If the repair site also needs to be sealed, use a shrink hose that is provided with an inner adhesive (hot-melt or hot-melt coating) on the inside. These heat-shrink tubes are also known as double-walled heat-shrink tubes. By the additional bonding or sealing of the repair site with the inner adhesive, the penetration of dirt and moisture is effectively prevented.

    To the heat shrink tubes with inner adhesive

    The correct technology
    is shown in the following pictures, how the insulation of a cable connection is done with the help of a heat shrink tube. 
    For better illustration on the pictures, the wires and heat-shrink tubing have been selected with different colors.

    Prepare the connection

    Before the two wire ends can be soldered together, it is necessary to twist the wire ends and then tin them. For thin wires, a simple and unregulated hand soldering iron is enough. For thicker wires, a soldering station with automatic temperature control makes sense. A "third hand" with alligator clips makes sense to hold the wires securely. As an alternative, a wooden board is also suitable, on which two wooden washes were glued.

    Connect wire ends

    Before the two wires are soldered together, it is necessary to push the suitable heat-shrink tubing over one of the two wires. It is important that the heat shrink tubing has a sufficiently large distance to the solder joint. Otherwise, the heat shrink tubing shrinks slightly when the cables are soldered together and cannot be pushed over the contact point.

    Isolate the connection point

    After soldering, the heat shrink tubing is pushed over the contact point and best shrunk round with a hot air gun. A normal hair dryer does not work because it cannot produce the required temperatures. Clever hobbyists can also take a lighter, a small hot-gas burner or even the heating area of the soldering iron in an emergency. It is important that the heat shrink tubing and cable insulation do not become too hot and melt.

    When processing heat-shrink tubing, it is essential to ensure that the work area is well ventilated!

    It is difficult to specify an exact shrink temperature, as this depends on the heat shrink tubing used and the temperature absorption of the material to be shrink. For this reason, the shrink sleeve is only briefly blown with the hot air gun at the beginning and thereby observed how the shrink hose behaves. It is important that the heat shrink tube is not worked on a spot, but is heated evenly from all sides until the desired result is achieved. 

    Insulating tubes are not shrink tubes

    Not every plastic hose offered in the electrical departments of DIY stores or technical department stores is a shrink hose. In addition to the heat shrink tubes, so-called insulation hoses are also offered, some of which look very similar to the heat shrink tubes. It only helps eínen to take a closer look at the product name or product description.

    Insulating hoses are used, as well as shrink hoses, for insulation, for cable protection and for bundling cables and wires. The preferred application areas for insulating hoses are vehicle, machine and device construction, as well as the electrical industry and service.

    Insulating tubes have no shrinking properties and the drawn-in wires and strands can be easily removed and re-drawn if necessary.