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Heat Shrinkable Tubing
a. Making Extruded Tubing Heat Shrinkable b. Shrink Ratio c. Longitudinal Shrinkage d. Inside Diameter and Wall Thickness e. PVC vs. Polyolefin Heat Shrinkable Tubing f. Available Colors g. Adhesive Lined (Dual Wall) Heat Shrinkable Tubing h. Printing and Hot Stamping i. Electrical and Wiring Harness Applications j. Non-Electrical Applications k. Storage and Shelf Life l. Cost Comparison of Heat Shrink Materials
Heat shrinkable tubing, commonly called "heat shrink" or "shrink tubing", not only serves to bundle, electrically insulate, and protect wires, electrical components and other objects, but also provides an environmental seal that can prevent liquid, gaseous and solid contaminants from reaching sensitive components. The original inside diameter of the tubing must be large enough to slip over the component to be covered, and the tubing can subsequently be shrunk onto the component by heating the tubing using a heat gun, flow through oven or other source of thermal energy. Grayline Heat Shrink Tubing
Tubing manufactured from certain polymers, such as PVC and polyolefin, can be made to be heat shrinkable by additional processing following initial extrusion. The exact processes used to manufacture heat shrinkable tubing are proprietary, but they involve the use of force to expand the diameter of the tubing at elevated temperatures. The tubing is semi-stable at its new larger size, as the subsequent addition of heat to the tubing will allow it to return to its initial extruded size, provided that the tubing is not restrained from doing so.
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Grayline heat shrinkable PVC tubing has a nominal 2 to 1 shrink ratio, meaning that if the tubing is heated and allowed to shrink fully, the diameter will be reduced to 1/2 of the original diameter. However, if the heat shrinkable tubing is restrained by an object being covered before it is allowed to shrink fully, it can only shrink down as far as the object will allow.
Grayline heat shrinkable polyolefin tubing is available with nominal 2 to 1, 3 to 1 and 4 to 1 shrink ratios, and it is also available with an internal adhesive coating that melts during the shrinking process to encapsulate the electrical components and provide a water-tight seal.
In addition, Grayline can also manufacture custom shrink ratio PVC tubing that is tailored to your specific application. For example, Grayline can manufacture 1.8 to 1 shrink ratio tubing with an expanded inside diameter of 0.155" that will yield a recovered inside diameter of 0.086". A lower shrink ratio product will result in a reduction in longitudinal shrinkage (see below).
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When heated, heat shrinkable tubing will shrink not only in diameter but to a lesser extent in length as well. The amount of length reduction ("longitudinal shrinkage") encountered is dependent upon the amount of reduction in diameter ("diametric shrinkage") that is allowed to occur in an application. Longitudinal shrinkage should be taken into account in any heat shrinkable tubing application, but in most situations the reduction in length is less than 10% of the original length.
In applications using longer lengths of heat shrinkable tubing in which longitudinal shrinkage is undesirable, it is possible to essentially eliminate longitudinal shrinkage by first applying heat to both ends of the tubing to shrink it to the substrate and secure it in place before completing the shrinking process along the remaining mid-section of the tubing.
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Heat shrinkable tubing is traditionally specified by the original ("expanded") inside diameter and by the final ("recovered") wall thickness, which is the wall thickness that would result if the tubing were allowed to shrink completely without restraint. As heat shrinkable tubing is reduced in diameter, the wall thickness increases proportionally. To illustrate, heat shrinkable tubing specified as having a 1/2" ID with a 0.025" wall thickness is supplied with an internal diameter of no less than 0.500" and a wall thickness of 0.012". If this tubing were to be shrunk completely without restraint, it would then have an inside diameter of no greater than 0.250" and a wall thickness of no less than 0.025". However, if the tubing is only partially shrunk before it is restrained by the component being covered, the resultant wall thickness will be less than 0.025". Therefore, the final wall thickness of tubing that has been shrunk over a component will depend on the exact application.
As a starting point, you may choose to select a tubing size that will shrink to approximately 75% of its expanded diameter when fully recovered in your application. For example, if your application will allow the heat shrinkable tubing to recover to a final diameter of 7/16", you could select a nominal size of 5/8", since 0.438"/0.625" = ~ 0.75.
Because it is flexible, the best way to measure the inside diameter (ID) of Grayline tubing is to use gage pins. However, even with the use of gage pins, there is a bit of subjectivity to the measurement, as one person can apply more or less force than another person to insert a pin while inadvertently stretching the tubing to do so. Some people choose to moisten the tubing before inserting the pin, in order to reduce sliding friction between the pin and the inside wall of the tubing.
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The primary differences between PVC and polyolefin heat shrinkable tubing are cost and recommended operating temperature range. PVC tubing has a lower cost than polyolefin tubing and should be used in applications that do not require the wider operating temperature range of polyolefin. As an example, PVC tubing is more likely to be found in the instrument panel and interior of an automobile, but polyolefin tubing is more likely to be found in the engine compartment.
PVC is a thermoplastic material, which means that it can be re-melted and re-solidified. Polyolefin is a thermoset material, which means that once it has been formed and cross-linked (either chemically or through the use of radiation), it cannot be re-melted. The cross-linking of polymer chains gives polyolefin it's wider operating temperature range.
Grayline is one of the very few manufactures in the world to offer chemically cross-linked polyolefin tubing, in both heat shrinkable and non-heat shrinkable forms that can be manufactured in custom sizes and colors. Since this product is not irradiated but instead is chemically cross-linked, small quantity production runs are cost effective. If you need a specially sized, custom color polyolefin heat shrink tubing to match other components on your product…you've come to the right place.
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Grayline PVC heat shrinkable tubing can be supplied in a crystal clear form, in transparent tints, and in a wide range of solid opaque colors, ranging from bright white to deep black. Grayline also offers custom color matching for those critical aesthetic applications. In general, polyolefin heat shrinkable tubing is only available in solid opaque colors. Grayline GP-125 polyolefin heat shrinkable tubing is an exception and can be custom color matched, even for small production runs.
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This heat shrinkable tubing contains an inner adhesive lining that melts upon application of heat, thus serving to encapsulate the object while the tubing shrinks. This type of tubing is recommended for applications in which environmental conditions require sealing against moisture or other contaminants.
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Both PVC and polyolefin heat shrinkable tubing are frequently used in wiring harnesses and other electrical applications to bundle, electrically insulate and environmentally protect wires and other electrical components. For use in these applications, Grayline heat shrinkable tubing is specifically designed to meet the rigorous specifications of UL/CSA (Underwriters Laboratories/Canadian Standards Association), ASTM (American Society for Testing and Materials), AMS (Aerospace Material Specification), EU (European Union), and various Automotive and Military Specifications.
Click here for more information about Grayline Wire Harness/Electrical Tubing.
Click here for a list and explanation of Common Electrical Tubing Specifications.
For exact product specifications met, please click here for Grayline's Tubing Selection Guide or see our individual product data sheets.
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Heat shrinkable tubing is used not only in electrical applications, but in many other situations to provide:
- Bundling of loose items
- Mechanical protection from abrasion, cutting, chipping, peeling, scuffing or denting
- Cushioning from impact
- Strain relief
- Prevention of fraying
- Thermal insulation
- Protection from environmental moisture, contaminants, UV light, chemicals, oxidation or corrosion
- Improved aesthetic appearance, including a glossy or matte finish, vibrant colors including neon and "Glow-in-the-Dark" colors, or clear coverings
- Marking & identification by color coding or the addition of printing to indicate part or model numbers, company name, logo or contact information, safety warnings, instructions for use, or date of manufacture
Please contact Grayline to see if heat shrinkable PVC or polyolefin tubing is the optimum solution in your application.
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Grayline heat shrinkable PVC tubing is somewhat heat sensitive and must be stored below 90° Fahrenheit (32° Celsius) and out of direct sunlight to avoid premature recovery. Although the recovery process is both time and temperature dependent, storage at the recommended temperatures should eliminate any shelf life concerns.
Click here for Heat Shrinkable PVC Handling & Storage Notice (English)
Click here for Heat Shrinkable PVC Handling & Storage Notice (Spanish)
The shelf life of our heat shrinkable PVC products is indefinite assuming storage conditions are relatively cool and dry. Prolonged exposure to a warm humid environment can cause hydrolysis. Also, UV exposure can degrade the properties as well as exposure to fluids that may extract plasticizer out of the compound such as hydrocarbon solvents, fuels, or lubricants. A basic inspection of the product is a good indication of whether it has sustained any damage due to poor storage conditions. The product should not have discolored, stiffened, or become gummy on the surface. In general, if the tubing looks and feels like normal, then it will perform like normal.
Grayline heat shrinkable polyolefin tubing has a greater ability to withstand high storage temperatures and there is normally not a shelf life concern, provided normal storage conditions are maintained. AMS-DTL-23053 (MIL-I-23053) products have initial shelf life periods of 1 to 5 years (depending on material type) and storage temperatures of 18-35°C (65-95°F) specified by the standard. The initial shelf life may be extended up to 12 years max. provided the tubing shrinks to less than or equal to the minimum recovered ID.
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The image below shows the approximate relative costs for various heat shrink tubing materials.
For additional details on how to choose the right heat shrink tubing for your application, request a copy of Grayline's White Paper, "Choosing the Right Heat Shrink Product for the Job - A User's Guide to Heat Shrink Tubing".
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