 |
 |
|||||||||
 |
||||||||||
 |
||||||||||
 |
 |
 |
 |
 |
 |
 |
 |
 |
||
 |
|
|
|
|
|
|
|
|
|
|
|
|||||||||||||||||||||||||||||||||||||||||||||||
|
Tubing BasicsThere are several important questions to consider when selecting a tubing product for your application:
Heat Shrinkable and Non-Heat Shrinkable CharacteristicsHeat shrinkable tubing is capable of being significantly reduced in diameter upon exposure to heat. Non-heat shrinkable tubing does not change in size when heated. Some polymers, such as PVC, are manufactured into both a heat shrinkable and a non-heat shrinkable form of tubing. Heat shrinkable tubing is supplied in a temporarily expanded size that allows the user to easily place it around the object to be covered before it is shrunk to a smaller size, thereby providing a tighter fit. Application of sufficient heat causes the tubing to contract in diameter until it comes into contact with the object being covered. The nominal size of heat shrinkable tubing is the minimum inside diameter that the tubing will have when it is supplied to the customer, in the expanded state. The recovered size of the tubing is the maximum inside diameter that the tubing will have if it is allowed to recover fully through the application of heat. The nominal recovered wall thickness is the wall thickness that would result if the tubing were allowed to recover fully. If your application does not allow for full recovery, the actual recovered wall thickness will be less than the nominal recovered wall thickness. For example, if you specify 1/2” HS 105C PVC heat shrinkable tubing (a product which has a nominal 2:1 shrink ratio) with a standard 0.025” wall, it will be supplied to you with an expanded inside diameter of at least 0.500”, but with a wall much thinner than 0.025”. If heat is applied and the tubing is allowed to fully recover, it will shrink to an inside diameter of 0.250” or less, and it will have a wall thickness of 0.025”. However, the actual recovered diameter is determined by your application, and if your application does not allow for full recovery, the actual recovered wall thickness will be less than the nominal recovered wall thickness. As a general guideline, you may choose to select a tubing size that will shrink to approximately 70% 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 0.435”, you could select a nominal size of 5/8”, since 0.435”/0.625” = 0.70. When heat shrinkable tubing is recovered, it primarily shrinks in diameter. However, there is a small longitudinal shrinkage that takes place as well. This longitudinal shrinkage can vary, depending upon the amount of recovery that is allowed to take place in your application. Most PVC products have maximum longitudinal shrinkage of approximately 10%, and most polyolefin products have maximum longitudinal shrinkage of approximately 5%. When specifying the cut length of heat shrinkable tubing, be sure to allow for such longitudinal shrinkage. If desired, samples can be provided for you to test in your exact application. Heat shrink tubing most commonly has a nominal maximum shrink ratio
of 2:1, but tubing having a nominal shrink ratio of 3:1 or 4:1 is also
available. Materials and Their Properties (Thermal, Mechanical and Electrical)Flexible tubing can be made from many different types of plastics, or polymers. Polyvinyl chloride (PVC), polyolefin and polyurethane are three common polymers used to manufacture tubing for a wide range of applications. Other polymers are also manufactured into tubing for special applications. As might be expected, the polymer from which flexible tubing is manufactured is the single most important factor in determining the final thermal, mechanical and electrical properties of the tubing. However, the processing conditions under which the polymer is manufactured into tubing also affect the final properties. One general classification that can be made among polymers is thermoplastic or thermosetting. A thermoplastic polymer, such as PVC, can be repeatedly melted and formed. However, a thermoset polymer cannot be reprocessed once it is irreversibly “set”. Heat shrinkable polyolefin materials are initially thermoplastic, but are crosslinked and thus "thermoset" after they have been extruded. The crosslinking improves properties such as heat and fluid resistance. Cross-linking is the term used to describe the irreversible thermosetting process in the manufacture of polyolefin tubing. Cross-linking involves the formation of three-dimensional covalent bonds between long molecular chains. An analogy is a piece of yarn, with each fiber in the yarn representing a long polymer chain of molecules. Although there is some slight resistance to doing so, individual fibers can be pulled relatively easily from the piece of yarn. However, if the yarn is soaked in glue and subsequently dried, the individual fibers will now be securely joined together, and they can no longer be separated from one another. The cross-linking process is analogous to this gluing process, permanently joining the long polymer chains together. PVC tubing should be your first consideration for either heat shrinkable or non-heat shrinkable tubing. Heat shrinkable PVC is a less expensive product than heat shrinkable polyolefin, and one that suits many applications quite well. In addition to the associated cost savings, it has excellent clarity in it’s clear form, it is easy to custom color match, and it has good UV, chemical and abrasion resistance. For many applications, this is the best choice. There are a number of different compounds that Grayline offers in the PVC family of products. Polyolefin heat shrinkable tubing is costlier to manufacture than PVC heat shrinkable tubing, but it does offer a wider operating temperature range, as well as an extended shelf life and less longitudinal shrinkage. In more demanding applications, the advantages of polyolefin warrant the additional cost. In addition to these common tubing materials, Grayline also offers tubing manufactured from other materials, such as polyurethane, polyethylene and polypropylene. Please contact Grayline to determine which material is best suited to your application. Tubing Specifications (UL, CSA, ASTM, DIN, AMS, Military, Automotive, etc.)Various agencies have outlined specific mechanical, thermal and electrical tests that samples of tubing must successfully pass in order to gain approval. Grayline offers engineered products that have been formulated to meet all of the common tubing specifications. For a list and explanation of common tubing related specifications, click here In some cases, the exact UL, CSA, ASTM, DIN, AMS, Military, Automotive or other specification for the tubing you require is known. For example, a particular wiring harness assembly drawing may specify that any heat shrinkable tubing used on the harness be compliant with the UL VW-1 specification, which indicates the need for a high level of flame retardance, in particular. By specifying tubing that meets this UL VW-1 standard, the harness designer is ensuring that an appropriate tubing product is used in this application. A special search tool is available that allows you to quickly search the entire Grayline product line by the specification that your tubing needs to meet. Click here to access the Search By Specification tool. For customers who may wish to change from their current tubing supplier to Grayline, a special search tool is available that allows you to easily cross-reference products from other manufacturers with the corresponding Grayline product offerings. Click here to access the Cross Reference to Other Brands tool. Dimensional ConsiderationsGrayline tubing products are available in a wide range of sizes. Tubing is most often specified by the inside diameter (ID) and wall thickness, but in certain applications, the outside diameter (OD) may also be critical. Standard ASTM sizes have been established for non-heat shrinkable tubing. Some of these sizes are expressed as a number (for example, #24), while others are expressed as a fraction (for example, 1/4”). It should be noted that fractional ASTM sizes indicate the minimum ID that the tubing will have. Normal manufacturing tolerances must be added to that minimum. For example, if ASTM 1/4” tubing is specified, the ID will be between 0.250” and 0.270”. In contrast, a decimal size specification indicates the target for the ID. Normal manufacturing tolerances must be added to that target. For example, if tubing with an ID of 0.250” is requested, the targeted ID is 0.250”, and the tubing will have an ID between 0.240” and 0.260”. Grayline also has custom ID, OD and wall thickness capabilities for those customers with special requirements. Certain minimum wall thicknesses are required for tubing to successfully pass specific electrical testing requirements. Specifying a wall thickness that is thinner than this minimum will not allow the tubing to meet these electrical testing specifications. Grayline tubing can be supplied either cut to length or on reels. Many customers prefer to have Grayline cut their tubing to the exact length required, thus saving a step in their own manufacturing process. Grayline non-heat shrinkable PVC tubing is cut to length during the manufacturing process, resulting in extremely straight cut pieces, available up to 10 feet in length. Other customers, whether for reasons of inventory reduction or operational flexibility, prefer that their tubing be supplied in reel form, allowing them to cut it to length as needed. However, long lengths subsequently cut from reels will have a curvature that may be undesirable in certain applications. Standard tolerances for the ID and wall thickness, as well as the length of cut pieces, have been established. Please contact Grayline for information on standard tolerances, as well as our close tolerance capabilities. Color and TransparencyGrayline PVC and polyolefin tubing products are readily available in a range of opaque and transparent colors, and many are also available in a clear form. Custom color matching is also available for many products. Tubing vs. Braided Fiberglass or Expandable SleevingIf your application calls for very high operating temperatures (up to 600 degrees Celsius), or extreme abrasion protection, you may want to consider the use of a braided fiberglass sleeving or expandable sleeving product. Grayline offers a wide range of braided fiberglass and expandable sleeving products to serve in demanding applications. Please contact Grayline to determine which material is best suited for your specific application. PVC Tubing | Heat
Shrinkable PVC Tubing | Heat
Shrinkable Polyolefin Tubing |
 |
||
 |
 |
|
|
|
