Learn About Tubing
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1. Extrusion of Polymer Tubing
2. 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
3. Non-Heat Shrinkable Tubing
a. Tubing Geometry
b. Fluid Transfer Applications
c. Electrical & Wiring Harness Applications
d. Other Tubing Applications
e. Storage and Shelf Life
4. Selecting a Material for Your Application
a. PVC and Polyolefin Considerations
b. Halogen-Free Tubing
c. Non-DEHP and Phthalate-Free Tubing
d. ROHS Compliant Tubing
e. REACH Compliant Tubing
f. Industry Specifications
5. Tubing Options, Custom Services Offered by Grayline
a. Cut to Length Tubing
b. Customer Diameters and Wall Thicknesses
c. Custom Color Matching
d. Special Tolerances
e. Printing, Hot Stamping
f. Heat Forming or Shaping of Tubing
g. Non-Circular Profiles
h. Tapered Tubing
i. Applying Tubing Directly to a Substrate
j. Tube-to-Tube Bonding
k. Special Packaging, Labels
1. Extrusion of Polymer Tubing
Tubing has a constant cross sectional shape, which allows it to be efficiently manufactured by melting polymer compounds and forcing them through the necessary tooling in a continuous process called extrusion. In this process, tubing can be made in lengths limited only by the capacity of the downstream handling equipment available.
In the extrusion of plastics, a raw polymer blend in the form of small beads or pellets is vacuum loaded into a hopper located above a gravity-fed barrel. The barrel, a cylindrical metal chamber that is electrically heated on its outside surface to temperatures of several hundred degrees F, contains a close tolerance rotating screw auger. The barrel and tooling temperatures, as well as the rotational speed of the screw, are precisely controlled.
The screw serves to mechanically shear the polymer pellets, adding frictional heating and mixing the polymer as it becomes molten, and to push the molten polymer forward to the end of the barrel. The tooling located at the end of the barrel is comprised of a pin and a hollow die. The pin is centered within the hollow die, and the tubular shape is formed as the molten polymer travels over the surface of the pin and inside the surrounding hollow die. The polymer tubing is solidified but has minimal mechanical strength as it exits the tooling and immediately enters a vacuum water tank. The vacuum serves to prevent the tubing from collapsing while the water cools the tubing, allowing it to harden and develop full mechanical strength.
By carefully controlling process parameters such as the speed of screw rotation, the vacuum exerted on the tubing in the cooling tank, and the amount that the tubing is drawn down by pulling it out of the extruder faster than it is pushed out by the screw, the diameter and wall thickness can be accurately controlled. Lasers are often used to monitor the geometry of the tubing as it is extruded.
Downstream of the extrusion process, the tubing is either cut to length inline or placed on reels. Tubing that is cut inline will be straighter and rounder than tubing that is first placed onto a reel and then taken off the reel for cutting.
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.
a. Making Extruded Tubing Heat Shrinkable
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.
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).
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.
d. Inside Diameter and Wall Thickness
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.
e. PVC vs. Polyolefin Heat Shrinkable Tubing
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.
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.
g. Adhesive Lined (Dual Wall) Heat Shrinkable Tubing
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.
Both PVC and polyolefin heat shrinkable tubing can be printed on or hot stamped.
i. Electrical and Wiring Harness Applications
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.
For a list and explanation of common tubing related specifications, click here.
For exact product specifications met, please click here for our Tubing Selection Guide or see our individual product data sheets.
j. Non-Electrical Applications
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.
Grayline heat shrinkable PVC tubing is somewhat heat sensitive and must be stored below 90 degrees Fahrenheit (32 degrees 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)
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.
The applications for flexible, non-heat shrinkable tubing are virtually endless and it is available in a wide array of polymer materials, including PVC, polyurethane, polyethylene, polypropylene, nylon, fluoropolymers, rubbers, and silicone.
Grayline 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 applications having 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.
b. Fluid Transfer Applications
Grayline flexible tubing products are suitable for transferring a wide range of fluids. Some of the product categories that we offer include chemical resistant tubing, food & beverage tubing, medical tubing, fuel & oil resistant tubing, pneumatic tubing and hydraulic tubing. If your specific fluid transfer application is not listed above, please contact Grayline for assistance.
Materials used for fluid transfer tubing include PVC, polyurethane, polyethylene, polypropylene, nylon, various fluoropolymers, rubbers, and silicone.
For higher pressure fluid transfer applications, a reinforced hose may be required. Grayline offers a variety of hose products having fiber braid reinforcement, semi-rigid polymer reinforcement, or steel/stainless steel reinforcement. Reinforcement may be either internal or external to the tubing wall, and we also offer over-braiding of non-reinforced hose.
Grayline fluid transfer tubing meets the requirements of various industry standards, including USP (United States Pharmacopeia) Class VI, NSF (National Sanitation Foundation) 51 and 61, FDA Food & Drug Administration) Title 21 and 3-A Sanitary Standards Inc. Grayline also offers non-phthalate fluid transfer products.
Various Grayline medical tubing products are designed to be sterilized using Gamma radiation, ETO (ethylene oxide), or autoclave processes.
c. Electrical & Wiring Harness Applications
Flexible tubing is 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 flexible 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.
For a list and explanation of common tubing related specifications, click here.
For exact product specifications met, please click here for our Tubing Selection Guide or see our individual product data sheets.
In addition to fluid transfer and electrical applications, flexible non-heat shrinkable polymer tubing is often used to provide:
- Bundling of loose items
- Mechanical protection from abrasion, cutting, chipping, peeling, scuffing or denting
- Cushioning from impact
- Strain relief
- 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
No special storage considerations are necessary for non-heat shrinkable tubing products, including PVC, polyurethane, polyethylene, polypropylene, nylon, fluoropolymers, rubbers, silicone and braided fiberglass sleeving.
4. Selecting a Material for Your Application
Grayline offers tubing manufactured from a variety of materials, including PVC, polyolefin, polyurethane, polyethylene, polypropylene, nylon, fluoropolymers, rubbers, and silicone.
There are many material options to consider when selecting flexible polymer tubing. As might be expected, the polymer from which flexible tubing is manufactured is the single most important factor in determining the final mechanical, electrical, chemical and thermal properties of the tubing. However, the processing conditions under which the polymer is manufactured into tubing also affect the final properties.
For general guidance in determining which material is best suited to your specific application, please review the information contained on our website, use our Tubing Selection Guide, or simply contact Grayline for assistance:
CLICK HERE TO TRY OUR TUBING SELECTION GUIDE
PREFER TO SPEAK WITH A TECHNICAL SALES REPRESENTATIVE? CLICK HERE TO EMAIL US, OR PHONE GRAYLINE AT 1-800-669-7986
a. PVC and Polyolefin Considerations
One broad classification that can be made among polymers is thermoplastic vs. thermosetting. A thermoplastic polymer, such as PVC, can be repeatedly melted and solidified. However, a thermoset polymer, such as polyolefin, cannot be reprocessed once it is irreversibly "set" by a post-extrusion process called cross-linking. Cross-linking involves the formation of three-dimensional covalent bonds between long molecular chains, and it improves certain properties such as heat resistance and tensile strength. A simple 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. For many applications, PVC is the optimum material choice, and Grayline offers a number of different PVC compounds.
With specific regard to heat shrinkable tubing, heat shrinkable PVC is less expensive than heat shrinkable polyolefin, and suits many applications quite well. In addition to the associated cost savings, it has excellent clarity in its clear form, it is easy to custom color match, and it has good UV, chemical and abrasion resistance. Polyolefin heat shrinkable tubing does offer a wider operating temperature range and slightly less longitudinal shrinkage. In more demanding applications, the advantages of polyolefin may warrant the additional cost.
b. Halogen-Free Tubing
For those applications warranting concern about potential toxic and corrosive smoke emissions during combustion of materials containing halogen compounds, Grayline offers halogen-free flexible tubing. Halogen compounds contain any of the five halogen elements (Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) or Astatine (At)). The use of halogen-free tubing is becoming more common in enclosed spaces occupied by humans, such as airplanes, subways, and trains, as the smoke emitted is far less toxic. Halogen-free tubing is also finding applications in areas housing sensitive or critical electronic equipment, such as security or communication centers, in order to minimize damage caused by corrosive smoke emissions. Grayline HF100 flexible tubing is flame-retardant yet halogen-free. Grayline also offers other halogen-free products that are not flame retardant.
Click here for more information about halogen-free tubing.
c. Non-DEHP and Phthalate-Free Tubing
In response to recent health concerns, Grayline also offers non-DEHP and phthalate-free flexible PVC tubing. The most common plasticizer additives used to make PVC flexible are DOP (Dioctyl Phthalate)/DEHP (di-2-ethylhexyl phthalate) and DINP (Di-isononyl phthalate).
Grayline MD80-NP-PVC flexible PVC tubing is manufactured from a compound using a non-phthalate plasticizer, resulting in a material containing less than 1000 ppm (less than 0.1%) total phthalate content.
Grayline MD70-PVC and MD80-GS-PVC flexible PVC tubing is DEHP-free.
The acronym stands for Restriction Of Hazardous Substances. RoHS is a European Union law (EU Directive 2002/95/EC) that prohibits the use of lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, or polybrominated diphenyl ethers in electrical products sold in the EU. All Grayline tubing except for NHS is compliant and does not contain the prohibited substances.
REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) is a European Union regulation (2006/1907/EC) that requires that chemical substances used or imported into the EU be registered, evaluated and authorized for specific uses. As a manufacturer of “articles”, Grayline is not required to register any substances.
The regulation also defines Substances of Very High Concern (SVHC’s) which must be reported to uses. There are currently 29 SVHC substances defined. One of these is the plasticizer DEHP which is used in some of Grayline’s PVC compounds. See Grayline’s REACH policy for more details.
In many cases, the tubing selected must meet industry specifications such as UL/CSA, ASTM, AMS, EU, USP, NSF, FDA, 3-A, as well as various Automotive and Military Specifications.
For a list and explanation of common tubing related specifications, click here.
5. Tubing Options, Custom Services Offered by Grayline
Many customers prefer to have us cut their tubing for them, not only to reduce their costs but to receive straighter and rounder lengths of tubing than they can obtain by cutting tubing from small diameter reels themselves. As a manufacturer, we can cut non-heat shrinkable tubing to lengths ranging from 1/8 of an inch to 10 feet using state of the art, high speed inline cutting equipment during the extrusion process. Heat shrinkable PVC tubing is cut to length from large diameter production reels, rather than small reels taken from stock.
b. Custom Diameters and Wall Thicknesses
As a manufacturer, Grayline isn't limited to stock sizes. If your application would benefit from a non-standard diameter or wall thickness, Grayline can help. Grayline has the manufacturing capability to extrude tubing in a continuous range of diameters and is not limited to the sizes of existing tooling.
Many of the polymers we use to manufacture flexible tubing can be custom colored, including both opaque and transparent polymers. Since Grayline blends our own colored compounds, we can use the appropriate pigment additives to match other parts in your assembly, match or coordinate with your corporate color scheme, or give you just the right shade of color for that critical aesthetic application. We even offer intense, glow-in-the-dark tubing that is manufactured using special photoluminescent additives.
Although Grayline has standard ID, wall and length tolerances that meet or exceed most application requirements, statistical process capability studies are used to determine if requests for tighter than standard tolerances can be met. Contact customer service to discuss your special tolerance requirements.
Grayline has high-speed inkjet printing capabilities that can be used to print inline during the extrusion process. Printing can be synchronized with the cutting process so that the printing can be placed in any desired position along the length of the tubing. If the product is reeled rather than cut to length, the center-to-center print spacing must be specified. Grayline can print characters from 1/16" to 5/16" tall, including up to four lines of text. Bar codes, serialized numbers and date/time codes are also available. The standard ink color is black.
When precise, high quality graphics such as company logos are required, hot stamping services are also available. The hot stamping process uses a heated die to apply ink to the tubing.
f. Heat Forming or Shaping of Tubing
Grayline welcomes the opportunity to review your part design to determine if a heat formed tube might be an option. Similar in concept to pre-shaped radiator hoses found in automobiles, heat formed tubing shapes are often used to precisely route fluids or wires around an obstacle, reduce the likelihood of kinking, and improve the overall appearance of the product.
Grayline has the ability to supply you with non-circular profiles as well as round tubing. For example, tubing cross sections can be oval shaped or "D" shaped. Tubing can also include internal ribbing to improve gripping ability over a substrate, or external ribbing to provide an improved surface texture.
By accurately varying the extrusion parameters, Grayline can manufacture tapered tubing, as is sometimes used in a "daisy chain" fashion in medical applications. As there are practical limitations to the amount of taper that can be incorporated in a design, please contact Grayline to discuss the requirements of your application.
i. Applying Tubing Directly to a Substrate
If you currently apply heat shrinkable tubing over a cylindrical substrate before using a flow-through oven to shrink it down, you may want to consider a cost-effective alternative that Grayline has developed, a process by which a PVC covering can be applied directly to a substrate. For some customers, this process has replaced the use of heat shrinkable tubing and its associated downstream heating equipment and labor requirements, resulting in a significant cost savings. Please contact Grayline to discuss your specific application.
Grayline offers multi-tube assemblies in which tubing is bonded side-by-side for convenient and efficient routing of wires or fluids. Please contact Grayline with the specific requirements of your application.
Grayline can provide your tubing in boxes, heat sealed bags, on reels, or in coil form. Grayline can also provide customer-specific labeling, including bar coding.
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