Avoiding errors in thermoset elastomer selection for wire and cable. (Tech Service).Selecting and compounding the right elastomer elastomer (ĭlăs`təmər), substance having to some extent the elastic properties of natural rubber. The term is sometimes used technically to distinguish synthetic rubbers and rubberlike plastics from natural rubber. for wire and cable production is a balancing act. Fabricators have to meet the often difficult engineering requirements of the application, match them to the material properties of the base compound and the processor's equipment, and deliver product that meets regulatory or other standards-based specifications. This article provides general guidelines guidelines, n.pl a set of standards, criteria, or specifications to be used or followed in the performance of certain tasks. for selecting the right material, touching on rubber family properties and processing with the objective of achieving the best quality at the lowest overall cost. Also included is a discussion of compounding and what to do when (as is often the case) you need a custom compound. Specifically, some of the considerations that lead fabricators to off-load See offload. the sometimes considerable difficulties of specialized spe·cial·ize v. spe·cial·ized, spe·cial·iz·ing, spe·cial·iz·es v.intr. 1. To pursue a special activity, occupation, or field of study. 2. compounding to a third-party supplier are addressed. Wire and cable elastomers Any given wire construction needs first to meet the requirements of the customer making the order. While the selection of compound based on material properties is relatively straightforward if all the parameters are known, fabricators often find themselves working in the dark because they lack a well-thought-out specification from their customer. Without any doubt, a good spec is the best preventative that a producer can have against selection error. But even when the specification is locked down, material choice is not often a matter of picking a compound off-the-shelf. Too heavy a reliance on quick, off-the-shelf "solutions" can result in seriously under- or over-engineered materials, and both types can impose heavy long-term costs. Under-engineering can cause product failure and sales losses, and over-engineering levies ongoing production costs that are higher than optimal. Experience shows that a good number of the orders for elastomer-based wire and cable insulation insulation (ĭn'səlā`shən, ĭn'sy  –), use of materials or devices to inhibit or prevent the conduction of heat or of electricity. and jacketing can
benefit from either custom compounds or specialty compounds, though of
course many application requirements can be met with standard
formulations. This need to draw on a large variety of compounding
solutions, both custom and standard, is a natural outcome of the
often-intense engineering behind high-performance wire and cable.End use conditions are often harsh, putting heavy demands on electrical performance, temperature, chemical resistance, etc. Furthermore, the expected life of cable insulation and jacketing is generally long. It is obviously critical to find the right elastomer for an application. Table 1 outlines key properties fur a number of attributes for a range of elastomers. Note that while table 1 is only a general guide, it is useful for matching application needs and desired performance parameters to candidates for base elastomers. For example, while ethylene ethylene (ĕth`əlēn') or ethene (ĕth`ēn), H2C=CH2, a gaseous unsaturated hydrocarbon. It is the simplest alkene. propylene propylene /pro·pyl·ene/ (pro´pi-len) a gaseous hydrocarbon, CH3CHdbondCH2. propylene glycol a colorless viscous liquid used as a humectant and solvent in pharmaceutical preparations. diene Dienes are hydrocarbons which contain two double bonds. Dienes are intermediate between alkenes and polyenes. Classes Dienes can be divided into three classes:
EPDM Enterprise Product Data Management EPDM Ethylene Propylene Dimonomer (industrial/commercial piping/plumbing components) EPDM Engineering Product Data Management ) has many outstanding attributes, its oil resistance is poor, so it would not be a good choice for a cable intended for machine shop or oil exploration use. Here, the specifier might want to go with nitrile nitrile: see rubber. (NBR NBR Number NBR Nightly Business Report (PBS show) NBR National Business Review (New Zealand weekly business newspaper) NBR National Bureau of Asian Research NBR National Board of Review ) or polychloroprene (CR). Similarly, wiring intended for outdoor use would clearly need excellent resistance to water, sun, oxidation oxidation /ox·i·da·tion/ (ok?si-da´shun) the act of oxidizing or state of being oxidized.ox·idative ox·i·da·tion n. 1. The combination of a substance with oxygen. 2. and (if meant for ground or temporary use) abrasion abrasion /abra·sion/ (ah-bra´zhun) 1. a rubbing or scraping off through unusual or abnormal action; see also planing. 2. a rubbed or scraped area on skin or mucous membrane. . However, table 1 only scratches the surface. Usage of this table is not as simple as going down the rows, because blends and variations in formulation formulation /for·mu·la·tion/ (for?mu-la´shun) the act or product of formulating. American Law Institute Formulation can tune out unwanted attributes and enhance other, more desirable ones. For example, a mining cable intended for in-mine power supply or remote control signals needs to be brightly colored for visibility in dim light, as well as extremely abrasion resistant. The answer could be to blend nitrile with polyvinyl chloride polyvinyl chloride (PVC), thermoplastic that is a polymer of vinyl chloride. Resins of polyvinyl chloride are hard, but with the addition of plasticizers a flexible, elastic plastic can be made. (PVC PVC: see polyvinyl chloride. PVC in full polyvinyl chloride Synthetic resin, an organic polymer made by treating vinyl chloride monomers with a peroxide. ) polymers, though neither by itself would be a good solution. An experienced compounder, brought into the design cycle early, can provide blends for properties that might otherwise be out of reach. There is often more than one elastomer or polymer that fits and more than one way to make a given construction. The key is to work with someone with a wide portfolio of base materials to choose from, with the ability to modify or enhance properties to overcome limitations or enhance good characteristics. Table 2 illustrates the range of fine-tuning available, even within the same base elastomer. Table 2 "zooms in" on an example range of products within EPDM with significantly different properties depending on formulation. Thus, key to meeting customer specifications is the ability to work with proven variations in compounding across a full set of elastomer and performance additive additive In foods, any of various chemical substances added to produce desirable effects. Additives include such substances as artificial or natural colourings and flavourings; stabilizers, emulsifiers, and thickeners; preservatives and humectants (moisture-retainers); and choices. Regulatory and standards requirements Fully as important as the specifications covering end-use performance are those of regulatory bodies or testing agencies. Most applications begin with compliance with UL (Underwriters Laboratories Underwriters Laboratories Inc. is a U.S. not-for-profit, privately owned and operated product safety testing and certification organization. Based in Northbrook, Illinois, UL develops standards and test procedures for products, materials, components, assemblies, tools and ) or CSA (1) (Canadian Standards Association, Toronto, Ontario, www.csa.ca) A standards-defining organization founded in 1919. It is involved in many industries, including electronics, communications and information technology. (Canadian Standards Association See CSA. ) in North America North America, third largest continent (1990 est. pop. 365,000,000), c.9,400,000 sq mi (24,346,000 sq km), the northern of the two continents of the Western Hemisphere. or IEC (International Electrotechnical Commission, Geneva, Switzerland, www.iec.ch) An organization that sets international electrical and electronics standards founded in 1906. It is made up of national committees from over 60 countries. IEC - International Electrotechnical Commission (International Electrotechnical Commission See IEC. (standard, body) International Electrotechnical Commission - (IEC) A standardisation body at the same level as ISO. ) test mandates in Europe, and go from there--often moving into areas of specific compliance with highly specialized industry standards. Compliance with these specifications often restricts the fabricator fab·ri·cate tr.v. fab·ri·cat·ed, fab·ri·cat·ing, fab·ri·cates 1. To make; create. 2. To construct by combining or assembling diverse, typically standardized parts: to the use of certain elastomer types or families. Processing considerations In addition, fabricators must balance costs with product requirements. And, the full cost of any production run includes not simply the compound cost, but also scrap rates, processing needs and a bevy bevy a flock of birds. of ancillary costs. Processing equipment A fabricator needs to consider the type of processing equipment intended for an application. Formulations and additives can change depending on the type of equipment. Because of its moisture and heat, the pressurized pres·sur·ize tr.v. pres·sur·ized, pres·sur·iz·ing, pres·sur·iz·es 1. To maintain normal air pressure in (an enclosure, as an aircraft or submarine). 2. steam of a CV (continuous vulcanization vulcanization (vŭl'kənəzā`shən), treatment of rubber to give it certain qualities, e.g., strength, elasticity, and resistance to solvents, and to render it impervious to moderate heat and cold. ) line tube or tunnel can impart different crosslinking behaviors to compounds than does electron beam A stream of electrons, or electricity, that is directed towards a receiving object. See electron beam imaging and electron beam lithography. (E-beam) crosslinking, with its dry environment. In addition, reaction by-products can remain in the polymer in CV processing, a fact that needs to be addressed in the formulation. Also, the heat and pressure of mold/autoclave cure can subject cable constructions to appreciable ap·pre·cia·ble adj. Possible to estimate, measure, or perceive: appreciable changes in temperature. See Synonyms at perceptible. internal thermal and mechanical stresses. Each curing technology thus requires a formulation that has been fine-tuned for it, making it necessary to determine the process up front to prevent costly errors pursuing formulations that are less than optimal for a given process. In addition, the physical form of the compounded product (for example, strips versus pelletized) is often equipment-dependent. Strip or pellet pel·let n. 1. A small pill; a pilule. 2. A small rod-shaped or ovoid mass, as of compressed steroid hormones, intended for subcutaneous implantation in body tissues to provide timed release over an extended period of time. dimensions are also critical--if too large, the fabricator will likely experience downtime The time during which a computer is not functioning due to hardware, operating system or application program failure. in clearing feeds, and/or surging and starving starve v. starved, starv·ing, starves v.intr. 1. To suffer or die from extreme or prolonged lack of food. 2. Informal To be hungry. 3. To suffer from deprivation. , with consequent con·se·quent adj. 1. a. Following as a natural effect, result, or conclusion: tried to prevent an oil spill and the consequent damage to wildlife. b. problems with dimensions. The key is to determine the form factor that keeps processing within a window of consistency. Related to compound form, processors also should consider appropriate packaging in relation to their work area. The right packaging protects unvulcanized compound from damage and contamination, and it minimizes waste disposal. In addition, as simple as it sounds, the wrong box or pallet size can turn the process floor into an accessibility nightmare. Finally, the correct type and amount of anti-tack agent is a key consideration. Elastomers with wrong levels of anti-tack will block and may incur delays and extra costs for recutting to restore the consolidated chunks of material to a process-ready compound. In-house (captive captive said of naturally wild or feral animals kept in captivity for educational and scientific investigation with no attempt being made to domesticate them. ) mixing vs. custom compounding Sometimes the most expensive error is that of focusing only on material cost. In the always-critical "make or buy" decision--that is, compound at home or turn to a supplier--there is the temptation to consider compound cost alone. The full cost picture is broader than simply the material cost, and often the best overall return is obtainable only by tapping a custom compounder to develop the needed elastomer. This is because the total cost of any given order depends not just on compound price alone, but also on such costs as: * Compounding equipment capitalization capitalization n. 1) the act of counting anticipated earnings and expenses as capital assets (property, equipment, fixtures) for accounting purposes. 2) the amount of anticipated net earnings which hypothetically can be used for conversion into capital assets. costs; * time and effort to develop compounds, including time and materials labor and materials (time and materials) n. what some builders or repair people contract to provide and be paid for, rather than a fixed price or a percentage of the costs. for samples, formulation development, lab mixing of pilot batches and the ongoing expense of technical expertise; * time and effort to maintain in-house equipment; * scrap disposal costs; and * material packaging and packaging waste costs. In addition, the cost of a less-than-optimal knowledge base can he staggering. Compounding-related costs can balloon as the result of: * Testing that fails to meet regulatory specifications, including loss of test fees (custom compounders can maintain extensive, and relatively independent, test facilities to help ensure accurate, repeatable pre-regulatory testing and to pave PAVE Cardiology A clinical trial–Post AV Node Ablation Evaluation the way for problem-free regulatory lab testing); * pilot compounding with inadequate controls over critical parameters, leading to costly delays in moving to full production (to stay in business, a custom compounder must consistently provide successful scale-up of pre-production methods and materials); * inadequate dispersion dispersion, in chemistry dispersion, in chemistry, mixture in which fine particles of one substance are scattered throughout another substance. A dispersion is classed as a suspension, colloid, or solution. of all compound ingredients, leading to inferior physical and electrical properties (formulation and dispersion consistency are the key attributes of vendor-supplied compounds); * losing time during scale-up due to the need to reestablish production control limits, as well as costs due to scrap (the experienced custom compounder can bring a compound to production along the shortest path, calling on years of experience to minimize problems and to troubleshoot To find out why something does not work and to fix the problem. Troubleshooting a computer often requires determining whether the problem is due to malfunctioning hardware or buggy or out-of-date software. See debug. any that arise); * insecure in·se·cure adj. 1. Lacking emotional stability; not well-adjusted. 2. Lacking self-confidence; plagued by anxiety. in materials availability--that is, tailing to meet requirements for compound quantities, including any unexpected demands from the end user (custom compounders can draw on a wide range of facilities and resources committed to meeting delivery and quality windows, up to and including toll and contract manufacturing); * compounding with inadequately quality controlled materials (the best custom compounders manage the quality of their materials from start to finish); * lack of ongoing technical service (custom compounders can dispatch A dispatch or dispatches can refer to:
The key is to identify and manage a compounding and supply source that can consistently meet the quality and quantity of materials slated for fabrication fabrication (fab´rikā´sh  n),n the construction or making of a restoration. . Minimum error, maximum production The best means of avoiding error in elastomer selection for wire and cable is through awareness of the full picture: by paying close attention to the specifications, standards and processing required, and by viewing costs as a whole. Premium formulations make sense in missile nosecone applications, but not much sense for bug zappers A bug zapper is a device that attracts and kills insects that are attracted by light. A light source attracts insects to an electrical grid, where they are electrocuted by a high voltage. The name stems from the characteristic zap sound produced when an insect is electrocuted. . At the same time, cable or wire going to a distributor is probably going to be sold for a variety of applications, and the design process must anticipate the possible operating conditions the product will see. In any case, the cost of the material is only one part of the full picture. Quality and availability are paramount, and, in the long run, optimal behavior of the material which depends on material quality, good formulation management, and good fabrication practices, brings the best economic reward. Such optimal behavior benefits from on-site cooperation between the end customer, the fabricator and the compounder, working together to select the best material optimally engineered for best total cost.
Table 1--general characteristics of a range of elastomers
for wire and cable
General-purpose elastomers
Properties Ethylene Butyl Nitrile
propylene rubber rubber
diene
ASTM designation EPDM IIR NBR
Durometer A 40-90 40-80 40-90
Sp. gr. (polymer) 0.86 0.92 1.00
Tensile strength 2,000 2,000 2,500
max PSI (Mpa) (13.8) (13.8) (17.3)
Low temperature
brittle point - [degrees]F -70 -70 -60
[degrees]C -57 -58 -51
Resilience G to E P G
Compression set G F G
Heat aging E G to E G
Abrasion resistance G G G
Tear strength P G F
Flame retardant
properties P P P
Weathering
characteristics E G to E F to P
Oxidation resistance E E G
Ozone resistance E G to E F
Oil resistance P P E
Acid resistance E E G
Alkali resistance E E G
Key characteristics/ Ozone re- Low gas Oil and
comments sistance perme- fuel
good ex- ability resis-
tendability tance
Typical wire and Engine Tapes Mining
cable usage ignition for ship/ cable
cable and marine jacket
portable (w/PVC
cord insu- modi-
lation fiers)
General-purpose
elastomers
Properties Poly- Styrene
chloro- butadiene
prene rubber
ASTM designation CR SBR
Durometer A 40-90 40-90
Sp. gr. (polymer) 1.24 0.94
Tensile strength 2,500 2,500
max PSI (Mpa) (17.3) (17.3)
Low temperature
brittle point - [degrees]F -65 -70
[degrees]C -54 -57
Resilience G to E G
Compression set F to G G
Heat aging G F to G
Abrasion resistance G G to E
Tear strength G F
Flame retardant
properties G P
Weathering
characteristics G to E P
Oxidation resistance G to E F
Ozone resistance G to E P
Oil resistance G P
Acid resistance G to E F to G
Alkali resistance G to E F to G
Key characteristics/ Flame Abrasion
comments and resistance
weather
resis-
tance
Typical wire and Mining Some
cable usage cable portable
jacket cables
Specialty elastomers
Properties Silicone Chlorosul-
rubber fonated
polyethylene
ASTM designation MO CSM
Durometer A 40-80 40-90
Sp. gr. (polymer) 0.95-1.6 1.18
Tensile strength 1,500 3,000
max PSI (Mpa) (10.3) (20.7)
Low temperature
brittle point - [degrees]F -90 to -180 -40
[degrees]C -68 to -118 -40
Resilience G to E F
Compression set F to E F to G
Heat aging E G to E
Abrasion resistance P G to E
Tear strength P F
Flame retardant
properties F to G G
Weathering
characteristics E E
Oxidation resistance E E
Ozone resistance E E
Oil resistance F G
Acid resistance G G to E
Alkali resistance E E
Key characteristics/ Broad ser- Excellent
comments vice temper- weather
ature range resistance
Typical wire and Engine Heater and
cable usage ignition appliance
wires cords
Specialty elastomers
Properties Chlorinated Hydro-
poly- genated ni-
ethylene trile rubbe
ASTM designation CPE HNBR
Durometer A 50-90 45-90
Sp. gr. (polymer) 1.16- 0.98-
1.32 1.00
Tensile strength 2,000 3,000
max PSI (Mpa) (13.8) (20.7
Low temperature
brittle point - [degrees]F -40 -67
[degrees]C -40 -55
Resilience F G
Compression set G G
Heat aging G G to E
Abrasion resistance G G
Tear strength F F to G
Flame retardant
properties G P
Weathering
characteristics G G
Oxidation resistance E G to E
Ozone resistance E E
Oil resistance G E
Acid resistance G to E G
Alkali resistance E G
Key characteristics/ Especially Similar to
comments suited for NBR; best
wire and in high
cable tensile
application
Typical wire and Heater and Specialty
cable usage appliance
cords
* E - excellent; G - good; F fair; P - poor
Table 2--representative EPDM elastomers for specific needs
(note wide range of Mooney, elongation values
Property EPDM 0104 EPDM 0103
Typical application OEM quality Aftermarket
automotive automotive
ignition wire ignition wire
Specific gravity 1.40 1.48
Mooney ML (1+4), 100[degrees]C 45 35
Tensile, PSI 1,550 1,250
(Mpa) (10.68) (8.61)
Elongation % 190 210
Color capability Wide range Wide range
Property EPDM 0101 EPDM 0101
Typical application EPDM/MQ Automotive
automotive igni- ignition wire
tion wire jacket jacket
Specific gravity 1.47 1.44
Mooney ML (1+4), 100[degrees]C 30 35
Tensile, PSI 1,100 1,250
(Mpa) (7.58) (8.61)
Elongation % 200 210
Color capability Wide range Wide range
Property EPDM 0102
Typical application 90[degrees]C insulat-
tion UL 62
class 2.5A
Specific gravity 1.34
Mooney ML (1+4), 100[degrees]C 25
Tensile, PSI 1400
(Mpa) (9.65)
Elongation % 300
Color capability Wide range
Donald (Don) J. Picard has wide technical and sales experience in vinyl vinyl /vi·nyl/ (vi´nil) the univalent group CH2dbondCH—. vinyl chloride a vinyl group to which an atom of chlorine is attached; the monomer which polymerizes to polyvinyl chloride; it is toxic , polyolefins, color concentrates, thermoplastic elastomers Thermoplastic elastomers (TPE), sometimes referred to as thermoplastic rubbers, are a class of copolymers or a physical mix of polymers (usually a plastic and a rubber) which consist of materials with both thermoplastic and elastomeric properties. (TPEs) and rubber. Prior to his current position, he served as account executive, Wire & Cable for PolyOne and Geon. Previously, he was regional account manager for Elastochem and earlier for M.A. Hanna Rubber Compounding. |
|
||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion