Preface

Everyone knows what Stainless Steel and Galvanised products are, right? Additionally, we all know the difference between 316 and 304, and the difference between PVC, Nylon and Polyurethane? How about the history of rope and more!

Just in case you were wondering, we’ve outlined below some simple explanations of “what is….” to help us all understand the differences.

The history of Rope

The beginning of rope making is lost in prehistory, but there are evidences of rope being made as far back as 15-20,000 BC These early ropes were twisted by hand or braided. The earliest indication of any type of mechanical advantage in making rope comes from early Egyptian evidence relating to the craft.

The Egyptians used a weighted rope tied to a stick to make rope. The rope to be made was tied to the weighted rope that was spun around the stick. The spinning imparted a twist to the strand. Three twisted strands would then be twisted together in the opposite direction. There is evidence of Southwest Indians in America about 1,000 AD making rope.

In the Middle Ages (from the thirteenth century to the eighteenth century), from the British Isles to Italy, rope was made using a "rope walk" method. This allowed for long ropes of up to 300 yards long or longer to be made. Short ropes are useless on tall ships which require ropes to be long, relatively uniform in diameter, and strong. Short ropes would require splicing to make them long. The strongest form of splicing is the short splice, which doubles the diameter of the rope at the area of the splice. This would cause problems in the rigging hardware such as buckles and pulleys.

In 1393 we have a representation of the first stage of rope making-that of spinning the yarn-taken from the Mandelshes Portrait Buch in Nuremburg. So little difference from what was practiced for the next five hundred years in Europe is, coming down to more recent times we find that rope-making had been going on for centuries with probably very little change, up to the time of the introduction of machinery and the establishment of the factory system

Human hair has been used to make ropes when other resources were not available: the isolated Islanders of St Kitts used to make them to abseil down the cliffs to steal birds eggs; Japanese monks in the 13^th century made them over 10 inches in diameter to lift bells weighing more than 120 tons. Can you calculate what size solid alloy steel cable, or galvanised or stainless steel would be needed to lift this size bell?

Finally, "Yarns, twines and ropes can be made by machine nowadays, but the rope makers of older days were accustomed to making all of these in a walk. The principal of the walk is that yarns are stretched out between revolving hooks, often 300 yards apart, and these hooks twist the yarns together…."

Toward the end of the Middle Ages/Renaissance the pulley machines were replaced by geared machines. The gearing has a major advantage over the pulley machines in that gears do not slip, do not require adjustment of the pulleys, and do not suffer broken pulley belts. However, the gearing also required a more careful fitting, and the jack gains significantly in weight. The weight can be a good thing or a bad thing depending on how portable one wishes the jack to be. In the medieval period, portability was not an important factor, and the weight of the jack (especially the flywheel) probably worked in favour of the wheel turner.

The beauty of these machines or similar machines which might be made today is that they replicate exactly (although in a more compact package) the way rope was made in the medieval times down through about 1970 when the last Bridport rope walk closed

What is a rope?

A rope is a bundle of fibres/threads/wires twisted together. So why not just use a thicker single strand? While a single strand should have the same strength as a rope of the same cross sectional area there are several reasons why a rope is often a better solution.

• If one fibre fails the rope remains intact - whereas a rope made of a single large fibre would fail catastrophically.
• Thin fibres often have higher strength than thick ones made from the same material. Glass fibres are a good example of fibres which are strong in tension when thin because they are unlikely to contain a strength limiting defect. Drawn polymer fibres have much better mechanical properties than polymer products made by ordinary polymer processing, but such fibres can only be made in small diameters.
• A multi-stranded rope is more flexible than a single strand of the same diameter - for example multi-stranded copper 13A cable is much easier to bend than the single strand copper wire of the same diameter used in ring-main cables.

What are we looking for in a rope?

The history of wire

Harry Brearley, who was born in Sheffield, England, in 1871, probably invented stainless steel. His father was a steel melter and through private study and night school he became an expert in the analysis of steel and its production. In 1908 Brearley was given the opportunity to set up the Brown Firth Laboratories, which was financed by the two leading Sheffield steel companies of the day. In 1912 Brearley was asked to help solve the problems being encountered by a small arms manufacturer, whereby the internal diameter of rifle barrels was eroding away too quickly because of the action of heating and discharge gases. Brearley was therefore looking for steel with better resistance to erosion, not corrosion. As a line of investigation he decided to experiment with steels containing chromium, as these were known to have a higher melting point than ordinary steels.
Using first the crucible process, and then more successfully an electric furnace, a number of different melts of 6 to 15% chromium with varying carbon contents were made. The first true stainless steel was melted on the 13th August 1913. It contained 0.24% carbon and 12.8% chromium. At this time Brearley was still trying to find a more wear-resistant steel, and in order to examine the grain structure of the steel he needed to etch (attack with acid) samples before examining them under the microscope. The etching re-agents he used were based on nitric acid, and he found that this new steel strongly resisted chemical attack. He then exposed samples to vinegar and other food acids such as lemon juice and found the same result. At the time, table cutlery was silver or nickel plated. Cutting knives were made of carbon steel, which had to thoroughly washed and dried after use, and even then rust stains would have to be rubbed off using carborundum stones. Brearley immediately saw how this new steel could revolutionise the cutlery industry but he had great difficulty convincing his more conservative employers. On his own initiative, he than had knives made at a local cutler's, R.F. Mosley. To begin with, Brearley referred to his invention as "rustless steel". It was Ernest Stuart; the cutlery manager of Mosley's who first referred to the new knives as "stainless" after, in experiments, he had failed to stain them with vinegar. "Corrosion resisting" steel would be really the better term, as ordinary stainless steels do suffer corrosion in the long term in hostile environments.

Reference: Stainless Steel World is a brand of KCI Publishing BV.

The History of Stainless Steel

Reference:

 Specialty Steel Industry of North America

What performs best?

Good performance at low weight?

Suspension cables require high Young's modulus and strength, but also low weight. Rather than using 2 selection charts, we can form specific properties that represent performance per unit weight. The chart opposite shows that many fibres have excellent specific properties - but of course these can only be exploited by building the fibres into a structured material like a rope or a fabric. The material bubbles in red show long-fibre properties; the other materials and material classes show bulk properties i.e. those you would expect if the material is not drawn into fibres. The strength for the bulk ceramics shown on the chart is compressive strength - the tensile strength is typically only 10% of this value; for the other materials the strength is similar in compression and tension; the strength for all fibres is for loading in tension.

What is Stainless Steel?

An extremely durable alloy of steel and chromium which can be polished to resemble a precious metal and is virtually immune to rust, discoloration and corrosion.

We associate “stainless” with household goods, knives, forks and spoons etc, they are easy to take care of, to wash and polish, but most importantly, they don’t “stain”! It was adopted as a generic name for these steels and now covers a wide range of steel types and grades for corrosion or oxidation resistant applications.

Stainless steels are iron alloys containing by weight, 1.2% or less of carbon and a minimum 10.5% or more of chromium. Other alloying elements are added to enhance their structure and properties such as formability, strength and cryogenic toughness. Iron must be the predominant element.

The main requirement for stainless steels is that they should be corrosion resistant for a specified application or environment. The selection of a particular "type" and "grade" (304 and 316 typically) of stainless steel must initially meet the corrosion resistance requirements. Additional mechanical or physical properties may also need to be considered to achieve the overall service performance requirements.

Why Stainless?

The generic term for grades of steel that contains more than 10% chromium, with or without other alloying elements. Stainless Steel may also have varying additions of Nickel, Molybdenum, Titanium, Niobium and other elements. Stainless steel resists corrosion, maintains its strength at high temperatures, and is easily maintained. The chromium in the steel combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide.

The corrosion resistance of stainless steel arises from a "passive", chromium-rich, oxide film that forms naturally on the surface of the steel. Although extremely thin at 1-5 nanometres (i.e. 1-5 x 10-9 metres) thick, this protective film is strongly adherent, and chemically stable (i.e. passive) under conditions which provide sufficient oxygen to the surface.

The key to the durability of the corrosion resistance of stainless steels is that if the film is damaged it will normally self repair (provided there is sufficient oxygen available). In contrast to other steel types which suffer from "general" corrosion where large areas of the surface are affected, stainless steels in the "passive state", are normally resistant to this form of attack.

Stainless steels cannot be considered "indestructible", however. The passive state can be broken down under certain conditions and corrosion can result. This is why it is important to select carefully the appropriate grade for a particular application.

The most common grades of stainless steel are:

TYPE 304 The most commonly specified austenitic (chromium-nickel stainless class) stainless steel, accounting for more than half of the stainless steel produced in the world. This grade withstands ordinary corrosion in architecture, is durable in typical food processing environments, and resists most chemicals. Type 304 is available in virtually all product forms and finishes.

TYPE 316 Austenitic (chromium-nickel stainless class) stainless steel containing 2%-3% molybdenum (whereas 304 has none). The inclusion of molybdenum gives 316 greater resistance to various forms of deterioration.

TYPE 409 Ferritic (plain chromium stainless category) stainless steel suitable for high temperatures. This grade has the lowest chromium content of all stainless steels and thus is the least expensive.

TYPE 410 The most widely used martensitic (plain chromium stainless class with exceptional strength) stainless steel, featuring the high level of strength conferred by the martensitics. It is a low-cost, heat-treatable grade suitable for non-severe corrosion applications.

TYPE 430 The most widely used ferritic (plain chromium stainless category) stainless steel, offering general-purpose corrosion resistance, often in decorative applications.

What is 304-316 grade?

Grade 316 has excellent corrosion resistance in a wide range of media. Its main advantage over grade 304 is its increased ability to resist pitting and crevice corrosion in warm chloride environments. It resists ordinary rusting in virtually all architectural applications, and is often chosen for more aggressive environments such as sea-front buildings and fittings on wharves and piers. It is also resistant to most food processing environments, can be readily cleaned, and resists organic chemicals, dye stuffs and a wide variety of inorganic chemicals.

Like other austenitic grades, 316 in the annealed condition is virtually non magnetic (i.e. very low magnetic permeability). While 304 can become significantly attracted to a magnet after being cold worked, grade 316 is almost always virtually totally non-responsive. This may be a reason for selecting grade 316 in some applications.

Typical applications for 316 include boat fittings and structural members; architectural components particularly in marine, polluted or industrial environments; food and beverage processing equipment; hot water systems; and plant for chemical, petrochemical, mineral processing, photographic and other industries.

Although 316 is often described as the 'marine grade', it is also seen as the first step up from the basic 304 grade.

Type 304 stainless steel is the standard alloy for use in wire rope and cable. It has about the same strength as galvanised rope or cable but is much more corrosion resistant. It can be used in most industrial atmospheres and has acceptable corrosion resistance when used in marine- and salt water.

Type 316 stainless steel is the standard high corrosion resistant steel for rope and cable. It is resistant to many chemicals in the pulp and paper, photographic, food processing and textile industries. It has the best pitting resistance in marine and salt water and can be used in temperatures up to 480°C (900°F).

The AISI defines the following grades among others:

• 200 Series—austenitic iron-chromium-nickel-manganese alloys
• 300 Series—austenitic iron-chromium-nickel alloys
• Type 301—highly ductile, for formed products. Also hardens rapidly during mechanical working.
• Type 303—equivalent to ISO^[2]2 A1. Free machining version of 304 via addition of sulfur
• Type 304—the most common; the classic 18/8 stainless steel; equivalent to ISO A2.
• Type 316—for food and surgical stainless steel uses; Alloy addition of molybdenum to prevent specific forms of corrosion; equivalent to ISO A4.
• 400 Series—ferritic and martensitic alloys
• Type 408—heat-resistant; poor corrosion resistance; 11% chromium, 8% nickel.
• Type 409—cheapest type; used for automobile exhausts; ferritic (iron/chromium only).
• Type 410—martensitic (high-strength iron/chromium); equivalent to ISO C1.
• Type 420—"Cutlery Grade" martensitic; similar to the Brearley's original "rustless steel". Also known as "surgical steel".
• Type 430—decorative, e.g. for automotive trim; ferritic.
• Type 440—a higher grade of cutlery steel, with more carbon in it, which allows for much better edge retention when the steel is heat treated properly.

Wire differences

Typical Stainless steel wire rope constructions - other options available, including plastic coated and galvanised steel wire

Figure are for guidance only for Stainless Steel wire products

Contact Rope & Cable for more precise specifications.

How is Stainless Steel made?

Stainless steel is produced in an electric arc furnace where carbon electrodes contact recycled stainless scrap and various alloys of chromium (and nickel, molybdenum etc. depending on the stainless type). A current is passed through the electrode and the temperature increases to a point where the scrap and alloys melt. The molten material from the electric furnace is then transferred into an AOD (Argon Oxygen Decarbonisation) vessel, where the carbon levels are reduced (remember stainless has a much lower carbon level than mild steel) and the final alloy additions are made to make the exact chemistry. Exhibit 1 shows the process from melting and casting either into ingots or continually cast into a slab or billet form. Then the material is hot rolled or forged into its final form. Some material receives cold rolling to further reduce the thickness as in sheets or drawn into smaller diameters as in rods and wire.

Most stainless steels receive a final annealing (a heat treatment that softens the structure) and pickling (an acid wash that removes furnace scale from annealing and helps promote the passive surface film that naturally occurs).

What is Galvanised Steel?

Steel coated with a thin layer of zinc to provide corrosion resistance in under body auto parts, garbage cans, storage tanks, or fencing wire. Sheet steel normally must be cold-rolled prior to the galvanizing stage. Our galvanised steel products have a zinc coating, which prevents corrosive elements such as water and salt from coming into contact with the steel, generally eliminating the possibility of rust. When steel is galvanised it is coated with rust resistant zinc. First the surface of steel is cleaned by friction with dilute acid then commonly dipped in a hot bath of zinc. The degree of galvanizing is usually represented as the zinc's weight per surface area rather than the thickness of the zinc, because this gives a better representation of how much metal has been applied. Steel often gets galvanised after individual parts have been formed, such as braces, nails, screws, beams, or studs. However, raw galvanised steel in sheets will withstand some bending and forming without flaking.

galvanised steel can be found almost everywhere. You might be living in a steel frame house. You are no doubt surrounded by steel parts in your car that allow it to emerge from rainstorms unscathed. Many people work in an office with metal roofing made of galvanised steel. Besides being inexpensive and effective, this metal is popular because it can be recycled and reused multiple times

What is PVC, Nylon and Polyurethane?

PVC

Polyvinyl chloride, commonly known as "PVC" or "vinyl," is one of the most common synthetic materials. PVC is a versatile resin and appears in thousands of different formulations and configurations. PVC is relatively inexpensive and is available in almost any colour. PVC lends itself well to applications that are going to be exposed to sunlight PVC would also be a good choice for an application that requires an increase in mass, or a particular colour. PVC is relatively soft and does not have good abrasion resistance.

PVC has the largest commercial application of any polymeric material.

Chemically, rigid PVC is very corrosion resistant to a wide range of pH and has many industrial uses such as plating tank lining, fume hoods, scrubbers, water treatment and solution tanks. As well, rigid PVC possesses good thermal and electrical insulation characteristics with rigid, cellular PVC enhancing the thermal insulating ability of PVC and providing improved impact resistance. PVC has poor abrasion resistance and should not be used for parts subjected to rubbing against rough or gritty surfaces. Rigid PVC is resistant to aliphatic hydrocarbons and alcohols; is swelled or dissolved by aromatic hydrocarbons, ketones and esters; and is soluble in halginated hydrocarbons which are commonly used in solvent cements for joining pipe and fittings.

Nylon

"Polyamide" (PA), far better known by its trade name "nylon."  Nylon and Thermoplactic Elastometers are numerous in types of compounds, each with its own special properties that may be more or less suitable for a particular application. Most are suitable for cycling over pulleys. The differences vary from high temperature environments to specific chemical exposures.

Nylon is, without a doubt, the most common engineering polymer today. Nylon, a crystalline material, possesses many useful characteristics and the wide variety of grades allows for the selection of desirable properties. Generally, tensile properties are high while impact properties are good to excellent. Coefficient of friction is low and abrasion resistance is high making Nylons suitable for bearings, gears, wear plates and applications where low to moderate loads are operating at low to moderate speeds and at moderate temperatures. All Nylons absorb moisture to varying degrees. Chemical resistance is good and Nylons show no stress cracking or crazing when exposed to solvents such as hydrocarbons, ketones or esters.

Nylon was the first purely synthetic fibre, introduced by Du Pont Corporation at the 1939. Synthetic nylon fibre is very strong but also very flexible.  The first application was for bristles for toothbrushes. Nylon remains an important plastic, and not just for use in fabrics.  In its bulk form, it is very wear-resistant, and so is used to build gears, bearings, bushings, and other mechanical parts.

Polyurethane

Polyurethane is a unique material that offers the elasticity of rubber combined with the toughness and durability of metal. Because urethane is available in a very broad hardness range (eraser-soft to bowling-ball-hard), it allows the engineer to replace rubber, plastic and metal with the ultimate in abrasion resistance and physical properties. Urethanes have better abrasion and tear resistance than rubbers, while offering higher load bearing capacity.

Urethanes have replaced metals in sleeve bearings, wear plates, sprockets, rollers and various other parts, with benefits such as weight reduction, noise abatement and wear improvements being realized.