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Latest from NHI...

Types of Pulleys (series) (4)

Monday, 25 January 2016 11:15

Spun vs. Split vs. Etc.

In this fourth and final installment we’ll be discussing the processes used to create pulleys. Spinning, splitting, stamping, molding, machining, casting and powder metallurgy each have their own strengths & weakness. We’ll also discuss best uses as some processes suit certain industries or applications better.

 

Spinning involves taking a stamped blank, typically having a domed or cup shape, and forming it between an upper & lower mold and form tooling. The part is held tightly between the molds (e.g. 25,000psi) and spun at high rates of speed (e.g. 900rpm). As the part spins, form tooling comes in and presses against it, forcing the material to change according to the shape of the form and mold which matches the desired groove profile. A typical pulley can use anywhere from two to four form tools, each attached to its own machine arm/holder which forms the part in consecutive stages.

Strengths: Pulley is a single piece which helps maintain consistent material thickness throughout the pulley

Weaknesses: Tolerances cannot generally be held as tight compared to processes like machining

Best Uses: Both drive and idler pulleys, standard single groove and poly-V pulleys, moderate to large sizes, all applications, steel

 


 …held tightly between the molds

 (e.g. 25,000psi)…


  

Splitting takes a flat stamped blank (think dinner plate) and forms it between a set of upper & lower molds and split/form tooling. The part is held tightly between the molds (e.g. 25,000psi) and spun at high rates of speed (e.g. 900rpm). As the part spins, the split tooling (think knife) comes in and presses against the edge of the blank. This causes the material to start to split in half. The form tool then comes in forcing the material to change according to the shape of the mold and desired groove profile. The material is pressed firmly against the molds, forcing it into its final shape. A typical pulley uses two individual form tools (one splitter/knife and one form), each attached to its own machine arm/holder which forms the part in consecutive stages.

Strengths: Pulley is a single piece which reduces thin points that can be created by assembling separate pieces.

Weaknesses: Tolerances cannot generally be held as closely as they otherwise can be in processes like machining.

Best Uses: Both drive and idler pulleys, standard single groove and poly-V pulleys, moderate to large sizes, all applications, steel

 

Stamping uses compound or progressive dies in a press to convert coils or sheets of metal into the desired shape/component. Depending on the size of the pulley a press uses anywhere from 30 to 800 tons of force.  The press may use what’s called a progressive die or a single stage (compound) die. A single stage die is just that, a die with a single stage where the pulley is stamped in one stroke/revolution of the press. A progressive die has several stages where the metal is moved from stage to stage and stamped into shape over the course of several strokes of the press. Generally, stamping in itself cannot create a whole pulley. It can only create one half at a time so two halves must be assembled using rivets and/or welding as a secondary process.

Strengths: Highly efficient and thus low cost

Weaknesses: Because of the size of presses and tooling needed to stamp metal, thinner materials are used which reduces overall strength compared to other processes like spinning and splitting.

Best Uses: Idler pulleys, standard single groove pulleys, small to moderate sizes, moderate applications, steel

 


 …press uses anywhere from

 30 to 800 tons of force.


 

Molding melts plastic pellets/beads by use of a reciprocating screw & heaters, forcing the now molten material through a small nozzle and into a mold. The material cools inside the mold, the mold separates in half and the molded part is removed. Molded parts from a cold runner system require finishing processes to remove excess plastic. This can be done by robotics. Hot runner systems do not necessary require extra processing. 

Strengths: Highly efficient process and thus low cost

Weaknesses: Material can melt or break/shatter under high load or high heat applications. Due to shrinkage during cooling, tolerances cannot be held as closely as with other processes. Inside and outside corners/edges must be rounded in order for the finished part to be properly removed from the mold.

Best Uses: Idler pulleys, standard single groove pulleys, moderate sizes, low load & low heat applications, nylon

 

Machining can take several forms including hobbing. In each instance a computer numerical control (CNC) or similar machine is used with precision tooling to remove material from a bar or slug. This process is controlled by a computer program entered into the machines terminal. Because each movement and process is controlled so finely, finished product can adhere to minute tolerances.

Strengths: The smallest of tolerances can be held.

Weaknesses: This is the slowest process by far and may require additional finishing processes depending on the part.

Best Uses: Both drive and idler pulleys, standard single groove and poly-V pulleys, timing pulleys, gears, small to large sizes, all applications, steel, aluminum, brass

 

Casting involves melting material and pouring that material into a mold. This can be done under pressure or not. Once the material cools the mold can be separated and the cast part (also called a casting) can be removed. The casting typically requires secondary operations including removing excess material and machining specified surfaces in order to hold tighter tolerances.

Strengths: Very strong and durable finished product.

Weaknesses: Castings are very heavy compared to pulleys made in other processes.

Best Uses: Both drive and idler pulleys, standard single groove pulleys, gears, small to large sizes, heavy load applications, aluminum, brass, iron (ductile & gray)

 

Powder Metallurgy is similar to both molding and casting in that a material is put into a mold to form the desired product. The difference is that a powder is used and, under pressure, forced into the mold. The subsequent part is fairly brittle and must be sintered in order for the powdered material to fully bond.

Strengths: More cost effective than many processes

Weaknesses: Tends to be more brittle than steel and other processes which reduces applicable uses

Best Uses: Bore adapters/plugs, hubs, small to moderate sizes, moderate applications

 


 Who knew there was

 so much to pulleys?


  

Throughout the course of these four installments we’ve covered quite a lot of information, from pulley basics & types to materials & processes used. Who knew there was so much to pulleys?

 

If you have any questions or just want to chat please don’t hesitate to send an email to This email address is being protected from spambots. You need JavaScript enabled to view it. or leave a comment here. We’ve been doing this since 1960. We know a thing or three.

 

New Hampshire Industries (NHI) 

68 Etna Rd, Lebanon, NH 03766

Monday, 18 January 2016 11:15

Drive vs. Idler

In this third of four installments we will be detailing what makes a drive pulley different from an idler pulley and what each typically look like.

 

To begin, what is a drive pulley? According to thefreedictionary.com a drive pulley is one “that drives a conveyor belt”. Could it be that simple? Not entirely. A drive pulley is a pulley that applies force to the belt, cable, chain, etc. to drive the system it’s attached to. A shaft connects the pulley to an engine or motor. A drive pulley drives the system it’s attached to.

 


 A drive pulley spins

 with its shaft


 

What is an idler pulley? Merriam Webster simply calls an idler pulley “a guide or tightening pulley for a belt or chain”. A more complex definition, describing more of the function of an idler comes from audioenglish.org. It’s “a simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope”. An interesting point is that an idler can provide tension to either side of the belt depending on the assembly and application. Typical applications have the drive pulley on the front side of the belt and the idler on the flat backside of the belt.

 


 An idler pulley does not

 spin with its shaft


 

Put simply, a drive pulley spins with its shaft and an idler does not.

 

There are instances where a drive (below right) and idler (below left) look very much the same.

 

Typically they look very different. From the definitions above do you know which of the below pictures are drives and which are idlers?

Key differences include the presence of a static shaft at the center of a drive pulley (upper set of pulleys above) and a bearing or special bushing at the center of an idler (lower set of pulleys above). The idler must spin freely so it can be driven where the drive pulley must be able to transfer and apply force generated by the engine or motor it’s attached to.

 

Another large difference you may have already noticed is the space allowed for a belt. Typical drive pulleys have a narrow groove, also known as a V groove, which the belt sits in. Tension applied to the belt snugs it into the V groove, allowing the groove to pinch and grip it. Idler pulleys have a larger flat groove that allows a belt to freely move along its surface.

 

What if a pulley is a drive pulley but isn’t attached to the main source of force, the engine or motor? The pulley is being driven by another source (typically a drive pulley on the engine or motor) but is also driving more pulleys or components of an assembly. It’s both driven and driving. That would simply be a driven pulley.

 


 A driven pulley both

 drives and is driven


 

To recap; a drive pulley spins with its shaft. An idler pulley does not spin with its shaft. A driven pulley spins with its shaft but is being driven by a source other than the engine or motor, typically a drive pulley.

 

If you have any questions or just want to chat please don’t hesitate to send an email to This email address is being protected from spambots. You need JavaScript enabled to view it. or leave a comment here.

 

New Hampshire Industries (NHI)

68 Etna Rd, Lebanon, NH 03766

 

Monday, 11 January 2016 11:15

Powder vs. Steel vs. Etc.

In this second of four installments we will be laying out the materials pulleys are typically made of. Pulleys can be made out of practically any solid material though the strength and durability will vary greatly.

 

The Line Up

Aluminum

Brass

Iron (Ductile & Gray)

Nylon (with & without Fiberglass)

Powdered Metal

Steel (Alloy, Carbon, Stainless)

 


 Pulleys can be made out of

practically any solid material


 

 

The Break Down

Aluminum

Basics: Ductile, Malleable, Lightweight, Nonmagnetic, High corrosion resistance

Stats: Density 2.70 g/cm3, Melting point 660°C, Thermal conductivity 237 W/(m∙k), Electrical resistivity 28.2 nΩ∙m (at 20°C), Hardness 160-550 MPa

Uses: Timing pulleys in low load applications such as lighting systems, automated positioning, robotics, and printers

 

Brass

Basics: Ductile, Highly Malleable, Durable, Non sparking when struck

Stats: Density 8400-8700 kg/m3, Melting point 890-1025°C, Thermal conductivity 109 W/(m∙k), Hardness 60 BHN

Uses: Gears in low load, low friction applications such as clocks

 

Iron (Ductile & Gray)

Basics: Ductile, Malleable, High tensile strength. Gray graphite flakes and silicon are added to produce gray iron while graphite nodules are added to produce ductile iron. Graphite flakes produce stress points leading to cracking while the nodules’ round shape inhibits such cracking, making ductile iron far more ductile than gray iron.

Stats: Density 7.87 g/cm3, Melting point 1538°C, Thermal conductivity 80.4 W/(m∙k), Electrical resistivity 96.1 nΩ∙m (at 20°C), Hardness 200-1180 MPa

Uses: Cast pulleys of all types are particularly useful in heavy load applications where the weight of the pulley is not an issue

 

Nylon (with & without Fiberglass)

Basics: Extremely Lightweight, Nonmagnetic, Noncorrosive

Stats: Density 1.15-1.20 g/cm3, Melting point 155-351°C, Thermal conductivity 0.19-0.25 W/(m∙k)

Uses: Low load and/or low heat applications as the material can melt from heat or friction

 

Powdered Metal

Basics: Highly customizable, Usually porous

Stats: Highly varied compositions depending on elements used 

Uses: Most types of pulleys in moderate applications as it tends to be more brittle than formed steel

 


 It’s the ‘Jack of all Trades’


 

Steel (Alloy, Carbon, Stainless)

Basics: Ductile, Malleable, High tensile strength. Contains alloys of iron and carbon, an alloy steel contains additional alloys, carbon steel is rated on its carbon content as low, medium and high and stainless steel must contain a minimum of 10.5% chromium by mass.

Stats: Varied compositions depending on ratios of alloys

Uses: Most types of pulleys in most applications, it’s the ‘Jack of all Trades’. Stainless steel is particularly sought after for corrosive environments as it will not corrode or rust.

 

Aluminum, brass and steel typically have higher strength properties while iron, nylon, and powered metal lend themselves to more highly customized parts as the material is essentially poured into a mold, into any shape you like.

 

Additional resources not listed above include e-How, Gates, PMP.com, ETB.com.

 

If you have any questions or just want to chat please don’t hesitate to send an This email address is being protected from spambots. You need JavaScript enabled to view it. or leave a comment.

 

New Hampshire Industries (NHI)

68 Etna Rd, Lebanon, NH 03766

 

 

 

Monday, 04 January 2016 12:15

Overview

In this first of four installments we will be discussing the general meaning of the term pulley as well as giving a brief overview of the remaining three installments; Powder vs. Steel vs. Etc., Drive vs. Idler, and Spun vs. Split vs. Etc.

 

So what is a pulley? According to Merriam Webster a pulley is “a wheel used to transmit power by means of a band, belt, cord, rope or chain passing over its rim”. Dictionary.com provides a further definition stating that a pulley is “a wheel driven by or driving a belt or the like, used to deliver force to a machine, another belt, etc., at a certain speed and torque”. We’ve seen much of the same in our experience, whether the pulley is on a mower deck, in an elevator system, or in underwater robotics. A pulley is a wheel used to transmit power by means of a belt or cable.

 

What types of pulleys are there?

 

Savvy e-Learning and Bill Nye explain three types of pulleys; fixed, movable and a pulley system.

A fixed pulley is fixed some distance from the object being moved and rotates on an axle. The pulley rotates but does not leave its location. This type of pulley changes the direction of your pull but it does not reduce the amount of force needed to move an object. Let’s say you need to lift an object weighing 100lbs but you can only lift 50lbs by yourself. If you used a fixed pulley you’d still need two of you to lift the object. What about a moveable pulley? A movable pulley is fixed to the object being lifted while the rope or cable being used has one end fixed some distance away. The pulley rotates on its axle but moves with the object being lifted. This halves the force needed as the object is now being lifted, in essence, by two ropes. One from the fixed end of the rope to the pulley and the other from the pulley to the end of the rope you’re pulling. You could lift the 100lbs object by yourself though it would still take some work. What if you combined a fixed and moveable pulley into a pulley system? Combining the pulleys greatly reduces the amount of force needed though the amount of rope and space needed to accomplish this increases. Using a pulley system you could lift that same 100lbs object with ease. This is also called mechanical advantage and is covered well by Khan Academy in a three part series.

The variety of pulleys made today is quite remarkable. In next week’s installment, Powder vs. Steel vs. Etc. we’ll discuss the differences in the materials used to create pulleys. Did you know pulleys can be made of recycled plastic? Later, we’ll discuss the main two types of pulleys used as designated by their function, Drive vs. Idler. You can find both types on a single mower deck. The final installment of Types of Pulleys will be Spun vs. Split vs. Etc. in which we will talk about the ways pulleys are created and we’ll share some pictures of the monstrous machines used.

 

If you have any questions or just want to chat please don’t hesitate to send an email or leave a comment.

 

New Hampshire Industries (NHI)

68 Etna Rd, Lebanon, NH 03766

 

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