A raw material is the basic material from which a product is manufactured or made.

Product is a “thing produced by labor or effort” or the "result of an act or a process"⁶. A product is made of components and complies with a set of specifications.

Components are parts of a product that comply with a set of specifications. A component is a product too.

“Manufacturing is the process of converting raw materials, processed materials and components into products”⁶.

Processed materials are materials that have been refined or built by humans from raw materials. Examples: paper, steel, or glass.

A rebuilt product is a new product created using discarded products, raw materials, processed materials and components. Rebuilding recovers the residual value added to a product at the end of its life.

“Recycling means reusing a material or a component or a product not necessarily in its original form”⁷. The adoption of recycling techniques allied with good design practice can do much to conserve raw materials and energy if we allow for materials and components to be reclaimed from products after their useful life is over, we minimize waste and we save money. Waste minimization followed by recycling does offer the potential for considerable savings without major sacrifices on the part of the consumer. Figures 1 and 2 depict the life process of a product and an electrical machine respectively⁸. Recycling may take place at the end-of-life of an electrical machine or at any stage of the life process of an electrical machine⁹.

Figure 1
Disaggregated product-process chain of a product life⁴

Figure 2
Disaggregated product-process chain of a rotating electrical machine life

The first class is the reuse of materials or components. “An example of the first class is typified by the returnable bottle, which makes several trips from bottler to consumer and back again where it is cleaned and refilled”⁷. Reuse may be allocated the highest value in the recycling classes in that least energy and process complexity is normally expended in getting the material or article back into use. Typical reused items are compressed gas cylinders, the 200-litre drum (a worldwide standard) and the intermodal container (also a worldwide standard). The frame of a rotating electrical machine or the tank of a transformer could be another example. A special case of the first class of recycling is remanufacturing. In this paper remanufacturing is “the process of returning a used product to original-equipment-manufacturer performance specification and giving the resultant product a warranty equal to that of a newly manufactured equivalent”¹⁰. Repair is in this paper: “the correction of specified faults in a product”.

The second class is direct recycling. “An example of the second class is the returnable bottle as our first example; once the bottle is unfit for reuse and the bottle is cleaned and broken down to cullet at the glass-works and used to make more bottles. The most direct recycling occurs at the factory where the product is made, e.g. broken bottles fed back to the melting chamber”⁷. All conductor material in windings at end-of-life of an electrical machine may be recycled directly. Also, frame materials, shaft materials, transformer oil, conductors in windings and metals in magnetic cores may be recycled directly. Direct recycling has an intermediate availability in that both energy expenditure and process complexity may be required in getting the material back into use.

“The third class is indirect recycling. Continuing with our glass bottle, it is probable that it will end up in domestic refuse where it can be extracted by screening and separation. These bottles will be of different colors and varying degrees of cleanliness and are unsuitable for cullet use unless costly optical sorting is used”⁷. The bottles may be ground up and used for a skid-resistant road-surfacing material. Similarly, electrical insulation solids may end up as road-surfacing materials too. Indirect recycling is the lowest form of recycling. Normally, once processed in this phase, the material is no longer available for use except for landfill or incineration.

An electrical machine is the generic name for a product that converts mechanical energy to electrical energy, converts electrical energy to mechanical energy, or a product, the transformer, that transfers electrical energy from one circuit to another through inductively coupled conductors. Electrical machines are divided into three main categories based on how it converts energy. Generators convert mechanical energy to electrical energy. Motors convert electrical energy to mechanical energy. Transformers transfer electrical energy between coupled conductors.

A rotating electrical machine is the generic name for a rotating product that converts mechanical energy to electrical energy or converts electrical energy to mechanical energy.

“An electrical machine designed for recycling purposes is a machine easy to assemble and easy to disassemble. A component of an electrical machine designed for recycling purposes is a component easy to assemble and easy to disassemble too”^{1) (11}. Such electrical machine uses materials that do not age significantly on operation, or it uses materials that can be restored economically to un-aged specifications or it uses materials whose electrical, magnetic and mechanical characteristics qualify as non-aged or improve with aging; such electrical machine components may be used economically later on another machine. Electrical machines designed to be recycled have high reliability and availability, low initial and operating costs and low losses.

Industry tendencies on rotating electrical machines manufacturing will see more original-equipment-manufacturers outsourcing development of rotating machines components. We anticipate a world of cooperation where¹¹:

• Component developers as insulation and ferromagnetic sheet producers, coil and core manufacturers, shaft and frame builders will form partnerships or will establish strategic alliances to share designs and information for machine developments.

• Original-equipment-manufacturers will assume more the role of integrators.

• There will be competition based upon specialized knowledge and scale production (trade based upon specialization using comparative advantages).

• Low cost component developers will expand their operations to capture and internalize technology.

Ferromagnetic cores are generally the largest and heaviest components of an electrical machine. Soft magnetic cores for electrical machines require magnetic materials known as silicon-steel. But, few instances of recycling applications have been identified for silicon-steel besides direct recycling as steel. Steel is the most recycled metal, but when silicon-steel is recycled directly ferromagnetic properties are not recovered. Silicon acts as contaminant and only small amounts of silicon-steel can be added in each melting batch. Additional processing is needed to achieve magnetic properties.

Recycling options of ferromagnetic cores must be assessed evaluating aging mechanisms (aging coefficient). Silicon- steel ferromagnetic properties change little with use. This aging is associated with increases in core loss and magnetizing current. A positive value of the aging coefficient indicates an increase in losses or a decrease in permeability. However, insulating coating between sheets can age.

With proper processes and techniques, silicon-steel ferromagnetic cores from large transformers after end-of-life can be reused in new cores of, if these new cores comply with specifications. Also, if these new cores have same guarantees as they were manufactured with virgin silicon-steel, the new owner of the electrical machine will have all its needs satisfied. We do not suggest manufacturing ferromagnetic cores with old, lower quality silicon steel.

Since the introduction of amorphous core transformers for electric power distribution in 1991, these devices are now coming due for disposal. In response, the industry recycles the amorphous cores of the transformers into ferro-boron, and has been operating this process since 2009. The possibility of recycling the ferro-boron directly as amorphous alloy could make a sustainable closed loop, the production, operation, and disposal phases of distribution transformers cores¹³.

A compacted powdered iron core utilizes iron powder, which is first coated with a silicate and then over coated with a resin. The treated powder is compressed and then annealed. This results in a core component characterized by overall core losses as low as in conventional laminated cores. At the end life of an electrical machine using powdered iron cores, the iron powder might be recovered and reused as an already processed material¹³.

Permanent magnets can be reused too, but these special situations do not represent meaningful quantities, although these applications can have strategic meaning¹⁴.

The squirrel cage rotor is a component of an induction motor where the winding and the core cannot be disassembled easily. Reuse of the assembled squirrel cage rotor is a practical manner to handle recycling for this component.

Ideally, squirrel cage rotors should be exchanged with machines of same capacity and different manufacturers. To achieve this objective, stator and rotor cores must be of standard dimensions, i.e. length of active parts, diameters and air gaps. Dimensions of squirrel cages and the rotor cooling system should comply with standards too.

We present in Table 1, suggested standard air gaps for induction motors as a function of mechanical power output and synchronous speed for medium size, induction motors, totally enclosed construction, class B insulation (design B) and 60 hertz. These air gaps were determined using empirical equations and adjustments from experience¹⁵.

Table 1
Suggested standard air gaps induction motors (mm) (totally enclosed induction motors)

External mounting standard dimensions and preferred output values of medium size induction motors are defined in IEC and NEMA standards to assure interchangeability of machines^{16) (17) (18) (19}. We propose to add to these standard dimensions, three internal dimensions: the air gap, the rotor diameter and the ferromagnetic stator active length for specified induction motors and preferred output values. The air gap could be measured in millimeter and defined up to one tenth of a millimeter. For example, an air gap of 0.9 mm may be referred as gauge 9 air gap. Also, an air gap of 1.6 mm could be referred as gauge 16 air gap. The rotor diameter could be measured in millimeter too and defined up to one millimeter. For example, a rotor diameter of 254.0 mm will be referred as rotor diameter gauge 254. The ferromagnetic stator active length could be measured in millimeter too and defined up to one millimeter using same gauges. We present in Table 2, suggested standard diameters for squirrel cage rotors and in Table 3, suggested standard rotor ferromagnetic active lengths for same machines as described for Table 1^{15) (16) (17) (18) (19}.

We know, standard sizes (Tables 1, 2 and 3) do not consider voltage, starting torque requirements, special applications, specific KVA/HP or atmospheric requirements, but, we consider electrical machines should be manufactured with standard dimensions to be developed, and cost reductions are achieved.

Table 2
Suggested standard diameters squirrel cage rotors (mm) (totally enclosed induction motors, no cooling channels)

Table 3
Suggested effective lengths squirrel cage rotors (mm) (totally enclosed induction motors, no cooling channels)

Claw rotors are easy to disassemble and these rotors offer more flexibility to recycle than squirrel cage rotors. The rotor can use permanent magnets that can be reused too. The claw rotor could be recycled as a component in the same manner a squirrel cage rotor can be recycled and these electrical machines must use standard dimensions too (air gap, rotor diameter, active rotor length).

Small single phase motors illustrate the recycling problem presented by large numbers of electrical machines used by the consumer. The main consideration in this section is for the single-phase motor of fractional horse power capacity found in home laundry equipment like a home washing machine, drier or combination washer-drier^{3) (21}. Similar cases are found in small dc motors in cars manufactured today and in the future, the driving motor of an electrical car¹⁴. As all large scale operations, the financial result of the operation is the first consideration.

Small single phase motors of the kind discussed are found worldwide in about 500 million appliances with more than 50 million appliances at end-of-life yearly. There are also take-back appliances policies, both in the European Union and in China^{2) (21}. It is anticipated, soon, appliances will be collected at some locations distributed worldwide. Our consideration is to collect those single-phase motors and to recycle them. Again, motors should be standardized in power ratings, speed and dimension and a large operation for motors automatic disassemble and components reuse could be thought. Motor-frames and squirrel cage rotors could be reused and stator steel and copper could be recycled directly.

Our estimation of the mid-size induction motors installed base was about 300 million machines worldwide with about 20 million machines at end-of-life yearly. This group offers a case of a large-scale remanufacturing operation.

The remanufacturing of the squirrel cage rotors has been discussed already. To remanufacture the stator, we may have to consider the stator electromagnetic core and the frame as a single component to avoid disassembling the core.

* Corresponding author: Jesús Rafael Pacheco Pimentel e-mail: jpacheco@usb.ve