Patent Description:
The manufacture of electric items utilises insulating resins and varnishes to e.g. improve the electrical, mechanical and heating performance of the items, and to reduce noise emissions and corrosion.

In most cases, the items are impregnated with a resin or varnish by methods including: brushing, spraying, dipping, (vacuum dipping and vacuum and pressure dipping), trickling and rolling. The technique selected depends on the item type and properties sought.

The impregnation process fills voids in the items with a liquid resin or varnish which is transformed into a solid after a chemical and physical reaction known as polymerisation.

The resins and varnishes most typically used include, but are not limited to, unsaturated polyesters (imides) with vinyl toluene, styrene, diallyl phthalate, acrylates and styrene's. Other resins include alkyl, phenolic, and epoxy resins in, or absent of, solvents and with or without catalysts.

The insulating resins and varnishes are selected based on the properties sought and other factors including: ease of use, polymerization speed and storage stability.

It is also desirable to address the environmental impact of the use of these resins and varnishes which are typically applied with organic solvents and use energy costly processing techniques.

It is an object of the present invention to develop more environmentally friendly resins for impregnating electrical items and improved systems and methodology for treating such items.

In accordance with a first aspect of the present invention there is provided a latent curable, single component, epoxy resin comprising, by weight:.

Preferably the aliphatic polyamine is a modified polyamine.

The aliphatic polyamine may be modified, by any means known in the art including, but not limited to: polyethylene polyamine adducts with nitriles, alkylene oxides, aldehydes, and ketones, as well as mono and di-epoxides.

Examples of such modified polyamines are disclosed in<NPL>, Incorporated by reference, and the <NPL>.

In accordance with a second aspect of the present invention there is provided an item of electrical equipment comprising a component which has been bonded to another component, coated, or impregnated with a resin, which is the catalysed reaction product of the epoxy resin of the first aspect of the present invention and has an average molecular weight of less than <NUM>.

Preferably the epoxy resin, when cured, has the following properties:.

The item of electrical equipment includes two types of machines: rotary and static machines, with or without additional components, such as, for example, permanent magnets, shafts, housings, and commutators.

Rotary machines include, but are not limited to: a motor comprising a stator winding and rotor, generator or alternator, whereas static machines include, but are not limited to, a static electrical winding, transformer, reactor, choke coil or inductor.

The item will typically comprise a component to be insulated, such as a conductive winding.

In the most favoured embodiment the item is totally impregnated with the resin.

These items are made into products, such as, industrial motors, traction motors, electric vehicles, automobiles, home appliances or power tools.

According to a third aspect of the present invention there is provided a system for producing an item of electrical equipment as per the second aspect of the invention comprising:.

Preferably the system comprises a plurality of ovens that items pass through sequentially to cure the resin, and the temperature of each oven increases as the item passes through the sequence, to optimise the curing process.

Thus, the system further comprises an item handling means for conveying the items within the system, including between the plurality of ovens. The item handling means may comprise, for example, robotized manipulators, conveyors and sensors.

Preferably, but not essentially, the first heating chamber is heated by magnetic induction. In a particularly favoured embodiment, a multiple induction is used to reduce hysteresis of the transfer of heat from the surfaces closer to the inductor to the rest of the item. Magnetic induction is fast, cheap and efficient and obviates a requirement for thermal insulation.

In a favoured and simplified system, the tank for the resin is an, as supplied, container (e.g. metal drum, can or cartridge) of resin which is linked to the system which may form an arm of an item manufacturing or assembly line. This can be used directly or more preferably feeds a secondary tank where lower volumes or given doses of the resin may be thermally and physically controlled.

At present many items are removed from a manufacturing assembly line and taken for resin treatment elsewhere because the process is slow and "dirty".

The system of the third aspect of the invention and the associated methodology of the fourth aspect, described hereafter, overcome these problems and provide a relatively fast and "clean" process which does not have the large capital costs and associated high energy running costs of current processing regimes.

Most preferably the system immerses items in the resin and removes excess resin quickly and efficiently providing better item finishing. The system achieves this by incorporating a centrifuge in the immersion chamber which can reach high speeds in short times to displace excess resin.

The electrically insulating resins, such as those of the first aspect of the invention, have viscosities at <NUM>□D (typically of between <NUM> and <NUM> poise) which, on first appearance would leave a person skilled in the art thinking they would be unsuitable. However, on heating they become more mobile, such that at <NUM>□D they have a viscosity of between <NUM> and <NUM> poise. Under negative pressure e.g. <NUM> Bar (<NUM>-<NUM>) they can impregnate the voids in and around e.g. copper windings quickly, and excess resin can be easily displaced by for example using centrifugation before the resin is gelled.

The process also allows for accurate control of the amount of resin deposited, since with automation consistency can be achieved.

Preferably, but not essentially, the second heating chamber is heated by magnetic induction. This chamber functions to gel the resin.

Once gelled, the item is transferred to an oven or series of ovens where it is held for a given time at a given temperature until it is fully cured. This is preferably an automated process controlled by computer but may be done manually.

Other component elements of the system include a cooling chamber, preferably together with an air compressor, air cooler and vacuum pump.

According to a fourth aspect of the present invention there is provided method of treating an item of electrical equipment comprising a component which requires an electrically insulating resin to be applied, comprising the steps of:.

Preferably between steps:
ii) and iii) excess resin is removed.

Most preferably the excess resin is removed by a centrifugation step.

The method may apply the resin by one of: impregnation, brushing, spraying, dipping, rolling and / or trickling.

Where the method applies the resin by dipping this may be vacuum or vacuum and pressure dipping.

Most preferably the method applies the resin by impregnation, most preferably under a vacuum.

This involves submerging the item in the resin and forcing the resin into voids under vacuum.

After impregnation the item is removed (or the impregnation chamber emptied) and excess resin removed, most preferably using a centrifugal force.

Where the process utilises the apparatus or system of the third aspect of the invention the preferred method comprises the steps of:.

Preferably in
v) the centrifuge operates at a speed of between <NUM> and <NUM> rpm.

Preferably the vacuum pump operates at about <NUM> Bar (<NUM>-<NUM>).

Whilst the system may employ a variety of component parts of varying designs it has been found advantageous to utilise a centrifuge and oven having the following features.

Preferably the centrifuge has a double chamber such that moving parts are not in contact with the resin. This increases the durability and stability of the process. To ensure a compact design, and both quick fill and quick emptying, it is preferred that the resin inlet and outlet tubes are substantially semi-circular in cross section maximising the space within the impregnating chamber and e.g. the item being impregnated.

Preferably the ovens comprise an entrance and exit through which e.g. a robotized manipulator introduces and removes an item to or from the oven. Movement may be in both the longitudinal and vertical (up-down) direction. The entrance and exit apertures are most preferably opened and closed by way of pneumatic gates which ensure effective temperature management of the oven. The interior walls of the oven are covered by stainless steel and the oven is insulated with e.g. rockwool. The ovens include temperature sensors for temperature management and air circulation means, such as a centrifugal fan.

The system and method giving rise to novel items (on a size for size basis, based on e.g. the processing of an electric motor stator winding of size <NUM> x 100x <NUM> and a weight (with copper winding) of <NUM>) have numerous benefits over the existing systems and methods used to provide items treated with different resins including:.

A typical latent curable, single component, epoxy resin (<NUM>) of the invention is provided in Example <NUM> below:.

A resin as per Example <NUM> is used to electrically insulate an item (<NUM>) as for example, illustrated in <FIG>. The item is a rotor or stator comprising a component (<NUM>), in this case a copper winding (<NUM>), that requires to be insulated by treatment with the resin (<NUM>).

Referring to <FIG> the system/ apparatus (<NUM>) for producing an item of electrical equipment (<NUM>) comprises:.

The cooling chamber further comprises an air compressor (<NUM>), air cooler (<NUM>) and vacuum pump (<NUM>). It may comprise a "fountain" contact mold with the circulation of a cold fluid.

The centrifuge (<NUM>), within the impregnation chamber (<NUM>), is illustrated in more detail in <FIG>, however before describing it in more detail, the process of the invention is described with reference to <FIG>.

In general, the process comprises the steps of:.

However, as illustrated across <FIG> and <FIG> it comprises the steps of.

The infusion chamber (<NUM>) with centrifuge (<NUM>) is illustrated in more detail in <FIG> where it is shown connected to resin tank (<NUM>) and with an item (<NUM>) held suspended, in an upright position along a rotor (<NUM>) axis (X-X), about which the item is spun. Connecting tubes (138a) facilitate filling (<NUM>) and emptying (<NUM>) of resin to and from the resin tank (<NUM>) and a separate tube (138b) leads to the vacuum pump (<NUM>). A large motor (<NUM>) drives the centrifuge and is located in a chamber (<NUM>) below the infusion chamber to provide stability.

Examples of items processed using the resins, system and methodology are further illustrated in Examples <NUM> to <NUM> below.

The example given describes the impregnation of an electric motor stator winding. The stator, and associated winding, is of dimensions: internal diameter <NUM>, external diameter <NUM>, height <NUM>. It has a weight, with the copper winding, of <NUM>.

The item is processed in a system as described with reference to <FIG>.

The stator is pre-heated using magnetic induction. A localised magnetic field with a specific intensity and frequency) is applied to the stator. Induction also causes the heat to be transferred to the winding which is manufactured using materials with good heat conduction properties.

The resin is heated in its supply container (<NUM>), weight <NUM>. A heated strip maintains the resin at about <NUM> to ensure greater viscosity and optimum impregnation, and a mixing lid is used to keep the temperature uniform.

Impregnation occurs under vacuum to ensure any voids are completely filled. Excess resin is removed using centrifugal force (<NUM>). The impregnation chamber (<NUM>) is made of stainless steel and the centrifuge can spin to a rpm of <NUM>. The dimensions are sized in accordance with the item to be processed. A <NUM> Bbar (<NUM>-<NUM>). (residual) vacuum pump (<NUM>) is connected to the impregnation/centrifuge chamber.

Magnetic induction is used to heat the item to the gelling temperature, which is at leat about <NUM> □C and up to about <NUM>□C. This may take about <NUM> minute to ensure initiation of polymerisation. The item is then transferred to the curing ovens (<NUM>) where the item is processed for given times at constant temperatures which increase as the item is moved through the system.

The stator is preferably cooled by surface contact with a profiled mould, using liquids at varying pressure and temperature. A vacuum (<NUM>) process is used to remove condensate produced by low temperatures.

The system steps are performed in a fully automated manner without the need for an operator or intervention alongside, or linked to, a production line.

Illustrative cycle run times are indicated below:.

This illustrative impregnation process did not include cooling which requires a further, approximately <NUM> minutes.

The resin deposited on the component was about <NUM> grams and the process used about 500W, with cooling.

Whilst impregnation and centrifugation are favoured for the application of the resin, there are applications where this is not possible, as set out in Examples <NUM> to <NUM> below:.

Very often the rotors on electric machinery have parts which do not require impregnation, for example shafts, contact manifolds and bearing seats, etc. For such items, a total impregnation technique cannot be used, and neither can the vacuum technique. Therefore, the trickling or rolling technique with the component in rotation must be used. Centrifugation is not required. The advantages remain the same.

The system can be used to secure together sheets at the pack height required and if necessary attach permanent magnets at the same time. This procedure is ideal for automotive applications where complex profiles make it almost impossible, as well as being shunned by designers, to use traditional securing systems. Furthermore, this technology eliminates the need for insulated sheeting because insulation is applied during the securing and impregnation processes.

Claim 1:
A latent curable, single component, epoxy resin (<NUM>) comprising, by weight:
i) <NUM> - <NUM> % of epichlorohydrin and bisphenol F;
ii) <NUM> - <NUM>% of epichlorohydrin and bisphenol A; and
iii) <NUM> - <NUM>% of a highly reactive catalyst, which is an encapsulated aliphatic polyamine, which cures above <NUM>
and in which the single component epoxy resin has a cure temperature of at least <NUM> to <NUM>.