BACKGROUND OF THE INVENTION Amorphous magnetic metal alloy ribbon contianing iron, boron and silicon has been used as magnetic circuits in transformers and other electronic components. The magnetic circuit using amorphous magnetic metal alloy is a low loss material. A typical magnetic core loss in a magnetic circuit using amorphous magnetic metal alloy ribbon is as low as 0. 2 Watts/kg at 1. 4 Telsa at 50 Hz, whereas the magnetic core loss in a similar magnetic circuit using best cold rolled non-oriented stampings used in rotating electrical machines such as motors and generators is more than 2 watts/kg under same conditions.

Therefore use of amorphous magnetic ribbon in magnetic circuits of rotating electrical machinery will reduce the electrical loses and improve the efficiency of these machines. To use amorphous magnetic ribbon as a core <BR> <BR> material in rotating electrical machines require a method of producing rigid blocks of electrical lamination from the amorphous magnetic ribbon. The invention provides a method of producing such rigid blocks of electrical laminations from thin amorphous magnetic ribbon for making the magnetic core which can be used in rotating electrical machines.

BRIEF DESCRIPTION OF THE INVENTION Low loss laminated magnetic core produced by the method according to the invention uses amorphous metal alloy ribbon in rolls. One of the best amorphous metal alloy ribbon used widely is an amorphous metal alloy containing 80% iron, 11% boron and 9% silicon made by Honeywell Corporation U. S. A. This magnetic ribbon is available in thickness of the order of 25 micron. There may be a certain amount of variation in the thickness of the ribbons during production, which produce air gaps while making a wound core. It was found that coating this magnetic ribbon with a thin coating of a heat curing solvent based epoxy and cutting the ribbon by shearing into predetermined sizes and stacking the epoxy coated cut ribbon pieces under pressure followed by heat curing the epoxy and profile cutting to desired shapes by known methods produces low loss magnetic core material compared to the conventional core magnetic materials used as magnetic circuits in rotating electrical machines. The stacking reduces the effect due to the variation in the thickness of the amorphous magnetic alloy ribbon in the final product. The stacked and cured lamination obtained by binding the amorphous magnetic alloy ribbon material is found to have considerable reduction in core loses compared to the best available cold rolled non oriented laminations now used. The rigid block of laminated magnetic core material produced according to this method is cut by known methods to obtain laminated core of required profile.

DETAIL DESCRIPTION The amorphous magnetic metal alloy ribbon from a spool is coated with a solvent based heat curing epoxy and dried and spooled again. Preferably the amorphous magnetic metal alloy ribbon has a composition of 80% iron, 11% boron and 9% silicon and has a thickness of about 25 microns. Any solvent based heat curing epoxy may be used with the invention. Epoxy system comprising XD4447 resin and XD4448 hardener made by C1BA Specialty Chemicals (India) Ltd. are quite suitable. The ratio between resin and hardener may be used depending upon the type of resin used and time required for curing during the process. These are well known to person skilled in the art who uses epoxy for similar uses and therefore not further elaborated. The coating may be preferably done by doctor blading technic and an epoxy coating thickness of 1 to 2 microns is preferred on the amorphous magnetic ribbon. The epoxy is only allowed to dry during the initial heating step. This can be done by selecting the drying temperature and time of drying depending upon the type of epoxy used. Typically drying temperatures of less than 1509C is used with heat curing epoxy supplied by CIBA specialties Ltd. The dried epoxy coated ribbon pieces are stacked in a suitable fixture and pressed. The pressure applied will depend upon the stack thickness and other parameters of the magnetic material.

In a typical case a pressure of 3 to 4 kgm/sq cm was applied to obtain a 4mm to 20 mm thick laminated block. The laminated block is then cured by heating in an oven. The curing temperature will depend upon the type of epoxy used and the time taken for curing. Typically curing is carried out at a temperature of 120°C to 200°C. The cured laminated rigid blocks are cut to have the required profile suitable for using as the core for rotating electrical machines by using cutting machine such as a water jet cutting machine.

The magnetic core laminations obtained by this process have a reduction of core losses of almost 90% compared to the conventional cold rolled non oriented magnetic laminations when used in magnetic circuits of rotating electrical machines.