Two machines do almost all of the cutting in a transformer core shop, and they are often confused because both take a coil of grain-oriented silicon steel and cut it. The difference is the direction of the cut. A slitting line cuts along the strip to produce narrower coils of the required widths. A cut-to-length line cuts across the strip to produce the finished laminations. One prepares the raw material; the other makes the parts.<\/p>\n
Silicon steel arrives from the mill as a master coil, typically around one metre wide. A core, however, is built from laminations of several different widths, one for each limb and yoke section. The slitting line unwinds the master coil, passes it between pairs of circular knives set to the required widths, and rewinds the resulting strips as separate narrower coils. A single pass can produce several strip widths at once, so a slitting programme is planned to use as much of the master coil width as possible and leave the least edge trim.<\/p>\n
The quality demands on a slitting line are edge quality and width accuracy. A rough or burred edge on the strip becomes a rough edge on every lamination cut from it, and a width error carries straight through to the core dimensions. On SREE’s SRZJ slitting lines<\/a> the knife arbors are hardened to HRC 50 to 59 with end runout held to 0.005 mm, which is what keeps the cut clean across the whole strip width. A line carries eleven knife pairs, enough for ten strips in one pass, from a minimum strip width of 40 mm, at line speeds of up to 120 m\/min and a width accuracy of \u00b10.1 mm.<\/p>\n The cut-to-length line takes one slit strip at a time and cuts it into laminations: it feeds the strip forward by the programmed length, punches the V-notch and any bolt holes, shears the ends at 45\u00b0 or 90\u00b0, and drops the finished piece onto a stacking table. The programme for one core lists every lamination shape and length, including the small length steps of a step-lap design. How a cut-to-length line works<\/a> goes through the stations one by one.<\/p>\n The quality demands here are different again: length and angle accuracy of the cut, burr height at the sheared edge, and repeatability from the first piece of a batch to the last. Speeds are higher than on a slitting line, up to 210 m\/min rated on a standard line, because the strip is narrower and the cuts are short.<\/p>\nWhat a cut-to-length line does<\/h2>\n
Side by side<\/h2>\n
| <\/th>\n | Slitting line<\/th>\n | Cut-to-length line<\/th>\n<\/tr>\n<\/thead>\n |
|---|---|---|
| Direction of cut<\/td>\n | Longitudinal, along the strip<\/td>\n | Transverse, across the strip<\/td>\n<\/tr>\n |
| Input<\/td>\n | Master coil, up to about one metre wide<\/td>\n | Slit strip coil of one width<\/td>\n<\/tr>\n |
| Output<\/td>\n | Several narrower coils<\/td>\n | Finished laminations, sorted by type<\/td>\n<\/tr>\n |
| Tooling<\/td>\n | Circular knife pairs on arbors<\/td>\n | Servo punches and a rotating mitre shear<\/td>\n<\/tr>\n |
| Key accuracy<\/td>\n | Strip width \u00b10.1 mm, edge quality<\/td>\n | Length \u00b10.2 mm per 2 m, angle \u00b10.02\u00b0, burr \u22640.02 mm<\/td>\n<\/tr>\n |
| Speed<\/td>\n | Up to 120 m\/min<\/td>\n | Up to 210 m\/min rated (240 m\/min peak on high-speed lines)<\/td>\n<\/tr>\n |
| Where it sits<\/td>\n | Between coil storage and strip storage<\/td>\n | Between strip storage and core stacking<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nDoes every core shop need both?<\/h2>\nNo. The question is whether you buy master coils or slit strip.<\/p>\n Buying master coils and slitting in-house gives you control over widths and lead time, lets you react to a new core design without waiting for a service centre, and usually lowers the material price per tonne. It costs a slitting line, floor space for coil and strip storage, and the planning effort to run good slitting programmes. It tends to make sense once monthly tonnage is high enough that the line runs regularly, or when the range of strip widths changes often.<\/p>\n Buying pre-slit strip from the mill or a service centre removes the slitting line and its storage from your floor. You pay for the service in the strip price and in lead time, and you depend on the supplier’s edge quality. Many distribution transformer plants start this way with a single cut-to-length line and add slitting later as volume grows.<\/p>\n What our installed base shows<\/b>Of the roughly 300 electrical steel machines SREE has delivered, cut-to-length lines outnumber slitting lines many times over. The usual sequence is a cut-to-length line first, running on purchased strip, with a slitting line added later when tonnage grows or when larger cores bring a wider variety of strip widths.<\/div>\n How the two lines connect<\/h2>\n |