Every cut-to-length line is sold with a speed in metres per minute, and buyers naturally compare lines on it. But nobody buys laminations by the metre. What a core shop needs to know is how many pieces the line makes in an hour, and how many tonnes that is in a month, for its own core designs. The two are related to strip speed, but not by a single multiplication. This article gives the method we use to estimate output for a proposal, with the assumptions stated so that you can put your own numbers in.<\/p>\n
High-speed lines in particular quote more than one speed, and the differences are real. On SREE high-speed lines: peak speed is 240 m\/min, the highest speed the drives reach, usable only on long pieces; rated speed is 210 m\/min, the continuous design speed; recommended working speed is 120 to 180 m\/min, where the line runs on typical lamination lengths, because a short piece leaves the flying stations little strip length in which to accelerate, cut and return. Standard lines quote a rated feed speed of up to 210 m\/min, but they stop for every cut, so the average over a shift is lower again.<\/p>\n
Output estimates should start from working speed. Peak speed is a drive specification, not a production figure.<\/p>\n
On a continuous-feed (high-speed) line, the theoretical piece rate is simply strip speed divided by average lamination length:<\/p>\n
pieces per minute = working speed (m\/min) \u00f7 average piece length (m)<\/i><\/p>\n
On a step-feed (standard) line, each piece costs a feed movement plus a stop for punching and shearing. A reasonable estimate is:<\/p>\n
seconds per piece = piece length (m) \u00f7 average feed speed (m\/s) + stop time per cut (s)<\/i><\/p>\n
where the average feed speed over a short move is well below the rated speed because the strip accelerates and decelerates, and the stop time covers the punch and shear cycle. Both figures depend on the class and configuration; we give them per line in a proposal.<\/p>\n
No line cuts for sixty minutes in every hour. Coil changes, programme changes, strip threading, stacking-table changes, first-piece checks and blade maintenance all take time. For planning we use a utilisation of 55 to 70 percent depending on how automated the line is and how often the core type changes; a line with several decoiler heads and an automated sorting end sits at the top of that range, a single-head line with manual table changes at the bottom.<\/p>\n
The mass of one lamination is its volume times the density of silicon steel, about 7.65 g\/cm\u00b3:<\/p>\n
mass per piece (kg) = length (m) \u00d7 width (m) \u00d7 thickness (mm) \u00d7 7.65<\/i><\/p>\n
A lamination 1.0 m long, 300 mm wide and 0.27 mm thick weighs about 0.62 kg. The same piece in 0.20 mm material weighs 0.46 kg, which is why moving to thin steel raises the piece count for the same tonnage; see processing thin CRGO<\/a>.<\/p>\n The numbers below are illustrative assumptions for the method, not a guaranteed specification for any line. For a firm figure we run the calculation on your drawings.<\/p>\nA worked example<\/h2>\n
| <\/th>\n | Standard line (step feed)<\/th>\n | High-speed line (continuous)<\/th>\n<\/tr>\n<\/thead>\n |
|---|---|---|
| Average lamination<\/td>\n | 1.0 m long, 300 mm wide, 0.27 mm thick, 0.62 kg<\/td>\n<\/tr>\n | |
| Assumed rate while cutting<\/td>\n | about 1.1 s per piece \u2192 about 55 pieces\/min<\/td>\n | 150 m\/min \u00f7 1.0 m \u2192 150 pieces\/min<\/td>\n<\/tr>\n |
| Theoretical pieces per hour<\/td>\n | about 3,300<\/td>\n | about 9,000<\/td>\n<\/tr>\n |
| Utilisation<\/td>\n | 60 %<\/td>\n | 60 %<\/td>\n<\/tr>\n |
| Pieces per hour, planned<\/td>\n | about 2,000<\/td>\n | about 5,400<\/td>\n<\/tr>\n |
| Tonnes per 8-hour shift<\/td>\n | about 10 t<\/td>\n | about 27 t<\/td>\n<\/tr>\n |
| Tonnes per month, 22 shifts<\/td>\n | about 220 t<\/td>\n | about 590 t<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n |