Becker, C. A.

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 The Knowledge Bank at The Ohio State University Ohio State Engineer   Title:  Merchant Mill Inspection Creators:  Becker, C. A. Issue Date:  Mar-1920 Publisher:  Ohio State University, College of Engineering Citation:  Ohio State Engineer, vol. 3, no. 2 (March 1920), 12, 22-23. URI:  http://hdl.handle.net/1811/34027  Appears in Collections: Ohio State Engineer: Volume 3, no. 2 (March, 1920)       12 The Ohio State EngineerMerchant Mill InspectionBy C. A. BECKER.I shall discuss in a brief manner the inspection ofthe product of merchant mills, also called bar mills,with which I have been somewhat associated in thepast.Before coming to the inspection itself, let me recallto your minds the processes which convert the rawore into the finished products. First, we find the ore,after being mined and transported by water or rail orboth to the blast furnace, being mixed with coke andlimestone and dumped into the huge throat of thefurnace, being changed during its downward courseinto the molten pig iron which is tapped at the bot-tom, completing the first stage in the making of steel.Then this molten pig iron is charged into the open-hearth furnace along with some steel scrap and lime-stone and in the course of about eight hours, aftermany chemical reactions have taken place which spacedoes not allow me to even touch upon, the furnace istapped and from it pours the liquid steel which iscarried by huge cranes, in the ladle into which it ran,to the teeming platform. The operation of teemingconsists in pouring, from a hole in the bottom of theladle, the steel into ingot molds. After sufficientcooling, the ingots are stripped, i. e., the molds arelifted off and the ingots are taken to the soaking pits.These pits are kept at a high temperature and theingots are heated to an even heat before being re-moved to take their trip through the rolls where theyare reduced to smaller and more easily usable sizes.The first mechanical operations in the reduction ofthe ingot are done in the blooming mills. Here theingot is rolled dowTn from a mass of metal maybe 20inches square and 6 feet high to say one 4 inchessquare and of quite a length. The products of theblooming mills are blooms and billets which supplythe wants of the merchant or bar mills.After the blooms and billets leave the bloomingmills they are chipped. Chipping consists in remov-ing from the surface of the product, by use of thechipping hammer, any surface laps or slivers which ifnot removed would appear in the finished product ofthe bar mill. With some grades of steel the bloomsand billets are pickled. Pickling consists merely ofplacing the steel in a vat of sulfuric acid solution todissolve off some of the surface oxides. The bloomsand billets after being thus treated are sent to the barmill in which they are to be rolled into rounds, flats,squares, etc.Every time an open-hearth furnace or electric fur-nace is tapped, the metal, which constitutes a heat, isgiven a heat number which follows the metal in anyparticular heat through all its various processes untilthe steel is rolled into its final form. All steel is notmade of the same composition so that heat numbersmust be accurately watched through every operation.The billets and blooms upon being received at thebar mill are used on the proper order, i. e., are rolledfor a certain customer whose specifications are statedon a mill order. The first operation in the bar millis the heating of the charge to a correct workingtemperature. After leaving the furnace the bloomsand billets are rolled to a size and shape as orderedon the mill order. The steel after leaving the last setof rolls is cooled and sheared into the proper length.After weighing and bundling, it is ready for loading.It does not leave the mill, however, until it is finallychecked by the inspection departments to the require-ments in the customer's order.The mill has its own inspectors to look over thefinal product and to pick the flaws and defects whichare to be expected in any product of a steel works.I shall enumerate a few of the defects found in theproduct of the merchant mills and explain their cause,if possible, as they are generally acceptetd today.1. Slivers.—If the metal is torn, we might say, inany part of the rolling operation, the surface of thispart thus torn will easily become oxidized at the hightemperature of rolling and cannot be made to reunitewith the body of the bar even with the aid of thegreat pressure exerted by the rolls. Slivers are some-times called laminations and are easily seen by theeye.2. Seams.—If a layer of iron oxide should in anyway interpose itself between any parts of a steelbar, the enclosing steel parts will have no attractionfor each other and consequently this condition pro-duces a weak steel. This state is brought about bythe improper manufacture of the steel.3. Pipes.—When a steel ingot cools it leaves moreor less of a cavity, usually in the top of the ingot,which as the ingot is rolled down stays with it as asource of weakness due to the oxidized surface of thecavity remaining in the center. The top part of theingot should be cropped off in the blooming mills. Itcan be seen as a brilliant spot in the center of thefinished bar.4. Laps.—Laps may be formed by improper roll-ing in which part of the metal is folded over anotherpart. This defect occurs along the length of the barin the direction of the axis of the bar. They differfrom seams in that seams are of short lengths.(Continued on page 22)22 The Ohio State EngineerMERCHANT MILL INSPECTION(Continued from page 12)5. Blow-holes.—Blow-holes are generally causedby insufficient removal of the oxygen in the steel.The oxygen combines with the carbon in the steel toform a gas which is imprisoned in the steel as it cools.This conditions weakens the steel and looks like apiece of Swiss cheese.6. Overheated Steel.—Over-heating the steel be-fore being rolled has a deteriorating effect on theproduct. This condition should not occur in a wellregulated furnace.7. Finned Bars.—Finns are caused by over-fillingthe passes in the rolls, the excess metal squeezing outbetween the rolls. Finned bars cannot be used inforgings, etc., until the finn is removed. In mill prac-tice the whole bar is generally scrapped and sent backto the open-hearth.9. Bars Out of Round.—If in the rolling of roundsthe difference between any two diameters is greaterthan the rolling tolerance, the bar is called out ofround. The tolerance, spoken of, means the allowablevariation from a true geometrical shape of the sizerequired. This tolerance is sometimes stated by thecustomer and at other times the tolerance is as setforth by the mill inspection department.10. Roll Marks.—The bars must be watched forroll marks. Passes wear out after a certain amountof usage and give a rough surface to the bar andsometimes roll it out of tolerance.11. Waviness.—A wavy effect sometimes occurs inrolling. This is especially noticed on light flats.12. Cambered Bars.—Cambered bars form a bowon the shuffle bars, i. e., the bars which shuffle thesteel from the cooling bed to the shear rolls. Thishappens mostly in the case of alloy steels and is duein great part to uneven heating in the heating fur-nace.I have mentioned a few common defects found inmill practice but they are by no means all which mayhappen. Many new defects are continually occuring,so that a good inspector must use, along with a knowl-edge of the further use to which the product will beput, a good share of common sense. He must weighin his own mind whether or not any defect will or willnot cause rejection by the customer, judged by thecustomer's uses for the steel. His first duty, however,is to see that the customer gets a suitable product.If at any time any of my readers should becomean inspector, along any line in fact, where one asso-ciates with men producing the product to be inspected,make it your first task to become friends of the men.An inspector who is well liked by the men will findhis work more easy, pleasant and efficient.After the bars are inspected on the mill, the in-spection department "pulls" tests on every heat andsize when required. This consists in placing the testpieces between two jaw like devices and exerting apull to see at what tension the piece will break. Othertests are made when thought advisable.Drillings are sometimes sent to the chemical labor-atory to be analyzed as a recheck on the compositionof the steel.Seams are generally detected by heating shortpieces, of the bars rolled, to a good working tempera-The Ohio State Engineer 23ture and then hammering them down under a drophammer. Any seams if present will become evidentby opening up. They may also be hammered cold butopen up more easily when hot. Seams may be seenwith the naked eye.The product is finally inspected in the car afterloading and before being sent out. The inspectionthus becomes quite thorough, as it must, since todaythe steel maker and roller must deliver the goods inorder to meet competition. The customer is becom-ing more particular as to the condition and quality ofthe steel he receives and so inspection is becomingmore and more critical to meet his demands.

Merchant Mill Inspection

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Merchant Mill Inspection

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