The chattering /)henomelloll often occurrillg ill case oj extremely heav)1 cold rolling up to .94 0 0 total reduction has beell illvestiga ted at a Ihreestalld talldem mill. The resulls obtailled are as Jollows : (1) The chatterillg arises Jrom impaired lubricatioll Jar which illstability oj emulsions alld inadequate st"ength oj oil film are res/)ollsible. (2) Th e fluctuatiolls in strip thickness and lellsioll durillg the chalterillg correspolld to the second mode natural vibration(requellcy oj Ihe Toll aligllments. The chattering takes place when the tellsioll flu clllatioll Jrequenc)1 coinsides with the second mode natural./r•equellcy. (3) A theoretical analysis is made all Ih e basis oj NJalhieu's equatioll to predict the stability criterion oj a roll alignment under givell rolling conditiolls. I II order to make the rollillg stable withoul chattering. the stabili(y criterioll. C;C c > (J k jk)2 jll IIlUSt be Julfilled. w here C alld C c : coifficiellts ~(viscous dmll/)ing and critical dall/ping. J k: variatioll ~r rollillg stifflless, alld k : mill moduills combined with equivalent s/)rillg constant ~(stri/) being rolled. U) One oj the IIIOSt /Jractica ble alld ~ffective measure to meet th e above criterioll is the use oj the lubricallt with good lubrici(y. A lIew lubricant containing orgallo-metallic z inc compounds for extreme j)ressure additive is developed to successfully /Jrevent the chatterillg.

No abstract

The sludge produced from the pickling of stainless bands settles to the bottom of the pickling tank and becomes an impediment to the operation. In The neutralized sludge is loaded into a lugger bag and can be used as a raw material for steei making.

Iron oxides can be reduced in a scale by batch annealing treatment in a reducing atmosphere of 7 vol% H2+93 vol% N2 at 1123 K for hot-rolled coils of type430 stainless steel. The heating processes cause cracks, a Cr2O3 layer in the scale and a Cr depleted layer on the substrate. It is possible to produce a large number of cracks in the scale by employing a scale breaker. The ease of descaling is positively related to the amount of bending elongation. Similarly with shot blasting, descaling becomes easier as the projection energy of the shot blasting increases. The pickling solution penetrates the scale through cracks on the surface of the strip, and its acid dissolves the stainless steel coil and part of the scale. The scale peels from the stainless steel coil in island-like exfoliation until the scale has been removed from the entire surface of the stainless steel coil.

In the preliminary studies, the followings are verified:(1 ) As a method of analyzing hydrofluoric acid, the iron-acetylacetone complexdiscoloration absorbance method is adopted.(2) As a method of ana]yzing nitric acid, the method of subtracting the concentration of hydrofluoric acid from the total acid amounts obtained by neutralization titration is adopted. As a method of analyzing the iron content, the iron-salicylic acid complex absorbance method is adopted, By fu[ly automating the series of analytical processes described above, the following are achieved:(1 ) The work load of line operators can be reduced, making substantial labor saving possible.