LIST OF ASPECTS AND SUPERFICIAL DEFECTS

Summary

 

MINOR DEFECTS:

# Lines of Lüders

# Brands of cold rolling cylinders

# Stains or traces of degreasing or pickling

# Woody appearance (“wood grain”)

 

MAJOR DEFECTS:

# Lack of fusion

# Rusty tinplate

# Arc points

# Blows, bites – fractures

# Scratches or scratches

# Lamination cylinder brands

# Vibration

# Cracks in the edges

# Inclusions (black stripes – bubbles)

# Calamine

# Differential marking defect on tinplate

# Oil stains

# Yellow edges or yellow spots on the TFS.

 

 

DEFINITIONS, ORIGIN AND CONSEQUENCES
OF ASPECT AND SURFACE DEFECTS

These defects are detected by visual observation during unwinding.

 

MINOR DEFECTS:

– Lüders lines:

Lines more or less long, often perpendicular to the direction of rolling.

Origin : due to a number of reasons (edge ​​defects, variable thickness …), tensile stresses during cold rolling are transferred to the areas of weaker section.

– Cold rolling cylinder brands:

The marks are of diverse forms quite clean, matte or brilliant, repetitive and of a constant step.

Origin : deterioration of the working cylinders, due to the passage of a foreign body between the cylinders or to a break or to crushed folds.

– Stains or traces of degreasing or pickling

White spots, more or less visible after tinning, isolated or grouped, in various forms: in the form of stelae, round or flame-shaped spots, oval spots followed by a less contrasted trail.

Origin : defective washes after degreasing or pickling.

 – Woody aspects (wood grain)

Continuous defect that can affect a whole part of the band, is presented as an alternation of matte bands and bright bands, forming a pattern that recalls the appearance of wood.

Origin : this defect is manifested only after the merger. Ill-known, it seems as if the first cause is the structure of the deposited tin layer (shape and size of the crystals) and that the matte-bright alternation is in relation to the alternating phases of the heating current.

Some factors predispose to this defect:

– slow fusion speed

– weak concentration of Sn

– high density of tinning current

– low electrolyte temperature.

 

 

 

MAJOR DEFECTS: The quality of the coating of tin or chromium or of the steel base, is altered very well on a more extensive surface.

– Lack of fusion

The band presents, if it is not fused, a matt white appearance. It may be an important band length or a localized defect.

– Facets: adjacent fused and non-fused zones.

– Stains: located generally in the center of the band.

Origins : insufficient electric fusion power

–         it does not allow to follow the thickness variations (facets)

–         regulation at too low a level (spots)

Consequences : the tin-iron alloy layer is very weak, if not null. Lack of brilliance

– Rusty tinplate

The surface of the tinplate is covered by rust spots more or less important in size and color.

Origins : the tin layer is not continuous, it rusts in the pores.

Consequences : not suitable for varnishing, poor resistance to corrosion.

– Arc points

Black spots, small in size, scattered or aligned, surrounded or not by a white halo.

Origins : – Electrical arcs caused by bad contact between the band and any other object that is under electrical tension.

– Arcs of conductors: generally due to poor condition of the surface of the conductors (damaged or dirty)

– Anode arches: due to the contact ± franc between the band and an anode under tension, misguided (not placed in the guide, worn or broken). In this case, the arc points are aligned on a line.

Consequences: The important arc points can be accompanied by holes, rejection of tin, burnt tin, burned chrome, burned base steel.

– Blows-spills-fractures

Very localized deformations of the band in different ways.

Punctual: points.

Linear: intermittent points, scratches.

Varied: fractures, blows, marks.

Generally the tinning is correct, the marks can be repeated with a constant step.

Origins : The band may be hit by foreign bodies (tin grains, slags, screws …) stuck or embedded in a roller, by displacement of a coil on a dirty floor, gravel, nuts, etc …; due to the collision between coils: by sliding of the turns when a rolling coil is displaced or when it is crushed (points of heart).

 

Consequences: The appearance of the veneer is not perfect: in addition, if the veneer should be varnished, the bottom of the pit may not be perfectly covered.

– Scratches or scratches

Origins: They are due to the friction, either of a fixed object (guide, channel, anode), or on a roller that has one or several points of contact and that does not turn at the correct speed.

Consequences: Tinned scratches do not diminish the quality of the sheet except for appearance reasons; however, for sheets intended for deep sausages, the most important scratches will be avoided; scratches not tinned or badly tinned cause welding difficulties.

– Rolling cylinder marks

They are brands of different shapes, either in excess thickness, or in vacuum, repetitive with a constant step.

Origins: Folds of the band, breaks in the band, nicks in the working cylinders – excess thickness in the band: materials stuck on the cylinders – gaps in the band.

Consequences: Dangerous for folding, drawing, stuffing: drilling risk, leaky cans. Bad brilliance of the tin.

– Vibration

It is characterized by a significant variation of thickness in the direction of rolling. The thickness can range from half the nominal thickness to twice this thickness.

Origins : Bad lubrication between the cylinders and the belt.

Consequences : Thickness not conforming.

– Cracks in the edges

They are ± important notches in the edges.

Origins: Cracks will form in the laminate; should be:

– at thinning of edge of hot bands

– to a very important reduction of a “box”

– the poor condition of the shear blades to cut the edges

– To excessive pressure of the entrance tables of the mills.

– Inclusions (black stripes – bubbles)

Characterized by scratches // in the direction of the lamination ± wide, ± numerous, ± visible (very thin, black stripes, open bubbles).

Origins : In hot rolling, impurities (CO2, oxides, dirt, aluminum) prevent the bubbles from resolving.

– Calamina 

It is characterized by small superficial incrustations // in the direction of the laminate, with a grayish matt appearance.

Origins : Oxide hot rolled and embedded in the metal surface (incorrect heating, bad cleaning of the ingot).

– Defects of differential marking on tinplate

The thickness of the marking lines must be visible and less than 1 mm.

– Oil stains

Oil stains due to a malfunction of the oil device or to oil projections are harmful for the adherence of the varnish.

– Yellow edges or yellow spots in the TFS

These defects are due to the quality of the chrome plating electrolyte, or to rinsing faults.