An intermediate mill is the middle stand group of a bar, wire rod or section rolling line, placed between the roughing and finishing groups. The roughing stands hand it a reduced section, and it brings that section, pass by pass, to the size and shape the finishing stands expect. Its rolls have to keep a groove profile through a long campaign while still carrying real rolling loads, so intermediate mill rolls are chosen for a balance of wear resistance and toughness.
Vimco Rolls Private Limited makes four roll types for the intermediate stands of TMT bar and wire rod mills: SG iron pearlitic, SG iron acicular, ICDP and indefinite chilled. This guide shows where each one fits, how the two most common options differ, and what to check before a stand changes grade. Every grade and hardness figure below is taken from our product pages.
Key takeaways
- The intermediate group decides how accurately the stock arrives at the finishing stands. When a groove here wears out of shape, the error travels down the line.
- On TMT bar and wire rod mills, the published grades for these stands span 50 Shore C (SGP-52) to 75 Shore C (SGA-72 and Bainitic Chill). ICDP reads about 70 to 85 near the surface on our depth chart.
- SG iron acicular and ICDP are the pair to compare for these stands, since both also serve the finishing stands.
- SG iron pearlitic connects the roughing and intermediate groups. Of the four, it is the only type we also make for roughing stands.
- Hardness below the surface varies a great deal between the four. Ask for the depth chart and the scrap diameter before you compare offers.
Where the intermediate group sits in a rolling line
A long-product mill moves the stock through three groups of stands. The roughing stands make the heaviest reductions on the billet that leaves the reheating furnace. The intermediate group follows, and the finishing stands bring the product to its final size. The whole line, from furnace to cooling bed, is described in our guide to the steel rolling process.
When the stock reaches the intermediate group, its section is far smaller than it was in roughing, and it speeds up after every pass. Bar and wire rod lines usually pass it through alternating oval and round grooves at this stage. Many lines also set their stands alternately horizontal and vertical, which squeezes the bar along both axes and avoids twisting it between passes.
The number of intermediate stands varies from one rolling mill to another, and a mill that rolls many sizes may bypass some of them for certain products. The task of the group stays the same. It has to deliver a bar of steady size and shape, at a steady speed, to the first finishing stand. That stand takes only a light reduction, so it has little room to correct size variation before the bar has to meet its final tolerance.
Every stand on a continuous line works in tandem with the next, and the bar is now long enough to be gripped by several of them at once. Each mill stand therefore has to hold a rolling speed matched to its neighbours. When an oval or round groove wears, the cross-section leaving it grows. That changes the size of the bar and also upsets the speed balance with the following stand.
What the middle stands ask of a roll
Conditions in the intermediate group fall between the two ends of the mill. Three of them shape the choice of grade.
- The load is still real. Each pass makes a meaningful reduction, so the roll needs strength and enough toughness to avoid cracking or breaking, above all in the first stands of the group.
- The groove profile now matters. Every groove must deliver stock with the dimensional accuracy the next pass expects. Wear that changes an oval or a round alters every pass after it, so wear resistance counts for far more than it did in roughing.
- The groove heats and cools on every turn. Contact with the hot stock heats the groove, and the cooling water chills it again before the next contact. Over a campaign this repeated cycle can craze the groove surface with fine cracks, the damage called fire cracking. Grades differ in how well they resist it and in how much water they need.
Because no single condition dominates, the intermediate grades sit between our roughing grades and the HSS rolls of the finishing stands on the hardness scale. For what a Shore C figure does and does not tell you, see the roll hardness guide.
Roll types made for intermediate stands
The table gives each Vimco Rolls grade made for intermediate stands, with the other stands each type serves. A type that works in two groups lets a mill carry its experience with that material from one group into the next.
| Roll type | Grades (Shore C) | Structure | Other stands it serves |
|---|---|---|---|
| SG iron pearlitic | SGP-52 (50-55), SGP-57 (55-60), SGP-62 (60-65) | Nodular graphite and carbides in a pearlitic matrix | Roughing stands of TMT bar and wire rod mills; finishing stands of structural and strip mills |
| SG iron acicular | SGA-62 (60-65), SGA-67 (65-70), SGA-72 (70-75) | Nodular graphite and carbides in a bainitic matrix, alloyed with extra nickel and molybdenum | Finishing stands of TMT bar, wire rod, rail, structural and strip mills |
| ICDP | IC-III, IC-IV, IC-V; about 70 to 85 near the surface on our depth chart | Double poured: an alloyed iron shell, bainitic with flake graphite, over a grey or nodular iron core | Finishing stands of TMT bar, wire rod and structural mills, and of strip, sheet and flat mills |
| Indefinite chilled | ICCI-I (55-60), ICCI-II (60-65), ICCI-III (65-70), Bainitic Chill (70-75) | Static cast iron with flake graphite and a controlled hardness gradient | Finishing stands of TMT bar, wire rod and structural mills, and of strip, sheet and flat mills |
For TMT bar and wire rod mills these four make up our full intermediate range. HSS is kept for the finishing stands and adamite for the roughing stands, so neither appears in the middle group of these mills.
SG iron acicular or ICDP on a TMT bar or wire rod stand
Both types serve the intermediate stands and the finishing stands of TMT bar, wire rod and structural mills. That makes them the natural pair to compare in the middle of the line. Each reaches its working life by a different route.
| Point | SG iron acicular | ICDP |
|---|---|---|
| How it is made | A spheroidal graphite iron roll | Shell and core poured as two separate metals, using spin casting together with static casting |
| Working layer | Nodular graphite and carbides in a bainitic matrix; the name acicular refers to its needle-like structure | Hard alloyed iron shell; its matrix is bainitic and its flake graphite thins out toward the centre |
| Source of toughness | The bainitic matrix, alloyed with nickel and molybdenum | The core, made of grey or nodular iron, which is softer than the shell |
| Grades | SGA-62, SGA-67 and SGA-72, covering 60 to 75 Shore C | IC-III, IC-IV and IC-V; nickel and chromium go up from IC-III to IC-V |
| Hardness with depth, on our charts | Drops slowly, reaching roughly 47 to 57 Shore C at 90 mm | Stays high through the shell, then falls away between 40 and 50 mm, where the core begins |
| Operating note | Reaches its full life only with enough cooling water | Flake graphite in the shell conducts heat well and lengthens roll life |
Three points help settle the choice for a particular stand:
- How deep are the grooves, and how many millimetres come off at every redress? On an ICDP roll the groove bottom has to stay inside the hard shell for the roll's whole life, down to the scrap diameter. Set the groove depth plus the planned redressing against the shell depth. Our SG iron acicular chart shows hardness dropping slowly with depth, with no sharp step.
- Can the stand supply the cooling? Our SG iron acicular page states that these rolls need sufficient water cooling to reach their potential. Before a trial, check how much water reaches the roll and whether the sprays cover the whole groove.
- What do your own records say? Both types are also made for finishing stands. If your mill already runs one of them there, its tonnes per groove and redressing history are a useful starting point for the intermediate stands.
Our ICDP rolls page compares the two in one table, with grades and alloying. Measure any trial in tonnes per groove against the grade it replaces, and use our roll life guide to turn that figure into tonnes over the full life of the roll.
Where SG iron pearlitic fits
SG iron pearlitic is the one intermediate type that we also make for the roughing stands of TMT bar and wire rod mills. Its graphite is nodular, which gives it more strength than cast iron with flake graphite and helps it cope with thermal and mechanical stress. Our product page also describes its strong anti-accident properties and stable hardness across the working layer.
A mill that uses it in roughing can carry the same material into the first intermediate stands at a higher grade, for example SGP-52 or SGP-57 at the roughing end and SGP-62 further down the line. The published grades stop at 65 Shore C, so the later intermediate stands, where groove wear weighs more, can move to one of the harder types in the table above. On our chart its hardness loses roughly 10 to 12 Shore C between the surface and a depth of 90 mm.
Where indefinite chilled rolls fit
Our indefinite chilled rolls are static cast, and their hardness is graded in a controlled way through the working layer. The flake graphite in their matrix helps them stand up to fire cracking, spalling and wear, and they suit products where surface finish matters. ICDP takes its name from the same iron: it is an indefinite chilled shell, poured separately over a softer core.
Four grades run from ICCI-I at 55 to 60 Shore C up to Bainitic Chill at 70 to 75. That is the widest published band of the four intermediate types, so a mill can raise the hardness stand by stand without changing material. Like SG iron acicular, these rolls depend on adequate water cooling for their service life. Their chart shows a steady decline, of roughly 13 to 17 Shore C between the surface and 90 mm.
Depth hardness of the four intermediate grades
Intermediate grooves are redressed between campaigns. Each redress turns worn metal off the barrel, so the roll diameter falls campaign by campaign and later grooves are cut in metal that began well below the surface. Our published hardness-depth charts show how differently the four types behave as the diameter comes down.
| Roll type | At the surface | At 90 mm | Shape of the curve |
|---|---|---|---|
| SG iron pearlitic | 52-65 Shore C | 42-53 | A gentle decline of roughly 10 to 12 |
| SG iron acicular | 63-73 Shore C | 47-57 | Gentle at first, steeper past roughly 60 mm |
| Indefinite chilled | 55-75 Shore C across the four grades (published) | 47-62 | A steady decline of roughly 13 to 17 |
| ICDP | 70-85 | 31-36, in the core | High through the shell, then a sharp drop at about 40 to 50 mm |
Apart from the published indefinite chilled range, every figure in the table is read off a graph, so read them as approximate values. With your quotation, ask for the depth chart of the exact grade along with both diameters, new and scrap. On an ICDP roll, confirm where the scrap diameter falls against the shell depth.
Structural, section, rail and strip mills
Outside TMT bar and wire rod lines, the intermediate range changes with the mill.
- Structural and section mills. Their intermediate stands can take any of the four: SG iron pearlitic, SG iron acicular, ICDP or indefinite chilled. These mills can also run adamite throughout, from roughing through the intermediate group to finishing.
- Rail mills. SG iron acicular is made for both their intermediate and their finishing stands.
- Strip mills. SG iron pearlitic and SG iron acicular serve the intermediate stands. ICDP and indefinite chilled rolls are made for the finishing stands of strip, sheet and flat mills.
Our rolling mill rolls overview maps every roll type to its stands, from the first roughing stand to the finishing block.
When an intermediate roll comes out early
Look at why the last campaign ended before you change the grade. The table links the usual signs from intermediate stands to the first thing to check.
| Symptom | Likely reason | Where to look |
|---|---|---|
| The finishing stands struggle to hold size late in an intermediate campaign | An oval or round groove upstream has worn beyond what a roll gap adjustment can correct | Measure the worn groove at every roll change and compare it with the pass drawing; then consider moving that stand up one grade in the same family |
| Fire cracks: a fine crazed pattern on the groove surface | Repeated heating by the stock and quenching by the roll water | How much water reaches the roll and whether the sprays cover the groove, since SG iron acicular and indefinite chilled rolls both rely on it |
| On an ICDP roll, each redress lasts fewer tonnes than the one before | The groove is approaching the softer core | Shell depth, groove depth and scrap diameter against the depth chart |
| A roll cracks or breaks in the first intermediate stands | Load or impact higher than that grade's toughness allows | Stock temperature and pass load at that stand, and whether a tougher grade such as SG iron pearlitic suits it better |
What to send us for an intermediate stand
To recommend a grade, we need to know the stand and its history:
- Mill type, the steel grades and the product sizes you roll.
- Which intermediate stand it is, counted from the roughing end, and whether it is horizontal or vertical.
- The pass on that stand, such as oval or round, with the pass drawing where one exists.
- The roll drawing, showing the new and scrap diameters.
- The grade you run now, its tonnes per groove, and the reason its campaigns end.
- How the stand is cooled.
Our in-house lab tests hardness, internal soundness by ultrasonic testing, microstructure and chemistry. The quality page lists the equipment.
Frequently asked questions
What is an intermediate mill?
An intermediate mill sits between the roughing group and the finishing group of a hot rolling train. It reduces the section handed over by the roughing mill, usually through oval and round passes on bar and wire rod lines, and delivers stock of steady size to the finishing stands.
What roll grades suit the intermediate stands of a TMT bar mill?
We make four types for them: SG iron pearlitic (SGP-52 to SGP-62, 50 to 65 Shore C), SG iron acicular (SGA-62 to SGA-72, 60 to 75), ICDP (IC-III to IC-V) and indefinite chilled (ICCI-I to Bainitic Chill, 55 to 75). Wire rod mills use the same four.
Should I use ICDP or SG iron acicular rolls in intermediate stands?
Either can work there. ICDP has a hard shell on a softer core, so the groove and every redress have to stay within the shell. SG iron acicular needs sufficient water cooling. Send us the stand position, the pass and the reason its campaigns end, and we will advise on the grade.
Are HSS rolls used in intermediate stands?
Our HSS rolls are made for the finishing stands of TMT bar and wire rod mills, plus the slitting and dog-bone stands of rebar mills. We do not offer them for intermediate stands.
Is an intermediate roll in a bar mill the same as the intermediate roll of a cold mill?
They are different rolls. In a hot bar or wire rod mill, intermediate rolls are the grooved rolls of the middle stand group. In a six-high cold mill, the intermediate roll sits between the work roll and the backup roll. This guide covers the hot rolling stands.
Planning a grade change on an intermediate stand?
Vimco Rolls Pvt Ltd started operations in 1972 and makes its rolls at its own plant in Dera Bassi, Punjab. Tell us where the stand sits in the intermediate group and what is shortening its campaigns, and we will propose a grade to trial.
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