Rolling Mill Housing Castings: Grade, UT Scope, and What Buyers Often Get Wrong

Specify a mill housing by stand type, roll separating force, and UT acceptance level — not by "cast steel". Use carbon cast steel (ZG270-500, GB/T 11352) for finishing and light section stands, manganese cast steel (ZG40Mn) for high-load roughing stands, and Cr-Mo cast steel (ZG35CrMo / ZG42CrMo) where fatigue strength matters. The housing that lasts is the one whose soundness and window geometry were specified before the pattern was made.

What a Rolling Mill Housing Does — and Why It Fails

The housing is the closed frame that carries the roll separating force and holds the roll gap. It is one of the heaviest single castings in a rolling line, with thick-to-thin section transitions at the window corners and the feet. Tiegu supplies rolling mill housing castings to steel mills and rolling-equipment builders worldwide, matching each order to a foundry that casts, heat-treats, and proof-machines the housing against your mill drawing before export.

They fail in predictable ways: shrinkage porosity in the heavy sections around the window and feet when the risering is not matched to the section modulus; window distortion and non-parallel faces that make roll change and pass alignment difficult; cracking at corners from residual stress after a hurried heat treatment; and rejections found only at final machining, weeks into the order. None of these show up in a plain "cast steel housing" purchase order.

Which Grade Should You Specify?

Match the grade to the stand and the load it carries. Roughing stands take the highest separating force; finishing stands are lighter but need dimensional stability.

Not sure which grade and UT level your stand needs? Contact us at tieguexport.com →

What We Verify Before Shipment

• Chemistry and mechanicals: we check C, Mn, Si, and any Cr/Mo addition against the order on the material certificate (MTC), together with tensile, yield, and elongation from the test coupon — a grade label alone does not prove the housing can take the rolling load.

• Soundness in heavy sections: ultrasonic testing per EN 12680-1 at the window corners, feet, and thick flanges, at an acceptance level written into the PO. Housings are ordered with an agreed NDT scope, not with "UT if required".

• Window geometry: window width, height, corner radii, and face parallelism are measured against the drawing — this decides whether the roll assembly fits and the pass line stays true, and it is checked to the agreed ISO 8062 tolerance class.

• Machining allowance and weld repair: machining allowance, datum faces, and the foundry's weld-repair policy are agreed up front, and repair records are supplied. Unreported weld repair on a load-bearing section is a rejection item.

Common Specifying Mistakes

• Writing "cast steel housing" with no UT acceptance level — porosity in a 200 mm section is found at final machining, not at the foundry gate.

• Treating the window as a casting-tolerance feature — window parallelism and machined faces must be a machining requirement, not a casting-tolerance hope.

• Cutting the heat treatment short to save time — residual stress releases in service, and the housing loses its geometry.

• Not agreeing the weld-repair policy — hidden repairs on load-bearing sections are the most common late surprise.

Specification Checklist

• [ ] Stand type, separating force, and duty cycle identified

• [ ] Grade chosen (ZG270-500 / ZG40Mn / ZG35CrMo-ZG42CrMo)

• [ ] Chemistry and mechanical properties required on the MTC

• [ ] UT acceptance level agreed (EN 12680-1) for window, feet, and thick flanges

• [ ] Window dimensions and parallelism specified as machined features

• [ ] Machining allowance, datums, and weld-repair policy written into the PO

FAQ

1. How much lead time should I plan for a mill housing?

Typically 16–24 weeks: pattern, moulding of a 10–40 t casting, heat treatment, rough machining, UT, and export packing — plus first-piece qualification on a new pattern. Send the mill drawing and stand data early, and submit a clear RFQ so the foundry can size risers and the UT plan before quoting.

2. Can a housing be repaired if UT finds indications?

It depends where. An indication in a thick, non-critical section can be excavated and repaired to an agreed welding procedure with records; an indication across a window corner or a machined fit face usually means rejection and recast. Agree the repair policy before the order — buyers who choose a supplier on price alone often learn the policy after the casting is made.

3. How do I know the window will fit the roll assembly?

Specify the window as a machined requirement with a stated tolerance, and ask for a dimensional report including parallelism to the roll axis. A first-article inspection on the first housing catches window and face deviations before the rest of the order is cast.

Tiegu is a China-based casting supplier serving international buyers through a vetted network of qualified Chinese foundries. We supply castings under a single commercial contract, managing supplier selection, technical confirmation, quality inspection, and export delivery from order to shipment.

Talk to Tiegu about your mill housings →