How a Railway Bogie Side Frame Is Made — The Complete Casting Process at an Indian Foundry

A CASNUB 22HS bogie side frame weighs approximately 850–900 kg. It is a single continuous alloy steel casting — not welded, not bolted — that connects two wheel axles, transfers the wagon’s payload to those axles, and maintains the geometric relationship of the bogie assembly over decades of service.

Making it correctly is not simple. Making it correctly and consistently — heat after heat, batch after batch — is the manufacturing challenge that separates good foundries from average ones.

This article walks through the complete manufacturing process for a CASNUB bogie side frame at LCPL’s Andal foundry — from scrap steel to dimensional inspection.

Step 1: Scrap Selection and Incoming Verification

The process starts before anything is melted. Railway bogie castings require alloy steel — specific chrome, molybdenum or other alloy additions that do not exist in random scrap. Scrap selection is the first quality control step.

At LCPL, incoming scrap is:

• Visually sorted by type — shredded steel, heavy melt, railway scrap, alloy returns
• Spectrometry-verified on a sampling basis using our in-house spectrometer
• Classified and stored separately by grade

Alloy-contaminated scrap that would throw off the intended heat chemistry is segregated. This is not universal practice in Indian foundries — it is a cost and process discipline decision. The consequence of skipping it is unpredictable heat chemistry and variable mechanical properties in the finished castings.

Step 2: Electric Arc Furnace Melting

LCPL’s 5-tonne EAF is charged with the pre-sorted scrap mix. The charge is calculated to hit the target steel chemistry after melting and refining.

The EAF operates in two phases:

Meltdown phase: The electric arc melts the scrap. Current draw is high and controllable; the furnace operator monitors temperature and visual state of the melt. Target tap temperature for railway alloy steel is approximately 1,640–1,680°C.

Refining phase: Once the charge is fully molten, the slag practice begins. Oxidising slag removes phosphorus from the melt — a chemistry critical point. The slag is poured off and a reducing slag is introduced to protect the steel and enable sulfur reduction. Alloying additions — ferro-chromium, ferro-molybdenum — are made during this phase to hit the target composition.

Final temperature adjustment and the spectrometry sample are taken in this phase. The spectrometry result confirms whether the chemistry is within specification before the heat is approved for tapping. If chemistry is outside the target range, corrections are made before tapping.

Step 3: Argon Purging and Ladle Refining

After tapping from the EAF into the ladle, argon gas is injected through a porous plug in the ladle floor. For a 5-tonne heat, argon purging duration is typically 8–12 minutes.

The visible effect is a boiling agitation on the melt surface — rising argon bubbles carrying dissolved hydrogen and nitrogen out of the steel, and floating inclusion particles to the slag layer.

Post-purging spectrometry confirms the final chemistry. If minor chemistry adjustments are needed, they are made in the ladle before the heat is approved for pouring.

This ladle refining step is what allows LCPL to consistently achieve low phosphorus, low sulphur, and low dissolved gas content in our bogie castings — not by hoping the charge was right, but by verifying and correcting before pouring.

Step 4: Pattern Making and No-Bake Moulding

The side frame casting requires a mould that accurately reproduces the RDSO drawing geometry — journal pocket dimensions, pedestal brace width, window openings, and the complex three-dimensional profile of the tension and compression members.

LCPL uses No-Bake chemically bonded sand moulding for all bogie components. The mould-making sequence:

1. The pattern (a precise replica of the desired casting, slightly oversized to account for shrinkage) is positioned in the mould box
2. Sand pre-mixed with resin binder and catalyst is packed around the pattern
3. The binder cures at room temperature over 20–40 minutes (depending on ambient temperature and binder formulation)
4. The pattern is withdrawn, leaving the mould cavity
5. Cores — internal sand forms that create hollow sections in the casting — are set in the mould
6. The mould halves are assembled and clamped for pouring

Critical dimensions of the mould cavity are checked with gauges before the cores are set. A mould found to be out of tolerance is reworked — not poured.

Step 5: Pouring

The ladle is transported to the moulding area. Pour temperature is monitored with an immersion thermocouple — too hot and the casting has excessive shrinkage and gas evolution; too cool and the steel freezes before completely filling the mould.

For a CASNUB side frame, the pour takes approximately 45–90 seconds. The gating system — the channels through which the steel flows from the pouring basin into the mould cavity — is designed to fill the mould progressively from the bottom, preventing turbulence that would cause oxide entrapment.

Risers — reservoirs of liquid steel positioned at heavy sections — feed the casting as it shrinks during solidification. A correctly designed and filled riser prevents internal shrinkage porosity in the heavy sections.

Step 6: Shakeout and Cleaning

After the casting has cooled sufficiently (typically 4–8 hours for a heavy bogie side frame), the mould is shaken out — the sand is separated from the casting and recovered for reclamation.

The casting at this stage has the gating system attached — runners, risers and pour basin. These are cut off using abrasive discs or gouging equipment. The cut surfaces are cleaned by grinding.

The casting then goes through shot blasting — high-velocity steel shot impacts remove residual sand, oxide scale and surface irregularities. After shot blasting, the casting surface is clean enough for visual inspection of the casting quality.

Step 7: Heat Treatment

The as-cast alloy steel side frame has the right chemistry but suboptimal microstructure — coarse dendrites, residual stresses, non-uniform alloy distribution.

Heat treatment corrects this:

Normalising: The casting is heated to 870–950°C (above the austenitising temperature), held for a calculated time based on section thickness, then air-cooled. This dissolves the as-cast dendritic structure and produces a uniform fine-grained austenite that transforms on cooling to a fine pearlitic microstructure.

Tempering (if quench and temper specification applies): After quenching (rapid cooling to produce martensite), the casting is tempered at 550–650°C to restore toughness while maintaining high strength.

The temperature uniformity of our heat treatment furnace is monitored by multiple thermocouples. The time-temperature cycle for each component type is recorded for traceability.

Step 8: Final Inspection

Spectrometry: Confirmation that the heat chemistry is within RDSO specification.

Mechanical testing: Test specimens (tensile bars and Charpy samples) cast from the same heat are machined and tested in LCPL’s in-house mechanical testing laboratory. UTS, yield strength, elongation, and Charpy impact are measured and recorded.

Dimensional inspection: Critical dimensions — journal pocket width, pedestal brace width, wheelbase (distance between journal pocket centres), bolster opening width — are measured against the RDSO drawing tolerances using calibrated gauges and fixtures.

Visual inspection: All accessible surfaces inspected for visible casting defects — cracks, cold shuts, non-fills, inclusions.

Only castings passing all four inspection stages are approved for despatch. The test certificates and dimensional inspection report travel with the casting to the customer.

FAQ — Bogie Side Frame Casting Process