How to Evaluate the Quality of Graphitized Petroleum Coke for Foundry

You evaluate the quality of graphitized petroleum coke (GPC) for foundry use by checking seven things together: fixed carbon, sulfur, nitrogen, ash, moisture, particle size consistency, and the COA with batch inspection. Fixed carbon alone does not tell you whether a GPC will perform in your furnace. As a foundry buyer, you need the chemistry to match your iron type and the supply to stay consistent from batch to batch. This guide shows you what each indicator means, how the indicators relate to each other, and how to read a COA before you place an order.

Foundry melting depends on predictable carbon adjustment. If you run an induction furnace with a high share of steel scrap, you rely on the carbon raiser to bring the melt to your target carbon. When the GPC varies from batch to batch, you may see:

• unstable carbon recovery from heat to heat
• inconsistent molten iron composition
• extra correction work and difficulty controlling casting quality

A lower price per tonne rarely offsets these costs. Judge GPC quality on the numbers that affect your melt, not on one headline figure. You can compare the points below against our listing for graphitized petroleum coke for foundry casting.

Why Fixed Carbon Is Important

Fixed carbon tells you how much usable carbon you get per kilogram. It drives carbon addition efficiency and, together with the other indicators, carbon recovery. A high fixed carbon GPC means you need less material for the same carbon addition.

Higher is not automatically better for your process, though. Fixed carbon is normally calculated by difference: 100% minus moisture, ash and volatile matter. That gives you a cross-check on any COA. If the reported fixed carbon, ash, volatile matter and moisture do not add up to roughly 100% on the same basis, ask the supplier to explain before you order.

What Fixed Carbon Level Should Foundry Buyers Check?

We do not give one absolute figure, because foundry processes differ. Iron type, furnace, scrap ratio and target carbon all change what you need. Confirm three things before you order:

• the carbon content your own process requires
• the supplier's written graphitized petroleum coke specification, including whether fixed carbon is reported on a dry basis
• the COA of the batch you will actually receive

Ask for a minimum value in the contract, not an "about" value.

Why Sulfur Control Matters

Foundries check sulfur early because it affects casting properties. In ductile iron, sulfur reacts with magnesium, so more sulfur means more magnesium is consumed during treatment and the risk of poor nodularity rises. In gray iron, sulfur influences graphite structure and has to stay inside your control range. Because you add the carbon raiser in quantity, its sulfur goes straight into the melt, and low sulfur graphitized petroleum coke reduces that contribution.

How to Compare Different Sulfur Grades

When you compare standard GPC with low sulfur GPC, compare on the same basis:

• the sulfur value stated on the COA, and the method used to test it
• the sulfur your addition rate actually brings in (carbon raiser added multiplied by its sulfur content)
• the sulfur limit of your own iron grade

Low sulfur products usually cost more. Whether the extra cost pays off depends on your iron type: a ductile iron foundry with tight sulfur limits usually benefits more than a gray iron foundry with a wider window. If sulfur control is critical for you, start with a low sulfur GPC and confirm the limit on the batch COA. Against calcined petroleum coke, GPC generally gives you lower sulfur, but check the numbers for each product.

Nitrogen is another impurity indicator, and it matters more for some foundry applications than others. Excess nitrogen can contribute to gas defects such as pinholes or fissures in certain castings, and the tolerance depends on your iron type and process. Graphitization removes much of the nitrogen from petroleum coke, which is one reason GPC is chosen over less processed carbon sources. Low nitrogen GPC is only useful if the COA reports it, and some COAs do not. If your process is nitrogen-sensitive, make a reported nitrogen value part of your specification.

Ash Content

Ash represents inorganic impurities such as oxides that do not burn off. In the furnace they end up in slag or dross, and every percent of ash is a percent that is not carbon. High or variable ash lowers carbon recovery and adds to slag handling. Read ash together with fixed carbon, because the two move in opposite directions.

Moisture Content

Moisture affects three things:

• Storage: damp material can cake and become harder to handle.
• Handling: wet GPC feeds unevenly and is harder to meter into the furnace.
• Actual carbon input: you pay for water by weight and get less carbon per kilogram.

Adding wet material to a hot melt can also cause splashing, so dryness is a safety point as well. Ask for moisture at shipment and check how the packing protects the material in transit.

Particle size affects melting efficiency, dissolution speed and handling method. Finer material dissolves faster but is more easily lost as dust. Coarser material loses less but dissolves more slowly. Common GPC particle sizes for foundry are 1-5 mm and 1-8 mm, and other sizes can be customized. Our listings also include 0-5 mm grades.

Two checks that many buyers skip:

• Size range and fines: ask for the allowed share below the lower size limit. High fines mean dust loss and unpredictable recovery.
• Consistency: compare the size distribution of several batches, not only the first shipment.

Match the size to your addition method, and read what affects the absorption rate of carburizer to see how size interacts with temperature, stirring and iron chemistry.

The COA is where quality claims become checkable, so it is the core of your purchase decision. Use the table below to read it item by item.

Beyond the numbers, check that the batch or lot number matches your shipment, that a test date and testing lab are stated, and that results come from a named method. Then request COAs from two or three past batches to see the spread. A COA with identical figures on every batch should make you ask whether it is really batch-specific.

Comparing only USD per metric tonne hides the cost of poor quality. When you evaluate a GPC supplier, compare these five points.

Product Consistency

Compare the spread in fixed carbon, sulfur and size across several past batches, not one best-case sample.

Quality Control

Ask how each batch is sampled and tested, and whether a retained sample is kept so you can resolve a dispute later.

Packing

Check bag type, labelling and moisture protection, and confirm whether jumbo bags or 25 kg bags suit your handling system.

Delivery Capability

Confirm lead time and loading arrangements in writing. Unstable delivery can force you to switch material mid-production, which is itself a quality risk.

Inspection Documents

Agree before the order whether you need third-party inspection, which COA format you accept, and which other documents you require.

Before a large order, ask for a sample and run it on several heats while you record carbon recovery. Compare the result with your current material, and use the charging methods in our guide on how to add carburizer to the furnace so the trial is fair.

Before ordering GPC, confirm each item below.

If you are still deciding between the two carbon additives, read GPC vs CPC: which carbon additive fits your furnace. To compare grades and sizes, browse our graphitized petroleum coke range or the wider carbon raiser category.

Send us your iron type, furnace, target carbon and particle size preference, and we can provide the current specification and a COA for you to review before you order. You can also email us directly at business@zaferroalloy.com.

Request Specification and COA