Small defects in a casting often start in the gating system. Sand, slag and dross carried in with the molten metal end up as inclusions, and a turbulent pour can trap gas. Many non-ferrous foundries tackle this with a simple part placed in the runner: a strainer core.
Sheet mica is one of the materials used for these strainers. This guide explains what mica strainer cores are, why foundries use them, and what to send Prime Natural Resources (PNR) when you want a quote.
What is a mica strainer core?
A mica strainer core is a piece of sheet mica punched with a pattern of holes. It is set into the sand mould across the path of the molten metal, usually in the runner or at the base of the sprue. Metal flows through the holes while the strainer helps hold back dross and loose material.
PNR's fabricated mica range lists strainer cores as sheet mica with 22 to 93 holes, used as strainers in brass, bronze and aluminium sand castings. PNR's product notes describe their job as helping to keep dross out of the casting.
Why foundries choose mica for strainers
Mica's natural properties suit a part that has to sit in hot metal for the length of a pour:
- Heat resistance. Natural mica is a mineral, not a polymer, so it does not melt at non-ferrous pouring conditions. PNR's published reference values give a maximum operating temperature of about 500–600 °C for muscovite and about 800–900 °C for phlogopite. Your foundry should confirm the right grade against its own alloy and pouring practice.
- Perfect cleavage and flatness. Mica splits into thin, flat, even sheets. That makes it easy to punch clean holes and to seat the strainer flat in the mould.
- Low moisture absorption. PNR's reference data lists moisture absorption as very low for both muscovite and phlogopite. Moisture in the mould is a common cause of gas defects, so a dry strainer material matters.
- Easy to handle. Mica strainers are thin and light, and they can be stocked in boxes and placed by hand.
For a side-by-side look at the two mica types, read muscovite vs phlogopite mica.
Where mica strainers fit in the product range
Strainer cores belong to PNR's fabricated mica: parts cut and punched to your drawing, size, shape and thickness. They are made from natural sheet mica, which starts as mica blocks and mica thins. PNR classifies pieces 2 to 7 mils thick as thins, and these are the raw material for fabricated mica.
If you buy other punched parts from us, such as mica washers or punched segments, you can combine them with strainer cores in one enquiry. The fabricated mica parts RFQ checklist covers the general points for any punched part.
What to specify when you ask for a quote
Strainers are made to your design, so the more complete your enquiry, the faster and more accurate the quote. Please include:
1. Alloy and application. Brass, bronze, aluminium or another alloy, and the type of casting. This helps us suggest muscovite or phlogopite.
2. Shape and outside size. Round, square or rectangular, with dimensions, or a drawing (PDF or DWG).
3. Hole pattern. Number of holes, hole diameter, spacing and the pattern layout. PNR's range runs from 22 to 93 holes. If you need something different, tell us.
4. Thickness. The sheet thickness you use now, and the tolerance you can accept.
5. Mica type and quality. Muscovite or phlogopite, and any visual quality requirement. If you are unsure, describe the current part and we will advise.
6. Quantity. Monthly or annual usage, and the size of the first order.
7. Samples. If you have a strainer you already use, a photo or a physical sample is the quickest way to match it.
8. Packing and destination. Delivery port or city, and any packing preference.
Packing and shipping
PNR normally ships processed and fabricated mica in cardboard or wooden boxes. Our standard box is 22 × 16 × 8 inches with 50 kg net. Sea shipments go from Kolkata Port. Urgent orders and samples can go by air cargo or courier, including DHL, FedEx, UPS and TNT. See packaging and shipment for details.
Testing before you switch
If you are moving to mica strainers from another material, or changing supplier, run a trial batch first. Check how the strainer seats in your mould, how the metal flows through it at your pouring temperature, and whether inclusion levels improve. Once a design works, keep the drawing and the agreed specification on file so that every repeat order matches.
Get a quote for mica strainer cores
PNR supplies natural mica and fabricated mica parts from Jhumri Telaiya, Koderma, in India's mica belt. Send us your drawing or sample details, alloy and quantity, and our team will come back with options.
Email: mica@pnrmica.in · Phone/WhatsApp: +91 82941 54582 · or use our contact page.
Technical values in this article come from PNR's published reference information. Confirm the finished-part specification with PNR before ordering.