A maintenance engineer needs a large bushing — 200 mm outer diameter, 100 mm long — for a heavy conveyor roller. Standard finished bushings of this size do not exist; custom tooling for moulding one part is expensive; a solid steel bushing corrodes and transmits every impact to the bearing. The solution is a polyurethane round blank: a large-diameter cast billet from which the part is machined to the exact required geometry and fit. TIMOL factory produces round blanks up to 300 mm in diameter for machining large bushings, wheels, rollers, guides, and structural parts. This article covers the difference from standard rods, the comparison table with analogues, and how to order a round blank in Ukraine.
What a Polyurethane Round Blank Is and When It Is Used
A round blank (kruglyak) is a large-diameter polyurethane casting that serves as a source material for machining. Unlike standard rods produced in fixed sizes for small-part machining, round blanks are cast to specification: the factory produces the exact diameter and length for the required part with machining allowances.
The primary application of round blanks is large bushings, wheels, and rollers for heavy-duty equipment: mining conveyors, metallurgical handling equipment, heavy presses, and agricultural machines. Parts of this size cannot be machined from standard stock because neither polyurethane rods nor their analogues are available in large diameters. The round blank format allows one casting to produce a single large part or several medium parts of the same hardness and formulation.
A practical advantage of the round blank format over a finished cast part of the required dimensions is the ability to apply machining allowances and correct the geometry of the finished surface on the lathe. Complex profiles — internal bores to interference fits, flanges, grooves, tapers — are machined with the accuracy not achievable by casting alone. The result is a part that fits the seat precisely without additional adjustment. Detailed descriptions of products machined from round blanks are in the product catalogue.
Comparison of Polyurethane Round Blanks with Analogues
The table compiles reference data for materials used to machine large-diameter parts: polyurethane, capron, UHMW-PE, SBR rubber, and structural steel.
| Material | Abrasion DIN 53516, mm³ | Operating t, °C | Hardness | Tensile strength, MPa | Density, g/cm³ |
|---|---|---|---|---|---|
| Polyurethane TIMOL | 38-39 | -60…+100 | 85A-95A | 39-87 | 1.05-1.25 |
| Capron PA6/PA66 | 30-90 | -40…+100 | 75D - 85D | 60-85 | 1.13-1.15 |
| UHMW-PE | 15-30 | -200…+80 | 60D - 70D | 17-45 | 0.93-0.95 |
| SBR rubber | 100-200 | -40…+80 | 40A - 80A | 8-20 | 0.94-1.1 |
| Structural steel | n/a | -40…+500 | 120-250 HB | 370-700 | 7.7-7.9 |
The comparison shows the working niche of polyurethane: abrasion 4-5 times lower than rubber, elasticity several times higher than capron (5-15 % rebound) and UHMW-PE (5-10 %), and 6-7 times lighter than steel. UHMW-PE has even lower abrasion (15-30 mm³) but creeps under sustained compression load, so for structural bushings and guides operating under sustained load it loses its geometry over time. Capron is close on abrasion but absorbs moisture (up to 8 % by weight), which causes dimensional change in a wet environment. Rubber wears quickly and yields on tensile strength.
For dynamic applications — bushings under impact, rollers on abrasive material, damper elements — polyurethane round blanks deliver the best combination of parameters. For sliding guides in a dry environment, UHMW-PE or capron can be considered; the choice depends on the specific operating conditions.
Engineer’s tip: when ordering a round blank for a bushing, add at least 10-15 mm to the required outer diameter as a machining allowance, and 5-10 mm to the bore as well. The casting does not produce a perfect cylindrical surface and may have slight taper; the lathe operation produces the exact geometry. Do not machine to zero allowance in a single pass — leave 0.3-0.5 mm for a finishing pass to achieve the required surface quality and dimensional tolerance.
Machining Round Blanks: Practical Recommendations
Large-diameter polyurethane round blanks are machined on a lathe with standard tooling. The main difference from machining metal is the heat sensitivity: blunt tooling and high feed rates generate friction heat that locally softens the polyurethane and causes the machined surface to be oversized. Sharp tooling, moderate feed rate, and water-based cutting fluid or compressed air to remove heat from the contact zone eliminate this effect.
Centering the round blank in the lathe chuck requires attention: large-diameter blanks may have slight out-of-roundness from casting. Centre the blank before clamping and verify the run-out with a dial indicator. Use steady rests for long blanks to prevent deflection under the cutting force. Final finishing passes at low feed rate produce a surface quality sufficient for most fits without additional grinding. The machining process for seals and cuffs is described in more detail in the reference information section.
How to Order Polyurethane Round Blanks in Ukraine
To place an order, supply the required outer diameter, length, hardness grade, and describe the part to be machined from the blank. If you have a drawing of the finished part, the technologist will calculate the blank dimensions with the necessary machining allowances. If there is no drawing, describe the seat dimensions and operating conditions.
TIMOL factory produces round blanks using the free-casting process in closed moulds. Both single blanks for one-off part machining and batches for a production run are produced. The free-casting process does not require expensive press tooling, so even a non-standard large diameter is produced economically.
For consultation, blank dimension calculation, and ordering, contact TIMOL factory. Engineers will select the formulation, calculate the machining allowances, and arrange production and delivery throughout Ukraine.