Hammer Grates | 10-150mm Apertures | ATF

Grate Bars: Product Sizing for Hammer Crushers

Grate bars (also called screens, discharge grates, or classifying liners) control the product size from hammer crushers by functioning as a classifying barrier that permits undersized material to pass through while retaining oversize particles for continued reduction by the hammer rotor. The three primary design parameters, aperture size, bar profile geometry, and open area percentage, collectively determine throughput capacity, product gradation curve, and energy consumption per ton of finished product. Aperture sizes range from 10 mm for fine grinding applications in hammer mills to 150 mm or larger for primary hammer crushers processing run-of-quarry feed. Open area percentages typically range from 40% to 70%, with higher open areas improving throughput but potentially allowing more oversize material into the product stream.

Grate bars experience a demanding combination of impact loading from direct hammer contact and abrasive wear from material passing through the apertures at high velocity. The wear mechanism varies by position within the grate assembly: bars directly in the hammer path experience severe impact requiring manganese steel grades (Mn14Cr2 or Mn18Cr2 per ASTM A128), while bars in lower positions see predominantly sliding abrasion where high-chrome white iron at 60-64 HRC or AR400/AR500 plate provides superior wear life. ATF manufactures grate bars for all major hammer crusher and hammer mill models with custom aperture sizing, and our engineering team can recommend optimal aperture configurations based on your target product gradation curve and feed material characteristics.