A Spare-Parts List for a Grate: What Fails First and How to Size the Order

A spare-parts stock is not about covering everything; it is about having the right items before they are needed. What fails first on a grate follows from how each part carries load and from the temperature it sits in, not from what it costs.

1. Four load groups, four different failure patterns

Only four groups of parts actually move on a grate:

• Hinged: pins, half-round bolts, square-head bolts, tying the bars into a chain or a row
• Rolling: support rollers and wheels, spreading the weight of the grate surface onto the rails
• Guiding: front wheels, rear guide devices, rails, holding the direction of travel
• Sealing: side seals and side liners, blocking bypass air at both flanks

The failure patterns differ. Hinged parts work loose and wear under thermal cycling, showing up as pins drifting and bars stepping out of line. Once rolling parts wear, our spare-parts pages put it plainly: the grate tends to travel poorly or run off to one side. Wear in guiding parts amplifies any misalignment directly. Seals thinning out let air bypass at both flanks, excess air rises and slagging follows. For why the rolling parts stay clear of dust, see the article on the roller support structure; for how the bars themselves fail, see the four failure modes.

2. The most expensive parts are usually not the ones to stock first

Ordering by price gets the list wrong. Cross beams and chain shafts carry the highest unit price, but they normally outlast seals and rolling parts. What gets replaced often is the cheap hardware: seals, liners, pins and bolts.

So the list needs two columns. Consumables are low-cost, high-volume items where one missing piece stops a whole row; count them by side or by metre, because a side seal runs continuously along the flank and wear does not stop at one short section. Long-lead items are high-cost parts that must be ordered against the original drawing or measured from the worn part; count them per machine and order before failure, not after.

3. Size the order by geometry, never write “one set”

“One set” on a purchase order means nothing. On a reciprocating grate the piece count comes from geometry: bars across the width equal usable grate width divided by pitch, rounded down with an allowance for the side seal; rows along the length equal effective grate length divided by bar length, with the overlap counted; the product of the two is the total. Chain-belt grates are counted by pitch and number of links.

So the inputs to give before ordering are usable width, effective length, pitch and bar length, not boiler rating. For how bar type affects pitch and piece count, see the article on the three bar types.

4. Three running signals that mean schedule an inspection

• More air bypass at the flanks: the same load needs the fan opened wider and excess air climbs
• Abnormal noise or a grate running off to one side: rolling parts, guiding parts or tension
• Uneven pushing or a fuel bed that will not move: hinged parts working loose or bars jamming

All three are visible while running, so there is no need to wait for a broken bar. Give five items at the quotation stage and the price and lead time mean something: drawing number or measured dimensions from the worn part, material grade and standard, quantity counted by location, the mating parts that should be replaced at the same time, and the acceptance basis (composition, hardness, metallography). The classified list of parts is on the grate spare parts page.