Spare Parts Stock Planning for Air Shafts and Winding Equipment

On a roll-handling line, much of the downtime comes not from major breakdowns but from a small part simply not being on the shelf when it is needed. A punctured bladder, a leaking air valve or a worn friction ring can be swapped in minutes, but if none is in stock the line may run at reduced capacity for days. On the other hand, stocking generous quantities of everything ties up capital and storage space unnecessarily. This article looks at how to plan a balanced spare parts stock for air shafts and winding equipment.

Which parts wear?

The first step in stock planning is knowing which parts are replaced regularly. On air shafts and the equipment around them, the typical candidates are:

Air shafts

• Bladder (air tube): the heart of the shaft; it can stop holding pressure after a puncture or through ageing.
• Lugs or leaves: surfaces in constant contact with the core can wear or suffer impact damage.
• Air valves and nipples: small but critical parts that can leak due to dirt, impact and wear.
• Seals and plugs: the elements that keep the inside of the shaft airtight.

Friction (differential) air shafts

• Friction rings and related components: because they work by controlled slip, they wear over time.

Safety chucks and brakes

• Bearings: run under constant load in safety chucks and bearing housings.
• Brake pads and friction elements: the wearing parts in pneumatic brakes.
• Powder in magnetic particle brakes: over long use it may need servicing and, where necessary, replacing to maintain performance.

Classify parts by criticality

Rather than stocking every part in the same way, a practical starting point is to classify parts by two questions:

1. If this part fails, does the line stop?
2. How long does it take to source this part?

Category	Characteristics	Stock approach
Critical, long lead time	Failure stops the line; slow to source	Must be held in stock
Critical, short lead time	Failure stops the line; easy to obtain	A small quantity may be enough
Non-critical	Failure does not stop production	Order when needed

On most lines, bladders, air valves and parts specific to the shaft ends fall into the first category. For single, critical positions such as the shaft carrying the parent roll, it is also worth considering a complete spare shaft rather than just parts.

Setting stock levels

A simple reorder point can be worked out on this basis:

Reorder point = (average consumption × lead time) + safety stock

For example, if you use a few of a given part per month and the lead time is a few weeks, an order should be placed when stock falls below what will last for that period. Safety stock is a buffer against fluctuations in consumption and supply delays.

For this calculation to be useful you need consumption data. Recording in maintenance logs which part was replaced on which shaft, and when, builds a realistic consumption picture within a few months.

Standardisation reduces stock

If different machines use shafts of different sizes and types, each needs its own spare parts. Where possible, aligning core sizes, shaft types and journal profiles allows the same spare part to serve several machines. This reduces both the number of different items held and the total stock value.

Start with an inventory: which shaft is on which machine, its dimensions, and the bladder and valve types it uses. This list becomes the main reference for stock planning and for ordering the correct part.

Storage conditions

• Rubber and elastomer parts (bladders, seals) should be kept in a cool, dry place away from direct sunlight, heat sources and ozone-producing equipment. These parts can age even when unused.
• First in, first out: use older stock first.
• Bearings should be kept in their original packaging and away from moisture.
• Label everything: clearly mark which shaft or machine each part belongs to and the date it entered stock.

Safety during replacement

However well prepared the spare parts are, the replacement itself should never be rushed. Stop the machine, secure energy sources according to the manufacturer’s lockout procedure and fully release the air from the shaft. Always follow the machine and shaft manufacturer’s manual for assembly order, tightening values and operating pressure.

Planned stock, planned maintenance

Spare parts stock should not be planned in isolation from the maintenance plan. Parts showing signs of wear during periodic checks are noted, replacements are scheduled in advance and stock is updated accordingly. This reduces both unexpected stoppages and unnecessary stock.

You can find the parts needed for your shafts and winding equipment on our spare parts and friction rings pages, and on the pneumatic brake product page for the brake side. If you are unsure about a part code or dimension, contact AYS Makina through our contact page.