Printing press spare parts: what can be sourced in China and what not

Printing press spare parts fall into three groups. Standard units (bearings, belts, motors, pneumatics, sensors) are made by many plants and are ordered by number and marking, including in China. Parts to a drawing (shafts, axles, gears, knives, the rubber covering of rollers) are made to dimensions or a sample. Proprietary units with the press maker's number (boards, control units, mechanisms that only the maker knows) are safer to take from the maker. A compatible copy can be found, but you are responsible for how it fits.

Three groups of spare parts

Standard units: why they can be taken anywhere

A bearing in a printing press is an ordinary bearing from an ordinary manufacturer. If a number is stamped on the ring, the bearing manufacturer itself makes that same number and sells it not only to the press maker. The same goes for belts, motors, pneumatics and most sensors: each has its own make and marking.

The main rule is to copy the number from the part itself in full, with all the letters, and not to take the number from the press catalog. The press catalog gives the press's own item number. It is needed to find the part at the press maker, but it will tell the bearing manufacturer nothing.

The second rule is not to buy a counterfeit. Counterfeits of well-known bearing brands are common. How to tell them apart is covered in a separate article.

Parts to a drawing: what the result depends on

A shaft, axle, gear or knife can be made to a drawing. If there is no drawing, the part is measured. The plant will ask for:

1. All dimensions, including seats and chamfers.
2. Tolerances on the mounting dimensions. Without them the part may not fit in place or may work loose.
3. Material and heat treatment, hardness.
4. Coating: chrome, nickel, rubber.
5. For a gear, the module, number of teeth and helix angle.

The more exact the data, the lower the risk. Before a lot it is reasonable to order one part and fit it on the press.

Roller rubber. Ink and dampening rollers are covered with rubber. It is not changed on your own: the old roller is sent for recovering, the core is ground and covered anew. Roller manufacturers make different rubber compounds for different inks. One for UV inks, another for dampening with alcohol and without alcohol. When ordering recovering, say which inks and which dampening you print with. The wrong compound swells or hardens, and the print drifts in color.

Proprietary units: where the risk is

Control boards, consoles, units and proprietary mechanisms are designed by the press maker. Only the maker knows how the unit works with the rest of the press. Compatible copies of such parts are on the market, including made in China. They can work, but:

• Nobody guarantees compatibility. The copy was tested on one press, and yours may be a different series or version.
• Warranty. Large printing press makers give a warranty on their original parts if their service engineers fit them. If the press is under warranty or a service contract, find out before ordering how a non-original part will affect it.
• Repair instead of replacement. A faulty board can sometimes be repaired. Ask the maker's service about this before looking for a copy.
• Old presses. Makers keep spare parts even for presses that are no longer built. Before looking for a copy, ask the maker or its service.

If you do take a copy, name it honestly: "compatible with such-and-such press", not "original". That is how an honest seller describes it too. A part sold as an original at the price of a copy is a reason for caution.

What to send for sourcing

• The make, model and year of the press. The serial number from the nameplate.
• The item number from the press's spare parts catalog, if there is one.
• Photos of the part from all sides, with a ruler. A photo of the marking on the part itself.
• For standard units, the number from the part or a photo of the nameplate.
• For parts to a drawing, the drawing or the measured dimensions.

How we do it

• By the number from the part, a photo of the nameplate or a drawing, we look for the item at the manufacturing plant. What we find, with the price, photos and specifications, we send before the order.
• We call a compatible part compatible, not original, and write how it differs.
• We inspect the lot at the plant before shipment: part number, dimensions, lot, packaging.