Every one of these steps has to be got right — there are no shortcuts.

A slurry pump does not last because its casing is thick. What takes the beating, day in and day out, is the impeller, the volute liner and the side plates — the wetted parts. How those parts are made largely decides how long the pump will run. Here is the process, in the order it happens on the shop floor.

Fig. 1 — Manufacturing process flow: two routes, metal and rubber, converging on one final inspection

1. Charge and melt: pin the chemistry down first

Wetted parts are usually cast in high-chromium white iron, around 26–28% chromium — the material covered by ASTM A532 Class III Type A, sold in the trade as A05 grade. High chromium means more M7C3 carbides form as the metal freezes, and those carbides run 1,500–1,800 HV. That is where abrasion resistance comes from.

The charge is weighed out before it goes into the furnace. Once molten, a sample is taken and read on a spectrometer: carbon, chromium, molybdenum and nickel come back in one go, and any shortfall is corrected. Sulphur and phosphorus are held down — both make the iron brittle, and a brittle impeller chips under impact. Get the chemistry wrong and no amount of good heat treatment afterwards will make up for it.

2. Moulding and pouring

Resin-bonded sand moulds are the norm; sand strength and permeability have to be watched. Where the gates and risers go is experience, not theory: the last place to freeze has to be the riser, so feed metal can get in and the casting stays free of shrinkage.

Pouring temperature follows the process card. Pour too fast and you get entrained air and sand inclusions; too slow and the thin sections chill first, and the thick-to-thin transition tears. After shakeout, gates and risers are cut off, the casting is shot-blasted and the flash is ground away. Rough work, but it decides whether the machining that follows locates properly.

3. Heat treatment: where the real work happens

As cast, the part is hard — but the structure is wrong, and it is brittle. Heat treatment is what turns it into something that resists wear without cracking.

The cycle: heat to 950–1,050 °C and hold, so carbides distribute evenly; air cool or force-air cool to quench, transforming the matrix to martensite; then temper at 200–300 °C to relieve stress and claw back some toughness. Finished hardness usually lands between HRC 58 and 65.

Cracking is the risk here. Where a thick section meets a thin one, uneven heating or cooling will split it. So how parts are stacked in the furnace, how fast the temperature rises and how they cool afterwards are fixed rules, not judgement calls.

Test coupons go through with every heat. Hardness is measured, metallography is examined, and the records are kept — so if a spare part is ever questioned, the curve from that heat can be pulled out.

4. Machining: once it is hard, you change the tool

After quenching, ordinary high-speed steel will not cut it. There are only two options: anneal to soften, rough machine, then quench; or go straight at it with cubic boron nitride tooling and grinding.

What matters is a handful of fits — the impeller bore, the neck ring, the liner mounting faces. A few tenths out and the clearances go uneven, which shows up as lost efficiency or uneven wear and a shorter life.

5. Rubber parts: a completely different trade

On fine, rounded particles, rubber linings usually outlast metal. And they are made in a way that has nothing in common with the metal line.

The steel shell is blasted clean of oil, rust and old paint, then two or three coats of adhesive go on. Sheet rubber is cut to pattern and laid up in layers, rolled down as it goes to push every air pocket out. Trapped air is fatal: it expands in service and the lining lifts. The assembly then goes into an autoclave, where heat and pressure complete vulcanising and turn the plastic compound into elastic rubber. Afterwards it is holiday-tested with a spark tester and inspected by eye. Pinholes or blisters mean rework.

6. Assembly and final testing

Impellers are balanced, normally to ISO 1940 grade G6.3. Then the pump is assembled and hydrostatically tested for leaks in the pressure-containing parts. Finally it runs on the test loop while flow, head, efficiency, vibration and bearing temperature are measured — and where the customer asks for it, NPSH testing as well. Once all of that passes, it is a pump we can ship.

Everything above — casting, heat treatment, machining, assembly and testing — happens inside the EXCELLENCE PUMP plant; no critical operation is subcontracted. The reason is simple: every extra hand-over makes it harder to hold consistency between batches, and if spare-part life will not repeat, a maintenance plan cannot be built on it.

If you want the detail on any particular step, or you have a duty in mind, talk to the EXCELLENCE PUMP engineers — bring drawings and data.