Is Monel harder than nickel?
Test 1: Build Quality
Simply measuring key points on the valve section is a good indication of manufacturing quality. The three benchmarks I use are the outside diameter of the piston, the inside diameter of the No. 3 valve housing, and the amount of air pressure each horn experiences.
Although the overall dimensions are different, the gaps in the two corners are the same. However, the Trumpet X's air weight is nearly 1/3 pound less, which is below our standards for new speakers. Low air pressure is caused by inconsistent piston diameters. Each piston on the Trumpet X is narrower at the top than at the bottom. This allows the air in the valve section to escape from the top of each valve, causing poor compression.
Test 2: Surface Condition
The most important factor in piston quality is surface condition. Valve action depends on the smoothness of the piston, durability depends on the hardness of the metal, and corrosion resistance depends on these two factors. Let's take a closer look at these three.
Smoothness
First, it's worth noting that nickel plating is very dense, resulting in a smooth surface. In simple terms, this means that the piston surface is very smooth and feels wet even when completely dry. Everything is going well now. Monel, on the other hand, has a very rough surface after annealing. This graininess causes piston drag and provides a place for acids and dirt to adhere, causing rapid corrosion.
Secondly, one of the most time-consuming steps in piston construction is the final grinding. The process of pushing the piston into the valve housing can make or break any trumpet. To save time and money, many of our competitors cut corners when it comes to grinding. In some cases, student and intermediate instruments are not ground at all. Proper fit and valve action were sacrificed to cut costs. Another common tip is to use a low grit abrasive. The benefit for the manufacturer is that the pistons can be ground to size quickly. However, coarse grit leaves tiny cross scratches on the surface, called cross scratches. Cross-hatching can cause uneven wear, sluggish valve action, and off-center piston pressing into the case wall. Crosshatching can also hold dirt and saliva, again speeding up the corrosion process. To prevent this from happening, we grind the pistons with a fine grit compound. This not only creates a smooth, even surface, but also allows for a tighter fit. While this method takes longer, the finished product is unparalleled.
hardness
Surface hardness is key to long-lasting valve operation. No matter how tight the tolerances or how smooth the surface, if the piston is soft it will wear out quickly. Most importantly, the surface needs to be hard at all times. Different hardness areas can cause uneven wear, which not only slows down the piston but can also damage the interior of the valve housing.
A common argument in favor of Monel is that it is harder than nickel. This may come as a shock, but it's true. Monel is much harder in its original state. However, Monel is very easy to anneal. This is due to softening from exposure to high temperatures. The high temperatures required to braze piston liners. Yes, the process of turning a piece of Monel into a piston is what ruins it. That leaves a surface that's hard in some places and soft in others, mostly around the ports. Soft spots wear out faster than the rest of the piston, causing poor fit, sluggish action, blow-by, and loss of compression. It's not quite the flared piston you want.
Nickel, on the other hand, is less susceptible to annealing. The required temperatures are much higher. The extremely hard nickel plating eliminates the small amounts of annealing that may occur, resulting in a consistently hard surface. This provides even wear throughout the life of the piston. Not only that, but the hardness of the nickel plating makes it an ideal bearing surface and allows it to be ground to surprisingly tight tolerances. Has all the ideal attributes for building a flared piston.
I had a local metal fabricator test some pipes for me. They tested the surface hardness of raw and annealed Monel as well as raw and nickel plated. In the image below, the higher the number, the harder the metal surface is. I think the results speak for themselves.
