Accelerated wear is a complex subject so our remarks will be restricted to PHLAUER™ Mixers and Shearmakers.
Mixer wear points are the housing sides, paddles, discharge, the rotor shaft under the seals and seals. Shearmaker wear points are blades, shaft under the seals, and seals.
Regardless of what your material is, you should look at a part that may wear, and what it will cost you if it fails including the cost of the part, labor to change it, and the lost quality and production. Loss of quality from wear can be a costly item. If you can do something to reduce the wear for an extended period, you can make a judgment on the cost/benefit.
Protecting your rotor shaft is an easy example. You can buy the machine with replaceable sleeves for $1200 to $2000 per end, whether carbon or stainless. They will last at least 10 years or more. But other repairs to a rotor with grooves, and then replacing seals and sleeves could cost $12,000. These are simple things where heat treated C1045 to C30 or stainless with hard chrome plate are adequate. Ours is a solid to split replacement.
Accelerated wear on the body itself requires more art, judgment and hopefully experience. Some applications such as sand and cement, we are confident we have a minimum 20-year solution, and we know supplying carbon steel is a disservice to the customer.
Where you have to start is by defining what is causing the wear. Once that is determined judgment can be applied. Particle size and shape play a significant part, just like coarse and fine grinding wheels. Our theory is that very fine particles, under 50 micron, don’t tend to wear even if it has an abrasive name. As the particle size goes up, so does the wear curve, until you reach a point (I’ll say 3/8”) where there is so much surface presented that the curve goes back down.
Common causes of wear are:
- Gouging of the surface.
- Impact that cracks and pops little pieces out of the surface.
- Combination of gouging and impact.
- Friction heat, as with grains.
- Chemical attack.
- Galvanic action
- Exceeding the surface speed of the materials.
The “rules of thumb” are:
- Gouging – have the product repel itself or go with harder materials, or use some material as sacrificial.
- Impact – using material with good Sharpy impact properties
- Gouging and impact – you may be able to use one alloy material depending on the weight, or you can cushion the impact with carbon steel backing.
- Friction heat – add thickness to dissipate the heat or use UHMW.
- Chemical Attack – this can be tough. You can use a coating or stainless but if there is also gouging you may want to explore other alternatives.
- Galvanic Action – use isolation or sacrificial plugs
Exceeding the surface speed – change the material. We have seen this in seals so much that we invented our own, and also in metals. We started using AR 400 heat treated plate in our very first machines because of my history and know how with the product. For our mixer housing and paddles, we have been monitoring machines doing 1 million lbs. per day of sanded products, and because of our slow speed and short mix times, there is no measurable wear on the housing, and only 0.017” found on one paddle using ultrasonic measuring. This was after 8 years.
For Shearmaker blades in cement AR400 works fine, but add sand and they disintegrate because of surface speed. We have to use tool steels to get the surface speed we need.
The answer to everything seems to be “it depends”. With our history in sand and cement, we make the mixer body of AR400. If you don’t have history, then you may want to consider a liner. When using a liner, it will have to be replaced at some point, and the mixer should be made with the access and reasonable way to remove it. Tiling could be a good option on bigger machines.
There is confusion about stainless steel and wear from gouging or impact. It is not a good wearing material, not as good as carbon steel. The confusion seems to come for the fact that is work hardens, meaning when we roll or bend it, it becomes harder. It does not wear harden.
The most abrasive installation we have is adding molasses to a ceramic. The long paddles are 1” thick AR400 and wear at ¼” per week. We are trying carbide and haven’t arrived at a good cost/benefit point. We are putting through 15 tons per hour for 5 x 20 hr. days. A UHMW liner is giving reasonable wear resistance and is easier to clean.
The second most abrasive is mill scale. We have arrived at a good cost/benefit and are still trying to improve. The job we took over is giving an excellent return to the customer. We thought carborundum was abrasive before we mixed this product. We have two machines doing 10 tons per hour each 24/7.
We have over 50 AR400 machines operating with excellent results. One customer where we introduced the AR400 said that the premium for AR was worth it because of the reduction in maintenance costs on the discharge.
We have a machine on dairy feed where we are experimenting with AR400 impregnated with Teflon. We replaced a previous machine we sold of another design that had tremendous maintenance problems with the discharge wearing bigger than the door. Our objective is to reduce this wear with the AR400 and some of this could be friction heat so the Teflon may also help as well as making the machine easier to scrape down.
A lot of fabricators are afraid of breaking rolls or brakes with AR400, but we have done so much of it that we have developed a lot of know how. Hardness ratings are exponential, so AR200 is not half as hard—maybe it is ¼. High manganese plates are even less. We recommend going to the harder alloy.
There is a lot of stress in an AR machine from the forming and welding. All machines are shipped water tight, but about 1 out of 20 machines will move from shipping, installation, or the material rotating inside it and the discharge will start to leak. We will send a man to repair it anywhere in the world. When it is setup the second time, it does not happen again.
Also in our arsenal are removable and replaceable paddles.
Contact us for more information or for an equipment demonstration.