The Optimal Surface Finishes for a Hydraulic Cylinder Barrel

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The Optimal Surface Finishes for a Hydraulic Cylinder Barrel

Honingcraft have carefully honed their skills in the hydraulic cylinder manufacturing business over many years. They assure you that from start to finish, every honing process is done with the highest quality in mind, with the best surface finish to suit your needs. 

Hydraulic cylinders usually fail because of damage to seals. Achieving the highest possible surface finish of the hydraulic cylinder barrel increases the productive lifespan of a cylinder. In this interview, we talk to Micron Technologies (Micron) Founder and CEO Justin Dowdle about the optimum surface finish for hydraulic cylinder barrels. We also touch on the differences between different kinds of surface finish technology and find out about different ways to measure hone surfaces.

Expert talk

Micron is a leading provider of  bore sizing and surface-finishing technologies, to the African continent. Micron is a thought leader and premium supplier to the hydraulic industry, and  a well-known name in bore sizing, bore making and bore finishing technologies. 

Justin has spent the last 20 years representing international powerhouse Sunnen and working closely with them over the years has given him invaluable insight and expertise on the subject.

Micron, through the partnership with Sunnen, supplies both Honing and Deep Hole Drilling / Roller Burnishing equipment, so there is no supply bias in their advice.  

Roller Burnishing and Honing

Both processes are used to alter the size, geometry and surface finish of a cylinder bore. Although they achieve a similar outcome, the method of achievement is very different.

Justin says, “Honing is an abrasive cutting process. It uses conventional or super abrasives to cut chips of metal to correct the bore geometry. By changing the grade of the abrasive, we are able to create a surface finish that is optimal for a hydraulic cylinder seal”.

Roller burnishing, on the other hand, uses carbide inserts to cut material. “The “burnishing” in roller burnishing refers to intricate roller-wheels that compress the peaks left on the surface”, he says. This is what creates the smooth surface finish.

Advantages and Disadvantages

Roller Burnishing

The roller burnishing process is a high production application that is considerably faster and more cost efficient than honing. In most cases, the bore can be sized (geometry created) and finished in a single pass of a tool. 

“It is used for high-production, lower-quality applications. Roller burnishing is very size specific and does not benefit companies who manufacture cylinders in a variety of sizes and specifications. “You want to be producing high volumes of the same diameter when it comes to roller burnishing”, Justin shares.

Another limitation is that the surface is being cut by using the carbide insert. The surface now has peaks and valleys on a microscopic level. The burnishing process forces a set of roller wheels under load down the bore. As they rotate they squash and flatten those peaks. 

“Flat peaks allow for a fantastic finish, but with time and repeated reciprocations of the hydraulic piston and seal running up and down the surface, the squashed peaks can create sharp edges which are undesired and end up damaging the seals and ultimately leading to premature seal failure. 

Honing

Honing is more expensive because it uses an abrasive cutting process  – much like a grinding wheel. It requires multiple passes of the honing tool along the length of the bore to create the size and roundness of the bore and parallel tolerance that is desired. 

Justin continues, “It is generally a two-stage process. The first stage uses a coarse abrasive to remove material to improve the roundness and parallelism of the bore. Finishing abrasives are then used in the second step; unlike roller burnishing that squashes the peaks, honing cuts the peaks and leaves the valleys – creating what is widely referred to as a plateau finish. A surface finish that has a deep valley where the peak is removed gives a “table mountain” effect that creates a fantastic bearing surface for the hydraulic seal to travel along while maintaining the valleys which retain oil and keep the surface lubricated”.

With honing there is no risk of peaks lifting and cutting the seals. It has much better wear resistance and sealing characteristics and is therefore the preferred method for critical, high performance  applications like mining machines. “Manufacturers should ensure that the cylinder is produced to the highest possible standard. Repair costs are a fraction of what the downside losses  could be if the equipment  fails prematurely. When machine downtime is not an option, honing is the way to go”, says Justin.

Types of Honing

Broadly speaking, honing is a bore sizing and surface preparation process. There are two types of honing tools. You get  flexible honing tools and rigid honing tools. A flexible honing tool is versatile and inexpensive. “A flexible tool is great for surface preparation only. Because of its flexible nature, it lacks the necessary pressure to really remove material. It will also adjust to variations in bore geometry, so is not suitable for creating round, parallel bores. If your requirement is just to the deglaze or polish a surface – then flexible tools provide a cheap and easy solution”.  

Rigid tools are more expensive by nature but have the benefit of both geometry and surface finish correction. The beauty of a rigid tool is that  it expands to where the bore is at its smallest and hence it can correct the bore profile with the least amount of material removal. 

“We apply a cutting pressure to actively remove material, but by doing that we can focus the material removal on where the bore is the smallest – which is a critical application to understand. It gradually opens the smallest area up until it matches the rest of the bore and thereby creates its parallel and roundness characteristics” he explains.

Honing Parameters

Once you know what application you are honing, you want to make sure you also have an optimum sealing surface. Justin compares it to buying a new car.  Modern manufacturing processes have overcome this, but in years past, the vehicle would have a “run-in” period. 

Driving around slowly for a limited time allows all the engine components to wear in. After the first oil change, the surface peaks and imperfections would end up in the oil sump. Once changed, you could use your car as it was optimally intended. 

Honing can create a surface that already replicates that worn-in or plateau finish as mentioned above. “We want a surface finish that is free of peaks. It cannot be too rough, as  that causes excessive wear. Equally important is that the finish must not be too smooth!  We want nice deep valleys to retain the lubrication required to reduce friction, heat and wear. A good two stage honing process will “wear in” the surface of the bore and remove the resulting debris to prevent that from happening when a cylinder is being used in the field.

Surface Measuring Technology

But how do we measure these surfaces to ensure that we are achieving the optimum surface finish? Surface measuring technology, aka surface finish readers, has evolved significantly. They used to be scarce and expensive and limited to the realm of OEM manufacturers and companies that had big budgets. 

Portable units can now be carried around. They are convenient and easy to use. The technology has developed and we can now measure surface finishes and determine multiple levels within a surface structure. These units can be purchased from Micron if needed. 

Justin concludes, ”More importantly, in honing we can now measure the height of the peaks, depth of the valleys and can also measure the bearing ratio. That is basically the plateau or surface along which the piston will run. This is where it gets interesting in optimising hydraulic surfaces. Manufacturers can produce optimum surface finishes with optimum seal life”. 

Honingcraft uses Sunnen technology, supplied and supported by Micron Technologies, to ensure that its customers build cylinders that don’t fail prematurely.

If you need expert surface finishing like Honing, Chroming and Grinding, reach out to Honingcraft. They strive to achieve the optimal surface finish for hydraulic cylinder manufacturing.  Contact Honingcraft today.

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