Essentials of Honing Machines for Hydraulic Cylinder Repair

At the heart of every hydraulic system is the hydraulic cylinder. The hydraulic cylinder creates the power to drive the process, whether that process opens and closes gates along a conveyor belt, raises and lowers the blade on earth-moving equipment, or activates a large door in a factory so that a forklift can quickly pass through.

Evaluating Hydraulic Cylinder Health

Given all the environments where you find hydraulic systems—some clean and some very dirty—manufacturing engineers must keep in mind the health of the hydraulic cylinder and its various components, especially the cylinder bore. When it’s time for routine maintenance or to fix components that have worn out or are malfunctioning, hydraulic cylinder repair shops must have the latest knowledge and tooling so that repair personnel can restore the surface finish, which includes ID honing, crosshatching, and tube honing. These are all vital processes to ensure a smooth-functioning cylinder bore and hydraulic system.

Why Surface Finish Is Vital to Hydraulic Cylinder Function

Pressure in an industrial hydraulic cylinder ranges from a low of 3,000 PSI to as high as 10,000 PSI. Even at the low end, the integrity of the hydraulic cylinder assembly and the finish on the cylinder bore are vital to effective, consistent, and reliable operation. The honing process is the most expedient way to achieve this finish. A quality finish in the cylinder bore is vital to the hydraulic system operating properly.

Looking to best way to restore ID surface finish? Contact CRC Distribution and ask about our automated honing equipment.

Surface Finish Features in Cylinder Bores

When you look at the surface of a recently honed cylinder bore, it appears to be smooth. This is seldom the case. There are several ways to gauge surface finish. 

• Roughness--Under a microscope, the honed surface of a cylinder bore reveals closely grouped peaks and valleys. Roughness is measured as Ra value, Ra standing for roughness average, or the average deviation between those peaks and valleys. The smaller the Ra, the finer the surface.
• Waviness--Waviness refers to larger undulations in the honed surface, a product of vibrations of the mandrel. Waviness is a low-grade surface texture and is undesirable for most industrial hydraulic applications.
• Lay--Lay refers to the direction of the surface pattern. Lay is usually determined by the machining method (grind, boring, honing, etc.) and the type of tools used.

Common Cylinder Bore Defects

There are also other irregularities in a cylinder bore, most of which can be remedied by correctly honing the component. These include:

• Diameter size—Poor measurement or worn stones can lead to a difference between the designated measurement and the final result.
• Oval bores—Often caused by movement or wobbling of the mandrel, or from prolonged use without routine maintenance.
• Bellmouth—Microscopic unevenness in the surface of the cylinder bore, typically with a wider measurement (often only a few microns), occurring at one end of the cylinder bore or both ends.
• Rainbow—A bore that arches off-center between the two ends. Sometimes also referred to as waviness.
• Barrel shape—A microscopically smaller bore on either end and wider in the middle.
• Tapered bores—Wider at one end of the bore than the other.

Honing can also remove surface imperfections such as scoring and pitting of the cylinder bore, which are often the result of worn seals and insufficient lubrication of the hydraulic system.

What Is Honing?

Honing is the process of returning the surface finish of the cylinder bore to OEM specifications. Precision honing is a subtractive process that produces an optimized surface on the inner diameter (ID) or wall of the bore. The correct surface finish reduces friction and wear on seals and pistons, and ensures maximum power generation. Quality hydraulic systems come from the original equipment manufacturer (OEM) with precision surface finishes in the cylinder bore, engineered so that the cylinder maintains maximum pressure for its intended process. These cylinder bores stand up to repeated use, often in brutal conditions. Eventually, though, this use causes parts to wear, exacerbated by delayed maintenance (it happens to the best of us), problems in other system components, or applications that push the cylinder beyond its capability. Mishaps such as overheating, contaminated hydraulic fluid, or the scoring of a piston during the replacement of seals are all events with the potential to damage the cylinder bore. Unless repair experts address these irregularities in the surface finish during the hydraulic cylinder repair process, the cylinder will operate at less than optimum levels and only worsen.

CRC Distribution carries a complete line of honing equipment and tools. Call and speak to our experts today.

The Honing Process Explained

Honing involves using a mandrel outfitted with special abrasive strips or stones of borazon, diamond, and other abrasives. The mandrel is attached to a power source that ensures rotation at a consistent speed and pressure so that the operator can achieve exact precision and results. During the honing process, the abrasive strips or stones spinning inside the cylinder bore remove minute amounts of cylinder material, ensuring an optimum finish that allows pistons and seals to move flawlessly during the hydraulic process. In most cases, honing also involves a lubricant delivered to the surface. This lubricant cools the process and carries away the minuscule particles of material. Lubricants can be oil-based, water-based, and sometimes vegetable-oil-based.

Honing is a precise operation that can achieve tolerances of =/-0.0002 inches. It is also a less intrusive or destructive process. Grinding or boring, the other options for cylinder refinishing, can leave microscopic fractures in a cylinder wall that compromise the integrity of the hydraulic process.

Correct Honing Produces Crosshatching of the Cylinder Bore

At first glance, you may look at the interior of a bore and see a smooth finish, but closer examination reveals uniformly angled striations in the surface. This is crosshatching, a series of uniform microscopic peaks and valleys on the cylinder surface. Not every hydraulic cylinder has the same crosshatch pattern. The lay of the crosshatching  typically ranges somewhere between 30o and 45o, depending on the OEM specifications. Hydraulic cylinder repair experts also check the depth of the Ra of the crosshatching and use the appropriate abrasive grit to achieve the desired result. A larger grit will achieve a higher Ra. A smaller grit will leave a finer RA. The surface finish of a hydraulic cylinder bore should have an Ra  of ≤ 0.8, but always check your specifications for the unit you are working on.

The Goal of Crosshatching

Crosshatching is an important part of the surface finish of a cylinder bore. The peaks and valleys in the cylinder surface created by crosshatching retain a small amount of lubrication on the cylinder bore surface. This lubrication protects the piston rings and creates a superior seal, guarding against the loss of compression. This lubrication also means less wear on hydraulic seals and pistons, resulting in less frequent need for hydraulic cylinder repair.

Tips for Optimum Results in Honing and Crosshatching

Hydraulic cylinder repair facilities and the experts working there draw upon years of training and experience to achieve the best result when honing and crosshatching a hydraulic cylinder. Here are some best practices:

• Ensure the cylinder and tools are clean and free from excess debris, lubrication, and other contaminants.
• Identify the cylinder material, such as 1026 carbon steel, chrome-plated bores, etc., which might dictate your use of abrasive grits.
• Examine the ID surface of the cylinder to identify specific problems, including scoring and pitting or incorrect crosshatching.
• Measuring to identify other issues such as barreling, bellmouth, rainbow, etc.
• Research and use the correct abrasive grit at the appropriate speed.
• Research and use an appropriate lubricant for your material and application.
• Check and double-check all measurements and specifications.
• Examine the finished product closely to ensure uniformity of the crosshatch pattern and the elimination of surface blemishes and other irregularities.

Want to get the best results from your hydraulic cylinder crosshatching? Contact CRC Distribution to find out how.

The Benefits of Properly Honing Hydraulic Cylinder Bores

Expert honing of hydraulic bores during hydraulic cylinder repair and maintenance means that your equipment operates at peak performance. Proper crosshatching extends the life of the hydraulic cylinder and protects seals, pistons, and other components. Manufacturing entities and other businesses that rely on peak performance from their hydraulic systems also maintain high productivity and worker safety.

Using the Right Honing Machine

CRC Distribution offers two automated honing machines, the HONIX 15 (15 feet) and the HONIX 20 (20 feet), designed and manufactured by Hydraulitechs. Both offer hydraulic-over-electric design, automatic delivery of lubrication, and are fully adjustable for any size hydraulic cylinder repair project.

CRC Distribution Understands Honing

CRC Distribution, founded more than twenty-five years ago, supplies hydraulic system repair equipment to machine shops and manufacturers. We have earned a reputation as one of the premier experts on hydraulic cylinder repair and honing. They also carry several products vital for any shop that regularly performs honing.

Call CRC Distribution, the experts in hydraulic cylinder repair supplies.