How to select lubricants
September 15, 2006
Dirt, rust, and wear, cost tube producers and fabricators millions of dollars annually, and they can be the bane of tube processes. Analyzing the criteria for selecting the lubricants can help you select the best lubricant extend tool life and improve bends.
Matching the best lubricant with your applications requires a comprehensive evaluation of your goals, your operation, and how your operation may change in the future.
This article is Part III of a multipart series that addresses how to eliminate tube producing and fabricating problems. Part III discusses the use of lubricants to reduce tool wear and improve bending. Part II addressed the use of cleaners. Part I, which appeared in the April/May issue, discussed how to select a rust inhibitor.
Tube and pipe fabricators are under more pressure than ever before to produce quality parts in shorter time frames and at lower prices. Nothing interferes with that goal more than tool wear or tube malformation. Lubricants commonly are applied to tooling and material to reduce wear, extend tool life, and improve tube bending.
Environmental regulations for lubricants and chemicals used in the industry are tightening. Many new lubricant technologies have been developed to address these more stringent requirements. New lubricants and lubricant blends can eliminate volatile organic compounds (VOCs), lower extractable oils when subjected to acid for waste treatment purposes, reduce waste, eliminate the use of biocides and defoamers, and improve the overall cleanness and efficiency of an operation.
However, to implement these new lubricant technologies effectively, you need to perform an in-depth analysis of your application as well as the total manufacturing process. Selecting a metal forming lubricant in today's manufacturing climate requires a comprehensive evaluation of your goals, your operation, and how your operation may change in the future.
The following are common lubricant descriptions:
Straight oils and soluble oils are the most common forms of lubricants. However, the use of synthetics continues to grow, because they do not leave an oily residual film on parts or presses.
In some instances, however, other lubricants are more applicable. For example, a gel or paste is suitable for mandrel tube bending, because its viscosity allows it to adhere to the inside of the tube, creating a boundary between the mandrel and the tube that prevents galling or scoring.
Answering the following questions may help you choose the optimal lubricant for your application.
About 22 percent of the Earth's fresh water is ground water, which picks up minerals as it flows through soil and rock. If it picks up excessive amounts of calcium and magnesium, the water is considered "hard."
Total hardness is measured in milligrams per liter (mg/l) or parts per million (PPM). You can evaluate the hardness of your water using Figure 1.
Hard water can cause the lubricant to be sticky. Some lubricants contain specially blended additives that prevent the residual film from getting tacky or sticky.
If you have soft water, you should use a low-foaming lubricant. The lubricant manufacturer can blend defoamers into the lubricant, which can help prevent overusage.
While many tubular parts are similar, certain features of one lubricant might provide better results than another for a particular application. Evaluating all aspects of manufacturing the part—including preprocessing and postprocessing—will help ensure that the lubricant is compatible.
For example, if you will be welding, painting, or cleaning the lubricated tube, a synthetic lubricant would be a good choice because often you can weld through the residual film without smoke and without affecting the porosity or integrity of the weld.
If the metal is very thick, a chlorinated oil might be required to attain the necessary tool life and to provide burr-free edges.
If you will bend the tube, a synthetic lubricant is usually a good recommendation. Some applications still require chlorinated mineral oil technology, but as synthetic technology advances, chlorinated oils are being used less. The lubricant recommendation depends on the severity of the operation and what you are looking for in terms of cleanness, performance, and residual film.
Additives can include biocides, extreme-pressure additives, fragrances, and defoamers. New lubricants already contain many of these substances, thereby eliminating the need for additives.
Your company may prohibit the inclusion of oil, chlorine, chlorinated fatty acids, or solvents in your lubricants. It is important to tell the lubricant manufacturer about any restrictions so that the lubricant is in compliance.
A lubricant's suitability varies from metal to metal. What works best on carbon steel might not work best on galvanized steel or stainless steel. Knowing what types of alloys the lubricant will be in contact with will ensure optimal results and eliminate the costly scrap caused by using the incorrect lubricant.
For instance, sensitive alloys such as aluminum and titanium can be pitted or stained by many traditional sulfurized or chlorinated lubricants. However, with the advent of inhibitors, which are designed to prevent staining on sensitive alloys, both oils and synthetics can be used on many metals without affecting them.
|Scoring||Low or poor film strength Improper application Mixture too lean Poor wetting properties Lack of EP additives|
|Wrinkling||Mixture too rich Too much lubricity Improper or overapplication|
|Breakage||Mixture too lean Film too heavy (hydraulic effect) Improper application Low film strength|
The application method—dripping, swabbing, brushing, roll coating, flooding, spraying, or misting—affects lubricant selection. If the lubricant is sprayed or dripped, it must be fluid enough to allow for an even application. Inversely, if it is brushed on, the lubricant must not be too thin. In addition, if a water-soluble lubricant is used in a recirculating system, the lubricant needs additives that prevent biological degradation.
The number of lubricant applications, as well as the stages at which they occur (for instance, before all operations or at alternate operations), makes a difference in lubricant selection.
If the lubricant is applied only once, for example, it must have a high film strength and excellent lubricating properties to last throughout all stages of the operation.
Lubricant selection also is affected by how the tubes are handled or stored, what they might come into contact with, and how long they will be stored. If they will be stacked, they will need a lubricant that provides adequate rust protection and will not cause staining if the parts are compressed.
If the tubes will be stored for weeks or months, the film might need to provide rust protection and be of a consistency that remains fluid over time. If they go directly to a paint line, welding, assembly, or cleaning, they might not need a rust preventive.
If the tubes are cleaned immediately, the lubricant type can affect the wash system. If you use a high-foaming synthetic lubricant, for instance, you might experience more foam in the washer. However, many synthetics are surfactant-based and will facilitate better cleaning in your washer.
If you use an oil, you need to determine if the cleaner will emulsify or split the oil out. If the cleaner splits the oil out, you'll need to be sure to remove the oil so it is not redeposited on the tubes.
Answering these questions can help you successfully integrate a lubricant in your tube fabricating operation for minimized part wear and maximized performance.