Why Belt Oil Skimmers Are Perfectly Useless

Estimated reading time: 5 minutes

Belt oil skimmers are the most widely used machine tools for removing floating tramp oil from coolant surfaces. Sadly, the price of the equipment is given importance over its effectiveness when it comes to the machine tool application.

Every machine tool manufacturer includes belt skimmers with their machines, and in every machine tank, we find floating tramp oil- every time. The presence of tramp oil on the coolant despite a belt-type oil skimmer indicates the ineffectiveness of these oil skimmers for machine tool coolant application. 

For selecting an effective oil skimmer, please refer to to- 2021 ultimate guide on oil skimming.

What is a belt oil skimmer? And how it works?

Belt skimmers use an endless belt of corrosion-resistant steel or synthetic material- usually polyurethane. This belt passes through a pulley arrangement which ensures the belt remains in tension. A small geared motor drives this belt and pulley arrangement. 

The floating oil sticks to the belt material, and as the oil skimmer motor starts, the oily belt rotates, and the oil sticking to the belt come up. The belt then passes through wiper blades that scrape the oil.

7 Pitfalls of using belt oil skimmers

Basic design philosophy

The coolant or metalworking fluid is stationary in the belt skimmer while the skimmer moves on its surface. The stationary coolant is the primary reason for its degradation, as it accelerates bacterial growth. Hence, belt-type oil skimmers fall short of their objective by the very nature of their design. 

Under sizing, the belt oil skimmers

A common misconception is that you can buy a smaller skimmer based on a lit-per-hour skimming capacity to save money. However, purchasing a small or mini-unit instead of an industrial-sized skimmer can be an ineffective method of oil skimming. Machinists should select the oil skimmers based on the surface area, not just the amount of oil removed. While designing an oil skimming system, designers need to consider a factor of safety of at least two, i.e., if the oil addition rate is x, an oil skimmer of 2x capacity is required.

However, in the case of belt oil skimmers, this means- 

1. Increasing the belt width
2. Increasing the number of skimmers

Both the above alternatives are sub-optimal since-

1. Increasing the belt width means more area is needed for installation in the machine tank.
2. As the number of belt oil skimmers on a tank increases, the maintenance costs also increase as the belt, motor, and wiper blades are consumable. Monitoring every belt skimmer becomes a tedious and non-value-adding task.

Improper placement of the belt oil skimmers

Placing the belt oil skimmers at an appropriate location is very important for any belt oil skimming system to be as effective as possible. Belt oil skimmers should be opposite the inflow, and the tail pulley should be submerged two inches below the coolant surface. 

Using a coolant tank that does not allow the oil to rise and float will not permit successful oil skimming. Belt oil skimmer users should ensure that the installation location on the coolant tank gives enough residence time for the oil to float. Hence, having a smaller coolant tank is not beneficial for a belt-type oil skimmer to be effective.

A stable coolant surface is needed for the belt oil skimmer to be effective. A turbulent coolant surface will break the oil film, and the oil will not rise and float on the surface. Hence, belt oil skimmers are ineffective while the machine is running. However, given its design, the belt skimmer cannot remove oil fast enough while the coolant is stationary when the machine is not running.

Type of tramp oil to be removed

Manufacturers base the belt oil skimmer’s capacities on optimum conditions and homogeneity of oil. However, in the case of machine tool coolant application, various oils get mixed in the coolant, e.g., lubricating oil, hydraulic oil, rust prevention oil, etc. Each oil is different in its physical as well as chemical characteristics. Hence, it is next to impossible to design a belt skimmer that will effectively remove each type of oil since it depends on the belt material.

Also, we have observed that belt oil skimmers perform better with high-viscosity oils rather than low viscosity at ambient temperature.

Belt oil skimmers also work better at ambient temperatures rather than elevated temperatures. As the fluid temperature increases, the belt material loses its structural integrity and tension. The wiper blades also wear faster in high-temperature fluids.

Choosing the wrong oil skimming material

There are several things to consider when choosing an oil skimmer belt material. Some plastics do not stand up to heat or strong chemicals. Specific metal belts do not skim coolants effectively. Smooth belts do not pick up floating emulsified oils. 

Hence, picking a reputable oil skimming provider and telling them all the information about your application is essential. They should know that no two applications are alike, and not all belts and skimmers are interchangeable.

Maintenance needed for belt oil skimmers

Belt-type oil skimmers look small and are usually inexpensive. However, people who invest in them because of low capital costs pay later in maintenance costs. A belt oil skimmer will only remove oil if it is properly maintained. Users should regularly perform basic maintenance tasks to keep their belt oil skimmer running. Are the wipers contacting the belt smoothly? Is the belt riding away from the sides of the pulley? Are the troughs and wipers clear of debris? Users must follow a proper maintenance schedule if they want their belt skimmer to provide the best oil removal performance possible.

Buying based on price

Like most things in life, you get what you pay for. Buying from small, unheard-of oil skimmer manufacturers will probably result in no customer support when maintenance issues pop up and little to no knowledge of how to resolve those issues. Furthermore, you will need to.

1. Replace parts over time. 
2. Change or upgrade units
3. Use different belt materials. The vendor should know and suggest an appropriate belt material per the application.

Disreputable vendors typically do not have a selection of materials or parts. Additionally, it is common for smaller, unknown companies to go out of business after a few years.

Customers replace the belt skimmer with a different brand when spare parts are needed. Paying a low price upfront might result in you paying more in the long run. Investing in a quality oil separation system like a coalescer is best.

It will operate efficiently and consistently for a more extended period. The delta that you pay higher as capital cost for the coalescer pays dividends for years with improved coolant life and zero maintenance costs.