One of the most common finishing operations for metal parts is surface cleaning and light deburring. Generally, large workpiece volumes – sometimes thousands of components -- must undergo such surface refinement operations every day. When it comes to finishing quality and cost efficiency, the mass finishing technology, especially continuous flow vibratory systems, is by far the best choice! Continuous flow equipment is equally suitable for handling sturdy, tough workpieces as well as delicate, fragile components that must not touch each other during the entire finishing operation. The most common continuous flow mass finishing systems are linear continuous flow machines with a rectangular work bowl and the so-called multi-channel rotary vibrators. While choosing the right machine for a particular finishing task is key to achieving optimum results, there are other important aspects that must be considered. For example, how can the power consumption for the highly energy-intensive drying operation be minimized? Or, to what extent can the finishing operation be automated? And, last but not least, how can the contaminated process water be cleaned and recycled at minimum costs?

Why surface cleaning, de-flashing and light deburring is so important

It is absolutely important that prior to downstream manufacturing stages and final assembly, metal components such as castings, die castings, forgings, stampings, machined or powdered metal components undergo a cleaning and deburring operation. They must not only be free of surface contaminants like stamping oil, coolants, mold-release agents, etc., but also be free of any debris like loose flashes. In addition, sharp burs must be broken by slightly rounding them off. 

These surface contaminants, flashes and sharp burs would not only interfere with manufacturing and assembly operations, but could also severely injure employees and cause costly equipment failure.

Continuous flow surface finishing

Such cleaning and deburring tasks are predominantly performed with mass finishing equipment. And, since the cycle time for such jobs usually does not exceed 20 minutes, they are primarily handled by continuous flow vibratory finishing equipment.

In continuous flow operations, the workpieces are continuously fed into the machine at one end of the work bowl. After passing through the entire length of the processing channel, they exit at the other end. 

There are two major machine types:

Linear, continuous flow vibratory systems

The machines consist of a rectangular work bowl with a special vibratory drive system mounted underneath the bowl. With a drive power of up to 40 kW, linear continuous flow vibrators are the most powerful and most productive mass finishing machines on the market. They are ideal for handling large volumes of sturdy, non-delicate workpieces that can freely tumble over each other without causing any serious nicking or scratching. The workpiece size can vary from a few centimeters up to 600 mm, and weights can amount to more than 50 kg.

Multi-channel rotary vibrators

These machines, also known as “Rotomatic” systems, consist of a spiral-shaped processing channel with a special vibratory motor mounted in the center. With a channel length of 12 to 27 m (!), the multi-channel systems are ideal for processing very delicate, fragile work pieces that – because of the risk of nicking or scratching -- must not touch each other during the finishing process. 

Workpiece handling

Continuous flow finishing systems can be easily integrated into in-line manufacturing cells where the raw workpieces arrive sequentially – one after the other – for example from a stamping line, a die-casting unit or from a machining center.

However, continuous flow systems are equally suitable for handling workpieces arriving in bins from off-line manufacturing operations. In this case, they must be separated so that they can be fed into the machine one at a time.

How to create stable and safe 

continuous flow finishing 

processes?

Some basic technical aspects must be considered to make a continuous flow process stable and safe:

Workpieces cannot get mixed up

Whenever different workpiece types are to be finished, the operator must ensure that the workpieces do not get mixed up. Therefore, he must completely evacuate workpieces from the previous production run from the bowl before new ones are fed into the machine.  

Prevention of media carry-out

Processing media carried out from the machine with the finished workpieces can cause catastrophic effects on downstream manufacturing or assembly operations. Therefore, the finishing machines must be equipped with an effective screening system that reliably separates the media from the finished workpieces. For this reason, continuous flow systems are generally equipped with a separate, independent vibratory screening unit. Of course, this applies equally to ferro-magnetic workpieces, which are separated from the media by magnetic separators.

Prevention of media lodging in the work pieces

Media lodged in workpieces can be as catastrophic as loose media carried out with the finished components. To prevent such lodgings, the machines must be equipped with a generously sized, well-functioning undersized media screening and discharge system.

Reducing the costs for expensive drying operations

Prior to subsequent manufacturing steps, the finished workpieces must be completely dry. This is usually done in hot air drying systems like belt driers or vibratory driers containing a drying medium. The required heating energy can be substantial, up to 67 kWh! With today’s  electricity costs, this can be a huge cost factor.

A leading manufacturer of mass finishing equipment has recently developed a new hot air drying system that cuts the energy requirements for the drying operation by up to 75%: In a heat pump/condensation system, the moist air from the drier passes through a dehumidification module, where the moisture condenses on the fins of the air cooler. In a subsequent air heater, the dehumidified air is then reheated to the required drying temperature.

This system not only reduces the drying costs by up to 75%, but also offers the additional advantage that the overall drying temperature is considerably lower so that the workpieces leave the drier at a lower temperature. 

The same manufacturer could also substantially reduce the heating costs of his vibratory driers with drying media: By installing the heating element directly under the work bowl – instead of mounting it to the machine base – the average energy requirements for drying could be reduced by 50%.

Automation

Comprehensive automation hardware allows easy upgrade of continuous flow finishing equipment into automatic systems. There are all kinds of loading tools like skip loaders, vibratory feed hoppers, conveyor belts, roller conveyors, etc. In combination with the right system controls, this automation hardware allows any degree of automation. The possibilities range from partial automation to fully automated, unmanned systems with no manual handling at all. The only human function left over is the supervision of the entire installation on a remote computer screen. 

Below are some examples of automated systems:

Last but not least: Intelligent, cost-efficient handling of the process water

With very few exceptions, practically all mass finishing processes require finishing compounds and water. In a 24/7 production environment, certain mass finishing operations consume several million liters of water and more than 40 tons of compound per year. This is not only bad for the environment but also quite costly. Therefore, it is not surprising that in most mass finishing operations, centrifuges are used for cleaning and recycling the process water. This helps reduce water and compound consumption by 90 to 95% and, therefore, represents a significant contribution to saving valuable resources, building a cleaner environment and, of course, saving costs. 

But managing a centrifugal water cleaning and recycling system is quite complex. It requires the regular monitoring of operating parameters like pH-value of the water, the compound concentration, the water hardness, the chemical oxygen demand (COD), possible bacterial infection of the water, or water conductivity. 

With a digital process water management tool, the same equipment manufacturer has greatly simplified the handling of the centrifugal water cleaning and recycling systems: Special sensors automatically measure all critical water parameters. The innovative software then analyzes the measured parameters and proposes appropriate corrective action. The “artificial intelligence” of the digital system completely eliminates the risk of human error, which can cost a company literally thousands of dollars or euros.

Contributing Editor MFN and Rösler Oberflächentechnik GmbH

E-mail: holzknecht.usa@gmail.com