VOL. 3 February ISSUE YEAR 2002


in Vol. 3 - February Issue - Year 2002
Batch or Continuous Mass Finishing
Trowal Inline System

Trowal Inline System

MC Work Channel

MC Work Channel

Trowal Multi Channel Machine

Trowal Multi Channel Machine

In the Spotlight

USF Walther Trowal GmbH & CO. KG is a pioneer in surface finishing located in Haan, Germany, with worldwide facilities and representations. It manufactures finishing machines, abrasive media & compounds as well as water treatment plants for finishing effluents.

Mass finishing of metal components can be conducted in batch mode or continuously. Important for the determination of the process mode is the cycle time and the quantity of parts.

When is a batch process to be selected?

Mass finishing of metal parts with the target of strong radiusing or deburring, fine surface finish or high lustre, requires intensive processing (finishing) in standard vibratory finishing or high energy machines.
Some parts even need to be processed in multi step operations with different types of media and/or compounds to achieve the requested surface quality or edge breaking.
All these finishing tasks require long cycle times and often a change of media or compounds during the process. In such cases batch operation must be chosen in combination with the proper mass finishing equipment.
Typical batch processing machines are tub vibrators, circular or helical shaped bowls, centrifugal force disk finishing machines and even the well known finishing barrels.
The batch of  components with the pre-selected abrasive or polishing media is loaded into the batch type finishing machine. Chemical compound is continuously added to the finishing process. 
The process will run for a certain period of time until the requested finishing results are achieved.
Any process cycle requiring more than 30 mins should be run in batch mode.
Walther Trowal of Haan, Germany, offers a wide range of batch type mass finishing machines from simple tubs to sophisticated and PLC-controlled high-energy machines which are frequently tailor-made to the customer's requirements.

When is a continuous process to be selected?

Deburring, cleaning and deflashing processes in mass finishing normally only require short cycle times. Aluminum die castings, steel parts after stamping for degreasing and sharp edge removal or castings with light and accessible flashes can be processed in a continuous mode provided large quantities of parts need to be processed.
The continuous mass finishing process requires a single part-by-part feeding into the machine with either special loading systems or parts being transported straight from machining centres or stamping presses to the finishing machine. A continuous mass finishing machine is only economical if parts loading and unloading can be automated or - at least - mechanised to minimise labour costs.
Continuous mass finishing machines are available in linear tub and spiral bowl machines in various sizes. Each machine type has its preferred field of application.
While the continuous linear tub machines are mainly used in the die cast industry for larger components, the spiral bowl types (so-called Multi-Channel machines) are the preferred machine for processing light and delicate parts.

Walther Trowal  in co-operation with Wheelabrator - developed the linear tub vibrator in the early 50's for General Motors Automotive to deburr rocker arms on a continuous basis. In almost 50 years hundreds of linear tub vibrators with various lengths and tub widths were manufactured and delivered by Walther Trowal mainly into the automotive industry and to automotive suppliers.
Continuous linear tub vibrators linked with automatic loaders, parts washers,
dryers and effluent treatment and recycling plants are common standard in the modern die casting production. Tub lengths of 3,5 - 7 m ( 138 - 275") and widths of 410 up to 910 mm (16 - 36") can be manufactured depending on the size of the components to be finished. Cycle times from 5 to 30 min are easily adjustable by a separate,  independently driven vibrating discharge channel.

But large linear tub vibrators also require  big loads of abrasive media causing a high amount of media wear. Especially when processing heavy and large parts the media consumption cost will be substantial. In such cases the economics of the process must be evaluated very carefully. Also floor space is an issue due to the linear operation. The longer the necessary cycle time the more machine length is needed. Therefore, only large quantities of components will justify this process.

The spiral bowl, also called "Multi-Channel", is characterised by a narrow process channel width with the channel spiralling from inside out or from outside in. There are machines with external and some with internal parts/media separation. Most spiral bowl machines are driven by a centrally located vibratory motor. Normally the operating amplitude is rather low producing a less aggressive, gentle grinding action.
Therefore, the spiral bowl machines are mainly used for continuous processing of light and delicate parts that do not allow nicks and bending.
Logically the parts loading should take place at the inner section to allow parts to spread out rather than bank and hit each other while travelling through the spiral process channel. The parts and media separation is preferably done outside of the machine on a separately driven screen machine with media return conveyor.
The spiral machines are available in channel lengths of 9 m (354") up to 25 m (984") and channel widths of 100 mm (4") up to 350 mm (14"). The through-flow speed is difficult to adjust for different cycle times; therefore, the channel length will determine the process cycle. An average cycle time indication is 1 min/m (1 min/ 39"). This means that a max. cycle time of 25 min can be achieved.
Spiral bowl continuous machines require less floor space than linear machines and can be easily incorporated in machining centres or small part die casting production.

Walther Trowal manufactured and delivered the first spiral bowl machines (Multi-channel models type MC) in Europe for Bosch machined aluminium pump housings and INA bearing cages. The MC machines opened the market for high tech delicate components which previously could not be processed continuously in mass finishing equipment.

For Information: 
Walther Trowal GmbH&Co.KG
Rheinische Str. 35 - 37
42781 Haan, Germany
Tel: +49-2129-571-0
Fax:  +49-2129-571-225
E-Mail: info@walther-trowal.de