Cleaning/finishing materials.

A cleaning department is a key center of the foundry that requires direct management oversight to maximize its expensive mix of labor (estimated to be one-third of a foundry's total labor bill), process materials and costly, maintenance-sensitive equipment.

Cleaning operations remove molding material, risers, fins, ingates and other excess surface metal; clear holes or passageways; and remove fused and penetrated sand defects to prepare castings for finishing.

Cleaning begins at shakeout and precedes finishing operations. Consumable materials--such as saw blades, cutting and grinding wheels, abrasive and nonabrasive cleaning systems, and shot and grit--are cleaning department essentials.

Cleaning costs weigh heavily on a foundry's budget and command close foundry management supervision to control:

* work flow, handling and storage efficiency to, through and from the cleaning department;

* consumable materials expenses;

* total casting cleaning process time;

* maintenance scheduling to optimize equipment productivity and return on investment.

Gates and risers often break off during shakeout or are knocked off laboriously with a sledge hammer. This gradually gave way to simpler, quicker methods that use mechanical wedges, saws, grinders, belts and blades, shotblasting and assorted power tools.

Gates, sprues, runners and risers are removed by a number of manual or automated cutoff and surface cleaning machines. Some of the consumables used in the cleaning and finishing room are:

Saw blades--These are used to cut any metal and thickness that can be positioned to accommodate the saw; conventional saw blades can be resharpened (more expensive carbide-tipped blades cannot) and require lubrication and a coolant to prolong tool life and add to cutting efficiency.

Friction saws blades--Their high speed (3000-15,000 fps) builds up nonpenetrating heat in the casting (1600-2800F), softening the metal to be cut and facilitating sawing action. A low-cost tool, it is effective for stainless steel, armor plate, steel alloys of almost any hardness and all ferrous metals. They are precise enough to sever stubs and fins accurately and close to the casting surface.

Cutoff/grinding wheels--These wheels are among the fastest ways to clean any metal casting. They use abrasive-coated or bonded wheels to remove large appendages and to reduce pads or surface flaws. Economical abrasive wheels are mounted on swing frames suspended from bridge cranes (for use on castings too large to manipulate), floor stand grinders, fixed chop stroke or locked-head, push-through cutoff machines. They are used in conjunction with floor-mounted, multiaxis casting positioners.

Relationship of Shot Size to Coverage

SAE shot size      Approximate shot
(mid-range)        pellets per pound

780                       8,000
660                      14,000
550                      26,000
460                      45,000
390                      65,000
330                     110,000
280                     210,000
230                     360,000
170                     520,000
110                   1,700,000
70                    6,000,000

Fig. 2. Relationship of shot size is the key to effective work
coverage; smaller shot yields better coverage.
Relationship of Shot Size to Impact

SAE shot size      Approximate relative
(mid-range)           impact value

780                      800
660                      500
550                      300
460                      165
390                      100
330                       60
280                       36
230                       22
170                       12
110                        5
70                         1

Fig. 3. Table illustrates the relationship between shot size
and impact value; a 2:1 diameter ratio equals impact an energy
ratio of 8:1.

Grinding disks for handheld, floor stand or swing grinder machines are available in a wide variety of sizes, shapes and abrasive grain finishes suitable for any metal. Automated and CNC programmable axes snag grinding systems are available to reduce grinding time, extend grinding wheel life, add to operator safety and efficiency, and increase casting acceptability.

Metallic abrasive blast cleaning--This impact cleaning is neither cutting, grinding or abrading. It uses steel shot designated by the letters S-Steel and grit, angular crushed abrasive of any hardness range and designated as G-Steel. Five basic wear components are included in a blast cleaning machine: the throwing TABULAR DATA OMITTED wheel, a separator, a dust collector, and abrasive handling and work handling systems. All require maintenance to compensate for operational wear.

The shotblast machine uses high velocity steel shot or grit directed at a casting to provide the final surface finish and clean internal casting passages. Properly maintained blast cleaners minimize the cost of successive cleaning and finishing operations.

Small castings are cleaned by being rotated or tumbled on an endless belt under grit or shot blast. Larger castings are placed on revolving tables or are suspended from hooks where shot or grit is thrown at them as they slowly turn, exposing all surfaces to the blast.

The shot is only as effective as the direction, volume and speed of the shot is set for each casting.

Air-carbon arc cutting--Widely used to replace some grinding and chipping operations, it is one of the most economical methods for removing excess metal. Heat is generated by the electric arc created between a copper-coated, carbon-graphite electrode and the part.

Oxyacetylene cutting--This method removes gating and risers from ferrous castings. Preheated casting causes ignition of the |O.sub.2~ and the subsequent melting of the target metal, and is used with an oxygen lance for cutting appendages from large castings.

Thermal torching--Used for cutting heavy risers, thermal torches use steel, aluminum and magnesium alloy rods and high-velocity oxygen to create a burn of 10,000F or more. The torch creates a kerf, or slot, that is easily controlled by the operator. Cutting speed is based on the velocity of the oxygen stream and nozzle size.

Low-velocity oxygen torches are used as gougers to remove small defects more effectively than chipping (particularly in confined spaces) and for scarfing, or reducing large pads using medium velocity oxygen and a large nozzle.