Benchmarking Aluminum Gating Systems for Better Casting Quality.
Fourteen foundries designed a gating system for a standard sample casting in an effort to determine which aluminum gating practices are most successful.
While the basics of horizontal gating system design have been understood for more than 50 years, planning gating systems must take many other factors into account. The volume requirements for the part being manufactured, process control of metal and sand used to make the casting, the skill of the workforce, and time constraints In law, time constraints are placed on certain actions and filings in the interest of speedy justice, and additionally to prevent the evasion of the ends of justice by waiting until a matter is moot. imposed by the customer all affect gating design.
Molding equipment often dictates the placement and orientation of patterns on the plate to maintain proper mold density and draw sand pockets. Further, it can limit the type, shape and placement of pouring sprues, as well as risering techniques. Many automatic molding machines (Woodworking) A planing machine for making moldings
(Founding) A machine to assist in making molds for castings.
See also: Molding Molding , and even manual squeeze molding methods, mandate unique requirements for sprue sprue, chronic disorder of the small intestine caused by impaired absorption of fat and other nutrients. Two forms of the disease exist. Tropical sprue occurs in central and northern South America, Asia, Africa, and other specific locations. size, shape and location as well as pattern positions on the matchplate. In addition, the use of mold chills to provide directional solidification Directional solidification is a series of measures applied to control the feeding of castings. As most metals and alloys solidify, changing from the liquid state to the solid state they will undergo an appreciable volume contraction. will affect the productivity of the molding operation.
Melting and pour-off operations also are critical. Beyond having sufficient metal and labor to supply the molding line, an inability to maintain process control of the basic parameters of chemistry, gas and inclusion level, and temperature all affect casting shrinkage Shrinkage
The amount by which inventory on hand is shorter than the amount of inventory recorded.
The missing inventory could be due to theft, damage, or book keeping errors. (and the need for enlarged risers), misruns, general porosity porosity /po·ros·i·ty/ (por-os´it-e) the condition of being porous; a pore.
1. The state or property of being porous.
2. levels, surface finish, cleaning expenses and mechanical properties.
These factors drive and temper the need to squeeze as many units into the mold as possible in order to maximize productivity. Thus, the number of impressions, the placement of risers and runners, and their dimensions and location with respect to the downsprue, normally define the ultimate profitability of the work. Compromises often must be made in order to achieve the desired quality levels, and this is where the knowledge, art and skill of the production team will influence the cost of manufacture.
A benchmark study initiated by the AFS A distributed file system for large, widely dispersed Unix and Windows networks from Transarc Corporation, now part of IBM. It is noted for its ease of administration and expandability and stems from Carnegie-Mellon's Andrew File System.
AFS - Andrew File System Aluminum Gating and Risering Committee (2-H) identified and evaluated gating system designs used by aluminum sand foundries in an effort to determine which methods were most effective.
A representative group of 30 commercial aluminum sand foundries were asked to replicate a plastic pattern test shape (Fig. 1) and to mount as many impressions as would be normal in their operation. Quality requirements were furnished fur·nish
tr.v. fur·nished, fur·nish·ing, fur·nish·es
1. To equip with what is needed, especially to provide furniture for.
2. with the test shape, and participants were expected to furnish fur·nish
tr.v. fur·nished, fur·nish·ing, fur·nish·es
1. To equip with what is needed, especially to provide furniture for.
2. a minimum of three mold systems with gating and risers still attached.
The test casting was designed to permit a minimum of three castings on a 14 x 20-in. matchplate, and a maximum of nine impressions on a 20 x 24-in. automatic plate pattern. It consists of a rectangular box with a heavy section, two remote bosses connected by a feed rib and a thin section with misrun potential.
Foundries were asked to manufacture the samples as though they are "commercial" castings (Level 2-3),with an absence of significant porosity on the two machined surfaces. The machined areas partially covered both a cope and a drag horizontal plane horizontal plane
A plane crossing the body at right angles to the coronal and sagittal planes. Also called transverse plane.
horizontal plane and were intended to reveal any gating-induced trapped air or porosity. Planned quality assessments included X-ray to ASTM ASTM
American Society for Testing and Materials standards, a penetrant pen·e·trant
Penetrating; piercing: a penetrant wind from the north.
Something that penetrates or is capable of penetrating. test on the two machined surfaces and a pressure test on the drilled bosses. The projected volumes on the 319 alloy were for 1500 pieces/month.
Test castings were made to verify the utility of the shape at Reliable Castings, Inc., Sidney, Ohio Sidney is a city in Shelby County, Ohio, United States. The population was 20,211 at the 2000 census. It is named after English explorer Sir Phillip Sidney and is the county seat of Shelby CountyGR6. , and were modified to increase the diameter of the internal bosses and add a connecting rib. Plastic impressions then were made and distributed to the foundries.
As part of the process information, the foundries were asked to:
* report the pouring temperature and time in seconds;
* take two rapid prototyping Building a part one layer at a time using a method of additive fabrication such as 3D printing. Such parts are used for concept modeling to determine if the product design meets the customer's expectations. RPT RPT - Unify. Report Writer Language. samples at the time of pour with one solidified so·lid·i·fy
v. so·lid·i·fied, so·lid·i·fy·ing, so·lid·i·fies
1. To make solid, compact, or hard.
2. To make strong or united.
v.intr. under vacuum and the second under atmospheric pressure atmospheric pressure
or barometric pressure
Force per unit area exerted by the air above the surface of the Earth. Standard sea-level pressure, by definition, equals 1 atmosphere (atm), or 29.92 in. (760 mm) of mercury, 14.70 lbs per square in., or 101. ;
* save a spectrographic spec·tro·graph
1. A spectroscope equipped to photograph or otherwise record spectra.
2. A spectrogram.
spec disc at the time the castings are poured in order to sample the metal used;
* supply the general sand properties and a selling price.
Measurements were made to define the casting yield, gating and riser dimensions, the use of screens or filters, the number and placement of chills, and any apparent surface defects (Table 1).
Casting yield was measured by weighing the complete gated mold, removing the castings and recording their weight, and developing a ratio of casting weight a weight that turns a balance when exactly poised.
- B. Trumbull.
See also: Casting to poured weight.
Gating ratios for the sprues were developed by measuring the sprue diameter at the base, the cross-sectional area of any runners exiting from the sprue well and the total ingate width at the casting. If screens were used, the open area covered with metal was expressed as an area unit and compared to the sprue diameter. If the sprue area was less than the screen area, the choke point In military strategy, a choke point (or chokepoint) is a geographical feature (such as a valley or defile) which forces an army to go into a narrower formation (greatly decreasing combat power) in order to pass through it. was assumed to be at the base of the sprue, and the ratios were calculated accordingly. In those cases in which the screen was an actual obstruction or choke (jargon) choke - To fail to process input or, more generally, to fail at any endeavor.
E.g. "NULs make System V's "lpr(1)" choke." See barf, gag. in the gating system, or if an intermediate downstream choke was used, the first digit in the gating ratio is enclosed en·close also in·close
tr.v. en·closed, en·clos·ing, en·clos·es
1. To surround on all sides; close in.
2. To fence in so as to prevent common use: enclosed the pasture. in parentheses See parenthesis.
parentheses - See left parenthesis, right parenthesis. to highlight the downstream choke.
The RPT samples were measured for specific gravity specific gravity, ratio of the weight of a given volume of a substance to the weight of an equal volume of some reference substance, or, equivalently, the ratio of the masses of equal volumes of the two substances. (S.G.) in both the solidification so·lid·i·fy
v. so·lid·i·fied, so·lid·i·fy·ing, so·lid·i·fies
1. To make solid, compact, or hard.
2. To make strong or united.
v.intr. under reduced-pressure mode and the atmospheric pressure solidification mode. The difference in values between the two solidification modes was assumed to be related to the hydrogen gas content of the melt, and the reduced pressure In thermodynamics, the reduced pressure of a fluid is defined as its actual pressure divided by its critical pressure.
A visual assessment was made of the machined castings with special attention to visual shrinks and porosity on the cope and drag In foundry work, the terms Cope and Drag refer to the upper and lower parts of a two-part casting flask, used in sand casting. The flask is a wood or metal frame, which contains the molding sand, providing support to the sand as the metal is poured into the mold. surfaces. The milled surfaces produced different levels of surface finish and "smear smear (smer) a specimen for microscopic study prepared by spreading the material across the slide.
Pap smear , Papanicolaou smear see under test. ." The large, flat area of the casting was machined with a fly cutter, and the internal pad was milled with a 1.5-in. end mill, producing less smear and possibly even inducing some enlargement enlargement,
n an increase in size.
n.pr See hyperplasia, gingival, Dilantin.
n of microporosity. On both surfaces 0.04 in. of stock was removed.
Radiographic radiographic (rā´dēōgraf´ik),
adj relating to the process of radiography, the finished product, or its use. inspection of the castings was conducted at the XRI (EXtensible Resource Identifier) An OASIS standard for a high-level naming/identification system for individuals, businesses, communities, services and data on the Internet. Testing facility, Holland, Michigan, using a double film technique to ASTM E-155 standards.
Penetrant testing of the castings was done with a red dye, water-washable system with emphasis on the two machined horizontal casting surfaces. A visual assessment of the number and size of indications was made, and a ranking system using a 1-5 (good-bad) scale was used to rate the result. Table 1 lists the ratings developed with separate assessments made of the cope and drag surfaces. When the castings were molded with the open end in the up" position, the rating number includes a superscript Any letter, digit or symbol that appears above the line. For example, 10 to the 9th power is written with the 9 in superscript (109). Contrast with subscript. "I" to designate the appropriate surface.
Due to expanded work schedules, only 14 foundries submitted sample castings with 1-8 impressions in time for the study. Two of these operations rigged a single impression pattern, with subsequent plans to make multiple impression equipment, but could not move beyond the initial trial shapes.
Each foundry chose a slightly different way of achieving the commercial quality casting. All of the test castings were compared to determine which gating design features offer the best results, and some of the most telling gating designs are presented in this article.
Foundry "B" used an automatic matchplate molding machine and rigged an eight-impression plate to pour the samples (Fig. 2a-2b). Four impressions were mounted on each side of a common runner/riser bar, which was supplied by a heavily choked choke
v. choked, chok·ing, chokes
1. To interfere with the respiration of by compression or obstruction of the larynx or trachea.
a. runner bar just downstream of the sprue well. A typical reverse-taper sprue was used to introduce metal to the mold, with a glass screen conventionally placed at the bottom of the sprue. Chills were not used.
As a result of the heavy choke, the gating ratio was (1):6:43. The use of the choke is a standard procedure to balance the effect of the reverse-taper sprue in this foundry, and it was effective in producing sound castings. The additional impressions did help the pouring yield, with a 67% level achieved with rectangular risers. On the initial visual inspection, some superficial cope dross was apparent on the sample castings but was removed with the 0.04-in. machining cut on both cope and drag surfaces.
The casting quality was excellent in the evaluation phases, with moderate porosity found on X-ray examination, but relatively few penetrant indications appeared on the machined surfaces. This was somewhat surprising in view of the relatively high porosity level measured in the RPT samples. Gas levels were moderately high at 2.6% porosity, and a "3" on the polished cross section of the RPT sample.
Castings produced by Foundry "D" utilize a proprietary gating system (Fig. 3) featuring an insulated in·su·late
tr.v. in·su·lat·ed, in·su·lat·ing, in·su·lates
1. To cause to be in a detached or isolated position. See Synonyms at isolate.
2. sleeve with a bottom ceramic filter. The combined assembly functions as both a riser and gating system. Round chills were used on both internal bosses.
The system exhibited a pouring yield of 63%. Casting quality was excellent, with no apparent defects found on X-ray and only light porosity found on the penetrant test.
Foundry "E" produced the test casting as a single impression squeezer casting (Fig. 4a-4b) on a 14 x 18-in, plate, with a heavy single riser and multiple chills. The novel features of the casting system are the very small (0.5-in.) downsprue and the use of a metal screen with 50% open area. With the small downsprue, the screen did not function as a choke, producing a gating ratio of 1:1.75:10.1. The pouring rate was not recorded, but was assumed to be on the low side of the rates in the study.
Casting quality was excellent, with no apparent defects found on X-ray and only a few minor penetrant indications on the machined surfaces. Gas level, as measured by the RPT, was low, and it is assumed that the cooling rate of the casting was fairly rapid because of the large chills used. These are believed to contribute to the absence of porosity.
Foundry "G" ran the sample castings on a squeezer line, with three impressions (Fig. 5a-5b) mounted on a 14 x 19-in. plate. The gating system and samples produced a 66% pouring yield.
The rigging rigging, the wires, ropes, and chains employed to support and operate the masts, yards, booms, and sails of a vessel. Standing rigging is semipermanent, consisting mainly of mast supports, the fore-and-aft stays, and the stays running from the masthead to each side includes a 1-in. downsprue with a glass screen at the base and relatively small runners exiting the well. The runner system is external from the risers, and has a "pop-off" cut on a runner extension to the third casting. The foundry used cylindrical cyl·in·dri·cal
Of, relating to, or having the shape of a cylinder, especially of a circular cylinder. risers with a notch and dimple in the top to promote feeding, a system that appears to be fairly effective from the appearance of the risers. Some choke reduction of the downsprue is provided by the screen, but the gating ratio is still among the closest to a pressurized pres·sur·ize
tr.v. pres·sur·ized, pres·sur·iz·ing, pres·sur·iz·es
1. To maintain normal air pressure in (an enclosure, as an aircraft or submarine).
2. system of those examined in the study. The choked ratio is (1):1.1:2.
The casting quality evaluations showed a Level 3 porosity on X-ray and more penetrant indications. Some cope dross was evident. Metal quality was considered to be a factor in some of the porosity, with 2.6% measured in the combined RPT evaluation. Some large pores also were visible in the polished surface of the RPT sample.
The samples (Fig. 6a-6b) submitted by Foundry "K" were molded on a squeezer line using a 16 x 20-in. plate with four mounted impressions. Of all the foundries, this was the only operation that used a gating system incorporating a ceramic filter. The major elements of the system are shown in the pictures and depict the filter placement and associated enlargement of the runner system. The additional volume of metal in the runner system to accommodate the filter, coupled with possibly oversized o·ver·size
1. A size that is larger than usual.
2. An oversize article or object.
adj. o·ver·size also o·ver·sized
Larger in size than usual or necessary. risers, contributed to a 53% pouring yield.
In the calculation of the gating ratio, the filter area was assumed to be large enough that it did not function as a choke, and the ratio was accordingly controlled by the downstream runner and ingates. This produced a ratio of 1:1.2:6.5 with the large 1.12-in. downsprue being a major control.
The risers were opened to the cope surface by the molder mold·er
v. mold·ered, mold·er·ing, mold·ers
To crumble to dust; disintegrate.
To cause to crumble. See Synonyms at decay. with a 2.5-in. pipe to promote additional feeding. This additional volume of feed metal probably caused the visual appearance of the lower rectangular risers, which appeared to be as free of shrinkage as the castings.
The quality assessments showed a slightly higher than average level of porosity on X-ray inspection and minor penetrant indications on both the machined cope and drag surfaces.
Foundry "L" produced molds on a 16 x 20-in, squeezer plate with four mounted impressions (Fig. 7a-7b). The gating system features the only group of samples submitted with a top riser on the castings. The riser measures 1.75 x 3.25 x 3.75 in. and is positioned to cover both the inside bosses and pad. Chills also are used on the bosses. The system is somewhat unique in that the ingates are not supported with any direct feed metal at the point of entry.
The downsprue is rectangular and measures 0.75 sq in. at the base to effectively choke the system. A glass screen does not affect the choke before metal flows through a somewhat restricted well and into the runner system. The gating ratio is 1.0:2.22:4.44.
Visual quality of the casting and machined surfaces was good, and the X-rays found only one casting with an elongated e·lon·gate
tr. & intr.v. e·lon·gat·ed, e·lon·gat·ing, e·lon·gates
To make or grow longer.
adj. or elongated
1. Made longer; extended.
2. Having more length than width; slender. pore pore (por) a small opening or empty space.
alveolar pores openings between adjacent pulmonary alveoli that permit passage of air from one to another. , suggesting trapped air. The penetrant testing similarly produced a few indications, with a 1 rating on both cope and drag surfaces.
Foundry "N" also uses an automatic molding machine with alternate sprue capabilities, but is using a reverse-taper sprue. The test castings (Fig. 8a-8b) were made on a 20 x 24-in, plate as a four impression pattern.
The 1.18-in.-diameter downsprue exits into a round bottom well and then splits into a double runner system with an almost immediate transition from a drag-to-cope to drag runner. The overlap is controlled to produce a choke effect on both sides with a total area or 0.43 sq in. The foundry personnel refer to this overlap and choke as a "cope dross trap." The choked gating ratio is (1):3:8.6.
Two cylindrical risers are positioned over the drag runner, each feeding a pair of castings. These risers also are dimpled on the top and show the same effective riser piping as those made by Foundries "G" and "J." The ingate to the casting is taken off the bottom of the riser, and a visible reverse shrink was developed on the flat bottom of all risers. The condition is believed to be partially the result of steam pressure from the evaporation evaporation, change of a liquid into vapor at any temperature below its boiling point. For example, water, when placed in a shallow open container exposed to air, gradually disappears, evaporating at a rate that depends on the amount of surface exposed, the humidity of mold moisture.
The visual quality of the castings and machined surfaces was good. The X-ray examination revealed porosity as Level 3, and penetrant testing produced ratings as 2 on both the cope and drag surfaces. The gas level in the melt was low (0.4%) on the combined RPT test, and 2.73 on S.G. of the reduced pressure sample.
Foundry "P" submitted castings produced on a squeezer line, with two impressions (Fig. 9a-9b) on a 14 x 16-in. plate. The castings featured a different form of gating with a metal screen used as a vertical filter element, a much heavier runner and riser system and a large overflow beyond the casting,
The downsprue is a tapered ta·per
1. A small or very slender candle.
2. A long wax-coated wick used to light candles or gas lamps.
3. A source of feeble light.
a. wedge with a 0.44 x 0.75-in, opening into the well. As metal leaves the well it quickly encounters a metal screen with only 50% open area. All sample castings had a large volume of film oxides stacked up at the screen, so this method appears to be a very effective trap. After the screen, the metal flows through a heavy drag runner to an overflow, and then backs into two mold cavities and a heavy open-top riser. The gating ratio is controlled by the area of the sprue choke and has values of 1:4.1:32.8. Three internal chills were used: one on the pad and two on the bosses.
This shop does not pour 319 alloy as a general rule, and accordingly poured the samples with C355. Casting quality was excellent with clean machined surfaces, X-ray at Level 1 porosity, and only a few penetrant indications on both the cope and drag surfaces.
One of the most puzzling aspects of the results is the lack of a correlation between the levels of gas in the melt, as judged by the RPT sampling, and the porosity results found on X-ray. An examination of the actual RPT buttons revealed wide differences in both size of sample, probable vacuum levels used in the testing, and even assumed inclusion levels as judged by the surface roughness of the samples and shape of the pores. A possible cause may have been a difference in performance of the RPT procedure and sample collection methods, which were not defined in the project plan.
Samples from three foundries were judged to have either "no apparent defects" or a Level 1 porosity on the X-ray examinations. These included samples D, E and P. Rating the gas buttons on a scale of 1-10, sample D would be a "5" (2.61 S.G., 4.0%); sample E would have a rating of "2" (2.73 S.G., 0.8%); and sample P would be rated at "2" (2.62 S.G. for C355, 0.5%).
Other considerations (such as pouring technique) not documented in the study could have a pronounced effect. These would include: skimming Skimming
An electronic method of capturing a victim's personal information used by identity thieves. The skimmer is a small device that scans a credit card and stores the information contained in the magnetic strip. the ladle to remove surface dross, the use of an adequate pouring basin or cup, keeping the sprue filled and adding metallostatic pressure to the runner system by elevating the pouring ladle above the mold.
The best answer may be that these test samples were to be made as commercial castings and were manufactured to that level of quality. Degassed melts were targeted in most cases, if that was the practice in the foundry and available at the time the castings were poured. With several exceptions, the sample group did meet the accepted definition of commercial castings and accordingly met the objectives of this study.
Without critiquing individual systems, the following practices are recommended:
* pouring basin--An adequate pouring basin is mandatory to keep the sprue completely filled at all times during the pour;
* sprue--A tapered sprue is desirable, with rectangular cross sections preferred. Where this is not possible, aggressive choking Choking Definition
Choking is the inability to breathe because the trachea is blocked, constricted, or swollen shut.
Choking is a medical emergency. When a person is choking, air cannot reach the lungs. of the metal stream as it exits the well appears to offer a significant benefit to casting quality;
* sprue well--Wells have been minimized in some of the gating systems, but it is felt to be beneficial. Designs with flat bottoms and adequate volume are preferred;
* runners--Runner sizes must be adequate to deliver fluid metal to the mold cavities without agitation agitation /ag·i·ta·tion/ (aj?i-ta´shun) excessive, purposeless cognitive and motor activity or restlessness, usually associated with a state of tension or anxiety. Called also psychomotor a. or jetting. Drag runners seem to be preferred, but cope traps for dross may provide benefit in some cases;
* risers--Cylindrical or ellipsoidal shapes are preferred to improve feeding efficiency and pouring yield. A molded-in top dimple seems to have a positive impact upon feeding. The riser should be positioned slightly away from the casting and have a bottom contour contour or contour line, line on a topographic map connecting points of equal elevation above or below mean sea level. It is thus a kind of isopleth, or line of equal quantity. that will ensure continued feeding from the thermal center;
* screens and filters--While they add cost, screens and filters may be required to achieve desired results. With a properly balanced system, their need is minimized;
* chills--Chills can solve problems, but also will add cost to the molding operation. Use modeling to confirm they are needed and that the size and mass of the chills are adequate. Other lower cost options may exist.
A better understanding is required of the relationship between hydrogen levels in the melt, the level and types of inclusions present, mold metal reactions contributing additional levels of hydrogen to metal entering the casting cavity, and the generation of negative pressures in the gating system which can help aspirate as·pi·rate
To take in or remove by aspiration.
A substance removed by aspiration.
The removal by suction of a fluid from a body cavity using a needle. mold moisture into the metal stream to add hydrogen to the system. This benchmarking study confirms the need for solutions that will minimize the microporosity observed in the samples.
This paper was adapted from a paper presented at the 1st International AFS Conference on the Gating, Filling and Feeding of Aluminum Castings. Proceedings are available through AFS Publications at 800/537-4237.
Pouring Characteristics and Test Results of Sample Castings Foundry Plate Imp. Yield (%) Pouring Gating S.G. Por. Chills Visual Rate Ratio (%) A 14 x 22" 4 49 1.60 1: 9.9: 17.0 2.71 1.1 2 / 2 B 20 x 24" 8 67 0.92 (1): 6: 43 2.67 2.6 none 1 D 16 x 20" 2 63 1.50 N/A 2.61 4.0 2 / 1 E 14 x 18" 1 36 1: 1.75: 10.1 2.73 0.8 4 / 1 F 14 x 19" 4 69 2.20 (1): 1.4: 8.5 2.72 Nil none 4 G 14 x 19" 3 66 1.60 (1): 1.1: 2.0 2.67 2.6 none 4 H 20 x 24" 4 65 1.55 1: 1.43: 5.33 2.20 18.2 1 / 5 J 20 x 24" (6) (64) 1: 2.4: 11.5 2.69 1.8 none 1 K 16 x 20" 4 53 1.65 1: 1.2: 6.5 2.74 Nil none 2 L 16 x 20" 4 52 1.98 1: 2.2: 4.4 2.70 0.8 2 / 1 M 14 x 18" 4 88 1.10 1: 3.0: 8.5 2.72 0.8 none 4 N 20 x 24" 4 73 1.37 (1): 3.0: 8.6 2.73 0.4 none 1 O 14 x 19" (4) (61) (0.5) 1: 6.0: 36.0 2.72 0.8 Fin 1 P 14 x 16" 2 43 1.40 1: 4.1: 32.8 2.62 0.5 3 / 1 Foundry X-Ray Penetrant Price ($)/1500 A Por. 2-3 C: 1; D: 2 7.95 B Por. 3 C: 1; D: 2 5.79 D NAD C: 3; D: 2 E NAD C: 1; D: 2 F Por. 3, Gas 2 C: 4; D: 2 G Por. 3 C: 3; D: 3 4.86 H Por. 4 C: 5; D: 4 5.47 J Por. 4 C: 2; D: 3 K Por. 4 C: 2; D: 3 6.56 L Elong. 1 C: 1; D: 2 M Sh. 8, Por. 4 C: 5; D: 5 N Por. 3 C: 1; D: 2 6.35 O Sh. 3 C: 2; D: 1 P Por. 1 C: 2; D: 2