38 modern casting / September 2000

reen sand moldmaking is

equal parts technology, pro-

cess and experience. How-ever, even with the highest levels of

technology, an efficient and perfected

mold production process, and amoldmaker with more than 30 years of

experience, molding related-problems

and defects still occur.The key when problems or defects

arise is to analyze the situation, isolate

the problem or defect, and eliminate it.In pursuit of this objective, modern cast-ing has published the following easy-to-

use reference tables for identifying mold-ing-related problems and casting de-

fects. Prepared by an AFS Molding Meth-

ods & Materials Div. Green Sand Mold-ing Committee (4-M) for the AFS book

An Operating Guide to High-DensityMolding, these tables list molding prob-lems or defects and the variables that

could be causing the problem/defect.

For example, for a mold that hasfriable edges, the molding variables that

could be causing the problem are (in

order of probable contribution): hotsand, low moisture, high methylene

blue clay, pattern problems, low meth-

ylene blue clay and/or equipment prob-lems. For the casting defect of veining,

the molding variables that could be

causing the problem are (in order ofprobable contribution): low cushion/

carbonaceous material, high mois-

ture, uneven mold hardness, lowmoisture, wrong preblend or mixture,

lack of mold vents, mold wall move-

ment, hard molds or cores, and/or

excessive metal temperature.These tables may not solve your mold-

ing problems, but they will help isolate

problem variables for easy identifica-tion. Often, isolating the molding-related

problem is more difficult than solving it

due to all the variables interacting inthe green sand molding process.

As an added value to its readers, mod-ern casting also has posted this easy touse reference table on its website at

www.moderncasting.com. This table can

be printed or copied to another docu-ment to be distributed to foundry quality

control and molding personnel.

—Alfred T. Spada, managing editor

For a free copy of this article circle No. 337 on theReader Action Card.

Identifying Molding Problems

A modern casting Staff Report

This easy-to-use reference table aids foundries in determining which variables

are causing their mold problems and/or resulting casting defects.

High-Density Molding-RelatedCasting Defects Causes

Shift ........................................................................................................ 12,11 and 18

Ram-Away ............................................................................................. 18,1, 4 and 3

Burn-in ............................................................ 1, 4, 24, 5, 9, 10, 19, 16, 21, 22 and 8

Blows ................................................................ 1, 3, 4, 10, 24, 19, 14, 20, 15 and 26

Scabs ............................................. 1, 15, 2, 4, 6, 7, 10, 21, 22, 13, 16, 28, 17 and 6

Sand Inclusions ........................................................2, 3, 4, 22, 28, 27, 24, 10 and 5

Cracked Casting ........................................................................... 1, 3, 11, 15 and 26

Crushes ....................................................................... 2, 3, 11, 18, 12, 23, 25 and 15

Drops .................................................................................... 1 and 4, 2 and 3, and 11

Porosity ........................................................ 20, 1, 4, 10, 9, 26, 22, 15, 28, 7 and 21

Hot tears ................................................................................. 1, 4, 15, 21, 22 and 26

Warpage .......................................................................................... 2, 3, 11, 5 and 16

Veining ................................................................. 13, 1, 16, 2, 28, 20, 17, 15 and 21

Rat-Tails ........................................................... 13, 1, 16, 2, 4, 28, 20, 27, 15 and 21

Shrink ........................................................................ 17, 5, 18, 11, 26, 22, 21 and 28

Buckles ............................................................. 13, 1, 16, 2, 4, 18, 20, 17, 15 and 21

Erosion Scabs .........................................................1, 5, 14, 9, 22, 19, 24, 21 and 28

Swells .................................................................................. 5, 1, 11, 17, 4, 28 and 16

Pin Holes ...................................................... 20, 1, 4, 10, 9, 26, 22, 15, 28, 7 and 21

Penetration ...................................................................... 20, 21, 1, 4, 5, 19, 24 and 8

Causes

1. High Moisture

2. Low Moisture

3. High Methylene Blue Clay

4. Low Methylene Blue Clay

5. Poor Ram or Squeeze

6. Mold Spray Application

7. Mold Spray Baumé

8. High Ferrostatic Head

9. Mold Spray Not Dry

10. Excessive Pattern Spray

11. Equipment Problems

12. Pin and Bushing Wear

13. Low Cushion/Carbonaceous Material

14. High Cushion/Carbonaceous Material

15. Hard Molds or Cores

16. Uneven Mold Hardness

17. Mold Wall Movement

18. Pattern Problems

19. Insufficient New Sand

20. Lack of Mold Vents

21. Excessive Metal Temperature

22. Gating

23. Build up on Flask

24. Hot Sand

25. Improper Coresetting

26. Melt Analysis

27. Contaminated Sand

28. Wrong Preblend or Mixture

Download these tables at www.moderncasting.com

modern casting / September 2000 39

Cracks in molds initiate at the surface of the mold cavity andextend through the zones of least resistance in the mold. Theresult is the formation of large thin fins in planes related tothe position of the casting in the mold. Cracked molds can bedue to pattern problems, equipment problems, oversizedcores, low methylene blue clay, coresetting and/or low sand-to-metal ratio.

Mold stickers are an irregular massive projection on the copesurface of the casting with an appearance that suggests detach-ment of a part of the mold wall. This mold problem usually isaccompanied by sand inclusions or missing material embeddedin the casting surface. Mold stickers can be due to hot sand,high moisture, low methylene blue clay, poor pattern sprayapplication, equipment problems, pattern problems, lowmositure, and/or wrong preblends or mixture.

Pinholes are small cavities (often the size of the head of a pin)located in extended colonies across the casting surface. Themolding-related causes of pin holes can include: a lack of moldventing, high moisture in the mold, low methylene blue clayand/or excessive pattern spray.

Sand inclusions in a casting are usually compact and occur inthe vicinity of the cope surface of the casting. Often they arevisible on the rough casting, but may appear only upon machin-ing. The molding-related causes of sand inclusions can include:low mold moisture, high or low methylene blue clay, gatingproblems, wrong preblend and/or sand mixture.

Cracked Molds Mold Sticker

Sand InclusionsPinholes

BackupSand

FacingSand

High-Density Molding Problems Causes

Cracked Molds ........................................................................ 12, 10, 8, 4, 15 and 17

Ram-Away ............................................................................................ 12, 1, 4 and 3

Push-Ups ........................................................................................ 10, 12, 8, 4 and 1

Sagging ......................................................................................... 12, 10, 4, 1 and 16

Stickers ........................................................................... 13, 1, 4, 14, 10, 12, 2 and 6

Friable Edges ............................................................................ 13, 2, 3, 12, 4 and 10

Sand Stickers in Hoppers ................................................................. 1, 4, 3, 13 and 6

Run-Outs ............................................................ 9, 11, 12, 10, 8, 5, 15, 18, 1 and 17

Shakeout Problems ................................................................................ 3, 1, 6 and 7

Losing Sand at Shakeout ................................................................... 1, 4, 3, 7 and 6

Hot Sand ....................................................................................... 10, 16, 7, 17 and 4

Short Sand Volume ............................................................................... 1, 4, 10 and 3

Causes

1. High Moisture2. Low Moisture3. High Methylene Blue Clay4. Low Methylene Blue Clay5. Poor Squeeze6. Wrong Preblend or Mixture7. Insufficient New Sand8. Oversize Cores9. Sand on Flask Flanges10. Equipment Problems11. Pin and Bushing Wear12. Pattern Problems13. Hot Sand14. Pattern Spray15. Coresetting16. Insufficient Sand17. Low Sand-to-Metal Ratio18. Low Joints