Are your products suffering from casting defects? The good news is they're entirely preventable. Read on for causes and prevention of the top casting defects.
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Your cast iron metal pan leaves the factory with pinholes, leading to a slew of complaints from your customers. What happened? How could you have prevented this from happening?
Foundry production is a complex multi-step process. The technical level of each process varies greatly. Skills of the operator, quality management and equipment can all affect the final quality of the casting.
The key to preventing product defects in your casted products is to set clear expectations and tolerances for quality issues with your supplier (related: How Experienced Importers Limit Product Defects in 3 Stages [eBook]).
But before you can do that, you need to have a clear understanding of the different types of casting defects and their causes. Only then can you prevent casting defects and avoid sending defective products to your customers.
WHAT ARE CASTING DEFECTS?
Metal casting is a manufacturing process in which molten metal is poured into a mold and allowed to solidify into a desired shape or component. Casting defects can occur for a wide variety of reasons such as pouring conditions, environmental conditions, alloy composition, and much more.
When a casting defect is present, it can hurt the integrity or functionality of the product. Some casting defects can be tolerated but most will need to be removed or prevented.
Read on or click the links below to jump to the section for each of these types of casting defects.
Gas porosity casting defects and causes
Gas porosity occurs when the metal traps gas (most often nitrogen, oxygen or hydrogen) during casting.
When the casting cools and solidifies, bubbles form because the solid form of the metal cannot hold as much gas as the liquid form. These bubbles appear on a casting as rounded, circular cavities or holes.
There are three types of casting defects related to gas porosity:
1. Pinholes
Pinholes, also sometimes referred to as porosities, are very tiny holes (about 2 mm) usually found in the cope (upper) part of the mold, in poorly vented pockets.
They usually appear in large numbers together, either at the surface or just below the surface of the casting. They are always visible to the naked eye and don&#;t require equipment to identify.
2. Subsurface blowhole
Blowholes, or simply blows, are larger cavities than pinholes.
A subsurface blowhole appears on the inside of a cast and usually isn&#;t visible until after machining.
Subsurface blowholes can be difficult to detect before machining, requiring harmonic, ultrasonic, magnetic or x-ray analysis.
3. Open holes
These blowholes appear on the surface of the cast and are easier to detect than subsurface blowholes.
Causes and prevention of gas porosity
There are several causes of cavity defects.
- Poor venting of mold and cores
- Insufficient drying of mold and cores
How can you prevent gas porosity?
Scars are shallow blows that appear on a flat surface, while blisters are scars covered with a thin layer of metal.
- Excessive moisture content of molding sand
- Inadequate gas permeability of molding sand
Potential solutions include:
- Incorporate good fluxing and melting practices: melt metal in a vacuum, in an environment of low-solubility gases or under a flux that prevents contact with the air
- Increase gas permeability of sand: coarser sands have a higher permeability
- Increase permeability of mold and cores. Allow air and gas to escape from the mold cavity
- Dry out molds and cores before use and store dry
- Increase rate of solidification by reducing metal temperature during casting
Shrinkage casting defects and causes
Shrinkage occurs because metals are less dense as a liquid than a solid.
A shrinkage cavity is a depression in a casting which occurs during the solidification process. Shrinkage porosity appears with angular edges, compared to the round surfaces of gas porosity. Cavities might also be paired with dendritic fractures or cracks.
Large shrinkage cavities can undermine the integrity of the casting and may cause it to eventually break under stress.
Shrinkage can result in two types of casting defects.
4. Open shrinkage defects
These are open to the atmosphere. Air compensated as the shrinkage cavity forms.
Pipes are open shrinkage defects that form at the surface and burrow into the casting. Caved surfaces are shallow, open shrinkage defects that form across the surface of the casting.
5. Closed shrinkage defects
Also known as shrinkage porosity, closed shrinkage defects form within the casting. Macro shrinkage can be viewed with the naked eye, but micro shrinkage cannot.
Closed shrinkage defects usually appear at the top of hot spots, or isolated pools of hot liquid.
Prevent shrinkage cavities by improving casting structure
Alloys always shrink when changing from molten to solid. This is because the density of a casting alloy in the molten state is lower than that in the solid state.
You should expect some shrinkage during solidification. Factor a shrinkage allowance into the pattern design before casting.
You can prevent shrinkage casting defects by improving the overall casting structure:
- Design a running (gate) system with risers that ensure a continuous flow of molten metal
- Increase local heat dissipation by inserting internal chills, cooling ribs or cooling coils
- Reduce casting temperature to limit the total volume deficit
Mold material casting defects and causes
Mold material casting defects are related to the mold material, which is most commonly sand. You and your supplier can typically address these casting defects and causes by modifying the mold.
6. Cuts and washes
Cuts and washes are areas of excess metal. These appear when the molten metal erodes the molding sand.
A cut appears as a low projection along the surface of the drag face, decreasing in height as it extends from one side of the casting to the other.
Causes and prevention of cuts and washes
Cuts and washes can be caused by molten metal flowing at a high velocity, causing too much metal to flow through the gate.
You can prevent cuts and washes easiest by:
- Designing the gating system properly
- Improving mold and core strength
- Adding more binders to the facing and core sand
7. Fusion
Fusion occurs when sand grains fuse with molten metal. It appears as a thin crust with a brittle, glassy appearance firmly adhered to the casting.
Causes and prevention of fusion
Two main factors can cause fusion:
Improving the refractoriness of the molding material and/or reducing the pouring temperature of the molten metal will help prevent fusion.
8. Run out
Run out is when liquid metal leaks out of the mold, leading to an incomplete or missing casting.
A faulty mold or flask is responsible for run out.
Prevention of run out and incomplete castings
To prevent this casting defect, design the casting mold with precision. Inspect and replace any defective molds before casting.
High temperatures can lead to excess wear and tear of the mold. Use quality raw materials for your mold that can resist high temperatures.
9. Swells
Swells are an enlargement of the casting. Swells typically take on the shape of a slight, smooth bulge on the vertical face of castings.
Causes and prevention of swells
Swell is usually caused by improper or soft ramming of the mold or a low strength mold.
Molds should be built to withstand liquid metal pressure. Otherwise, the mold wall may give way or move back, causing swelling.
Using a strong, properly rammed mold prevents swells.
10. Drops
Drops occur when pieces of sand fall into metal casting when it&#;s still liquid. Drops appear as an irregularly shaped projection on the cope (top) surface of a casting.
Causes and prevention of drops
Four potential causes for drops and their preventions include:
Low sand strength:
Use sand of a higher strength if this your culprit
Soft ramming:
Provide harder ramming
Insufficient fluxing of molten metal
: Properly fluxing molten metal removes impurities
Insufficient reinforcement of sand projections in the cope
: Reinforce sand projections using nails or gaggers to fix this issue
11. Rat tails, veins and buckles
Rat tails, or veins, appear as an irregular line or crack on the casting, when the surface of the molding sand buckles up. Rat tails usually occur on the surface of the mold bottom, an area covered with molten material.
Buckles are a more severe form of rat tails.
Causes and prevention of rat tails and buckles
Rat tails and buckles occur when excessive heat of the metal causes the sand to expand. This may be caused by:
Poor expansion properties of the sand
: Add combustible additives to sand.
A hot pouring temperature
: Reduce pouring temperature of metal.
Poor mold design
:
Large and flat sections are more prone to rat tails. The mold also should not be too hard, as it must allow for proper expansion.
12. Metal penetration
Metal penetration occurs when liquid metal penetrates gaps in the molding sand. The penetration is visible to the naked eye as a rough and uneven surface finish of the casting.
Causes and prevention of metal penetration
Metal penetration is due to:
Prevent metal penetration by fixing these areas. Use high strength, small grain size, low permeability and hard ramming of sand. Ensure a protective barrier against metal penetration by coating the surface of molds with a mold wash.
You can typically remove metal penetration by grinding down the rough surface of the casting.
Metallurgical casting defects and causes
There are two types of metallurgical defects to watch out for.
13. Hot tear/crack
Cracks appear in the form of irregular crevices in a branched pattern.
Some cracks are obvious and easily seen, while others can require magnification.
Cracks occur as the casting cools, towards the end of solidification.
Causes and prevention of hot tears and cracks
If the solidifying metal does not have sufficient strength to resist tensile forces during solidification, hot tears will appear.
Hot tears are mostly caused by poor mold design. Modifying the mold to improve collapsibility can easily resolve these issues.
14. Hot/hard spots
Hot spots are spots that are harder than the surrounding area. This is because they cooled more quickly than the surrounding material.
Hard spots can interfere with machining and increase tool wear.
Causes and prevention of hot spots
Hot spots are a direct result of improper cooling practices. There are two potential solutions if hot spots are your problem:
- Start by correcting cooling practice
Also consider changing the metal&#;s chemical composition
15. Burn On
Also consider changing the metal&#;s chemical composition
A burn on is a type of casting defect that occurs due to localized overheating and subsequent melting or burning of the sand mold or core. It is typically characterized by a discolored or blackened area on the surface of the casting.
When molten metal is poured into a mold, it releases a significant amount of heat. If the mold material, such as sand, cannot withstand this heat or if there are design flaws in the mold, it can lead to overheating and burning of the mold material. Some of the common causes of burns in casting include:
- Inadequate mold material
- Improper gating and risering
- Metal temperature
- Metal/mold interaction
Burn defects not only affect the aesthetic appearance of the casting but can also weaken its structural integrity. Therefore, it is important to minimize burn defects through proper design, material selection, and process control in the casting operation.
Pouring casting defects and causes
When molten metal is poured into a mold, it releases a significant amount of heat. If the mold material, such as sand, cannot withstand this heat or if there are design flaws in the mold, it can lead to overheating and burning of the mold material. Some of the common causes of burns in casting include:Burn defects not only affect the aesthetic appearance of the casting but can also weaken its structural integrity. Therefore, it is important to minimize burn defects through proper design, material selection, and process control in the casting operation.
Pouring metal defects arise during the process of pouring metal into the mold. If you have a pouring metal defect, it will fall into one of these categories:
16. Cold shut/lap
Cold shut is a type of surface defect. You&#;ll see a line or crack with a round edge on the casting surface.
This defect is visible to the naked eye and often results in rejecting the cast, as it creates a weak spot.
Causes and prevention of cold shut
When molten metal enters the mold from two gates, the streams will meet at a junction. Low temperatures can prevent fusion at the junction, causing the streams to solidify before fusion, creating a cold shut.
Cold shut is usually a result of a lack of fluidity of the molten metal, or a poor design of the gating system.
The best way to prevent cold shuts is to increase fluidity of the molten metal. This can be done in a few ways:
- Optimize gating system to minimize narrow cross-paths and ensure short flow paths
- Increase the pouring temperature to prevent premature solidification
- Improve gas permeability of the mold (through coarser grain size, etc.)
17. Misruns are closely related to cold shuts
Misruns occur when the liquid metal is too cold to flow to the extremities of the mold cavity before freezing and solidifying.
The liquid metal does not completely fill the mold cavity. The misrun is the unfilled portion or space in the mold.
Causes and prevention of misruns
The reasons for premature solidification are similar to those for cold shut. If you have a misrun, check:
- Mold design
- Gating system design and
- Molten metal fluidity
18. Cold shots
Splattering during pouring of a liquid can cause solid globules to form.
As these globules freeze, they become entrapped in the casting.
Cold shots are typically ball, drop or pearl shaped and loosely attached to the metal.
Causes and prevention of cold shots
To prevent splattering and cold shots, consider
- Modifying pouring procedures to minimize turbulence
- Adjusting gating system designs to reduce gate speed
19. Slag inclusion (scab)
These irregular metallic crusts are found on the casting surface. Scabs are typically only a few millimeters thick but can be seen by the naked eye. They usually have sharp edges, irregular shapes and are firmly bonded to the casting.
Scabs are closely related to rat tails and they usually appear together. Removal of scabs will typically reveal a rat tail underneath.
Causes and prevention of slag inclusion
Slag inclusion is caused when molten metal containing slag particles is poured into the mold cavities and solidifies.
Preventing slag inclusion is a simple fix. Remove slag particles from the molten metal before pouring it into the mold cavity.
You can remove slag by:
- Melting the metal with a flux, in a vacuum or in an inert atmosphere
- Adding ingredients to the mixture to cause slag to float to the top where you can easily see and remove it before pouring. Or use a special ladle that pours metal from the bottom.
- Adding a ceramic filter into the gating system
Casting shape defects and causes
These types of casting defects are related to the overall shape of the final casting.
20. Shift/mismatch
Mold shift is due to misalignment of upper (cope) and lower (drag) part of the mold. Mold shift is usually reflected as a horizontal displacement.
Core shift is similar to mold shift, but it&#;s the core that is misaligned, not the mold. Core shift is usually reflected as a vertical displacement.
Causes and prevention of shift
Some causes of shift can include:
- Loose box pins
- Inaccurate pattern dowel pins or
- Carelessness in placing the cope on the drag, causing misalignment
If you&#;re experiencing shift, try checking the match plate pattern mounting and alignment. Make sure to use proper molding box and closing pins.
21. Flash, fin and burrs
Flash is one of the most frequently occurring casting defects and also a common injection molding defect.
Flash, also known as casting fin or burrs, is any unwanted and excess material attached to a cast. It&#;s typically a thin sheet of metal that forms at the parting faces. Flash is a waste material that turns into dross after being re-melted.
Causes and prevention of flash, fin and burrs
Flash on the casting surface is due to a crack or gap on the core surface. Insufficient weight on the mold or improper clamping of the flask can lead to a gap.
Remedy this issue by reassembling the mold and cores. There should be enough weight on the top part of the mold so that the two parts fit together tightly.
Flash can vary from minor to very serious. If it&#;s not too serious, manufacturers can remove flash by breaking it off with a hammer or pliers and filing it down to the parting line. However, this can be a costly process.
22. Warping
Warping is an unwanted casting deformity that can occur over time, which results in a change in the dimensions of the final product.It can happen during or after solidification.
Causes and prevention of warping
Warping is typically a result of different rates of solidifications of different sections, which causes stress in adjoining walls. Large and flat sections are more prone to warping.
Normalizing heat treatment can remove residual stress in iron casting. A straightening between quench and aging processes might also be required for aluminum casting.
Limit Casting Defects Before They Leave The Factory
Knowledge of casting defects and causes is an essential first step to managing casting quality. However, brands and retailers will also want to establish an effective quality control process to minimize defects.
This means setting clear defect tolerances and quality expectations with your suppliers before production to help them understand your quality standards. You can also utilize quality control inspections to limit casting defects in your products before they leave the factory.
AQF Can Help
AQF is a leading Quality Control service provider, serving global brands, importers, and retailers of Consumer Products since . We provide a range of quality control inspections to help brands and retailers secure their supply chains. This includes supplier audits, pre-production inspections (PPI), during production inspections (DUPRO), and more.
Contact us today or sign up for AQF online to book your next service.
Editor&#;s Note: This article was originally published in SEPTEMBER by SUNNY WONG. It has since been updated to reflect current best practices, services, and capabilities.
Do you have experience in addressing any of these casting defects? Share your tips in the comment section below!
All models know the importance of making a good first impression, and none is more vital than a model casting. A casting is an interview that prospective models must attend so a brand can judge whether they&#;re the right fit for them. Models need to stand out from the crowd and show their potential.
Choosing the right clothes to wear can feel daunting, but don&#;t worry. Follow our list of do&#;s and don&#;ts and you can&#;t go wrong!
What NOT to Wear to a Model Casting
First, let&#;s start with the don&#;ts. While most of these are common sense, a few may come as a surprise to aspiring models.
Do Not Wear Too Much Make-Up
Agencies and brands are using the casting as an opportunity to see your natural beauty. Wearing a face full of make-up will only cover up your natural features. This doesn&#;t mean you can&#;t wear make-up at all; in fact, it&#;s expected that you will wear a bit. But you need to understand the importance of the no make-up make-up look.
It&#;s all about emphasising your natural features without looking cakey and without selling a false impression of your looks. What we mean by this is don&#;t feel the urge to overdraw your lips too much as it will be a surprise when they see you without make-up. There is a fine line between using make-up to bring out your best features and using it to completely change your appearance.
Natural yet flattering make-up is ideal for a model casting
- Practice with make-up so you know what works and what doesn&#;t. If you&#;re unsure, visit a make-up counter and ask them to help you colour-match your foundation and concealer shades. They can also advise on the best choices of eyeshadow and eyebrow pencils to suit your colouring.
- While brushes and sponges are a great way to apply face make-up, most experts tend to rely on the warmth of their fingers to really work the product onto the skin, leaving a seamless and natural finish.
- Choose eyeshadows that are natural and flatter your eye colour. Browns and taupes are great choices, or a slick of a subtle shimmery nude will also look great. If you don&#;t generally like or wear eyeshadow, run a dark brown pencil along your lashes to make them look thicker.
- Choose a good mascara that lengthens lashes without making them like spidery. A clean mascara wand is a great tool for brushing through lashes and removing any clumps.
- A natural bronze glow or a pop of colour on the cheeks will bring colour back to the skin. Cream make-up is ideal for this as it creates a natural colour while leaving the skin fresh.
- On the lips, choose a tinted balm that is close to your natural lip colour. You can use a lip pencil to lightly bring structure to your lip shape, but don&#;t overdo it.
- Eyebrows are fashionable to draw on at the moment, but try to create a natural yet flattering shape with the help of an eyebrow pencil or a brow mascara.
If you are concerned about a particular issue such as acne, please don&#;t worry. There are some supermodels who have spoken out about their issues with acne; it is a common skin complaint and won&#;t affect your potential career as a model. Visit a dermatologist or skin consultant for some advice and learn how to cover it carefully with the correct make-up.
Don&#;t Wear a Complicated Up-Do
It might feel tempting to spend time putting your hair into an elaborate up-do, but resist the urge. Agencies and brands want to see your hair in all its natural glory. Many models put their hair into a high ponytail or bun to show off their facial features, but they don&#;t spend hours making sure each hair is sprayed into place as they know they could be asked to take their hair down.
Style hair in a natural way that is flattering for your features. If your hair is naturally frizzy, spend time conditioning it and run some curling tongs through to define the curls. If your hair is straight, ensure the ends are cut off regularly and keep it clean and conditioned. For afro-caribbean hair, ask a professional hairdresser the best way to keep your curls moisturised and healthy. Whatever your hair type, the most important thing is to look after it as best as you can. Remember that at photoshoots there will be a hairdresser to style your hair, so you don&#;t have to be great at styling it yourself. But for castings, it needs to look effortlessly beautiful and compliment your look.
If you dye your hair, ensure it is done by a professional so it is even and well-maintained. Keep roots updated and visit the hairdresser regularly to maintain overall hair health.
Some models are brave and risk a bright hair colour, but be cautious &#; this limits the potential jobs you may get. Alternative models regularly have bright, unusual hairstyles because that is the clientele and brands they are representing. For regular modelling agencies, they usually request that hair is a natural colour.
Alternative models can take more risks with their hair as it&#;s expected from the clients and agencies
Do Not Wear Loud Print
Now is not the time to wear complicated, loud clothing. Yes, you might look great in it, but the clothes will be distracting potential employees from the real selling point &#; you. A casting&#;s purpose is to sell YOU, not your clothing or accessories. Tone down your apparel so it shows off your physique and doesn&#;t attract attention or mask your shape.
Avoid Badly Fitting Clothes
Oversized jumpers look great there&#;s no denying it, but they don&#;t have a place in a casting interview. The clothing you wear needs to flatter and compliment your natural body shape, not cover it up. Feel free to wear whatever you like on your way to the casting, but be ready to take off any bulky layers like coats or jumpers, particularly if they cover you up. The same goes for winter apparel like hats and scarves. It&#;s a good idea to bring a large big to pack your items into.
Avoid Garish Accessories
Everyone wants to stand out, but make sure you&#;re standing out for all the right reasons. Do not feel the impulse to wear something silly to stand out. Stick to delicate items of jewellery that &#; you guessed it &#; wont distract.
What to Wear to a Model Casting
Now that the don&#;t-wears are out of the way, let&#;s take a look at some of the things you should be wearing to a model casting.
Heels You Can Walk In
You don&#;t have to attend the casting in heels, but you will need to bring a pair. This is because most agencies and brands will want to see how you walk in them. While they will probably have a pair of heels on-hand, it&#;s best to bring your own so you a) know they fit and b) know you can walk in them. Stiletto heels are usually the best call in a nude or black shade. Choose heels as high as you are comfortable in. There&#;s no need to choose huge platforms and they don&#;t have to be designer. Just make sure they are clean (first impressions count and scuffed heels wont look the part) and comfortable.
Remember the large bag we said would come in handy earlier? It will be a great place to store your heels while you&#;re not wearing them.
Wear heels you can walk well in
Wear Good Underwear
They&#;re not going to necessarily see your underwear (unless you are attending an interview for something you may need to be in them for, such as a lingerie or swimwear shoot), but good underwear is essential for a number of reasons.
Firstly, underwear serves as the platform for your outfits. Ill-fitting underwear will make even the best outfit look lumpy and wrong. You want a good bra with no overflow that isn&#;t too loose or too tight. It&#;s strongly advised that you get fitted by a professional regularly so you know you&#;re wearing the right size. (Remember, ladies &#; our size fluctuates all the time due to a number of factors, not just weight loss or gain, so it&#;s imperative you get checked regularly!)
You also want underwear that is comfortable and line-free under clothing. Nude underwear is a great call because it will be less visible in any outfits you need to wear. Many models bring a nude thong in their bag.
Men also need to think about their underwear choice. Elasticated waistlines can create bumps in the slimmest of people, so be conscious that you are wearing the correct fit.
Choose a Modest, Flattering Outfit
For casting outfit inspiration, it&#;s a good idea to Google what supermodels have worn to their castings. You&#;ll notice they all tend to choose subtle, natural colours that flatter and work with their look.
A popular casting look is a skinny jeans and white t-shirt combination. Jeans are a great look, but you MUST select a pair that fit you properly. Jeans should be the right length and fit around your waistline.
A plain t-shirt is comfortable and flattering on everyone. A crisp white top makes the skin glow, but avoid white if you tend to be a bit messy &#; you don&#;t want to arrive at a casting with a stained top!
Some models show off their legs with a skirt or dress. If your pins are your pride, show them off! Make the most out of your greatest assets &#; remember, you&#;re trying to stand out from a crowd of beautiful people.
Another favourite are chunky heeled boots or trainers. Both are comfortable and flattering. Heeled boots will give shorter models a height boost, while stylish trainers (not your gym pair!) can look great too.
A jeans and t-shirt combo is a great casting outfit
What to Bring in Your Bag to Castings
Go to castings as prepared as you can be. An agency or brand will usually make specific requests about what to bring, so make sur eyou read these guidelines thoroughly.
This guidelines will differ depending on what kind of agency or brand you have applied to. They may ask you to shave your legs, or wear your hair in a specific style, or wear no make-up. Follow these guidelines to the letter.
Otherwise, it&#;s up to you to ensure you come fully prepared for every scenario. Here is a list of items that you should consider bringing.
- A hairbrush or comb. Men and women should ensure their hair looks unknotted and well-maintained.
- Spare make-up. You may want to touch up your make-up just before your appointment. Concealer and lip balm are usually the most important pieces to bring. Men should also think about using concealer to cover under-eye bags or blemishes.
- A book/magazine. Castings can usually require a lot of waiting around, so it&#;s a good idea to bring something with you to keep yourself entertained.
- Water and snacks. Keep yourself well hydrated and fed. It is not likely that food and drink will be available for you to purchase at the casting, so bring your own just in case. You may have to wait for hours at a casting, so consider these an essential thing to bring.
- charger. You don&#;t want your to die in case you miss an important work call or need the maps to find your way to your destination. Bring a charger just in case.
- Heels. As mentioned earlier, heels are a vital model bag staple for model castings.
- Underwear. Also mentioned earlier, many models bring a nude thong in case they need to try on an outfit where underwear may be visible.
- Important documents. You may need to bring some ID with you. You might also want to print out directions to and from the casting (in case your dies), and any information about the brand.
Make sure you bag is big enough to put in any extra layers you might be wearing.
Remember to get to your casting early, if possible. Give yourself plenty of time to get lost and run into delays. DO NOT turn up to your casting late &#; if you&#;ve missed your appointment, they will very likely turn you away. Agents and brands need to see hundreds of men and women and a late model will show unprofessionalism.
If you are looking for more details, kindly visit Casting Foundry Gate Filter.
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