RUBBER SHRINKAGE
WHAT IS RUBBER SHRINKAGE AND HOW IT IS IMPORTANT WHILE DESIGNING RUBBER MOLDS
One of the problems we face when manufacturing rubber products is “rubber shrinkage” – rubber parts always come out of the mould that manufactured them smaller than the cavity that produced the part; they have “shrunk”.
This phenomenon is generally known as “shrinkage” and to achieve the desired size of the finished part, it is necessary to increase the size of the mould cavity by some degree, allowing for a number of factors that create rubber shrinkage and affect the outcome, sometimes in unexpected ways.
dIfferent polymer types have their own general rubber shrinkage characteristics, with some shrinking much more than others and therefore the same mould may not produce the same size of part if the polymer type is changed.
The mould tool used to produce the parts is manufactured according to our best knowledge based on experience of using that particular compound, however it must be noted that this is not a guaranteed shrinkage rate for life as over time ingredients within an initial mix of compound may be discontinued and a substitute can result in different shrinkage rates. Operating parameters and post molding operations required, also affect the overall shrinkage.
Design engineers need to consider both of these factors when designing molded parts.
molding tolerances to ISO3302 offer guidelines in order to achieve a perfect rubber part.
Solution: The only proven way to ensure the tightest tolerances is to mould a test button with the batch of compound that is going to be used then, after measuring the shrinkage rate, have the mould tool made to the confirmed shrinkage. This generally proves unfeasible though as the next batch of compound using the same ingredients may shrink differently to the initial batch, thus making it very expensive and time consuming.
V Design and Tooling – is a company working in Tool Room and Industrial Automation domain.
We are specialized in Tear and Trim Flashless multicavity Rubber molds.
Our services:
– Rubber Molds
– Rubber Molding Presses
Core Competencies:
· Design and Development of Rubber Molds and Press Tools.
· Rubber Molds:
· Flash-less Molds – Tear and Trim Grooves for easy deflashing
· Easy Part Ejection – 3 Plate mold with Wells for easy part ejection
· Air vent grooves
· Hardened and Tempered – Guide pillar and Guide bush
· Slip pins for perfect guiding of plates
· Perfect Design as per shrinkage
Thanks & Regards,
Sunny Wadhwa
Director – Design
V Design & Tooling
www.vdesigntooling.com
WHAT IS MOLD FLASH
What Is Residual Mold Flash?
Flash is an excess plastic or rubber material that forms on the surface of molded parts. Flash, or flashing, affects the part’s surface finish and may also interfere with sealing. Flash is usually a cosmetic defect, but molders want to avoid the appearance of thin, unwanted lines that can suggest poor part quality or manufacturing defects.
Flash forms during the molding process. With injection molding, plastic or rubber material can leak between the mold’s surfaces, typically along the parting line. Flash may occur during the filling or first injection stage, or during the pack/hold phase. Neither conventional parts nor thin-walled parts are immune. With over-molding, material leaks between the base material and the mold instead.
Why Plastic / Rubber parts have flash
For plastic and rubber molders, it’s important to understand that flashing can occur anywhere that metal meets metal. The causes of flash are numerous, but can be divided into five main categories:
1. parting line mismatches
2. improper venting
3. problems with clamping pressure
4. inadequate sprue bushing support
5. processing issues that lower viscosity
1. Parting line mismatches can be caused by dirt, dust, contaminants, or residues that keep the mold from closing properly. Old or worn mold cavities that no longer fit together tightly can also cause flashing. With injection molding, the pressure that’s exerted on mold plates can deform these metal surfaces. Complex part geometries can cause parting line mismatches, too.
2. Improper venting also causes flash. If a rubber or plastic material is stiff, the mold’s vents may not be deep enough. If the material is fluid, the vents may not be thin enough. Problems with mold design aren’t always to blame. Rubber and plastic flashing can also be caused by old or worn vents that no longer meet required tolerances.
3. & 4. Problems with clamping pressure and inadequate sprue bushing support can cause flash, too. With injection molding, the pack/hold phase may push the mold’s parting line apart. Inadequate support for the sprue bushing can transfer pressure to the parting line, too. Thermal expansion in the sprue bushing can hold the mold open and cause flash to develop.
5. Processing issues that lower viscosity also cause flashing in molded parts. The specific causes include excessive melt temperature, overly-long residence times, moisture from inadequate drying, and the use of too much coolant with lubricating vehicles.
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What is Natural Rubber and how is it extracted?
Natural rubber is produced from plants and is classified as a polymer. Some polymers exist naturally and others are produced in laboratories and factories.
Natural rubber is one of the most important polymers for human society. Natural rubber is an essential raw material used in the creation of more than 40,000 products.
Application : Medical devices, surgical gloves, aircraft and car tires, pacifiers, clothes, toys, etc.
Natural rubber is made by extracting a liquid sap, called latex, from certain types of tree. There are over 2,500 types of tree that produce this sap but the overwhelming majority of latex for rubber production stems from the Hevea brasiliensis tree, or the aptly named rubber tree. These trees are native to South America but are today commonly found in Southeast Asia.
Rubber making process:
Tapping: Latex is gathered from the trees by making a cut in the bark and collecting the runny sap in cups. This process is called tapping.
Coagulation: In order to prevent the sap from solidifying, ammonia is added. Acid is then added to the mix to extract the rubber.
Rolling: The mixture is then passed through rollers to remove excess water.
Drying: Once this is complete, the layers of rubber are hung over racks in smokehouses or left to air dry. Several days later, they will then be folded into bales ready for processing.
V Design and Tooling – is a company working in Tool Room and Industrial Automation domain.
We are specialized in Tear and Trim Flashless multicavity Rubber molds.
Our services:
– Rubber Molds
- Compression mold
- Transfer Mold
- Injection molds
WHAT IS COMPRESSION MOLDING
Compression molding is the process of molding in which a preheated polymer is placed into an open, heated mold cavity.
It is the use of compression (force) and heat to shape a raw material e.g. hydraulic and pneumatic seals by using a metal mould.
This process is able to produce parts with a wide array of lengths, thicknesses, and complexities. The objects it produces are also high in strength, making it an attractive process for a number of different industries.
Four Main Steps
- A high strength, two part metallic mold is created that exactly matches the dimensions required to produce the desired part. The mold is then installed in a press and heated.
- The desired composite is pre-formed into the shape of the tool. Pre-forming is a crucial step that helps to improve the performance of the finished part.
- The pre-formed part is inserted into the heated mold. The tool is then compressed under very high pressure(depending on the thickness of the part and the type of material used).
- The part is removed from the tool after the pressure is released. Any flash around the edges is also removed at this time.
Advantages:
· advantage of compression molding is its ability to create very complex parts. While this technique can not quite reach the production speed of Rubber injection molding, it does offer more intricacies in geometry than typical laminated composites.
· With its ability to create complex parts with a huge variety of applications while keeping part cost and turnaround time a priority, compression molding is an advantageous process for manufacturers in a wide range of industries.
V Design and Tooling – is a company working in the Tool Room and Industrial Automation domain.
We are specialized in Tear and Trim Flashless multicavity Rubber molds.
Our services:
–
- Transfer Molds
- Compression Rubber Molds
- Injection Molds
Transfer Molds
- Transfer molding is similar to compression molding; however, the material is first placed in a transfer chamber prior to entering the mold.
- The transfer molding process uses a thermosetting charge, or preform, that manufacturers load into a chamber immediately ahead of the mold cavity to preheat it. The equipment then applies pressure to force the softened polymer to flow into the heated mold, where it cures.
- The difference between compression and Transfer is, instead of loading the polymer into an open mold, the plastic material is pre-heated and loaded into a holding chamber called the pot.
- The mold remains closed until the material inside is cured.
- The material (which may or may not be pre-heated) is placed into a holding chamber called the transfer pot.
- A hydraulically powered plunger pushes the material through a channel, called the sprue, into the mold cavity.
- The material remains inside the mold and is either cooled to solidify. Any material still within the sprue remains attached to the part as it solidifies.
- When the material is solid, the mold is opened and the part is ejected.
- The extra material from the sprue is trimmed off.
Pros:
- Reduced Cavity filling time: In many cases, transfer molded rubber products require few and simple pre-forms. One pre-form can fill hundreds of cavities. This is an advantage over compression molding, and can save a significant amount of time in the molding process. This is also an advantage over injection molding since there is not a runner to fill each cavity reducing the number of cavities.
- Design Flexibility: Transfer molding allows for sharper edges. Micro grind vents reduce the need for overflows allowing for near flash less parts, greatly reducing deflash process or allow flash limits to directly ship parts.
- Short production cycle: Transfer molding offers shorter cycle times than compression molding and can provide more consistency, too. The process allows for tighter tolerances and more intricate parts.
- Allows for Inserts: This process is ideal for products with metal inserts.
Cons:
- Complex molds: Since the design and mold tends to be complex, tooling can also become expensive.
- Waste material: Transfer pots typically produce higher volume waste than traditional overflows in compression tools. Transfer molding typically produces a large pad with sprues.
V Design and Tooling – is a company working in Tool Room and Industrial Automation domain.
We are specialized in Tear and Trim Flashless multicavity Rubber molds.
Our services:
– Compression Rubber Molds
– Transfer Rubber Molds
– Rubber Injection Molds
Rubber Injection Molds
Rubber injection molding rubber has its roots in the molding of plastics.
In the 1960’s, engineers developed a way to use the same principles in molding plastics to mold rubber, making rubber injection molding one of the most efficient rubber manufacturing processes.
The rubber injection molding process works by significantly heating the rubber and using a very high pressure to inject the rubber compound in to the mold.
Injection Molding process:
1. Material Preparation:
Natural or synthetic rubbers (elastomers) are compounded with additives to meet design use specifications.
The compounded rubber, more technically a thermo set elastomer (TSE) is generally fed in strips into the screw and barrel where it is warmed to temperatures approaching but below that of the rubber mold.
02. Injecting the Rubber:
The compounded material injected through channels in the tool into the cavities of the closed hot mold.
The combination of pressure, temperature and time facilitates the crosslinking of chemical bonds commonly referred to as vulcanization.
Process parameters are usually programmed into the press to control temperature, volume and rate that compound is injected into the mold cavities.
03. Final Product Removal:
The process engineer also programs the press to provide adequate time for complete crosslinking.
When the press opens, parts are removed and allowed to cool to ambient temperature before deflashing (if necessary), inspection and preparation for shipment.
Rubber injection molding is very cost efficient and reduces waste.
Machine used for Rubber Injection Molding:
Advantage of Rubber Injection Molding:
· Rubber injection molding produces parts with quicker cycle times than compression or transfer molding.
· The secondary need for preforms to make complete parts is eliminated. This is usually a labor-intensive step that can potentially affect the finished product through varying pre-form weights and shapes.
· Rubber injection molding gives the ability to make custom shapes with little flash or rubber waste.
· Improved versatility in durometer shores, which can run from Shore A 90 to Shore A 40.
· Material is preheated before it is forced into cavities. This decreases the viscosity of the material, allowing it to flow more easily into the cavities.
V Design and Tooling – is a company working in Tool Room and Industrial Automation domain.
We are specialized in Tear and Trim Flashless multicavity Rubber molds.
Our services:
– Compression Rubber Molds
– Transfer Rubber Molds
– Rubber Injection Molds
What is Rubber Vulcanization Process
While driving along roads we often see boards on roadside sheds saying “Vulcanization of the Tire done here”. Always wondering what does this Vulcanization mean, so let’s read below:
Vulcanization:
Ø Vulcanization of rubber is a process of improvement of the rubber elasticity and strength by heating it in the presence of sulfur, which results in three-dimensional cross-linking of the chain rubber molecules bonded to each other by sulfur atoms.
Ø Raw rubber is obtained in 2 different types:
- Natural Rubber: produced from latex – milky emulsion drawn from the rubber tree (Hevea brasiliensis) or some other plants. When coagulated latex transforms into soft, plastic and sticky substance (crude rubber), which is then vulcanized (cured). Natural rubber is composed of polyisoprene molecules.
- Synthetic rubbers: are Elastomers, elastic properties of which are similar to those of the natural rubber. Synthetic rubber may have chemical composition similar to the natural rubber (synthetic polyisoprene). Other kinds of synthetic rubbers are: polybutadiene,polyisobutylene (Butyl rubber), silicone.
- Raw rubber is soft, sticky and thermoplastic. It has low tensile strength and low elasticity.
- The properties of rubber can be dramatically altered by cross linking the polymer chains. This process, carried out with sulfur, is known as Vulcanization.
- After being molded, the rubber is heated in an oven-like chamber. While sulfur alone can vulcanize rubber, the addition of heat helps to speed up the process while also allowing for better results. The rubber is heated to a temperature of about 300 to 400 degrees Fahrenheit, after which it’s removed from the heating chamber and allowed to cool.
- Vulcanized rubber is about 10 times stronger than natural rubber and is also about 10 times more rigid. However, it is still very elastic, which means that is can be stretched reversibly.
- Vulcanization process was invented by Charles Goodyear in 1839.
Applications: From tires and footwear to keypads and gaskets, countless products are made of vulcanized rubber.
Next time when you vehicle tire is flat and you run to get repaired it to Tire puncture garage you may see technician working with this type of commonly used vulcanizing machine
The rubber tube which has got punctured is been vulcanized, so that bonding rubber piece which is glued to close the cut on the tube should get bonded with the tube to close the gap and avoid air leakage.
We are specialized in Tear and Trim Flashless multicavity Rubber molds.
Our services:
– Compression Rubber Molds
– Transfer Rubber Molds
– Rubber Injection Molds
Feel free to call on – +91-9960605115
- Why High-Quality Rubber Molds Improve Production Efficiency
n the manufacturing industry, efficiency is key to staying competitive and reducing costs. When it comes to producing rubber products, using high-quality molds can make a significant difference in your production process. At V Design and Tooling, we specialize in providing precision-engineered rubber molds that optimize manufacturing performance. Here’s why investing in high-quality rubber molds can drastically improve your production efficiency.
1. Consistent Product Quality
High-quality rubber molds are designed with precision, ensuring consistent and uniform products every time. When molds are accurate and reliable, the quality of the final product remains the same batch after batch, reducing the chances of defects. Consistency leads to fewer reworks and scrap material, ultimately improving production efficiency and reducing waste.
- Example: A well-made injection mold produces rubber components with minimal imperfections, reducing the need for post-production modifications.
2. Faster Production Speeds
With high-quality molds, the manufacturing process becomes faster due to their optimized design. Whether you’re using compression molds, transfer molds, or injection molds, high-quality molds enable faster cycle times and reduce the need for additional setup or adjustments. This leads to increased throughput and faster delivery times.
- Example: Advanced injection molds can reduce curing time, enabling higher production rates without compromising quality.
3. Durability and Longevity
Durable rubber molds made from high-quality materials last longer and can withstand the wear and tear of frequent use. Investing in quality molds reduces the frequency of mold repairs or replacements, which translates to fewer interruptions in the production process. The longer lifespan of the molds ensures that your production runs smoothly over time.
- Example: High-quality compression molds made from durable steel can handle hundreds of thousands of cycles, minimizing downtime.
4. Reduced Waste and Material Costs
Using precision-engineered rubber molds minimizes material wastage. Since high-quality molds ensure accurate shapes and sizes, you use the exact amount of material needed for each product. Reducing waste not only cuts material costs but also improves overall production efficiency by reducing the need to reprocess or discard poorly molded items.
- Example: An optimized transfer mold design allows for efficient material distribution, reducing excess material and scrap.
5. Improved Product Design Flexibility
High-quality molds can accommodate complex geometries and intricate designs without compromising on production speed. When manufacturers can easily integrate complex features into their products, it opens up opportunities to design more functional and diverse products without sacrificing efficiency.
- Example: Advanced injection molds can produce components with detailed features, such as inserts or undercuts, in a single step, saving time and cost.
6. Less Need for Post-Processing
High-quality molds typically require less post-production work, such as trimming, sanding, or polishing. Since the molds are designed to create precise products, the need for secondary operations is minimized. This reduces labor costs and saves time, contributing to overall production efficiency.
- Example: A precise compression mold ensures that parts come out nearly perfect, requiring only minimal post-processing.
7. Enhanced Precision in Complex Designs
When you need custom solutions with complex geometries, high-quality rubber molds offer the precision necessary for intricate designs. Whether you’re working with delicate parts or parts with specific tolerances, high-quality molds ensure that all aspects of the design are executed accurately, enhancing overall product quality and production speed.
- Example: Custom rubber molds used in industries like aerospace or medical manufacturing require high precision, which top-tier molds can easily provide.
Conclusion
High-quality rubber molds are a critical investment in enhancing production efficiency. By improving product consistency, reducing waste, and speeding up the production cycle, manufacturers can achieve better results with fewer costs and greater overall productivity. Whether you’re looking to improve your compression molds, transfer molds, or injection molds, partnering with a trusted mold manufacturer like V Design and Tooling ensures that your production processes run smoothly, efficiently, and effectively.
Contact Us Today Ready to take your production to the next level? At V Design and Tooling, we provide high-quality rubber molds designed to optimize your production efficiency. Contact us today to learn how we can assist with your custom mold needs.
+91-9960605115