Due to its structural characteristics, the design of vacuum flasks is more challenging than that of ordinary cups. How to design a vacuum flask with excellent insulation performance and durability for your business? What should be paid attention to? Read this article, and you will find the answer.
Theory of Vacuum Flasks
Vacuum flasks mainly achieve excellent insulation performance by a vacuum layer in the middle of the double-layer stainless steel walls to block heat conduction and convection. The inner walls of some vacuum flasks are plated with copper or silver to reduce heat radiation, thereby achieving long-lasting insulation.
4 Critical Design Factors for Vacuum Flask Performance
Distance Between Inner Liner and Outer Shell
The distance between the inner liner and the outer shell needs careful consideration. This will affect the heat retention performance and quality of your vacuum flask products.
Body
The typical gap between the inner and outer walls is 3mm, and no less than 2mm. There must be enough space for the vacuum layer to achieve the insulation effect. Generally, the larger the vacuum space, the better the insulation performance. However, an excessively large vacuum space will result in a larger water cup size and also increase the difficulty of vacuuming.
Buttom
The distance between the inner and outer walls at the bottom of the vacuum bottle is usually 10mm, with a minimum of 8mm. If the bottom vacuum gap is too narrow, the external atmospheric pressure after evacuation will push the outer wall’s bottom inward, causing it to make contact with the inner wall’s bottom.
Thickness of Stainless Steel Wall
When the diameter of the vacuum flasks is less than 70mm, a stainless steel wall with a thickness of 0.4mm is usually used. For an insulated water bottle with a diameter larger than 70mm, depending on the actual requirements, you can choose the stainless steel wall with a thickness of 0.5mm, 0.6mm or 0.7mm.
The thicker the stainless steel wall, the less likely the vacuum flask is to deform. And it will be more durable. But the cost will also be higher.
Thread Design
You need to know that stainless steel water bottle threads are mostly produced by roll threading rather than turning. Due to the physical characteristics of the rolling formation, its accuracy is not as good as that of turning. So designs featuring a small pitch or excessive thread height are infeasible.
Thread Height
The thread height refers to the height of the protrusion of the thread.
The suitable height of the bottle mouth thread is 0.5 to 0.9 millimetres. The height of the thread must not exceed 1 mm. If the thread height is less than 0.5 millimetres, the lid is likely to fall off. It may also lead to a decrease in sealing performance and cause the insulated water bottle to be leak-proof. The height of the threads on the lid should be less than 1.2 millimetres.
Thread Pitch
Pitch refers to the axial distance between the crests (the highest points) of two adjacent threads.
The pitch of the threads on the thermos flask is usually between 4 millimetres and 5 millimetres. If the pitch is less than 3 millimetres, the defective rate during the production process will be higher. The lifespan of the threads will also be shorter.
Additional Design Features
Here are some other designs that can enhance the insulation performance of the vacuum flask for your reference.
- Increase the capacity of the insulated water cup appropriately. Compared with insulated water bottles under the same conditions, the bottles that have a larger capacity have better heat / cold retention performance.
- Coating the outer surface of the inner liner with copper or silver can reduce heat radiation and achieve better insulation performance.
- Place the getter in the vacuum chamber. It can absorb the residual or long-term released gases after vacuuming, continuously maintaining a higher vacuum level for a longer period of time, thereby enhancing the insulation performance.
- Make the diameter of the vacuum flask opening smaller, so that less heat is lost from the flask opening.
- The main body of the cup lid is made of food-grade plastics with poor thermal conductivity, such as PP. Moreover, two layers of silicone sealing rings can be used to enhance the sealing system.
Materials Selection for Vacuum Flasks
Materials for the Vacuum Flask Body
SUS304 Stainless Steel（18/8）Vacuum Flask
SUS304 is the most widely used stainless steel material in the global vacuum flask industry. It has excellent processing performance and can be processed by various methods.
Insulated water bottles made from this material have excellent corrosion resistance and can be used to hold most acidic or alkaline beverages in daily life. It can also withstand a temperature range from -196°C to 800°C and can be used to hold boiling water and be used in various extreme applications.
SUS304J1 Stainless Steel Vacuum Flask
This material is similar to SUS304 stainless steel. Due to the addition of copper, 304J1 has superior processing performance compared to 304. Its price is also slightly lower than that of 304. It is suitable for products that are sensitive to cost, and those with great difficulty in deep drawing processing.
Vacuum flasks made from 304J1 stainless steel also have good corrosion resistance and can withstand boiling water. However, if your products will be exported to the European and American markets, before using this material, make sure to verify whether it complies with local regulations.
SUS316 / 316L Stainless Steel Vacuum Flask
Due to the addition of molybdenum, 316 stainless steel is more resistant to corrosion than 304 stainless steel. Among them, 316L has a lower carbon content, which helps reduce the corrosion risk after welding and ensures more stable performance of the insulated water bottle.
Vacuum flasks made from this material have better corrosion resistance. However, the price is higher than that of 304 stainless steel flasks. If your products target the high-end market, 316 and 316L stainless steel will be suitable materials.
201 Stainless Steel Vacuum Flask
The 201 stainless steel has poor corrosion resistance and cannot be used directly in contact with beverages. If you want to use 201 stainless steel, you can only use it to make the outer shell of the vacuum flask.
Materials for Lids
In addition to stainless steel, other safe plastics such as PP and Tritan can also be used. Among them, PP has the highest heat resistance, while Tritan is more durable and has higher transparency. The sealing ring material can be made of food-grade silicone or TPE.
When choosing materials, be sure to pay attention to the relevant safety standards and confirm whether the materials are BPA/BPS-free.
FAQ
Why Are Most Vacuum Flasks Round? Can It Be Made in a Square Shape?
After the vacuum flask is evacuated, every point on both the inner and outer walls is subjected to uniform and extremely high pressure. The circular structure is the most stable and least likely to cause the cup to deform. If you want to make vacuum cups of other shapes, the processing will be extremely difficult.
How Are the Corrosion Resistance Properties of a Vacuum Flask Evaluated?
The corrosion resistance of the vacuum flask is mainly evaluated according to the ISO 9227 salt spray test standard. According to the GB/T 10125 standard, no rust spots for 24 hours of continuous spraying is the basic qualified requirement for stainless steel products.
In actual material comparison, the neutral salt spray test of the insulated cup made of 304 stainless steel can achieve no obvious rust spots on the surface for more than 48 hours. The salt spray tolerance time of 316 stainless steel is higher than that of the 304 insulated cup.
What Printing Methods Can Be Used for Logos on Vacuum Flasks?
The common methods for vacuum flask printing logos include heat transfer printing, screen printing and laser engraving. The heat transfer patterns are bright and have strong adhesion. The cost of screen printing is relatively low. Laser engraving is physically carving the logo onto the surface, resulting in a long-lasting effect.
Does the Insulation Performance of the Recycled Stainless Steel Vacuum Flask Differ from that of the Original Stainless Steel Product?
The recycled stainless steel materials that have been certified have the same insulated performance as the original stainless steel. Experimental results show that after being remelted and reprocessed, the 304 recycled stainless steel coffee cups show no significant difference in insulated efficiency after 5 years in simulated daily usage conditions.
What Are the Necessary Requirements for the Packaging Materials When the Vacuum Flasks Are Exported to the EU and the US?
Export to the US: Food contact packaging materials, such as cardboard boxes, must comply with the requirements of the FDA 21 CFR. The material composition and food-grade declaration must be clearly marked on the packaging.
Export to the EU: Packaging materials must comply with the Packaging and Packaging Waste Regulations of the EU. The packaging materials must clearly indicate to be easy to disassemble and recycle. The total content of four heavy metals (lead, cadmium, mercury, and hexavalent chromium) in packaging waste shall not exceed 100 ppm. The inks used for packaging printing must not contain heavy metals.
Final Thoughts
No matter what kind of vacuum flask you want to make, Kreat will always be your first choice as a partner. Kreat is a professional vacuum flask manufacturer in China. We are very experienced, and we can promise you reliable product quality. We also provide OEM service. Click to contact us.
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