18
2025
-
10
Does the rim of your cup always turn white? Does the bottom of the cup keep getting punctured? It might be because you haven’t adjusted the heater’s temperature correctly! — A precise temperature-control strategy for zone-based heating on electric stoves
Author:
When you hold a smooth, flat plastic cup in your hand, you might not realize it has just been through a precision-controlled "hot spring journey." At the heart of this journey is the seemingly ordinary yet ingeniously designed electric furnace zoning system embedded within the cup-making machine.
Why is "partitioning" necessary?
Imagine if you placed a cold slab of butter on a frying pan—only the center would melt quickly, while the edges remained stubbornly solid. Similarly, when a plastic sheet is heated unevenly, it can lead to catastrophic results:
-
Overheating in the middle : The sheet material becomes soft and droops, even burning.
-
The surroundings are too cold. : Stretching and cracking during molding, with incomplete corner filling
-
Stress Concentration : Product deformation and warping after cooling
That's why modern cup-making machines all adopt Multi-zone independent temperature control The electric furnace system features common heating layouts with 6, 8, or even 12 zones, each of which can be independently set to a specific temperature—essentially creating a customized "gradient warming bed" tailored specifically for the sheet material.
How should the temperature be set in each zone?
Take the production of PP milk tea cups using a typical Zone 8 heating system as an example.
01, [Preheating Zone] (Zones 1-2): Low-Temperature Infusion
-
Temperature setting: 180–190°C
-
Core task: Gradually heat the sheet material as a whole, preventing the surface from softening too quickly while the interior remains cold—preparing it for subsequent high-temperature stretching.
02, [Core Heating Zone] (Zones 3–6): Precise Plasticization
-
Temperature setting: 200–220°C (distributed in a smile-shaped curve)
-
Core Task: This is the critical area for sheet forming. Typically, the temperature in the middle region is slightly lower, while the temperatures on both sides are slightly higher. This is because, during the conveying process, the sides dissipate heat more rapidly, requiring a higher temperature to ensure uniform softening across the entire sheet.
03, [ Molding Zone (Sections 7–8): Balanced Heat Preservation
-
Temperature setting: 190–200°C
-
Core task: Ensure the already softened sheet material achieves more uniform temperature distribution, eliminating internal stresses and guaranteeing that the entire material is in an optimal, consistent "rubbery state" before entering the mold.
The secret to setting the right temperature—teaching according to the "material."
01, Different materials require different strategies.
-
PP (Polypropylene) : A wider heating area and more uniform temperature (such as 190–210°C) are required due to its broader melting range.
-
PS (Polystyrene) : It needs to quickly reach its high-elasticity state temperature (e.g., 170–190°C), but overheating can easily lead to decomposition, requiring more precise control.
-
PET (Polyester) : High crystallinity requires a higher preheating temperature and makes it extremely sensitive to temperature fluctuations.
02, Different products, different formulations
-
Shallow cup/small cup: Requires a smaller draw ratio, and the overall temperature can be slightly reduced.
-
Deep cup/Large cup: Requires materials with better ductility, and the core area temperature needs to be raised.
-
Complex-structure cup: For areas with reinforcing ribs and special contours, the corresponding heating zone temperature needs to be increased to ensure complete filling.
How can you determine if the temperature reading is accurate? Common issues for real-time assessment
Inaccurate electric furnace temperature is the root cause of many quality issues. You can judge it this way:
-
The cup rim curls, turns pale, or cracks: This indicates the heating temperature in the corresponding area is too low, causing the molecular chains to be forcibly broken as the material stretches.
-
The bottom corner is too thin or punctured: This indicates the corresponding area is overheated, the material is too soft, and has been overstretched.
-
Should The cup body has wrinkles: the temperatures on both sides are too low, while the middle area is overheated, causing uneven material shrinkage.
-
Sheet material droops and touches the heater: Overall temperature is too high, or heating time is excessively long.
Final remarks
What appears to be a minor technical adjustment actually has a direct impact on product quality, efficiency, and cost. Only by mastering this "temperature code" can we help the sheet material strike the optimal balance between "hardness" and "softness," ultimately producing high-quality products that are more appealing to the market.
News
Shantou Xinhua Packing Machinery Co., Ltd.
Tel:+86-0754-82525115
Add:5th Jinye Road,No.2 Industry Area of Shengping.Daxue Road,Shantou ,Guangdong
Fax:+86-0754-88680313
E-mail: xinhua@stxinhua.com
Mobile website
Copyright © 2023 Shantou Xinhua Packing Machinery Co., Ltd.