What is the thermoforming of bathtub acrylic sheets?

The "Perfect Shaping" of Bathtubs: An In-depth Analysis of the Thermoforming Process of Acrylic Sheets

In modern bathroom Spaces, the independent bathtub with smooth lines and a warm touch is undoubtedly the focus for enhancing the quality of life. The core of its elegant form and outstanding performance lies in a process called "acrylic sheet thermoforming". It is like a magic that brings life to the bathtub, transforming a flat and tough sheet into a bathroom art piece that combines aesthetics and functionality. This article will take you on a deep dive into the mysteries of this process.

One: Getting to Know the Main Character: Special acrylic sheets for Bathtubs

Before delving into thermoforming, we first need to get to know the main character - acrylic sheets. It is not an ordinary plastic, but a composite material made of polymethyl methacrylate (PMMA), specially designed for bathroom products, and usually has the following structure:

Acrylic surface layer (surface layer) : The thickness is usually 2-3 millimeters, providing an extremely smooth, dense, brightly colored and easy-to-clean surface. It determines the final appearance texture and stain resistance of the bathtub.

Glass fiber reinforced layer (back layer) : Beneath the acrylic layer, a strong supporting structure is formed by combining resin with glass fiber mat (or woven fabric). This layer endows the bathtub with the mechanical strength, rigidity and impact resistance it requires.

The core of thermoforming lies in precisely heating and shaping this crucial acrylic surface layer.

Two: Thermoforming process details

The acrylic thermoforming of bathtubs is a precise and multi-step process, mainly divided into the following stages:

1. Mold preparation

Molds are the foundation of forming and are usually made of cast iron, cast aluminum or composite materials. Its surface must undergo high-gloss polishing to achieve a mirror-like effect, so as to replicate the perfect gloss onto the acrylic surface. Before molding, it is necessary to evenly apply a mold release agent on the mold to ensure that the bathtub shell can be demolded smoothly after cooling.

2. Plate fixation and heating

Place the cut rectangular acrylic sheets in a dedicated heating furnace, usually a large box furnace. The sheet is fixed by a frame to prevent it from sagging excessively during the heating process. The heating process requires precise control:

Heating temperature: Usually between 140°C and 160°C. If the temperature is too low, the sheet will become too hard and cannot be fully stretched, resulting in the failure of molding or the generation of stress. If the temperature is too high, it will cause the acrylic layer to bubble, turn yellow and even degrade.

Heating time: It is determined based on the thickness of the sheet and the performance of the furnace to ensure uniform heating of the entire sheet and reach the optimal "rubber state" softening point. At this point, the board becomes soft and highly malleable, but it does not flow.

3. Vacuum adsorption molding (Core step)

This is the most visually appealing and crucial step in the entire process:

Mold moving and covering: Quickly move the heated and softened acrylic sheet above the prepared bathtub mold and precisely cover it.

Sealing and vacuuming: The sealing frame on the equipment will press against the edge of the plate, creating a sealed space. Then, start the vacuum pump to completely remove the air between the mold and the sheet.

Perfect shaping: Under the effect of atmospheric pressure, the soft acrylic sheet is tightly and evenly pressed against every corner and curve of the mold, perfectly replicating all the details of the mold, including the drainage outlet, handrail position and other complex structures. This process is usually completed within tens of seconds.

4. Cooling and curing

The formed bathtub shell is still in a high-temperature state and needs to go through a controllable cooling process. Air cooling or water mist cooling and other methods can be adopted to gradually lower its temperature, shape it and restore its rigidity. The cooling rate should not be too fast; otherwise, it may cause the product to deform or crack due to internal stress.

5. Demolding and trimming

After the shell is completely cooled to room temperature, it is demolded with compressed air or other auxiliary tools to obtain a complete primary shell for the bathtub. Subsequently, the workers will trim off the excess burrs around the edges and polish the edges to prepare for the subsequent back-covering reinforcement.

Three: Advantages of Thermoforming Process

Why is the thermoforming process widely used in acrylic bathtubs? Because it brings incomparable advantages:

Outstanding surface quality: It can achieve a high-gloss, seamless and pore-free surface, which is both beautiful and hygienic.

Strong design freedom: It can almost shape any complex curve and form, meeting the diverse design requirements of modern bathtubs.

Excellent heat preservation performance: The thermal conductivity of acrylic material itself is low, so the bathtub has good heat preservation performance, and the body feels more comfortable when taking a bath.

The touch is warm and smooth: Compared with metal or ceramic, acrylic material has a warmer touch and is not cold.

Four:  Key Points and Challenges of Process Control

To produce high-quality bathtubs, the following points must be strictly controlled during the thermoforming process:

Temperature uniformity: Uneven heating can lead to inconsistent local stretching of the sheet, resulting in problems such as uneven thickness, whitening or stress concentration.

Uniformity of stretching: During deep drawing (such as the deep cavity of a bathtub), ensuring that the sheet material is not overly stretched and thinned in deep drawing areas like corners is a key technical issue. Excellent mold design and process parameters can effectively improve material flow.

Vacuum degree and sealing performance: It is essential to ensure sufficient vacuum degree and absolute sealing of the system; otherwise, defects such as blurred details and unclear edges and corners will occur.

Environmental cleanliness: If dust in the air falls on the sheet or mold during the heating or molding process, it will directly cause defects on the surface of the finished product.