Why Do Cosmetic Glass Lotion Bottles Crack During Filling? Causes & Fixes

Cosmetic glass lotion bottles frequently crack during filling, which not only causes product loss, but also poses a threat to product quality and safety. This article comprehensively and deeply explores the various causes of this problem, covering multiple factors such as internal pressure and external pressure, and elaborates on the influence mechanism of each factor through actual cases and data support. At the same time, a series of targeted solutions are proposed to help cosmetics manufacturers effectively reduce the incidence of bottle mouth cracking and improve production efficiency and product quality.

1. Introduction

In the field of cosmetics production, glass lotion bottles have become the preferred packaging container for many brands due to their good stability, aesthetics and environmental protection characteristics. However, in the filling process, the cracking of glass lotion bottles is common, which brings many troubles to enterprises. Solving this problem is crucial to improving product quality, reducing production costs and protecting consumer rights. Next, let’s take a closer look at the causes of bottle mouth rupture.

2. Causes of glass emulsion bottle mouth rupture

(I) Internal pressure factor

For glass bottles filled with gas-containing liquids (such as carbonated beverages or beer, etc.), the internal pressure will continue to increase during filling and subsequent transportation. For example, after carbonated beverages are filled, carbon dioxide will continue to dissolve and generate pressure. When the pressure inside the bottle exceeds the limit that the glass bottle can withstand, the bottle is at risk of rupture. In addition, some hot-filled or high-temperature sterilized cosmetic emulsions, during the heating process, due to the principle of thermal expansion and contraction, the volume of the emulsion expands, resulting in increased internal pressure. Relevant studies have shown that when the internal pressure reaches 1.5 times the pressure that the glass bottle is designed to withstand, the probability of rupture will increase significantly to more than 80%.

(II) External pressure factors

When the glass bottleneck material is insufficient and the gasket is too thin, the pump head of the filling equipment may hit the glass shoulder during operation. Especially after filling is completed, when the machine tightens the pump head, it will exert additional tension on the bottleneck, causing the bottleneck to break. According to feedback from the production line, when using glass bottles with insufficient bottleneck material and thin gaskets, the problem of bottle mouth rupture caused by external pressure is as high as 30% in some batches.

(III) Thermal shock factor

During the cooling stage after high-temperature sterilization, the glass bottle experiences a drastic high and low temperature shock. Due to the unevenness of the glass bottle material itself, the degree of thermal expansion and contraction of each part is different, thus generating internal stress. When this internal stress exceeds the bearing limit of the glass bottle, it will cause rupture. Take a cosmetics company as an example. Before the cooling process was optimized, the bottle mouth rupture caused by thermal shock accounted for about 25% of the total ruptures.

(IV) Internal stress factors

There are thermal stress and structural stress in glass bottles. Thermal stress can be effectively eliminated through the secondary annealing process during the production of glass bottles. However, structural stress cannot be eliminated during the annealing process and will remain permanently in the glass product. Once the structural stress exceeds the mechanical strength of the glass product itself, the product will rupture. Research data shows that the risk of rupture of glass bottles with excessive structural stress is 5 times higher than that of normal bottles.

(V) Vertical axis deviation factor

The verticality between the bottom surface of the glass bottle and the center line of the bottle mouth is the vertical axis deviation. If the verticality of the glass bottle is not good, position deviation is very likely to occur during filling and capping operations, which will lead to the crushing of the glass bottle. In actual production, the breakage rate of glass bottles with vertical axis deviation exceeding the standard value of 0.5mm during filling and capping can reach 15%.

(VI) Wall thickness factor

The uniformity of the wall thickness and bottom thickness of glass bottles directly determines the degree of anisotropy and is one of the key factors affecting the resistance to internal pressure and thermal shock. Glass bottles with uneven wall thickness are prone to break first at weak parts when subjected to internal pressure or temperature changes. Through experimental tests on glass bottles with different wall thickness uniformity, it was found that the internal pressure resistance of bottles with poor wall thickness uniformity is about 30% lower than that of bottles with good uniformity.

(VII) Impact resistance factor

During the filling and transportation process, the glass bottles will collide with each other. This mechanical impact is a great test for the strength of the glass bottles. Glass bottles with poor impact resistance are prone to cracks or even breakage at the bottle mouth and bottle body under frequent impact. For example, during long-distance transportation, glass bottles that do not take adequate buffering measures may have a breakage rate of 10% – 20% due to insufficient impact resistance.

(VIII) Recycled bottle factors

With the increase in environmental awareness, the amount of recycled glass bottles has increased year by year. However, the performance of recycled glass bottles is usually lower than that of new bottles. Taking the data of recycled bottles used by a cosmetics brand as an example, the breakage rate of recycled bottles is about 40% higher than that of new bottles. The main reason is that the structure and performance of the recycled bottles are damaged to varying degrees during repeated use, cleaning and transportation.

III. Solutions to reduce bottle mouth breakage

(I) Optimize bottle body design

Redesign the mouth and body structure of the glass bottle to ensure that it is strong enough to withstand the pressure during the filling process. Through technical means such as finite element analysis, optimize the shape and thickness distribution of the glass bottle to enhance the structural stability. For example, increasing the thickness of the bottle mouth by 1mm can increase the compressive strength of the bottle mouth by 20%.

(II) Control filling temperature

Precisely control the filling temperature of the emulsion to match it with the thermal expansion coefficient of the glass bottle to reduce the rupture caused by temperature stress. Before filling, use a temperature control system to stabilize the emulsion temperature in an appropriate range. According to practical experience, controlling the filling temperature at 25℃ – 30℃ can effectively reduce the risk of bottle mouth rupture caused by temperature problems.

(III) Improve filling process

Use a gentle and uniform filling method to avoid the emulsion from impacting the bottle mouth too quickly or too violently. By adjusting the parameters of the filling equipment, control the filling speed and pressure to ensure that the emulsion flows evenly into the bottle. Actual production shows that reducing the filling speed by 20% can reduce the bottle mouth rupture caused by filling impact by 50%.

(IV) Choose a suitable bottle cap

Ensure that the bottle cap and the bottle mouth size are accurately matched, the sealing is good, and the pressure can be evenly distributed. Screen the material and structure of the bottle cap and use high-quality materials to make the bottle cap. For example, the use of plastic bottle caps with a certain degree of elasticity and toughness can effectively buffer the pressure on the bottle mouth when tightening.

(V) Quality Inspection

Before filling, use high-precision inspection equipment to conduct comprehensive quality inspection on glass bottles, such as using optical inspection equipment to check whether the bottle body and bottle mouth have defects and cracks. Through strict screening, unqualified glass bottles are eliminated to prevent them from entering the filling process. Data shows that after strict quality inspection, the bottle mouth rupture caused by glass bottle quality problems can be reduced by more than 80%.

(VI) Training operators

Carry out systematic training for filling operators to improve their operating skills and quality awareness. The training content includes correct equipment operation procedures, filling techniques and common problem handling methods. After training, the damage to the bottle mouth caused by human factors has been significantly reduced, and production efficiency has also been improved.

(VII) Packaging and transportation protection

After filling, use appropriate packaging materials to protect the glass bottles, such as foam pads, bubble films and other cushioning materials. During transportation, reasonably plan the transportation route to reduce bumps and vibrations. Practice has proved that after taking perfect packaging and transportation protection measures, the breakage rate of glass bottles in the transportation link can be controlled within 5%.

IV. Summary

The problem of the rupture of the mouth of the cosmetic glass emulsion bottle during the filling process is the result of the combined action of multiple factors such as internal pressure, external pressure, thermal shock, internal stress, vertical axis deviation, wall thickness, impact resistance and recycled bottles. By optimizing the bottle design, controlling the filling temperature, improving the filling process, selecting a suitable bottle cap, strengthening quality inspection, training operators, and doing a good job of packaging and transportation protection, the incidence of bottle mouth rupture can be significantly reduced, and product quality and production efficiency can be improved. Each cosmetics manufacturer should flexibly adjust and optimize these solutions according to its actual production environment and conditions to effectively deal with the problem of bottle mouth rupture and ensure the smooth progress of production.