Questions to Dr. Vela

Dr. Vela:

What factors must I consider when manufacturing large pillar candles with a diameter of 10 cm and 1 meter length? I am currently utilizing PVC pipe as molds but it is difficult for me to unmold the candle. I am also having problems with the pillar guttering and dripping during burning despite me utilizing an appropriate wick for its diameter.

Dear colleague:

There are several details that can assist in facilitating/improving the process. Firstly, it’s unclear what type of PVC pipe you are currently using, but if it’s white PVC pipe (known as schedule 40 or drainage pipe), I suggest switching because this type of pipe is not suitable for molding candles.

PVC is sensitive to temperature, and schedule 40 pipe which has a thin-wall, distorts easily when hot wax is poured into it. This distortion can lead to demolding issues, especially with longer candles. I recommend using gray PVC pipe, known as schedule 80 or hydraulic pipe.

You’ll need to make a slight concession, as the nearest schedule 80 hydraulic pipe has an approximate inner diameter of 9.6 cm. Subtracting the shrinkage of the wax required for demolding, your candle won’t exceed 9.4 cm in diameter.

The best option for candle molds (but more expensive) is seamless aluminum pipe. Like schedule 80 PVC pipe, you’ll need to find the closest diameter to your current candle measurement.

Another aspect to consider is your wax formulation. Some waxes work better for molding than others. It’s essential that your formulation includes a crystal modifier additive to impart slight wax contraction upon solidification (cooling) thus facilitating separation from the mold surface for easier demolding.

There are various materials that may work for you, such as microcrystalline wax, stearic acid, polyethylene wax, and other polymers. The choice depends on what’s available in your region.

Regarding burning performance and dripping, the use of additives may help improve burning, especially stearic acid. A candle drips because the heat of the flame prematurely melts the edge of the wax pool (called “guttering”) causing the candle to drip.

The appropriate wick for a candle isn’t solely defined by the diameter. While the candle diameter can help “narrow down” to a wick size or gauge, the wax composition and behavior (such as viscosity) of each mixture are the predominant factors in selecting a suitable wick for the candle.

The most crucial aspect to prevent any candle from dripping is to ensure that the flame consumes the wax at the same rate it melts, ensuring that the wax pool remains dry during the candle’s burning. In other words, it shouldn’t fill with hot liquid wax.

Dear Dr. Vela,

I am experiencing an issue with my molded paraffin candles (they are bending and deforming), and I’m unsure if it’s due to the formulation or temperature. I need your assistance.

Dear Manufacturer,

The issue you describe is quite common in candles with small diameters (often referred to as taper candles) produced by any manufacturing method, whether it’s dipping, molding, drawing or extrusion. The problem can be attributed to both the base wax formulation and temperature.

For a candle manufacturer, controlling the temperature at which candles are stored, transported, or sold in the distribution channel is certainly beyond your control (except when they are in your own facilities). Therefore, it’s best to formulate the mixture to be as resistant as possible to deformation due to temperature.

The candles shown in your photos exhibit severe deformation. Without knowing what your wax formulation is, or the type of paraffin you use, I can only suggest conducting trials with different additives and dosages to determine the best solution for your candle, its packaging, and handling conditions.

Since you mention that you are manufacturing these candles by molding, I assume they are made on machines with tin molds. In this case, it is better NOT to use an additive with acidity (such as stearic acid) as it will eventually damage the mold finish.

Instead, I suggest using a polyethylene wax or some other polymer to modify crystallization and introduce increased hardness and heat resistance into your wax formula. These types of additives are used in low percentages, ranging from 0.2% to 2%, or between 2 and 20 grams per kilogram of mixture. Another option that some manufacturers use is to supplement the use of polyethylene waxes or other polymers with a low percentage (from 3% to 7%) of a hard microcrystalline wax with a high melting point. This combination works very well to provide high resistance to deformation due to temperature. Seek options and advice from your suppliers.

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