Unstable product weight

(1) Definition of defect

Product weight instability (injection molding instability) means that the weight of a plastic product is unstable or fails to reach a set standard weight, and is accompanied by variations that are out of range.

(2) Classification of causes

① Material reasons

A. Plastic material impurities, and impurities in the density of the material used, the density of the material is smaller, so the weight of the melted material differs.

B. Plastic drying degree is not enough; the water content is too large.

C. Plastic quality is unstable (there is the addition of recycled materials).

D. Plastic material is not stable.

② mold reasons

A. The gate is too small, resulting in the inability to fill the mold cavity.

B. Mold temperature is uneven or low.

 ③ Injection molding process reasons

A. Insufficient back pressure of molten plastic, resulting in gas inside the material, moving the same number of positions, the weight is small.

B. Hopper feeding is not stable, with part of the corner of the material hollow, resulting in deviation.

C. Insufficient injection time, not filled; the set injection time has been used. d. Insufficient holding time and pressure.

(3) Reasons for the injection molding machine

A. Wear and tear of the stop ring of the injection molding machine, during the process of injection, there is a phenomenon of backflow of the melt, resulting in an unstable injection volume.

B. Variation of the melt volume of the metering stroke or the material pad.

C. Insufficient clamping force, in which case the weight of the product increases.

D. Inadequate clamping force.

(4) Solutions

Material Countermeasures

 A. Use pure raw materials and clean production equipment to prevent impurities.

B. Dry the material sufficiently.

C. Use pure raw materials with no add-backs.

D. Use a clean production facility.

②Mold Countermeasures

A. Increase the gate.

B. Adjust the mold temperature.

C.  Use pure raw material without adding back material.

④ Countermeasures of the injection molding process

A. Increase the back pressure of the molten material, exhaust the gas in the barrel, and compact the molten material at the same time.

B. Remove the hopper for checking and unclogging.

C. Extend the injection time.

D. Extend the holding time and increase the holding pressure.

E. Increase the pressure of the injection machine.

⑤ Injection molding machine countermeasures

A. Replace the injection molding machine parts.

B. Detect the stability of the equipment.

C. Adjust the clamping force or replace the large tonnage of the injection molding machine.

---- The above content is selected from “Injection Molding Use of Technology”, thank you for your attention to Fomtec Machine !