The causes of welded joints in plastic products

Update:10 Nov 2018

Set the temperature, pressure, speed, back pressure, me […]

Set the temperature, pressure, speed, back pressure, melt motor speed is too high to cause decomposition, or pressure, speed is too low, injection time, insufficient pressure, low back pressure, due to the lack of high pressure and insufficient density can not be melted Silver streaks appear in the gas, proper temperature, pressure, speed and time should be set and multi-stage injection speed should be used.

Low back pressure and fast rotation speed allow air to enter the barrel, and the melt enters the mould. When the cycle is too long, the melt is decomposed in the barrel due to excessive heat.

Insufficient material, the feeding cushion is too large, the material temperature is too low or the mould temperature is too low, which affects the flow of the material and the moulding pressure, and promotes the formation of bubbles.

The molten plastic in the cavity meets in the form of multiple strands due to the intrusion of the insert holes, the discontinuous flow rate, and the region where the filling flow is interrupted, and a linear weld seam is produced because it cannot be completely fused. In addition, in the case of gate injection moulding, a welded joint is formed, and the strength at the welded joint is poor. The main reasons are as follows:


(1) The injection pressure and speed are too low, and the temperature of the barrel and the mould temperature are too low, so that the melt entering the mould is cooled prematurely and a weld seam occurs.

(2) When the injection pressure and speed are too high, a spray will occur and a weld seam will appear.

(3) The rotation speed should be increased, and the back pressure should be increased to decrease the viscosity of the plastic and increase the density.

(4) The plastic should be dried well, and the recycled material should be used less. If the amount of the release agent is too much or the quality is not good, the welded joint will appear.

(5) Reduce the clamping force and facilitate the exhaust.